Q&A with AI - Southern Fertilizer

1What is fertilizer? What are the effects of nutrients in fertilizers?

Fertilizers are chemical compounds (which may be inorganic or organic) produced by humans and applied to crops to help plants grow healthily, develop in a balanced manner, and achieve higher yields compared to crops grown without fertilization.

The effects of basic nutrients on crops are as follows:

In their life cycle, plants require at least 13 to 16 different nutrients, including nitrogen (N); phosphorus (P); potassium (K); calcium (Ca); magnesium (Mg); sulfur (S); silicon (Si); chlorine (Cl); manganese (Mn); iron (Fe); copper (Cu); zinc (Zn); boron (B); molybdenum (Mo); cobalt (Co); sodium (Na)… Monocot plants such as rice, sugarcane, maize, bamboo, etc. require a large amount of silicon, whereas dicot plants (woody plants) need very little. Leguminous crops require higher amounts of molybdenum and cobalt, while other crops almost do not. Crops such as coconut, mangrove species (sú, vẹt, đước, mắm…) require a relatively high amount of sodium, whereas rice growth is already inhibited at a salinity level of only 0.4%.

Below are the functions of some basic nutrients commonly encountered in plant life:

1/ Nitrogen (N):

In plants, nitrogen is involved in the structure of living substances (proteins), genetic materials (DNA, RNA), amino acids, and especially in the composition and structure of chlorophyll — the green pigment often likened to “machines” capable of converting water, CO₂, and light energy into organic substances (sugars, starches) for human harvest. Therefore, nitrogen is a nutrient that promotes rapid growth and development and is a major contributor to crop yield.

Plants absorb nitrogen in the form of monovalent soluble ions such as NO₃^– and NH₄⁺.
Nitrogen deficiency: Leaves change from green to light green and then yellow, progressing from older leaves to younger ones and from leaf tips to the base. Loss of green color reduces photosynthesis, directly decreasing yield and crop quality.
Excess nitrogen: Leaves tend to become large but thin, dark green to bluish-green. Imbalanced development between stems, leaves, and roots reduces plant resistance, making crops more susceptible to pests and diseases and increasing the risk of crop failure.
For nitrogen fertilizers, farmers should apply from sufficient to slightly deficient levels. To avoid excess nitrogen, it is best not to apply nitrogen fertilizers, especially urea, alone, but instead combine them with phosphorus, potassium, or use compound fertilizers such as NPK or NPK + TE.

2/ Phosphorus (P):

In plants, phosphorus is also involved in the structure of genetic materials (DNA, RNA) and some living substances (proteins). More importantly, phosphorus is a component of high-energy compounds (ATP, UTP, GTP…). ATP is considered the energy source for all life activities in plants; therefore, phosphorus is likened to “fuel for an engine” or a “battery for an electric vehicle.” Compared to nitrogen, plant demand for phosphorus is lower. For example, each ton of high-yield rice grain and corresponding straw contains about 22 kg of nutrients but only 7.1–8.1 kg of P₂O₅; each ton of Arabica coffee beans contains 17 kg of nutrients but only 2.5 kg of P₂O₅.

In soil, phosphorus is easily immobilized by microorganisms and acidic elements. Therefore, although plant demand for phosphorus is not high, phosphorus application is often high in acidic soils to both nourish crops and immobilize soil acidity, supporting root development. Phosphorus is considered a nutrient that promotes strong root growth and the formation of new organs such as tillers and flowers, and is also essential for photosynthesis and metabolism, directly affecting crop quality.
Phosphorus deficiency reduces energy availability for metabolic processes, limiting chlorophyll synthesis, root development, tillering, flowering, fruiting, and seed formation, ultimately reducing yield and product quality.
Excess phosphorus: In acidic soils such as those in the Mekong Delta or low-pH soils in the Central Highlands, excess phosphorus is rarely observed. However, excessive phosphorus can inhibit zinc uptake and promote premature ripening, affecting yield and quality.
Plants absorb phosphorus in the form of soluble ions in water and weakly acidic environments, such as HPO₄^2- and H₂PO₄^–. To supply these forms, farmers may use superphosphate, MAP, DAP, or fused phosphate fertilizers depending on soil pH conditions.

3/ Potassium (K):

Potassium does not form part of plant structures but plays a major role in physiological functions, significantly influencing plant growth and development.
Potassium activates at least 60 enzymes necessary for plant growth and helps maintain optimal cellular pH (7–8) for enzymatic reactions.
Potassium regulates stomatal opening and closing, enabling gas exchange, transpiration, nutrient transport, and temperature regulation. Potassium deficiency causes stomata to respond slowly, increasing water loss and susceptibility to drought stress.
Potassium enhances water uptake through osmotic regulation, improving drought tolerance.
It enhances photosynthesis, nutrient transport, sugar and starch movement, and storage in roots, tubers, fruits, and seeds.
Potassium strengthens plants, reduces lodging, increases resistance to pests and diseases, and improves yield and market value.
Plants absorb potassium as soluble K⁺ ions or K-chelate complexes.

4/ Calcium (Ca):

Calcium is a structural component of plant cell walls, forming calcium pectate that binds cellulose molecules, creating strong yet elastic cell walls. Calcium also regulates carbohydrate transport and secondary growth processes.

In soil, calcium helps balance soil pH; lime (CaO) is commonly applied to acidic soils.
Calcium deficiency leads to weak cell walls, poor root development, reduced nutrient absorption, and impaired growth.
Excess calcium may inhibit the uptake of magnesium and potassium.
Plants absorb calcium as divalent Ca²⁺ ions from soluble salts.

5/ Magnesium (Mg):

Magnesium is a core component of chlorophyll. Along with nitrogen, it is essential for photosynthesis, enabling plants to convert water, CO₂, and sunlight into carbohydrates.

Magnesium contributes to soil pH balance and is supplied through fertilizers such as fused phosphate.
Magnesium deficiency causes interveinal chlorosis, reducing photosynthesis and yield.
Excess magnesium can interfere with the absorption of other nutrients.
Plants absorb magnesium as Mg²⁺ ions or chelated forms.

6/ Sulfur (S):

Sulfur is involved in amino acid and protein synthesis, enhancing enzyme activity and supporting normal plant growth. Crops with distinctive aromas (durian, onion, garlic) and chlorine-sensitive crops benefit from sulfate-based fertilizers.

Sulfur is absorbed mainly as sulfate (SO₄^2-) ions.
Sulfur deficiency reduces protein synthesis and enzyme activity, slowing growth and reducing yield.
Excess sulfur can acidify soil and degrade organic matter.
Recommended sulfur content in fertilizers is 4–8% to avoid soil degradation.

7/ Zinc (Zn):

Zinc is a micronutrient required in very small amounts but is essential for enzyme activation, hormone synthesis, and protein metabolism.

Zinc deficiency mainly affects young tissues, causing shortened internodes and reduced leaf size.
Zinc availability decreases as soil pH and phosphorus levels increase.
Plants absorb zinc as Zn²⁺ ions or chelated forms, with chelates being the most effective.
Excess zinc can be toxic; application must be carefully managed.

8/ Boron (B):

Boron is a micronutrient essential for cell wall structure, carbohydrate transport, and reproductive development.

Boron stabilizes cell walls and supports sugar transport.
It plays a key role in pollen germination and fertilization.

Symptoms of boron deficiency:

Death of growing points, deformed leaves, cracked stems, poor flowering and fruiting.
Leaves may curl, turn pale or yellow. Depending on crop and soil conditions, additional nutrients such as iron, molybdenum, and cobalt may be added to specialized fertilizers.

2What is a good fertilizer? Give examples of some fertilizers that are suitable for rice in the Mekong Delta.

As we know, crops simultaneously use many different types of nutrients, from macronutrients and secondary nutrients to micronutrients and trace elements. However, soils always contain various nutrients depending on parent rock sources, natural conditions (weathering, leaching), and human cultivation practices, which create different soil types with distinct nutritional characteristics. Sandy, degraded soils lack almost all nutrients; black soils on basalt scoria are rich in nitrogen and phosphorus but relatively low in potassium; gently sloping red basalt soils are often deficient in potassium; steep red basalt soils are deficient in nitrogen, phosphorus, and potassium; alluvial soils with annual flooding are rich in potassium, whereas alluvial soils within dike systems without flooding and lacking sediment input are often deficient in potassium.

A relative concept of a good fertilizer has been proposed to basically meet the following usage requirements: “A good fertilizer is one that contains, at the same time, multiple nutrients that crops need but soils lack; contains nutrient contents that match what is stated on the packaging; and is suitable for farmers’ cultivation conditions.”

According to this concept, for iron-rich acid sulfate soils in the delta, an NPK 20-20-15 + TE (iron) fertilizer would be less suitable than an NPK 20-20-15 fertilizer without added TE; for red soils in the Central Highlands (with excess copper), NPK 20-20-15 is better than NPK 20-20-15 with additional TE (copper). A fertilizer labeled NPK 20-20-15 but containing only 85% of each nutrient is not as good as one labeled NPK 18-18-14 that actually contains 100% of each nutrient upon analysis. Granular potassium fertilizer is better than powdered potassium fertilizer when applied to rice fields where rice plants are already established.

Below are some fertilizers considered good for rice in the Mekong Delta:

NPK 20-20-15 + TE (B; Zn), mixed form with three colors;
NPK 25-25-5 + TE, mixed form with three colors;
NPK 16-16-8 + TE, mixed form and single-granule form;
Specialized fertilizer Bong Lua Bozinc for tillering, single-granule form;
Specialized potassium fertilizers such as RI-VL, R2FVL, KoTVL;
Specialized fertilizer Bong Lua BoZinc Golden Yield, single-granule form;
NAP Eco fertilizer, etc.

3What conditions are required for a manufacturer to produce good-quality fertilizer?

To produce good-quality fertilizer, manufacturers must meet the following requirements:

First, they must have a thorough understanding of fertilizers and the functions of each nutrient contained in fertilizers.
They must understand the target crops for which their products are intended.
They must understand the physical and chemical properties of the soils where the fertilizers will be applied.
Most importantly, they must possess advanced production and management technologies, and the enterprise’s management system—especially the quality management system—must meet high-quality standards.

4Which production technologies are considered advanced in NPK fertilizer manufacturing today? How can we determine whether a company’s quality management system is good and meets recognized standards?

Among NPK fertilizer production technologies, chemical technology is considered the most advanced. However, due to high investment costs, in Vietnam at present only the Dinh Vu (Hai Phong) and Lao Cai plants are able to produce NP (DAP) using chemical technology; NPK chemical production technology has not yet been established in Vietnam.

In Vietnam, the most advanced technology currently used for NPK production is rotary drum granulation with steam, combined with molten urea. This technology is currently applied by Southern Fertilizer, Binh Dien Fertilizer, Viet Nhat Fertilizer, Nam Sao Fertilizer, and a few other manufacturers.

Small and fragmented NPK producers mainly use pan granulation technology to create semi-finished granules, which are then blended into three-color products sold to farmers. Their single-granule round products often fail to meet quality standards, especially products with total nutrient content of 35 units or higher. The main limitation of pan granulation technology lies in its granule-forming mechanism, which results in insufficient nutrient content, making it impossible for product quality to meet requirements.

To determine whether a company’s quality management system is good, the following criteria can be used:

First, observe whether the company has its own laboratory. How many nutrients can it analyze? A professional manufacturer with good management must have a laboratory: within 3 hours, it should be able to analyze the three nutrients N, P, K and organic matter; within 3 days, analyze S, Ca, and Mg; and within 5 days, analyze trace elements (TE). A manufacturer without a laboratory cannot be considered to have a good quality management system.
Next, examine the level of their quality management system. For fertilizer production, compliance with ISO 9001:2008 is acceptable; ISO 14000 certification is even better; anything below these standards is considered inadequate. Southern Fertilizer meets ISO 9001:2008 and ISO 9001:2015 standards.

5What does it mean to use fertilizers in a way that is appropriate to a crop’s growth stages?

The use of fertilizers is considered appropriate to a crop’s growth stages when the amount of fertilizer supplied to the plant, together with the nutrients that the soil can release at each growth stage, is at an adequate and reasonable level; over-application should be avoided, especially nitrogen fertilizers.

Example: To support 1 hectare of rice from sowing to the beginning of tillering in the Mekong Delta, it is usually necessary to apply an additional 25–30 kg of N, 23–35 kg of P₂O₅, and about 8–10 kg of K₂O. When entering the tillering stage, the application rate often needs to be doubled compared to the previous stage to adequately nourish the mother plant and 4–6 tillers. However, when the plant begins panicle initiation (booting stage), the nitrogen rate should be reduced to about 20–23 kg; phosphorus should be reduced to a minimum, usually 3–8 kg (on acid sulfate soils), while potassium should be increased to an amount equal to or greater than nitrogen (20–25 kg). Across all three stages, the total balanced application is approximately 80–105 kg N, 50–70 kg P₂O₅, and 45–65 kg K₂O, adjusted according to soil conditions and cropping season. Using only DAP and urea for the third application (panicle initiation) is incorrect; applying too little phosphorus at the first application, applying potassium at a higher rate than nitrogen, or applying nitrogen alone are also incorrect.

In general, for all crops, nitrogen and phosphorus should be applied at higher rates early and lower rates later, while potassium should be applied at lower rates early and higher rates later. Based on the fertilizer formula, the appropriate application rate for each type of fertilizer can then be calculated.

6How do crops absorb nutrients? Which methods are primary and which are secondary? Is it good to use all methods at the same time? Why or why not?

Crops can absorb nutrients in two ways:

Method 1: Plants “feed” on nutrients through their root system—this is the primary method. A root system has billions of root hairs (the plant’s “mouths”), located mainly near the root collar (inner zone). Through osmotic pressure (mainly created by potassium ions) or active transport mechanisms (using carrier substances containing ATP), these root hairs absorb nutrient ions and transport them upward to nourish the plant.
Method 2: Plants absorb nutrients through stomata on the leaf surface when these openings are open. In monocot plants (such as rice), each square inch of the upper leaf surface contains about 33 stomata, while the lower surface contains about 14; in maize, the upper surface has about 52 stomata per square inch and the lower surface about 68. In dicot plants (such as fruit trees), stomata are mainly concentrated on the lower leaf surface. Stomata do not open during hot midday periods; therefore, plants cannot absorb nutrients by this method at that time because the stomata are closed.

This is a secondary method, and plants absorb only a limited amount of nutrients this way. The main mechanism of foliar nutrient uptake is reverse osmosis (opposite to the outward flow of water when stomata open, allowing nutrients to move inward). Moreover, nutrient solutions cannot be applied at concentrations higher than about 2% (usually only 1–1.5%), so the amount of nutrients absorbed is quite small. Another limitation is that when plant growth regulators are applied, leaves may grow excessively, becoming more attractive to insects and pests that cause diseases. However, the advantage of this method is its rapid effect. If plants are waterlogged for several days or suffer from drought, combining irrigation with foliar nutrient application can help meet nutrient needs when roots are unable to absorb nutrients.

Another important note is that when combining foliar fertilizers with pesticides or fungicides, compatibility must be carefully checked before use; if they are not compatible, they should not be mixed together.

7How can you distinguish between healthy plants and weak plants? How should fertilizers be applied to keep plants healthy?

Healthy plants and weak plants are two completely different conditions of crops, indicating the level of balanced growth and the plant’s tolerance to pests, diseases, and other adverse conditions.

A healthy plant grows in a balanced manner, has fewer pests and diseases, and is capable of producing high yields and good-quality agricultural products. In contrast, a weak plant develops unevenly, has low yield potential, poor tolerance, and produces low-quality products. For example:

Healthy rice plants:
- Have a thick leaf canopy with moderately sized leaves;
- Leaves are bright green and maintain their green color until harvest;
- Plants are sturdy, resistant to lodging, with strong straw;
- Less attractive to pests and diseases;
- Farmers are very likely to achieve a good harvest.
Weak rice plants:
- Have large but thin leaves;
- Leaves are dark green to bluish-green, and the green color fades quickly (leaves often dry at harvest);
- Plants are soft and weak, easily lodge, with weak straw;
- Highly attractive to pests and diseases;
- Farmers are at high risk of crop failure.

Whether plants are healthy or weak depends almost entirely on farmers’ cultivation practices, especially fertilizer management, particularly nitrogen (N) fertilization.

To keep plants healthy and well balanced, fertilizer application must be balanced, and nitrogen (N) should not be overused. The best and simplest way to achieve this is to avoid applying nitrogen fertilizers alone—especially urea (a “cold” fertilizer)—and instead apply nitrogen together with other nutrients such as phosphorus (P) and potassium (K). Urea contains a very high nitrogen content (46%), so using it alone easily leads to excessive application. The most effective approach is to use compound NPK fertilizers, especially specialized formulas produced by reputable manufacturers such as Hiep Phuoc, Cuu Long, Binh Dien, and others.

8Fertilizer application process for rice in the Mekong Delta

If we talk about a “process,” it must be specific to each particular variety, specific soil conditions, and specific cropping season; there cannot be a single process applicable to all seasons and all soil types. However, the fertilization regime for high-yield rice in the Mekong Delta can be generally summarized into three fertilizer applications per hectare as follows:

First application: when the rice plants are still small (seedling stage), 7–10 days after sowing. At this stage, apply 25–30 kg N, 23–35 kg P₂O₅, and 8–10 kg K₂O. Specifically, per hectare apply:
- DAP Bozinc fertilizer: 35–50 kg;
- Bong Lua Bozinc Tillering (NPK 19-13-9 + TE): 100–125 kg.
Second application: when the rice begins tillering, at about 20–25 days after sowing. At this stage, apply 38–48 kg N, 25–35 kg P₂O₅, and 18–25 kg K₂O. Specifically, per hectare apply:
- 200–250 kg of Bong Lua Bozinc Tillering (NPK 19-13-9 + TE).
Third application: when the rice begins panicle initiation (early booting stage), at about 40–45 days after sowing. At this stage, apply 17–22 kg N, 3–5 kg P₂O₅, and 19–23 kg K₂O. Specifically, per hectare apply:
- 100–150 kg of Bong Lua Bozinc Golden Yield (NPK 17-3-19 + TE).

Total for all three applications: 80–100 kg N, 55–70 kg P₂O₅, and 45–65 kg K₂O. If fertilizers with different formulations are used, the application rates for each stage should be recalculated accordingly, following the same method described above. In addition, depending on soil conditions and cropping season, specialized rice fertilizer sets such as L1 997, L2 998, L3 999 or R1, R2, R3, etc., may be used.

Note: For the Winter–Spring crop after flooding or the early Summer–Autumn crop after a long fallow period, lower application rates should be used. For the Summer–Autumn crop or consecutive Winter–Spring crops without sufficient fallow time, higher fertilizer rates should be applied.

9How should single-granule fertilizer and three-color blended fertilizer of the same nutrient content from Southern Fertilizer be applied?

For Southern Fertilizer products, if the fertilizer is a multi-colored or single-granule product manufactured using rotary drum steam granulation technology, it is highly suitable for both upland crops (due to its rapid solubility) and paddy rice. In contrast, conventional three-color blended fertilizers (blended from DAP, urea, and potassium) with the same nutrient content (N, P, K) such as NPK 16-16-8, 20-20-15, etc., are more suitable for paddy rice. This is because the bulk density and particle size of three-color blended fertilizers are not as uniform as those of single-granule fertilizers. Fertilizers produced using rotary drum steam granulation technology have a very high degree of uniformity in both bulk density and particle size. Single-granule (or multi-colored) fertilizers therefore have a broader range of applications than three-color blended fertilizers. Examples of multi-colored products from Southern Fertilizer include NPK 16-5-20+TE; NPK 17-7-17+TE; NPK 17-5-19+TE; NPK 18-5-18+TE, etc.

It is recommended to use three-color blended fertilizers for paddy rice to achieve higher efficiency than when used on upland crops. Single-granule (or multi-colored) fertilizers can be used across a wider range of soil types for both upland crops and paddy rice.

10What types of base-fertilizer NPK does Southern Fertilizer Joint Stock Company currently have? What are their technical characteristics and how should they be used?

In terms of quantity, the Company currently offers 199 different basal fertilizers, mainly in NPK form. However, to understand and use these products more easily, they should be divided into groups adapted to different growth stages of crops. Therefore, although there are 199 products, they fall into 4 main groups, specifically:

Balanced group: contains N, P, K in roughly equal amounts. Typical products in this group are NPK 13-13-13 (+TE), NPK 14-14-14 (+TE), NPK 15-15-15 (+TE), or NPK 20-20-15 (+TE), and other products with similar compositions. The feature of this group is that it can be applied at any growth stage, with only minor adjustments by adding small amounts of other fertilizers. For example, NPK 15-15-15: during vegetative growth (stem and leaf), add urea (15% urea + 85% NPK); during flowering, use 100% NPK; during fruit or grain filling, add KCl (15% KCl + 85% NPK). Thus, this group can be used for almost any crop.
High nitrogen, high phosphorus, moderate potassium group: used only during vegetative growth (stem, leaf, and bush development). Typically, N > 16%, P2O5 ≥ 11%, K2O ≥ 5%. Typical products include NPK 16-16-8 (+TE), NPK 18-12-8 (+TE), NPK 25-25-5 (+TE), etc.
Low nitrogen; high phosphorus and high or very high potassium group: used only during the reproductive stage to promote bud, flower, and fruit development (for legumes, nitrogen is not needed in the final stage). Typical products include NPK 15-15-20 (+TE), NPK 12-12-17 (+TE), NPK 12-8-18 (+TE), NPK 10-14-14 (+TE), NPK 8-14-12 (+TE), etc. This group is not widely available in the market.
Moderate nitrogen, low phosphorus, high or very high potassium group: used from the flowering induction stage onward. Typical products include NPK 16-8-16 (+TE), NPK 16-8-18 (+TE), NPK 17-7-17 (+TE), NPK 15-9-13 (+TE), etc. If the soil is low in acidity (phèn) and basal phosphorus is sufficient (superphosphate 300 kg/ha), these products can also be applied during vegetative growth or bush development. For example, for rice on alluvial soil with low acidity during the recent Winter–Spring season, after applying 300 kg/ha superphosphate, at the first top-dressing (7–10 days after sowing), 100–125 kg NPK 17-7-17 (+TE)/ha can be applied; at 20–25 days, 200–250 kg NPK 17-7-17 (+TE); and at panicle differentiation (40–45 days after sowing), 100–150 kg NPK 17-7-17 (+TE) can be applied, achieving very high effectiveness.

11What are the benefits of using single superphosphate compared with using DAP and fused phosphate fertilizers?

Using single superphosphate has the advantage of being low-cost. In addition to supplying readily soluble phosphorus (HPO₄^2-), superphosphate also provides a large amount of easily available calcium and sulfur for crops. For crops with weak root systems or at early growth stages when roots are still weak, the use of superphosphate is very effective. On soils with a pH of 5.5 or higher, especially saline coastal soils, superphosphate shows much better performance than other phosphate fertilizers due to its specific characteristics. Southern Fertilizer offers the Long Thanh single superphosphate product, which is currently available in many provinces and cities nationwide.

12Which substance is considered the most important in determining the quality of foliar fertilizers? Please name some foliar fertilizer products from Southern Fertilizer that are well received by customers in the market.

The substances that play an important role in determining the quality of foliar fertilizers include mineral nutrients such as nitrogen, phosphorus, potassium, calcium, magnesium, micronutrients, as well as plant growth regulators. However, depending on actual agricultural needs, the importance of these substances varies, specifically as follows:

When root systems are poorly developed due to acid sulfate conditions or organic toxicity, nitrogen (N), phosphorus (P), calcium (Ca), and magnesium (Mg) are considered the most important.
When the root system is normal and basal fertilization is adequate, but the plant is deficient in micronutrients such as zinc (Zn) or boron (B), micronutrients become the most important. The trace elements (TE) in Yogen foliar fertilizers are typically in chelated form, which is very easy for plants to absorb, resulting in high efficiency compared with micronutrients in conventional inorganic salt forms.
When plants grow normally but seed quality is low or growth is affected by unfavorable weather conditions, plant growth regulators (such as auxins and gibberellins) become important, helping plants grow faster, more uniformly, and promoting synchronized ripening.

Yogen foliar fertilizers from Southern Fertilizer have built a strong reputation thanks to the optimal combination of these components, and are therefore highly favored by farmers.

Typical products that promote rapid plant growth include Yogen No. 2 (30-10-10); super-phosphate products that help roots recover quickly and promote abundant and synchronized flowering such as Yogen No. 22 (10-50-10); and products that strengthen vines and tubers, specifically for sweet potatoes and other tuber crops, such as Yogen No. 20 (6-30-30). These products are manufactured using Japanese technology production lines and currently enjoy strong credibility in the market.

13In line with the trend toward safe agriculture, organic agriculture, and clean agriculture—which limit the use of chemical fertilizers—does Southern Fertilizer Joint Stock Company offer products that meet these requirements? If so, what are they?

As a large company and one of the leading fertilizer suppliers for Vietnamese agriculture over many years, Southern Fertilizer, in addition to chemical fertilizers, also offers many other fertilizer products for agriculture as well as products serving industry and daily life. These include foliar fertilizers, organic fertilizers, and industrial products such as sulfuric acid (H₂SO₄) and sodium silicofluoride. Among these, organic fertilizer products fully meet the requirements and trends of organic agriculture.

The organic fertilizers of Southern Fertilizer are characterized as clean organic products, derived from seed-based raw materials; therefore, their molybdenum content is consistently higher than that of other organic fertilizers. This is a key strength of Southern Fertilizer’s organic products, making them especially suitable for crops grown for flowers, fruits, and seeds. Clean agriculture products are those that enable crops to absorb nutrients in effective ionic forms, with the right nutrients, in sufficient amounts, and applied correctly.

Typical products in this group include: KHC 3-3-2-22M; 2-3-2-15M; 4-2-2-15M; 2-4-2-25M; Biogold; Cuulong 015, etc.

14For rice in the Mekong Delta, does Southern Fertilizer offer any specialized fertilizers? How effective are they compared with single-nutrient fertilizers?

Due to differences in soil characteristics across cultivation areas, Southern Fertilizer offers several specialized fertilizer sets for rice in the Mekong Delta, for example:

Set 1 (three-color blended fertilizers) – 3 products:
- Bong Lua 1.997 (NPK 22-14-4 + TE), used for the first topdressing, 8–10 days after sowing;
- Bong Lua 2.998 (NPK 18-12-7 + TE), used for the second topdressing, 20–25 days after sowing;
- Bong Lua 3.999 (NPK 20-0-18 + TE), used for the third topdressing, 40–45 days after sowing.
Set 2 (three-color blended fertilizers) – 3 products:
- Bong Lua 1M (NPK 16-13-6 + TE), used for the first topdressing, 7–10 days after sowing;
- Bong Lua 2M (NPK 17-12-7 + TE), used for the second topdressing, 20–25 days after sowing;
- Bong Lua 3M (NPK 18-0-16 + TE), used for the third topdressing, 40–45 days after sowing.
Set 3 (three-color blended fertilizers) – 2 products:
- Cuu Long 01 (NPK 18-13-8 + TE), used for both the first topdressing (7–10 days after sowing) and the second topdressing (20–25 days after sowing);
- Cuu Long 02 (NPK 17-4-23 + TE), used for the third topdressing, 40–45 days after sowing.
Set 4 (compound single-granule fertilizers) – 2 products:
- Bong Lua Bozinc Tillering: NPK 19-13-9 + TE, used for the first topdressing (7–10 days after sowing) and the second topdressing (20–25 days after sowing);
- Bong Lua Bozinc Golden Yield: NPK 17-3-19 + TE, used for the third topdressing, 40–45 days after sowing.
Set 5 (three-color blended fertilizers) – 3 products:
- R1+VL (NPK 20-10-5 + VL), used for the first topdressing, 7–10 days after sowing;
- R2+VL (NPK 17-10-5 + VL), used for the second topdressing, 20–25 days after sowing;
- R3+VL (NPK 20-5-10 + VL), used for the third topdressing, 40–45 days after sowing.
Set 6 (three-color blended fertilizers) – 3 products:
- R1 (NPK 22-16-5 + TE), used for the first topdressing, 7–10 days after sowing;
- R2 (NPK 23-10-5 + TE), used for the second topdressing, 20–25 days after sowing;
- R3 (NPK 23-5-20 + TE), used for the third topdressing, 40–45 days after sowing.

Among these six specialized sets, each will show superior advantages depending on specific soil conditions. Products in these specialized sets are manufactured using high-technology production lines (rotary drum steam granulation), which allow the addition of special micronutrients, thereby significantly improving application efficiency. Results from the Winter–Spring 2015–2016 crop at the large-scale fields in My Loc, Tam Binh (Vinh Long), and several other areas in the Mekong Delta showed that, compared with single-nutrient fertilizer programs, the Bozinc specialized sets saved fertilizer, reduced pesticide applications from five times to only once, increased yields by 5–8%, and improved overall efficiency by about 15% compared with conventional practices (not to mention that the agricultural products produced were very safe).

15Can specialized fertilizers for rice, if not fully used, also be applied to other crops such as vegetables and fruit trees?

Many people believe that fertilizers labeled as specialized for rice will not be effective when used for other crops; this perception is not entirely correct. To answer accurately: nutrients, once applied, can be absorbed by any crop—the key point is whether those nutrients are suitable for a particular growth stage of the crop. If specialized fertilizers such as Bong Lua Bozinc Tillering (NPK 19-13-9 + TE) or L1-1997 (NPK 20-10-5 + TE) are not fully used, they can be completely suitable for other crops during the vegetative growth stage (stem and leaf development). For example, they can be applied to longan trees during the flush (new shoot) stage, or to vegetable crops during their vegetative growth stage.

Similarly, if specialized fertilizers such as Bong Lua Bozinc Golden Yield (NPK 17-3-19 + TE), L2-1998 (NPK 16-8-12 + TE), or R3 (NPK 23-5-20 + TE) are not fully used, they can be applied to fruit trees during the reproductive growth stage (fruit development), or to crops such as sugarcane and vegetables at their later growth stages. Therefore, these fertilizers are not unusable for other crops when applied appropriately.

16What are plant growth regulators?

Plant intracellular growth regulators, also known as phytohormones, are natural products of plant life processes. They participate in regulating metabolic activities and the formation of new organs at all stages of plant growth and development. The most commonly known phytohormones today include auxins, gibberellins, cytokinins, abscisic acid, and ethylene.

An important point to note is that during plant growth and development, multiple phytohormones are present simultaneously, but in very different proportions. A key characteristic of these plant growth regulators is that even at very low concentrations, they are capable of inducing effects that alter the plant’s morphological and physiological characteristics, and they are able to move within the plant.

17What roles do plant growth regulators play in crops?

Plant growth regulators play a very important role in controlling plant growth and development. In other words, almost all physiological activities of plants involve the participation of growth regulators. Depending on the specific type of plant growth regulator, they may take part in the following fundamental processes:

Regulating leaf formation, bud differentiation, and the increase in plant height and stem diameter.
Regulating flowering and fruit set in both main and off seasons.
Regulating root formation in plants, cuttings, and layered branches.
Regulating the preservation of flowers and fruits on the plant and during storage.
Regulating the aging (senescence) processes of plant organs. To study the effects of individual substances, Southern Fertilizer offers Yogen foliar fertilizer products that can be sprayed directly onto specific plant parts, containing individual growth regulators at different concentrations.

18How many ways are there to supply plant growth regulators to crops?

Plant growth regulators can be supplied to crops through the following methods: spraying onto plants; soaking tubers or cuttings in solutions; applying directly onto plants; and injecting directly into plants. Depending on the purpose and requirements, users may apply one of these methods, or combine several methods for the same research or production target.

Spraying onto plants: Used for crops grown for leaves, flowers, fruits, and stems. Spray concentrations are calculated in mg per liter or milliliters per liter. Depending on the growth stage of the plant, appropriate concentrations are applied. During one growth cycle, plants may be sprayed multiple times. When spraying, environmental conditions should be taken into consideration.
Soaking tubers or cuttings in solution: To increase contact time and absorption efficiency, tubers or cuttings can be soaked in solutions containing plant growth regulators at appropriate concentrations. This method is used to stimulate germination, break dormancy in certain tubers and seeds, and to propagate plants through cuttings by promoting rapid root formation.
Applying directly onto plants: When the two methods above cannot be applied, a more concentrated solution can be applied directly onto the plant. Plant growth regulators may be mixed with various carriers (such as kaolin, etc.) to form a paste that is applied to the plant. This method is commonly used for air layering to promote rapid root formation on layered branches.
Injecting directly into plants: This method is mainly used in applied research. For example, substances may be injected directly into buds, dormant eyes of tubers, or into plant stems (through nodes or internodes), thereby determining the effects of specific growth regulators at different concentrations on the research subject.

19How do plant growth regulators affect crop yield and product quality?

Plant growth regulators have the ability to regulate plant growth and development, thereby leading to increased crop yields. Depending on the harvest purpose—whether for leaves, flowers, fruits, stems, or roots—specific growth regulators or combinations of them should be used. In general, when plant growth regulators are sprayed at the correct growth stage, yields can increase on average by 10–15%, and in many cases even higher, reaching 15–50%. The yield increase depends greatly on cultivation conditions such as fertilization, water supply, and crop varieties. For example, spraying gibberellin on grapevines can increase yield by 20–100%, whereas spraying on leafy vegetables usually increases yield by no more than 30% per harvest.

Spraying gibberellin or α-NAA on soybean plants before peak flowering helps the plants grow better, increases the number of leaves, increases both the number and size of root nodules, and raises soybean yield by 15–17%. For peanuts, spraying gibberellin, α-NAA, and β-NOA can increase yields by 8–15% compared with the control.

When plant growth regulators are used alone for spraying crops, yields can increase as described above; however, product quality may be affected. At low application concentrations, yield increases are modest and quality is maintained. At high concentrations, yields may increase rapidly, but quality tends to decline (such as reduced sugar and vitamin content and increased water accumulation). Therefore, in practical production, plant growth regulators should not be used alone—especially at high concentrations—to increase biomass while neglecting quality. In formulations, micronutrients and N, P, and K should be added to ensure the quality of agricultural products.

20Do any products of Southern Fertilizer use plant growth regulators?

Among the products of Southern Fertilizer, not all contain plant growth regulators; however, certain specialized products are supplemented with growth regulators because these active substances help increase crop yields under unfavorable weather conditions or when seed quality does not meet standards. For example, some Yogen foliar fertilizers are supplemented with small amounts of essential plant growth regulators to enhance root formation, flowering, and uniform ripening.

An important factor that builds the reputation of Yogen foliar fertilizer products is the harmonious balance between readily available nutrients—especially micronutrients—and plant growth regulators. As a result, these products not only increase crop yields but, more importantly, maximize the quality of agricultural products.

21How do micronutrient deficiency symptoms appear in crops?

Nutrient deficiency symptoms in plants are expressed in a very direct way. In the middle parts of branches or plants, symptoms usually indicate deficiency, sufficiency, or excess of macronutrients. In young tissues or at the growing tips, symptoms usually indicate deficiencies of secondary nutrients and micronutrients. For example, when the growing tips show young leaves turning white and becoming shorter in coffee plants, it is often a sign of sulfur (S) deficiency. When coffee plants are deficient in boron (B), young shoots dry up and leaves fall. When rice is deficient in iron (Fe), plants become stunted and young leaves turn pale or whitish. In summary, micronutrient deficiency symptoms usually appear on young leaves or at the growing tips of plants. To remedy this condition, farmers should supplement with organic fertilizers and certain micronutrients in basal fertilizers, or apply foliar fertilizers such as Yogen from Southern Fertilizer.

22How should Long Thanh phosphate fertilizer from Southern Fertilizer be applied to poor, infertile soils, and what is the appropriate timing for application?

The Long Thanh Superphosphate Plant, under Southern Fertilizer Joint Stock Company, produces various product lines such as powdered superphosphate, granular superphosphate, organic phosphate fertilizers, etc. These phosphate fertilizer products supply available phosphorus (P₂O₅) for crops and also provide several secondary nutrients, such as calcium.

They supply calcium required by plants. Superphosphate dissolves immediately, directly affects the root system, and is readily absorbed by plants; therefore, root systems develop strongly and become more active. Long Thanh superphosphate is not only suitable for poor and infertile soils but is also appropriate for almost all types of cultivated soils. It is commonly applied as a basal fertilizer before planting. It can also be used as a topdressing fertilizer, but at only one-quarter to one-third of the basal application rate. The recommended basal application rate ranges from 300 to 1,500 kg per hectare.

23What is the difference between DAP and NPK fertilizers from Southern Fertilizer compared with those from other companies? Does mixing Long Thanh superphosphate fertilizer with urea cause moisture absorption or liquefaction?

DAP fertilizer, whose chemical name is Diammonium Phosphate, contains nitrogen and phosphorus. NPK refers to nitrogen (total), phosphorus (available), and potassium (total). In terms of macronutrient composition, there is no difference compared with products of the same type manufactured by other companies. The difference lies in the fact that the raw materials used to produce these products are carefully selected from large, stable suppliers that meet international standards, and are processed through modern, advanced technological production lines to create NPK compound fertilizers. In addition, these products are supplemented with secondary and micronutrients, which help improve nutrient uptake efficiency in crops.
Long Thanh superphosphate is produced through a chemical reaction that has strong hygroscopic properties. Therefore, when it is mixed with urea fertilizer, it often causes the outer coating of urea granules to peel off, leading to moisture absorption and caking. For this reason, superphosphate should only be mixed with urea and applied immediately, and should not be left overnight.

24My land includes loam soil, gray soil, and basalt soil. Which type is better? How can soil be improved to become more fertile?

Different soil structures have different chemical and physical properties. Soil structure affects the soil’s ability to retain nutrients, or in other words, it influences nutrient availability in the soil and nutrient uptake by crops. Soils are commonly classified into sandy soil, loam soil, and clay soil based on the sand/clay ratio, as follows:

Loam soil: 45% sand, 40% silt, and 15% clay.
Gray soil: Has a high sand content, with low clay and colloid content.
Red basalt soil: Contains 60–70% silt and clay particles. This soil is suitable for annual crops and long-term industrial crops.

Therefore, the soil that requires the most improvement is gray soil. To improve its fertility, it is necessary to annually add organic matter such as humus, farmyard manure, and organic fertilizers, thereby increasing buffering capacity and balancing the chemical and physical properties of cultivated soil.

25How should cassava (manioc) be planted and cared for to achieve high tuber yield and high starch content?

Cassava (manioc, tapioca) can be grown in many different types of terrain. Cassava yield depends on many factors, among which cultivation practices and varieties play a decisive role in determining yield and starch content. To achieve a minimum yield of 45 tons per hectare, the amount of nutrients removed from the soil includes approximately 285 kg of nitrogen (N), 90–100 kg of phosphorus (P₂O₅), and 400–450 kg of potassium (K₂O), in addition to secondary and micronutrients. Based on these figures, cassava removes a very large amount of potassium from the soil. Therefore, nutrients must be replenished in amounts corresponding to what the crop has taken up.

Based on the above analysis, some products from Southern Fertilizer can be used, such as Long Thanh superphosphate and NPK 16-16-8 + TE for basal application. During the tuber formation and starch accumulation stage (30–45 days), fertilizers such as NPK 15-9-19 + TE, NPK 15-5-15 + TE, NPK 15-15-15 + TE, or NPK 15-5-20 + TE can be applied.

Based on the amount of nutrients removed from the soil and the corresponding NPK formulas, the required fertilizer rates per hectare can be calculated. This amount should be divided into 2–3 applications.

26How should fertilizers be used for durian trees to prevent watery/hard flesh and achieve fragrant, yellow flesh?

Durian (scientific name: Durio zibethinus Murray) originates from Southeast Asia, has many varieties, and is cultivated in many countries in the region. In Vietnam, it is grown from the Central region southward. Durian is a woody perennial tree. Trees grown from seed usually bear fruit after 7–8 years, while grafted trees can bear fruit after 3–4 years. Durian prefers alluvial soils and fertile basalt soils, has relatively low drought tolerance, and grows best at a soil pH of 5–6.

During the fruiting stage, fertilizer inputs should limit chlorine (Cl). According to several studies, chlorine reduces aroma and causes watery or hard flesh in durian. Southern Fertilizer offers several fertilizer lines suitable for post-harvest or early-season application such as NPK 20-10-10 + TE; 16-16-8 + 9S + TE; 20-20-15 + TE; or 19-11-7-4S + TE. Specialized fertilizers designed to limit chlorine during fruit development include NPK 15-15-15 + TE New, 13-13-13 + TE, and 16-16-16 + TE. These products mitigate chlorine effects by using potassium sourced from SOP (sulfate of potash). In addition, Yogen foliar fertilizer lines can be used to support flowering, fruit set, and fruit enlargement.

27What should be done when durian trees suffer from gummosis (sap bleeding) even though fertilizer application is adequate?

When durian trees suffer from gummosis (sap bleeding), according to plant pathology, the main cause is the fungus Phytophthora. The disease can spread through various pathways, including transmission of pathogens from other sources via air, as well as unfavorable conditions such as insufficient light and waterlogged soils, which create conditions for disease development.

Although the trees may be fertilized with nutrients such as nitrogen, phosphorus, and potassium, the application rates may be unbalanced—especially with excess nitrogen. Therefore, to limit gummosis, it is first necessary to apply appropriate plant protection products, prune and remove infected branches, maintain proper planting density for good air circulation and sufficient light, and apply fertilizers in a balanced and appropriate manner.

28How should avocado trees be cared for to produce high yields?

In Vietnam, climatic and soil conditions suitable for avocado cultivation are found mainly in the Southeast and the Central Highlands. The optimal temperature is around 25°C, with a soil pH of 5–6. During the productive stage, avocado trees have high demands for nitrogen and potassium. The appropriate NPK ratio during this period ranges from 1:1:1 to 3:2:3. With these ratios, products from Southern Fertilizer such as NPK 15-15-15 + TE or NPK 15-10-15 + TE can be used. In addition, other products from the company such as NPK 15-9-19 + TE, NPK 12-8-18 + TE, NPK 12-12-17 + TE, etc., may also be applied. Annual supplementation with farmyard manure, organic fertilizers, and lime is also recommended.

29How should passion fruit be planted and cared for to achieve high yields and prevent diseases?

Passion fruit (scientific name Passiflora edulis) is a climbing vine. There are two types of passion fruit: yellow-skinned and red-skinned. The yellow-skinned type originates from Australia and Taiwan and is well adapted to cool climates with an average temperature of 18–20°C and elevations of about 800–1,000 meters above sea level. The plant is capable of flowering and fruiting year-round and produces very high yields. For passion fruit to grow and develop well, a healthy root system is essential, and organic matter is always necessary to maintain soil fertility. Therefore, proper attention should be given to organic fertilizer application. During the stage when the plant has not yet flowered or fruited, apply 3–5 kg of organic fertilizer mixed with 0.3–0.5 kg of NPK Con O 16-16-8 + 9S + TE or NPK 20-20-15 + TE per plant. When the plant is preparing to flower, apply 0.5–1 kg of NPK Con O 16-16-13 + TE or 15-15-15 + TE. After fruit set, apply 0.3–0.5 kg of NPK Con O 13-13-13 + TE or 15-15-15 + TE per plant. In addition, Yogen foliar fertilizers can be used to enhance flowering and fruit set.

To prevent diseases in passion fruit plants, it is necessary to regularly spray preventive plant protection products, prune and remove infected branches, and keep field borders clean and well ventilated.

30What are the fertilizer requirements for dragon fruit, and how should it be cared for properly?

Dragon fruit (scientific name Hylocereus undatus) originates from tropical regions and is grown in hot climates in many Southeast Asian countries such as Thailand and Taiwan. In Vietnam, dragon fruit is mainly cultivated in the southern provinces. Dragon fruit is a light-loving plant, tolerant of heat and drought, but intolerant of cold, poorly tolerant of salinity, and does not tolerate waterlogging. It can grow on various soil types such as degraded gray soils (Binh Thuan), acid sulfate soils (Tien Giang), and red soils (Long Khanh). The plant can adapt to a wide range of soil acidity levels. When planting dragon fruit, soils with a cultivation layer at least 30–50 cm deep should be selected, and to achieve high yields, irrigation and moisture retention are needed during the dry season.

Fertilizer requirements for newly planted dragon fruit include: organic fertilizer at 15–20 kg per post, and NPK Con O 16-16-8 + 9S + TE or NPK 20-20-15 + TE at a rate of 0.2–0.5 kg per post. When dragon fruit enters the fruit-bearing stage, fertilization should be carried out as follows:

After pruning, apply 0.5–0.7 kg per post of NPK 20-20-15 + TE or NPK 15-15-15 + TE.
40–45 days after pruning, apply 0.3–0.5 kg per post of NPK 18-5-18 + TE.
80–90 days after pruning, apply 0.3–0.5 kg per post of NPK 20-20-15 + TE or NPK 15-15-15 + TE.
After each new fruiting cycle, apply 0.4–0.7 kg per post of NPK 15-9-20 + TE, NPK 18-9-21 + TE, or NPK 15-15-15 + TE.
After each harvest season, supplement with 3–5 kg per post of traditional organic fertilizer.

Additional use of Yogen foliar fertilizers from Southern Fertilizer can help stimulate flowering and support fruit development.

Due to the effects of short-day and long-day light conditions on flower bud differentiation, artificial lighting is used in dragon fruit cultivation to induce off-season flowering and fruiting. However, when forcing off-season production, plants require higher nutrient levels, and additional use of Yogen foliar fertilizers is recommended to stimulate flowering and support fruit development.

31How should grapevines be planted and cared for to achieve economic efficiency?

Grapevines (Latin name commonly Vitis) originate from temperate regions; however, in Vietnam, grape-growing areas—mainly concentrated in Ninh Thuan—are adapted to tropical conditions. During the establishment stage, organic fertilizers, Long Thanh superphosphate, NPK 16-16-8 + 9S + TE, or NPK 20-20-15 + TE are used. When entering the production stage, different NPK formulations are applied depending on each growth phase.

After harvest, grapevines are cared for similarly to the establishment stage. In preparation for bud initiation, it is recommended to use high-phosphorus NPK fertilizers such as NAP Eco or NPK 16-20-0 + 3S + TE. When young fruits begin to form, use NPK Con O 12-12-17 + TE or 15-15-15 + TE at a rate of 300–400 kg/ha, divided into 2–3 applications. Spray Yogen foliar fertilizer every 7–10 days to support flowering and fruit set. Use plant protection products and growth stimulants at the correct dosages to avoid chemical residues or fruit cracking, and conduct regular monitoring for timely intervention.

32How should fertilizers be applied to banana plants to achieve high bunch and fruit yield?

Banana (Latin name commonly Banana) is a crop that can be planted year-round.

The plant is sensitive to water. Suckers grow from the mother plant, and after 7–13 months, the plant produces a bunch. Banana care practices are as follows:

Apply 10–15 kg of farmyard manure per planting hole as basal fertilizer.
Apply topdressing 2 months after planting at a rate of 30–50 grams per plant using NPK Con O 16-16-8 + 9S + TE.
After 3–4 months of planting, apply NPK Con O 16-16-13 + TE or NPK 20-20-15 + TE.
In the 5th month, use NAP Eco or NPK Con O 15-10-15 + TE at a rate of 200–300 grams per plant.
After harvest, remove the mother plant and supplement with organic fertilizer at a rate of 0.7–1 kg per clump, using NPK Con O 16-16-13 + TE.
After flowering, apply fertilizer once a month at a rate of 0.5–0.7 kg per clump. NPK Con O 12-12-17 + TE, NPK 16-16-13 + TE, or NPK 20-20-15 + TE can be used.

33How should fertilizers be applied and care provided to pomelo trees to produce sweet and high-quality fruit?

1. Soil conditions and general care

Loose, well-drained soil, pH 5.5 – 6.5
Prune branches to create an open canopy with adequate light
Control pests and diseases, especially leaf miners, mites, and root fungi

2. Establishment stage (first 1–3 years)

Use balanced NPK fertilizers such as:
- NPK 16-16-8 + 9S + TE
- NPK 20-20-15 + TE
Combine with well-decomposed manure / organic fertilizer to improve soil fertility

3. Pre-flowering stage

Limit nitrogen, increase phosphorus (P) to induce flower bud differentiation
Recommended options:
- NAP Eco
- NPK 16-16-13 + TE

4. Post fruit set – fruit development stage

Increase potassium (K) to promote rapid fruit growth, sweetness, and firmness
Recommended:
- NPK 19-9-19 + TE
- NPK 18-9-21 + TE
Suggested dosage: 1–2 kg/tree per application

5. 1–2 months before harvest

Apply potassium moderately, limit nitrogen
Possible options:
- NPK 15-10-15 + TE
- NPK 15-15-15 + TE
Dosage: 2–3 kg/tree

6. Supplements and important notes

Periodically spray foliar fertilizers to supplement micronutrients (B, Zn, Mg) to enhance sweetness
Apply lime once every 1–2 years (700–1,000 kg/ha) to stabilize soil pH
Avoid late nitrogen application → prevents bland fruit and thick peel

34How can plants be induced to flower and set fruit out of season?

One or a combination of the following methods can be applied, depending on the crop:

Physical methods:

Water stress (temporary drought induction)
Stop nitrogen application to adjust the C/N ratio
Smoke treatment (for certain specific crops)

Chemical methods:

Use active substances that support flower bud differentiation such as: Paclobutrazol, Thiourea, KNO₃, GA₃…
Apply fertilizers with high phosphorus content (NAP Eco, Yogen Super Phosphate…)

Mechanical methods:

Girdling (bark ringing), partial root pruning
Bark scoring, leaf removal

35What diseases commonly affect pepper (black pepper) plants? How should fertilizers be applied to limit quick wilt and slow decline?

General information about black pepper (Piper nigrum)

Origin
• Black pepper originates from India.

Planting density
• General range: from 1,100 to 2,500 poles/ha.
• Central Highlands region: from 1,800 to 2,200 poles/ha.

Plant health issues and diseases

Plant characteristics
• Root system includes underground roots and aerial clinging roots.
• Highly sensitive to disease-causing agents.

Causes of diseases
• Nematodes: Meloidogyne incognita.
• Pathogenic fungi (often in combination with nematodes):
– Fusarium sp.
– Phytophthora sp.
– Pythium sp.

Common diseases and pests
• Root-knot nematodes.
• Wilt (slow decline or quick wilt).
• Pepper stunt disease (virus).
• Anthracnose, branch dieback.
• Stink bugs, sap-sucking insects.

Cultivation techniques and nutrition

Black pepper cultivation requires careful and meticulous practices to prevent and limit diseases.

Cultivation techniques

Land preparation.
Propagation of cuttings.
Plant care.
Pruning and lowering vines.

Technical requirements
• Soil must be thoroughly treated with lime and phosphorus.
• Adequate fallow period before planting.
• Organic fertilizers or manure must be fully composted.
• Do not use fresh manure.

Nutrition (use of inorganic NPK fertilizers)

Establishment stage
• NPK Con O 16-16-8 + 9S + TE.
• NPK 20-20-15 + TE.

Production stage
• NPK Con O 12-12-17 + TE.
• NPK 17-5-19 + TE.
• NPK Con O 15-10-15 + TE.
• NPK 19-9-19 + TE.

Notes on nitrogen and potassium levels

Nitrogen (N)
• High or excessive nitrogen reduces plant resistance.
• Makes plants more susceptible to diseases.
• Recommended amount should not exceed 200 kg N/ha/year.

Potassium (K)
• Potassium levels should be equal to or higher than nitrogen.
• Suitable potassium ratio is 1.2–1.5 times that of nitrogen.

36For black pepper plants that have been planted for one year, is it necessary to apply additional fertilizer at the end of the rainy season?

Vegetative growth stage of the black pepper garden

• The pepper garden is in the vegetative growth stage and needs to maintain appropriate nutrition for stable development.

• Under rainfed cultivation conditions, the plants need to be well nourished to prepare for the dry season.

• At this stage, plants need to be strong to ensure good growth and increase tolerance to the harsh conditions of the dry season.

• Timely and adequate nutrient supplementation is necessary to maintain plant vigor.

Recommended fertilizer types

• Use fertilizers with higher nitrogen (N) and phosphorus (P) content than potassium (K) to stimulate stem, leaf, and root growth.

• Some suitable fertilizers include:
– Con O NPK 16-16-8 + 9S + TE.
– Con O NPK 18-14-8 + TE.
– Con O NPK 19-11-7 + 6S + TE.

Organic fertilizer supplementation

• It is recommended to combine application with well-decomposed farmyard manure.

• Con O organic fertilizer can be used to improve and increase soil fertility.

• Organic fertilizers help loosen the soil, improve moisture retention, and support sustainable plant development.

37When black pepper plants are about one month away from harvest, should additional potassium fertilizer be applied to reduce fruit drop?

Pre-harvest stage of black pepper plants

• About one month before black pepper plants enter the harvest period, it is generally not recommended to apply additional nutrients.

• At this stage, pepper berries have already stabilized in maturity, and additional fertilization, including potassium, brings little effect in reducing fruit drop.

Causes of fruit drop

• Inadequate and unbalanced care and fertilization during earlier growth stages.

• Insufficient irrigation, especially under dry weather conditions.

Temporary remedial measures

• Foliar spraying of plant growth regulators that help limit fruit drop.

• Ensure adequate irrigation and maintain proper soil moisture to help stabilize plant physiology.

If you wish, I can:

Standardize the entire black pepper fertilization schedule by growth stages
Condense it for quick data entry into a management system
Rewrite it in a Q&A technical format for a support page

38How should fertilizers be applied correctly for rubber trees?

Rubber Tree (Hevea brasiliensis)

Rubber trees are divided into two main care stages during their growth cycle: the establishment stage and the tapping (production) stage.

1. Establishment Stage

This is the stage when the tree needs to develop a large biomass, focusing on root system and canopy development.

Nutritional requirements:

Develop a strong root system.
Increase chlorophyll content to enhance photosynthesis.

Recommended fertilizer types (NPK from Southern Fertilizer JSC):

Con Ó NPK 16-16-8 + 9S + TE.
NPK 18-14-8 + TE.
NPK 19-11-7 + 6S + TE.
NPK 20-20-15 + TE.

Application timing:

Apply 2–3 times at the beginning, middle, and end of the rainy season.

2. Tapping (Production) Stage

Care practices and nutritional requirements differ from the establishment stage, with priority given to Nitrogen (N) and Potassium (K).

Nutritional characteristics:

Nitrogen (N) and Potassium (K) contents are usually higher than Phosphorus (P).
The recommended NPK ratio is typically 2-1.5-2 (N-P-K).

Recommended fertilizer types (examples):

Con Ó NPK 15-10-15 + TE.
NPK 17-10-17 + TE.
NPK 20-15-20 + TE.

Fertilizer application guidelines:

Nitrogen rate: Equivalent to 80–100 kg/ha.
- For grey soils, this may be increased to 120–140 kg/ha.
Application technique: Incorporate fertilizer into the soil at a depth of 10–15 cm.
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39How should sugarcane be cared for, and which fertilizers are best to use?

Sugarcane (Saccharum officinarum): Nutrient Requirements and Fertilizer Recommendations

1. Nutrient requirements to achieve a yield of 100 tons/ha

Macronutrients (kg/ha):

Nitrogen (N): 142–200 kg
Phosphorus (P₂O₅): 42–85 kg
Potassium (K₂O): 314–425 kg
Calcium (CaO): 40 kg
Magnesium (MgO): 47 kg
Sulfur (S): 25 kg

Secondary and micronutrients (kg/ha):

Silicon (Si): 400 kg
Sodium (Na): 6 kg
Iron (Fe): 2–3 kg
Manganese (Mn): 1 kg
Copper (Cu): 0.05–0.11 kg
Zinc (Zn): 0.02–0.05 kg
Boron (B): 0.1–0.2 kg
Molybdenum (Mo): 0.001 kg

Conclusion on nutrient demand:

The demand for Potassium (K₂O) is the highest (314–425 kg).
Next is the demand for Nitrogen (N) (142–200 kg).
The demand for Phosphorus (P₂O₅) is the lowest (42–85 kg).
Adequate supplementation of secondary and micronutrients is required, especially Silicon (400 kg).

2. Recommended NPK ratios

Depending on soil conditions, commonly recommended NPK ratios include:

2-2-1 (N-P₂O₅-K₂O)
2-1-2
2-1-2.2

Recommended NPK formulations:

Con Ó NPK 16-16-8 + 9S + TE
Con Ó NPK 16-8-16 + 9S + TE
NPK 17-7-17 + TE
NPK 17-5-19 + TE

3. Fertilization recommendations by growth stage

Stage 1: New planting or tillering stage (basal application)

Use Long Thanh superphosphate as a basal fertilizer.
Basal application of Con Ó NPK 16-16-8 + 13TE may also be used.

Stage 2: Internode elongation and sugar accumulation (topdressing)

Apply topdressing 2 or 3 times.
Applicable NPK types include:
- Con Ó NPK 16-8-16 + TE
- NPK 17-5-19 + TE
- NPK 15-15-15 + TE

Notes on fertilizer form:

Priority should be given to compound or single-granule blended fertilizers for higher efficiency.
Limit the use of mixed three-color blended fertilizers.

40Which types of fertilizer should be applied to cashew trees, and how much fertilizer is sufficient?

Cashew Tree (Cashew Nut – Anacardium occidentale)

Characteristics: A crop that is not very soil-demanding, well adapted to tropical climates.
Planting density: 125–400 trees/ha.
Trend: High-yielding cashew varieties (imported or hybrid) have higher nutrient requirements than traditional local varieties.

1. Basic Establishment Stage (Year 1 to Year 3)

Nutrient requirements:

Nitrogen (N) and Phosphorus (P₂O₅) are prioritized over Potassium (K₂O).

Recommended NPK formulas:

NPK Con Ó 16-16-8+9S+TE (N:P:K ratio = 2:2:1).
NPK 20-20-15+TE.

2. Bud Differentiation and Flowering Stage

Nutrient requirements:

Fertilizers with higher Nitrogen (N) content than Phosphorus (P₂O₅) and Potassium (K₂O) are required (usually 2–3 times higher).

Recommended NPK formulas:

NPK Con Ó 16-8-8+TE.
NPK 20-5-5+15S+TE.

General fertilization guidelines for both stages:

Application rate (flowering stage): 300–500 kg/ha (equivalent to 1–1.5 kg/tree/application).
Timing: Apply in 2–3 splits:
- Beginning of the rainy season.
- Mid rainy season.
- End of the rainy season.
Application method: Apply around the canopy and incorporate into the soil at a depth of 5–10 cm.

41How should tea plants be fertilized to achieve the best yield and quality?

Tea (Camellia sinensis): Nutritional Requirements and Fertilization Recommendations

Suitable range: Tropical and subtropical climates (from 43°N to 28°S).
Economic cycle: Very long, from 40–60 years.
Harvested product: Young leaf shoots.
Time to first harvest: Begins after 2–3 years of planting.

1. Symptoms of Macronutrient Deficiency

Nitrogen (N) Deficiency:
- The plant produces few shoots.
- Shoots appear light green with reddish tints.
- Low yield.
Phosphorus (P2O5) Deficiency:
- Leaves are dull green.
- Poor root development.
- Severe deficiency may cause branch dieback.
Potassium (K2O) Deficiency:
- Leaves age quickly and fall early.
- Leaf edges turn light gray.
- Bark shows many silvery-white layers.
- Sparse shoots.
Other elements: Pay attention to supplementing secondary nutrients (S, Mg) and micronutrients (Zn, Cu).

2. Recommended NPK Fertilization by Stage

A. Basic Construction Stage (Year 1 and 2):
- Recommended: NPK “Con Ó” type 16-16-8+9S+TE.
- Or 20-20-15+TE.
B. Commercial Stage (From Year 3 onward):
1. Year 3:
  - Recommended: NPK “Con Ó” type 15-15-15+TE.
  - Dosage: 800–1000 kg/ha.
2. High-yield period:
  - High application rate: 1800–2500 kg/ha, up to 3000–3300 kg/ha.
  - Possible NPK formulations:
    - NPK Con Ó 20-10-10.
    - NPK 16-8-8.
  - Frequency: Split into 4–5 applications.
  - International recommendation (example): NPK 15-9-19 or 18-8-8 can be used.
C. Organic Supplement:
- Periodically supplement manure every 2–3 years.
- High application combined with manure can achieve yields from 6 tons up to over 10 tons of shoots/ha.

42How should tobacco plants be fertilized, and which type should be used to ensure high-quality tobacco leaves?

Tobacco (Nicotiana tabacum)

Classification: Short-cycle industrial crop.
Harvested product: Leaves.
Soil characteristics:
- Preferred soil: Sandy loam, light and loose soil.
- pH: 5.5–6.
Planting density: 15,000–20,000 plants/ha.
Cultivation process: Sow seeds and grow in seedling trays, then transplant to the field.

1. Recommended Fertilizer Supplementation

Organic fertilizer:
- Manure or chicken manure: 25–30 tons/ha.
- Burnt lime: 1–2 tons/ha.
Recommended NPK fertilizers:
- NPK Con Ó 15-9-20+TE.
- NPK Con Ó 12-12-17+TE.
- NPK Con Ó 18-9-21+TE.
Application rate:
- Basal application and top-dressing 1 & 2: 300–400 kg/ha per application.

2. Important Notes on Fertilizer Use

Limit: Generally avoid fertilizers containing chlorine (Cl).
Benefit: Using chlorine-free fertilizers will make tobacco leaves more yellow and improve fiber quality.

43How to cultivate and care for peanut (groundnut) plants, and how should peanuts be fertilized to achieve high yield?

Peanut (Groundnut – Arachis hypogaea)

Distribution range: 40°N to 40°S.
Soil characteristics:
- Suitable: Light, loose, well-drained loamy soil.
- pH: 6–6.5.

1. Symptoms of Nutrient Deficiency

Phosphorus (P) deficiency: Leaves turn **red or brown**.
Calcium (Ca) deficiency: Leaves turn **white**.

2. Recommended Basal Fertilization and Soil Improvement (Gray Soil Regions)

Required: Organic fertilizer, phosphate, and lime during soil preparation.
Basal application for soil improvement:
- Long Thành superphosphate: 400–500 kg/ha.
- Burnt lime: 700–1000 kg/ha.
- Manure: **5–10 tons/ha**.

3. Nutrient Requirements Extracted from Soil (kg/ha)

Nitrogen (N): 192 kg/ha (highest).
Calcium (CaO): 79 kg/ha.
Potassium (K2O): 80 kg/ha.
Phosphorus (P2O5): 48 kg/ha (lowest).

4. Recommended Inorganic Fertilization

- Basal application:
  - Long Thành superphosphate.
  - NAP Eco.
- Top-dressing with NPK:
  - NPK Con Ó 16-16-13+TE.
  - NPK 15-20-15.
  - NPK 15-15-15+TE.

Top-dressing guidelines:
- Total top-dressing: 300–350 kg/ha.
- First application: 15–20 days after thinning.
- Second application: 25–35 days after thinning.

44How should onion and garlic plants be cared for to prevent root rot and leaf rot?

Onion and Garlic (Allium spp.)

Plant type: Pseudostem.
Optimal temperature: Prefers cool conditions in early and late growth stages.
Soil characteristics:
- Preferred soil: Neutral.
- pH: High, from 7–7.5.
Planting density: 300,000–500,000 clumps/ha.

1. Recommended Basal Fertilization

Organic fertilizer and soil improvement:
- Manure: 15–20 tons/ha.
- Lime: 700–1200 kg/ha.
NPK fertilizer:
- NPK Con Ó 16-16-8+13TE.
- Application rate: 100–150 kg/ha.

2. Recommended Top-Dressing

Essential nutrients to supplement (kg/ha):
- Nitrogen (N): 150–200 kg N/ha.
- Phosphorus (P2O5): 100–150 kg P2O5/ha.
- Potassium (K2O): 200–220 kg K2O/ha (highest).
Recommended NPK formulations:
- NPK Con Ó 16-6-19+1.2MgO+TE.
- NPK 15-15-15+TE.
- NPK 15-10-15+TE.
- NPK 16-8-16+TE.
- NPK 12-12-17+2MgO.
Application guidelines:
- Total top-dressing: 700–1000 kg/ha.
- Frequency: Divide into 4 applications, each 12–15 days apart (after planting).
- Technique: Fertilizer can be dissolved for the first top-dressings and lightly incorporated into soil.

45Southern Fertilizer Company, do you have any fertilizers that help coffee and fruit trees flower and set fruit uniformly in winter?

Southern Fertilizer Company Products for Coffee and Fruit Trees

Product range is diverse, suitable for different soil types.
Specialized product lines:
- Foliar fertilizers that promote synchronized flowering:
  - Yogen 16.
  - Yogen 22.
  - Super phosphate.
- Other basal/top-spray products:
  - NAP Eco.
  - DAP (can be applied to the soil or sprayed).
- Basal or foliar fertilizers: Yogen Mitsuivina.

Contact and Consultation Information

Contact: Dealers in the distribution network of Southern Fertilizer Company.
Consultation hotline: 1900555546 (for detailed guidance on fertilizers that help plants flower and set fruit uniformly).

46After harvesting coffee, during which irrigation should fertilizer be applied, and should the fertilizer contain a high or low amount of sulfur?

Post-Harvest Crop Care and Fertilization in the Dry Season

After harvest, the following care steps should be performed:

Prune branches to shape the canopy.
Remove ineffective branches and suckers.

1. Recommended Dry-Season Fertilization

Application timing: Fertilizer should be applied during the 2nd and 3rd irrigation of the dry season.
Reason for choosing the 2nd irrigation: After the first irrigation, the roots start producing more root hairs, enabling the plant to **absorb nutrients efficiently** at the critical time for **flower bud differentiation**.
Special fertilizers for the dry season:
- Con Ó Dry-Season Micronutrients.
- NPK Con Ó 20-5-5+15S+TE.
- NPK 22-4-4+13S+TE.

2. Sulfur (S) Requirement

Recommended amount: Supply 40–60 kg/ha of effective sulfur (ionic form).

47Coffee trees have dry branches and fruit drop, and even after fertilizing, the problem persists. What are the causes, and how can it be remedied?

Analysis of Dry Branches and Young Fruit Drop in Crops

1. Dry Branches

Causes: Dry branches can be caused by multiple factors:
- Nutrient deficiency (insufficient or unbalanced fertilization).
- Natural aging of the plant.
- Impact of pests and diseases.
Remedial measures: Farmers need to carefully investigate each factor to determine:
- Whether the amount of fertilizer applied is appropriate and sufficient.
- Whether the phenomenon is caused by pests or diseases.

2. Young Fruit Drop

Early stage: Physiological fruit drop is a normal phenomenon.
Level of concern: If 40–50% of fruits per branch drop, the main cause of fruit drop needs to be investigated.
Factors affecting fruit drop:
- Pest or disease attack.
- Insufficient or unbalanced NPK fertilization.
Remedial measures: Appropriate solutions should be applied based on the identified cause.

3. Important Notes During the Commercial Stage (Fruit Setting)

Balanced nutrition: Coffee trees need balanced fertilization.
Potassium (K) priority: Use fertilizers with high potassium content.
Support fruit setting: Supplement with certain foliar fertilizers that support fruit development.

48What is the proper fertilizer application rate for coffee in the 5th and 6th year of age, during the dry season and the rainy season?

Coffee in the Commercial Stage (5th and 6th Year)

Stage: Trees in the 5th and 6th year, during the commercial production period.
Nutritional requirements: Different from the basic construction stage.

1. Recommended Nutrient Amounts (kg/ha)

Nitrogen (N) and Potassium (K2O): Recommended at around 280–300 kg/ha or more.
Phosphorus (P2O5): 90–120 kg/ha.

2. Recommended Fertilizers by Season

Dry season (apply during the 2nd and 3rd irrigation):
- NPK Con Ó 20-5-5+15S+TE.
- NPK 22-4-4+15S+TE.
Rainy season (apply 3–4 times):
- NPK Con Ó 17-7-17+TE.
- NPK 18-5-18+TE.
- NPK 19-9-19+TE.

3. Timing for Rainy Season Fertilization

Apply 3–4 times at:
1. Beginning of the rainy season.
2. Mid rainy season.
3. End of the rainy season.

49My farm has 1,300 coffee trees, but the yield varies between 4 and 7 tons/ha depending on the year, even though I apply fertilizers regularly each year (2 applications of phosphate in the dry season, 3 applications in the rainy season). How should I use fertilizers to achieve high and stable yields?

Fluctuating Yield in Robusta Coffee (Coffea robusta) and Solutions

1. Yield Characteristics and Planting Density

Rule: The yield of perennial coffee trees usually shows annual fluctuations.
Typical planting density (Robusta coffee): 1,000–1,100 trees/ha.
Example of abnormal yield drop:
- Average yield: 5.5–6.0 tons/ha (with 1,300 trees/ha).
- Year of decline: Only 4.0 tons/ha (a drop of 27%–36%).

2. Causes of Abnormal Yield Decline

Abnormal yield drop may be caused by:

Unfavorable weather conditions.
Poor resilience of the trees.
Imbalanced fertilization practices (NPK).
Insufficient or untimely irrigation.

3. Nutritional Recommendations (Nutrient Amounts and Fertilizer Types)

Recommended nutrient amounts (kg/ha):
- Nitrogen (N) and Potassium (K2O): Around 280–300 kg/ha or more.
- Effective Phosphorus (P2O5): 90–120 kg/ha.
Recommended fertilizers by season:
- Dry season (increase Nitrogen and Sulfur):
  - NPK Con Ó 20-5-5+15S+TE.
  - NPK 22-4-4+15S+TE.
- Rainy season (more balanced, increase Potassium):
  - NPK Con Ó 16-8-16+TE.
  - NPK 17-7-17+TE.

4. Ensuring Optimal Yield

Coffee trees will achieve optimal yield when:

The above fertilizer cycle and application rates are applied throughout the year.
Sufficient irrigation is ensured.
Effective pest and disease control is implemented.

50Is it true that if a coffee harvest in a given year achieves high yield, the fertilizer amount should be increased proportionally in the following season to increase yield?

Factors Affecting Crop Yield and Nutritional Recommendations for Coffee

Main factors affecting crop yield include:
- Variety.
- Fertilizers.
- Care and cultivation techniques.
- Weather.
- Soil conditions.

1. Additional Nutrient Requirements for Coffee

On average, for every 1 ton of dry coffee beans, the additional nutrient requirement is:
- Nitrogen (N): 60 kg.
- Phosphorus (P2O5): 20 kg.
- Potassium (K2O): 60 kg.

2. Recommended Nutrient Amounts (Coffee from the 4th Year Onward)

In addition to the standard recommended nutrient levels, the applied amounts of pure nutrients should be:
- Nitrogen (N): From 280 kg/ha.
- Phosphorus (P2O5): 90–120 kg/ha.
- Potassium (K2O): 280–300 kg/ha.

3. Principles of Fertilization

Absorption limit: Nutrient uptake has a maximum threshold; beyond this, the plant cannot absorb additional nutrients.
Note: Do not increase fertilizer amounts beyond the plant’s actual nutrient needs.

E. RECOMMENDATIONS FOR USING SOUTHERN FERTILIZER PRODUCTS FOR MAIN CROPS

1. Area Conversion Units

1 ha (hectare): 10,000 m².
1 Sào in Southern Vietnam (commonly called “công”): 1,000 m².
1 Sào in Central Vietnam: 500 m².
1 Sào in Northern Vietnam: 360 m².

2. Principles for Using NPK Formulations

Depends on:
- Age of the plants.
- Growth stage.
- Soil characteristics.
Farmers can use NPK formulations in similar groups and adjust the ratios to suit local conditions.

Explore Southern fertilizer, different types of fertilizers, fertilization techniques, crop care practices, and guidelines for proper fertilizer use.

1Fertilizer

2Available Nutrients

3Chemical Fertilizers

4Inorganic Mineral Fertilizer

5Organic Fertilizers

6Single-Nutrient Fertilizers

7Mixed Fertilizer

8Single-Granule Compound Fertilizers

9Complex Fertilizer

10Urea Nitrogen Fertilizer (CO(NH₂)₂)

11Ammonium Sulfate ((NH₄)₂SO₄)

12Ammonium Nitrate (NH₄NO₃)

13Apatite Phosphate Fertilizer (Ore)

14Superphosphate

15Monoammonium Phosphate (NH₄H₂PO₄ – MAP)

16Diamoni Phosphate (NH4)2HPO4 - DAP)

17Fused Calcium Magnesium Phosphate - FMP

18Kali clorua (KC1 - MOP)

19Kali sunfat (K2SO4 - SOP)cccccc

20Foliar fertilizer

Frequently Asked Questions