How to Address DAP Crises

                                                                                                                         Prof. R. S. Sengar and Dr. Reshu Chaudhary  

Reasons of DAP Crises

                                                        

1. Global Supply Chain Disruptions– Russia-Ukraine War (2022-23): Russia is a major exporter of ammonia and phosphates, and sanctions/logistical hurdles reduced global DAP availability.

China’s Export Restrictions: China, the largest DAP producer, imposed export bans (2021-22) to secure domestic supply, reducing global stocks.

2. High International Prices– Phosphate Rock & Ammonia Cost Surge: Due to energy crises (natural gas shortages in Europe), DAP production costs rose sharply.

India’s Import Dependency: India imports ~30-40% of its DAP (mainly from China, Morocco and Saudi Arabia), making it vulnerable to price volatility.

3. Domestic Production Shortfalls– Limited Raw Material (Rock Phosphate): India has minimal rock phosphate reserves, relying on imports.

Fertilizer Plant Shutdowns: Some Indian plants faced maintenance issues, reducing local DAP output.

DAP CONSUMPTION Wheat Production:

                                                           

DAP: Di-Ammonium Phosphate: 

18% Nitrogen (N):– Drives foliage growth, protein synthesis, and plant resilience.

46% Phosphorus (P):– Essential for root development, energy transfer (ATP), and yield. DAP Breakdown Process Dissolution in Soil Water Phosphate Ion Release Ammonia Volatilization & Nitrification Phosphate Fixation in Soil.

Result: Only 10-25% of applied P is used by crops in the first year (rest becomes slowly available). Reaction of Phosphate with Zinc Sulphat Phosphate Ion Forms.

In Acidic Soils (pH < 6.5):– Primary Form: H₂PO₄⁻ (Dihydrogen Phosphate).

Most plant-available form (easily absorbed by roots).

Negatively charged (1⁻), making it easier for plant roots to absorb than HPO₄²⁻ (2⁻).

Fits better into root membrane transport proteins.

In Neutral to Slightly Alkaline Soils (pH > 7.0):–

Primary Form: HPO₄²⁻ (Hydrogen Phosphate).

Less available to plants (stronger binding to calcium in alkaline soils).

Absorbed at ~10–30% efficiency compared to H₂PO₄⁻ due to its higher charge.

In Highly Alkaline Soils (pH > 8.5):– Primary Form: PO₄³⁻ (Phosphate).

Insoluble in soil (forms minerals like calcium phosphate in alkaline conditions).

Virtually unavailable to plants unless solubilized by acids (e.g., root exudates, sulphur).

1-unit of pH shift (e.g., 7 → 6) can double P availability by favoring H₂PO₄⁻. As per ICAR study, Punjab, India Wheat yields drop by 20–40% in alkaline soils due to P fixation 70% of applied P gets fixed as Ca₃(PO₄)₂ (unavailable). Phosphorus Reactions in Soil

Adsorption– Binding of phosphates to soil particles; also referred to as fixation.

Desorption– Release of phosphates from soil particles.

Precipitation– Reaction of phosphate with another substance to form a solid mineral.

Dissolution– Release of phosphorus that occurs when soil minerals dissolve. Occurs slowly over long periods of time.

Mineralization– Conversion of organic phosphorus to inorganic phosphate by microorganisms breaking down organic compounds.

Immobilization– Conversion of inorganic phosphate to organic phosphate and incorporation into the living cells of soil microorganisms Role of Phosphorus.

Energy Currency (ATP):– Critical for ATP production, fueling all metabolic processes (photosynthesis, nutrient transport).

Root Development:– Promotes strong, extensive root systems→ better water/nutrient uptake.

Early Growth Vigor:– Essential for seedling establishment and rapid early-stage growth.

Reproductive Success:– Supports flower formation, seed development, and fruit quality.

Stress Resilience:– Enhances drought tolerance and disease resistance.

Mobility in Soil Solution:-  Forces of attraction between nutrient ions and soil and water molecule determines their behavior and mobility in soil.

Cations such as K+ bond to negatively charged soil particles thus are not as abundant in soil water and tend to have low mobility.

Anions such as NO3- do not as readily bond to soil, therefore are more abundant and more mobile in soil water.

Phosphorus is an exception, as it exists as an anion but has low water solubility, making it relatively immobile in the soil.

Factors Affecting Phosphorus Availability Soil pH - Phosphorus (P) binds tightly to soil particles, becoming "locked" and unavailable to plants.

pH controls this lock:– Acidic soils (pH < 6) P binds with iron/aluminum → insoluble.

Neutral soils (pH 6–7): P remains soluble and plant-accessible (ideal).

Alkaline soils (pH > 7): P reacts with calcium → forms immobile compounds. 3-4 4-5 6.0-6.9 7.0 7.5-8.5 8.5 Other Factors

Clay content– As the amount of clay in the soil increases, sorption capacity increases as well. Clay particles have a large amount of surface area where phosphate sorption can take place. (Higher clay = more sorption= lesser P availability) (Sorption capacity is soil’s ability to "hold" nutrients (like P) on its surface via chemical bonds).

Organic Matter:– Mineralization of organic matter provides a significant portion of phosphorus for crops, so higher organic matter levels will tend to result in greater phosphorus availability. (higher OM= Lesser P binding= More P availability).

Other Anions:– Phosphate availability is higher when other anions, such as bicarbonate, carbonate, silicate, sulphate, or molybdate are abundant in the soil solution. These anions compete for sorption sites on soil particles, which reduces the amount of phosphate that can be adsorbed.

Climate & Soil conditions– Conditions such as temperature, moisture, soil aeration (oxygen levels), and salinity (salt content/electrical conductivity) can affect the rate of phosphorus mineralization from organic matter decomposition. Organic matter decomposes releasing phosphorus more quickly in warm humid climates and slower in cool dry climates. Phosphorus is released faster when soil is well aerated (higher oxygen levels) than when it is saturated.

Conclusion

                                                       

In DAP crises condition, farmers have to try to improve the availability whatever present in soil in unavailable form.

• It can be done by incorporating sulphur-rich fertilizers like Fertis / Cosamil Gold, Techno-Z/Zinda, Sulanex-Z and Sulextra in adequate quantity.

• These products plays a significant role in enhancing dissolution (breaking down minerals into soluble forms), desorption (release of adsorbed nutrients from soil particles) in soils and enhance Organic Matter Decomposition.

Use Techno-Z/Zinda or Sulanex-Z as substitute of Zinc Sulphate that have Zinc Oxide which does not reacts with phosphates. Phosphate (P) dissolution:

• In alkaline/calcareous soils, P gets fixed as Ca-P (insoluble).

• Sulphuric acid reacts with Ca-P, releasing soluble phosphate: Sulphur Promotes Desorption (Release of Adsorbed Nutrients)

• Sulphate (SO₄²⁻) ions compete for the same adsorption sites, displacing PO₄³⁻ into soil solution. Organic Matter Interaction

• Sulphur enhances microbial activity, promoting organic matter decomposition. This releases organically bound nutrients (e.g., P, N) into soluble forms. Study & References ICAR-Indian Institute of Soil Science (Bhopal, 2018)

• Study: Acidification of alkaline soils (pH 8.2) for wheat cultivation. • Finding: 200 kg/ha elemental Sulphur (S⁰) reduced pH to 7.1 in 3 months.

• Result: P availability increased by 35%, wheat yield improved by 22%. •Reference: [J. Indian Soc. Soil Sci., 66(2), 2018] Study & References University of California Agriculture (2015) •Study: Sulphur requirement for California’s alkaline soils.

•Finding: •250–300 kg/ha elemental Sulphur (S⁰) lowered pH by 1.0–1.2 units in loamy soils.

• Sandy soils required ~150 kg/ha S⁰ for the same effect.

• Reference: UC ANR Publication 8235 Study & References FAO (2017) - "Soil Fertility Management"

• Guideline: • 150–200 kg/ha S⁰ for sandy soils (pH drop by 1 unit). • 300–400 kg/ha S⁰ for clay soils (due to higher buffering).

• Source: FAO Soils Portal Study & References Practical Case Study (India).

• Location: Punjab wheat fields (pH 8.3 → 7.2).

• Treatment: 250 kg/ha S⁰ + irrigation.

•Result:

• pH dropped to 7.1 in 4 months.

• DAP use reduced by 25% (P availability ↑ by 40%).

Writer: Professor R. S. Sengar, Director Training and Placement, Sardar Vallabhbhai Patel University of Agriculture and Technology, Modipuram, Meerut.