Interaction Between Irrigation and Fertilizers
Concept
- Water availability influences nutrient uptake – nutrients move to roots mainly by mass flow (N, Ca, Mg, S) and diffusion (P, K, Zn), both of which depend on soil moisture.
- Nutrient status influences water use – adequate fertilizers increase root growth, canopy development, transpiration, and thus water requirement.
- Balanced interaction → higher yield, WUE, and NUE.
Positive Interactions
(a) Nutrient Uptake Enhanced by Irrigation
- Nitrogen: moves by mass flow; optimum moisture prevents leaching (excess) and volatilization (deficit).
- Phosphorus: moves by diffusion; requires soil moisture for mobility.
- Potassium: uptake reduced under drought, but improves with adequate irrigation.
- Micronutrients (Zn, Fe, B): better solubility under adequate soil moisture.
(b) Irrigation Efficiency Improved by Fertilizers
- Adequate N → vigorous crop → better transpiration efficiency.
- Balanced fertilizers (NPK) → optimum canopy → reduces unproductive water losses.
- Fertilizer application improves biomass per unit water used (WUE).
- Negative Interactions
- Excess irrigation → nutrient leaching (N, K, S, B, NO₃⁻).
- Deficit irrigation → nutrient fixation, reduced mobility (P, K, micronutrients).
- Imbalanced fertilizer use + heavy irrigation → secondary salinization, sodicity.
- Localized fertigation without moisture balance → salt injury near root zone.
- Irrigation–Fertilizer Scheduling
- Irrigation scheduling must coincide with nutrient demand at critical growth stages.
- Example:
- Wheat: CRI stage → high demand for N + irrigation.
- Maize: Tasseling–silking → high water and N demand.
- IW/CPE ratio concept helps synchronize irrigation with fertilizer use.
- Fertigation (Integration of Irrigation and Fertilizers)
- Application of soluble fertilizers through drip/sprinkler irrigation.
- Advantages:
- Saves 30–50% fertilizer.
- Saves 30–40% irrigation water.
- Increases yield by 15–25%.
- Precision placement → reduces leaching losses.
- Widely used in horticulture (banana, tomato, grapes) and cash crops (cotton, sugarcane).
- Irrigation–Fertilizer Interaction in Different Soils
- Light-textured soils (sandy): high leaching → frequent irrigation + split fertilizer application needed.
- Heavy-textured soils (clayey): poor drainage → danger of denitrification, nutrient fixation → controlled irrigation + balanced fertilization.
- Saline–sodic soils: excess irrigation without amendments → further degradation; gypsum application with irrigation required.
- Some Important Facts
- 50–60% of applied N is lost due to poor irrigation–fertilizer management.
- Balanced NPK + irrigation can increase WUE by 15–25%.
- Fertigation efficiency: N (90%), P (60%), K (80%).
- Micro-irrigation with fertigation can save 30–50% fertilizer and enhance yield 20–40%.
- In India, only ~5% of total irrigated area uses fertigation → huge potential for expansion.
- Summary for Exam
- Irrigation and fertilizers are complementary.
- Water governs nutrient availability and mobility; nutrients govern water use efficiency and yield.
- Mismanagement leads to leaching, fixation, salinity, and nutrient losses.
- Fertigation under micro-irrigation is the best strategy for synchronizing irrigation–fertilizer interaction.
