Nitrogen fertilizer use efficiency in rice

Contents  Introduction  Nitrogen dynamic in lowland rice soil  Methods of Nitrogen losses from rice fields  Ways of increasing Nitrogen fertilizer use efficiency  Summary

Introduction Nitrogen - major nutrient limiting yield of wetland rice most difficult plant nutrient to manage (large number of transformation pathways) - requirement differ with upland and lowland rice Lowland rice - submerged or waterlogged conditions Upland rice - inadequate water Growth stages and yield component are affected 1. Tillering stage – panicle number 2. Panicle initiation stage – grain number 3. Ripening stage – grain weight -

Nitrogen fertilizer use efficiency Increase in yield of the harvested fraction of the crop per unit of nutrient supplied by nitrogen fertilizer With first increment of fertilizer – highest efficiency With additional increment – reduced efficiency Yield Added N Fertilizer

Efficiency of added nitrogen fertilizers can be described by, Grain yield x N uptake = Grain yield N uptake N applied N applied - represent the change in a given parameter First term -Physiological efficiency which plant N is Used to increase grain yield. Second term -Uptake efficiency per unit N applied Third term -Agronomic efficiency or increase in grain yield per unit N applied

FUE = (B – A) X 100 (20 – 10) Fertilizer amount addedYield (tons) 1o kgA 20 kgB Example - Yield response of three hypothetical varities Added N Fertilizer Yield Variety 1 Variety 2 Variety 3 Japonica varieties – superior to indica varieties Improved plant type – high response to added fertilizer

Nitrogen dynamic in lowland rice soils Industrially manufactured N fertilizer provide largest fraction for rice - Urea, Ammonium sulphate Recovery of fertilizer N applied to wetland – % Main causes Nitrogen transformations and losses from soil Improper management practices - - Ways of nitrogen losses for low land rice plants - Leaching - Nitrification and denitrification - Fixed between clay particles - Ammonia volatilization

NH 4 + NO 2 - Nitrification NO 3 Nitrification - NO 3 - Leaching N 2 Denitrification N 2 Standing water Oxidized layer Reduced layer N 2 /O N Fertilizer Nitrogen transformations in low land rice soil - Uptake NH 3

Ammonia volatilization – Cause 5-47 % losses of added fertilizer Denitrification – % losses Submerged soil are ideal environment for denitrification - Oxidized surface layer promotes nitrification (Mikkelsen 1987) NH 4 + NO Immobile cat ion,- Mobile anion - Deeper reduced layer favors denitrification

Methods to increase Nitrogen fertilizer use efficiency

Improved timing of nitrogen application Apply at critical growth stages and time Controlled release nitrogen fertilizer - Sulphur coated urea (SCU) - Mud bold urea Split application of fertilizers Basal dressing (10 kg/ac) 2-3 top dressing of urea ( kg/ac depending on yield potential) Early N application promote excessive vegetative growth and shading on lower leaves Use of nitrification and urease inhibitors - At tillering and at panicle initiation. -

Deep placement of fertilizer to reduced layer fertilizer Reduced layer Oxidized layer - Reduce nitrification and denitrification Adoption of proper management practices - Supply adequate nutrients other than nitrogen - Weed control - Proper water management (Contribute to efficient uptake of nitrogen) - Pest / disease control

Summary Nitrogen fertilizer use efficiency is low (35-40 %) Increase cost of production in rice cultivation Inefficient use of N fertilizer leads to gaseous losses of nitrogen to atmosphere - Contribute to global climate change Nitrate may leached in to ground water and cause ground water pollution Nitrogen use efficiency in rice production is essential for Sustain yield increase that needed to meet the demand of a growing world population To provide proper income for farm families Preserve environmental quality Minimize energy cost

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