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 number2. Panicle initiation stage – grain number3. Ripening stage – grain weight

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Nitrogen fertilizer use efficiency

Increase in yield of the harvested fraction of the crop per unit of nutrient supplied by nitrogen fertilizerWith first increment of fertilizer – highest efficiencyWith 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 added Yield (tons)

1o kg A

20 kg B

Example -

Yield response of three hypothetical varities

Added N Fertilizer

YieldVariety 1

Variety 2

Variety 3

Japonica varieties – superior to indica varietiesImproved 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 – 35-40 %

Main causes Nitrogen transformations and losses from soil Improper management practices

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Ways of nitrogen losses for low land rice plants- Leaching- Nitrification and denitrification- Fixed between clay particles- Ammonia volatilization

NH 4+ NO2

-NitrificationNO3

Nitrification -

NO3-

Leaching

N2

Denitrification

N2

Standing water

Oxidized layer

Reduced layer

N2 /O N Fertilizer

Nitrogen transformations in low land rice soil

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UptakeUptake

NH3

Ammonia volatilization – Cause 5-47 % losses of added fertilizer

Denitrification – 28-33 % losses

Submerged soil are ideal environment for denitrification

- Oxidized surface layer promotes nitrification

(Mikkelsen 1987)

NH4

+NO3

-- Immobile cat ion, - Mobile anion

- Deeper reduced layer favors denitrification

Methods to increase Nitrogen fertilizer use efficiency

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 fertilizersBasal dressing (10 kg/ac)2-3 top dressing of urea (55 -125 kg/ac depending on yield potential)

Early N application promote excessive vegetative growth and shading on lower leaves

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Use of nitrification and urease inhibitors

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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 cultivationInefficient 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 pollutionNitrogen use efficiency in rice production is essential for

Sustain yield increase that needed to meet the demand of a growing world populationTo provide proper income for farm familiesPreserve environmental qualityMinimize energy cost

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