Rice is by far the most important crop in Nepal and accounts for about 50% of the total agricultural area and production in the country. It is grown on about 1.45 million ha, and total production since 1988/89 has hovered between 3.2 million and 2.5 million tonnes. Rice contributes approximately one-fourth of the GDP and more than 75% of the working population is engaged in rice farming for at least 6 months of the year. Furthermore, rice provides nearly 50% of the calorie requirement.
What is nutrient management?
Nutrient management involves using crop nutrients as efficiently as possible to improve productivity while protecting the environment. The key principle behind nutrient management is balancing soil nutrient inputs with crop requirements. When applied in proper quantities and at the right times, added nutrients help achieve optimum crop yield.
Why is nutrient management necessary?
Nutrient management planning helps to reduce contamination to waterways by plant nutrients. Without proper management, nutrients can dissolve in soil water and go into surface or groundwater through leaching or runoff. This could contaminate surface and groundwater, and on-farm drinking water, community wells and other drinking water sources can be affected. Valuable nutrients could be lost, resulting in reduced crop yields or additional costs for commercial fertilizers.
RICE NUTRIENT MANAGEMENT
While discussing nutrient management we firstly need to know about the factors which affect nutrient availability in the rice field. There are several factors that directly or indirectly affect the nutrient availability for the optimum production of rice in the field.
Factors affecting nutrient availability in a rice field
Total nutrient content of the soil
Nutrient supplying capacity of soil
The moisture content of the soil
Soil texture and structure
Organic matter content of the soil
Soil microbial activity
Ionic composition of soil solution
To overcome nutrient deficiency or excessiveness judicious application of nutrients is necessary. The right amount of nutrients for rice fields might vary from place to place. It is mainly due to differences in soil fertility, INS, NUE, crop variety and planting time, irrigation facility, climate and so many other factors. Hence, recommendations should be made based on the above factors and laboratory tests of soil. In Nepal, there is a recommended dose of fertilizers, which is made by concerning these above factors.
The general recommendation of fertilizers in Nepal
Upland rice/ Rainfed condition: 60:20:20 kg NPK/ha
Lowland rice/ Irrigated condition: 100:30:30 kg NPK/ha
Zinc deficiency in rice shows symptoms of Khaira disease. Apply Zinc Sulphate
@ 20-30 kg/ha at the time of final field preparation
This recommended dose of fertilizer is applied by keeping time in concern. This dose needs to be at the right time around the year for the best result in the rice field.
Time of application :
Apply manures at the time of first field preparation (15 days before planting)
Basal dose: apply a full dose of Phosphorus, Potassium and half dose of Nitrogen at the time of final field preparation
The remaining half dose of Nitrogen is split into two doses and top dressed at around 30 (tillering stage) and 60 (panicle initiation stage) days after sowing or transplanting.
Method of application
There are different methods for the application of fertilizers. It includes:-
- Broadcasting:–Broadcasting is the spreading of fertilizer uniformly over the entire field.
- Side dressing:-Side dressing is the application of fertilizers along the surface of the crop row.
- Drilling:-Drilling is the placement of fertilizers in the subsoil layer of the crop row just below the seed.
- Band placement:-Band placement is the application of fertilizer in a continuous band below the seed and side of the crop row.
- Foliar application:-Foliar application is the spraying of fertilizer solutions containing one or more nutrients on the foliage of growing plants.
- Fertigation:-It refers to the application of water-soluble fertilizers through irrigation water.
In the rice field, nitrogen importance is huge and it plays a very important role in the production of rice. The soil containing the right amount of nitrogen with other essential nutrients will give a higher yield than the normal field. We should check the nutrient status of the soil on a regular basis so that we can get the information and act accordingly.
Pathways for loss of nitrogen
Leaching and runoff
These are the pathways of nitrogen loss from the field. This should cease to produce a higher yield because nitrogen has a very important role in the rice field to increase the level of production.
Management of nitrogenous fertilizer :
The objective of the management of nitrogenous fertilizer is to reduce losses and increase nitrogen use efficiency (NUE). NUE is the increase in the economic yield of crops per unit of nitrogen applied. The methods to reduce nitrogen loss in paddy field are:-
Method of application: Soil surface of rice field is classified as oxidized (up to 1 cm depth) and reduced zones. Apply fertilizer at reduced zone by incorporating it into the soil, rather than at oxidized zone where there are chances of denitrification and leaching of ammoniacal fertilizers
Time of application: apply fertilizer during critical stages of the plant (tillering and panicle initiation stages)
Amount of application: Apply fertilizer according to the demand of the crop by splitting it into 2-3 doses
Selection of suitable fertilizer: Ammoniacal forms of fertilizer are better than nitrate form because there are fewer chances of denitrification and leaching loss. Ammoniacal forms of fertilizer are Urea, ammonium sulphate, ammonium phosphate, etc.
Use of slow-release materials or coated urea: Urea is coated by oilseed cake, neem cake, mud or Sulphur and applied on paddy fields. These coated urea release nitrogen slowly and minimizes the losses through denitrification and leaching. Granular urea also has slow-release property
Use of nitrification inhibitors: are the chemicals that slow down the process of nitrification and increase nitrogen use efficiency. Examples: Thiourea, N-serve, potassium azide, nitrapyrin, etc used @ 5% of fertilizer
Providing ample time for decomposition: of organic manure so that nutrients in the organic form are readily available in mineral forms for plants. Otherwise, there will be immobilization of N due to ammonium fixation.
Use of mulch: reduces loss of N by ammonium volatilization.
These are some ways of managing nutrients in the rice field. Besides nutrients, water and weeds also need to be managed to increase the production of rice.