SITE-SPECIFIC NUTRIENT MANAGEMENT (SSNM)
Site-specific nutrient management (SSNM) enables rice farmers to optimally supply their crop with essential nutrients. With SSNM, plant-essential nutrients are supplied as and when required to ensure the ‘feeding’ of the rice crop to optimally meet its nutrient needs.
The SSNM approach involves three steps:
Rice yields are location and season specific — depending upon climate, rice cultivar, and crop management. The yield target for a given location and season is the estimated grain yield attainable with farmers’ crop management when N, P, and K constraints are overcome.
The amount of nutrients taken up by a rice crop is directly related to yield. The yield target therefore indicates the total amount of nutrients that must be taken up by the crop.
The SSNM approach promotes the optimal use of existing (indigenous) nutrients coming from the soil, organic amendments, crop residue, manure, and irrigation water. The uptake of a nutrient from indigenous sources can be estimated from the nutrient-limited yield, which is the grain yield for a crop not fertilized with the nutrient of interest but fertilized with other nutrients to ensure they do not limit yield.
Fertilizer N, P, and K are applied to supplement the nutrients from indigenous sources and achieve the yield target. The quantity of required fertilizer is determined by the deficit between the crop’s total needs for nutrients — as determined by the yield target — and the supply of these nutrients from indigenous sources — as determined by the nutrient-limited yield.
The required fertilizer N is distributed in several applications during the crop growing season to best feed the crop’s need for supplemental N. Fertilizer P and K are applied in sufficient amounts to overcome deficiencies and maintain soil fertility.
In the SSNM approach, fertilizers are applied using the following principles to achieve high yield and high efficiency of plant use:
1. Apply only a moderate amount of fertilizer N to young rice within the 14 days after transplanting (DAT) or 21 days after sowing (DAS), when the need of the crop for supplemental N is small.
2. Apply fertilizer N after 14 DAT or 21 DAS based on the crop’s need for supplemental N, as determined by leaf N status. The leaf color chart (LCC) is a tool that could be used for assessing leaf N status and the crop’s need for N.
3. Apply all fertilizer P near transplanting or sowing.
4. Apply fertilizer K twice — 50% near transplanting or sowing and 50% at early panicle initiation. When fertilizer K rates are relatively low (for example, ≤30 kg K2O ha−1), all fertilizer K can be applied near transplanting or sowing.
Site Specific Nutrient Management
