Site Specific Nutrient Management

Phosphorous and Potassium Management

USING THE SSNM APPROACH TO FORMULATE LOCALLY ADAPTED K RECOMMENDATIONS

The SSNM approach can be used to formulate a K recommendation adapted to any irrigated or favorable rainfed rice environment. Table 4 shows the steps in formulating locally adapted recommendations for high- and low-yielding seasons.

Table 4. Example of K management plans for two contrasting rice-growing seasons. Yield targets depend upon location and can be higher or lower than those in this example.

Steps in formulating the recommendation	High-yielding season	Low-yielding season
1. Attainable yield target (t ha⁻¹)	7	5
2a. K-limited yield; yield without fertilizer K (t ha⁻¹)	5	5
2b. Yield response (t ha⁻¹)	2	0
3. Total fertilizer K₂O required, from Table 4 (kg ha⁻¹)
Low straw input (< 1 t ha⁻¹)	105	45
Medium straw input (2-3 t ha⁻¹)	80	20
High straw input (4-5 t ha⁻¹)	60	0

Step 1: Estimate an attainable yield target. This is the yield attainable by farmers with good management practices and under average climatic conditions.

Step 2: Estimate the K-limited yield or yield without fertilizer K.

Step 3: Estimate the total fertilizer K₂Orequired based on the yield target and K-limited yield from Table 2. Total fertilizer K₂O requirement can also be determined with the nutrient decision support system (NuDSS).

Step 4: Typically apply the fertilizer K₂O twice with about 50% before 14 DAT or 21 DAS and 50% at early panicle initiation. If the fertilizer K requirement is relatively low (≤30 kg K₂O ha⁻¹) and the soil is not sandy, all the K can be applied early before 14 DAT or 21 DAS.

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