Site Specific Nutrient Management

Potassium (K) addition plot technique

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Potassium Addition Plot Technique Version 1.1

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Determination of crop yield

1. At crop maturity, harvest the central 5-m² area in the K addition plot (Fig. 1).

2. Likewise, harvest a representative 5-m² area in the designated area outside the K addition plot (Fig. 1).

3. Make sure that all the grains in the 5-m² areas are collected, and harvested samples are properly placed in labeled bags.

4. Thresh and clean the harvested grain samples.

5. Sun dry the grain sample to constant weight.

6. Convert the sample weight to yield in t ha⁻¹ by using the formula:

Yield (t ha⁻¹) = [(Sample yield in kg)/5] x 10

7. Determine the K response:

K response = Grain yield in K addition plot – grain yield in farmer’s K practice

Determination of filled and unfilled grain

1. At crop maturity, take four representative panicles from plants immediately surrounding the central 5-m² harvest area in the K addition plot and the plot with farmer’s K management (Fig. 1).

2. Strip all spikelets, both filled and unfilled, from the panicles and place in a tray or container. Perform this procedure separately for both K addition plot and farmer’s K management practice.

3. Separate and count the total number of filled (FSpNo) and unfilled spikelets (UFSpNo).

4. Calculate filled spikelet percentage using:

[FSpNo/(FSpNo+UFSpNo)] x 100

Fig. 1. Illustration of the layout for a K addition plot and harvest areas for determination of grain yield and grain filling in a farmer’s field.

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