SITE-SPECIFIC NUTRIENT MANAGEMENT (SSNM)
Zinc addition plot technique
The improved management of fertilizer N, P, and K can help farmers attain higher yields and profit. As higher yields are attained the requirement of the crop for nutrients in addition to N, P, and K increases; and micronutrients such as zinc might become deficient. Farmers consequently need to know whether the soil-supplying capacity of zinc at a given location is sufficient for high yields. The zinc addition plot technique is a simple tool to assess whether farmers should apply zinc fertilizer to attain high yield and profit.
The zinc addition plot technique involves broadcasting zinc sulfate, an effective source of plant-available zinc, to a small plot superimposed in farmers’ fields. The grain yield from the zinc plot is compared to the yield from an adjacent plot managed similarly but without addition of zinc. Higher yield in the zinc addition plot indicates a deficiency of zinc and highlights the need for applying zinc fertilizer to achieve high yield.
Zinc addition plots should ideally be placed across a range of soil types. There is a relatively higher likelihood of zinc deficiency on lighter textured soils, on calcareous (high pH) soils, and in low-lying areas with prolonged submergence of soils. Hence, these types of soils if present should be included among the selected locations for zinc addition
Layout and installation
1. Select locations in farmers’ fields with the following characteristics:
a. A relatively representative level of soil fertility and history of previous fertilizer use.
b. Relatively good management of the crop and fertilizer N, P, and K by the farmer.
c. No shade or effect from adjacent trees.
2. Immediately after the farmer transplants rice or direct seeds rice, measure out a 5 x 5 m (25 m2) area in the field for the zinc addition plot (Fig. 1). Place bamboo or wooden stakes on the four corners of the plot.
3. Surround the plot with a small soil bund with a height sufficient to prevent movement of surface water inside and outside the plot. For transplanted rice, do this about 14 days after transplanting; for direct seeded rice, do this 10-14 days after sowing rice.
4. Then uniformly broadcast a pre-weighed amount of zinc sulfate within the plot about 14 days after transplanting or 10-14 days after sowing wet-seeded rice. The added zinc sulfate should be sufficient to supply 5 kg Zn ha−1.
5. After 4 days, place channels in the soil bund (i.e., break the soil bund) to allow water to freely flow in and out of the zinc addition plot. The plot would then receive irrigation water as part of the normal practice of irrigating the farmer’s field.
6. Within 20 days after transplanting and sowing rice identify a representative 5 x 5 m area in the farmer’s field at least 10 m away from the zinc plot. This area must have the same cropping and fertilizer history as the area where the zinc addition plot is placed. Mark this area with bamboo or wooden stakes. It will be used for measuring rice yield without zinc addition.
7. Manage the rice within the zinc addition plot exactly as in the adjacent farmer’s field.
Management of zinc addition plots
Farmers use their own field management and irrigation operations practices. All field operations and all NPK fertilizer applications must be identical in the zinc addition plot as in the adjacent farmer’s field and in the area designated for the measurement of yield in the farmer’s field.
Determination of crop yield
1. At crop maturity, harvest the central 5-m2 area in the zinc addition plot (Fig. 1).
2. Likewise, harvest a representative 5-m2 area in the designated area outside the zinc addition plot (Fig. 1).
3. Make sure that all the grains in the 5-m2 areas are collected and the 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 zinc response:
Zn response = Grain yield in Zn addition plot – grain yield without added Zn
Fig. 1. Illustration of the layout for a zinc addition plot and harvest areas for determination of grain yield in a farmer’s field.
Site Specific Nutrient Management
