Eqations for calculating N-fertilizer rates for maize from soil analysis
1992
Amnat Suwanarit | Piya Chalermglin | Jarong Rungchong (Kasetsart Univ., Bangkok (Thailand). Faculty of Agriculture. Dept. of Soil Science)
Comparisons were made among reliability of 9 chemical methods for evaluating the availability to maize of N in soils and for calculating N-fertilizer rates that would produce high maize yields while minimize N fertilizer and give no detrimental environmental effects. The study was made with field-plot experiments at 20 sites. Four methods were found superior to the others. Considering with other factors in addition to the reliability, the method measuring organic matter content and that measuring nitrate extracted from soil with a nitrate specific electrode were recommended. The equations for these two methods were: (1) log (100 - y) = 2 - 0.347 b - 0.0377 x, and (2) log (100 - y) = 2 - 0.0432 b - 0.0238 x, respectively, where y was the obtained grained grain yield in percent of the maximum yield b the index of soil-N availability [as percent of soil organic matter for Equation (1) and ppm N for Equation (2)] and x rate of the required fertilizer N in kg N per rai (6.25 rais = 1 ha).
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