Equations for Calculation N-Fertilizer Rates for maize from Soil Analysis

Abstract

                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 gave no detrimental environmental effects. The methods studied were: (1) measuring soil organic matter by Walkley and Black’s method, (2) measuring total soil N by Kjeldahl’s method, (3) extracting soil N with acidified K₂CrO₇ solution, (4) extracting soil N with basified KMnO₄ solution, (5) extraction soil N with acidified KMnO₄ solution, (6) extraction soil N with a solution of CaCl₂ and K₂SO₄, (7) extracting soil nitrate according to Keeney and Nelson (1982) and then measuring the extracted nitrate by Kjeldahl method, (8) extracting soil nitrate according to Iversen et al. (1985) and then measuring the extracted nitrate with nitrate specific electrode and (9) measuring nitrate in maize shoots at 1 month of plant age. The study was made with field-plot experiments at 20 sites using Suwan-3 maize.

                  Four methods, namely methods (1), (2), (7) and (8) were found superior to the others. The equations for calculating rates of N for maize from these methods were: (a) log (100 – y) = 2 – 0.347 b – 0.0377 x for method (1), (b) log (100 – y) = 2 – 0.000593 b – 0.0298 x for method (2), (c) log (100 – y) = 2 – 0.0389 b – 0.0326 x for method (7) and (d) log (100 – y) = 2 – 0.0432 b – 0.0238 x for method (8); where y was the obtained grain yield in percent of the maximum yield; b, the index of soil-N availability [as % of soil organic matter for method (1) and ppm N for methods (2), (7) and (8)] and x, rate of the required fertilizer N in kg N per rai(6.25 rais = 1 ha). Considering with other factors in conjunction to the reliability, methods (1) and (8) were recommended.