EVALUATION OF SOIL TESTS FOR N REQUIREMENT OF MAIZE
Keywords:Nitrate-N, greenhouse, available N, continuous cropping, organic carbon
Soil test methods for nitrate-N, total N and organic C were evaluated in the greenhouse, using 20 soils mostly from farmer's fields, in Nigeria. The results indicated that NO3-N was the best index of available N for a short 4-week period but the poorest under continuous cropping over eight weeks. Total N and organic C values were superior to nitrate-N on long cropping system.
The three soil Nitrogen indices were also evaluated and calibrated in a field study on five bench mark soils for two seasons. The results indicated that NO3-N was correlated significantly with total N and organic C, and these were in turn correlated with relative yield in the field. Deficiency values were 20 ppm NO3-N, 0.11% total N and 1.26% C. Organic C and total N were highly correlated for the soils; therefore, it is possible to use either organic C or total N values for predicting response of crop to N application.