Correlation between various chemical indices for soil nitrogen availability and growth, yield, nitrogen uptake and the response of corn to fertilizer nitrogen
1992
Piya Chalermglin
Correlations between nine chemical methods, to evaluate the availability of nitrogen in soil to corn, and growth, yield and nitrogen uptake as well as the response of corn to rates of fertilizer nitrogen were examined. Field experiments were conducted at 20 sites on soils with organic matter ranging from about 1 % to 3 % and with pH 4.5 to 7.5 in Nakhon Ratchasima, Nakhon Sawan and Suphan Buri provinces from August 1989 to February 1992. The results showed that four methods, namely, soil organic matter measurement, total soil nitrogen measurement, measurement of soil extractable nitrate by distillation and measurement of soil extractable nitrate specific electrode, were outstanding. The equations relating grain yields with the chemical indices and the rates of fertilizer nitrogen for the four methods were as the follows, respectively: 1) log (A-y) = log (A- 0.347b-3.77x10(** (2)x, 2) log (A-y) = log A-9.33x10(** (4)b-2.98x10(** (2)x, 3) log (A-y) = log A-3.89x10(** (2)b-3.26x10(** (2)x and 4) log (A-y) = log A-4.32x10(** (2)b-2.38x10(** (2)x. Where A is the maximum yield, b soil test value, x the rates of fertilizer N (kg N/rai, 6.25 rai = 1 ha) and y the obtained yield (% of maximum yield). Correlation coefficients between the actual grain and the calculated grain yield by the four chemical methods were 0.92**, 0.92**, 0.92** and 0.91**, respectively.
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