Author
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Olness, Alan |
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Submitted to: Agronomy Abstracts
Publication Type: Abstract Only Publication Acceptance Date: 11/8/1996 Publication Date: N/A Citation: N/A Interpretive Summary: Technical Abstract: Soil pH affects the rate of microbial mineralization of organic matter and the subsequent production of nitrate-N (NO-3-N). Production of NO-3-N during the spring in the 12-state Cornbelt region was analyzed using SAS PROC MODEL procedure. The change in NO-3-N in the surface 0- to 30-cm depth increment of the soil from pre-plant to V-5 growth stage of corn in non-fertilized plots was evaluated as a function of soil pH. Because the change in NO-3-N appeared to reach a maximum at about 6.7 and was negligible at pH < 5.0 or >8.5, a b*{sech**2[k*(pH-psi)]} function was applied to the data. The data were evaluated as 1) the entire set, 2) only that set which evidenced net accumulation in the 0- to 60-cm depth increment, and 3) only maximal values within a pH increment of 0.1 units. The coefficient of pH, k, varied from 0.7 to 1.05 and the optimal pH, psi, varied from 6.65 to 6.70. The function coefficient, b, increased from 19.8 for the entire data set to 31.4 for profiles with net NO-3-N accumulation to 89.6 for a model of the maximal values of NO-3-N; the value of the coefficient is probably > 90. The largest r**2 value (> 0.42) was obtained with maximal values of NO-3-N within a pH increment of 0.1 units. Model residuals were uniformly distributed with regard to pH but consistently underestimated large values and overestimated small values of observed d[NO-3-N]*dt**-1. |
