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Reasons for Differences among Soils in Placement of Phosphorus for Maximum Predicted Uptake
Author(s) -
Kovar J. L.,
Barber S. A.
Publication year - 1989
Publication title -
soil science society of america journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.836
H-Index - 168
eISSN - 1435-0661
pISSN - 0361-5995
DOI - 10.2136/sssaj1989.03615995005300060021x
Subject(s) - soil water , phosphorus , fertilizer , chemistry , phosphate , zoology , fraction (chemistry) , analytical chemistry (journal) , environmental chemistry , soil science , geology , biochemistry , biology , chromatography , organic chemistry
Previous research on placement of phosphate fertilizer has shown that the fraction of the soil fertilized with P affected P uptake by the crop, and that the fraction fertilized for maximum P uptake varied among soils. Placement effects on P uptake have been successfully simulated with a mechanistic uptake model. Values of parameters in the model describing P supply to the root depend on P li , the initial concentration of P in the soil solution, and P si , the initial P concentration of the solid phase that rapidly equilibrates with P li . The objective of this research was to determine the importance of differences among soils in changes in P li and P si with increasing rate of P added, on the effect of P placement. Previous research has shown that, as P rate in the fertilized soil increases proportionally with a reduction in the fraction of the soil fertilized, P li increased curvilinearly and P si increased linearly. These relations were de‐on calculated P uptake with differing P placements was examined rate of P added, a, c and h are constants and d and g are predicted values of initial P li and P si , respectively. The effect of varying the coefficients a and c for the P li function and of h for the P si function on calculated P uptake with differing P placements was examined in this study. Standard deviations for c and h of 25% of the mean for 33 diverse soils were obtained from previous research. However, these data also showed that log a was correlated negatively with c ( r = −0.92). Hence, in a study of curvilinearity of P li with P added, it was necessary to adjust log a as c was changed. When log a was decreased as c was increased, the fraction of the soil to fertilize for maximum uptake decreased and predicted P uptake with optimum placement increased. When h was increased while holding c and log a constant, there was only a small increase in predicted P uptake and no change in fraction of the soil to fertilize for maximum P uptake. Hence, changes in P li had a greater effect on predicted P uptake with changes in P placement than changes in P si .