Abstract
Some legumes are known to reduce rhizosphere soil pH which in turn usually increases soil solution P, Pli and therefore increases P uptake. In an initial experiment with a nonlegume [corn (Zea mays L.)], observed P uptake agreed closely with predicted P uptake while with a legume [alfalfa (Medicago sativa L.)], observed P uptake was greater than predicted P because the rhizosphere was acidified, Pli increased, and more P was absorbed. Using a pot experiment, this investigation calculates the change in rhizosphere pH and Pli necessary to have predicted P uptake obtained with a mechanistic uptake model agree with observed P uptake. The pot experiment was conducted with alfalfa, faba bean (Vicia faba L.) and Austrian winter pea (Lathyrus hirsutus) grown on Chalmers silt loam (fine‐silty, mixed, mesic Typic Haplaquolls) limed to pH levels of 5.72, 6.30, 7.22 and 8.30. Predicted phosphorus uptake at each pH level was calculated with the uptake model using the data for bulk soil. The relation of predicted P uptake to initial soil pH was determined, then this relation was used with observed P uptake to calculate rhizosphere pH. Subsequently, Pli as a function of pH was determined and used to calculate rhizosphere Pli. In this study, the calculations indicate that legumes reduced rhizosphere soil pH by 0.39 to 0.77 units and increased P availability by 20.8 to 241.7%.
Notes
Visiting Assistant Professor and Professor of Agronomy, respectively.
Journal Paper No. 12839. Purdue University Agriculture Experiment Station, W. Lafayette, IN. 47907. Contribution from the Department of Agronomy.