Phosphorus Supply Characteristics of 33 Soils as Influenced by Seven Rates of Phosphorus Addition
- John L. Kovar and
- Stanley A. Barber *
Soil P supply to plant roots increases after addition of P fertilizer due to both the increase in soil solution P (Pl) and adsorbed P (Ps) that equilibrates rapidly with Pl. Little information is available on the effect of added P on the concurrent increase in Pl and Ps. The objective of this research was to investigate the relation between P added and increase in Pl and Ps of 33 soils. Surface soils collected from the U. S. and Canada were equilibrated moist for three weeks with seven rates of P ranging from 0 to 655 mg P kg−1. High rates of application occur where P is placed in a small fraction of the soil. Values for Pl were obtained from P analysis of displaced soil solution and values for Ps from a 24-h extraction with anion exchange resin. For all soils relation of Pl, curvilinear with P addition, x, was described by Pl = axc + d. Values for c, the curvilinearity, varied from 1.03 to 3.15. There was a negative correlation between c and exchangeable Ca (r = −0.65*, significant at the 0.05 probability level) and soil solution P concentration before P addition, Pli, (r = −0.61*). Adsorbed P increased linearly with P addition for all soils, the slope of the relation varying from 0.35 to 0.86. The slope indicates the fraction of added P extracted with the anion-exchange resin. There was a positive correlation between the slopes and the effective diffusion coefficients, De, for P in the soils (r = 0.47*). There was no significant correlation between c and the adsorption line slope. Development of methods for predicting the effect of added P on Pl and Ps will be useful in quantifying their increase in soil resulting from P addition.
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