Phosphorus Supply Characteristics of 33 Soils as Influenced by Seven Rates of Phosphorus Addition

Abstract

Abstract Soil P supply to plant roots increases after addition of P fertilizer due to both the increase in soil solution P ( P l ) and adsorbed P ( P s ) that equilibrates rapidly with P l . Little information is available on the effect of added P on the concurrent increase in P l and P s . The objective of this research was to investigate the relation between P added and increase in P l and P s 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 P l were obtained from P analysis of displaced soil solution and values for P s from a 24‐h extraction with anion exchange resin. For all soils relation of P l , curvilinear with P addition, x , was described by P l = ax c + 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, P li , ( 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, D e , 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 P l and P s will be useful in quantifying their increase in soil resulting from P addition.