Model for Long‐term Phosphate Reaction Kinetics in Soil

Publisher Website
Google Scholar
Abstract
A simplified reaction kinetics model for long‐term P‐sorption in soils receiving large quantities of P‐rich animal manure is presented. Results from soil analyses for samples taken in 84 fields in nine different soil types indicate that the oxalate extractable P provides a good estimation of total P. Sorption experimental data for reaction periods up to 249 d show that measured sorption is proportional to In(t). Total sorption, F, (at long reaction periods) that includes P already present (Pox) appears to be proportional to the sum,M, of oxalate‐extractable Fe and Al. These results are described with a model where soil reactivity is related linearly to M, and the reaction kinetics are expressed in terms of a composite concentration time variable, I. This leads to the relationship F = kM In(I), where k is a characteristic of the soil. Comparisons with results in literature indicate that the concentration dependence of the reaction is accurately described by using I instead of time as a variable. Differences in reactivity (k) for different soil horizons or soil types are apparent from the different k values for topsoils and subsoils. Sorption measured during 40 h (Fr) may be extrapolated to long‐term (1–2 yr) sorption (Fm) for each soil separately without correction of the value of I for the reaction period in the field by simply setting Fm = Pox + 1.8 Fr. For a P concentration of 5 mmol L−1 this leads to a value of αm = Fm/M = 0.63 ± 0.14 for topsoils. Extrapolation using the average k value found for short‐term sorption experiments results in the same value of αm.

This publication has 0 references indexed in Scilit: