Comparison of the Phosphorus Sorption Characteristics of a Conservation Reserve Buffer and an Adjacent Crop Field

Abstract

The U.S. Department of Agriculture's Conservation Reserve Program (CRP) was established by the Food Security Act of 1985. Since its inception, thousands of acres of cropland in stream riparian zones have been converted to conservation buffers through the planting of trees and native grasses. The objectives of this study were to determine the phosphorus (P)–sorption characteristics of the surface soil in a 13‐year‐old CRP buffer and an adjacent continuously cropped production area from which the buffer was created and to assess differences in P‐sorption maxima and P‐buffering capacity between the sites. Phosphorus sorption was modeled with both the simple Langmuir and the two‐surface Langmuir equations. There were significant differences in all P‐sorption parameters between the cropped area and the buffer over most of the depth increments studied. The cropped area soil had higher sorption max (Smax), binding energy (k), and P equilibrium buffering capacity (PEBC) than the buffer soil. However, the buffer had higher equilibrium P concentration (EPC). These findings imply that it may not be appropriate to assume that a buffer will act as a P sink simply because it is not receiving P fertilization. Any assessment of buffer or filter strip effectiveness for P retention should include an examination of the P‐sorption properties of the soils present.