Effect of cover crops on phosphorus and trace metal leaching in agricultural soils

Abstract

Soil macropores can enhance the loss of phosphorus (P) and metals via preferential flow pathways in soils fertilized with broiler litter. Cover crops can enhance soil macropores and contribute to preferential flow pathways. Our objective was to determine the effect of cover crops on total P (TP), colloidal P (CP), dissolved reactive P (DRP), dissolved P (DP), total metals, dissolved metals, and colloidal metals in leachate from loamy sand soil cores consisting of soil macropores and fertilized with broiler litter. The cover crop, a mixture of cereal rye and crimson clover, was planted in the late fall in the field. The main crop, planted the following spring, was strip-tillage cotton. Following cotton harvest, intact undisturbed cylindrical soil cores (15 cm diameter and 50 cm depth) were collected from cover crop (CC) and no cover (NC) parts of the field. In the laboratory, for half of the leachate trials with the CC soil cores and half of those with the NC soil cores, we broadcasted broiler litter on the soil surface of the cores using a 10 Mg/ha application rate. For the other half of the trials with the CC cores and the other half with the NC cores, no litter was applied. Rainfall simulations were conducted on each core, and leachate was collected after it flowed down through each soil core. The leachates collected during the rainfall simulations were analyzed for TP, CP, DRP, DP, total metals, dissolved metals, and colloidal metals. The TP, CP, and DP concentrations were significantly greater from CC cores fertilized with broiler litter, than from NC cores fertilized with broiler litter. The mean leachate concentration of TP in soil cores fertilized with broiler litter was 4.07 and 1.54 mg L⁻¹ for CC and NC, respectively. Application of broiler litter resulted in CP loss, which was less than 10 % of TP. Similar trends were observed in dissolved and total trace metal losses. The preferential flow through soil macropores increased the mobility and velocity of solute movement in the cover cropping system.