Tillage and Liquid Swine Manure Application Effects on Subsurface Drain Flow and NO₃-N and PO₄-P Leaching Losses under Corn-Soybean Cropping System

Agricultural production systems in the Midwestern states of the United States of America are considered to be contributing significantly to Hypoxia related problems in the Gulf of Mexico. Therefore, a field study was conducted at the Iowa State University’s Northeast Research Center, near Nashua, Iowa to evaluate the effects of tillage and liquid swine manure application on NO₃-N and PO₄-P leaching losses to subsurface drain system under corn and soybean production system. Liquid swine manure was applied in the fall after crop harvest, followed by a pass of chisel plow to incorporate manure into the surface soil within 48 hours of manure application. Six-year (2001-2006) data were collected and analyzed in a randomized complete block design to determine the effects of tillage and manure application on subsurface drain flow, NO₃-N and PO₄-P leaching losses with subsurface drain water and crop yields. Results of this study indicated that treatment effects on subsurface drainage volume were significant at p=0.05 showing spatial and temporal variability of NO₃-N concentrations in subsurface drainage water (p<0.01). The NO₃-N concentrations in subsurface drain water were found to be higher in all treatments but were two-folds greater in the plots receiving manure every year. No significant effects of treatments were observed on total PO₄-P leaching losses and PO₄-P concentrations in subsurface drain water as well as on corn and soybean grain yields. Corn grain yields showed an increase of 1.8% in manure applied corn plots. No significant difference, however, was found between soybean plots receiving manure every year and soybean plots with no manure application.