Effects of liquid swine manure applications on NO3–N leaching losses to subsurface drainage water from loamy soils in Iowa

Abstract

<p>Long-term applications of organic or inorganic sources of N to croplands can increase the leaching potential of nitrate–nitrogen (NO₃–N) for soils underlain by subsurface drainage “tile” network. A field study was conducted for 6 years (1993–1998) to determine the effects of liquid swine manure and urea ammonium nitrate (UAN) solution fertilizer applications on NO₃–N concentrations and NO₃–N losses with subsurface drainage water under continuous corn (<em>Zea maize</em> L.) and corn after soybean (<em>Glycine max.</em> L.) production systems. The field data collected at Iowa State University's northeastern research center near Nashua, Iowa, under six N-management treatments and each replicated three times, were analyzed as a randomized complete block design. The flow weighted average (FWA) NO₃–N concentrations in tile flow were affected significantly (<em>P</em> < 0.05) by N-application rates from swine manure, growing season and treatment effects. Peak (FWA) NO₃–N concentrations values of 31.8 mg L⁻¹ under swine manure and 15.5 mg L⁻¹ under UAN in subsurface drain water were observed in 1995 following the dry year of 1994. The 6-year average crop rotation effects on NO₃–N losses with tile flows were not found to be significantly affected either with swine manure or UAN-fertilizer applications but showed significant increase in corn grain yields under both the systems. Liquid swine manure, averaged across the 6-year period, resulted in significantly (<em>P</em> < 0.05) greater NO₃–N losses with tile flows by 53% (26 kg N ha⁻¹ versus 17 kg N ha⁻¹) and showed no difference in corn grain yields in comparison with UAN-fertilizer applications under continuous corn production system. These results emphasize the need for better management of swine manure application system during the wet and dry growing seasons to reduce NO₃–N leaching losses to shallow groundwater systems to avoid contamination of drinking water supplies.</p>