|Karlen, Douglas - Doug|
Submitted to: Agriculture Ecosystems and the Environment
Publication Type: Peer reviewed journal
Publication Acceptance Date: 1/27/2005
Publication Date: 6/3/2005
Citation: Bakhsh, A., Kanwar, R.S., Karlen, D.L. 2005. Effects of liquid swine manure applications on NO3-N leaching losses to subsurface drainage water from loamy soils in Iowa. Agriculture Ecosystems and the Environment. 105:118-128. Interpretive Summary: Midwestern soils that have drainage tile installed to remove excess water and improve crop production can be direct sources of nitrate nitrogen to streams and lakes. This six-year field study demonstrated no significant change in average nitrate nitrogen losses through tile drainage water due to crop rotation (continuous corn versus a corn-soybean rotation). Fertilization with liquid swine manure resulted in greater nitrate nitrogen losses through tile drainage water than for the urea ammonium nitrate (UAN) fertilizer treatment, but the actual amount of nitrogen applied through the manure and UAN were not equal. The results clearly demonstrate the importance of developing better application systems and swine manure management practices to minimize nitrogen losses from tile-drained soils. The primary beneficiaries of this research will be public and private nutrient management planners and persons involved with developing new agricultural policies that strive to balance productivity and environmental protection.
Technical Abstract: Long-term applications of organic or inorganic sources of nitrogen (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 six years (1993 to 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 (Zea maize L.) and corn after soybean (Glycine max. L.) production systems. The field data was collected at Iowa State University's Northeastern Research Center near Nashua, Iowa. 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 (P<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 (P<0.05) greater NO3-N losses with tile flows by 53% (26 vs. 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.