|STUEDEMANN, JOHN - Retired ARS Employee
Submitted to: Soil and Tillage Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/3/2013
Publication Date: 11/1/2013
Publication URL: http://handle.nal.usda.gov/10113/57858
Citation: Franzluebbers, A.J., Stuedemann, J.A. 2013. Soil-profile distribution of inorganic N during 6 years of integrated crop-livestock management. Soil and Tillage Research. 134:83-89.
Interpretive Summary: Excessive accumulation of soil nitrate-N from agricultural production systems can threaten water and air quality. Careful management by balancing N inputs and N outputs is needed to achieve high production and preserve environmental quality. Scientists from the USDA-Agricultural Research Service in Raleigh NC and formerly from Watkinsville GA conducted a field experiment to determine soil nitrate accumulation under diverse cropping systems including grazing of cover crops by cattle in Georgia. Cropping systems with greatest nitrogen fertilizer application rate led to largest accumulation of nitrate in the soil profile. Using no tillage management of soil was beneficial in reducing nitrate concentration, while maintaining and improving crop and animal yields. Grazing of cover crops had minimal effect on soil nitrate concentration, and therefore, should not be viewed as a threat to water quality contamination by accelerating nutrient turnover. Results of this study suggest that both conservation tillage and resource-efficient utilization of cover crops as forage for cattle can be combined to avoid nitrate contamination potential of agricultural systems in the southeastern USA.
Technical Abstract: Excessive accumulation of soil nitrate-N can threaten water and air quality. How integrated crop-livestock systems might influence soil-profile nitrate-N accumulation has not been investigated. Therefore, we determined soil nitrate-N accumulation during 6 years of evaluation of diverse cropping systems on a Typic Kanhapludult in Georgia, USA. Of the total change in soil nitrate-N content that occurred during 6 years (increase of 14 kg N/ha/yr), an average of 60% occurred in the primary rooting zone (0-90-cm depth) and 40% occurred in the zone below typical rooting (90-150-cm depth). Soil nitrate-N accumulation was greater in cropping systems with greater N fertilizer input, while it was surprisingly insensitive to differences in harvested N output. Soil nitrate-N accumulation was greater under conventional tillage than under no tillage at all soil depths (5.1 +/- 4.2 kg N/ha/yr greater at a depth of 90-150 cm), suggesting soil disturbance was a key factor in mobilizing N and keeping it more disassociated from the organic-inorganic cycling system. Grazing of cover crops had variable effects on soil nitrate-N content: greater soil nitrate-N content in the rooting zone at the end of 1 year (no other occurrences of this effect during later years), greater soil nitrate-N content in the zone below typical rooting at the end of 3 and 4 years, and lower soil nitrate-N content in the rooting zone at the end of 6 years. These results confirm the beneficial effect of no-tillage management on moderating nitrate-N accumulation in the soil profile and indicate a mostly neutral effect of cover crop grazing on soil nitrate-N accumulation.