ABSTRACT:
Research on watershed runoff losses from cotton (Gossypium hirsutum L.) cropping systems in limestone soil regions is limited. Runoff of water, sediment, total N, NH4-N, NO3-N, and solution and particulate P were measured from a 3-8-ha (9.4-ac) watershed during three years of conventional tillage (CvT) cotton, followed by three years of conservation-tillage (CsT) cotton. The study was conducted from 1984 through 1989 in the Limestone Valley region of northern Alabama, on slopes of 1-6 percent and Decatur (Rhodic Paleudults) and Emory (Fluventic Um-bric Dystrochrepts) soils. Although CsT resulted in a higher proportion of annual rainfall as runoff than CvT, about twice as much sediment was discharged from the watershed with CvT than with CsT [average of 2,979 vs. 1,311 kg ha−1 yr−1, (2,660 vs. 1,170 lbs ac−1 yr−1) respectively]. A few intense storms during late winter through early spring, before full cotton canopy, contributed to most of the erosion losses in CvT. Annual mean concentrations of NO3-N in runoff were equally low for both tillage systems, ranging from 1.3 to 2.2 mg L−1 during the six years. Winter rye was very effective in diminishing NO3-N concentrations in runoff from January to spring fertilization. A temporary period of elevated NO3-N and P concentrations occurred in runoff sampled shortly after surface application of NP fertilizer in April, especially with CsT. In our study, most of the runoff P loss was associated with the solution rather than the particulate phase, and more P runoff occurred with CsT than with CvT In balance, however, CsT is more environmentally acceptable than CvT for cotton production, assuming prudent NP fertilizer management.
Footnotes
J.M. Soileau is a research soil scientist with Agricultural Research and Practices, Tennessee Valley Authority, Muscle Shoals, Alabama 35660-0101. J.T. Touchton and B.F. Hajek are Professors in the Department of Agronomy and Soils, and K.H. Yoo is an Associate Professor in the Department of Agricultural Engineering, Auburn University, Auburn, Alabama 36849. The authors gratefully acknowledge assistance in this project from the following: TVA Field Engineers J.C. Adams, B.O. Bell, R.E. Covington, J.E. Eidson, T.E. Montgomery, B.L. Thompson, and J. Walker; Auburn University lab analyst R. Sharpe; Gilbert Farm operator D. Entrekin; and statistician Dr. Julio Henao of the International Fertilizer Development Center. Contribution from the National Fertilizer and Environmental Research Center, TVA, and Alabama Agricultural Experiment Station 3-912992P. Mention of brand names is for descriptive purposes and does not constitute product endorsement by the authors, TVA, or Auburn University.
- Copyright 1994 by the Soil and Water Conservation Society
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