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ARS Home » Southeast Area » Tifton, Georgia » Southeast Watershed Research » Research » Publications at this Location » Publication #231671
Title: Effects of Cover Crop Systems on Soil Physical Properties and Carbon/Nitrogen Relationships in Coastal Plain Soils under Conservation Tillage

Author
item Hubbard, Robert
item Strickland, Timothy - Tim
item PHATAK, SHARAD - UGA

Submitted to: Soil and Tillage Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/29/2012
Publication Date: 1/31/2013
Citation: Hubbard, R.K., Strickland, T.C., Phatak, S.C. 2013. Effects of Cover Crop Systems on Soil Physical Properties and Carbon/Nitrogen Relationships in Coastal Plain Soils under Conservation Tillage. Soil and Tillage Research. Pages 276-283.

Interpretive Summary: A study was conducted to determine the extent to which different combinations of cover crops in conservation tillage systems affect soil physical properties and C/N levels in a sandy coastal plain soil. The study had triple cropping systems with sunn hemp or fallow as the first crop, fallow or crimson clover as the second crop, and fallow or sweet corn at different N rates as the third crop. The study showed positive effects of cover crops in conservation tillage on soil C and N. Cover crops under conservation tillage increased C and N levels in the soil, which in turn had positive effects on soil bulk density, saturated hydraulic conductivity, and moisture retention. The increases in C caused decreased bulk density and increased saturated hydraulic conductivity and moisture retention. When sunn hemp was included in the rotation as a late summer cover crop, it added significantly more C to the soil than cropping systems including only crimson clover as a winter cover. In general, the soil in the row had lower bulk density and greater soil moisture retention than that of the interrow. The changes in soil physical properties and increased soil carbon and moisture contents generated positive feedbacks that stimulated microbial activity and associated nitrogen cycling efficiencies in the surface layer of the Tifton loamy sand used for the study. Organic matter decomposition rates are high and much of the surface soil quality is maintained by soil organic matter. Overall the study indicates that high residue input from fall and winter cover crops is important for the maintenance of plant-available nitrogen in the very sandy soils of the southeastern coastal plain region. GRACEnet Publication.

Technical Abstract: Uncertainty exists concerning the impact of cover crops with conservation tillage on the total agricultural environment. A study conducted from 2002 – 2005 by USDA-ARS and the University of Georgia assessed the effects of cover crops on C/N sequestration and soil physical properties in a sandy coastal plain soil. The cropping systems were (A) sunnhemp (Crotalaria juncea L.), crimson clover (Trifolium incarnatum L.), sweet corn (Zea mays L.); (B) sunnhemp, fallow, sweet corn; (C) fallow, crimson clover, sweet corn; (D) fallow, fallow, sweet corn; or (E) fallow, fallow, fallow. Three N rates (0, 75, or 150 kg ha-1) were tested on the corn for cropping systems A, B, and C, while N rates of 0, 75, 150, 225, and 300 kg ha-1 were used for cropping system D. No N was applied to cropping system E. Carbon/nitrogen sequestration was determined from samples of the top 2.5 cm of soil collected quarterly. Soil physical property measurements were made on minimally disturbed cores (7.6 cm height X 7.6 cm diameter) collected from the top 7.6 cm of soil both within the row and interrow of each plot seven times during the study using an impact type sampler. Soil physical property measurements on the cores included bulk density (BD), saturated hydraulic conductivity (Ks), and volumetric soil moisture content (') over a range of matric suctions. No differences were found in soil physical properties based on cropping system or N rate treatment, but significant differences were found between sampling positions. There were significant differences in BD, Ks and ' between soil in the rows and that in the interrows for all treatments. Bulk densities were lower, Ks were greater, and ' were greater in the rows than in the middles. The study showed that cover crops under conservation tillage increased C and N levels in the soil, which in turn had positive effects on BD, Ks, and '. The increases in C caused decreased BD and increased Ks and '. Significantly greater C, lower BD and greater ' were found in the rotations with sunn hemp as crop 1 as compared to rotations with fallow as crop 1. The changes in soil physical properties and increased soil carbon and moisture contents generated positive feedbacks that stimulated microbial activity and associated nitrogen cycling efficiencies in the surface layer of the Tifton loamy sand used for the study. Organic matter decomposition rates are high and much of the surface soil quality is maintained by soil organic matter. Overall the study indicates that high residue input from fall and winter cover crops is important for the maintenance of plant-available nitrogen in the very sandy soils of the southeastern coastal plain region.