Effects of cover crop systems on soil physical properties and carbon/nitrogen relationships in the coastal plain of southeastern USA

• Published in: Soil & tillage research Vol. 126; pp. 276 - 283
• Main Authors: Hubbard, Robert K., Strickland, Timothy C., Phatak, Sharad
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 01.01.2013; Elsevier
• Subjects: Agronomy. Soil science and plant productions; Biological and medical sciences; Bulk density; Fertilizer use efficiency; Fundamental and applied biological sciences. Psychology; Nitrogen use efficiency; Saturated hydraulic conductivity; Soil moisture retention; Soil science; United States; North America; America; Bulk density; Saturated hydraulic conductivity; Soil moisture retention; Nitrogen use efficiency; Fertilizer use efficiency; Nutrient recovery; Cover crop; Property of soil; Hydraulic conductivity; Nitrogen; Southeast; Carbon; Physical properties; Fertilizers; Coastal plain; Saturated medium; Soil science; Water holding capacity
• ISSN: 0167-1987; 1879-3444
• DOI: 10.1016/j.still.2012.07.009

► The effects of the cover crops sunn hemp and crimson clover on soil physical properties and C/N relationships are reported for a sandy coastal plain soil under conservation tillage. ► Cover crops increased soil C and N levels, decreased bulk density, increased saturated hydraulic conductivity, and increased soil moisture retention. ► Inclusion of sunn hemp as a late summer cover crop added significantly more C than cropping systems with only crimson clover as a winter cover. ► Inclusion of sunn hemp increased corn biomass production and fertilizer use efficiency compared to crimson clover or fallow plus fertilizer cropping systems. Uncertainty exists concerning the impact of cover crops with conservation tillage on the total agricultural environment. A study conducted from 2002 to 2005 by USDA-ARS and the Univ. of GA assessed the effects of cover crops on soil physical properties and C/N relationships in a sandy coastal plain soil. The cropping systems were (A) sunn hemp (Crotalaria juncea L.), crimson clover (Trifolium incarnatum L.), sweet corn (Zea mays L.); (B) sunn hemp, fallow, sweet corn; (C) fallow, crimson clover, sweet corn; (D) fallow, fallow, sweet corn; or (E) fallow, fallow, fallow. Three N rates (0, 67, or 133kgha−1) were tested on the corn for cropping systems A, B, and C, while N rates of 0, 67, 133, 200, and 267kgha−1 were used for cropping system D. No N was applied to cropping system E. Soil physical property measurements made on minimally disturbed cores (7.6cm height×7.6cm diameter) collected from the top 7.6cm both within the row and interrow of each plot seven times during the study included bulk density (BD), saturated hydraulic conductivity (Ks), and volumetric soil moisture content (θ) over a range of matric suctions. Carbon/nitrogen levels were determined from samples of the top 2.5cm of soil collected quarterly. Three year mean biomass added to the soil from sunn hemp ranged from 6.9 to 9.8Mgha−1, while that from crimson clover ranged from 3.3 to 5.0Mgha−1. The input of cover crop biomass increased soil C (0.3–4.7mgg−1) and N (0.1–0.5mgg−1), which contributed to improvements in soil structure and fertility. Significantly greater C (2.2mgg−1 vs. 1.8mgg−1), lower BD (1.71Mgm−3 vs. 1.73Mgm−3) and greater θ at field capacity (0.126 vs. 0.113cm3cm−3) were found in the rotations with sunn hemp as crop 1 as compared to rotations with fallow as crop 1. There were significant differences in BD, Ks, and θ between soil in the rows and that in the interrows for all treatments. In general, BD were lower, Ks were greater, and θ were greater in the rows than in the interrows. Overall the study indicated that high residue input from fall and winter cover crops is important for adding C, retaining plant-available N in organic matter, increasing fertilizer use efficiency, and improving soil physical properties in the very sandy soils of the southeastern (SE) USA coastal plain region.