No abstract

leach into groundwater after crop harvest in the fall, and depending on the species, can sequester atmospheric C Biculture legume-cereal cover cropping may enhance above-and and/or N, thereby reducing the amount of N fertilizer belowground biomass yields and C and N contents. The increase in C and N supply to the soil has the potential to improve soil quality

Sainju, U. M., Whitehead, W. F. and Singh, B. P. 2003. Cover crops and nitrogen fertilization effects on soil aggregation and carbon and nitrogen pools. Can. J. Soil Sci. 83: 155-165. Cover crops and N fertilization rates may influence soil aggregation and associated C and N pools, thereby affecting soil quality and productivity. We compared the effects of legume [hairy vetch (Vicia villosa Roth) and crimson clover (Trifolium incarnatum L.)] and nonlegume [rye (Secale cereale L.)] cover crops and N fertilization rates {half N rate [HN: 90 kg N ha -1 yr -1 for 3 yr of tomato (Lycopersicon esculentum Mill.) followed by 80 kg N ha -1 yr -1 for eggplant (Solanum melogena L.)]} and full N rate [FN: 180 kg N ha -1 yr -1 for 3 yr of tomato followed by 160 kg N ha -1 yr -1 for eggplant]}on soil aggregation and C and N pools in whole-soil and aggregates. The pools were organic C, total N, potential C mineralization and potential N mineralization (PCM and PNM), microbial biomass C and microbial biomass N (MBC and MBN), and particulate organic C and particulate organic N (POC and PON). Field experiment was conducted in a Greenville fine sandy loam (fine-loamy, kaolinitic, thermic, Rhodic Kandiudults) from 1995 to 2000 in Fort Valley, Georgia, USA. While the amount of soil present in aggregates decreased with decreasing size class, the amount was greater with nonlegume and FN than with HN and legume cover crops in the 2.00-to 0.85-mm size class. Organic C, PCM, and MBC contents in whole-soil were greater with nonlegume, but MBN and PON were greater with legumes than in the control with no cover crop or N fertilization. Organic C and total N concentrations in aggregates were greater in 2.00-to 0.50-mm than in 4.75-to 2.00-mm, <0.25-mm, or <4.75-mm (whole-soil) size classes, but PNM and MBN were greater in <0.50-or <4.75-mm than in 4.75-to 2.00-mm size classes. As POC and PON decreased with decreasing aggregate-size class, POC in the <0.85-mm size class was greater with nonlegume and PON in the 2.00-to 0.85-mm size classes was greater with legumes than with the control and N rates. Nonlegume may increase soil aggregation, microbial activities, and C sequestration, but legumes may increase N mineralization in the soil compared with no cover crop. Nitrogen fertilization also may improve soil aggregation. Nitrogen mineralization and C and N sequestration may be greater in aggregates <2.00 mm diameter. Cover crops and N fertilization may improve soil quality and productivity, particularly in intermediate and small size (<2.00 mm) aggregates. , aux États-Unis. Bien que la concentration du sol diminue avec la granulométrie, les agrégats de 2,00 à 0,85 mm contiennent plus de sol avec une couverture de non-légumineuses et une fertilisation FN qu'avec les légumineuses et une fertilisation HN. Le sol intégral se caractérisait par une quantité de C organique, un PCM et une MBC plus élevés avec les non-légumineuses qu'avec les légu-mineuses, mais le sol protégé par les légumineuses présentait de plus grandes MBN et PON que celui des parc...

Soil carbon (C) sequestration in tilled and nontilled areas can be influenced by crop management practices due to differences in plant C inputs and their rate of mineralization. We examined the influence of four cover crops {legume [hairy vetch (Vicia villosa Roth)], nonlegume [rye (Secale cereale L.)], biculture of legume and nonlegume (vetch and rye), and no cover crops (or winter weeds)} and three nitrogen (N) fertilization rates (0, 60 to 65, and 120 to 130 kg N ha(-1)) on C inputs from cover crops, cotton (Gossypium hirsutum L.), and sorghum [Sorghum bicolor (L.) Moench)], and soil organic carbon (SOC) at the 0- to 120-cm depth in tilled and nontilled areas. A field experiment was conducted on Dothan sandy loam (fine-loamy, siliceous, thermic Plinthic Paleudults) from 1999 to 2002 in central Georgia. Total C inputs to the soil from cover crops, cotton, and sorghum from 2000 to 2002 ranged from 6.8 to 22.8 Mg ha(-1). The SOC at 0 to 10 cm fluctuated with C input from October 1999 to November 2002 and was greater from cover crops than from weeds in no-tilled plots. In contrast, SOC values at 10 to 30 cm in no-tilled and at 0 to 60 cm in chisel-tilled plots were greater for biculture than for weeds. As a result, C at 0 to 30 cm was sequestered at rates of 267, 33, -133, and -967 kg C ha(-1) yr(-1) for biculture, rye, vetch, and weeds, respectively, in the no-tilled plot. In strip-tilled and chisel-tilled plots, SOC at 0 to 30 cm decreased at rates of 233 to 1233 kg C ha(-1) yr(-1). The SOC at 0 to 30 cm increased more in cover crops with 120 to 130 kg N ha(-1) yr(-1) than in weeds with 0 kg N ha(-1) yr(-1), regardless of tillage. In the subtropical humid region of the southeastern United States, cover crops and N fertilization can increase the amount of C input and storage in tilled and nontilled soils, and hairy vetch and rye biculture was more effective in sequestering C than monocultures or no cover crop.

Nitrate N in the soil is susceptible to leaching with fall and winter precipitation and can pollute groundwater. Winter cover crops to scavenge residual NO‐3 through root extension are a possible solution. A 2‐yr field study was conducted on a Greenville fsl (fine, kaolinitic, thermic Rhodic Kandiudults) in central Georgia to determine root distribution of legume and nonlegume winter cover crops and their ability to absorb soil NO‐3 and accumulate it in aboveground biomass. Cereal rye (Secale cereale L.), hairy vetch (Vicia villosa Roth), and crimson clover (Trifolium incarnatum L.) were planted in a prepared seedbed in the fall and accumulated biomass was incorporated into the soil in the spring. Seasonal variations in root distribution were measured by minirhizotron and soil separation methods. Soil mineral N concentration and aboveground biomass yield and N uptake were determined at regular intervals during the growing season. Total minirhizotron root count (MRC; no. roots cm−2 soil profile) at the 1‐ to 50‐cm soil depth increased at the rate of 0.01 roots cm−2 d−1 in hairy vetch in the fall to 0.38 roots cm−2 d−1 in crimson clover in the spring, as temperature increased. Roots were well distributed to the 50‐cm soil depth. Compared with the other cover crops, rye had significantly greater total MRC from Dec. 1996 to Feb. 1997 and total root length density (RLD; cm root length cm−3 soil) at the 0‐ to 30‐cm depth from Nov. 1995 to Apr. 1996 and in Jan. 1997, and the subsequent NO‐3 inorganic N concentration in the soil was lower and aboveground biomass yield was greater. MRC was positively correlated with RLD in Nov. 1995, Apr. 1996, and Jan. 1997. A significant positive correlation was observed between MRC and aboveground biomass yield or N uptake (r = 0.52 to 0.68, P ≤ 0.05) and a negative correlation between MRC and soil NO‐3 concentration (r = ‐0.51 to ‐0.55, P ≤ 0.05) early in the growing season. Rye had the greatest root density and aboveground biomass, and scavenged more soil NO‐3 early in the growing season. Nonlegume cover crops, such as rye, may be more effective in reducing residual NO‐3 and potential leaching of NO‐3 from the soil early in the growing season than are legume cover crops, such as hairy vetch or crimson clover.