Soil Carbon and Nitrogen Storage in Aggregates from Different Tillage and Crop Regimes

Abstract

No-tillage (NT) has the potential to enhance C and N sequestration in agricultural soils of the southern USA, but results may vary with crop species. The objectives of this study were to investigate the impacts of NT, conventional tillage (CT), and crop species on soil organic carbon (SOC) and nitrogen (SON) sequestration and distribution within aggregate-size fractions in a central Texas soil after 20 yr of management. No-tillage increased SOC over CT at the 0- to 5-cm depth by 97, 47, and 72%, and SON by 117, 56, and 44% for continuous grain sorghum [Sorghum bicolor (L.) Moench], wheat (Triticum aestivum L.), and soybean [Glycine max (L.) Merr.J, respectively. Crop species had significant impacts on SOC and SON sequestration. On average, the wheat monoculture had greater SOC (9.23 Mg C ha -1 ) at the 0- to 5-cm depth than sorghum (6.75 Mg C ha -1 ) and soybean (7.05 Mg C ha -1 ). No-tillage increased the proportion of >2-mm and 250-μm to 2-mm macroaggregate fractions in soil compared with CT. At the 0- to 5-cm depth, NT increased SOC compared with CT by 158% in macroaggregate fractions, but only 40% in 2-mm, 250-μm to 2-mm, 53- to 250-μm, and <53-μm fractions, respectively. Long-term impacts of NT included a greater proportion of macroaggregates and increased C and N sequestration, but impacts were dependent on crop species and varied with soil depth.