Abstract: Rice (Oryza sativa L.)-based cropping systems are different from other crop rotations because of the flood-irrigation scheme, which can influence the rate of soil organic matter decomposition, water-stable soil aggregation, and carbon (C) and nitrogen (N) sequestration over time. A study was conducted on a silt-loam soil (fine, smectitic, thermic, Typic Albaqualf) in eastern Arkansas to evaluate the effects of rice-based crop rotations (with maize (Zea mays L.), soybean (Glycine max L.), and winter wheat (Triticum aestivum L.)), tillage (conventional tillage and no-tillage (NT)), and soil depth (0–5 cm and 5–10 cm) after 10 years of management on water-stable macroaggregates (WSA) and their C and N concentrations (g kg−1), C:N ratios, and contents (g m−2). The total amount of WSA (WSATotal >0.25 mm in diameter) and the distribution of WSA among five different size classes (0.25–0.5, 0.5–1, 1–2, 2–4, and >4 mm in diameter) within each treatment combination were evaluated. The concentration of WSATotal was 1.2 to four times greater under NT/0- to 5-cm soil depth (9.2–16.0 g kg−1) than under other tillage-depth combinations. Macroaggregate concentration in the 0.25- to 0.5-mm size class was greater under continuous rice (9.3 g kg−1) and rice rotations with maize (7.6–8.0 g kg−1) than in rotations with wheat (4.9–6.5 g kg−1). The NT/0- to 5-cm combination had three to six times greater WSATotal C (235 g m−2) and N (20.6 g m−2) contents than all other tillage-depth combinations (C, 38.3–80.5 g m−2; N, 3.5–5.7 g m−2), which did not differ. Despite field management differences from using seasonal flood-irrigation in rice, this study demonstrates that the extent of tillage and crop rotation effects on soil macroaggregation and the associated macroaggregate-associated C and N contents were proportionate to trends commonly reported in dryland crop rotations.
1Department of Crop, Soil and Environmental Sciences, University of Arkansas, Fayetteville, Arkansas.
2Rice Research and Extension Center, Stuttgart, Arkansas.
3Agriculture Statistics Laboratory, University of Arkansas, Fayetteville, Arkansas.
4Department of Biological Sciences, University of Arkansas, Fayetteville, Arkansas.
Address for correspondence: Dr. Jill M. Motschenbacher, Department of Crop, Soil and Environmental Sciences, University of Arkansas, 115 Plant Science Bldg, Fayetteville, AR 72701. E-mail: firstname.lastname@example.org
Financial Disclosures/Conflicts of Interest: This research was partially supported by the Arkansas Rice Research and Promotion Board, Arkansas Soybean Promotion Board, Arkansas Corn and Sorghum Promotion Board, Arkansas Wheat Promotion Board, and the University of Arkansas.
Received July 22, 2013.
Accepted for publication December 13, 2013.