Rice rotation and tillage effects on soil aggregation and aggregate carbon and nitrogen dynamics

Rice (Oryza sativa L.) production in Arkansas is tillage intensive. Traditional tillage (TT) has been shown to reduce soil quality. The objectives of this study were to assess the impact of TT and no-till (NT) management on soil water-stable aggregate (WSA) content, aggregate C and N concentrations, and aggregate C and N contribution to the bulk soil at two soil depths in seven rotations. For continuous rice or rotations containing rice every second year, total and mean WSA content in the 0- to 5-cm soil layer was greater under NT than TT. There was no difference in total WSA content between soil depths for the TT treatment, with the 5- to 10-cm layer (69 g kg(-1)) numerically greater than the NT 5- to 10-cm layer. Water-stable aggregate content increased when residue-rich crops such as corn (Zea mays L.) and wheat (Triticum aestivum L.) were included in the rotation and decreased when soybean [Glycine max (L.) Merr.] was grown. The inclusion of wheat as a winter crop in rotation with rice resulted in the greatest bulk soil WSA C and N contents. Including soybean in rotation with rice resulted in reduced bulk soil WSA C and N contents. Bulk soil WSA C and N contents were determined more by the WSA content than the WSA C and N concentration. No-till and increasing the frequency of rice in rotations resulted in greater soil WSA content and subsequent increased C and N content in the bulk soil.