Long-Term Effects of Rice Rotation, Tillage, and Fertility On near-Surface Soil Carbon and Nitrogen Cycling.

A majority of the rice (Oryza sativa L.) produced in the United States is produced on alluvial soils in the Mississippi River Valley and adjacent areas in the lower coastal plain of Louisiana and Texas, or in the Sacramento River Valley of California. Rice-based cropping systems are different from other row crops due to the flood-irrigation scheme used from about one month after planting to a few weeks prior to harvest. The frequent cycling between anaerobic (i.e., flooding during the growing season) and aerobic (i.e., generally, the remainder of the year) conditions can influence the rate of soil organic matter decomposition, which can greatly influence soil organic carbon (SOC) and total nitrogen (TN) storage in the soil over time. Therefore, a study was conducted on a silt-loam soil (fine, smectitic, thermic, Typic Albaqualf) at the Rice Research and Extension Center near Stuttgart, Arkansas to evaluate the long-term effects of six different rice-based crop rotations [with corn (Zea mays L.), soybean (Glycine max L.), and winter wheat (Triticum aestivum L.)], tillage [conventional-tillage and no-tillage (NT)], and soil fertility (optimal and sub-optimal) after 11 years (1999-2010) of consistent management on SOC and TN contents in the top 10 cm. Results showed that SOC and TN contents increased more than 30% over time in rotations which included winter wheat. Continuous rice increased 16% in SOC content and the rice-soybean rotation increased 19% in TN content over time, whereas there were no differences in the other crop rotations evaluated. Furthermore, SOC content was greater under NT and TN was greater under NT after the 11-year period, when compared SOC and TN contents under the tilled treatment. This long-term research study is important because the results enable a greater understanding of the effects that conservation management practices have on SOC and TN storage in rice-based cropping systems commonly used in Mississippi Delta region of the United States.