Soil Microbial Communities and Function in Alternative Systems to Continuous Cotton

Cotton (Gossypium hirsutum L.) monoculture under conventional tillage has been the predominant cropping system in the Southern High Plains region of the United States since the 1940s. This study evaluated other cropping systems and land uses for their potential to increase soil quality and enhance soil functioning compared with continuous cotton (Ct-Ct), including a mixture of grasses in the Conservation Reserve Program (CRP), a pasture monoculture [Bothriochloa bladhii (Retz) ST. Blake] and a cotton-winter wheat (Triticum aestivum L.) corn (Zea mays L.) rotation (Ct-W-Cr). Soil microbial communities were evaluated according to microbial biomass C (MBC) and N (MBN), fatty acid methyl ester (FAME) profiling, and molecular cloning techniques. Soil MBC was higher under the alternative systems at 0 to 5 cm (CRP > pasture = Ct-W-Cr > Ct-Ct), 5 to 10 cm (CRP = Ct-W-Cr > pasture > Ct-Ct), and 10 to 20 cm (CRP = pasture = Ct-W-Cr > Ct-Ct). Soil DNA concentration was correlated with key soil quality parameters such as microbial biomass (r > 0.52, P < 0.05), total C (r = 0.372, P < 0.1), and total N (r = 0.449, P < 0.05). The 16S rRNA gene banding patterns (0-5 cm) of undisturbed systems (CRP and pasture) were more similar to each other than to Ct-Ct and Ct-W-Cr. Fungal/bacterial FAME ratios were higher under CRP and pasture than under Ct-Ct at 0 to 5 and 5 to 10 cm. This study found increases in sensitive soil quality parameters under alternative management compared with cotton monoculture.