Dryland cropping systems influence the microbial biomass and enzyme activities in a semiarid sandy soil

Indicators of soil quality, such as microbial biomass C and N (MBC, MBN) and enzyme activities (EAs), involved in C, P, N, and S cycling, as affected by dryland cropping systems under conventional (ct) and no tillage (nt) practices were evaluated for 5 years. The soil is sandy loam with an average of 16.4% clay, 67.6% sand, and 0.65 g kg(-1) OM at 0-10 cm. The crops evaluated were rotations of grain sorghum (Sorghum bicolor L.) or forage sorghum (also called haygrazer), cotton (Gossypium hirsutum), and winter rye (Secale cereale): grain sorghum-cotton (Sr-g-Ct), cotton-winter rye-sorghum (Ct-Rye-Sr-g), and forage sorghum-winter rye (Sr-f-Rye). The tillage treatments did not affect soil MB and EAs of C cycling (i.e., beta-glucosidase, beta-glucosaminidase, alpha-galactosidase), P cycling (alkaline phosphatase, phosphodiesterase), and S cycling (arylsulfatase)-except for separation due to tillage for Sr-f-Rye and Ct-Rye-Sr-g observed in PCA plots when all EAs were evaluated together. After 3 years, rotations with a winter cover crop history (Ct-Rye-Sr-g and Sr-f-Rye) enhanced soil MBN (up to 63%) and EAs (21-37%) compared to Sr-g-Ct. After 5 years, Sr-g-Ct and Ct-Rye-Sr-g showed similar soil MBC, MBN, EAs, total carbon (TC), and organic carbon (OC). A comparison of Sr-g-Ct plots with nearby continuous cotton (Ct-Ct) research plots in the same soil revealed that it took 5 years to detect higher TC (12%), MBC (38%), and EAs (32-36%, depending on the enzyme) under Sr-g-Ct. The significant improvements in MB and EAs found, as affected by dryland cropping systems with a history of winter cover crops and/or higher biomass return crops than cotton, can represent changes in soil OM, nutrient cycling, and C sequestration for sandy soils in the semiarid Texas High Plains region. It is significant that these soil changes occurred despite summer crop failure (2003 and 2006) and lack of winter cover crops (2006) due to lack of precipitation in certain years.