Long-term soil microbial community and enzyme activity responses to an integrated cropping-livestock system in a semi-arid region

Abstract

Water availability is a primary limiting factor facing agricultural systems in most semi-arid regions across the world. This study is part of a larger long-term project to develop and evaluate integrated crop and livestock systems in order to reduce dependence on underground water sources by optimizing cotton ( Gossypium hirsutum) production in the Texas High Plains of U.S. Selected microbial, chemical and biochemical properties were studied (between 7 and 10 years) in a clay loam soil (fine, mixed, thermic Torrertic Paleustolls) under continuous cotton compared to an integrated cropping-livestock system that included cotton, forage, and Angus-cross-stocker beef steers (initial body weight 249 kg). For the integrated system, steers grazed in sequence a perennial warm-season grass ‘WW-B. Dahl’ old world bluestem ( Bothriochloa bladhii) paddock, and then rye ( Secale cereale L.) and wheat ( Triticum aestivum L.) grown in two paddocks (stages) of a rotation with cotton. Our previous studies after 5 years showed greater microbial biomass C (MBC) in perennial pasture (193 mg kg −1 soil) and the rotation when sampled under rye or cotton (average of 237 mg kg −1 soil) compared to continuous cotton (124 mg kg −1 soil) at 0–5 cm. After 7 years, MBC became significantly higher in the rotation independent of the crop compared to continuous cotton in this study. At the end of 10 years, total C was higher in both the rotation and pasture of the integrated cropping-livestock system (average across grazing treatments: 17.3 g kg −1 soil) compared to continuous cotton (11.4 g C kg −1 soil). Soil MBC and several enzyme activities were higher under non-grazed areas compared to grazed areas within the integrated cropping-livestock system in some samplings. Microbial community structure of pasture soil showed higher FAME indicators for G− (i.e., a17:0 and cy19:0) and actinomycetes (i.e., 10Me17:0) under grazed areas compared to non-grazed areas. Microbial community structure of pasture soil showed higher fungal populations compared to continuous cotton. The rotation showed intermediate sum of bacterial FAME indicators among systems (continuous cotton > rotation > pasture) and a tendency for numerically slightly higher fungi:bacterial ratios compared to continuous cotton. This study demonstrated increases in microbial biomass and enzyme activities of C-, N-, P- and S-cycling within an integrated cropping-livestock system that may represent positive changes in soil functioning compared to continuous cotton.