Enzyme activities and microbial community structure in semiarid agricultural soils

This study investigated the effect of management on beta-glucosidase, beta-glucosaminidase, alkaline phosphatase, and arylsulfatase activities and the microbial community structure in semiarid soils from West Texas, USA. Surface samples (0-5 cm) were taken from a fine sandy loam, sandy clay loam, and loam that were under continuous cotton (Gossypium hirsutum L.) or in cotton rotated with peanut (Arachis hypogaea L.), sorghum (Sorghum bicolor L.), rye (Secale cereale) or wheat (Triticum aestivum L.), and had different water management (irrigated or dryland), and tillage (conservation or conventional). The enzyme activities were higher in the loam and sandy clay loam than in the fine sandy loam. Soil pH was not affected by management, but the soil organic C and total N contents were generally affected by the different crop rotations and tillage practices studied. The trends of the enzyme activities as affected by management depended on the soil, but in general crop rotations and conservation tillage increased the enzyme activities in comparison to continuous cotton and conventional tillage. The soil enzyme activities were significantly correlated with the soil organic C (r-values up to 0.90, P < 0.001), and were correlated among each other (r-values up to 0.90, P < 0.001). There were differences in the fatty acid methyl ester profiles between the fine sandy loam and the sandy clay loam and loam, and they reflected the differences in the enzyme activities found among the soils. For example, a 15:0 ranged from 1.61 +/- 0.25% in cotton-peanut/irrigated/no-till in the fine sandy loam to 3.86 +/- 0.48% in cotton-sorghum/dryland/conservation tillage in the sandy clay loam. There were no differences due to management within the same soil.