Soil microbial properties under permanent grass, conventional tillage, and no-till management in South Dakota

The objective of this study was to determine how no-till and conventional tillage affected microbial properties of soil quality, using permanent grass fields as a standard of local high-quality soils. Agricultural fields in South Dakota were matched within soil type and location so that each set contained one field managed in permanent grass cover, one managed for annual crops using conventional tillage, and one managed for annual crops using no-till. Microbial biomass and activities, particularly those related to nitrogen and phosphorus availability were examined in 0-15 cm soil samples. Most measures of microbial activity were similar in the two annually cropped management systems but less than under permanent grass. Soils managed under permanent grass contained approximately 160% greater labile carbon and 50% greater microbial biomass, and supported approximately 150% greater dehydrogenase enzyme activity, 50% greater respiration, and 180% greater acid phosphatase activity, than no-till and conventionally tilled soils, which were similar in these measures. Grassed soils also mineralized 460% greater N under anaerobic conditions and 80% greater N under aerobic conditions, while potential nitrification was 25% greater on average than cropped soils. Mycorrhizal fungi colonized 76% of observed root segments under grass, 63% under no-till, and 55% under conventional tillage. Among the suite of tests in this study, only alkaline phosphatase activity and C mineralized in 12 days were significantly different under no-till and conventional tillage, both greater under no-till. Crops grown in a no-till system may be expected to resist low available P as well as other stresses better than crops in conventionally tilled soils due to greater activity of alkaline phosphatase and marginally increased mycorrhizal colonization of roots. No-till management in central South Dakota has allowed enhancement of readily mineralizable C and alkaline phosphatase activity.