Microbial properties of soils: effects of management and pedogenesis

Abstract

Soil microorganisms are a critical component of ecosystem services provided by soil. Soil management drives soil physical, chemical, and biological properties. Pedogenesis and management interact to change microbial structure and function in the soil profile. Soil microbial properties may vary temporally with crop development and crop species. The objective of this study was to explore the pedogenetic and anthropogenic controls on key soil microbial properties by (i) assessing the profile of a claypan soil under conventional tillage (CT), no-till (NT), and hay meadow (HM); (ii) assessing seasonal changes of soil microbial properties in a corn/winter wheat/soybean rotation under CT and NT; and (iii) assessing vertical changes of soil microbial properties in response to long-term (28 yrs) tillage and mineral and organic fertilization. Selected microbial properties included extracellular enzyme activity, microbial structure as measured by phospholipid fatty acid (PLFA), as well as soil chemical properties. Soil C, enzyme activities, and microbial biomass were greatest in HM soils, followed by NT and then CT in the claypan soil. Wheat in the rotation increased hydrolase activity and bacterial biomass more than corn, while microbial activities were stable during soybean growth. Increased enzyme activities in the claypan layer resulted from the combination of clay-enzyme interaction and impacts from management practices. In a Mollisol soil, an increase in C-acquiring enzyme activity and microbial PLFAs in a buried A horizon was a result of root growth under no-till practice and mineral fertilization. Surprisingly, long-term mineral fertilizer applications had little effect on enzyme activities and microbial biomass. Long-term organic fertilization increased soil C, enzyme activities, and PLFAs but decreased arbuscular mycorrhizal fungi (AMF) throughout the soil profile to a depth of 90 cm. Microbial properties are controlled by crop and soil management at the soil surface and by the interaction of management and pedogenetic properties deeper in the soil profile. Incorporating grasses in the crop rotation may allow nutrients to be extracted from deeper within the soil profile, enhancing the utilization of the entire soil profile and providing additional nutrient resources to cash crops. Incorporating wheat in the crop rotation supports greater microbial activity and biomass after corn harvest, especially in no-till management. Additional research is required to delineate further causative factors impacting enzyme activity in the claypan layer, a finer resolution in soil microbial community at the species level to explore the linkage between ecological function and microbiome structure, and a network analysis for the soil-plant-microbe interactions.