Short-term dynamics of soil carbon, microbial biomass, and soil enzyme activities as compared to longer-term effects of tillage in irrigated row crops

The effects of disturbance on soil quality are difficult to determine because soil is inherently variable and physical and chemical soil properties change too slowly to reflect recent management history. Microbial and biochemical soil properties have been suggested as early and sensitive indicators of changes in soil quality as they manifest themselves over shorter timescales and are central to the ecological function of a soil (Karlen et al. 1994 ; Bandick and Dick 1999 ). Soil enzyme activities in particular are increasingly used as indicators of soil quality because of their relationship to decomposition and nutrient cycling, ease of measurement, and rapid response to changes in soil management (Dick 1994 ; Dilly et al. 2003 ). In a long-term study, Kandeler et al. ( 1999 ) found that enzyme activities were significantly increased in the top 10 cm of the profile after only 2 years of minimum and reduced tillage compared to conventional tillage. In contrast, significant effects of tillage treatments on microbial biomass, nitrogen (N) mineralization, and potential nitrification were not observed until after 4 years.