Temporal variability of selected soil microbiological and biochemical indicators under different soil quality conditions in south-western Nigeria

We evaluated the temporal variation of microbial biomass C, beta-glucosidase, acid phosphomonoesterase (acP), alkaline phosphomonoesterase (alP), and protease activity over 18 consecutive months. The likely causes for the seasonal variability at a non-degraded and a degraded site in south-western Nigeria were identified. Microbial biomass, alP, and beta-glucosidase activity were sensitive indicators of soil quality changes over time. Microbial biomass C correlated significantly with soil moisture conditions and soil organic matter-related parameters. AlP and beta-glucosidase activities were not controlled by climatic conditions over the course of two rainy seasons and one dry season but were temporally related to microbial biomass C and total C and N. Due to the steadiness of the alP activity over time the enzyme is considered a suitable indicator with which to monitor long-term changes of soil quality. Single sampling during the course of a year is adequate. Both microbial biomass and beta-glucosidase activity fluctuated highly. They were sensitive indicators to monitor short-term variations of soil quality with. Sampling for microbial biomass ought to be limited to the rainy seasons, whereas the measurement of beta-glucosidase activity need not be restricted seasonally. Due to the short-term variability found, sampling should be repeated. AcP and protease activity fluctuated highly during the course of a year and exhibited pronounced inter-seasonal differences. The marked seasonal changes could not be ascribed to soil moisture conditions and only poorly to major ecological C soil processes. This was more pronounced for acP than for protease. Hence, neither parameter was considered a sensitive and meaningful indicator of soil quality changes over time.