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

Abstract.

We evaluated the temporal variation of microbial biomass C, β-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 β-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 β-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 β-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 β-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 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.