Effects of mowing, spring precipitation, soil nutrients, and enzymes on grassland productivity

Abstract

Little research has assessed how the timing and intensity of grazing might affect plant biomass, available nutrients, soil extracellular enzyme activity (EEA), and how climate change might influence these responses. We tested the effect of two spring precipitation schemes (70, 100% of ambient), two mowing intensities (moderate, severe), and two mowing season treatments (June, October) on plant and soil properties. We detected an interactive effect of precipitation, mowing intensity, and mowing season on plant biomass. When plots were mowed at a moderate intensity, water reductions had irregular effects on plant biomass depending on the mowing season. Plant biomass was also 11% greater in plots mowed at moderate than at severe intensities. Most soil nutrients were unaffected by treatments except for calcium. Soil EEA was unaffected by treatments; however, the activity of a phosphorus (P)-acquisition enzyme was more than four times greater than the activity of nitrogen (N)-and carbon-acquisition enzymes. A substantial amount (adjusted R 2 = .51) of plot-to-plot variation in plant biomass was explained by three soil properties especially an N-acquisition enzyme and to a lesser degree by plant available P and soil pH. The grassland had a high degree of natural buffering capacity as most soil properties were resistant to shifts in 6-yr spring precipitation and 5-yr simulated grazing intensity and season. Grassland plant biomass varied by treatments and was seemingly limited by biogeochemical constraints especially the prevalent need to mobilize P and a secondary need to acquire N as plant biomass increased.