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

Authors: Reinhart, Kurt; KOMATSU, KIM - Smithsonian Environmental Research Center; Vermeire, Lance

Submitted to: Agrosystems, Geosciences & Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/7/2022
Publication Date: 11/17/2022
Citation: Reinhart, K.O., Komatsu, K., Vermeire, L.T. 2022. Effects of mowing, spring precipitation, soil nutrients and enzymes on grassland productivity. Agrosystems, Geosciences & Environment. 5(4). Article e20320. https://doi.org/10.1002/agg2.20320.
DOI: https://doi.org/10.1002/agg2.20320

Interpretive Summary: Problem Climate change is predicted to shift the average annual precipitation and is likely to affect grazing resources (forage composition and amount). In addition, shifts in precipitation may interact with grazing management practices to affect grassland systems and grazing resources. Accomplishment We examined plant and soil responses after five years of experimentally simulating grazing and six years of climate change at a grassland. Small chronic reductions in spring rainfall did not affect forage production. We detected a complex effect of precipitation, mowing intensity, and mowing season on plant biomass. Treatments had minimal effects on soil properties.

Technical Abstract: Background & Aims Altered precipitation and grazing management may affect grassland systems and grazing resources. Little research has assessed how the timing and intensity of grazing might affect plant biomass, available nutrients, and soil extracellular enzyme activity (EEA), and how climate change might influence these responses. Methods We examined plant and soil responses after 5-yr of experimentally simulating grazing and 6-yr of climate change at a calcareous grassland. We applied a full factorial (3 × 2 × 2) experiment with three spring precipitation variability (rainfed control, -30% of ambient, +30% of ambient), two mowing intensity (moderate, severe), and two mowing season treatments (June, October). Tap water addition treatments were confounded by water impurities and excluded from analysis. We also determined the best predictors of variation in plant biomass from 10 soil nutrients and activity of six enzymes. Results At the end of the experiment, 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 severe intensities. Most soil nutrients were unaffected by treatments, except for calcium (Ca2+). Soil Ca2+ was 10% less in water-restricted than rainfed control plots. Soil EEA was unaffected by treatments; however, the activity of a phosphorus (P)-acquisition enzyme was =4 times greater than the activity of nitrogen (N)- and carbon-acquisition enzymes. Although treatments had minimal effects on soil properties, a substantial amount of plot-to-plot variation in plant biomass was explained by three soil properties, especially a N-acquisition enzyme and to a lesser degree by plant available P and soil pH. Conclusions The tested grassland indicated a high degree of natural buffering capacity as most soil properties were resistant to shifts in spring precipitation and simulated grazing intensity and season. Calcareous 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.