Grazing intensity determines pasture spatial heterogeneity and productivity in an integrated crop‐livestock system

Abstract

Spatial heterogeneity is a property of natural ecosystems. Integrated crop‐livestock systems (ICLS) aim to mimic natural ecosystem functions as pillars of sustainable intensification, and grazing is a process that potentially affects spatial heterogeneity. Then, we investigated the effect of different grazing intensities, defined according to a range of sward heights (intensive grazing, 10 cm; moderate grazing, 20 cm; moderate‐light grazing, 30 cm; light grazing, 40 cm; and ungrazed), on the spatial heterogeneity and biomass productivity of mixed Italian ryegrass (Lolium multiflorum Lam.) and black oat (Avena strigosa Schreb.) pastures. The mixture was grazed by steers under continuous variable stocking, using put‐and‐take animals to maintain targeted sward heights. The pasture was in rotation with soybean in an integrated crop‐livestock system for 15 years. Data concerns pasture phase on the 15th rotation cycle. Cattle grazing at moderate to light intensities increased pasture spatial heterogeneity and total aboveground primary productivity, while intensive grazing led to homogeneous overgrazed canopies with frequent bare soil patches. Pre‐grazing sward structure suggests that the summer crop rotation buffers the contrasts created by grazing at different intensities. This study suggests that moderate to light grazing intensities increase pasture productive efficiency and create more heterogeneous canopies in ICLS, while intensive grazing should be avoided.

Managing grazing intensity to reduce the global warming potential in integrated crop–livestock systems under no‐till agriculture

“…We hypothesized that the reduced net primary production of winter pasture under intensive grazing (Nunes et al, 2018) would result in the soil surface being more markedly exposed to wind and solar radiation (Tang et al, 2019), as water and temperature stresses are known to have an adverse impact on the activity of methanotrophic communities (Liu et al, 2007). In the summer season of 2016, when soil CH 4 fluxes differed more markedly among grazing intensities, WFPS was largely below 50%, which also possibly increased CH 4 and oxygen (O 2 ) diffusivity in soil, thus leading to increased rates of CH 4 uptake by methanotrophic bacteria (Saggar, Tate, Giltrap, & Singh, 2008).…”

Spatiotemporal Distribution of Cattle Dung Patches in a Subtropical Soybean-Beef System under Different Grazing Intensities in Winter

“…The addition of livestock grazing cover crops in the period between the cultivation of two main cash crops, which is the case of our study, creates heterogeneity. This heterogeneity results from the accumulation of excretions (dung and urine) and the act of grazing itself (defoliation) or associated effects such as the act of trampling and can be noticed in the patterns of vegetation [57] and soil parameters [22]. Vegetation heterogeneity in annual winter pastures has been shown to be related to grazing intensity with more pronounced spatial patterns under light than heavy grazing intensity [57].…”

“…This heterogeneity results from the accumulation of excretions (dung and urine) and the act of grazing itself (defoliation) or associated effects such as the act of trampling and can be noticed in the patterns of vegetation [57] and soil parameters [22]. Vegetation heterogeneity in annual winter pastures has been shown to be related to grazing intensity with more pronounced spatial patterns under light than heavy grazing intensity [57]. This was attributed to overgrazing, which created homogeneous, short swards with frequent bare soil sites as a result of intense cattle locomotion while foraging for food.…”

“…This was attributed to overgrazing, which created homogeneous, short swards with frequent bare soil sites as a result of intense cattle locomotion while foraging for food. On the other hand, pastures as tall as 0.4 m were heterogeneous and yielded more forage production (kg of herbage DM ha −1 ) over the stocking period due to the greater leaf area index, which improved daily accumulation rates [57]. In these conditions, cattle significantly improve their gains compared with intensely grazed areas (i.e., sward heights of 0.1 m) [58].…”

Mechanisms of Grazing Management in Heterogeneous Swards

“…Livestock distribution has fractal properties and is in part determined by the heterogeneity of resources such as forage, water, and shade [7,8]. In addition to the inherent heterogeneity, grazing disturbance (as well trampling and excreta deposition) is an important source of variability in the vegetation [9,10] because herbivores' selectivity generates a mosaic of tall and short patches that in turn affect future grazing. Sward growth rate is nonlinear, and therefore pasture production is not fully determined by average sward height at paddock scale but also depends on the spatial distribution of sward height [11,12] ( Figure A1).…”