Research Approaches for Comparing Grazing Management Strategies.

Grazing research is inherently challenging because of the complexity and dynamic nature of the interactions among soil, plant, and animal components of grassland ecosystems. In addition, high cost per experimental unit for grazing research may necessitate compromises in statistical or biological rigor to accommodate economic realities. These inherent complexities and high costs have lead in some cases to shortcomings in research methodology. A comprehensive search of the pastureland literature was carried out through the Conservation Effects Assessment Program, and methodological weaknesses and knowledge gaps were identified. The objective of this presentation is to identify those weaknesses and gaps and make suggestions regarding how they might be addressed in future research. There are several methodological concerns. First, much of the pastureland research was conducted for 2 to 3 yr. This is insufficient time for some treatment effects to be fully manifested, leading to erroneous conclusions. A second concern is that scientists measuring animal performance on pasture may lack sufficient prior knowledge of plant responses to grazing stress, and the sward state at which animal responses are compared may favor one forage over another. An area of significant interest has been the comparison of rotational and continuous stocking. Most of this research has been done on experiment stations necessitating use of small paddocks, however, it has been suggested that advantages of rotational stocking are most likely observed on larger, farm-scale paddocks. The literature also indicates that the choice of a fixed or variable stocking rate approach to grazing research influences the relative performance of grazing methods. Lastly, pasture sampling techniques have often been inadequate in studies comparing grazing methods, failing to account for the relative stability of sward state under continuous stocking and the rapid changes occurring under rotational stocking. In terms of research gaps, the most striking is the lack of data describing effects of grazing strategies on soil, water, and wildlife components of the ecosystem. Expanding traditional forage-livestock grazing trials to include these responses may provide the justification and funding opportunities for future comparisons of key grazing strategies and forage species on pastureland.