The influence of ecological grazing and crop management on soil water: A meta-analysis

Background/Question/Methods

Climate change is expected to increase rainfall variability, exposing agricultural systems to increased risks related to flooding and drought events which directly affect crop productivity and environmental outcomes. One strategy to protect agricultural systems from the negative effects of rainfall variability is to create crop and soil management practices that improve soil water dynamics. Prior research has demonstrated that ecological agricultural practices can lead to such improvements.  

Therefore, the objective of this study is to quantify how different agroecological practices impact soil hydrology using a meta-analytic methodology. To begin, we used the EBSCO Discovery Service^TM to find peer-reviewed papers that measured infiltration rate and also included ecological practices, specifically selecting studies with improved grazing management, livestock integrated into cultivated lands, perennial crops or agroforestry practices, and crop rotations. Experiments needed to have a more conventional agriculture practice (continuous grazing, croplands without animals integrated, annual crops, or crop monocultures) as a control to be included in our database. As this analysis continues, it will be expanded to investigate soil hydrological properties such as total porosity and the water retained at field capacity. We used R statistical software to analyze the dataset both with linear mixed models and bootstrapping methods.

Results/Conclusions

To date, we have analyzed 29 studies and 118 paired observations, including 11 grazing studies (54 observations), 9 perennial or agroforestry studies (29 observations) and 8 crop rotation studies (33 observations). Systems that incorporated perennial grasses or agroforestry increased infiltration rates by the greatest percentage (> 100%) compared to a conventional cropping system. Crop rotations also led to a mean increase in infiltration rate (44%). Integrating livestock into previously cultivated lands decreased infiltration rates (-12%) however improved grazing systems (decreased stocking rate or density, increased complexity of management) increased infiltration rates (+21%). Although adding animals to new systems had an undesirable impact on infiltration, improvements were attained through grazing management and incorporating perennials. While these agroforestry and crop rotations studies did not include livestock, it is possible that including such practices into livestock systems would also be beneficial for infiltration rates. The length of time that ecological practices were in place was also important. We found that studies needed to be in place for more than three years before the positive effects of ecological practices were observed. Overall, our analysis indicates that ecological practices can lead to improvements in infiltration, but effects are dependent upon the treatments and management.