The Impact of Continuous Living Cover on Soil Hydrologic Properties: A Meta-Analysis

Increased rainfall variability due to climate change threatens the efficacy of critical soil ecosystem services. One strategy to negate effects of too much or not enough rainfall is to improve soil water properties. Practices that offer "continuous living cover" can enhance soil water storage and other soil hydrologic properties relative to annual crop systems, but to what extent such benefits can accrue, under different conditions, remains under-quantified. To address these uncertainties, we conducted a meta-analysis that included 27 studies representing 93 paired observations measuring two soil hydrologic properties: porosity and the water retained at field capacity. All experiments compared the impact of continuous living cover practices (cover crops, perennial grasses, agroforestry and managed forestry) to annual crop controls. Continuous living cover significantly increased total porosity (8.0 +/- 2.2%) and the water retained at field capacity (9.3 +/- 2.7%). There was some evidence indicating improved effects in relatively drier environments (< 900 mm annual rainfall) and in regions with sandier soils. There was no evidence of publication bias, and a sensitivity analysis indicated that overall effects were robust. The similar direction and magnitude of improvements in both properties could be evidence of similar physical and chemical processes impacted by the continuous presence of living roots. Overall, our findings suggest that continuous living cover practices may be a potential adaptation strategy to combat rainfall variability. Furthermore, properties such as porosity and field capacity may serve as proxies to determine how management influences soil water and heath more broadly.