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

Abstract

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. Improving soil health and resilience into the future is a critical priority for 21st century agriculture, given increased demands on agriculture, including climate change (Amundson et al., 2015). As a result of a warming atmosphere, increased rainfall variability is already measured in the recent record and is projected to intensify into the future (IPCC, 2013;Pryor et al., 2014). Increased rainfall variability threatens the efficacy of key soil ecosystem services that are necessary for both crop production and environmental protection, including erosion prevention, nutrient loss reduction and water storage. Agricultural practices that focus on enhancing soil water storage have multiple co-benefits that might also reduce environmental damages and crop losses through better maintenance of soil water (Sposito, 2013;Stewart and Peterson, 2015).One approach to regenerating soil health is the adoption of cropping practices that ensure "continuous living cover" of the soil, or the presence of live roots in the ground throughout the entire year ( Jordan and Warner, 2010). This approach is in contrast to annual cropping systems that typically have extended periods of bare soil, and it affords the direct benefits of preventing nutrient loss (through plant uptake) as well as erosion protection (through minimizing the impact of rainfall and ...

A global analysis of the impact of zero‐tillage on soil physical condition, organic carbon content, and plant root response

“…Change in FC nearly followed the course of MWD change in the soil profile, suggesting similar contributing factors in modifying these parameters through ZT practice. Maintaining continuous living cover over soil surface had proven benefit on the soil porosity and water content at FC (Basche & DeLonge, ). There must be a differential effect of soil texture on the aggregate stability vis‐a‐vis FC water content (Wills et al, ); however, the same could not be confirmed due to a limited number of studies meeting the criteria for the subgroup analysis.…”

Cover Crops Reduce Nitrate Leaching in Agroecosystems:A Global Meta‐Analysis

“…In the literature, publication bias is assessed using funnel plots that compare effect sizes to precision (inverse of sampling variances) or sample sizes (Møller and Jennions, 2001; Philibert et al, 2012). However, funnel plots are not an appropriate tool to detect bias in our analysis because sampling variances were not available in most of the studies included and the sample sizes did not have sufficient range to create meaningful funnel plots (Basche and DeLonge, 2017). Therefore, we indirectly evaluated this meta‐analysis for biases toward publishing significant positive or negative results using histogram of the individual effect sizes (Basche and DeLonge, 2017).…”

“…However, funnel plots are not an appropriate tool to detect bias in our analysis because sampling variances were not available in most of the studies included and the sample sizes did not have sufficient range to create meaningful funnel plots (Basche and DeLonge, 2017). Therefore, we indirectly evaluated this meta-analysis for biases toward publishing significant positive or negative results using histogram of the individual effect sizes (Basche and DeLonge, 2017). Histograms of overall effect size estimates suggested that observations were equally distributed between slightly positive and slightly negative values, indicating no publication bias (Supplemental Fig.…”

Comparing infiltration rates in soils managed with conventional and alternative farming methods: a meta-analysis

“…The literature search was conducted using EBSCO Discovery Service ™ (detailed in Basche and DeLonge 25 ) and only included field experiments in English language peer-reviewed literature through 2015 (the earliest publication that met our criteria was from 1978). Keyword strings included “infiltration W1 rate” AND “crop*” for all searches, and additional keywords were used for individual practices (Table 1).…”

“…While these treatments have differences in species and management, they share the critical feature of continuous living cover through perennials. Given the limited number of total studies, we aggregated these into a single class (as in Basche and DeLonge 2017 25 ). Two of the eight experiments ultimately included in this practice also had livestock grazing as part of the treatment (compared to an annual crop system with no livestock; Table 1 in S1 File).…”