Effects of environmental factors on the influence of tillage conversion on saturated soil hydraulic conductivity obtained with different methodologies: a global meta-analysis

The saturated hydraulic conductivity (K-sat) is a key soil hydraulic property governing agricultural production. However, the influence of the conversion from the conventional tillage (CT) to conservation tillage (CS; including no tillage, NT, and reduced tillage, RT) on the K-sat of soils is not well understood and still debated. In this study, we applied a global meta-analysis method to synthesize 227 paired observations for soil K-sat from 69 published studies and investigated factors influencing the effects of conversion to CS on K-sat. Results showed that soil layer, conservation tillage type, soil texture type, and cropping system management did not have significant effects on the influence of conversion to CS on K-sat. When the K-sat was measured by the rainfall simulator, the conversion to CS significantly (p < 0.05) increased the surface and subsurface soil K-sat by 41.7 % and 36.9 %, respectively. In addition, the subsurface K-sat also tended to increase under CS practices when the K-sat was measured by a tension disc infiltrometer. However, when the K-sat was measured by a hood infiltrometer, ring infiltrometer, constant/falling head, and Guelph permeameter, the conversion to CS had no significant effects on the K-sat. It is observed that, when the conversion period was less than 15 years, the K-sat under CS showed a greater increase for a longer conversion period. Climatic and topographic factors, including the mean annual temperature (MAT) and the mean annual precipitation (MAP), were statistically related to the responses of K-sat to tillage conversion at the global scale. Quadratic polynomials can describe the relationships between them. These findings suggested that quantifying the effects of tillage conversion on soil K-sat needed to consider experimental conditions, especially the measurement technique and conversion period.