Abstract
The saturated hydraulic conductivity (Ksat) is a key soil hydraulic property governing agricultural production. However, the influence of conversion from conventional tillage (CT) to conservation tillage (CS) (including no tillage (NT) and reduced tillage (RT)) on Ksat of soils is not well understood and still debated. In this study, we applied a global meta-analysis method to synthesize 201 paired observations for soil Ksat from 59 published studies, and investigated factors influencing the effects of conversion to CS on Ksat. Results showed that the Ksat measured by hood infiltrometer, tension disc infiltrometer, and Guelph permeameter produced a similar pattern under CS practices, with non-significant (p > 0.05) increase of 6.6 %, 3.6 % and 4.9 %, respectively. However, conversion to CS significantly (p < 0.05) increased Ksat by 32.0 % for ring infiltrometer, while it decreased Ksat by 3.2 % for constant/falling head (p > 0.05). Soil layer, CS type and soil texture had no significant (p > 0.05) effects on the influence of conversion to CS on the Ksat, but the Ksat under CS showed a greater increase for a longer conversion period (time since conversion). In addition, mean annual temperature (MAT) was found to be an important driver controlling the response of Ksat to tillage conversion at the large scale. These findings suggested that quantifying the effects of tillage conversion on soil Ksat needed to consider experimental conditions, especially the measurement technique and conversion period.
Highlights
The saturated hydraulic conductivity (Ksat), which reflects soil permeability when the soil is saturated, is critical for calculating water flux in soil profile and designing irrigation and drainage systems (Bormann and Klaassen, 2008)
These findings suggested that quantifying the effects of tillage conversion on soil Ksat needed to consider experimental conditions, especially the measurement technique and conversion period
Measures, such as residue retention and film mulching, must be similar between paired controls (CT) and treatments (CS) during the selection process; (4) means, standard deviations (SD) (or standard errors (SE)) and sample sizes were directly provided or could be calculated from the studies; (5) if one article contained Ksat in multiple years, only the latest results were applied since the observations should be independent in the meta-analysis (Hedges et al, 1999); (6) for Guelph permeameter, only the one-head technique was considered for meta-analysis
Summary
The saturated hydraulic conductivity (Ksat), which reflects soil permeability when the soil is saturated, is critical for calculating water flux in soil profile and designing irrigation and drainage systems (Bormann and Klaassen, 2008). It is an essential soil parameter in agro-ecological, hydrological and biogeochemical models across different scales. Ksat, such as Guelph permeameter (Reynolds and Elrick, 1985) used in field and constant/falling head permeameter applied on intact (undisturbed) or repacked soil cores (Klute and Dirksen, 1986).
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