Reply on RC1

Kaihua Liao

doi:10.5194/soil-2021-118-ac2

Abstract

Abstract. The saturated hydraulic conductivity (Ksat) 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 Ksat 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 Ksat from 69 published studies and investigated factors influencing the effects of conversion to CS on Ksat. 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 Ksat. When the Ksat was measured by the rainfall simulator, the conversion to CS significantly (p<0.05) increased the surface and subsurface soil Ksat by 41.7â% and 36.9â%, respectively. In addition, the subsurface Ksat also tended to increase under CS practices when the Ksat was measured by a tension disc infiltrometer. However, when the Ksat was measured by a hood infiltrometer, ring infiltrometer, constant/falling head, and Guelph permeameter, the conversion to CS had no significant effects on the Ksat. It is observed that, when the conversion period was less than 15Â years, the Ksat 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 Ksat 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 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

Introduction

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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