Effect of long-term organic amendments on the full-range soil water retention characteristics of a Vertisol

Abstract Enhancement of soil water holding capability is of great interest for the management of agro-ecosystems to increase water use efficiency and crop yields. Application of organic amendments has been reported to affect the wet range of the soil water retention characteristic (SWRC, pF ≤ 4.2) differently and knowledge of the impact on the dry range of the SWRC (pF > 4.2) is limited. In this study, we evaluated the effect of 33 years application of inorganic fertilizer and organic amendments, including wheat straw, cow and pig manure on the full range of the SWRC of a Vertisol. Results showed that long-term application of inorganic fertilizer did not significantly affect soil water retention. The addition of organic amendments, i.e. wheat straw, pig or cow manure in combination with inorganic fertilizer significantly increased the wet range of the soil water retention, which was attributed to improved soil structure by increased SOC content. However, plant available water content was not significantly improved by organic amendments. Application of organic amendments decreased or had no effect on soil water retention at pF > 5.5, indicating the hygroscopic water was less impacted by SOC content. Our results showed that the effects of organic amendments mainly improved the retention of the capillary water but not the adsorption of hygroscopic water. This provides new insights on the understanding of water behaviors in Vertisols.