Reduced soil water repellency suggests the need for timely replenishment of soil organic matter in long-term traditional farming

Long-term land use and management practices can affect soil organic matter (SOM) and cause changes in soil water repellency (SWR), the extent of which is related to SOM content and composition. Many studies have focused on explaining the generation of SWR and have emphasized the relation between the occurrence and persistence of SWR and SOM; however, few studies have attempted to revisit the amount and quality of SOM based on changes in SWR. In this 10-year study, SWR and SOM were evaluated after traditional tillage versus a one-time straw return, and the effect of traditional tillage on SOM was illustrated through changes in SWR. The findings indicated that SOM and humic acid (HA) contents and the degree of humification decreased by 8.58 %, 24.93 %, and 20.44 %, respectively, after 10 years of traditional tillage. Furthermore, the H/C molar ratio of HA decreased by 13.38 %, and the aliphatic/aromatic C ratio and the hydrophobic/hydrophilic C ratio decreased by 24.05 % and 31.08 %, respectively, resulting in a weakening of HA hydrophobicity. The primary cause for the decline in SWR over extended periods of traditional tillage was the reduction in both the amount and quality of SOM and the decreased hydrophobicity of HA. By contrast, during the initial phase of one-time straw return, there was a notable increase in the amount and quality of SOM and HA hydrophobicity, resulting in a slight water repellency of the soil; however, this increase only lasted for 3 years. The decrease in the degree and persistence of SWR reflects the decrease in the amount and quality of SOM after long-term traditional tillage, which should be supplemented SOM promptly. We recommend supplementing straw again after 3 years of the one-time straw return. By illustrating the correlation between SWR and SOM, we hope to provide land managers with new perspectives regarding SOM, which is negatively affected by long-term land use, especially in soils under long-term traditional tillage.