Effects of mowing frequency on the interspecific water relationships of a walnut (Juglans regia L.)-alfalfa (Medicago sativa L.) intercropping system

Mowing is used as a management practice in tree-grass agroforestry, but the water relationships between trees and grasses have been divergent. Here, we aim to reveal the effect of mowing frequency on the interspecific water relationships.

Walnut (Juglans regia L.) was intercropped with alfalfa (Medicago sativa L.) from 2021 to 2022, and the responses of soil moisture, plant roots and moisture sources, water use efficiency (WUE) and water consumption to different mowing frequencies (once, twice and thrice) were investigated.

The soil moisture did not respond significantly to the mowing frequency; mowing significantly increased the root length density of alfalfa in all soil layers, especially in the 0–20 cm layer; mowing twice and thrice affected the water sources of walnut and alfalfa, and it increased the proportion of walnut trees that used deep soil water (up to 64.60%) and the proportion of alfalfa that used surface soil water (up to 58.5%); The WUE of walnut did not respond significantly to mowing, while that of alfalfa did (the highest average WUE of 5.44 mmol C/mol H₂O was found when alfalfa was mowed twice, which increased by 4.42% over the WUE of the mowing once treatment (CK)); compared to CK, the total water consumption of the intercropping system was unchanged when mowed twice but increased significantly when mowed thrice.

In the early stages, the walnut-alfalfa intercropping system can be managed by mowing twice, which can improve the WUE of alfalfa and maintain soil moisture.