Abstract:

The aim of this study was to clarify how different species of cover grass affect soil evaporation， canopy air humidity， and soil water storage in an apple （Malus pumila） orchard in spring， and to determine how cover grasses affect the available water content in soil. A field experiment was conducted from 2019 to 2021 at the Wuluo Modern Agriculture Demonstration Garden， Wuyi County， Hebei. Changes in， and interactions among， the leaf area index （LAI） of the grass population， photosynthetically active radiation （PAR） transmittance， soil temperature， water evaporation， air relative humidity in the fruit tree canopy， soil water content， and water storage were evaluated when overwintering grasses ［February orchid （Orychophragmus violaceus）， hairy vetch （Vicia villosa）， and triticale （×Triticosecale Wittmack）］ and perennial grasses ［cocksfoot （Dactylis glomerata） and white clover （Trifolium repens）］ were planted between the apple tree rows. It was found that the soil evaporation in sod culture was 3.14 mm higher with overwintering grasses than with perennial grasses from April to May in 2021. The effects of overwintering grasses on soil evaporation differed between before and after returning to the field. Before returning to the field， overwintering grasses reduced soil evaporation by 20.5% compared with perennial grasses due to the rapid growth rate， large population LAI， low PAR transmittance， low temperature in 0-25 cm soil profile， and low soil water content. After overwintering grasses were returned to the field， the soil evaporation was 29.0% higher than in the plots with perennial grasses. There was a significant linear positive correlation between air relative humidity at 1 m height in the fruit tree canopy and reduced soil water storage in the 1 m soil profile. Compared with perennial grasses， overwintering grasses consumed 39.20 mm more stored soil water， and increased the air relative humidity by 15.5%. Compared with clear tillage， sod culture reduced soil evaporation by 27.80 mm， and increased stored soil water consumption by 52.50 mm. In conclusion， the ability of cover grasses to reduce soil evaporation in spring could not compensate for the consumption of soil water by grass growth， which ultimately resulted in reduced soil available water content. Compared with perennial grasses， overwintering grasses were more conducive to improve air humidity in orchards on the North China Plain in spring， but consumed a large amount of stored soil water. In practice， irrigation systems for apple orchards in spring should be optimized according to how different grass species affect the soil water content.

Key words: inter-row cover grass, apple orchard, soil evaporation, air humidity, soil water content