Objectives To explore the important role of orchard grass in promoting tree growth and development, improving soil physical and chemical environment and soil fertility, in order to solve the common problems of poor site conditions, difficult soil improvement, low organic matter content and lack of supplementary ways in orchards in China, and provide important supporting technology for sustainable development of fruit industry.

Methods Taking seven grass species introduced from the United States, including sideoats grama (Bouteloua gracilis), rough dropseed (Sporobolus asper), little bluestem (Sporobolus asper), sand lovegrass (Eragrostis trichodes), weeping lovegrass (Eragrostis trichodes), switchgrass (Panicum virgatum), Canada wildrye (Elymus canadensis) as experimental materials, and clear tillage and white clover (Trifolium pretense) as control, the experiment of growing grass among young trees of annual apple in Mazhuang experimental base of Tai'an City in spring of 2017 was carried out to explore the effects of different grass treatments on the growth and development of fruit trees and soil environment of orchards in two consecutive years.

Results 1) The biological characters of the 8 materials were different, among which the leaf width and plant height, density, coverage, aboveground and underground biomass of weeping lovegrass were the best. 2) The seven grass treatments have significant effects on improving the soil environment. From June to July, the soil temperature treated by growing weeping lovegrass decreased the most and the decrease of grass treatment was 23.62% and 27.45% respectively compared with that of clean tillage. From June to August, the pH value of the soil treated by growing little bluestem for two years was the lowest, which was 6.83%, 7.07%, and 7.19% lower than that of the same month. The soil porosity treated by growing weeping lovegrass increased by 6.76%, 8.35% and 9.09% respectively compared with that of clean tillage. 3) The soil microbial quantity in soil was increased by grass growing in orchard, and the effect was more obvious with the time of grass growing. The number of fungi and actinomycetes in soil treated with weeping lovegrass for two years was the largest. The number of bacteria in the soil treated with rough dropseed for two years was the highest. The number of bacterial OTUs treated with sand lovegrass for two years was the largest, at 5323, which was 7.93% higher than that of clear tillage. 4) Different grass treatments significantly improved the soil nutrients in the orchard. The soil organic matter content of growing weeping lovegrass was the highest, and the organic matter content of two-year-old grass was 23.53% higher than that of one-year-old grass. The contents of available iron, manganese, copper and zinc in soils after different grass treatments were significantly higher than those of clear tillage. 5) The contents of mineral elements in leaves of different grass treatments were significantly different from those of clear tillage. The contents of nitrogen elements in leaves were significantly reduced, and the contents of phosphorus, potassium, magnesium, iron, copper and zinc in leaves were significantly increased.

Conclusions Different grass treatments in the orchard have important effects on apple saplings, soil environment and soil nutrients, which improved the content of mineral elements in the leaves of young trees, reduced soil temperature and pH, and improved soil porosity and soil organic matter and soil microorganisms. Grass treatments are conducive to exploring ways to improve the soil and trees of orchard gardens and promote the sustainable development of fruit industry in China.