Effects of film mulching on soil aggregate structure stability and fine root distribution of rain-fed apple in eastern Gansu

Different orchard management methods can affect the growth and distribution of fruit roots, the stability of soil aggregates and the ability of organic carbon storage, and then change the response relationship of root-soil complex. The fine root growth of apple orchard surface soil（0-20 cm） with different plastic film mulching years（2 a, 4 a, and 6 a） was investigated in the dry tableland of Longdong, Northwest China. The combination of dry and wet screening methods was used to classify soil aggregates（>2 mm, 0.5-2 mm, 0.25-0.5 mm, and 0.25 mm Mechanical stability aggregates content(DR), > 0.25 mm water-stabled aggregates content(WR), Mean weight diameter（MWD）, geometric mean diameter（GMD）, percentage of aggregate destruction rate（PAD）, water stability coefficient（WSC）, and the content of organic carbon were calculated. The response of soil physical structure and fine root growth to long-term film mulching was analyzed, the relationship between soil aggregate stability and organic carbon sequestration was explored, and the stability mechanism of physical structure of loess soil was revealed. The results showed that film-mulching six years inhibited fine root growth by increasing soil clay, the proportion of physical clay and changing pore structure, and the root weight, root length and root surface area were only 20.97%, 24.66% and 41.25% of conventional tillage（CK）; The DR, MWD and GMD of surface soil aggregates were 82.2%, 74.02% and 59.38% of CK; The protective effect of PAD and WSC were 121.17% and 54.56% of film-mulching two years, compared with that of short-term film mulching. Film-mulching two years improved the force stability and water stability of soil aggregates as well as the degree of soil aggregates, and improved the soil structure. At the same time, the organic carbon improvement effect of mechanical stability and water stability aggregates was better than that of film-mulching six years, which was 115.66% and 116.6% of film-mulching six years. Although the ability of large aggregates to hold organic carbon was higher than that of micro aggregates, due to the long-term stability decline of coated aggregates, the DR of film-mulching six years was only 82.2% of CK, which was not conducive to the protection of organic carbon, so that the decisive effect of soil organic carbon level on the stability variation of aggregates was only 29.55%. The frequent dry-wet alternation caused by continuo