Effect of mulching materials on the amount of soil microorganisms of apple root zone in Loess Plateau

Abstract:【Objective】The study amied to investigate the effects of different mulching materials on the soil physicochemical properties and soil microorganisms in apple orchards of Loess Plateau to provide a theoretical basis for the apple orchard management in the future.【Methods】The soil samples were collected from the row middle of four- year- old apple trees (Fuji) that treated with different mulching materials including the hay (GC), sand (SS), PE black film (HM), horticultural mulching (DB), and clear tillage (CK) during the period from February to December, 2018. The soil moisture content, pH, total nitrogen content, total phosphorus content, total potassium content, available nitrogen content, available potassium content, and available phosphorus content were determined by collecting the soil samples of 0 to 60 cm from the row middle of four-year-old apple trees. Similarly, the amount of soil fungi, bacteria, and actinomycetes were determined using the dilution coating plate method, and the soil samples were collected from the soil layers of 0 to 20 cm, 20 to 40 cm and 40 to 60 cm, respectively at the dormancy, full flowering, fruit formation, fruit expansion, and fruit ripening stages. Meanwhile, the correlations of fungi, bacteria, and actinomycetes numbers at different layers of soil were analyzed.【Results】The four different mulching treatments increased the soil water content significantly by 2.6% to 5.0% (p＜0.05) in comparison to the CK, and also the soil water content was positively correlated with the microbial amounts. Compared with the CK treatment, the SS treatment increased the soil alkalinity significantly, whereas the HM and DB treatments decreased the soil pH value significantly. Furthermore, the different mulching treatments exhibited different effects on the nutrient contents in the soil. The soil total nitrogen content, total potassium content, total phosphorus content, available potassium and phosphorus content were increased, whereas the soil available nitrogen content was decreased by the GC and SS materials in comparison with the CK treatment. Among the soil nutrients parameters, the soil total potassium content was increased significantly (p＜0.05). In addition, the HM and DB treatments increased the soil total phosphorus content, available nitrogen content, available phosphorus content, and available potassium content with a variable degree, but decreased the total potassium content and nitrogen content finally in the soil. Among the four mulching treatments, the DB treatments significantly increased the contents of soil available nitrogen, phosphorus and potassium by 26.67%, 113.40% and 48.47%, respectively. During the growth period of 4-year-old apple trees (Fuji), the four mulching treatments effectively increased the amounts of the soil microorganisms, but the amount of soil microorganisms decreased gradually with the increase of the soil depth at different periods. During the five growth stages of apple trees, the amount of soil fungi reached its maximum during the dormant stage, whereas the amount of soil bacteria reached its peak at the fruit expansion stage. The number of actinomycetes reached the minimum at the fruit maturity stage in the soil treated with the four different mulching materials, especially the GC treatment presented the significant effect on the changes of actinomycetes amount. Compared with the CK treatment, the amount of soil fungi was increased by 47.91% and 11.10% at the soil layer from 0 to 60 cm after GC and DB treatments, respectively; the number of soil bacteria was increased by 9.41% after SS treatment, while decreased by 27.51% to 61.81% at the same soil depth after treatment with GC, DB and HM material, respectively; the amount of soil actinomycetes was significantly increased by 29.59% and 96.07% after treatment with the HM and GC materials, respectively.【Conclusion】The methods of hay mulching and horticultural cloth mulching could significantly enhance the soil water content, improve the soil nutrient conditions, increase the amount of the soil fungi and actinomycetes, and could be used as the land management mode for apple orchards in Loess Plateau.