Abstract: The hillside peach orchard in Qin'an County of Gansu Province is an important peach tree cultivation region in the semiarid Loess Plateau of China under rain-fed production systems(without irrigation), where precipitation is the major water resource for peach tree growth. Increasing crop water-use efficiency(WUE) through water conservation in the soil is an important component of dry land farming. Mulching is among the water management practices for increasing WUE which greatly reduced the seasonal drought limits on peach production. We assume that the fruit quality is also affected by variation of the soil environment caused by mulching treatments, such as nutrition, enzyme, soil structure, etc. Thus, a better understanding of the soil nutrition and carbohydrate and nitrogen partitioning in mulching treatments aimed at fruit quality and peach tree vegetative growth was necessary. However there is no in-depth study on soil nutrient change and the influence of the enzyme activity in orchard where the ridge film mulching has been applied for a long time. In this study, field experiments were performed from 2012 to 2015 in Qin'an County(105° 41' 51" N,34° 49' 88" E, 1 360 m above sea level) which is located in the southwest Loess Plateau in Gansu Province, China. This semiarid region is characterized by a continental, monsoonal climate, the 30-year mean annual temperature is 11.4℃, and the average annual precipitation is 449 mm. The soil from the ground down 60 cm is loessial, with 12.3 g·kg^-1 average organic matter content and a pH of 8.7. The experimental orchard was planted with peach trees(Prunus persica cv.‘Qinwang’ + rootstock ‘Prunus davidiana(Carr.) Franch’) 5 years prior to the study. Soil organic matter, nitrogen, phosphorus, potassium, and the changes of enzyme activity were analyzed continuously at different soil layer(0-30 cm and 30-60 cm) under the condition of PFM(plastic film mulching for the whole year), JM (mulch in late February and uncover the film in late June)and CT(clean tillage). The results showed that:Compared with CT, PFM and JM significantly changed available nutrient of the soil, but there were differences between PFM and JM. At soil layer from the ground down 30 cm, alkali-hydrolyzable nitrogen in PFM and JM were increased by 27.7% and 14.6% respectively than that in CT. Compared with JM, available phosphorus in PFM was decreased by 31.0%, and available potassium was increased by 5.0%. At the soil layer from the depth of 30 cm to 60 cm, if compared with JM, alkali-hydrolyzable nitrogen in PFM was increased by 9.7%, available phosphorus and available potassium in PFM were decreased by 11.5% and 12% respectively. The PFM and JM significantly increased the activity of soil urease and phosphatase, decreased the rhizosphere catalase activity. At soil layer from the ground down 30 cm, urine enzyme activity in PFM and JM were increased by 21.5% and 51.42% respectively, phosphatase activity were increased 11.2% and 21.4% respectively than those in CT, JM was more beneficial to the improvement of the microorganism and enzyme activity, and also to the orchard soil nutrient transformation and nutrient utilization.

Key words: peach orchard, ridge film mulching, soil nutrients, soil enzyme activity