Abstract:

This study examined soil nutrient differences between clean-cultivated orchards and those with grass or similar ground cover to identify the effect of orchard management regime on soil properties in arid regions of China. We identified 45 pairs of orchards in 12 counties of the Longdong area of Gansu Province for sampling. The two orchards in each pair were near to each other and matched for age and type of fruit tree， but differed in that one was clean-cultivated， while the other was managed with herbage ground cover. Systematic analysis was conducted on the variations of soil organic matter （SOM）， total nitrogen （TN）， total carbon （TC）， total phosphorus （TP）， alkaline-hydrolyzable nitrogen （AN）， and pH in the soil surface. The impacts of climatic conditions， soil types， and grass cultivation practices were deliberated upon. The results showed that： 1） In comparison to clean tillage， the soil SOM， TN， TC， AN， and pH levels were increased by 26.7%， 7.1%， 10.4%， 18.2%， and 2.5%， respectively， where herbage ground cover was present， while TP decreased by 8.3%. The 45 pairs of orchards were categorized for the same 6 parameters as increased， unchanged or decreased when herbage ground cover was present and the resulting frequency ratios of percentage of the 45 paired sites increased∶percentage of sites increased under herbage cover SOM， TN， TC， AN， pH and TP levels were 44.4%， 35.6%， 53.3%， 37.8%， 73.3% and 26.7%， and decreased were 24.4%， 33.3%， 24.4%， 26.7%， 22.2%， and 51.1%， respectively. 2） Annual rainfall showed a significant positive correlation with SOM， TC， AN， and pH （P<0.05）. At sites with annual rainfall greater than 400 mm， both SOM and TC rates of change exceeded zero. However， annual air temperature did not have a significant impact on TP and pH， but exhibited a positive correlation with SOM and AN （P<0.05）. 3） A significant positive correlation was observed between the number of years since establishment of herbage cover and the rates of change in TN， TP， AN， SOM， and TC （P<0.05）. There was a trend of a negative linear association between pH and the number of years since herbage establishment， however， this trend did not achieve statistical significance. The rates of change in SOM， TN， TC， AN， and TP all increased with time since establishment of orchard ground cover， with TP showing the highest growth rate at 8.2 g·kg^-1·yr^-1. Furthermore， orchards with ground cover established for more than 4 years demonstrated higher levels of SOM and TN compared to those clean-cultivated orchards. 4） The rate of change of TP under sown vegetation cover （-18.3%） was significantly more negative than that in natural grassland （4.9%）， while the opposite was true for pH， with sown ground cover exhibiting a faster rate of pH increase than naturally occurring herbage. The rate of TC increase in dark loessial soil was 25.7% higher than that in yellow loam soil， while the rate of TP decrease was 27.6% faster in dark loessial than yellow loam soil （P<0.05）. These results offer a scientific foundation for optimizing and promoting orchard grassing techniques in the Longdong area. They can also assist fruit growers in selecting appropriate grassing methods and management practices based on local climate conditions and soil types， so as to improve orchard soil fertility and promote the sustainable development of orchard ecosystem.

Key words: orchard grass, soil, nutrient content, Longdong region