Study On Growing Green Covers In Pear Orchard

As an excellent soil management system, green covers in orchard has been developed to be a cropping pattern in developed countries. In this dissertation, six-year-old'Xueqing'pear was used as experimental material, including with White Clover(Trifolium repens L),perennial ryegrass(Lolium Perenne L)or Alfalfa(Medicago sativa) , cleaning tillage was used as the control (CK). The changes of soil temperature and humidity,soil properties and photosynthesis were measured after sod culture for two years. The effect of planting grass on fruit tree growth, photosynthesis characteristics as well as the yeild and quality of fruits were discussed. The main results were as follows:(1) Under different management systems of green covers , the trend of changes of temperature at 0～20cm,20～40cm layers of soil was basically identical. From May to September,Soil temperature fluctuated between 22℃and 25℃, and water content at 0～80cm layers of soil was between 25% and 40%.The temperture fluctuations, which were due to the rainfall, were smaller under the treatments of perennial ryegrass and White Clover, compared with the wider changes under cleaning tillage treatment.(2) The soil organic content increased by green covers. During the fruit enlargement period to fruit mature, the average content of soil organic matter with grass was higher than that of cleaning tillage. The highest soil organic content appeared in white clover cover system, in which the content incearsed by 34.1% compared with CK. In all treatments, the organic content decreased progressively following the depth from 0cm to 80cm.(3) The green covers raised the mineral nutrients content of soil with the treatment of white clover, the content of the total nitrogen and phosphorus increased by 18.9% and 6.5% respectively. In the treatments of white clover, alfalfa and perennial ryegrass, the content of available phosphor increased by 1.1%,15%and16.68%separately,while available potassium by 48.28%, 51.33% and 47.97%.(4) There was a crucial relevance between soil nutrients content and relevant enzymes activities. In this experiment, the catalase activity was proved to be negatively correlated with total phosphorus content, with r value of -0.5672;the catalase activity was proved to be significantly positively correlated with total potassium,with r value of 0.7172;the activities of urease, catalase and polyphenol oxidase were positively correlated with soil total nitrogen content.(5) The grass planting increased water use efficiency, reduced water evaporation, and also enhanced photosynthetic rate of the leaves. The highest water use efficiency appeared in the treatment of white clover planting.(6) Fruit quality improved with different grass planting treatments. Fruit titratable acid changed significantly in perennial ryegrass covered orchard, while no visible difference was detected in other treatments. Single fruit weight, soluble solids, fruit firmness, starch and sugar content increased in different grass planting treatments.