Soil Conditions Causing Defoliation Of Fruit Trees In The Early Stage And The Effects On Fruit Quality In The Arid Area Of Weibei River

Apple is one of the fruits with the highest trade volume, having great nutritive value and economic value. The rapid development of apple production spurred other business at the same time, making a big proportion locally. The arid area of Weibei River was thought to be the right place for high quality apple planting, and there had been planting apples for 30 years or so, which not only was a dominant economic business but also played a role in improving the landscape and ecological environment. However, defoliation in the early stage of apples had become one of the most universal and serious problems in the arid Area of Weibei River, and this problem was become more serious year by year, affecting the apples'quality and quantity. This also had become an obstacle for the sustainable development of apple production and discouraged the farmers. Thus, it is the key for the sustainable development of apples production to study the evolution of soil quality in orchards and explore the mechanism of defoliation.Although scholars domestic and overseas had done a lot of work interms of defoliation in the early stage of apple tree, some of them assumed this problem was due to plant diseases and insect pests and there was still an open in studying the relationship between the problem and soil status. The research work was done in Yuandi Town, Xunyi County, Shaanxi Province, and the orchards were over 20 years old, having the same variety and the defoliation problems. We surveyed the measures and the properties of the orchard soils, explored the reasons which affected apple qualities, in hope of finding out the concrete soil factors for the problem and guiding the scientific management of orchards. The main results gained were below:1. The soil quality in the defoliation orchards had degraded significantly. Compared with the defoliation orchards, the soil compactness and soil bulk density were lower in the non defoliation orchards and farmland locally, and the value increased as the soil depth increased. That is to say, it had become a big problem that the subsoil had become hard. In the 0-10 cm the soil compactness made no difference between the soils in orchards and farmland, but the soil compactness was higher in the defoliation orchards than in the non defoliation orchards and farmland. The value expanded sharply under 30 cm in the soil, more than 1150KPa. The compaction in the middle of soil had stressed the fruit roots obviously, affecting the fruit trees to grow freely.The soil bulk density was lower than 1.30g/cm3 in the 0-20 cm soil, but was more than under 30 cm in the soil. For fruits, the topsoil was less important to them because there were few roots in an arid environment. However, the soil bulk density was more than 1.50g/cm3 in the lower place in soil, which exceeded the comfort zone of 1.00-1.30g/cm3 for apple trees.Consequently, the soil bulk density in the lower layers had become a problem for fruit trees. Compare soil profile moisture capacity of rainy season, find out that above 30cm the orchard and farmland soil moisture capacity were not significant, but below 30cm soil layer , deciduous orchard soil moisture was significantly less than farmland and heath fruit orchards. Proved that cause in deciduous orchard soil compaction (bulk density decreases), restricting water seepage is not conducive to deep soil moisture recovery, increased deep soil desiccation, and drying of the soil has a solid lead of (hardness increase), the formation of poor water circulation , leading to early defoliation of fruit trees will be year after year the event. Subsoiling orchard for a certain role to prevent early defoliation.Soil aggregation is the basic condition to keep soil physics properties. In this study showed that there was positive correlation between soil hardness and soil water content in farmland and orchard, which indirect proof that poor aggregation condition in orchard of Weibei area. Moreover, through measuring the composition of soil aggregates showed the poor aggregation was main reason leading to densification in orchard soil profile. The only aggregate with mechanical stability was in 5mm size class. The amount of soil aggregate in >5mm size class was greater in farmland than in orchard, especially the amount of soil aggregate in >0.25mm size class was highest in farmland, followed by undeciduous orchard and deciduous orchard, which showed that poor aggregation in deciduous orchard soil was the main reason to lead to soil hardness and limit water infiltration when precipitation. To protect surface soil aggregation is of prime importance to improve water condition and mechanical strength of soil.Soil chemical quality degradation appeared in deciduous orchard. Orchard soil organic matter was lower than it was in farmland. Less organic fertilizer applied in orchard and the leaves were moved to control pest. Soil organic matter content was greater in deciduous orchard surface soil when compared with undeciduous orchard, however, it was another situation in 60~100cm soil layer. It was surveyed that no fallen leaf or less if applying organic fertilizer or straw in pit before planting fruit trees. To manage and foster pit before planting fruit trees have positive effect on preventing fallen leaf in early period of orchard. The soil calcium carbonate content changes in the 4.54-12.02% in Weibei Area, in the soil surface and between the middle layer not formed the movement and deposition of calcium significantly. Deciduous orchard soil calcium carbonate content is lower than non-deciduous fruit orchards, may be deciduous orchards poor soil aeration, and soil air CO2 concentration is generally high, so calcium carbonate easy to move into heavy calcium carbonate, place a clear differentiation of calcium carbonate, also led to the deterioration of soil aggregate stability.With the soil depth increased soil nitrogen content showed a decreasing trend. The soil nitrogen levels in the non-deciduous and deciduous orchardin have the same more than 35cm of soil, no significant difference, the differences began to appear in the 35cm following, non-deciduous orchard soil nitrogen content higher than the deciduous fruit.Deciduous orchard fruit disease has seriously affected the quality of fruit. Comparison of deciduous fruit orchard and non-deciduous fruit quality, although both are crisp taste of high quality fruit, However,the hardness of deciduous fruit orchards is less than non-deciduous orchards, so affected fruit storage and transportation. Fruit density is to some extent reflect the inclusion of fruit number,the results show that non-deciduous fruit orchard greater than deciduous orchard. Non-deciduous fruit sugar content is greater than the deciduous fruit orchards. So, deciduous orchards severely reduced fruit quality, and affect the value of goods and nutritional value of fruit, not conducive to the sustainable development of fruit industry.