渭北旱塬果园自然生草对土壤水分及苹果树生长的影响

土壤水分不足是渭北旱塬苹果生产中的首要问题。为了提高果园土壤贮水量,促进果树生长,该试验以果园清耕和人工生草(三叶草)为对照,探讨渭北旱塬果园自然生草(繁缕和牛繁缕群落)对土壤水分及苹果树生长的影响。结果表明:自然生草在苹果开花坐果期可提高0~80 cm土层土壤水分,在幼果膨大期和花芽分化期可提高0~120 cm土层土壤水分,在果实采前膨大期可提高0~160 cm土层土壤水分,而人工生草则降低了土壤水分。自然生草和人工生草主要影响0~80 cm土层土壤水分,且对0~40 cm土层土壤水分影响较大,对120 cm以下土层影响较小。自然生草的土壤蒸散量较人工生草和清耕分别减少了17.30和8.07 mm,单果重分别提高了15.46%和6.21%,产量分别提高了21.29%和6.10%,土壤水分利用效率分别提高了25.09%和7.64%。自然生草不但可提高果园土壤贮水量,而且可提高果实单果重与产量,渭北旱塬应积极推广果园自然生草。

Effects of self-sown grass on soil moisture and tree growth in apple orchard on Weibei dry plateau

Abstract: The Weibei plateau is one of the most productive regions of apples in China and also in the world. However, annual precipitation in this region is limited and is unevenly distributed over seasons. The deficiency of soil moisture has been the main factor to restrict the production of high-quality apples in the Weibei plateau. Although artificial-planted grass could improve soil organic matter and soil micro-environment, it could also induce competitions of soil moisture and nutrients with fruit trees and further inhibit fruit tree growth and consequently reducing apple yields and quality. On the contrary, self-sown grass has experienced many years of natural selection, more capable of adapting to local ecological environment, which is very likely to improve orchard soil environment and even promote a virtuous cycle in orchard ecosystem. However, there has been quite limited investigation on the potential influence of self-sown grass on soil moisture and apple tree growth in the region of Weibei plateau. Therefore, in this study, self-sown grass, chickweed (Stellaria media) and cattle chickweed (Malachium aquaticum), were systematically investigated in Weibei plateau, and with artificial-planted grass, white clover (Trifolium repens) and clean tillage as control. The soil water storage, evapotranspiration, single fruit weight, fruit yields and other relevant parameters were continuously monitored. The results showed that the coverage of the self-sown grass were greater than that of the artificial-planted grass, but the height, aboveground biomass, roots biomass, roots depth and the ratio of roots biomass to aboveground biomass were significantly lower (P<0.05) with the self-sown grass than those with the artificial-planted grass. In addition, self-sown grass and artificial-planted grass mainly affected the soil water storage at depth of 0-80 cm, especially at soil depth above 40 cm. Their influences to soil layers deeper than 120 cm were fairly limited. To be more specific, while the soil water storage at soil depth of 0-80 cm on the self-sown grass orchard increased in flowering and fruit-bearing stage, it decreased on the artificial-planted grass orchard throughout the entire growing stages. For the soil depth of 0-120 cm on the self-sown grass orchard, the soil water storage increased in young fruit enlargement stage and flower bud differentiation stage. Similarly, the soil water storage at soil depth of 0-160 cm also increased on the self-sown grass orchard during fruit enlargement stage before harvesting. The soil water storage of the artificial-planted grass orchard recovered slowly in rainy season (from August to October), and was also lower than that of the clean tillage orchard and the self-sown grass orchard, this would negatively affect fruit enlargement before harvesting, therefore reducing fruit yields, and even further inhabiting flowering and fruit-bearing and the growth of new shoots in the coming year. As to the differences of soil evapotranspiration, the self-sown grass orchard highly significantly reduced the orchard evapotranspiration in April and May (P<0.01), and significantly in August (P<0.05). This would potentially contribute to young fruit enlargement and fruit enlargement before harvesting. Although the precipitation of experiment year was higher than the long-term average annual precipitation, evapotranspiration of the artificial-planted grass orchard and clean tillage orchard were still greater than the precipitation that occurred at the same period by 32.55 and 23.32 mm. Meanwhile, the soil evapotranspiration on the self-sown grass orchard was only were 15.25 mm more than the precipitation occurred at the same period. Among the different grass orchards, the amount of evapotranspiration from the self-sown grass orchard decreased by 17.30 and 8.07 mm when compared with that of the artificial-planted grass orchard and clear tillage orchard. Our results indicated that self-sown grass could effectively alleviate soil water storage shortage in the apple orchard on the Weibei plateau. The apple shoots and branch tapering grade with self-sown grass were more vigorous than that with the artificial-planted grass and clean tillage. Compared with the artificial-planted grass and clean tillage, the single fruit weight of the self-sown grass increased by 15.46% and 6.21%, the fruit yields improved by 21.29% and 6.10%, and soil water use efficiency enhanced by 25.09% and 7.64%. The self-sown grass could not only improve orchard soil moisture, but could also stimulate shoots growth and further improve fruit quality and fruit yields. Therefore, the self-sown grass should be extensively promoted in the Weibei plateau.