Effects Of Acid Deposition On Soil-Vegetable Systems And Cyclings Of Nitrogen And Phosphorus

There have been many studies about the effects of acid deposition on the soil-vegetable systems. It was also generally accepted that acid deposition could suppress the growth, reduce the yield and the quality, decline the planting feasibility and manifold the plant diseases and insect pests of the vegetables. However, most of the results have been derived from laboratory experiments and investigations, which might be not sufficient to reflect the actual influences under the field conditions, because they were obtained by different research methods and in different environmental conditions. So far, little attention has been paid to the effect of acid deposition on the element cycling in the soil-plant systems. Furthermore, most of these researches were limited to the forest ecosystem. The soil-vegetable system, as an artificial ecosystem, differed from natural ecosystem in nutrient element cycling, for the latter could be self-sustaining. In the soil-vegetable system, nutrient elements would be lost more or less in every cycling period, so it should be controlled artificially to maintain the sustainable development of the system. Though it was uncertain that how and to what degree the influence would be, it could still be deduced that acid deposition could affect the material cycling by two ways: one was to change the characteristics of the nutrient balance through inputting some material to the system directly; the other was to influence the whole mass circulation by acting on other matters.In this paper, the on-site-monitor and simulative experiments were combined to evaluate the effect of acid deposition on the turnover of nitrogen, phosphate in the soil-vegetable systems, aimed to provide scientific basis for ameliorating vegetable garden environment, improving productivity, making best use of soil resources, preventing and remedying soil contamination, on the point of nutrient cycling, by means of system analysis, within the boundary of soil-vegetable system.The on-site-monitor experiments were laid out in three plots with different pollution degree by acid deposition to understand the turnover of nitrogen, phosphate under different pollution conditions. Based on previous works and the investigation of this item, the Jiulong village at Jiulongpo District was chosen as representative of heavily acidic deposition polluted area (HPA), the downtown of Beibei District as lightly polluted area (LPA) and Zhuanlong village at Beibei District as control area (CK). About 150 square meters of vegetable fields were selected in HPA, LPA and CK, respectively, and leaching water receivers were installed under 60cm soil depth to collect leaching water. Considering the different sensitivity to acid deposition, the sensitive (tomato), mediate sensitive (cowpea) and non-sensitive (cabbage) vegetableswere selected for experiments. The field experiments were carried out at these sites from May 2000 to July 2001, three seasons of vegetables were rotation of cowpea-cabbage-tomato. In order to compare with the effects of the acid deposition on soil-vegetable system, farming practices such as cultivation method, fertilizing and irrigation etc. were kept as same as possible. During the experiments, samples of rainfall, deposited dust, leaching water, vegetable and soil were periodically taken for analyses of relevant parameters.Considering that the main sources of soil-vegetable ecosystem's nitrogen, phosphate were input by fertilization, a two-factor, four-level experiment was designed in order to study the vertical migration of nitrogen, phosphate in soil, on the conditions of different pH-value and fertilizer dose. This experiment included treatment with simulated rain of four pH levels (pH3.5, pH4.5, pH5.5 and pH6.5) and fertilizer in four doses (Control, Organic fertilizer, Chemical fertilizer, Organic and Chemical fertilizer). The soil chosen for model experiment was collected from vegetable garden in the control area, which parent material was the purple sandy and silt rocks of the Shaximiao formation of the Jur...