| The problems of soil acidification have got the unprecedented concern and attention. There has a series of problems about soil fertility and environment qualities because of soil acidification. For example, it accelerates the leaching and loss of soil nutrients, causes the degeneration of soil structure and releases some pollutants that like Al3+ and heavy metals. And soil acidification also reduces the enzyme activity. Because of this phenomena above all, it will make the degradation of forests, reduce the production and quality of crops, pollute the surface and ground water and make the aquatic organisms into dangerous. The mustard tuber plantation is the major agro-industry of Fuling district, Chongqing municipality. However, there have been some problems such as poor harvest and continuous cropping obstacles of mustard tuber plantation because of the soil have acidified.In order to understand the situation of soil acidification and take some protective measures timely, Nantuo town was chosen as the research object which has a long history of mustard tuber plantation. The region’s major soil type is neutral purple soil and paddy soil.283 soil samples were sampled to research the soil acidification situation, which include 203 corn-mustard tuber rotation soils and 80 rice-mustard tuber rotation soils. And we chosen 52 samples to research the characteristics of soil acidify process. Three plants material, include the leaves of mustard tuber and the straws of rice and corn, and three chemical amendments, include CaCO3, MgCO3 and CaO, which were used to ameliorate the acidified soil. The main results were as follows:(1) In the all 283 soil samples,174 soil samples’ pH value less than 6.5 and 148 soil samples’ pH value less than 5.5 that acidified seriously, which accounted for 61.48% and 52.30% to total soil samples. In the 80 rice-mustard cropping system samples, which 60 samples have been acidified and 54 samples have been seriously acidified. In the 203 corn-mustard cropping system samples, which 114 samples have been acidified and 97 samples have been seriously acidified. It can be concluded that the soil in the research area has been acidified to some extent and should be drawing more attention. Through a further study of 52 soil samples:It has a huge increase of the soil potential acid. Exchangeable Al3+ has a significant proportion of the soil potential acid content in the strong acid soil and has a great influence on the soil potential acid content and soil pH. Water-soluble Al3+ is a direct factor that decides soil pH value in the strong acidified soil. We can calculate the soil pH value through the soil water-soluble Al3+ content. There is no exchangeable Al3+ and only a little exchangeable H+ in the un-acidified soil.(2) The exchangeable Ca2+, Mg2+, K+, Na+ content of acidified soil were 9.55±5.85 cmol(+)·kg-1.25±0.680cmol(+)·g-1,0.209±0.950cmol(+)·kg-1 and 0.250±0.113cmol(+)·kg-1 accordingly. Soil base saturation percentage (BSP) was 77.55±19.09%. The acidified soils still contain an abundant of exchangeable Ca2+ and exchangeable Mg2+ in the contrast of yellow soil and red soil, which has a significant function to prevent soil further acidification. Soil pH value has a significance negative correlation to the proportion of water-soluble base cations in exchangeable base cations. So, along with the further developing of soil acidification, exchangeable base cations are easy to translate into water-soluble base cations. The effectiveness of base cations can increase in a short-term, but it also easy to being leached.(3) Soil acidification didn’t have a significant impact on the content of soil organic matter (OM), totally nitrogen (TN) and totally phosphorus (TP). But after a long term soil acidification may induce the loss of soil potassium. And there was a close relation between soil acidification and soil available phosphorus (AP) content. The mustard tuber plantation acidified soils’ acid-damage deviation and acid-damage capacity were lower than un-acidified purple soil, even lower than yellow soil and red soil. The soil acid-damage intensity lower than un-acidified purple soil and yellow soil, but higher than red soil. The soil’s acid-damage deviation and acid-damage capacity decreased with the decrease of soil pH. Soil acidification didn’t have significance influence on soil’s mineral composition. The causes of research area soil acidification are decided by many factors that both include natural and artificial reasons. One of biggest artificial reasons is the large scale usage of chemical fertilizers like calcium superphosphate.(4) Application of plant materials can improve soil pH value. It had the best improvement effect when use 80 g·kg-1 straw of rice as the ameliorator after 150 days incubation in all treatments. The soil pH value is 6.19, which improve 1.93 pH units compare to the contrasting soil. All of the ameliorators reduced the content of exchangeable acid, exchangeable Al3+and exchangeable H+, and improved the content of exchangeable basic cations and water-soluble basic cations. Along with the increase of the using of every plant material, the improvement effect increased. It can be concluded that there was a significance improve effect when use 400 g mustard tuber leaf or 80 g rice straws per kilogram soil.(5) The chemicals significantly improved the soil pH value, reduced the soil exchangeable acid content and increased the soil base saturation, and had a better improve effect to soil acidity indexes than plant materials. It had a significance ameliorable effect to acidified soil when use 2g CaCO3 or 2g MgCO3 or 1g CaO per kilogram soil, and the soil pH value reach up to 6.33,6.82 and 6.30. The soil pH value further improved with the increase usage of chemical ameliorators, but it without too much practical significance.(6) Plant materials and chemical improver have different features. Under the same amount, plant material improvement effect was much less than the chemical improver. But plant materials good for nutrient coordination, convenience and take low cost because of obtain materials from local sources. According to the local actual situation, we put forward the following improvement plant straw and chemical application when the mustard tuber harvested, putting the leaves returning on-site and then add lime 750 kg per hectare. Crush the straw after harvest corn or rice, and cover it with soil to accelerate the decomposition of straw, Decrease the application of calcium superphosphate and increase the application of organic fertilizer as far as possible. So after several years of slow improvement, the soil will eventually have a high fertility environment to crops to grow. |
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