| In recent years, soil acidification has gradually become evident in Chinese croplands, which has been a major constraint to sustainable agriculture production. In order to further explore the spatial and temporal changes and influencing factors of soil acidification, reveal the reasons for variation of soil acidification in different region, quantify the effects of soil acidification on crop growth and examine the effective measures to control soil acidification, a field-experimental study was conducted in Jiaodong Peninsula, where soil acidification showed a serious trend with intensive fertilizer input in the low-buffer soils. In the present study, we collected the data from the second national soil census, the national project of formula fertilization by soil testing, and the statistical yearbook as well as the meteorological observation data at regional scale, and then we analyzed soil acidification characteristics, farmland management measures and the effects of soil acidification on soil nutrients and plant growth. We also quantified the effects of soil acidification on wheat-maize system, including its soil chemical properties, root and shoot growth, and grain yield in typical soil plots or areas with severe acidification. With2-year yield experiments, the control strategies and the pathways to alleviate soil acidification were investigated, based on principle of rhizosphere ions balance and soil buffer capacity. The main results and conclusions were shown as follows:1.1.In intensive agriculture systems, soil acidification was prominent in Jiaodong area; high fertilizer input and low buffer capacity of soil were thought to be the main factors. The degree of soil acidification in Jiaodong was higher than the national average level, and its soil pH decreased by an average of1.6units compared with1980s, and its soil acidification exists in the whole1.5-m-deep soil profile. The rainfall and acid rain in this region contributed little to soil acidification. The main factors affecting soil acidification of farmland in Jiaodong were nitrogen cycle (63%), cation removal (30%) and biological nitrogen fixation (7%). Soil acidification caused by fertilizer was mainly due to ammonium nitrification and crop uptake. Soil acidification was found in all four kinds of cropping systems in Jiaodong area, with a soil pH range from4.91to5.87, among which the acidification of vegetables system was the most serious, then followed by wheat-maize-peanut system, apple garden system and wheat-maize rotation system. Different management methods in cropping systems affected soil pH changes. The straw return to filed and rational use of animal manure alleviated the decline of soil pH, and even effectively increased soil pH. With wheat and maize straw return for more than10years, the soil pH was increased to5.97, and continuous wheat and maize straw return for several years maintained soil pH at a relatively stable level. For the soil acidification caused by application of chemical fertilizer over10years, soil organic carbon was increased, available manganese and copper contents increased2and6times compared to the suitable level, and the manganese toxicity and copper toxicity became the main obstacle factors restricting Jiaodong’s agriculture production.2. By quantitative analysis of typical soil with severe acidification, we certified the effects of soil acidification on cereal crops, especially on nutrient uptake and harmful metal element absorption and translocation. With severe soil acidification, soil CEC decreased by17.3%, exchangeable calcium and magnesium were significantly decreased by21%and35%, the available soil aluminum, manganese and copper were significantly increased by1.9times,1.8times and22times respectively. Aluminum, manganese and copper toxicity, and magnesium and calcium deficiency are major limiting factors in the severe acidification farmlands. Soil acidification caused significant adverse impacts on wheat and maize growth, plant growth was significantly inhibited. The field detection and tracking survey indicated that, aluminum toxicity symptoms mainly located in plant root tips, which would become swollen and twisted. The total root length of fine roots with less than0.3mm diameter reduced by90-97%; soil acidification severely limited nutrient uptake by plants. The shoot biomass decreased by10-20%of CK. The contents of harmful elements in wheat-maize straws and grains at harvesting stage significantly increased; aluminum, manganese and copper contents increased by4.5,1.4and8.1times in wheat straws, and3.8,2.4and3times in grains, respectively. The contents of aluminum and manganese increased by1.5and1.9times in maize straws, and2and2.6times in maize grains, respectively. The yield components were significantly reduced, acres spike number and grain number of wheat per spike decreased significantly, thousand grain weight and grain number per row of maize corncob were significantly reduced, and the yield of wheat and maize were reduced significantly by84%, seriously reducing the yield and quality of maize and wheat.3. According to the characteristics of soil acidification and its effects on crop growth in Jiaodong, and based on the anion and cation absorption and soil buffer theory of root regulation, we found out rhizosphere managements could effectively alleviate soil acidification. With2-years field experiments, we verified the alleviation effects of soil acidification, and put forward the regulatory pathways and strategies to slow soil acidification with rhizosphere managements. Effects of2-year field experiments on soil properties mainly showed:when controlled and reduced the application of nitrogen fertilizer, soil acidification was effectively reduced, but could not increase soil pH (this method was applicable to a lower soil acidification degree). The application of lime, alkaline NPK fertilizers (calcium nitrate+calcium magnesium phosphate+silicon calcium potassium), organic materials (manure and straw), to some extents, increased soil pH; soil pH increased by0.1-0.5units with continuous application of these meterials in2years. Application of lime, alkaline PK, alkaline NPK fertilizer, chicken manure treatment significantly reduced soil exchangeable Al by36-81%in the first year,56-86%in the second year; it also significantly decreased soil available Mn by25-62%in the first year, and35-71%in the second year. In contrast, soil exchangable calcium increased by36-56%after2years. Application of lime, alkaline PK, alkaline NPK fertilizer significantly reduced the available copper content in soil by11-22%after1year, and25-31%after2years. For consecutive2-year application of alkaline, alkaline PK fertilizers, NPK fertilizers and manure increased soil exchangeable magnesium content by50-75%.4. The effects of improvement measures for soil acidification on peanut growth were analyzed with2-year field experiments. Alkaline PK, alkaline NPK fertilizer, fowl manure and lime treatments significantly decreased the manganese content in peanut straw by39%,46%,35%and34%in2012, and47%,56%,38%and49%in2013, respectively. There was a most evident decrease in the manganese content in peanut straw in the treatment of alkaline NPK fertilizer (decreased by56%), and2-year continuous treatment effect was better than that of the first year. With two-year continuous application of the alkaline PK, alkaline NPK fertilizer, chicken manure, lime and maize straw, calcium contents in peanut straw increased, especially in the alkaline NPK treatment, which increased by36%. Alkaline PK fertilizer, Alkaline NPK fertilizer treatments after2-year continuous application significantly increased the magnesium content in peanut straw by27%and18%, respectively. However, after2-year continuous application of lime, zinc content in peanut straw significantly decreased by52%. The2-year application of chicken manure increased copper content in peanut straw by23%, Alkaline PK, Alkaline NPK, chicken manure and lime treatments reduced the manganese content in peanut seeds by28%,40%,30%and40%, respectively. Application of lime, alkaline PK, alkaline NPK, manure significantly increased the yield of peanut by8-16%in the first year and27-47%in the second years. Peanut nodule number and nodule fresh weight were also increased significantly,hInconclusion, the analysis results showed that the main remediation strategies in intensive agriculture production involve control and reduction of the application rates of nitrogen fertilizer. According to different extents of soil acidification, alkaline nitrogen can be used instead of acidic fertilizer, and thus reduce soil acidification which is induced by root absorption based on anion and cation balance. Phosphorus and potassium application can be improved toward increasing the soil exchangeable cations through choosing related fertilizer types, and the organic materials and straw return to soil can improve the buffering capacity of soil to acidification.In a word, the integration of the control strategies or pathways mentioned above could be important approaches to alleviate soil acidification in intensive farming system for maize in Jiaodong region. |
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