| The trend of soil acidification is becoming more and more serious,which reducing crop yield and has seriously affected the sustainable development of agriculture in rice-oilseed rape rotation area of southern of China.In this study,we selected paddy soil with a pH of 4.5 in jinxian county,jiangxi province,and the pH gradient of the soil was set?pH 4.5,5.0,5.6,6.3,6.8,7.3?.The field positioning experiment of rice-rape rotation system in 2015-2018.The soil and plant samples from 2016 to 2018 as research objects,the relationship between soil acidity and soil chemical properties,microbial indicators and yield was analyzed.Exploring the optimum p H and acid damage threshold of rice and rape in rice oil rotation area.The reasons of crop loss and low utilization of nutrients caused by soil acidification were explained from the aspects of soil chemical property,nutrient and microbial property,which provided theoretical basis for the improvement of acidified soil in paddy field.The main research results are as follows:?1?With the amounts of lime and soil pH increase,the agronomic characters of oilseed rape and rice increased significantly.The quadratic linear simulation of oilseed rape yield and soil p H showed that the optimum p H for rape growth was 6.4?equivalent to the amount of 6145kg·hm-2 lime?.Compared with the maximum yield,when the oilseed rape yield decreased by 50%was p H4.7,so pH4.7was determined as the acid damage threshold of oilseed rape.By the same method,the optimum value of rice growth pH6.8?equivalent to the amount of 7474 kg·hm-2lime?and the acid damage threshold was pH4.2.With the soil pH increase,the nutrient uptake of rape and rice increased first and then decreased.The nutrient uptake of oilseed rape and rice reached the highest at pH 6.3 and 6.8 respectively.?2?With the amounts of lime and soil pH increase,the content of mineral nitrogen in oilseed rape and rice seasons increased first and then decreased;the content and saturation of exchangeable cation increased significantly,and exchangeable cation mainly consisted of exchangeable calcium;the content of organic matter increased,but the difference between treatments was not significant;the contents of available phosphorus and available potassium in soil decreased significantly;the total amount of exchangeable acid,the content of exchangeable H+and the content of exchangeable AL3+in soil decreased significantly,exchangeable AL3+is the main body of exchangeable acid in soil;soil pH is significantly negatively correlated with AOA abundance and positively correlated with AOB abundance.The abundance of AOB was positively correlated with the content of mineral nitrogen.?3?The correlation analysis of soil chemical properties and ammonia-oxidizing bacteria shows that there is a good correlation.Principal component factor?PCA?analysis was carried out on the indicators related to crop yield and nutrient utilization.The indexes of oilseed rape season were divided into three categories and rice season into four categories.The correlation between crop yield,nutrient uptake and principal component factor scores was analyzed,and the results showed that the yield and nutrient uptake of rapeseed were positively correlated with the first principal component and the second principal component.In the first principal component,pH,exchangeable acid,CEC and mineral nitrogen content contribute the most to the yield and nutrient uptake of rape,followed by AOB abundance and organic matter content of the second principal component.Rice yield was only positively correlated with the first principal component,and soil pH,exchangeable acid,CEC,mineral nitrogen and AOB in the first principal component contributed significantly to rice yield and nutrient uptake.In this study,high content of exchangeable acid,low salt-base ion and low AOB abundance involved in nitrogen conversion are the main factors that lead to crop loss and low nutrient utilization in highly acidic soil.The optimal amount of lime applied to the acid soil in the rice-oilseed rape rotation system area?pH 4.5?was about 6,500 kg·hm-2,and the goal of soil improvement was about pH 6.5.Therefore,reasonable application of lime to adjust soil pH and improve soil acidity environment can obtain stable and high yield of crops in rice-oilseed rape rotation system areas in south China. |
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