Response Of Crop Yield To Acidification And PH Threshold In Red Soil Region

The unreasonable fertilization and agricultural managements led to soil acidification,associates with the loss of the macro-element and the increase of exchangeable aluminum and heavy metals.It limits the growth of crops,restricts the sustainable development of agriculture.In this study,the responses of maize and wheat biomass to the acidification of two parental red soils(Quaternary red soils and red sandstones)were studied by pot experiment in Qiyang,Hunan province.At the same time,the domestic and foreign literatures were collected to analyze the response trend of four crop yields(rice,maize,wheat and soybean)to soil acidification and the threshold of acid damage and the effect of the change of element concentration on crop yield during soil acidification.By analyzing the effect of lime on crop yield,the scientific and rational application technology of lime to improve acid soil was discussed.The main findings are as follows:The results of the pot experiments showed that the thresholds of acid resistance were respectively 5.24 and 5.56 when cultivated maize in the red soil of Quaternary red soil and red sandstone,and were 5.87 and 5.12 when cultivated wheat.The results of literature data indicated that the responses of maize,rice,wheat and soybean to soil acidification were in accordance with the trend of S-curve.The threshold of acidity damage was as follows: wheat(5.5)> soybean(5.4)> maize(5.1)> Rice(4.7).The results of pot experiments and literature review are basically consistent.It revealed that the sensitivity of different crops to soil pH was different,and the sensitivity of the same kind of crops to different soil pH was also different.Soil organic matter showed curvilinear correlation with pH value.When pH was6.22,the organic matter content is the highest and is also favorable for the growth of crops.Soil available nitrogen,available potassium and exchangeable calcium were significantly and positively correlated with pH value.When the concentration was respectively 4-12 cmol/kg,100 mg/kg and 150 mg/kg,the crop growth was better.There was no significant relationship between soil available P and pH value.Soilexchangeable aluminum was negatively correlated with pH value.When the content of exchangeable aluminum was more than 1.7 cmol/kg,the crop yield began to decrease.It is the main cause of crop yield reduction that the decrease of soil pH is accompanied by the decrease of nutrient elements such as available nitrogen,available potassium,exchangeable calcium and exchangeable aluminum and the increase of the concentration of toxic elements such as exchangeable aluminum.Application of lime can improve the acid soil,increase crop yield,especially for vegetables and corn.When the initial pH value was 3.1 ~ 6.6,the rate of crop yield increase showed the trend that was rising first and then decreasing by the increase of the initial pH value.When the initial soil pH was 4.3,the yield increasing effect was the best.When soil initial pH was between 5.8~6.6,there was no increase for crop yield.Therefore,the target pH value was 5.8 for acid soil improvement.In the range of pH value(pH,4.5-5.5)of acid soil,the dosage of lime is best at 3000-6000 kg per ha for the promotion of crop yield,and the yield increasing effect of slaked lime is better than that of lime and limestone powder.