Study On Reducing Fertilization Of Lettuce In Acid Purple Soil With Different Fertility Levels

Fertilization is the main measure to increase production in modern agriculture.Since 1980,the chemical fertilizer application of China had increased at a rate of 3.44%per year.And it had become the country with the highest total fertilizer and unit area application.Long-term large amount of fertilizer application,unreasonable fertilizer structure and unbalanced distribution of fertilizers led to reducing the fertilizer utilization,decreasing the soil organic matter content and increasing soil acidification.Therefore,reducing the amount of chemical fertilizer application has a great research potential in improving fertilizer efficiency utilization and reducing agricultural non-point source pollution,and it is also the general trend of sustainable development of modern agriculture.As one of the vegetables widely cultivated and eaten in southern China,lettuce has a large cultivation area in Chongqing.In the past ten years,lettuce growers had increased the applications of chemical fertilizers,especially chemical nitrogen fertilizers to raise the level of agricutural income.This phenomenon was very common,and it had caused the degradation of lettuce quality,especially the increased of nitratea cumulation.At the same time,due to the excessive application of chemical fertilizers,the acidification of soil was particularly serious.In the lettuce growing areas of Chongqing,the soil area with pH less than 5.5 accounted for more than half.However,most of the research on lettuce focused on the replacement of potassium fertilizer and nitrogen fertilizer by organic fertilizer,while the research of excessive application of nitrogen fertilizer and the soil problems caused by that were rare.In this study,the effects of different amounts of soil conditioner on the yield,quality and soil properties of lettuce were studied by field experiment combined and laboratory analysis.On this basis,the effects of fertilizer reduction measures on lettuce and soil characteristics on acid soils with different fertility were studied.Through the analysis of soil conditioning potential of soil conditioner and the analysis of lettuce yield influence factors,the soil fertility limiting factor and the main yield influencing factors were found to determine the optimal reduction fertilization measures.This explained the feasibility of chemical fertilizer reduction measures on acid soil and the necessity of soil acidity improvement.The main results were as follows:?1?Fertilization treatment significantly increased the yield of lettuce,but the yield difference between the treatment with the conditioner and the conventional fertilization treatment was not significant.Different amounts of soil conditioner?high 3000 kg/hm²,medium volume 2000 kg/hm²,low 1000 kg/hm²?significantly increased the Vc content in the stem of lettuce,but the impacts of soluble sugar,nitrate,amino acid,crude protein was not significant.Compared with conventional fertilization,the application of soil conditioner had a significant effect on improving the utilization rate of fertilizer,and it also improved the ability of lettuce to absorb nutrients.The application of conditioners had no significant effect on the soil nutrient content,but it significantly increased the soil base saturation and the soil pH value.The main reason was that the application of soil conditioner significantly reduced the content of soil exchange acid,especially the exchange of aluminum contents,and it reduced the toxicity of aluminum ions to lettuce.?2?In high-fertility acid soil,the reduced fertilization measures significantly increased the yield of lettuce,and the treatment that reduced nitrogen by 15%and cooperated with organic fertilizer and conditioner?TOF1?was best.The treatment that reduced nitrogen by 30%and cooperated with organic fertilizer and conditioner?TOF2?had the most significant effect on the quality of lettuce,and TOF2treatment significantly increased the content of vitamin C,soluble sugar and amino acid in lettuce,and it also had a certain effect in reducing the nitrate contents.Compared with conventional fertilization?CF?,reduced fertilization measures significantly increased fertilizer utilization.The reduced fertilization measures could increase the soil organic matter,available phosphorus and available potassium.On the other hand,it significantly increased the salt-based ion saturation of the soil and reduced the exchange acid content.Comprehensive analysis of yield,quality,soil fertility and economic benefits,the best treatment was TOF1,followed by TOF2.?3?On the low-fertility strong acid soil,the reduced fertilization measures could significantly increase the yield of lettuce,and the TOF2 yield was the best.In addition,it also significantly improved the quality of lettuce,which was specifically increased in vitamin C,soluble sugar and amino acid content.Compared with conventional fertilization,reduced fertilization measures could significantly improve fertilizer utilization.In addition,the reduced fertilization measures could increase the soil organic matter,available phosphorus,and available potassium,and it also significantly increased the soil base ion saturation and reduced the exchange acid content.?4?The application of organic fertilizer and conditioner had better acid-regulating effect on acid soil,and it significantly increased soil pH,soil acid neutralization capacity?ANC?.It could be seen from the soil acid titration curves of the three study areas that when the soil pH droped to about 3.5,there was a buffer mechanism in the soil,and the obvious degree of the buffer mechanism was significantly correlated with the original pH of the soil.The results of correlation analysis showed that the yield of lettuce was positively correlated with salt saturation and exchangeable calcium,and it was negatively correlated with organic matter and exchangeable aluminum.Path analysis showed that the exchange calcium and available phosphorus had the greatest impact on the yield of lettuce,and both of them had positive effects on lettuce yield,and it indicated that the lettuce soil should pay attention to the improvement of exchangeable calcium and effective phosphorus.Stepwise regression analysis constructed a stepwise regression equation of yield and exchange calcium,available phosphorus:y=2686.883X_ECa+238.57X_AP-6802.85,this regression equation indicated that the yield of lettuce could be initially predicted by measuring the content of exchangeable calcium and available phosphorus in the soil.