Differences Of Fertilizer Application Between China And US And Effects Evaluation Of Organic Substitution

Paddy-upland rotation system is an important grain production system in China.The stable and increased rice yield plays a vital role in ensuring national food security.Fertilizer has made great contribution to food security in China,but the blind and excessive application of chemical fertilizer has also brought a series of ecological and environmental problems.The technology of partial substitution of chemical fertilizers with organic fertilizers has become a key technology vigorously promoted by the Ministry of Agriculture and Rural Affairs because it can reduce the application amount of chemical fertilizers and enrich the soil on the premise of not reducing crop production.Therefore,it is of great significance to understand the current situation of chemical fertilizer application in China,clarify the gap between China and developed countries（the United States）,and clarify the effect of organic fertilizer application on rice yield and soil quality.Firstly,based on published literature and data,this study systematically analyzed the differences between China and the United States in terms of fertilizer application amount and fertilizer utilization efficiency over the past 40years.Secondly,meta-analysis was used to quantitatively analyze the effects of organic fertilizer types,application strategies and application years on rice and wheat yield and soil quality and their responses to different soil conditions.Finally,based on the location test,the effects of organic substitution on paddy soil quality in rice-tanker system and rice-wheat rotation system were comprehensively evaluated by soil quality index method.Comparison of chemical fertilizer application between China and the US shows that,since the reform and opening up,chemical fertilizer application per unit area of cultivated land in China has increased rapidly,reaching the peak value in 2015(446kg hm^-2),an increase of 406%compared with 1978,which is nearly twice of the internationally recognized upper limit of chemical fertilizer application.However,the amount of chemical fertilizer applied per unit area of cultivated land in the US showed a trend of slow increase,reaching 142 kg hm^-2 in 2012,only 38%more than in 1978.The fertilizer application intensity of wheat,maize and rice in China is 1.92,1.04 and 0.97 times of that in the US,respectively,but the fertilizer yield in China is only 84.2%,57.3%and 82.5%of that in the US.The main reasons for the large amount and low efficiency of chemical fertilizer application in China are the late start of the policy and the incomplete system,the low level of fertilization technology,especially the weak application of new agricultural technology.Meta-analysis results of organic fertilizer application on crop yield and soil quality showed that organic fertilizer application had similar effect on rice and wheat yield increase（about 3%）,but the improvement of soil quality was more obvious.Compared with chemical fertilizer application alone,organic fertilizer application significantly decreased soil bulk density（5.68%）,and significantly increased SOM,TN,TP,AN,AP,AK,MBC and MBN contents in the range of 11%-38%,but had no significant effect on soil p H.Among different types of organic fertilizers,biochar and common organic fertilizers（livestock manure,compost,biogas slurry and commercial organic fertilizer,etc.）had better effect on soil quality improvement than straw.The effect of organic fertilizer combined with chemical fertilizer on crop yield was better than that of single application of organic fertilizer,but the effect of soil quality improvement was not as good as that of single application of organic fertilizer.The effect of increasing crop yield and improving soil quality was gradually enhanced with the increase of organic fertilizer application years.Organic fertilizer application had the most significant effect on crop yield under acidic soil conditions.Soil bulk density,total nitrogen,available phosphorus,available potassium and microbial biomass nitrogen were significantly correlated with annual rice and wheat yield（P<0.05）.Organic alternative for Paddy-upland rotation soil quality positioning test results show that the minimum data set of the effects of the substitution ratio of different organic and inorganic fertilization on soil quality of rice-rape rotation system was P cycle enzymes,available P and microbial biomass nitrogen and organic matter.The soil quality of different treatments showed that 40%chemical replaced by organic fertilizer was significantly better than 20%chemical fertilizer replaced by organic fertilizer and it was significantly better than that of single chemical fertilizer.The minimum data set of the effects of different organic fertilizers on soil quality of rice-wheat rotation system was bulk density,total nitrogen,available phosphorus and microbial biomass carbon.The soil quality of different treatments showed that there was no significant difference between 40%chemical fertilizer replaced by commercial organic fertilizer and 40%chemical fertilizer replaced by vermicomposting organic fertilizer,and it was significantly better than that of single chemical fertilizer.