Effects And Evaluation Of Different New Type Of Fertilizers On Reducing Agricultural Nitrogen And Phosphorus Non-point Source Pollution

Cereal and vegetable rotation system is a common planting pattern in the Three Gorges Reservoir area.Although the high-intensity planting ensures grain yield,the excessive fertilizer application causes serious agricultural non-point source pollution.How to reduce agricultural non-point source pollution has gradually become a major topic of green and sustainable development of agriculture.Controlling the generation of pollutants and their entry into the environment from the source,reduce the nutrient loss in the process of agricultural production,optimize the nutrient absorption of crops,and then increase the yield and reduce the environmental cost by using new type of fertilizers is of great significance.In this paper,a typical small watershed in the Three Gorges Reservoir region was taken as the research object.Based on a field survey,the local planting structure and the current situation of fertilizer management were investigated.Then the environmental costs of the grain and vegetable rotation system were quantified.A scenario was conducted to discuss the possibility in reducing environmental costs by changing the amount and form of fertilizer.A soil column leaching simulation experiment was used to reveal the mechanism of different new fertilizers in preventing N leaching.Field experiments were conducted to verify the comprehensive effects in crop yield and environmental cost.The current study could contribute to the prevention and control of agricultural non-point source pollution in the Three Gorges Reservoir area from the perspective of source reduction.The main research results are as follows:（1）The current situation of fertilizer management and the quantification of environmental cost were revealed by a field survey.There were small differences in production and economic benefit between mustard-maize rotation system and mustard-rice rotation system,but there were significant differences in fertilizer application rates between maize and rice.The nitrogen,phosphorus and potassium application rates of maize were 305 kg/hm²,92.2 kg/hm² and 66.6 kg/hm² higher than that of rice,respectively.The active nitrogen loss,acidification effect and eutrophication effect of mustard-maize rotation were 147.3%,73.1%and 146.2%higher than that of mustard-rice rotation per unit yield,respectively.The greenhouse gas effect was 38.9%lower than that of mustard-rice rotation.The active nitrogen loss,acidification effect and eutrophication effect caused by mustard-maize rotation system were 44.6%,27.1%and 44.1%higher than those caused by mustard-rice rotation system,respectively,while the greenhouse gas effect caused by mustard-rice rotation system was 33.3%lower than that caused by mustard-rice rotation system.The overall environmental cost of mustard-rice rotation system is lower,but the proportion of paddy fields planted is getting smaller.Scenario analysis showed that optimization of fertilizer application rate and application of new type of fertilizers could effectively reduce the environmental cost of grain and vegetable rotation system,and realize source reduction and non-point source pollution control.（2）The effect and mechanism of different new type of fertilizers on the preventing N leaching were studied by a soil column leaching simulation.In the soil column leaching solution,the cumulative leaching loss of total nitrogen was simulated by farmers’conventional fertilization treatment（Con）>Optimized fertilization treatment（OPT-1）>Organic fertilizer to replace 50%recommended inorganic nitrogen treatment（OPT-3）>Controlled release fertilizer replaces 50%recommended inorganic nitrogen treatment（OPT-2）>Nitrification inhibitor treatment（OPT-4）>No fertilization treatment（CK）treatment.OPT-2,OPT-3 and OPT-4 treatments were 8.8%,7.7%and 16%lower than those of Opt-1,respectively.The peak value of soluble total nitrogen content was present as Con>OPT-2>OPT-4>OPT-1>CK>OPT-3.The cumulative leaching loss of total nitrogen could be significantly reduced by reducing the amount of fertilizer and changing the form of fertilizer.Meanwhile,changing the form of fertilizer could further reduce the leaching loss on the basis of reducing the amount of fertilizer application.The total nitrogen residue in soil of each optimal fertilization treatment was lower than that of Con treatment,which could effectively reduce nutrient loss.The residual amount of NH₄⁺-N in OPT-2 and OPT-3 was 41.4%and 57.5%lower than that of OPT-1,respectively.The content of NO₃^--N in CK,OPT-2 and OPT-4 treatment decreased gradually with soil depth,and the overall residual NO^-₃-N in OPT-4 treatment was 31.8%lower than that in OPT-1 treatment.（3）Field experiments were conducted in the cereal and vegetable rotation system in the hilly region of Southwest China to verify the effects of different new type of fertilizers applications..The effects of different treatments on the yield of maize and mustard,crop nutrient uptake at each growth stage and soil nutrient concentration were compared.Results showed that compared with Con treatment,the OPT treatments can ensure maize and mustard production,and had no significant influence on plant nutrient uptake.Application of new type of fertilizers can significantly reduce the nitrate nitrogen in the soil residues,prevent nitrogen migrate to deep soil and reduce the leaching loss and environmental cost.