Effects Of Organic Fertilizer,Biological Agent And Chemical Nitrogen Fertilizer On Yield And Grain Quality Of Rice And Its Mechanism

Rice is one of the most important food crops in the world.More than 65%of the Chinese population depend on rice as their main food source.In the practical production process,excessive chemical nitrogen fertilizer input will lead to rice yield reduction,nitrogen efficiency reduction,soil fertility reduction and environmental pollution.Reasonable application of organic fertilizer plays an important role in improving nitrogen utilization efficiency,soil productivity and soil fertility.At present,there are few studies on the effects of different proportions of organic fertilizer and chemical nitrogen fertilizer on rice yield,crop population quality,rice quality and soil properties.Therefore,Nanjing 9108 and Huaidao 5,which have a wide planting area in Jiangsu Province,were selected as test varieties in this study.The treatment with no nitrogen fertilizer and the treatment with organic fertilizer accounted for 0%,20%,40%and 60%of the total nitrogen application,respectively.By measuring agronomic traits,crop population quality,nitrogen absorption,rice quality and soil physicochemical properties of rice,the optimal combination ratio of organic fertilizer and chemical nitrogen fertilizer under mechanical interpolation conditions was investigated.In addition,under the optimal ratio of organic fertilizer and chemical nitrogen fertilizer,microbial agents including Bacillus subtilis and Trichoderma harzianum were applied respectively,in order to clarify the effects and mechanism of biological agents on rice yield,grain quality and soil physicochemical properties under high yield conditions,and to provide theoretical and practical basis for scientific and reasonable fertilization mode and high yield,high N use efficiency and high grain quality of rice.The main research results are as follows:1.The yields of Nanjing 9108 and Huaidao 5 reached the maximum under the treatment of organic fertilizer accounting for 20%of the total nitrogen application rate,and the treatment of organic fertilizer accounting for 40%of the total nitrogen application rate was also higher than that under the treatment of chemical nitrogen application alone(conventional control),but the high proportion of organic fertilizer would reduce the rice yield to some extent.With the increase of the proportion of organic fertilizer,the panicle number per unit area of Nanjing 9108 and Huaidao 5 showed a downward trend,the grain number per panicle and total spikelets showed a trend of first increase and then decrease,and the seed setting rate showed a trend of continuous increase.Through the quadratic fitting curve of the effects of different proportions of organic fertilizer and chemical nitrogen fertilizer on rice yield,it can be concluded that Nanjing 9108 and Huaidao 5 had the highest yield when the proportions of organic fertilizer and chemical nitrogen fertilizer were 26.7%and 26.5%,respectively.Under the optimal ratio of organic fertilizer and chemical nitrogen fertilizer application,increased application of biological agents could further increase rice yield by increasing panicle number per unit area and total spikelet amount,and effectively increase rice leaf area index and aboveground dry matter accumulation.2.Compared with chemical N application alone(conventional control),organic fertilizer combined with chemical N application could significantly improve the above-ground N accumulation and N use efficiency of rice,and the improvement was most significant when organic fertilizer accounted for 20%of total N application.The agronomic use efficiency,absorption use efficiency,physiological use efficiency and partial productivity of the two tested varieties were increased by 1 1.27%-16.61%,13.01%-16.29%,0.29%-1.54%and 4.926.90%,respectively,when organic fertilizer accounted for 20%of total nitrogen application compared with chemical nitrogen application alone.Under the condition of increased application of biological agent,the aboveground nitrogen accumulation under the treatment of no biological agent was significantly lower than that under the treatment of Bacillus subtilis and Trichoderma harzianum from the panicle differentiation stage,while the increased treatment of Bacillus subtilis was higher than that under the treatment of Trichoderma Harzianum at each growth stage of rice,but the difference was not significant.In addition,the activities of nitrate reductase,glutamine synthetase and glutamate synthetase in rice leaves were increased under the treatment of additional bioagent compared with that without bioagent.With the increase of the proportion of organic fertilizer to the total nitrogen application,the percentage of brown rice,milled rice and head rice increased first and then decreased,achieving the best when organic fertilizer accounted for 20%of the total nitrogen application,while the percentage of chalkiness and the degree of chalkiness increased gradually.3.The results indicated that the reasonable proportion of organic fertilizer to total nitrogen application was beneficial to the improvement of rice processing quality,but with further increase of the proportion of organic fertilizer to total nitrogen application,the appearance quality would gradually deteriorate.In summary,the rice processing quality,appearance quality,and cooking and taste quality reached a relatively high level when the proportion of organic fertilizer was 40%.The brown rice percentage,milled rice percentage and milled rice percentage of the rice with biological agent application were increased compared with that with no application of biological agent.The chalkiness grain percentage and chalkiness degree of the rice were decreased,and the processing quality and appearance quality were improved,and the gum consistency and protein content of rice were increased,while amylose content was decreased by biological agents application.The peak viscosity,and breakdown value of rice flour were also improved compared with the treatment without inoculant.Trichoderma harzinum was superior to Bacillus subtilis,and the cooking quality was improved.4.With the increase of the proportion of organic fertilizer in total nitrogen application,soil nitrogen content showed a trend of first increasing and then decreasing,and reached the maximum value under the treatment of organic fertilizer accounting for 20%of total nitrogen application.However,when organic fertilizer accounted for 60%of total nitrogen application,soil total nitrogen content was lower than that under conventional nitrogen application.It can be seen that rational application of organic fertilizer is conducive to the improvement of soil total nitrogen content,but excessive proportion of organic fertilizer will reduce soil total nitrogen content.In the second experiment,compared with the treatment without bacterial agent,the two treatments with application of biological agent significantly increased the contents of soil total nitrogen and soil organic matter,and significantly increased the activities of soil urease,sucrose and catalase.According to the results of this experiment,the treatment with increased application of Bacillus subtilis had a better performance in improving soil fertility.