| In the context of the rapid development of intensive agriculture in China,the issue of the rational use of a large number of planting and breeding wastes has increasingly attracted attention in the field of agricultural ecology and environment.The reasonable return of livestock manure and straw organic materials can not only reduce fertilizer input,improve farmland ecological environment problems,but also promote the comprehensive utilization of planting and breeding waste resources.Therefore,this study is based on the location test points of the multi-year rice-wheat rotation system in the gray alluvial paddy soil of the Chengdu Plain,researched three types of fertilization combinations（different straw application rates,pig manure application rates,straw and pig manure ratios）on the effects of soil nitrogen change characteristics,microorganisms related to nitrogen conversion,and nitrogen conversion intensity.Preliminarily explored the mechanism of directional regulation of soil nitrogen activation and transformation process by the application of planting waste materials.It provides a scientific basis for the replacement of some inorganic fertilizers by planting and breeding wastes in the rice-wheat production system area of Chengdu Plain.The main findings are as follows:（1）Compared with conventional chemical fertilizer（U）treatment,50%pig manure combined with chemical fertilizer（50%M）,single application of 100%（100%M）,200%（200%M）pig manure treatment and conventional fertilizer with half-amount of straw（U1/2S）treatment,both can significantly increase the total nitrogen and alkaline nitrogen content of rice（wheat）in the middle and late stages（Booting stage and mature stage）,which are increased by 26.08%～55.55%（6.17%～13.11%）and 5.29%～11.18%（14.37%～34.15%）,respectively,compared with U treatment.The increase in total nitrogen is greater in the rice season,and the most obvious increase in alkaline nitrogen content is in the wheat season,which provided a sufficient nitrogen supply for the growth of rice and wheat.For soil inorganic nitrogen form transformation,50%M treatment reduced the soil ammonium nitrogen content of rice（wheat）tillering stage by 37.8%（32.78%）and nitrate nitrogen content by 2.38%（30.37%）compared with U treatment.It reduced the accumulation of ineffective nitrogen in the early stage of rice and wheat growth.The200%M treatment had a higher soil inorganic nitrogen content in the middle and later stages of the rice-wheat season,significantly increased by 40.94%～322.22%（ammonium nitrogen）and 0.87%～69.1%（nitrate nitrogen）than the 50%M treatment.The supply of inorganic nitrogen will not be conducive to the transfer of nitrogen to the grain,resulting in the accumulation of ineffective dry matter at stems and leaves of wheat and rice,and leading to overgrowth and inadequate maturity.（2）Compared with U treatment,conventional fertilizer combined with total straw（US）treatment reduced the number of soil ammonifying bacteria and nitrifying bacteria in the middle and late stages of rice and wheat.Among them,the number of soil ammoniating bacteria in rice and wheat at the heading stage decreased significantly by 29.59%and42.91%（p<0.05）.In the treatment of different amounts of pig manure returned to the field,the treatment of 200%M increased the amount of soil nitrifying bacteria（an increase of36.87%～46.59%）and the amount of denitrifying bacteria in the mature period of rice season compared with 25%～50%pig manure combined with chemical fertilizer treatment（the increase is 183.30%～193.61%）.The effect of different straw application rates（U1/2S,US）on the number of soil aerobic azotobacteria bacteria in the middle and late stages of rice and wheat is significant,and the closer to the maturity period,the advantage of U1/2S treatment is more obvious,of which the wheat season is significantly increased by170.25%compared with U treatment（p<0.05）,the rice season increased by 11.78%（p<0.05）.（3）From the perspective of nitrogen conversion intensity,the intensity of soil ammonification of the U treatment rice and wheat tillering stage was higher than that of different straw use treatments.The increases in the rice and wheat seasons were 15.28%～22.44%and 9.43%～15.29%,respectively,which may increase the nitrification reactant concentration;However,the intensity of soil denitrification of 200%M and 100%pig manure combined with straw（M3S）treatment in the later stage of rice and wheat growth was significantly higher than that in U treatment,with increases of 7.04%,5.19%（rice season）and 95.68%,97.10%（Wheat season）,respectively.synchronized with the changes in soil nitrification and denitrification bacteria in the same period,this not only led to an increase in dry matter accumulation in the aboveground part of rice and wheat during the late growth period,resulting in overgrowth and late-ripening of crops,but also increased the risk of nitrogen in the soil of rice and wheat entering the atmospheric environment in a gaseous form during the later growth period.（4）Among the treatments with different application rates of straw,the rice yield of the US treatment was the best,reaching 6764.40 kg·ha-1,while the wheat yield was the best with U1/2S treatment,which was a significant increase of 30.78%compared with the US treatment.In the groups with different application rates of pig manure,the application of 50%M and 100%M treatments significantly increased the dry matter accumulation of wheat shoots in the jointing-mature stage,of which the highest increase was at 100%M treatment in the mature stage,however,its output was significantly reduced by 11.37%compared with 50%M treatment（p<0.05）.In the different ratios of straw and pig manure,M3S treatment is easier for rice to build good dry matter accumulation characteristics and increase rice yield.In the wheat season,50%pig manure combined with straw（UM2S）treatment is more effective in increasing yield and yield.In summary,conventional chemical fertilizers combined with half-quantity straw,50%pig manure combined with chemical fertilizers,and 50%pig manure combined with straw treatment can adjust the soil inorganic nitrogen content under rice-wheat rotation conditions reasonably,promoted the nitrogen supply better meet the nitrogen nutrient requirements of rice and wheat at each growth stage,but the application of 200%pig manure and 100%pig manure combined with straw treatment significantly increased the intensity of soil denitrification of the rice-wheat rotation system in the middle and late periods,increased the environmental risk of soil nitrogen loss,and at the same time leads to an increase in the accumulation of ineffective dry matter in rice and wheat,which leads to overgrowth and late-ripening and ultimately affect crop yields. |
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