Research On The Optimum Ratio Of Organic Fertilizer Replacing Chemical Fertilizer Nitrogen And Its Effect

In order to find out the effect of substituting organic fertilizer-N for partial chemical fertilizer-N on rice planting and its effect,In this trial,field experiment combined with indoor analysis method was used to select the optimal replacement ratio of organic fertilizer-N to replace fertilizer nitrogen-N,and then explore the effect of organic fertilizer-N on the optimal ratio of fertilizer nitrogen-N.The effects of pig manure compost substituting 10%,20%,30%,40% and 50% of chemical fertilizer-N on rice yield,nitrogen utilization efficiency and nitrogen level in surface water was studied to determine the optimal replacement ratio.By studying the effects of pig manure(PM),pig manure compost(PMC),Chinese milk vetch(CMV)and rice straw(RS)returning(which CMV and RS returning occurred in early and late rice period,respectively)on rice yield,nitrogen use efficiency and soil microorganism to find out its effect.The results of the work were as follows:(1)Relative to chemical fertilizer-N application treatment(CU),a 20% substitution ratio of organic fertilizer-N significantly increased early rice yield by 13.9% and nitrogen utilization efficiency by 4.7 percentage points;a 20%～30% substitution ratio of organic fertilizer-N significantly increased late rice yield by 13.6%～18.6% and nitrogen utilization efficiency by 4.4～4.9 percentage points.The best substitution ratio was 21.0% and 21.4% respectively according to the fitting equation between the substitution ratio and the yield of early and late rice.(2)The higher the ratio of organic fertilizer-N replacing chemical fertilizer-N,the lower the concentration of total nitrogen or ammonium nitrogen in surface water.Compared with CU,a 10%～50% substitution ratio of organic fertilizer-N significantly decreased the total nitrogen concentration in surface water by 10.0%～59.2%;the ammonium nitrogen concentration in surface water decreased significantly by 14.8%～41.2% when the organic fertilizer-N substitution ratio was more than 20% after basal fertilizers application;and when the organic fertilizer substitution ratio was more than 30%,the ammonium nitrogen concentration in surface water decreased significantly by 14.3%～38.9% after tillering fertilizers application.(3)Compared with CU,PM,PMC,CMV(early rice)+ RS(late rice)treatments promoted the yield and yield components of rice.Among them,PMC had the best effect,which increased the yield of early and late rice by 19% and 21%,followed by CMV(early rice)+ RS(late rice),by 15% and 8% respectively,and PM had no effect on increasing yield,but could stabilize yield.In terms of nitrogen use efficiency,all organic-inorganic fertilization treatments could improve the nitrogen use efficiency of early and late rice,PMC was the best stemming from the agronomic utilization rate of early and late rice increased by 40.0% and 40.5%,partial productivity of nitrogen fertilizer increased by 21.1% and 22.9%,physiological utilization rate of nitrogen fertilizer increased by 12.6% to 24.9%,absorption and utilization rate of nitrogen fertilizer increased by 8.3 and 8.7 percentage points,respectively.(4)Fertilization could improve soil organic matter and total nitrogen content in paddy field.The improvement of soil organic matter in double cropping paddy field was the most obvious by Chinese milk vetch returning or rice straw returning,which showed soil organic matter content increased by 6.1%(P > 0.05)and 14.4%(P < 0.05)compared with CU after harvest of early and late rice,respectively.Pig manure compost had the best effect on soil total nitrogen content in paddy field,soil total nitrogen content increased by 15.9%(P < 0.05)and 14.3%(P < 0.05)compared with CU after harvest of early and late rice.The dynamic changes of ammonium nitrogen and nitrate nitrogen content in paddy soil decreased with the continuous growth of rice,which indicated CU had the higher decline range,while organic fertilizer-N replacement treatments had a slightly slower decline.At the later stage of rice growth,the contents of ammonium nitrogen and nitrate nitrogen in organic fertilizer-N replacement treatments were higher than those in CU treatment.(5)Organic fertilizers replacing chemical fertilizer-N was beneficial to improve soil microbial OUT,Shannon,Ace and Chao indexes.Application of organic fertilizer can improve soil bacterial diversity and abundance of double cropping rice.In addition,the dominant of bacterial species did not be changed in different fertilization treatments,but their relative abundance changed.In summary,our findings suggest that a 20% substitution ratio of pig manure fertilizer-N was the optimal N management for double-cropping rice cropping in southern China.