Differences In Nitrogen Use Of Rice And Environmental Effects Under The Application Of Nitrapyrin And Biochar In The Paddy Fields

Rice is the main crop planted in taihu lake basin.In order to pursue high yield,farmers often apply a large amount of chemical fertilizers.However,excessive nitrogen fertilizer not only reduces the nitrogen use efficiency(NUE),but also leads to increase nitrogen loss and a series of environmental problems.Therefore,it is urgent to improve the NUE and reduce the nitrogen loss in paddy fields.Nitrification inhibitor and biochar are commonly used as soil synergists.Nitrapyrin(CP)can inhibit the conversion from ammonium nitrogen to nitrate nitrogen,so that nitrogen applied into the soil can exist in the form of NH4+-N for a long time for rice absorption.However,excessive ammonium nitrogen increases the risk of nitrogen loss.And biochar is a new way of biomass resources use,because it is a substance containing carbon that formed by pyrolysis of biomass at high temperatures with no oxygen,thus it keeps the pore structure of biomass,and has stable physical and chemical properties such as a larger specific surface area,strong adsorption ability and good adsorption effect on nitrogen compounds.In order to clarify the difference in nitrogen use of rice and environmental effect under the addition of nitrapyrin(CP)and biochar in paddy fields,a pot experiment with chemical fertilizer application(CN)as control was conducted to study the effects of biochar(B),nitrapyrin(CP)and the compound application(BCP)on rice yield,difference of nitrogen use in different stages,ammonia volatilization loss and greenhouse gas emission(CH4,N2O).The research can provide theoretical basis for efficient and green rice production.The main results are as follows:(1)Effects of nitrapyrin(CP)and biochar addition on rice yieldsThe addition of nitrapyrin and biochar had no significant effect on rice yields,but the addition of nitrapyrin had a tendency to increase rice yield.The rice yield under biochar addition treatment was lower than that under CN treatment in 2017,and comparable to that under CN treatment in 2018.In addition,compared with single addition treatment(B and CP),the yield of nitrapyrin combined with biochar treatment(BCP)was lower in 2017 and comparable to that of B treatment,but higher in 2018 and comparable to that of CP treatment.The results of path analysis showed that spike number and grain number per spike were the key factors to determine yield.In addition,the path coefficient of 1000-grain weight in 2018 is also high,which is the common factor determining the yield.Compared with CN treatment,CP mainly increasing grain number per spike(2017,2018)and 1000-grain weight(2018)to increase rice yield.The lower spike number and grain number per spike were the main reasons that the yield of B treatment was lower than that of CN treatment in 2017.Although the number of spikes of B treatment is still lower than that of CN treatment in 2018,the number of grains per spike and 1000-grain weight are both higher,so the yield is equivalent to that of CN treatment in 2018.The results also showed that the lower spike number and grain number per spike were the reason that the yield of BCP treatment was lower than that of CP treatment in 2017.Compared with that of 2017,the number of spikes,grain number per spike and 1000-grain weight of BCP treatment were similar to that of CP treatment in 2018,so the yield was higher.(2)Effects of nitrapyrin(CP)and biochar addition on nitrogen uptake and distribution of riceIsotopic tracer results based on 15N showed that the NUE of panicle N fertilizer was the highest,followed by tiller fertilizer,and the basal fertilizer was the lowest.The nitrogen absorption and utilization results showed that the only application of nitrapyrin(CP),the only application of biochar(B)and combined application of the two synergists(BCP)increased the nitrogen absorption from soil by 32%,2%and 14%,respectively,compared with CN treatment.In addition,CP raised nitrogen uptake from fertilizer in the basal fertilization stage,the tillering stage and the panicle fertilization stage,so the three phases of grain nitrogen use efficiency increased significantly,and its recovery efficiency(RE)increased by about 9%.The addition of biochar treatment(B)significantly reduced the nitrogen absorption from fertilizer during the tillering stage,thereby reducing the nitrogen content and nitrogen absorption of plants,and showed a trend of reducing its recovery efficiency(RE),which was reduced by 12%in 2017 and 17%in 2018,respectively.Compared with CN treatment,the plant nitrogen uptake from soil and fertilizer nitrogen utilization in basal fertilizer and tillering stages and transport capacity(grain nitrogen utilization efficiency and nitrogen harvest index)of BCP treatment are higher,but as a result of fertilizer nitrogen utilization efficiency of panicle fertilizer stage is low,therefore,its recovery efficiency(RE)was the same as CN treatment.The compound addition of nitrapyrin and biochar had no obvious interaction effect on nitrogen uptake and utilization in rice.(3)Effects of nitrapyrin(CP)and biochar addition on ammonia volatilization emissions in paddy fieldsTwo synergists significantly increased the ammonia volatilization from paddy fields,accounting for 25%-35%of the N rate.And the ammonia volatilization in fertilizer periods accounted 86%-91%of the total loss,which is the main period of ammonia volatilization.Compared with CN treatment,CP treatment obviously increased the NH4+-N concentration of the flood water and ammonia volatilization loss,which increased by 59.18%and mainly occurred during a week after the basal fertilizer stage(138%),and spike fertilizer stage(48%),and non-fertilization stage(78%).There was a promoting effect of biochar on ammonia volatilization with typical phased characteristic.The increasing effect of biochar on ammonia volatilization in the early stage is higher than that in the later stage,when the NH4+-N concentration and pH in flood water also showed the same trend.In addition,the coupling of nitrification inhibitor and biochar significantly increased the total ammonia volatilization loss due to the promotion effect of CP and B.(4)Effects of nitrapyrin(CP)and biochar application on greenhouse gas emissions from paddy fieldsCH4 emissions was the main greenhouse gas emissions in the paddy field,in this study,the CH4 and N2O emissions in the rice season are 9.85～15.53 g·m-2 and 0.02～0.07 g·m-2,respectively.The peak of CH4 emissions was 10-40d after transplanting.It all showed a small peak of the N2O emissions after every time of fertilization and drainage in the rice field.Compared with the peak emission flux of CH4 between treatments,the peak emissionflux of CP or B treatment was the same as that of CN treatment(about 15 mg·m-2·h-1),and the peak emission flux of BCP treatment was significantly higher than that of other treatments.The peak emission flux of N2O in the whole growth period of CN and B treatment all appeared on the 19th day after transplanting(the 5th day in tillering stage),while that of nitrapyrin addition treatment(CP and BCP)appeared on the 5th day and the 2nd day in basal fertilizer stage,respectively.Compared with the CN treatment,the B treatment had no obvious effect on the emissions of CH4 and N2O in paddy fields,which were 9.74 g.m-2 and 0.03 g·m-2.respectively,and had no significant influence on GWP and GHGI.CP treatment had a tendency of increasing the cumulative emission of N2O compared with the CN treatment,but the difference was not significant.Moreover,the greenhouse gas emission in the rice field was mainly CH4,so there was no significant influence on GWP.In addition,CP treatment had the advantage of increasing production to a certain extent,so it tended to reduce GHGI.Nitrapyrin and biochar coupling addition significantly increased CH4 and N2O emissions in the rice field,and the cumulative emissions increased by 58%and 2 times,respectively,compared with that of CN treatment.Therefore,the BCP treatment has a tendency to increase GWP and GHGI.The results showed that only application of nitrapyrin or biochar had no significant effect on the greenhouse gas emission in the paddy field,but the combined application of the two soil synergists significantly increased the greenhouse gas emissions.The above results showed that the addition of nitrapyrin was beneficial to increase rice yield and nitrogen absorption and transport capacity,and had no significant effect on greenhouse gas emissions,but increased ammonia volatilization loss in the paddy field.The addition of biochar had a trend of decreasing nitrogen utilization rate,had no significant effect on greenhouse gas emission,and increased ammonia volatilization loss in paddy fields.The addition of biochar could not solve the problem of increasing ammonia volatilization emissions caused by the addition of nitrapyrin,and the combination of the two showed a trend of increasing greenhouse gas emissions from paddy fields.