Ammonia Volatilization And Nitrous Oxide Emission From Double Rice System In Red Paddy Soil Under Different Fertilizing Systems

A field experiment was conducted at experimental site of TaoYuan agro-ecological station,Chinese Academy of Sciences,at Hunan Province.The experimental paddy soil was developed from the Quaternary red clay after different fertilizing systems of 18 years. To study the pattern of nitrogen loss and its influence factors in double rice system,nitrous oxide emission and ammonia volatilization were investigated with static chamber and closed airflow chamber method,respectively.The mechanism of nitrogen balance and nitrogen transformation under different fertilizing systems were illustrated to provide theoretical approaches for increasing nitrogen use efficiency in paddy field.The results showed that:1.The patterns of nitrous oxide emission during the early and the late rice period varied significantly.At the early rice stage,N₂O fluxes were lower because of continued flooding,with a flux peak occasionally.While during the late rice period,N₂O fluxes were promoted by drainage and field drying,especially at later growth stage.There was no significant difference between different treatments as a result of high spatial variation.2.N₂O emission in paddy soil was influenced by water status,temperature and fertilizer application,among which water status was dominant factor.Drainage or intermitted wetting and drying could enhance N₂O emission significantly,while under continued flooding condition,N₂O flux peak was poorly observed.Temperature had no obvious effect on N₂O emission.The amendment of organic manure could increase N₂O flux since providing more nitrogen for denitrification and nitrification,however,the effect of fertilizer application on N₂O emission was regulated by water status.3.N₂O fluxes during late rice period were higher than early rice period,with accumulated fluxes of 0.06～0.46 kg·hm^-2 and 0.23～0.93 kg·hm^-2,respectively.N₂O fluxes at winter fallow stage were higher than those at rice growth stage,with accumulated fluxes of 3.25～20.56 kg·hm^-2.4.Compared with others,N₂O weighted average and accumulated fluxes in organic-inorganic fertilizing system(OM) were constantly the highest during rice growth and winter fallow period.In NP and NK treatments,N₂O fluxes were higher than in NPK treatment.At the early rice stage,N₂O weighted average and accumulated fluxes in NP treatment were the highest,reaching 10.61 ug·m^-2·h^-1 and 0.22 kg·hm^-2,respectively.The second was NK treatment;while at the late rice stage,N₂O fluxes in NK treatment were the highest,followed by NP treatment and NPK treatment.5.Ammonia volatilization under different fertilizing systems showed similar pattern, reaching peaks in 1-3 days after rice transplanting and declining subsequently,and nearly no emission after a week.The rate of ammonia loss increased with the rate of fertilizer application.During the early rice period,accumulated amount of NH₃ loss ranged from 1.6 kg·hm^-2 to 3.6 kg·hm^-2 at basal fertilizer stage and from 5.8 kg·hm^-2 to 18.2 kg·hm^-2 at tillering stage,occupied 5.0%～13.4%and 15.4%～37.4%of the rate of fertilizer application, respectively.During the late rice period,the accumulated amount of ammonia volatilization was 4.5～7.9 kg·hm^-2 at basal fertilizer stage,12.3～26.8 kg·hm^-2 at tillering stage and 1.4～2.4 kg·hm^-2 at earing stage,occupied 11.1%～19.3%,24.2%～52.8%and 14.0%～29.6% of the rate of fertilizer application,respectively.6.Compared with non-fertilizer treatment,the application of urea could increase ammonia volatilization.Under equal N application condition,NK treatment lost more N through ammonia volatilization,with 13.7 kgN·hm^-2 and 37.1 kgN·hm^-2 at the early rice stage and the late rice stage,respectively.The application of organic fertilizer had different effect on ammonia volatilization at the early rice stage and the late rice stage.During the early rice period,OM treatment had the highest emission,up to 21.1 kgN·hm^-2,and 11.6 kgN·hm^-2 and 8.0 kgN·hm^-2 in NPK and JF treatment,respectively.Supplement of rice straw and green manure didn't show positive effects on ammonia volatilization,its influence was even weaker than the effect of chemical fertilizer.During the late rice period, the total amount of NH₃ loss in OM and JF treatment were 32.8 kgN·hm^-2 and 20.6 kgN·hm^-2,higher than in NPK treatment,which might depend on decomposed level of rice straw as basal fertilizer and climate condition at rice growth stage.7.There was a positive relationship between ammonia loss and NH₄⁺-N concentration and pH in surface water.Climate condition and fertilizing method also influenced ammonia volatilization significantly.The production and emission of ammonia would be promoted under high temperature,little rainfall and bright light conditions.Deep fertilization was beneficial to absorb and fix NH₄⁺ from urea hydrolyzation,which limited ammonia volatilization by decreasing NH₄⁺ in surface water.However,surface broadcasting could promote significantly NH₄⁺-N concentration in surface water so that increase the potential of NH₃ production and emission.8.Fertilizer application could increase rice yield significantly.It is essential to apply balanced N,P and K fertilizer for high and stable yield.Both single nutrient and unbalanced nutrient resulted in low yield.Moreover,cooperated with organic fertilizer could improve rice productivity and decline year-to-year variance coefficient to adapt various climate and environment.The yields of early and late rice in OM treatment were always the highest compared to others,compare to CK,their yields increased 164.3%,45.0%,respectively. The second was JF treatment,its yields increased 126.5%,39.7%than in CK respectively, followed by NPK treatment of 111.0%,44.7%,higher than NP and NK treatment.9.N applied in the absence of P or K could decline fertilizer use efficiency,which was influenced markedly by surrounding environment.Fertilizer use efficiency would be increased under balanced fertilizer,especially supplied with organic fertilizer.Nitrogen use efficiency was the highest in NPK treatment,up to 31.8%,followed by JF treatment of 30.9%.Although grain yield in OM treatment was the highest,nitrogen use efficiency was lower than others,which might resulted from excessive fertilizer application rate.10.Long-term unfertilized or unbalanced fertilization would result in serious nutrient deficiency of paddy ecological system.The nitrogen deficient amount of NP and NK treatments were 16.4 kg·hm^-2 and 44.7 kg·hm^-2,respectively.The similar phenomenon was found in balanced fertilizer application treatment(NPK) since a higher nitrogen removement by crop harvest.Supplement of organic manure based on chemical fertilizer application could improve nitrogen balance situation of paddy ecological system,with nitrogen surplus of 70.5 kg·hm^-2 and 4.3 kg·hm^-2,respectively,in OM and JF treatment.