| Rice is one of the three staple food crops,the rice seedling area exceed 0.3 billion hectares,which account for 26.7% of planting area of grain crops,and 18.2% of planting area of crops in 2016.More than half population live on rice in China,therefor,ensuring rice yield plays a major role in food security of China.Nitrogen fertilizer is one of the main nutrients for rice growth,scientific and reasonable applicate nitrogen fertilizer is important not only for maintaining rice yield,but for improving rice quality and reducing N loss as well.Currently,the exsiting problems of the nitrogen application including excessive use of nitrogen fertilizer,unreasonable nitrogen application methodwould cause a series of environmental problems.In order to improve the nitrogen utilization situation,the experiments were conducted in the agricultural environmental science observation station of yueyang agriculture department,Hunan.The effect of fertilizer types and fertilization pattern on yield of double season rice,ammonia volatilization,N runoff loss,the change of functional microbes and the difference of the functional microbes,etc.were analyzed.The objectives of this study were providing theoretical basis for increasing the yield of double season rice,enhancing nitrogen fertilizer efficiency and decreasing the nitrogen loss.The main results were as follows: 1.Six treatments were conucted to study the rice yields,N loss and N use efficiency in paddy soils,control(T1),common fertilizer(T2),slow-release fertilizer(T3),high slow-release fertilizer(110 kg N hm-2 for early rice and 120 kg N hm-2 for late rice)plus side bar application(T4),medium slow-release fertilizer(90 kg N hm-2 for early and late rice,respectively)plus side bar application(T5)and low slow-release fertilizer(70 kg N hm-2 for early and late rice,respectively)plus side bar application(T6).The results showed that combined application of slow release N fertilizer and side bar application method increased rice yield,promoted N use efficiency and reduced N loss in paddy fields.(1)Particularly for T2,yields of both early and late rice in T4 increased respectively by 13.2% and 4.7% and decreased rice planting density and applied N amount.The yields of both early and late rice under T4 treatment were respectively 7.3% and 1.7% higher than that of T3 treatment.(2)Side bar fertilization significantly reduced N loss,the surface runoff reduce by 3.5%–29.4%,compared with T2 treatment.An annual runoff amount of 0.466–0.673 kg(N)hm-2 was observed for N loss after side bar fertilization.(3)Side bar fertilization significantly increased N use efficiency.N use efficiency under T4 treatment were 1.70 and 1.22 times higher than T2 and T3 treatments,respectively.The highest N agronomic efficiency for early rice and late rice were T4 and T6,which were 20.2 kg kg-1,33.9 kg kg-1,respectively.There were no significantly difference in N physicial efficiency between different fertilizer treatments whether early rice or late rice,except the T6 in later rice.Partial factor productivity of N increased with fertilizer N decreasing.No significant difference in soil N dependent rate were observed both in early and late rice.In conclusion,high slow-release fertilizer plus side bar application was the best fertilization mode in the study area.2.A field experiment was conducted and five treatments were used in the study: control(CK),farmers' fertilization practice(FP),complexed organic-inorganic fertilizers(CT),slow-release fertilizer surface broadcast application(SR),slow-release fertilizer side depth application(SF).The results showed that the ammonia concentration in the flood water and ammonia volatilization of each day showed as FP>CT?SR>SF?CK.16 days after the fertilization,compared with other treatments,FP treatment showed the highest ammonia volatilization,NO3--N and NH4+-N runoff loss amount.The ammonia volatilization,NO3--N and NH4+-N runoff loss amount of FP treatment were 30.2,11.3 and 15.4 kg N hm-2,respectively.The ammonia volatilization,NO3--N and NH4+-N runoff loss amount of SF treatment were18.9,4.1 and 6.8 kg N hm-2,respectively,compared with FP treatment,the ammonia volatilization,NO3--N and NH4+-N runoff loss amount decreased 37.3%,64.0% and 55.7%.For FP treatment,the ammonia volatilization and runoff induced N loss account for 37.9% of the total nitrogen input,while SF treatment showed the lowest N loss proportion with 19.9%,the N loss of CT and SR treatment were 32.6% and 27.7%,respectively.In conclusion,slow-release fertilizer application could decrease the ammonia volatilization and runoff loss to some extent,while slow-release fertilizer combined with side depth application was the best application method of all the treatments.3.We assessed the relationships between soil physicochemical properties,denitrification and nitrification activities,and the underlying microbial communities in a surface layer of paddy field soil treated with different fertilization methods.Five treatments were carried out in this study,soil was unfertilized(control),treated with conventional chemical fertilizer(CF),CF plus pig manure(MC),or slow-release fertilizer(SR),or by slow-release side bar fertilization(SB).Soil was sampled after one season of early and late rice growth.We determined soil physicochemical properties,potential nitrification rates(PNR),denitrification enzyme activities(DEA),and ammonia-oxidizing archaeal(AOA),ammonia-oxidizing bacterial(AOB)and denitrifiers community composition.The results showed that fertilization significantly increased the amount of NH4+-N in the soil of SB and MC treatments,whereas MC lowered the NO3--N level.DEA was higher for MC and CF than the other treatments.The PNR in MC-treated soil was significantly lower than that in CF-treated soil.There were no significant differences in AOA and nir S copy numbers;however,nir K and nos Z copy numbers were higher for MC compared with CF.The number of AOA terminal restriction fragments(TRFs)increased significantly with N addition and reached the highest level for SB,whereas the number of AOB TRFs did not change significantly between treatments.Similarly,the number of nir K TRFs increased under fertilization,with the highest number obtained for SR;however,no significant change was observed for nir S and nos Z TRFs across different treatments,except for their relative abundance.All AOA amo A genotypes were in archaeal group 1.1b,whereas 95% AOB were in Nitrosospira cluster 3a.More than 40% of nir S OTUs were affiliated with Herbaspirillum,a key N-cycle player in this paddy soil.In conclusions,the SB and MC treatments had significant effects on soil N,DEA,and PNR levels,and affected the community of N-functional microbes.SB in combination with pig manure would contribute to the improvement of paddy soil fertility.Compared with common urea,under the same fertilization pattern,slow controlled release nitrogen fertilizer could significantly reduce the nitrogen release rate in flooded paddy fields,and effectively reduce the risk of N loss such as ammonia volatilization,N runoff and leaching,etc,For the pattern of the side bar fertilization applied the fertilizer into the rice root-zone,which was conducive to the rapid and efficient absorption and increase rice growth,as well as enhance rice yield.Furthermore,the nutrient of deep fertilizatoin could be adsorped by soil,which substantially reduced the fertilizer loss amount and improved fertilizer use effciency. In conclusion,it is of great significance in improving N use efficiency and enhancing rice yield to popularize the side bar application of slow controlled release nitrogen fertilizer in the double rice paddy fields in south China. |
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