Effects Of Straw Incorporation And Domestic Sewage Irrigation On The Rice Yield Formation And Its Environmental Effects

Sewage is one of the important sources of agricultural nonpoint source pollution.TN concentration in the tail water after treatment is still as high as 15-20 mg·L-1,much higher than the Class V standard(TN=2 mg·L-1 of surface water.It can cause eutrophication when discharged into water bodies,but the nitrogen(N),phosphorus(P)and organic carbon is essential nutrient for agricultural crops.Also,the tail water contain some microorganisms which can degrade organic matter efficiently,if it was reused in the paddy field with straw return,it may stimulate the soil microorganism and influence the decomposition of straw and the nitrogen transformation.Soil column experiments were established at the experimental farm of the Jiangsu Academy of Agricultural Sciences,Nanjing City,Jiangsu Province,in the Taihu region of China in 2015 and 2016 to elucidate the mechanism of wheat straw returning and domestic sewage irrigation on rice yield formation and environmental effects,whether it could improve the yield and reduce C and N emissions of paddy fields to the environment while purify the water body simultaneously.In total,six treatments:straw returning + domestic sewage irrigation(SWN1),straw returning + tap water irrigation(STN1),straw returning + tap water irrigation + Zero-N treatment(STNO),sewage irrigation(WN1),tap water irrigation(TN1),and tap water irrigation + Zero-N treatment(TN0),were prepared.Each treatment was replicated three times.The aim is to focus on observing the straw decomposing process and the nutrients release dynamics,rice yield and nitrogen uptake,and environmental discharge of paddy field.The results can provide basis for the applying fertilizer rational and nutrient recycling,thus promote the win-win for food production and environmental protection.The results of the field experiment showed as follows:(1)The straw decomposing process and the nutrients release dynamicsThe decomposition and nutrient release characteristics of returned wheat straw were studied by using nylon mesh bag method and Fourier transform infrared(FTIR)spectroscopy under tap water irrigation and domestic sewage irrigation from paddy fields in 2015,respectively.The results showed that the decomposition and nutrient release rate of returned wheat straw increased over time under two different irrigation types,which was fast inthe early stage and then slowed down gradually;At harvest the decomposition rate of wheat straw were 74.1-80.7%,and the release rate of nitrogen,phosphorus and potassium can be up to 78.7-84.3%,29.5-44.8%,and 95.5-97.5%,respectively;Sewage irrigation promotes decomposition ratio of returned wheat straw and the release of nitrogen,phosphorus and potassium in the straw,no significant difference was observed in the decomposition ratio,while significant differences were observed in total nitrogen release rate at the initial growth stage,in total phosphorus release rate from tillering to heading,in total potassium release rate at the heading and maturity stage between two irrigation water types,respectively;The FTIR spectra of residual wheat straw was similar between two different irrigation types,indicated that functional groups of wheat straw did not differ between all of the treatments,while FTIR absorption peaks and intensities were different at 1030,1630,2920,and 3330 cm-1 indicating the differences in content of amide compounds and silicon stable matters.(2)Rice yield and nitrogen uptake and utilizationThe results showed that,compared with no fertilization,all the fertilizer treatments enhanced significantly rice grain yields,the yield increased by 9.3-20.5%,there was no obvious difference in different fertilization treatments.The grain yields did not decrease under N application amounts with a reduction by 45.2%compared with conventional fertilization under tap water irrigation,nitrogen uptake and use efficiency showed no significant difference between all of the treatments.All those results showed that the treatment of straw returning combined with domestic sewage irrigation would be an appropriate fertilization and scientific application methods that could reduce chemical N applied,ensure high yield of rice,and effectively ensure the utilization rate of N fertilizer.(3)Ammonia emissions from paddy fieldsA soil column experiment was conducted to study the effect of straw returning and domestic sewage irrigation on the dynamic of NH4+-N concentration and pH in the flood water,and ammonia volatilization of paddy fields in 2015 and 2016.The results showed that the NH4+-N concentration in flood water were significantly increased by wheat straw returning while significantly decreased by domestic sewage irrigation.The cumulative ammonia volatilization in the whole rice season under tap water irrigation and straw removal treatment was 58.3?60.3 kg·hm-2,accounting for 24.3?25.1%of the total N applied.The N loss ratio of ammonia volatilization was significantly increased to 42.2?45.7%by wheat straw returning,while significantly decreased to 17.3?19.9%under straw removal and 30.7?32.7%under straw returning by domestic sewage irrigation.Significant positive interaction was observed between straw incorporation and domestic sewage irrigation on ammonia volatilization loss.The average N loss from ammonia volatilization during the tillering stage was the highest among the three fertilization stages,accounting for 7.4?24.4%?7.5?19.9%of the total N applied in 2015 and 2016,respectively.In addition,ammonia volatilization fluxes showed a significant positive correlation with the flood water NH4+-N concentration,irrespective of the irrigation water,but no significant correlation with pH.These results indicate that straw returning increased ammonia volatilization losses,domestic sewage irrigation can effectively reduce ammonia volatilization losses,and can simultaneously replace 45.2%of chemical nitrogen fertilizer by the N contained in the domestic sewage.The combination of domestic sewage irrigation and straw returning would be an ecological and environmental-friendly measure for rice nitrogen management in Taihu Lake region.(4)Greenhouse gas emissions from paddy fieldsThis study was conducted using Static-Gas Chamber method to examine the effects of straw returning and domestic sewage irrigation on the dynamic of CH4 and N2O emissionsfrom paddy fields from 2015 to 2016.The results showed that,compared to straw removal treatments,straw returning significantly increased the CH4 emissions by approximately 7-9 times under domestic sewage irrigation and 13-14 times under tap water irrigation,respectively.Straw returning increased the N2 emissions by 49.1?94.5%under two water types irrigation.However,domestic sewage irrigation could decrease CH4 emissions by 24.5?26.6%and N2O emissions by 37.0?39.0%under straw returning compared to tap water irrigation treatments,respectively.Global warming potentials(GWP)and greenhouse gas intensities(GHGI)were significantly increased with straw returning compared with those of straw removal,while decreased by domestic sewage irrigation under straw returning compared to tap water irrigation.Significant interaction between straw returning and domestic sewage irrigation on CH4 and N2O emissions was observed.Due to the rich N in the domestic sewage,domestic sewage irrigation could reduceapproximately 45.2%of chemical nitrogen fertilizer input without yield loss.Therefore,domestic sewage irrigation could be recommended as an environment-friendly and resource-saving agricultural management measure for paddy fields with straw returning to reduce the chemical N input,GHGs emissionsand maintaining the high rice productivity.