| Biogas slurry is a new type of green fertilizers with comprehensive essential nutrient element and abundant active organic matter,which may supply the nutrients for crop growth and lower the costs in crop production,as well as mitigate the environmental risk induced by itself.A field experiment was conducted to study the precise application of biogas slurry in rice cultivation and its environmental effect.The treatment included no fertilizer(CK),chemical nitrogen fertilizer(HF100%),biogas slurry application with the nitrogen dose equivalent to 40%(ZY40%),70%(ZY70%),100%(ZY100%),130%(ZY130%),and 250%(ZY250%)of local conventional N fertilizer rate.Following the lacal conventional fertilization,the optimal nitrogen dosage was 225kg/hm2.The main purpose of the field study was to investigate the effects of biogas slurry application on rice yield,nitrogen use efficiency,and ammonia volatilization.In addition,a pot experiment was conducted to explore the potential approach for ammonia volatilization mitigation with the purpose of biogas slurry effective utilization in rice paddies.The main results are as follows.The rice yield had a positive linear relationship with the applied biogas slurry sourced N rate when it was less than 213.9 kg/hm2,and rice yield could be increased by 9.05 kg per 1 kg biogas slurry sourced N applied.However,rice yield was not increased anymore when the biogas slurry sourced N input was higher than 213.9kg/hm2.The yield of rice was 9.90 x 103 kg/hm2 when application rate of biogas slurry in rice cultivation was 213.9 kgN/hm2.The nitrogen use effaciency of rice increased first and then decreased with the increase of biogas slurry application rate,and reached the maximum when the amount of biogas slurry was 225 kgN/hm2,and was significantly higher than that of other biogas slurry.After the slurry application,the NH4+-N concentration in surface water was reduced rapidly,and then gradually become stable,while slurry application had no significant effect on NO3--N concentration in surface water.The concentration of NH4+-N in field water decreased rapidly after 1 to 3 days after the application of biogas slurry,and then decreased gradually to reach the stable level.The nitrate nitrogen concentration in field surface was much lower than that in ammonium nitrogen concentration,and most of the time was less than 1.0 mg/L,showing a trend of first rise and fall,in the biogas slurry after use within 3 to 6 days to reach the peak.The total amount of ammonia volatiles in paddy field increased with the increase of the amount of biogas slurry,and Ammonia volatilization mainly happened in the7?10 days after fertilizer application,and the N loss caused by ammonia volatilization accounted for 14.52%?17.64%of the biogas slurry sourced N application rate.Compared to chemical fertilizer application,rice grain yield,nitrogen use efficiency,and the soil Nmin were similar under biogas slurry application with the same amount of N,while the ammonia volatilization intensity(kg NH3 per kg rice yield)was significantly reduced by 22.6%.According to the results of this study,the rational use of biogas slurry in paddy field could have good economic and environmental benefits.In order to further mitigate the ammonia volatilization by biogas slurry application,four levels of surface water table depth(0cm,5cm,10cm,15cm),three biochar application rates(0,1%,2%)and three pH levels of the biogas slurry(original biogas slurry,pH of 7.0,pH of 6.0)were set to study the effects of these three factors on ammonia volatilization.The results showed that the accumulation of ammonia volatiles under water table depths of 0 cm,10 cm and 15 cm were reduced by 80.24%,20.52%and 35.44%than that under water table depth of 5 cm at the same nitrogen level.The ammonia volatilization under pH adjusted biogas slurry(pH of 7 and 6)application was significantly lower by 43.85%and 72.52%,respectively,than that under original biogas slurry application.However,there was no significant effect of biochar application on volatilization of ammonia from biogas slurry application. |
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