Effects Of Liquid And Residue From Biogas Slurry On Nitrogen Leaching From Paddy Soils And Control Of Nitrogen Leaching With The Combined Application Of Nitrogen Fertilizer Synergists And Biochar

As an important area for the development of agriculture and animal husbandry in China,the Taihu Lake Basin has long faced problems such as excessive fertilizer use,high separation between planting and breeding,and difficulties in agricultural waste treatment,which have led to ineffective pollution control and low resource cycling efficiency.This has put great pressure on the environmental protection and sustainable development of agriculture in the Taihu Lake Basin.While the use of biogas slurry and biogas residue in the "integrated planting and breeding" ecological farming model can effectively solve these problems,there may be a risk of nitrogen leaching when using them for fertilization or application.This article conducts a preliminary investigation on the production of agriculture and animal husbandry,as well as the treatment and utilization of waste in the Taihu Lake Basin.Through outdoor soil column simulation experiments,it explores the nitrogen leaching effects and laws of biogas slurry and biogas residue as fertilizers throughout the entire growth cycle of rice.Under soil conditions with fertilizer mixed with biogas slurry,a leaching simulation experiment was conducted to investigate the impact of ammonium and urease inhibitors and the combined use of biochar on the nitrogen leaching effect and process in the soil.The main research conclusions of this paper are as follows:(1)Reducing the amount of chemical fertilizer and using biogas slurry or biogas residue for fertilization in rice paddies can help reduce nitrogen leaching and increase soil nitrogen retention.Compared with the full fertilization group(CT),the average total nitrogen concentration of irrigation water in the groups using a reduced amount of chemical fertilizer mixed with biogas slurry or biogas residue decreased by 12.71% to 29.22% and 13.31% to 30.43%,respectively,and the average total nitrogen concentration of leachate decreased by 8.41% to 16.20% and 9.61% to14.56%.The total nitrogen leaching loss was reduced by 12.11%-21.09% and 9.47%-19.25%,respectively.Furthermore,the ammonium nitrogen content of the surface soil in the groups using biogas slurry or biogas residue was increased by 14.81% to 59.44% and 9.02% to 39.90%,respectively,and the nitrate nitrogen content was increased by 11.56% to 34.65% and 4.18% to14.74%,compared with the CT group.This indicates that reducing the amount of chemical fertilizer and using biogas slurry or biogas residue can reduce nitrogen runoff losses and leaching risks,increase nitrogen content in the surface soil,and reduce the migration of nitrate nitrogen to the bottom of the soil.(2)Reducing the amount of chemical fertilizer and using biogas slurry or biogas residue for fertilization can also increase crop yield and nitrogen utilization efficiency,and improve soil microbial diversity.Although using a reduced amount of chemical fertilizer alone can reduce nitrogen leaching and increase nitrogen fertilizer utilization efficiency,it can also cause a decrease in rice yield by 1.83% to 5.99% compared with the CT group.In contrast,the rice yield of the groups using a reduced amount of chemical fertilizer mixed with biogas slurry or biogas residue increased,with the rice yield of the groups using a 30% reduced amount of chemical fertilizer mixed with biogas slurry(30%RT+M1)and biogas residue(30%RT+M2)increasing by 3.33% and 2.66%,respectively,and the nitrogen utilization rate increasing by 17.61% and 16.34%.In addition,compared with CT group and blank group(CK,no nitrogen fertilizer),fertilizer reduction combined with biogas slurry or biogas residue could improve soil microbial richness,but the evenness decreased.(3)Under the condition of reducing fertilizer by 30% and applying biogas slurry,there is a significant difference in the nitrogen leaching inhibition effect of different types and amounts of nitrogen fertilizer efficiency enhancers(DCD nitrification inhibitor and NBPT urease inhibitor).The groups with 5% DCD(D1),10% DCD(D2),0.5% NBPT(N1),and 1.5% NBPT(N3)can reduce the nitrogen leaching in the leachate,and the total nitrogen accumulation leaching amount is reduced by 6.72% to 64.35% compared with the control group(CK,300 kg N/ha).However,the groups with 15% DCD(D3)and 1.0% NBPT(N2)exacerbate the loss of nitrogen.Overall,the nitrogen fertilizer efficiency enhancers with a dosage of 5% DCD and 0.5% NBPT have a better inhibitory effect on nitrogen loss.The ammonium nitrogen content in the surface soil of all groups that applied the nitrogen fertilizer efficiency enhancers was higher than that of the CK group,indicating that the application of nitrogen fertilizer efficiency enhancers can inhibit the nitrification of ammonium nitrogen.However,the nitrate nitrogen content in the soil was still relatively high in all groups.Compared with the other groups,the nitrate nitrogen content in the soil of the D1 and N1 groups continued to decrease with the increase of soil depth,and was lower than that of the other groups at a depth of40 cm,indicating that the inhibitory effect of the D1 and N1 groups on nitrate nitrogen leaching was better.(4)Under the condition of reducing fertilizer by 30% and applying biogas slurry,there is a significant difference in the nitrogen leaching inhibition effect of two nitrogen fertilizer efficiency enhancers used in conjunction with biochar prepared at different calcination temperatures.Except for the group with 0.5% NBPT + biochar prepared at 500℃(N500),which exacerbates the leaching of nitrogen,the other groups can reduce the leaching of nitrate nitrogen and total nitrogen.Among them,the group with 0.5% NBPT + biochar prepared at 300℃(N300)had the most significant effect,and the total nitrogen accumulation leaching amount decreased by 36.29% and 77.29%compared with the N1 group and the CK group,respectively.The surface soil of the N300 group and the D300 group,with 5% DCD + biochar prepared at 300℃,had a higher content of ammonium nitrogen,and the nitrate nitrogen content in the soil at different depths was lower.Therefore,the combination of 0.5% NBPT and 5% DCD with biochar prepared at 300℃ can better inhibit nitrogen leaching and reduce the nitrate nitrogen content in the soil.(5)When DCD,NBPT,and biochar are used together,the three groups that combined 5% DCD and 0.5% NBPT with biochar prepared at 300℃(DN300 group),500℃(DN500 group),and 700℃(DN700 group)can significantly reduce the accumulation leaching amount of nitrate nitrogen and total nitrogen in the leachate.Among them,the DN300 group had the best inhibitory effect.Compared with the CK group,the D300 group,and the N300 group,the total nitrogen accumulation leaching amount decreased by 92.83%,92.54%,and 68.44%,respectively,indicating that the three can play a synergistic role in inhibiting nitrogen leaching.In addition,the ammonium nitrogen content in the surface soil of the DN300 group reached 116.26 mg/kg,while the nitrate nitrogen content in the soil at different depths was only 0.36-1.21 mg/kg,indicating that this condition is conducive to the retention of nitrogen and the absorption of nitrogen by crops.Furthermore,the microbial evenness and richness in the soil of the DN300 group were improved.Therefore,the DN300 group had the best effect on inhibiting nitrogen leaching and suppressing soil nitrification.In summary,reducing fertilizer usage and applying biogas slurry or biogas residue can effectively reduce the risk of nitrogen leaching and,to some extent,increase rice yield and nitrogen utilization.The group that reduced fertilizer usage by 30% and applied biogas slurry had the best results.Under the condition of reducing fertilizer usage and applying biogas slurry,using nitrogen fertilizer synergists or combining with biochar has a certain effect on controlling nitrogen leaching.Through comprehensive analysis of nitrogen leaching indicators,soil nitrogen retention characteristics,and soil microbial diversity,using biochar prepared at 300℃ with 0.5% NBPT and5% DCD has the best effect on controlling nitrogen leaching.This article explores the effect of biogas slurry and biogas residue on returning to farmland and further methods for controlling nitrogen leaching,providing relevant references for promoting the sustainable development of integrated crop-livestock systems in the Taihu Lake Basin and achieving deep reduction of agricultural non-point source pollution in the basin.