Effects Of Rice Straw-derived Biochar On Retention Of Nitrogen And Phosphorus In Paddy Field

With the implementation of urban and industrial point source pollution control,the proportion of agricultural non-point source pollution in pollution sources had gradually increased.The problem of eutrophication of water bodies caused by nutrient loss from farmland had caused widespread concern,and non-point source pollution caused by unscientific management of fertilizers and irrigation in rice cultivation could not be underestimated.Exploring new materials and technologies that promoted nitrogen and phosphorus retention in the paddy field ecosystem had significance for controlling nutrient loss in paddy fields.In this paper,rice straw-derived biochar was used as the main material.Combining indoor simulation and outdoor pot experiment,the effects of different materials on the adsorption and retention of nitrogen and phosphorus were analyzed from the surface water,soil and plants in the paddy field system.The application of rice straw-derived biochar(SB)and its mixed materials with fly ash(FA)and flue gas desulfurization gypsum(FGDG)on the release of soil nitrogen and phosphorus into the water was studied,as well as the effect of SB and its mixed materials on the absorption and retention of nitrogen and phosphorus in rice.The main results of the paper are as follows:(1)With the concentration of nitrogen and phosphorus in water solution between0 and 20mg/kg,SB had the best adsorption of nitrogen,and FGDG had the best adsorption of orthophosphate among the 8 selected materials.The maximum adsorption capacity of SB for ammonium nitrogen and nitrate nitrogen was 3.15mg/g and 0.46mg/g,and the FGDG for orthophosphate was 4.48mg/g.(2)The adsorption capacity of straw biochar to nitrogen and phosphorus in water was better than that of shell biochar.FA and FGDG only had obvious adsorption effects on high concentration nitrate nitrogen,and the adsorption of phosphorus was better than other biochar.(3)In the simulated irrigation experiment,the application of the SB,FA and FGDG promoted the retention of soil nitrate nitrogen and the release of ammonium nitrogen.Only FGDG could promote the retention of orthophosphate in soil.The application of 3% FGDG reduced the release of nitrate nitrogen and orthophosphate in unfertilized soil by 52.3% and 96.5%.The application of 1% FA reduced the concentration of nitrate nitrogen in water by 22.6% within 12 h.(4)In the simulated irrigation experiment,there was a difference in the retention of soil nitrogen and phosphorus from the SB and FA or FGDG mixed materials to the single application of materials.The mixed application of SB and FA promoted soil retention of ammonium nitrogen.In the fertilized soil with ammonium nitrogen lower than 40mg/kg,the mixing ratio 2:1 of SB and FA made the maximum reduction of ammonium nitrogen in the surface water up to 32.1%.In the fertilized soil with phosphorus of 40 mg/kg,the mixing ratio 2:1 of SB and FGDG made the maximum reduction of orthophosphate content by 58.9%.(5)In the pot experiment of the simulated paddy field system,the SB single application at 1% application rate had the best effect on the retention of inorganic nitrogen and phosphorus in the surface water.The ammonium nitrogen after tillering fertilizer and inorganic phosphorus after panicle fertilizer in surface water decreased by 51.3% and 51.7%.The mixing of SB and other two materials was more conducive to the reduction of nitrogen and phosphorus in soil surface water than its single application.Among them,SB and FA mixed in 1:1 reduced the ammonium nitrogen concentration by 68.3%.(6)In the pot experiment,the application of SB had no significant effect on the total phosphorus content of the paddy soil system regardless of single application or mixing.Application of SB or its mixing with FA could increase the total nitrogen content of the soil.Among them,the total nitrogen content of the soil treated with SB and FA mixed in 2:1 increased the highest,reaching 57.7%.(7)In the pot experiment,the mixed application of SB and FA could promote the absorption of nitrogen by plants,and the maximum increase in total nitrogen of plants and rice was 28.9% and 12.2%,and the net weight of rice increased by 4.2%.The mixed application of SB and FGDG in the ratio of 2:1 reduce the total nitrogen of rice by17.4%.