| The supply and balance of nutrient is important factor to increase and stabilize crop yield.Nitrogen fertilizer(urea,67%)is the largest amount of agricultural inputs to nutrient supply,and provides a rapid supply of chemical nutrients for agricultural production and ensuring high yield of crops.However,the low utilization rate of nitrogen fertilizer in agriculture leads to environmental pollution for the atmosphere and water,and reactive nitrogen has become a major ecological and environmental problem in the world.Biochar as an environmentally friendly measure to improve soil organic carbon in farmland has been recognized for its carbon sequestration,greenhouse gase mission reduction,soil improvement and yield improvement.However,the cost of mass application limits the agricultural extension of biochar.The National Development and Reform Commission supported the industry development of straw biochar-based fertilizer in 2012,and proposed the transformation of straw biochar-based fertilizer to improve the fertilizer industry in 2013,while straw straw biochar-based fertilizer has been in the industrialization promotion.The biochar-based fertilizer can effectively reduce chemical nitrogen application and maintain high crop yield due to the interaction between biochar and nitrogen(amide or ammonium nitrogen)based on electrical adsorption,physical adsorption and organic functional group binding.We have developed a biochar-based fertilizer similar to soil aggregate structure containing organic binder,minerals,stable and active organic matter(biochar)and inorganic nutrient compounds,which has been in the national demonstration promotion.However,there is no systematic study on the mechanism of biochar-based fertilizer for the improvement of fertilizer N use efficiency rate,and the effect of mineral properties to the interaction with biochar on N leaching release for promoting crop uptake is an important scientific and technological basis to explore the high yield and high efficiency of biochar-based fertilizer.In the study,we used laboratory simulation test,greenhouse test and field test to compare different type and proportion of mineral-biochar and urea composite(biochar blended urea)for the exploration of the internal structure of biochar blended urea,and leaching dynamics of N in the soil-water system,and the effect of biochar blended urea on crop growth and environmental effect,while using 15N tracer technique to reveal the fate of urea-N from biochar blended urea in soil and crop system.It also provides scientific basis foe the stable N release and soil aggregate structure of biochar blended urea,and further for the transformation and development of N fertilizer and the demonstration and promotion of biochar-based fertilizer.The main research results are as follows:1.For the leaching behavior of biochar with clay mineral and urea,we compared different biochar urea composite with mineral,biochar and urea as proportion of 9:5:10 with biochar from wheat straw,maize straw,rice straw,green waste and pig manure,bone and tea waste for the preparation of biochar blended urea fertilizer(Bio-U).In soil column test,it was found that N leaching rate of Bio-Us with green waste biochar and maize straw biochar significantly reduced by 11%and 16%compared with the urea treatment on the 1st day,and was significantly lower than other treatments,but the accumulative nitrogen leaching rate showed no difference among treatments.Therefore,the Bio-U with green waste biochar and maize straw biochar as carriers showed better N fixation.2.In the research,the effect of clay mineral on the structure and N leaching of biochar blended urea was studied.Biochar blended urea was modified by adding clay mineralsepiolite in the process of pelleting to preparation of biochar-mineral-urea composite(BioMUC).The main components were biochar from municipal garden biomass waste(20%),bentonite(25%),sepiolite(12%)and urea(40%).FTIR showed it formed a higher proportion of C/N functional groups,such as NHC=O/NH2-C.SEM showed that the surface was covered by elongated crystals of sepiolite,and urea crystals existed in the internal structure surrounded by minerals and biochar,and organo-mineral layer on the external surface in the pores of biochar.Afterwards,the N leaching of mineral modified biochar blended urea was studied by soil column leaching test.In the soil column experiment,compared to urea fertilizer(UF),biochar-mineral urea composite(Bio-MUC)showed significant reduction of nitrogen leaching over the 30 days in cropland soil.The N leaching rate of Bio-MUC was significantly lower than that of UF by 44%and Bio-U by 35%on 1st day.The Bio-MUC promoted the accumulative proportion of ammonium nitrogen in the leachate with the increase of leaching time.The amount of DOC in Bio-MUC leachate was significantly lower than that in UF,which showed Bio-MUC improved the stability of DOC.Subsequently,the residual biochar collected from the soil after leaching test,the inner surface of the biochar pores was seen by SEM coated with an organo-mineral layer,with a small but detectable quantity of N both in the biochar and in this organo-mineral layer.3.Inspired from the second experiment,organic binder was used to further enhance the mineral-organic interaction.The modified biochar blended urea was mainly composed of biochar from maize straw(20%),bentonite(25%),sepiolite(9%),sodium carboxymethyl cellulose(2%).chitosan(1%)and urea(40%)for the biochar-mineral-organic binder-urea(Bio-MOUC),which were prepared for granulating.SEM showed that the surface presented a coating layer of mixture by organic matter and mineral leading to enhance the densification.In the internal structure,filamentous organic substances were observed between biochar and mineral,and the surface groups of biochar reacted with minerals.Transmission scanning electron microscope of Bio-MOUC showed that the pores of biochar became the storage chamber of fertilizer and the organic-mineral layers formed in the pores of biochar.Compared with Bio-MUC by mineral modification,the modification by organic binder(Bio-MOUC)significantly reduced the cumulative leaching rate of nitrogen within 5 days,which cumulative leaching rate of nitrogen on 5th day was 17%lower than that of Bio-MUC.The Bio-MOUC further increased the accumulative proportion of ammonium nitrogen in the leachate than Bio-MUC.It indicated that Bio-MOUC further reduced N leaching rate due to organic-mineral layers formed on the surface and biochar pore,which can protect and hold the nitrogen in the fertilizer.4.In a 50-day pot experiment with corn seedling,the application of Bio-MUC significantly improved the maize biomass,nitrogen use efficiency and root growth.The root morphology analysis showed that the root volume of maize in Bio-MUC increased by 38%compared with urea treatment.It can be seen that biochar blended urea modified by sepiolite showed promotion of root growth,which was beneficial to the absorption of nitrogen fertilizer by crops to promote crop growth.A field experiment of wheat season was carried out in Changshu Municipality.It was designed in same nutrient condition,and six treatments including no nitrogen fertilizer treatment(CK),urea fertilizer treatment(UF),modified biochar blended urea treatment(BU),urea fertilizer in N reduction treatment(UFr),modified biochar blended urea in N reduction treatment(BUr)and mixture of urea and biochar in N reduction treatment(UBCr).The results showed BU significantly increased wheat yield and nitrogen agronomic utilization efficiency.Compared to UF,BU significantly increased total nitrogen content and total free amino acid content in grain by 32%and 18%,respectively.Meantime,BU increased soil DOC content compared to UF.Although the BU had no effect on the soil total nitrogen content,it significantly increased the soil alkal-hydrolyzed nitrogen content and soil microbial biomass nitrogen content.Moreover,the static chamber was used to analyze the effect of biochar blended urea on ecosystem greenhouse gas emissions in wheat season.Compared with urea fertilizer,the BU fertilized treatments had no effect on CO2 and CH4 emissions,but significantly reduced the total N2O emission of ecosystem by 23-28%,with decrease for GWP,GHGI and EF.5.The N use efficiency and residual N distribution of biochar blended urea in crop-soil system was analyzed by using 15N tracer technique in an microplot of static chamber inside the field plot.BU and BUr increased urea-N use efficiency of wheat with 45%and 55%,significantly higher than UF and UFr with 32%.Fertilizer-N use efficiency of grain in UF and UFr was 20%and 19%,but in BU and BUr with 29%and 37%.The results of two-way ANOVA analysis showed that urea type had a significant effect on the urea-N uptake in the grain and root,with no significant effect of fertilizer application rate,and there was no interaction between the nitrogen fertilizer type and application rate.There was no significant difference for the total residual rate of urea-N between biochar blended urea and urea in 060 cm soil,but change in 0-20 cm,20-40 cm,40-60 cm.The residual urea-N rate of BU was mainly concentrated in 0-20 cm soil(32%),which was significantly higher than that in UF(20%).The residual fertilizer-N rate of BU in 20-40 cm soil was only 8%,and significantly smaller than that in UF(21%).The results of two-way ANOVA analysis showed that the urea type and the application rate had a significant effect on the residual urea-N rate in 0-20 cm,but the residual rate of fertilizer-N in 20-40 cm was significantly affected by the type of nitrogen fertilizer.It can be found that BU improved the fertilizer-N use efficiency of crop,and contributed to the accumulation of N-fertilizer in 0-20 cm soil and reduced the residual fertilizer-N migration to deep soil to facilitate the supply of soil N turnover in a long term.In conclusion,modification by clay mineral and organic binder could promote the aggregate function of biochar-based nitrogen fertilizer to reduce nitrogen leaching,increase nitrogen uptake by crop leading to improvement in crop yield and quality,improve soil organic carbon and manage soil N turnover,and reduce greenhouse gas emissions,which benefit to the formation of a high cycle of agricultural waste for the development of sustainable green agriculture. |
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