New Miscanthus Biomass Utilization Pathway

Miscanthus lutarioriparius,as a Chinese unique species of Miscanthus genus,is a C4perennial grass which largely distributes in wetland areas of middle-downstream of the Yangtze River,China.Only in Dongting Lake area in Hunan,cultivar and semi-natural areas covers approximate 10 thousand ha.Due to its characters with high biomass productivity and richness in cellulose,M.lutarioriparius can be used as optimal feedstock materials to produce paper and biochar.However,the paper-making industry has collapsed because of poisonous by-product wastes.The stop of paper manufacture leads to large amount of M.lutarioriparius resources staying at sluggish stage.What’s worse,there are many other agricultural issues such as heavy cadmium（Cd）contamination and low fertilizer use efficiency,etc.Thus,we selected M.lutarioriparius as raw materials for producing biochar.Then,the M.lutarioriparius based biochar was further used to produce soil conditioner and biochar-based control-release fertilizers（BCFs）.We conducted several experiments on effects of the interactions among other Cd passivators on rice Cd uptake,photosynthetic characteristics and rice yield.Besides,we also carried out water leaching and soil column leaching experiments to determine the control/slow-release effects of BCFs.In addition,we further determined the effects of BCFs on N/P/K use efficiency,yield,and Cd uptake of rice.All these experimental results were expected to provide a new idea and pathway for exploiting M.lutarioriparius resources in Dongting Lake area and to promote local development of ecological economy and agriculture.The results showed as the following:（1）The optimum interaction ratio of M.lutarioriparius derived biochar:humid acid:potassium silicate:calcium magnesium phosphate:zinc sulfate:slaked lime was 200:60:3:30:4:120（i.e.composition of the M.lutarioriparius soil conditioner）and the corresponding recommended application rate was 417 kg·mu^-1.Three experimental treatments,whose compositions closed to the above optimum interaction ratio,were used to explore the application effect of M.lutarioriparius soil conditioner on rice yield.Results showed that application of the three tested treatments could decrease the Cd content of rice plants to0.88¹.65 mg·kg^-1（i.e.the Cd reduction potential of 54.4%⁷5.8%）and of rice grains with husk to 0.13⁰.17 mg·kg^-1 with a Cd reduction potential of 47.3%⁵9.7%.Additionally,applications of all three treatments could increase the rice grain yields with the highest potential of 126 kg.mu^-1（i.e.increasing rate of 25.6%）.（2）Results showed that the application of M.lutarioriparius biochar-based soil conditioner could significantly（P<0.05）advance the rice heading time.Compared to the control without M.lutarioriparius biochar-based soil conditioner,the rice heading time was4¹2 days earlier with the most significant improvement effects achieved by the application of SC3 soil conditioner.In addition,the photosynthetic related traits could be improved effectively as well after the application of the three tested soil conditioners.The photosynthetic rates of the soil conditioner treatments were higher 22.8%⁶2.4%higher than the control with the most significant improvement effects by the T2 treatment.While the stomatal conductance,intercellular CO₂ concentration and transpiration rate in rice leaves under the treatment of the soil conditioner SC1 showed the most significant improvement by a potential of 57.0%,8.2%and 18.2%,respectively.Additionally,three soil conditioners could significantly promote the accumulation of medium trace elements in rice leaves.Compared to the control,the content of Mg,Fe and P was increased by 22.79%²4.80%、82.2%⁸9.8%、19.6%⁵8.5%,respectively.Moreover,rice yield was increased by 24.2%³5.0%comparing with the control as well,showing the soil conditioner SC2 the best.（3）Single-time leaching rate of N/P/K for four types of biochar-based compound fertilizers（BCFs）in water leaching experiment reached at the maximum at the first day.The cumulative leaching rate of BCF1 and BCF2 showed excellent control-release behavior in total 28 days.The cumulative N/P/K leaching rate of these two BCFs was 57.6%⁶4.0%,34.8%³6.2%and 55.1⁶3.9%,respectively.In soil column leaching experiment,N and K release behavior of four BCFs was significant（P<0.05）on days 3,while significant（P<0.05）differences of P leaching rate among four BCFs existed at the 14^thh day.In addition,there were no significance（P>0.05）among cumulative leaching rates of four BCFs and they were significantly lower than that of chemical compound fertilizer.N/P/K cumulative leaching rate of four fertilizers were 8.6%¹2.7%,5.2%⁷.3%and 15.6¹6.7%,respectively.（4）Application of BCFs showed obvious improvement in N,P₂O₅ and K₂O use efficiency.Compared to the control,grain productivity and agronomic use efficiency of N under BCF1^BCF3 treatments were significantly（P<0.05）improved by 39.2.5%⁶7.7%and 40.8%⁷6.8%,respectively.Both grain productivity and agronomic use efficiency of P₂O₅ under BCFs treatments were significantly（P<0.05）improved by 105.9%²34.5%and112.3%²04.0%,respectively,in comparison with the control.Under BCF2^BCF4treatments,grain productivity and agronomic use efficiency of K₂O separately showed significant（P<0.05）improvement by 33.4%¹01.9%and 44.6%⁸3.5%.In addition,compared to the group treated by chemical compound fertilizer,the rice grain and plants content of cadmium were significantly（P<0.05）reduced to 0.18⁰.24 mg·kg^-11 and 1.32².90 mg·kg^-1,respectively.Compared to the control,cadmium uptake rate under BCFs treatments were reduced by 52.3%⁸0.5%.However,there was no significant（P>0.05）effects on rice yield after application of BCFs.