Effects Of Rice Husk And Its Biochar On Lei Bamboo Soil Nitrogen Leaching And N₂O Emissions

The Lei bamboo(Phyllostachys violascens)shoot industry is the largest industry in the rural economy of Zhejiang Province,and the demand for Lei bamboo shoots increases with the improvement of people's living standards.Long-term rice husk mulching and large amount of chemical fertilizer application,which are the common management measures in the Lei bamboo plantation,can promote the rapid growth of the Lei bamboo shoots,but these practices may also result in excessive accumulation of soil nutrients,leading to soil nitrogen surplus and aggravating nitrogen leaching loss and nitrous oxide(N₂O)emissions from Lei bamboo forests.Rice husk biochar has a porous structure and a large specific surface area,and adding rice husk biochar would reduce soil bulk density and improve soil aeration,which would be of great importance to the sustainable development of bamboo forests.Therefore,different levels(10 t ha^-1 and 30 t ha^-1)of rice husk and its biochar were used to investigate the effects of rice husk and its biochar on soil nitrogen leaching and N₂O emissions in a Lei bamboo soil,using a greenhouse pot experiment.The main results of our study are summarized as follows:1)The addition of the high-level biochar significantly reduced the cumulative leaching of dissolved organic nitrogen(DON)and leachate DON concentration in comparison to the rice husk and low-level biochar addition treatments.Inorganic nitrogen only accounted for a small proportion of total dissolved nitrogen(TDN)and DON was the predominant proportion,the change in TDN in leachates was similar to the variation in DON in leachates.The inorganic nitrogen in leachate was mainly in the form of nitrate nitrogen(NO₃^--N),which accounted for 98.83%-99.22%of the total leached inorganic nitrogen.2)The inorganic nitrogen in leaching mainly existed in the form of NO₃^--N,which accounted for98.83%-99.22%of the total leaching of inorganic nitrogen.Compared with the treatment with high-level rice husk,the addition of high-level biochar reduced the accumulated leaching of DON.Compared with the control treatment,the addition of high-level rice husk significantly increased DON concentration in leaching.In the study period,the predominant form of N in TDN of soil leaching was NO₃^--N,followed by DON.The range of DON leaching loss/TDN leaching loss ranged from 5.91%-15.34%,and the proportion of ammonium nitrogen(NH₄⁺-N)leaching loss in TDN was the smallest.3)There was no significant difference in the concentrations of soil NH₄⁺-N among different treatments at the first day and 25^th day after nitrogen(N)application.At the 165^th day after N application,the high-level rice husk treatment significantly increased the soil NH₄⁺-N concentration by 42.43%compared with the control.At the first day and the 25^th day after N application,Soil NO₃^--N concentration in the high-level rice husk treatment was significantly higher than those in the other treatments.At the262^nd day after N application,the concentration of soil WEN in the high-level rice husk treatment was significantly higher than those in the other treatments.After adding rice husk and its biochar,the copy number of nos Z?gene in Lei bamboo forest soil showed a gradual increase,and the maximum value occurred at the 262^nd day after N addition.4)Rice husk addition significantly increased soil cumulative N₂O emissions,high-level biochar addition significantly reduced soil cumulative N₂O emission,but soil cumulative N₂O emission from the low-level biochar treatment did not differ from that from the control treatment.Based on the sterilization experiment for the last sampling soil(262^nd day after N application),it showed that the biotic process predominantly contributed to the total N₂O production in the control treatment,accounting for 84.30%,followed by high-level rice husk addition treatment.The N₂O production in the low-level biochar addition treatment mainly sourced from the abiotic process,which accounted for 58.30%,while the contributions of abiotic process in the other treatments were lower.Soil N₂O emission was significantly negatively correlated with soil NH₄⁺-N concentration and p H,but significantly positively correlated with the concentration of NO₃^--N,TN and WEN in the soil.4)Our study demonstrated that converting rice husk to biochar could reduce N₂O emissions and TDN leaching loss in Lei bamboo soil.Applying a large amount of rice husk in Lei bamboo forest significantly promoted soil N₂O emissions,and applying high-level biochar could reduce soil N₂O emissions.In addition,rice husk biochar combined with NH₄⁺-N fertilizer produced less N₂O than NO₃^--N fertilizer.Therefore,compared with NH₄⁺-N fertilizer application alone,the application of NH₄⁺-N fertilizer and the addition of high-level rice husk biochar have the potential to reduce N₂O emissions in Lei bamboo forests in the future.