添加不同外源氮对水稻秸秆腐解和养分释放的影响

探究添加不同外源氮对水稻秸秆腐解规律和养分释放特征的影响，为提高水稻秸秆养分利用提供理论依据。该研究采用室内恒湿网袋培养法，设置4个处理：不添加外源氮（CK）；添加尿素（PU）；添加尿素硝酸铵（UAN）；添加石灰氮（CaCN2）。结果表明：水稻秸秆腐解规律表现为0～5 d腐解速率最大，为0.39～0.47 g/d；5～30 d腐解速率较快，为0.12～0.16 g/d；30～150 d腐解缓慢并趋于平稳，腐解速率为0.045～0.050 g/d。与CK相比，添加外源氮可以显著提高水稻秸秆的累积腐解率（P < 0.05）。虽然秸秆累积腐解率在不同外源氮处理间差异不显著，但是不同外源氮的添加对水稻秸秆不同时期的腐解特征有着显著影响。主要表现在0～30 d PU、UAN和CaCN2处理水稻秸秆腐解速率分别为0.21、0.20和0.19 g/d，PU处理比UAN和CaCN2处理分别高5.00%和10.53%；在该时间段纤维素和半纤维素腐解率占累积腐解率的比例分别为63.65%和47.02%，这表明纤维素和半纤维素腐解主要集中在秸秆腐解前期，且PU处理对纤维素和半纤维素的促腐效果最佳。30～150 d PU、UAN和CaCN2处理腐解速率分别为0.046、0.046和0.050 g/d，CaCN2比PU和UAN处理高8.70%；在该时间段木质素腐解率占累积腐解率的比例为82.45%，这表明木质素腐解主要集中在秸秆腐解后期，且CaCN2处理对木质素的促腐效果最佳。由此可见PU处理前期促腐效果最佳，CaCN2处理后期促腐效果最佳。综合不同外源氮对水稻秸秆的促腐效应，建议不同种类外源氮进行配施，以达到最佳促腐效果。

Effects of adding different exogenous nitrogen on rice straw decomposition and nutrient release

Abstract: A straw returning technique has been one of the most important measures for the comprehensive utilization of straw in ecological agriculture in the world. The soil fertility can also be improved to protect the environment during the sustainable development of farmland. The amount of straw returning is ever increasing in China in recent years. It is necessary to optimize the straw returning for higher efficiency during resource utilization. The nitrogen content can also be added to adjust the carbon-nitrogen ratio of straw for the rapid decomposition, thus improving the nutrient release rate with the better straw returning. In this study, different exogenous nitrogen sources were added to determine the dynamic changes of rice straw during decomposition. The suitable nitrogen source was also screened. Indoor cultivation was adopted at the constant humidity. Four treatments were set, including the control (CK), the application of urea (PU), the application of urea ammonium nitrate (UAN), and the application of lime nitrogen (CaCN2). The results showed that the highest decomposition rate of rice straw was achieved at 0-5 d with 0.39-0.47 g/d, followed by the 5-30 d with 0.12-0.16 g/d, and the lowest was 0.045-0.050 g d-1 during 30-150 d. The addition of exogenous nitrogen significantly increased the cumulative decomposition rate of rice straw (P<0.05), compared with the CK. There was no significant difference in decomposition rate, whereas, a relatively significant difference was found in the decomposition characteristics of rice straw at different stages among the three treatments of exogenous nitrogen. Specifically, the decomposition rates of rice straw in the PU, UAN, and CaCN2 treatments in 0-30 d were 0.076, 0.077, and 0.078 g/d, respectively. The decomposition rates of the PU, UAN, and CaCN2 treatments at 30-150 d were 0.46, 0.46, and 0.50 g/d, respectively. The cellulose, hemicellulose, and lignin were attributed to the decomposition rates of rice straw at different stages. The maximum decomposition rates of cellulose treated with the PU, UAN, and CaCN2 were 13.23%, 3.78%, and 2.13% higher than those with the CK, respectively. The PU treatment also presented the best promoting effect on cellulose decomposition. The decomposition rates of hemicellulose treated with the PU, UAN, and CaCN2 were 5.89%, 6.40%, and 4.74% higher than those with the CK, respectively. The PU and UAN presented the best promoting effects on hemicellulose decomposition. The PU and UAN treatments contributed the most to improving the early decomposition rate of rice straw. The maximum decomposition rates of lignin treated with the PU, UAN, and CaCN2 were 30.19%, 25.28%, and 41.98% higher than those with the CK, respectively. The CaCN2 treatment presented the best promoting effect on the lignin decomposition, thus improving the decomposition rate of rice straw in the late stage. Consequently, the different types of exogenous nitrogen can be combined to achieve the best decomposition. This finding can provide a theoretical basis to improve the nutrient utilization of rice straw for the feasibility and sustainability of straw returning.