水田土壌からのNO排出量に及ぼす稲わらと豚糞堆肥の効果

Effect of rice straw and swine manure biochar on NO emission from paddy soil.

• Zhanbiao Yang
• Yi Yu
• Rujing Hu
• Xiaoxun Xu
• Junren Xian
• Yuanxiang Yang
• Lixia Liu
• Zhang Cheng

抄録

水田土壌からのNO排出に及ぼす稲わらバイオチャー（RSBC）と豚糞バイオチャー（SMBC）の影響を分析した。これらのバイオチャーを1%と5%の割合で土壌に添加し、イネの生育の伸長期、圧造期、成熟期におけるNO排出量、土壌性状、土壌酵素活性を測定した。その結果，NOフラックスは添加後2時間以内に開始し，その後3段階の生育過程で有意に減少した。累積 NO 放出量は、生炭施用により 45.14～73.96%抑制され、5%SMBC が最も低い値を示した。また、バイオ炭施用は土壌pH、土壌有機炭素（SOC）、NO濃度、ウレアーゼ活性を有意に上昇させ、土壌NH、硝酸還元酵素活性を低下させた。回帰分析の結果、NO の累積排出量は NH と正の相関があり、土壌 pH、SOC、NO と負の相関があることがわかった。さらに、SEM解析の結果、バイオ炭の施用は脱窒プロセスを弱め、NHレベルがNO排出量に最も大きな影響を与えることが明らかになった。以上のことから、RSBCとSMBCは、土壌pHを上昇させ、硝酸還元酵素活性を低下させ、NH含量を低下させることで、水田土壌の窒素循環を制御し、NO排出を抑制していることがわかった。

We analyzed the effects of rice straw biochar (RSBC) and swine manure biochar (SMBC) on NO emission from paddy soil. The biochars were added to soil at the rates of 1% and 5% (w/w), and NO emission, soil properties and soil enzyme activities were determined at the elongation, heading and maturation stages of rice growth. The NO flux started within 2 h of adding the biochar, and decreased significantly thereafter during the three growth stages. The cumulative NO emission was suppressed by 45.14-73.96% following biochar application, and 5% SMBC resulted in the lowest cumulative emission. In addition, biochar application significantly increased soil pH, soil organic carbon (SOC), NO levels and urease activity, and decreased soil NH and nitrate reductase activity. Regression analysis indicated that cumulative NO emission was correlated positively to NH, and negatively to soil pH, SOC and NO. SEM further revealed that biochar application weakened the denitrification process, and the NH level had the most significant impact on NO emission. Taken together, RSBC and SMBC regulated the nitrogen cycle in paddy soil and mitigated NO emission by increasing soil pH, decreasing nitrate reductase activity and NH content.