生物质炭对集约化菜地N2O排放和蔬菜产量的影响

【目的】 本试验评价了生物质炭对菜地土壤温室气体排放和产量的长期效应。 【方法】 田间试验在江苏省南京市集约化种植菜地进行。共设置4个处理，分别为对照 (CK)、单施氮肥处理 (N)、施用氮肥 + 新生物质炭 (NC_F，C_F在2016年6月施用) 以及施用氮肥 + 4年陈化生物质炭 (NC_A，C_A在 2012 年6月施用)。生物质炭施用量为40 t/hm2。2016年11月至2017年11月连续种植4季蔬菜，分别为小青菜、空心菜、苋菜、菠菜，并伴有休耕期。每季蔬菜施氮量均为N 240 kg/hm2，其中空心菜收获三茬，在第一茬收获后按照N 240 kg/hm2 追肥一次。采用静态暗箱–气相色谱法测定N₂O浓度。 【结果】 观测期内各处理菜地N₂O排放主要集中在第二季和第三季，其单位产量N₂O排放量分别为0.038～0.131 kg/t和0.107～0.482 kg/t，而第一季和第四季的单位产量N₂O排放量分别是0.033～0.209 kg/t和0.007～0.070 kg/t。土壤温度和矿质氮变化未显著影响土壤N₂O排放通量；整个观测期内土壤充水孔隙度 (WFPS) 介于37%～93%之间，土壤含水量变化显著影响 (P < 0.01) 土壤N ₂O排放通量。与N处理相比，整个轮作周期内NC_F和NC_A处理N₂O周年累积排放量和周年排放系数均显著降低，两个施生物质炭处理之间差异不显著；NC_F处理N₂O周年累积排放量和周年排放系数降幅分别为35.6%和46.2%，NC_A处理降幅分别达38.8%和49.9%。与N处理相比，NC_F和NC_A处理均增加了集约化菜地蔬菜产量，增幅分别为4.6%和17.9%，NC_A处理达到显著水平，两个施生物质炭处理之间差异不显著。此外，NC_F和NC_A处理分别显著降低单位产量N₂O排放量49.8%和41.3% (P < 0.01)。 【结论】 在集约化菜地土壤中经4年陈化后的生物质炭仍然具有较强的减排和增产能力。与新施入的生物质炭相比，施用4年后的生物质炭增产效果更显著；施用生物质炭对集约化蔬菜生态系统减排和改善作物生产具有长期效应。

Effects of biochar on mitigating nitrous oxide emission from an intensive vegetable field and crop yields

【Objectives】 The study evaluated the long-term effect of biochar amendment on both greenhouse gas (GHG) emissions and crop yields, which are crucial for the efficient field application of biochar. 【Methods】 A field experiment was conducted on an intensive vegetable field in 2016 in Nanjing, Jiangsu. Four treatments included no nitrogen fertilizer control (CK), urea in each crop (N), urea in each crop and fresh biochar (NC_F) once in 2016, and urea in each crop and field-aged biochar which was amended into the field for four years in 2012 (NC_A), with biochar amendment at 40 t/hm2. Vegetables of pakchoy, water spinach, edible amaranth and spinach were planted in sequence during the observed consecutive year from November 2016 to November 2017. Urea (N 240 kg/hm2) was applied once as basal fertilization for each crop, except for water spinach which received an extra topdressing N 240 kg/hm2 after its first harvest with 3 harvests in total. The static chamber-gas chromatograph method was used to measure dynamically nitrous oxide (N₂O) emissions. 【Results】 The N₂O was mainly emitted during the second and third crop seasons, with yield-scaled N₂O emissions of 0.038–0.131 and 0.107–0.482 kg/t, respectively, with being 0.033–0.209 and 0.007–0.070 kg/t for the first and fourth crop seasons, respectively. Neither soil temperature nor inorganic nitrogen was correlated significantly with N₂O emission in all treatments. Significant correlation (P < 0.01) was detected between soil moisture and N ₂O fluxes with WFPS (water filled pore space) ranging from 37%–93% during the experimental period. Relative to the N treatment, the NC_F treatment significantly reduced the annual N₂O cumulative emissions and the annual N₂O emission factors by 35.6% and 46.2%, respectively. Relative to the N treatment, the NC_A treatment significantly reduced the annual N₂O cumulative emissions and the annual N₂O emission factors by 38.8% and 49.9%, respectively. Compared with N treatment, the NC_F and NC_A treatments improved crop yield by 4.6% and 17.9%, respectively, being significant for the NC_A treatment. Moreover, relative to the N treatment, the NC_F and NC_A treatments significantly reduced yield-scaled N₂O emission by 49.8% and 41.3%, respectively. 【Conclusions】 Since field-aged biochar showed obvious effects on N₂O mitigaion and crop yield after 4 years, biochar incorporation showed long-term effect on GHGs mitigation and crop improvement in the intensive vegetable ecosystem.