地膜覆盖与施肥对秸秆碳氮在土壤中固存的影响

【目的】作物秸秆不仅含有较高的有机碳,而且含有丰富的矿质营养元素。秸秆还田是东北黑土地区培肥土壤和农业可持续发展的重要技术措施。然而不同地膜覆盖（简称“覆膜”）及施肥方式下秸秆碳（C）和氮（N）在土壤中的固持特征还不是很明确。本研究通过定量分析秸秆碳对土壤有机碳（SOC）和秸秆氮对土壤全氮（TN）的贡献,探讨不同覆膜和施肥条件下秸秆碳和氮在土壤中固定的差异,以期为土壤肥力提升和东北黑土地保护提供依据。【方法】基于覆膜与施肥的长期定位试验,选择覆膜和不覆膜（裸地）栽培条件下不施肥（CK）、单施氮肥（N₄）和有机肥配施氮肥（M₂N₂）处理,在表层（0—20 cm）土壤添加¹³C¹⁵N双标记秸秆后在田间原位培养150 d,测定SOC含量及其δ¹³C值、TN含量及其δ¹⁵N值,分析SOC中秸秆来源C（¹³C-SOC）、TN中秸秆来源N（¹⁵N-TN）和土壤碳氮比随时间的动态变化特征。【结果】施肥、覆膜及其它们的交互作用显著影响（P<0.05）¹³C-SOC和¹⁵N-TN含量。整个培养期间,M₂N₂处理秸秆碳对SOC的贡献率（¹³C-SOC/SOC）和秸秆氮对TN贡献率（¹⁵N-TN/TN）平均分别为10.48%和3.18%;施肥（N₄和M₂N₂）处理¹³C-SOC/SOC和秸秆碳残留率在覆膜方式下平均分别为12.65%和37.14%,不覆膜方式下分别为12.08%和34.50%。同一栽培方式培养第150天,N₄处理¹³C-SOC/SOC和秸秆碳残留率平均分别为14.33%和39.40%,其他施肥处理平均分别为11.77%和33.21%;CK处理¹⁵N-TN/TN平均为4.56%,分别比N₄和M₂N₂处理高26.00%和44.53%。培养第150天,秸秆氮残留率在覆膜和不覆膜条件下CK处理最高,平均为10.03%;不覆膜N₄处理最低,为7.87%。无论覆膜与否,N₄处理¹³C-SOC与¹⁵N-TN比值为32—39,其他施肥处理均<30。【结论】秸秆碳氮在土壤中的固存对覆膜与施肥的响应敏感。单施氮肥有利于秸秆碳在土壤中的积累和有机碳的更新,不施肥处理秸秆氮对土壤氮库的固定起正反馈效应,而有机肥配施氮肥土壤碳氮的更新相对滞后。

Effects of Plastic Film Mulching and Fertilization on the Sequestration of Carbon and Nitrogen from Straw in Soil

【Objective】Crop straws not only contain high content of organic carbon (C), but also are rich in mineral nutrients. Straw returning to field is an important technique for improvement of soil fertility and sustainable development of agriculture in the region of Black Soil in Northeast China. However, the sequestration and characteristics of C and nitrogen (N) from straw in soil under different plastic film mulching and fertilization treatments were not clear. In this study, the contributions of straw C to soil organic C (SOC) and straw N to soil total nitrogen (TN) were quantified to compare the differences of straw C and N in soil among different mulching and fertilization treatments, so as to provide a basis for improvement of soil fertility and protection of Black Soil in Northeast China.【Method】Based on a long-term mulching and fertilization experiment, the ¹³C¹⁵N double-labeled straw was added to the topsoil (0-20 cm) from the different fertilization treatments, including no fertilization (CK), chemical N fertilizer application (N₄), and organic manure combined with chemical N fertilizer (M₂N₂), with/without mulching, and then which were incubated in-situ in the field for 150 days. The contents of SOC and TN and the values of δ¹³C and δ ¹⁵N were measured to analyze the dynamics changes of SOC derived from straw C (¹³C-SOC), TN derived from straw N (¹⁵N-TN) and their ratio with time.【Result】Fertilization, mulching and their interactions significantly influenced the contents of ¹³C-SOC and ¹⁵N-TN (P<0.05). During the whole incubation period, the contribution percentage of¹³C-SOC to SOC (¹³C-SOC/SOC) and that of ¹⁵N-TN to TN (¹⁵N-TN/TN) were 10.48% and 3.18% under M₂N₂ treatment, respectively; the¹³C-SOC/SOC and residual percentage of straw C in soil under fertilization (N₄ and M₂N₂) treatments were on average 12.65% and 37.14% under mulching, and averaged 12.08% and 34.50% under no mulching, respectively. On the 150^th day of incubation under the same cultivation mode, the ¹³C-SOC/SOC and residual percentage of straw C in soil were on average 14.33% and 39.40% under N₄ treatment and averaged 11.77% and 33.21% in the other fertilization treatments, respectively;¹⁵N-TN/TN under CK treatment was with an average of 4.56%, and was 26.00% and 44.53% higher than that in N₄ and M₂N₂ treatments. The residual percentage of straw N was the highest under CK treatment with/without mulching, with an average of 10.03%, which was the lowest under N₄ treatment without mulching, with a value of 7.87% on the 150^th day of incubation. Regardless of mulching or not, the ratio of ¹³C-SOC to ¹⁵N-TN ranged from 32 to 39 in N₄ treatment, but was lower than 30 in the other fertilization treatments. 【Conclusion】The sequestrations of straw C and N in soil were sensitive to mulching and fertilization. The single application of chemical N fertilizer promoted the accumulation of straw C and the renewal of organic C in soil, and the long-term no fertilization played a positive feedback effect on the sequestration of straw N in soil N pool, while the renewal of soil organic C and N in organic manure combined with chemical N fertilizer lagged behind that in the other fertilization treatments.