浅埋滴灌下玉米秸秆不同还田年限土壤有机碳固存特征及其影响因素

Characteristics and influencing factors of soil organic carbon sequestration for different maize straw returning years under shallow buried drip irrigation

外源有机物(秸秆)添加直接影响耕层土壤有机碳的周转,研究浅埋滴灌条件下玉米秸秆持续还田土壤有机碳固存及其影响因素对西辽河平原灌区玉米可持续生产与耕地地力提升具有重要意义。本文基于连续7年的田间定位试验,设置玉米连作秸秆连年全量还田0年(0a)、3年(3a)、5年(5a)和7年(7a)4个处理,探讨玉米秸秆不同还田年限对土壤结构、胞外酶活性、有机碳组分含量、碳储量、固碳量和碳库管理指数的影响。与0a处理相比,0~30 cm土层3a、5a和7a广义土壤结构指数分别增加1.65%、1.99%和3.33%,土壤三相结构距离分别降低5.55%、6.65%和12.7%;0~30 cm土层3a、5a和7a土壤β-1,4-N-乙酰氨基葡萄糖苷酶和土壤β-葡萄糖苷酶活性分别提高4.34%、13.0%、15.9%和12.1%、16.3%、20.9%,土壤纤维素酶和土壤蔗糖酶活性分别提高5.86%、13.4%、19.2%和12.6%、21.3%、34.1%;不同处理间几何平均酶活性和总体酶活性差异显著,0~30 cm土层3a、5a和7a几何平均酶活性和总体酶活性较0a分别提高8.63%、15.90%、22.25%和9.12%、17.19%、25.09%。土壤有机碳、易氧化有机碳、水溶性有机碳和微生物量碳含量及其储量均表现为3a、5a和7a显著高于0a,0~30 cm土层3a、5a和7a土壤有机碳和土壤易氧化有机碳含量较0a分别提高13.4%、32.7%、42.7%和17.5%、27.5%、42.5%,土壤水溶性有机碳和土壤微生物量碳含量较0a分别提高13.2%、18.5%、28.5%和33.9%、45.3%、56.1%;同时0~30 cm土层3a、5a和7a土壤有机碳和易氧化有机碳储量分别提高11.6%、29.5%、36.2%和14.9%、23.8%、35.5%,土壤水溶性有机碳和微生物量碳储量分别提高10.7%、15.2%、22.3%和31.0%、41.0%、48.5%。0~30 cm土层5a和7a土壤固碳量均显著高于3a;0~30 cm土层各处理碳库指数和碳库管理指数差异显著,5a和7a较3a分别提高17.0%、26.1%和7.00%、19.9%。土壤结构稳定性、胞外酶活性与土壤固碳量和碳库管理指数的相关分析和冗余分析结果表明,土壤β-1,4-N-乙酰氨基葡萄糖苷酶活性、液相体积分数、三相结构距离、纤维素酶活性和β-葡萄糖苷酶活性是影响玉米秸秆不同还田年限土壤有机碳固存的主要因素,其解释率分别为76.0%、4.10%、3.30%、1.70%和3.40%。浅埋滴灌下玉米秸秆连续还田7年改善了土壤结构的稳定性,提高了与土壤碳素相关的土壤胞外酶活性,进而提升了土壤有机碳固存和碳库指数。

The addition of exogenous organic matter(straw)directly affects the turnover of organic carbon in the topsoil,and soil organic carbon sequestration and influencing factors of continuous return of maize straw under shallow buried drip irrigation is of great significance for the sustainable production of maize and the improvement of farmland fertility in the irrigation area of the Xiliaohe Plain.The study spanned seven consecutive years of field positioning experiments,during which we assessed 0(0a),3(3a),5(5a),and 7 years(7a)of the full return of straw to examine the effects of the number of straw returning years on soil structure,extracellular enzyme activity,and carbon component content,storage,sequestration,and pool management indices.Compared with 0a treatment,the generalized soil structure index in the 0−30 cm soil layer of 3a,5a and 7a treatments increased by 1.65%,1.99%and 3.33%,respectively,and there were corresponding reductions of 5.55%,6.65%and 12.7%,respectively,in the soil three-phase structure distance.Furthermore,the activities ofβ-1,4-N-acetylglucosaminidase andβ-glucosidase in the 0–30 cm soil layer of 3a,5a and 7a treatments increased by 4.34%,13.0%,15.9%and 12.1%,16.3%,20.9%,respectively,and similarly,the activities of cellulase and sucrase in the 0−30 cm soil layer of 3a,5a and 7a treatments increased by 5.86%,13.4%,19.2%and 12.6%,21.3%,34.1%,respectively.We also detected significant differences in the geometric mean enzyme activity and total enzyme activity in response to different treatments,and the geometric average enzyme activity and total enzyme activity recorded in the 0−30 cm soil layer of 3a,5a and 7a treatments,which increased by 8.63%,15.90%,22.25%and 9.12%,17.19%,25.09%,respectively.In addition,we found that the content and storage of soil organic carbon,easily oxidized organic carbon,water-soluble organic carbon,and microbial biomass carbon in 3a,5a and 7a treatments were all significantly higher than the corresponding values measured in 0a treatments,with the content of soil organic carbon and easily oxidized organic carbon in the 0−30 cm soil layer of 3a,5a and 7a treatments increasing by 13.4%,32.7%,42.7%and 17.5%,27.5%,42.5%,respectively,and the content of the soil water-soluble organic carbon and microbial biomass carbon increased by 13.2%,18.5%,28.5%and 33.9%,45.3%,56.1%,respectively,Similarly,the storage of soil organic carbon and easily oxidized organic carbon in the 0–30 cm soil layer of 3a,5a and 7a treatments were found to have increased by 11.6%,29.5%,36.2%and 14.9%,23.8%,35.5%,respectively,and the storage of water-soluble organic carbon and microbial biomass carbon had increased by 10.7%,15.2%,22.3%and 31.0%,41.0%,48.5%,respectively.Compared with 3a treatment,we detected significantly higher soil carbon sequestration in the 0–30 cm soil layer of 5a and 7a treatments.Moreover,compared with 3a treatment,there were significant differences in the carbon pool index and carbon pool management index obtained for the 0–30 cm soil layer,with the carbon pool index for 5a and 7a treatments increasing by 17.0%,26.1%and 7.00%,19.9%,respectively.Redundancy and correlation analyses of influencing factors and soil organic carbon sequestration revealed that the soilβ-1,4-N-acetylglucosaminidase activity,liquid volume fraction,soil three-phase structure distance,soil cellulase activity,and soilβ-glucosidase activity were the main factors influencing soil organic carbon sequestration during different straw returning years,with explanatory rates of 76.0%,4.10%,3.30%,1.70%and 3.40%,respectively.Under shallow buried drip irrigation,the continuous return of maize straw over 7 years was found to improve the stability of the soil structure and activity of soil carbon-related extracellular enzymes,and promoted the decomposition and transformation of returned straw by soil microorganisms,thereby enhancing soil organic carbon sequestration and the carbon pool index.