陈仕林 蒙炎成 胡钧铭 俞月凤 李婷婷 张俊辉 陈渊 韦本辉 韦翔华
摘要:【目的】研究免耕保護性耕作下秸秆覆盖对蔗田土壤有机碳与CO2排放的影响,为旱地蔗田土壤有机碳库调控管理提供科学依据。【方法】2018—2019年以秸秆覆盖第2年宿根蔗田为研究对象,设粉垄免耕宿根蔗秸秆覆盖(SR1)、粉垄免耕宿根蔗无秸秆覆盖(SR2)、常规免耕宿根蔗秸秆覆盖(CT1)和常规免耕宿根蔗无秸秆覆盖(CT2)4种处理,在甘蔗分蘖期、伸长期和成熟期采集0~15和15~30 cm土层土壤样品,分析土壤总有机碳、土壤易氧化有机碳、土壤微生物量碳及CO2排放通量,并计算蔗田土壤碳库管理指数(CPMI)。【结果】秸秆覆盖提高了免耕蔗田土壤总有机碳含量,甘蔗收获后0~15和15~30 cm土层土壤总有机碳含量SR1处理较SR2处理分别提高33.60%和22.08%,CT1处理较CT2处理分别提高18.13%和42.22%。秸秆覆盖增加了免耕蔗田土壤易氧化有机碳含量,甘蔗收获后SR1处理0~15和15~30 cm土层土壤易氧化有机碳含量较SR2处理分别提高11.86%和37.78%,CT1处理较CT2处理分别提高54.84%和31.03%。秸秆覆盖提高了粉垄免耕蔗田土壤微生物量碳含量,甘蔗收获后SR1处理0~15和15~30 cm土层土壤微生物量碳含量较SR2处理分别提高83.21%和126.43%。秸秆覆盖改变了免耕蔗田CO2排放通量,SR1处理CO2排放峰值较SR2处理提高26.26%,CT1处理较CT2处理提高79.18%。粉垄免耕提高了蔗田CO2排放通量,粉垄免耕CO2排放峰值是常规免耕的1.66~2.35倍。秸秆覆盖提高了蔗田土壤碳库管理指数,0~15和15~30 cm土层碳库管理指数SR1处理较SR2处理分别提高16.99%和55.90%,CT1处理较CT2处理分别提高29.50%和28.53%;秸秆覆盖下,粉垄免耕0~15和15~30 cm土层碳库管理指数较常规免耕分别提高67.58%和102.54%。【结论】秸秆覆盖提高了粉垄免耕蔗田土壤总有机碳、易氧化有机碳和微生物量碳及碳库管理指数。该模式可作为旱地蔗田土壤有机碳库调控的一种重要手段。
关键词: 保护性耕作;免耕;秸秆覆盖;土壤有机碳库;蔗田
中图分类号: S566.1;S156.92 文献标志码: A 文章编号:2095-1191(2021)02-0307-10
Abstract:【Objective】In order to study the effects of straw mulching under no-tillage conservation tillage on the chara-cteristics of soil organic carbon and CO2 emissions in sugarcane fields, and provide scientific basis for the regulation and management of soil organic carbon pool in dryland sugarcane fields. 【Method】From 2018 to 2019, the second year of continuous straw mulching was used as the research object of ratoon sugarcane fields, with smash ridging no-tillage ratoon sugarcane straw mulching(SR1), smash ridging no-tillage ratoon sugarcane straw mulching(SR2), and conventional no-tillage ratoon cane straw mulching(CT1) and conventional no-tillage ratoon cane without straw mulching(CT2) four treatments. Soil samples of 0-15 cm and 15-30 cm soil layers were collected during the sugarcane tillering, elongation and maturity periods. Total organic carbon, easily oxidizable organic carbon, microbial biomass carbon and CO2 emission flux were analyzed, and the sugarcane soil carbon pool management index(CPMI) was calculated. 【Result】Straw mul-ching increased the total organic carbon content of no-tillage sugarcane fields. After sugarcane harvest, the soil total organic carbon of 0-15 cm and 15-30 cm soil layer was increased by 33.60% and 22.08% in SR1 treatment compared with SR2 treatment, respectively. Compared with CT2 treatment, soil layers of 0-15 cm and 15-30 cm in CT1 treatment increased by 18.13% and 42.22% respectively. Straw mulching increased the oxidizable organic carbon content of the soil in no-tilla-ge sugarcane fields. After sugarcane harvest, SR1 treatment increased the oxidizable organic carbon content of 0-15 cm and 15-30 cm soil layers by 11.86% and 37.78% respectively compared with SR2 treatment. The content of oxidizable organic carbon in 0-15 cm and 15-30 cm soil layers in CT1 treatment increased by 54.84% and 31.03% respectively compared with CT2 treatment. Straw mulching increased the soil microbial biomass carbon content in smash ridging no-tillage sugarcane fields. After sugarcane harvest, SR1 treatment increased by 83.21% and 126.43% of soil microbial biomass carbon content in 0-15 cm and 15-30 cm soil layers compared with SR2 treatment, respectively. Straw mulching changed the CO2 emission flux of no-tillage sugarcane fields. The peak CO2 emissions of SR1 treatment increased by 26.26% compared with SR2 treatment. Compared with CT2 treatment, CT1 treatment increased by 79.18%. Smash ridging no-tillage improved the CO2 emission flux of sugarcane fields. The peak CO2 emission of Fenlong no-tillage was as 1.66-2.35 times as that of conventional no-tillage. Straw mulching improved the soil carbon pool management index of sugarcane fields. The carbon pool management index of 0-15 cm and 15-30 cm soil layers in SR1 treatment increased by 16.99% and 55.90% compared with SR2 treatment, respectively. Compared with CT2 treatment, CT1 treatment increased by 29.50% and 28.53%, respectively. Under the straw mulching, the carbon pool management index of the 0-15 cm and 15-30 cm soil layers of the smash ridging no-tillage soil layer increased by 67.58% and 102.54% respectively compared with the conventional no-tillage. 【Conclusion】Straw mulching can increase soil total organic carbon, oxidizable organic carbon, microbial biomass carbon content and soil carbon pool management index in smash ridging no-tillage sugarcane fields. This model can be used as an important means to regulate the characteristics of soil organic carbon pool in dryland sugarcane field.
Key words: conservation tillage; no-tillage; straw mulching; soil organic carbon pool; sugarcane field
Foundation item: Project of the Ten,Hundred and Thousand Talent of the New Century in Guangxi(2018221);Guangxi Innovation Driven Key Project(Guike AA17204037-3); Innovation Team Project of Guangxi Academy of Agricultural Sciences(Guinongke 2018YT08, Guinongke 2021YT040)
0 引言
【研究意义】广西是我国甘蔗主产区之一,甘蔗产量高低及品质优劣对平衡甘蔗市场供应意义巨大(李杨瑞和杨丽涛,2009)。但亚热带红壤山区季节性干旱、土壤贫瘠、生产条件落后等因素严重制约了广西的甘蔗生产(李炳杨,2018;杨星星等,2020)。土壤总有机碳作为土壤的重要组成部分,是衡量土壤肥力高低的重要指标之一(郑梓萱和曾辰,2017),其微小变化可能影响土壤CO2的排放(陈朝等,2011;黄涛等,2013)。传统翻耕频繁扰动土壤结构,易造成水土流失,改变土壤碳库及养分分布(胡钧铭等,2018a)。合理的农田管理措施对调控土壤碳库和温室气体排放具有积极作用(Chplot et al.,2015;Gao et al.,2015;Garcia-Franco et al.,2015)。农业生产上通过免少耕或地表覆盖等保护性耕作减少土壤侵蚀,有利于农业可持续生产(田慎重等,2010)。因此,研究秸秆覆盖下保护性耕作对蔗田土壤有机碳库的影响,对改善蔗田土壤有机碳库管理具有重要意义。【前人研究进展】秸秆还田既可解决秸秆废弃物资源化利用难题,又可改善土壤有机碳活性和微生物多样性,增加土壤有机质(刘定辉等,2008;崔凤娟等,2012),已被广泛应用于农业生产中(吕凯等,2019)。卜玉山等(2010)在春玉米和春小麦上的研究认为,秸秆覆盖后,农田土壤温度下降且水分不易流失,是提高土壤总有机碳含量的重要原因。李蓉蓉等(2017)在黄土高原旱塬区的研究表明,秸秆覆盖显著增加麦田0~10和10~20 cm耕作层土壤总有机碳及微生物量碳含量。王改玲等(2017)研究表明,秸秆覆盖可提高土壤碳库管理指数,是改善土壤碳库的主要途径之一。叶新新等(2019)研究发现,秸秆还田后腐解产生的有机质被土壤微生物分解、吸收,微生物大量繁殖,对土壤微生物量碳含量提高效果明显。王旭东等(2020)通过Meta-analysis法研究发现,经过秸秆覆盖后,土壤环境得到改善,土壤总有机碳含量显著增加,增幅可达7.7%~14.6%。皇甫呈惠等(2020)通过长期定位试验发现,秸秆还田与氮肥协同作用可显著提高土壤总有机碳含量和易氧化有机碳含量。刘颖颖等(2020)研究认为,秸秆与紫云英协同还田改变了土壤养分供给,对稻田土壤总有机碳的提高效果优于秸秆单独还田。【本研究切入点】近年来,粉垄深旋耕技术在甘蔗生产上得到较广泛的应用(韦本辉等,2011),粉垄深旋耕可打破犁底层,适于提高旱地土壤蓄水(李华等,2013;李轶冰等,2013)。但目前有关秸秆覆盖下粉垄耕作对红壤黏土蔗田土壤有机碳库影响的研究鲜见报道。【拟解决的关键问题】以粉垄耕作秸秆覆盖第2年宿根蔗田为研究对象,通过对宿根蔗田不同时期土壤总有机碳含量、土壤易氧化有机碳含量、土壤微生物量碳含量、CO2排放及耕层土壤碳库管理指数变化的深入研究,科学评估秸秆覆盖对粉壟蔗田土壤有机碳的影响,为旱地蔗田土壤有机碳库调控管理提供科学依据。
1 材料与方法
1. 1 试验材料
供试甘蔗品种为桂糖42号。供试秸秆为豆科秸秆(干基含N 1.63%、P 0.17%、K 1.86%),由广西农业科学院经济作物研究所提供。试验选用豆科秸秆而未采用蔗叶还田,是因为豆科绿肥和豆科作物秸秆易于腐解,便于直接覆盖还田(胡钧铭等,2018b),而蔗叶还田操作难度大,且蔗叶表面具有蜡质,腐解缓慢,难以大面积实施应用(樊保宁等,2020)。
1. 2 试验方法
试验于2018—2019年在广西南宁隆安县那桐镇进行。试验新植蔗田设粉垄耕作和常规耕作(对照)2种耕作方式,每种耕作方式设秸秆覆盖和无秸秆覆盖2种处理,共4个处理(表1)。每处理3重复,每处理小区面积148.5 m2。粉垄耕作2018年3月15日采用粉垄深旋耕机(五丰1SGL-200)进行耕作,深度40 cm;常规耕作采用拖拉机旋耕20 cm犁田整地。新植蔗于2018年3月30日下种,行距80 cm,2019年1—2月采收。新植蔗采收后,利用田间蔗蔸进行宿根蔗生产,追踪研究秸秆覆盖对粉垄蔗田土壤有机碳影响的各项指标。甘蔗生长季施用三元复合肥(氮∶磷∶钾=16∶16∶16),施肥量2250 kg/ha,甘蔗种植前期(耕作时同步施肥)底肥占70%,后期(苗期和伸长期)追施占30%。豆科秸秆于宿根蔗苗期按2252 kg/ha用量覆盖于甘蔗行间近根部30 cm处。宿根蔗于2019年12月采收。田间管理按广西双高甘蔗生产规范进行。
在宿根蔗分蘖期、伸长期和成熟期采用S形多点法采集0~15和15~30 cm土层土壤样品。在甘蔗全生育关键期进行气体采集,采样时间分别为5、6、8、9、10和12月,每月进行2次气体取样,取样时间间隔1 d,共采样12次,采样时间为9:00—11:00,采样前后记录气箱内温度。每个采样点在盖胶塞后用50 mL注射器采样,共采样4次,每次采样间隔10 min。每次试验3次重复。
1. 3 测定项目及方法
土壤总有机碳含量采用重铬酸钾氧化—外加热法测定(鲍士旦,2000),土壤易氧化有机碳含量采用KMnO4氧化法测定(张仕吉等,2016),土壤微生物量碳含量采用氯仿熏蒸—K2SO4提取法测定(林先贵,2010)。蔗田温室气体CO2排放通量采用分离式静态箱—气相色谱法测定(郑佳舜等,2019),碳库管理指数等相关指标的计算(徐明岗等,2006)如下:
1. 4 统计分析
试验数据采用Excel 2010进行整理并制图,以SPSS 19.0进行单因素方差分析(LSD)和Duncans多重检验。
2 结果与分析
2. 1 秸秆覆盖对粉垄蔗田土壤总有机碳的影响
由图1可看出,在甘蔗生育期中,除分蘖期SR1处理,成熟期SR2和CT1处理外,其余各处理0~15 cm土层土壤总有机碳含量均高于15~30 cm土层。分蘖期SR1和CT2处理、伸长期SR1处理、成熟期CT2处理的土壤总有机碳含量在0~15和15~30 cm土层间差异显著(P<0.05,下同)。
在0~15 cm土層土壤中,同种耕作模式下,除伸长期常规免耕处理外,其余各处理土壤总有机碳含量表现为秸秆覆盖处理显著高于无秸秆覆盖处理。在甘蔗成熟期,秸秆覆盖显著提高了免耕宿根蔗田土壤总有机碳含量,SR1-1处理较SR2-1处理提高33.60%,CT1-1处理较CT2-1处理提高18.13%。秸秆覆盖条件下,蔗田土壤总有机碳含量表现为粉垄免耕显著高于常规免耕,在分蘖期、伸长期和成熟期,SR1-1处理土壤总有机碳含量分别为18.93、18.51和18.45 g/kg,较CT1-1处理分别提高50.36%、62.94%和36.16%。
在15~30 cm土层土壤中,同种耕作模式下,除伸长期常规免耕处理外,其余各处理土壤总有机碳含量表现为秸秆覆盖显著高于无秸秆覆盖。在甘蔗成熟期,秸秆覆盖显著提高了粉垄免耕宿根蔗田土壤总有机碳含量,SR1-2处理较SR2-2处理提高22.08%,CT1-2处理较CT2-2处理提高42.22%。秸秆覆盖条件下,蔗田土壤总有机碳含量表现为粉垄免耕宿根蔗田显著高于常规免耕。在分蘖期、伸长期和成熟期,SR1-2处理土壤总有机碳含量分别为20.00、17.01和17.97 g/kg,较CT1-2处理分别提高66.67%、60.32%和30.12%。可见,秸秆覆盖或粉垄免耕均能有效提高蔗田土壤总有机碳含量。
2. 2 秸秆覆盖对粉垄蔗田土壤易氧化有机碳的影响
由图2可看出,在甘蔗生育期中,除分蘖期SR1和CT1处理外,其余各处理0~15 cm土层土壤易氧化有机碳含量均高于15~30 cm土层。除分蘖期SR1和成熟期SR2处理外,其余各处理的土壤易氧化有机碳含量在0~15和15~30 cm土层间差异不显著(P>0.05,下同)。
在0~15 cm土层土壤中,同种耕作模式下,在分蘖期和伸长期,秸秆覆盖处理土壤易氧化有机碳含量高于无秸秆覆盖处理,但差异不显著。在甘蔗成熟期,秸秆覆盖提高了免耕宿根蔗田土壤易氧化有机碳含量,SR1-1处理较SR2-1处理提高11.86%,CT1-1处理较CT2-1处理提高54.84%。秸秆覆盖条件下,在分蘖期和成熟期,蔗田土壤易氧化有机碳含量表现为粉垄免耕显著高于常规免耕。在分蘖期、伸长期和成熟期,SR1-1处理土壤易氧化有机碳含量分别为0.39、0.52和0.66 g/kg,较CT1-1处理分别提高160.00%、20.93%和37.50%。
在15~30 cm土层土壤中,同种耕作模式下,秸秆覆盖处理土壤易氧化有机碳含量高于无秸秆覆盖处理,且在分蘖期和成熟期,SR1-2处理土壤易氧化有机碳含量显著高于SR2-2处理。在甘蔗成熟期,秸秆覆盖提高了免耕宿根蔗田土壤易氧化有机碳含量,SR1-2处理较SR2-2处理提高37.78%,CT1-2处理较CT2-2处理提高31.03%。秸秆覆盖条件下,在分蘖期和成熟期,蔗田土壤易氧化有机碳含量表现为粉垄免耕显著高于常规免耕。在分蘖期、伸长期和成熟期,SR1-2处理土壤易氧化有机碳含量分别为0.55、0.48和0.62 g/kg,较CT1-2处理分别提高243.75%、11.63%和63.16%。可见,粉垄免耕和秸秆覆盖均能显著提高蔗田土壤易氧化有机碳含量。
2. 3 秸秆覆盖对粉垄蔗田土壤微生物量碳的影响
由图3可看出,在甘蔗各生育期中,除伸长期SR1、SR2和CT1处理及成熟期CT2处理外,其余处理0~15 cm土层土壤微生物量碳含量均高于15~30 cm土层,且各处理在0~15和15~30 cm土层间差异不显著。
在0~15 cm土层土壤中,同种耕作模式下,除伸长期常规免耕处理外,秸秆覆盖处理土壤微生物量碳含量均高于无秸秆覆盖处理。在甘蔗成熟期,秸秆覆盖提高了免耕宿根蔗田土壤微生物量碳含量,SR1-1处理较SR2-1处理提高83.21%,CT1-1处理较CT2-1处理提高10.27%。秸秆覆盖条件下,除分蘖期外,蔗田土壤微生物量碳含量均表现为粉垄免耕显著高于常规免耕,伸长期和成熟期SR1-1处理土壤微生物量碳含量分别为284.25和409.13 mg/kg,较CT1-1处理分别提高146.36%和150.06%。
在15~30 cm土层土壤中,同种耕作模式下,除成熟期CT2处理外,秸秆覆盖处理的土壤微生物量碳含量均高于无秸秆覆盖处理。在甘蔗成熟期,秸秆覆盖提高了粉垄免耕宿根蔗田土壤微生物量碳含量,SR1-2处理较SR2-2处理提高126.43%。秸秆覆盖条件下,除分蘖期外,蔗田土壤微生物量碳含量表现为粉垄免耕显著高于常规免耕。在伸长期和成熟期SR1-2处理土壤微生物量碳含量分别为358.81和327.82 mg/kg,较CT1-2处理分别提高128.88%和112.98%。可见,秸秆覆盖或粉垄免耕均能显著提高蔗田土壤微生物量碳含量。
2. 4 秸秆覆盖对粉垄蔗田CO2排放的影响
从图4可看出,在甘蔗整个生育期内,不同处理CO2排放通量表现为SR1>SR2>CT1>CT2。2019年5—12月SR2和CT1处理蔗田土壤CO2排放通量变化趋势基本一致,SR1、SR2和CT1处理蔗田土壤CO2排放通量随甘蔗生长发育呈先增大后减小的变化趋势,CT2处理则相反。甘蔗苗期和分蘖期土壤CO2缓慢排放,进入伸长期CO2排放通量大幅增长,且达到峰值,然后进入成熟期,排放通量开始下降。同种耕作模式下,排放通量峰值表现为SR1>SR2,CT1>CT2,SR1处理较SR2处理提高26.26%,CT1处理较CT2处理提高79.18%,表明秸秆覆盖能促进蔗田CO2排放。同种覆盖处理下,不同耕作模式CO2排放通量表现为SR1>CT1,SR2>CT2,即粉垄免耕CO2排放通量高于常规免耕,粉垄免耕CO2排放峰值是常规免耕处理的1.66~2.35倍。
2. 5 秸秆覆盖对粉垄蔗田土壤碳库管理指数的影响
甘蔗不同生育时期4个处理中,以CT2为参照土壤,根据土壤碳库管理指数(CPMI)方法可得到SR1、SR2和CT1各层土壤的碳库管理指数(表2)。由表2可知,在甘蔗分蘖期、伸长期和成熟期,不同处理各土层碳库指数(CPI)均表现为SR1>SR2>CT1>CT2;0~30 cm土层土壤碳库指数平均值总体也表现为SR1>SR2>CT1>CT2。
甘蔗不同生育期中,除伸长期15~30 cm土层土壤碳库管理指数表现为SR1>CT1>SR2>CT2外,其余各处理均表现为SR1>SR2>CT1>CT2。0~30 cm土层土壤碳库管理指数平均值表现为SR1>SR2>CT1>CT2,表明秸秆覆盖提高了土壤碳库管理指数。同种耕作模式下,0~15和15~30 cm土层碳库管理指数SR1处理较SR2处理分别提高16.99%和55.90%,CT1处理较CT2处理分别提高29.50%和28.53%。秸秆覆盖下,粉垄免耕0~15和15~30 cm土层碳库管理指数较常规免耕分别提高67.58%和102.54%。可见,秸秆覆盖是改善粉垄免耕蔗田土壤质量的主要手段。
3 讨论
作物根系在土层的空间布局影响土壤有机碳的积累,如深松耕作促使玉米根系主要分布于20 cm土层以下(张丽等,2015;Liu et al.,2015),而秸秆覆盖后,秸秆可被微生物腐解,能提高土壤总有机碳含量,促进土壤有机质积累(严昌荣等,2010;杨晶等,2010;关振寰等,2014)。土壤总有机碳变化主要发生在0~30 cm土层,且在0~10 cm耕作层中变化更明显(Doran et al.,1998;Mikhailova et al.,2000)。本研究结果表明,秸秆覆盖或粉垄免耕保护性耕作均能有效增加蔗田土壤总有机碳含量,且秸秆覆盖和粉垄免耕同步实施对蔗田土壤总有机碳含量提高效果最佳。其原因可能是频繁的土壤耕作易破坏土壤结构,加快土壤有机质分解,不利于土壤总有机碳积累(Chen et al.,2016),但合理的保护性耕作有助于改变养分在耕层的分布(蒋发辉等,2020),且秸秆中碳元素分解与转化是土壤总有机碳的重要来源,合理耕作配合秸秆还田对提升土壤地力有积极作用(Paustian et al.,1997;董珊珊和窦森,2017;闫洪奎和王欣然,2017;田慎重等,2020)。
土壤易氧化有机碳是考察土壤质量优劣的重要指标之一,受田间管理措施的改变较敏感(Chen et al.,2009)。土壤微生物量碳是土壤中最活躍的因子,易受到耕作方式的影响(陶水龙等,1998;Doran et al.,1998),频繁耕作会扰乱土层结构,不利于土壤微生物量碳积累(Nelson et al.,2006)。免少耕等保护性耕作能增加土壤肥力,提高土壤有机质含量,利于土壤蓄水保墒及土壤环境的改善(王长生等,2004)。本研究结果表明,秸秆覆盖与粉垄免耕保护性耕作同步实施提高了土壤易氧化有机碳含量和土壤微生物量碳含量。其原因可能是因为试验地为蔗田土壤粉垄耕作后的第2年,免耕保护性耕作对土层结构扰动较小,促进了土壤团粒结构的稳定,为土壤微生物活动提供了适宜的环境条件(崔凤娟等,2012;哈斯格日乐等,2019),土壤微生物活动频繁,降解土壤动植物残体加快,进而提升了土壤有机碳及微生物量碳含量(隋跃宇等,2009);秸秆还田经腐解后,转化为外源有机物料进入土壤被微生物吸收和利用,微生物繁殖加快,促使有机质向土壤活性碳库输入(田慎重等,2010;张英英等,2017),也有助于提高土壤易氧化有机碳含量和微生物量碳含量。本研究还发现,土壤微生物量碳含量在甘蔗分蘖期至成熟期随生育期推移而波动,在甘蔗成熟期最高,该变化动态与李云玲等(2004)在玉米地上的研究结果一致,分析其原因,可能与甘蔗分蘖期和伸长期生长旺盛,对土壤养分需求增多有关。环境的改变使植物与土壤微生物养分竞争加剧,更多营养物质被植物吸收,导致土壤微生物量碳含量下降(江淼华等,2018)。
耕作和秸秆覆盖是影响农田温室气体排放的重要管理措施(Pandey et al.,2012)。Busari等(2015)研究发现,免耕等保护性耕作可改变土壤物理、化学和生物等性质,对减少CO2排放有积极作用(张国和王效科,2020)。但本研究发现,粉垄免耕与秸秆覆盖同步实施增加了土壤CO2排放。其原因可能是粉垄耕作打破了犁底层,使土壤变得疏松透气,微生物活动频繁,促进了CO2排放(Wei et al.,2017);此外,土壤有机质分解、植物残体腐解和植物根系呼吸等因素也会影响土壤CO2排放(Oorts et al.,2007),秸秆的腐解加速了微生物对有机质的分解和转化,进而增加了CO2排放通量(Bavin et al.,2009;贺京等,2011)。土壤碳库管理指数是反映农田管理对土壤养分和碳库动态变化影响的重要指标(张国盛和黄高宝,2005)。碳库管理指数升高可促进土壤腐殖质的形成和土壤环境的改善(范如芹等,2010),碳库指数降低则土壤肥力下降,土壤性质恶化(郭宝华等,2014)。本研究结果表明,秸秆覆盖与粉垄免耕保护性耕作同步实施可有效提高土壤碳库管理指数,与陈尚洪等(2008)、展茗等(2009)在稻田上的研究结果一致。原因可能在于保护性耕作可降低土壤紧实度,提高土壤有机碳活性(张霞等,2018)。同时,秸秆在高温高湿环境下易分解,利于土壤微生物数量和微生物活度上升,进而促进土壤活性碳库的积累(蔡太义等,2011)。
4 结论
秸秆覆盖对粉垄免耕蔗田土壤质量改善有一定的积极作用,可提高土壤总有机碳、易氧化有机碳和微生物量碳及碳库管理指数,但同时提高了CO2排放通量。该模式可作为旱地蔗田土壤有机碳库调控的一种重要手段。
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(責任编辑 王 晖)