耕作方式对华北农田土壤固碳效应的影响

研究不同耕作方式对华北农田土壤固碳及碳库管理指数的影响,可为探寻有利于农田固碳的耕作方式提供科学依据。该研究在中国农业大学吴桥实验站进行,试验于2008年设置了免耕秸秆不还田(NT0)、翻耕秸秆不还田(CT0)、免耕秸秆还田(NT)、翻耕秸秆还田(CT)和旋耕秸秆还田(RT)5个处理。研究测定分析了土壤容重、有机碳、易氧化有机碳含量及不同耕作方式下的碳库管理指数。通过对不同耕作方式下0～110cm土壤的分析,结果表明,随着土层的加深,土壤有机碳含量不断下降,NT显著增加了表层(0～10cm)土壤有机碳含量,而>10～50cm有机碳含量较其他处理(NT0除外)有所下降,深层(>50～110cm)处理间差异不明显;土壤容重与有机碳含量呈显著的负相关关系(P<0.01);0～30cm土层有机碳储量以NT最高,CT与其无明显差异,二者较CT0分别高出13.1%和11.0%,而至0～50cm土层,CT的碳储量最高,但与NT无显著差异(P<0.05);与CT0相比,NT0降低了各层土壤易氧化有机碳含量,而NT则在0～10cm土层表现为增加;RT、CT分别显著增加了0～10、>10～30cm土层的碳库管理指数。结果表明,秸秆还田可改善土壤质量,提高农田碳库管理指数,同时碳库管理指数受耕作方式的影响也较大,尤其是CT和RT;NT通过减少土壤扰动、增加有机质的输入,可提高上层土壤有机碳的储量。     

未来30年川东平行岭谷区县域农田SOC动态模拟

以位于川东平行岭谷的典型县——垫江县为研究对象,探讨在特定气候模式下未来30 a研究区农田土壤有机碳(SOC)及其动态变化,为研究区未来耕地可持续利用与管理提供数据支持和科学依据。利用生物地球化学模型DNDC,选取IPCC AR4报告中的BCCR_BCM 2.0的B1模式,在基于研究区土壤性质和农业管理制度等建立的GIS区域数据库的支持下,模拟研究区2011—2041年SOC动态变化。结果表明:1)DNDC模型能够较好地模拟特定气候条件下SOC及其动态变化,模拟值和观测值的相关系数r为0.981,达到0.01水平下的极显著相关关系;模拟值和观测值的RMSE值为16%,模拟结果较好。2)未来30 a研究区农田0~20 cm土层SOC密度和储量均呈显著增加态势,单位面积碳增量2 637.07~8 091.55 kg(C)·hm~(-2),增幅为10%~34%,新增固碳量2.7×10~5~8.3×10~5 t,年均增速87.9~269.7 kg(C)·hm~(-2)·a~(-1)。3)未来30 a川东平行区县域农田土壤总体呈持续碳增汇状态,研究区固碳、丢碳以及相对平衡三者间的差异将逐渐凸显。     

江苏沿海垦区暗管排水农田轮作对土壤有机碳的影响模拟

针对江苏沿海垦区地势平坦、降雨量大,农业生产易受涝渍灾害影响,而新开垦农田土壤贫瘠、有机质含量极低的问题,该研究基于江苏省东台市内省水科院农田暗管排水试验基地的气象、土壤、作物等数据,联合运用田间水文模型-DRAINMOD和土壤有机碳模型-DNDC（Denitrification-Decomposition Model）,研究了轮作和秸秆还田方式对暗管排水农田土壤有机碳（Soil Organic Carbon,SOC）累积过程的影响。结果显示：对于地下水位埋深较浅的沿海垦区,在DRAINMOD准确预测暗管排水农田地下水位动态的基础上,运用DNDC模型可以更好的预测土壤有机碳的累积过程;以现有土壤有机碳含量（2.95 g/kg）为初始值,DNDC模型32 a长序列模拟发现,冬小麦-玉米轮作配施全量秸秆还田措施效果最佳,可提升耕层土壤有机碳含量至17.85 g/kg;冬小麦-玉米-冬小麦-绿肥（紫花苜蓿）轮作配施全量秸秆还田措施可提升耕层土壤有机碳含量至16.12 g/kg,具有很好的固碳效果。与研究区现有明沟排水系统相比,暗管排水可快速降低地下水位,减少涝渍胁迫,作物产量提升3.9%,耕层固碳速率提升39.39%。暗管排水条件下,湿润年频繁降雨造成了土壤干湿交替变化,由此激发了高强度土壤的呼吸作用,导致了一定程度的SOC损失;建议采用农田控制排水措施来抑制过度排水,减少高强度土壤呼吸对SOC累积过程的不利影响。研究成果可为沿海垦区农田地力提升和农业碳中和提供参考。     

中国东北地区农田生态系统中碳库的分布格局及其变化

本文以中国东北地区为对象,采用针对农业土壤碳库和痕量气体排放估算建立的反硝化分解(DNDC)模型,在建立有关中国东北地区气候、农业土壤和农业生产的分县数据库基础上,估算了中国东北地区农田土壤碳库储量,为1.27(0.92-1.62)GtC(1015g),平均为C63.57thm-2,是全国C平均值45.38thm-2的1.4倍,并发现东北地区农田土壤碳量有较明显的地区差异,东北部较高,西南部较低,从西南向东北方向土壤有机碳含量逐渐增加。经过一年的耕种后,农田土壤碳总的变化量为-22.97(-35.57—-10.37)TgC,变化率为-1.809%,C平均为-1.36thm-2,是全国C平均变化量-0.731thm-2的1.86倍,也有较明显的地区差异,北部减少幅度较大,西南部相对变化不大或有所增加。通过DNDC模型模拟研究发现我国东北地区经过耕种土壤碳损失量为0时,初始土壤有机质含量为18.3gkg-1。这点是土壤碳经过耕种后增加或减少的临界点。并通过情景分析,提出了增加东北地区农田土壤碳储量的措施。     

辽宁省农田土壤有机碳变化的模拟研究

农田土壤长期受到人类干预,与自然土壤相比,其与大气之间的碳交换强度更大。以辽宁省农田生态系统为研究对象,采用生态系统碳循环模型-CENTURY模型模拟辽宁省农田耕层土壤有机碳(0~20 cm)在1951~2005年的动态变化,并以2005年大量样点的分析结果为基础,估算有机碳储量。研究表明:全省2005年农田耕层土壤有机碳密度平均为2.66kg m-2,其中辽东山区辽中南平原区辽西低山丘陵区,全省农田耕层土壤碳储量为112.15 Tg;CENTURY模型模拟的农田土壤有机碳与实测值有较好的一致性。     

长期施肥下石灰性潮土有机碳变化的DNDC模型预测

为探讨长期不同施肥条件下土壤有机碳的变化规律及DNDC模型的应用,利用封丘石灰性潮土不同施肥措施下的长期定位试验数据,选取CK、NPK、1/2NPK+1/2OM、OM4个处理,分析了15年来作物产量及土壤有机碳(SOC)的变化特征,并用DNDC模型预测了试验地近100年(2000~2099)的SOC变化趋势。结果表明,各施肥处理的多年产量平均值和对照处理差异显著;施用化肥(NPK和1/2NPK+1/2OM)处理和有机肥(OM)处理间也有显著差异;产量最高为NPK处理,达10811 kg/ha,CK处理最低,但1/2NPK+1/2OM处理产量与NPK处理无显著性差异。15年来土壤耕层(0—20cm)有机碳平均值,以OM处理最高,达到7.90 g/kg,显著高于1/2NPK+1/2OM、NPK处理;而CK处理仅为4.15 g/kg。从15年来有机碳的变化看出,CK处理略有下降,NPK处理较为平稳,而1/2NPK+1/2OM和OM处理呈现不断上升趋势,OM处理上升幅度较1/2NPK+1/2OM处理大。对试验地SOC变化趋势长期(100a)的模拟结果显示,与初始土壤SOC含量相比,100a后不施肥处理(CK)土壤有机碳含量下降了52%,化肥(NPK)处理土壤SOC含量较为稳定,而1/2NPK+1/2OM处理和OM处理土壤有机碳增加明显,大约25a后基本上稳定,100a后分别较2000年增加了24%和25%。从实测数据的分析和DNDC模型模拟分析可以看出,有机肥和化肥配施能获得较高作物产量,并能有效地增加土壤SOC含量,从而提高土壤的可持续利用能力。     

北方旱区免耕对农田生态系统固碳与碳平衡的影响

农田系统对大气CO2库呈碳汇还是碳源效应取决于土壤有机碳的固定和温室气体释放之间的平衡,而耕作措施会改变土壤有机碳含量和储量,影响农田系统的碳循环与碳平衡。该研究以北方旱区山西临汾20 a长期保护性耕作定位试验为基础,田间原位测定土壤呼吸和土壤有机碳含量,确定各类农业投入碳排放参数,利用碳足迹方法综合分析不同耕作措施(传统耕作CT和免耕NT)下农田生态系统碳平衡。结果表明:在化肥、机械等农业投入产生的间接碳排放量方面,化肥投入碳排放量约占系统农业总投入碳排放量的73.5%~77.4%,是农业投入中主要的碳源。由于免耕减少了翻耕、旋耕和秸秆移除3道程序,NT比CT少排放约5.1%,NT产量显著提高28.9%,且碳生产力大于CT。0~60 cm土壤有机碳储量NT(50.86 Mg/hm2)比CT(46.00 Mg/hm2)高10.5%。与CT相比,在小麦休闲期和生育期NT土壤呼吸CO2释放总量高于CT。但根据农田系统碳平衡公式分析得出,NT更有利于农田生态系统固碳,呈碳汇效应,而CT表现为碳源。因此,长期免耕耕作能够提高农田土壤固碳量,减少大气温室气体排放,对于改善北方旱区土壤碳库和减排效果是一个良好的选择。     

基于贝叶斯推断的DNDC模型参数校正与不确定性评价研究

实现土壤有机碳(SOC)动态模拟结果的不确定性定量评价是农田管理决策成败的关键之一。采用贝叶斯推断和马尔科夫链蒙特卡洛方法(MCMC),对DNDC模型模拟江苏省宜兴市一个具有22年稻-麦轮作历史的田块的SOC动态变化,进行模型参数校正和模拟结果的不确定性定量评价。结果表明,DNDC模型适宜长期监测田块的SOC动态变化的模拟,但模型的模拟结果存在一定的不确定性;在DNDC模型输入参数数据质量不明的情况下,利用贝叶斯推断和MCMC方法能够有效地实现模型输入参数的自动校正和SOC模拟结果不确定性的定量评价,从而为实现区域或国家尺度农田SOC动态模拟的不确定性定量评价提供理论和方法依据。     

不同有机物料还田对华北农田土壤固碳的影响及原因分析

中国农业面临着废弃物数量大、污染严重,农田土壤生产力低的现实问题。该研究以增加农田土壤固碳为目标对砂质农田进行有机物料还田,将秸秆、猪粪、沼渣和生物炭4种物料用尿素调节等氮还田,对农田土壤有机碳、颗粒有机碳、可溶性有机碳和微生物量碳的含量进行测定,并探究不同有机物料还田对土壤有机碳的影响原因。研究结果表明:物料还田3a后,生物炭、猪粪和沼渣处理土壤有机碳(SOC)比秸秆处理分别高262.4%、26.8%和20.7%;2014—2015年生物炭处理的土壤微生物量碳(MBC)较秸秆处理降低2.9%~35.5%,猪粪处理和沼渣处理的土壤可溶性有机碳(DOC)分别提高17.1%~60.1%和7.2%~64.8%;2014—2015年生物炭、猪粪和沼渣处理土壤颗粒有机碳(POC)较秸秆处理提高10.8%~148.2%、9.5%~58.3%和11.3%~57.6%;物料还田后,土壤总有机碳(TOC)和POC呈极显著的回归关系(R2=0.67,P0.001),土壤DOC与MBC有极显著相关性(R2=0.52,P0.001)。与秸秆还田相比,生物炭还田有利于土壤POC的累积进而促进土壤有机碳的提升,猪粪和沼渣则通过提高土壤MBC、DOC和POC的含量,促进土壤有机碳的周转和固定。从农田土壤固碳角度而言,生物炭,猪粪和沼渣还田优于秸秆还田。     

转变耕作方式对长期旋免耕农田土壤有机碳库的影响

土壤深松是解决长期旋免耕农田耕层浅薄化、亚表层（>15～30 cm）容重增加等问题的有效方法之一,而将长期旋免耕农田进行深松必然导致农业生态系统中土壤有机碳（soil organic carbon,SOC）及碳固定速率的变化。因此,为对比将长期旋免耕转变为深松前后农田土壤有机碳库变化,该研究利用连续12a 的旋耕和免耕长期定位试验以及在此基础上连续6 a旋耕-深松和免耕-深松定位试验,对比了转变耕作方式对农田土壤0～30 cm有机碳含量、周年累积速率及其固碳量的影响。研究结果表明,经过连续12 a的旋耕和免耕处理（2002－2014）,2014年免耕处理土壤0～30 cm有机碳储量比试验初期（2002年）提高38%,旋耕处理降低了30%,而对照常规处理无显著差异。免耕处理土壤0～30 cm有机碳储量比旋耕处理高约2.6倍（2014年）。长期免耕显著提高了土壤0～30 cm的有机碳含量,2002~2014年其土壤0～30 cm固碳量为16.69 t/hm2,但长期旋耕导致土壤0～30 cm SOC含量显著降低,表现为土壤有机碳的净损耗,年损耗速率为?0.75 t/hm2。而长期旋耕后进行深松（旋耕-深松处理）6年其土壤0～30 cm的有机碳含量较原旋耕处理提高32%～67%,且显著提高了土壤固碳量及周年累积速率;免耕-深松土壤0～30 cm的有机碳周年累积速率较免耕处理下降了42%。长期旋耕造成有机碳水平下降的条件下,将旋耕处理转变为深松处理在短期内更有利于促进土壤有机碳的积累,而将长期免耕处理转变为深松措施,降低了土壤有机碳的累积速率和固碳量。     

免耕对土壤团聚体特征以及有机碳储量的影响

以实施7年的中国科学院禹城综合试验站冬小麦夏玉米轮作免耕长期定位试验场为对象,研究免耕条件下土壤水稳性团聚体和有机碳储量的变化,为进一步评价免耕措施对黄淮海平原土壤结构和质量的影响提供科学依据。设置免耕(NT)、免耕秸秆不还田(NTRR)、常规耕作(CT)3种处理,分析土壤表层(0~20 cm)及深层(20~60 cm)水稳性团聚体分布特征、土壤有机碳以及团聚体有机碳的变化和相互关系。研究结果表明:由于减少了对土壤的破坏以及增加了秸秆还田和有机肥的施用,与常规耕作相比,NT和NTRR可提高表层土壤有机碳含量和储量、水稳性团聚体平均重量直径(MWD)和几何平均直径(GMD),以及大团聚体有机碳的含量和储量。其中,秸秆覆盖比施用有机肥对表层土壤有机碳储量和0.25~2 mm团聚体有机碳储量的提高具有更显著的作用。与表层不同,深层土壤有机碳和大团聚体有机碳的含量和储量表现为NT相似文献   

耕作与轮作方式对黑土有机碳和全氮储量的影响

土壤有机碳(SOC)及全氮(TN)对土壤肥力、作物产量、农业可持续发展以及全球碳、氮循环等都具有重要影响。为探索不同耕作和轮作方式对耕层黑土SOC和TN储量的影响,本文以吉林省德惠市进行了8 a的田间定位试验中层黑土为研究对象,对免耕、垄作和秋翻三种耕作方式及玉米-大豆轮作和玉米连作两种轮作方式下SOC和TN在各土层的含量变化进行了分析,并采用等质量土壤有机质储量计算方法,对比分析了不同处理对0～30 cm SOC和TN储量的影响。结果表明,与试验开始前相比,玉米-大豆轮作系统中,秋翻下SOC和TN储量均有所降低;免耕显著增加了0～5 cm SOC及TN含量,但SOC在亚表层亏损,导致其储量并未增加;而垄作处理下SOC及TN含量在0～5、5～10 cm的均显著增加,0～30 cm储量亦分别增加了4.9%和10.7%。玉米连作系统的两种耕作处理(免耕和秋翻)下SOC和TN储量均有所增加,且TN储量增幅均高于玉米-大豆轮作系统,其中免耕下TN储量增幅是玉米-大豆轮作的3.2倍。所有处理下C/N均呈降低趋势,其中垄作0～5 cm C/N由12.05降至11.04,降低幅度分别是免耕和秋翻的3.2和2.8倍。综上可知,对质地黏重排水不良的中层黑土,玉米-大豆轮作系统下免耕并不是促进SOC固定的有效形式,而垄作则促进了黑土SOC和TN的积累,这不仅有利于土壤肥力的改善,而且是使农田黑土由CO2"源"变为"汇"的有效形式之一。与玉米-大豆轮作相比,玉米连作下三种耕作方式都有利于SOC和TN积累。     

Soil organic carbon and C abundance as related to tillage, crop residue, and nitrogen fertilization under continuous corn management in Minnesota

Long-term field experiments are among the best means to predict soil management impacts on soil carbon storage. Soil organic carbon (SOC) and natural abundance ¹³C (δ¹³C) were sensitive to tillage, stover harvest, and nitrogen (N) management during 13 years of continuous corn (Zea mays L.), grown on a Haplic Chernozem soil in Minnesota. Contents of SOC in the 0–15 cm layer in the annually-tilled [moldboard (MB) and chisel (CH)] plots decreased slightly with years of corn after a low input mixture of alfalfa (Medicago sativum L.) and oat (Avena sativa L.) for pasture; stover harvest had no effect. Storage of SOC in no-till (NT) plots with stover harvested remained nearly unchanged at 55 Mg ha⁻¹ with time, while that with stover returned increased about 14%. The measured δ¹³C increased steadily with years of corn cropping in all treatments; the NT with stover return had the highest increase. The N fertilization effects on SOC and δ¹³C were most evident when stover was returned to NT plots. In the 15–30 cm depth, SOC storage decreased and δ¹³C values increased with years of corn cropping under NT, especially when stover was harvested. There was no consistent temporal trend in SOC storage and δ¹³C values in the 15–30 cm depth when plots received annual MB or CH tillage. The amount of available corn residue that was retained in SOC storage was influenced by all three management factors. Corn-derived SOC in the 0–15 cm and the 15–30 cm layers of the NT system combined was largest with 200 kg N ha⁻¹ and no stover harvest. The MB and CH tillage systems did not influence soil storage of corn-derived SOC in either the 0–15 or 15–30 cm layers. The corn-derived SOC as a fraction of SOC after 13 years fell into three ranges: 0.05 for the NT with stover harvested, 0.15 for the NT with no stover harvest, and 0.09–0.10 for treatments with annual tillage; N rate had no effect on this fraction. Corn-derived SOC expressed as a fraction of C returned was positively biased when C returned in the roots was estimated from recovery of root biomass. The half-life for decomposition of the original or relic SOC was longer when stover was returned, shortened when stover was harvested and N applied, and sharply lengthened when stover was not harvested and N was partially mixed with the stover. Separating SOC storage into relic and current crop sources has significantly improved our understanding of the main and interacting effects of tillage, crop residue, and N fertilization for managing SOC accumulation in soil.     

长期保护性耕作提高土壤大团聚体含量及团聚体有机碳的作用

【目的】团聚体形成被认为是土壤固碳的最重要机制。本文以河南豫西地区长期耕作试验为研究对象,研究了长期保护性耕作对土壤团聚体性质及土壤有机碳(SOC)含量的影响,为探讨土壤固碳机理,优化黄土高原坡耕地区农田耕作管理措施,实现土壤固碳减排、培肥土壤提供理论依据。【方法】长期耕作试验开始于1999年,试验处理有免耕覆盖(NT)、深松覆盖(SM)和翻耕(CT)。利用湿筛法筛分第3年(2002年)和第13年(2011年)0—10cm和10—20 cm土层中,2000、250~2000、53~250和53μm级别的水稳性团聚体,计算团聚体平均质量直径(MWD),并测定了各级别团聚体的有机碳(SOC)含量。【结果】1)连续13年免耕覆盖和深松覆盖显著提高了土壤表层0—10 cm的SOC含量,分别比翻耕增加了33.47%和44.48%。2011年免耕覆盖和深松覆盖SOC含量较2002年上升了1.92%和8.59%,翻耕下降了18.97%。2)与翻耕相比,免耕覆盖和深松覆盖2000μm团聚体含量显著提高了40.71%和106.75%;53~250μm团聚体含量显著降低了19.72%和22.53%;团聚体平均质量直径显著提高了20.55%和39.68%,显示了土壤结构的明显改善。3)免耕覆盖和深松覆盖显著提高了表层土壤所有团聚体有机碳的含量,尤其以2000μm团聚体提升最多。与翻耕相比,2000μm团聚体有机碳分别提高了40.0%和27.6%。4)免耕覆盖和深松覆盖下表层土壤大团聚体有机碳含量随耕作年限增加,微团聚体有机碳随耕作年限降低。2000μm的土壤团聚体有机碳含量2011年较2002年分别升高了23.93%和7.12%,53~250μm微团聚体有机碳含量分别下降了19.58%和13.27%。【结论】长期保护性耕作(包括免耕覆盖和深松覆盖)可显著提高表层土壤大团聚体含量,降低微团聚体含量,提高团聚体的水稳性,改善土壤结构。同时可增加土壤团聚体有机碳含量,提高土壤肥力。长期保护性耕作在河南豫西丘陵地区是一种较为合理的耕作方式。     

耕作方式对干旱绿洲滴灌复播大豆农田土壤有机碳的影响

为探讨不同耕作措施对不同层次土壤碳的影响,从而评价出滴灌条件下最有利于复播大豆农田固碳的耕作方式,于2012-2014年开展了冬小麦收获后土壤采取翻耕覆膜(tillage plough,TP)、翻耕(tillage,T)、旋耕(rotary tillage,RT)和免耕(no-till,NT)4种不同耕作方式的复播大豆田间试验,研究麦后不同土壤耕作方式对复播大豆农田0~100 cm土层土壤容重、总有机碳(soil organic carbon,SOC)及碳库管理指数(carbon pool management index,CPMI)的影响。结果表明,各处理土壤SOC和易氧化有机碳(easily oxidized organic carbon,EOC)含量随着土层的加深基本呈不断下降趋势。免耕、旋耕处理显著增加了表层0~10 cm土壤的SOC和EOC含量,而TP处理显著增加了耕层20~30 cm的SOC和EOC含量,60~100 cm土层TP处理的SOC含量显著低于其他处理,但各处理间EOC含量差异不显著;土壤容重与总有机碳含量呈显著负相关关系(P0.01);0~60 cm土层不同耕作方式CPMI平均值以免耕处理最高,分别比旋耕、翻耕覆膜、翻耕处理的增加了4.41%、9.90%、22.06%,表明免耕、旋耕能够提高0~60 cm土壤的总体CPMI,而耕翻覆膜显著提高20~30 cm耕层土壤CPMI值。该研究为干旱绿洲滴灌条件下选择最有利于复播大豆农田固碳的耕作方式提供了理论依据。     

Tillage and residue management effects on temporal changes in soil organic carbon and fractions of a silty loam soil in the North China Plain

Soil degradation and associated depletion of soil organic carbon (SOC) have been major concerns in intensive farming systems because of the subsequent decline in crop yields. We assessed temporal changes in SOC and its fractions under different tillage systems for wheat (Triticum aestivum L.) – maize (Zea mays L.) cropping in the North China Plain. Four tillage systems were established in 2001: plow tillage (PT), rotary tillage (RT), no‐till (NT), and plow tillage with residues removed (PT0). Concentrations of SOC, particulate organic carbon (POC), non‐POC (NPOC), labile organic carbon (LOC), non‐LOC (NLOC), heavy fraction carbon (HFC) and light fraction carbon (LFC) were determined to assess tillage‐induced changes in the top 50 cm. Concentrations of SOC and C fractions declined with soil depth and were significantly affected by tillage over time. The results showed that SOC and its fractions were enhanced under NT and RT from 0 to 10 cm depth compared with values for PT and PT0. Significant decreases were observed below 10 cm depths (P < 0.05) regardless of the tillage system. The SOC concentration under NT for 0–5 cm depth was 18%, 8%, and 10% higher than that under PT0 after 7, 9, and 12 yr of NT adoption, respectively. Apparent stratification of SOC occurred under NT compared with PT and PT0 for depths >10 cm. All parameters were positively correlated (P < 0.01); linear regressions exhibited similar patterns (P < 0.01). Therefore, to maintain and improve SOC levels, residue inputs should be complemented by the adoption of suitable tillage systems.     

Changes in soil organic carbon and its chemical fractions under different tillage practices on loess soils of the Guanzhong Plain in north‐west China

Over the past 20 years, conservation tillage has been used on the loess plateau of north‐west China to improve the sustainability of local agriculture. There had been particular concern about loss of soil organic matter associated with traditional tillage. We examined the influence of four tillage treatments: conventional tillage (CT), subsoiling tillage (SST), rotary tillage (RT) and no‐tillage (NT), with two straw residue management treatments (return and removal) on the distribution with soil depth (0–20 cm, 20–40 cm) of total organic carbon, labile organic carbon (KMnO₄‐C) and bound organic carbon. The study was carried out on a Loutu soil (Earth‐cumuli‐Orthic Anthrosol) over seven consecutive years of a winter wheat (Triticum aestivum L.)–summer maize (Zea mays L.) crop rotation. By the end of this period, conservation tillage (SST, RT and NT) led to greater storage of soil organic carbon (SOC) (22.7, 14.9 and 16.3% with straw return in contrast to 21.4, 15.8 and 12.3% with no straw return, respectively) compared with CT in the surface soil (0–20 cm). The reduced tillage treatments (SST and RT) both increased significantly the highly labile organic carbon (HLOC) content of the surface soil (50% in both SST and RT) and mildly labile organic matter (MLOC) (49.4 in SST and 53.5% in RT) when straw was removed. The largest pool of bound carbon was observed in the Humin‐C pool, and the smallest in the free humic acids C (FHA‐C) in each tillage treatment. Conservation tillage led to an increased content of FHA‐C and CHA‐C. Results from correlation analyses indicate that SOC enrichment might have resulted from the increase in HLOC, MLOC, FHA‐C and CHA‐C over a short period. Labile organic carbon was associated with the organic carbon that was more loosely combined with clay (FHA‐C and CHA‐C). We conclude that both SST and RT are effective in maintaining or restoring organic matter in Loutu soils in this region, and the effect is greater when they are used in combination with straw return.     

短期免耕对黑土有机碳、全氮和速效养分的影响

对中层黑土上连续监测了6年的玉米免耕和秋翻两种耕作处理下的耕层土壤有机碳、全氮和速效氮、磷、钾进行了分析。结果表明:耕作处理对土壤养分的影响主要表现在不同的土壤深度上,免耕造成了土壤有机碳和全氮的分层化,即表层0~5 cm有机碳和全氮含量明显高于亚表层,而秋翻土壤有机碳和全氮分布则比较均匀。免耕处理的速效养分均表现为表层与亚表层存在明显差异。免耕处理下有机碳、全氮和速效氮、磷、钾在土壤表层发生明显富集。     

Soil carbon and nitrogen changes as affected by tillage system and crop biomass in a corn–soybean rotation

A wide range of tillage systems have been used by producers in the Corn-Belt in the United States during the past decade due to their economic and environmental benefits. However, changes in soil organic carbon (SOC) and nitrogen (SON) and crop responses to these tillage systems are not well documented in a corn–soybean rotation. Two experiments were conducted to evaluate the effects of different tillage systems on SOC and SON, residue C and N inputs, and corn and soybean yields across Iowa. The first experiment consisted of no-tillage (NT) and chisel plow (CP) treatments, established in 1994 in Clarion–Nicollet–Webster (CNW), Galva–Primghar–Sac (GPS), Kenyon–Floyd–Clyde (KFC), Marshall (M), and Otley–Mahaska–Taintor (OMT) soil associations. The second experiment consisted of NT, strip-tillage (ST), CP, deep rip (DR), and moldboard plow (MP) treatments, established in 1998 in the CNW soil association. Both corn and soybean yields of NT were statistically comparable to those of CP treatment for each soil association in a corn–soybean rotation during the 7 years of tillage practices. The NT, ST, CP, and DR treatments produced similar corn and soybean yields as MP treatment in a corn–soybean rotation during the 3 years of tillage implementation of the second experiment. Significant increases in SOC of 17.3, 19.5, 6.1, and 19.3% with NT over CP treatment were observed at the top 15-cm soil depth in CNW, KFC, M, and OMT soil associations, respectively, except for the GPS soil association in a corn–soybean rotation at the end of 7 years. The NT and ST resulted in significant increases in SOC of 14.7 and 11.4%, respectively, compared with MP treatment after 3 years. Changes in SON due to tillage were similar to those observed with SOC in both experiments. The increases in SOC and SON in NT treatment were not attributed to the vertical stratification of organic C and N in the soil profile or annual C and N inputs from crop residue, but most likely due to the decrease in soil organic matter mineralization in wet and cold soil conditions. It was concluded that NT and ST are superior to CP and MP in increasing SOC and SON in the top 15 cm in the short-term. The adoption of NT or CP can be an effective strategy in increasing SOC and SON in the Corn-Belt soils without significant adverse impact on corn and soybean yields in a corn–soybean rotation.