不同施肥年限下作物产量及土壤碳氮库容对增施有机物料的响应

【目的】研究不同年限下增施有机肥及秸秆还田对作物产量及剖面土壤碳氮库容的影响,旨在为华北平原冬小麦-夏玉米轮作区增强土壤肥力、提高作物产量提供依据。【方法】以农业部昌平潮褐土生态环境重点野外科学观测试验站为平台,分别在长达11年和27年的2个不同施肥年限试验区采集4个施肥处理,即氮磷钾（NPK)、氮磷钾+22.5 t·hm ^-2有机肥（NPKM）、氮磷钾+33.75 t·hm ^-2有机肥（NPKM+）、氮磷钾+秸秆还田（NPKS）不同土层深度的土壤样品,分析冬小麦-夏玉米产量和土壤碳氮库容剖面分布特征。 【结果】（1）增施有机肥及秸秆还田处理对作物的增产效应随施肥年限的延长而逐渐增强。与NPK处理相比,施肥11年限的NPKM、NPKM+和NPKS处理分别提高小麦和玉米产量为18.6%、15.8%、3.5%和39%、42%、35%;而27年的各施肥处理对小麦和玉米产量的增产幅度分别为41%、51.5%、23%和31%、33%、58%。（2）随着施肥年限的延长,增施有机肥及秸秆还田均能持续提升土壤碳、氮库容。连续施肥11年后,土壤碳、氮库容分别为25—114 Mg·hm ^-2、2.2—9.0 Mg·hm ^-2;而27年后土壤碳、氮库容分别为29—146 Mg·hm ^-2、2.5—12.1 Mg·hm ^-2。随着土壤剖面的加深,不同施肥年限中土壤碳、氮库容均表现为先逐渐增加后逐渐降低的趋势,均在80 cm处达到峰值。在80 cm土层峰值处,27年施肥处理中NPK、NPKM、NPKM+、NPKS土壤碳库和氮库分别为102、128、146、123 Mg·hm ^-2和8.3、9.7、12.1、9.1 Mg·hm ^-2,而11年施肥年限内各处理土壤碳、氮库均表现为差异不显著（P>0.05）。和NPK相比,不同年限中增施有机肥及秸秆还田均降低了不同土层的土壤碳氮比。同时,随着施肥年限的延长,土壤碳氮比越稳定。（3）随着施肥年限的延长,各处理土壤累积碳、氮库均呈现增加趋势。连续施肥11年后,NPKM、NPKM+、NPKS比NPK提升土壤累积碳、氮库容分别为5.2%、11.2%、9.2%和21.2%、26.6%、38.8%;连续施肥27年后NPKM、NPKM+、NPKS比NPK提升土壤累积碳、氮库容分别为26.3%、41.1%、21.8%和26.2%、44.9%、4.0%,且随着施肥年限的延长,施用有机肥对土壤累积碳库容的提升高于秸秆还田的趋势愈加明显,而对土壤累积氮库容的提升效果低于秸秆还田。 【结论】在氮磷钾化肥基础上增施有机肥及秸秆还田会提高作物产量、增强土壤碳氮库容、提升土壤肥力,且随着施肥年限的延长,效果愈加明显。同时,施用有机肥对作物产量、碳库的增强效应强于秸秆还田,而对氮库的提升效果低于秸秆还田。     

Long-term straw return influenced ammonium ion retention at the soil aggregate scale in an Anthrosol with rice-wheat rotations in China

Soil aggregates are an important controlling factor for the physico-chemical and biological processes such as ammonium(NH₄⁺) retention. Straw return to the field is increasingly recommended to promote soil carbon(C) sequestration and improve crop yields. However, the effects of straw return on NH₄⁺ retention at soil aggregate level in agricultural soils have seldom been investigated. This study aimed to evaluate the influences of long-term straw return...     

长期有机无机配施黑土土壤有机碳对农田基础地力提升的影响

【目的】探讨长期不同施肥方式对提升东北黑土土壤有机碳和农田基础地力的差异。【方法】以国家黑土肥力和肥料效益长期监测试验（1989-2011年）资料为基础,采用 DSSAT ver.4.0作物生长模型模拟：（1） CK（对照,不施肥）;（2）NPK（施氮磷钾肥）;（3）NPKM（有机肥+NPK化肥,M指有机肥）;（4）l.5NPKM（NPKM处理的1.5倍）;（5）NPKS（秸秆+NPK化肥,S指玉米秸秆）5种施肥方式下东北黑土区春玉米20年的农田基础地力产量,在分析长期不同施肥措施下基础地力与土壤有机碳的演变规律的基础上,进一步探讨两者之间的数量化关系。【结果】经过20年施肥管理,NPK、NPKM、1.5NPKM和NPKS施肥处理春玉米农田基础地力产量分别增长了53.4%、78.0%、101.2%和69.4%,而CK处理的基础地力产量随时间延长呈下降趋势。到2008年,1.5NPKM、NPKM、NPKS、NPK 4个处理的土壤有机碳含量分别比CK处理的土壤有机碳含量增加了65.6%、65.1%、26.0%和21.7%,土壤有机碳储量分别提升了69.9%、44.2%、25.2%和16.7%。土壤有机碳含量与春玉米基础地力产量呈显著正相关（P＜0.01）,土壤有机碳含量每增加1 g?kg^-1,春玉米农田基础地力产量大约提高220 kg?hm^-2。【结论】土壤有机碳是黑土区基础地力的主要驱动因素,有机肥或秸秆与化肥配施提升了土壤有机碳,因而能有效提高春玉米农田基础地力产量和基础地力贡献率。增加有机物料投入是黑土区农田基础地力培育的最佳施肥措施。     

长江下游稻麦轮作农田不同施肥措施的固碳潜力分析

基于长江下游稻麦轮作农田27个长期试验点184组样本数据,采用Meta分析法研究无机氮肥（N）、无机氮磷钾肥配施（NPK）、单施有机肥（O）和有机无机肥配施（OF）4种施肥措施下农田土壤有机碳含量相对年变化量、固碳持续时间以及在固碳周期内的固碳比例。结果表明,N、NPK、O和OF处理均能增加农田表土有机碳含量相对年变化量,分别为0.05、0.19、0.22和0.31 g·kg-1·a-1,其中,以OF等处理下为最大。两熟制和三熟制农田表土有机碳含量相对年变化量分别为0.26和0.21 g·kg-1·a-1;随着监测时间的延长,N、NPK、O和OF等4种处理下农田表土有机碳增加速率逐渐降低,农田土壤固碳持续时间分别达19、36、51和47 a,以O处理最长。整个固碳周期内土壤所能增加的有机碳比例分别为6.93%、18.98%、22.34%和32.33%,以OF处理下为最高。从农田土壤固碳角度考虑,有机无机肥配施为长江下游稻麦轮作农田较为适宜的施肥方式。     

稻麦轮作下紫色土有机碳活性及其对长期不同施肥的响应

【目的】研究稻麦轮作系统中紫色土总有机碳、活性有机碳和活性有机碳不同组分的变化特征及其对长期不同施肥措施的响应,揭示稻麦轮作系统长期不同施肥管理下有机碳质量和内在组成的变化。【方法】采集22年长期定位试验不施肥(CK)、单施化学氮肥(N)、化肥氮磷钾配施(NPK)、化肥氮磷钾+秸秆还田(NPKS)、高量化肥氮磷钾+等量秸秆还田(1.5NPKS)和化肥氮磷钾+厩肥(NPKM)处理0—20、20—40、40—60 cm土层的土壤,测定了总有机碳、活性有机碳及其不同活性组分的含量,计算土壤碳库管理指数和不同活性组分的分配比例,分析了活性有机碳及其各组分与总有机碳的关系。【结果】长期不同施肥显著影响了各土层总有机碳和活性有机碳含量,与不施肥相比,所有施肥处理均维持或提高了土壤总有机碳、活性有机碳含量和碳库管理指数,其中化肥氮磷钾+秸秆还田(NPKS)处理0—20、20—40和40—60 cm土层总有机碳含量分别提高32.5%、25.7%和5.3%,活性有机碳含量提高37.0%、44.7%和9.3%,碳库管理指数提高38%、49%和9%,其提升幅度高于其他施肥处理。长期不同施肥显著提高了各土层高、中、低活性有机碳含量,有机无机肥配施处理(NPKS、1.5NPKS、NPKM)提升效果高于单施化肥处理(NPK、N);但施肥对各活性组分占活性有机碳比例的影响较小,并没有改变各活性组分的分布格局。土壤活性有机碳及其高、中、低活性组分的含量与土壤深度有关,0—20 cm耕层土壤活性有机碳及高、中、低活性组分的含量均高于20—40和40—60 cm土层。不同土层高、中、低组分占活性有机碳的比例也存在较大差异,0—20 cm土层高、中、低活性组分占活性有机碳的比例平均为23.6%、35.6%和40.7%;下层土壤各活性组分的含量均下降,其中20—40 cm土层低活性组分下降程度较大,导致其占活性有机碳的比例下降至24.7%,而高活性和中活性组分的比例增加至30.5%和44.8%。土壤活性有机碳及其各组分与总有机碳含量呈显著线性正相关,表明土壤活性有机碳可以较好地反映总有机碳变化。【结论】稻麦轮作条件下,长期不同施肥可维持或提高土壤总有机碳、活性有机碳及其不同组分的含量,提高土壤碳库管理指数,氮磷钾肥配合秸秆还田总体提升效果较好,是促进土壤总有机碳和活性有机碳累积、改善土壤有机碳质量的推荐施肥措施。     

Fractionation of soil organic carbon in a calcareous soil after long-term tillage and straw residue management

No-tillage (NT) and straw return (S) collectively affect soil organic carbon (SOC). However, changes in the organic carbon pool have been under-investigated. Here, we assessed the quantity and quality of SOC after 11 years of tillage and straw return on the North China Plain. Concentrations of SOC and its labile fractions (particulate organic carbon (POC), potassium permanganate-oxidizable organic carbon (POXC), microbial biomass carbon (MBC), and dissolved organic carbon (DOC)), components of DOC by fluorescence spectroscopy combined with parallel factor analysis (PARAFAC), and the chemical composition of SOC by ¹³C NMR (nuclear magnetic resonance) spectroscopy were explored. Treatments comprised conventional tillage (CT) and NT under straw removal (S0), return of wheat straw only (S1), or return of both wheat straw and maize residue (S2). Straw return significantly increased the concentrations and stocks of SOC at 0–20 cm depth, but NT stratified them with enrichment at 0–10 cm and a decrease at 10–20 cm compared to CT, especially under S2. Labile C fractions showed similar patterns of variation to that of SOC, with POC and POXC more sensitive to straw return and the former more sensitive to tillage. Six fluorescence components of DOC were identified, mainly comprising humic-like substances with smaller amounts of fulvic acid-like substances and tryptophan. Straw return significantly decreased the fluorescence index (FI) and autochthonous index (BIX) and increased the humification index (HIX). No-tillage generally increased HIX in topsoil but decreased it and increased the FI and BIX below the topsoil. Relative abudance order of the chemical composition of SOC was: O-alkyl C>alkyl-C>aromatic-C>carbonyl-C. Overall, NT under S2 effectively increased SOC and its labile C forms and DOC humification in topsoil and microbially-derived DOC below the topsoil. Return of both wheat and maize straw was a decisive factor in promoting SOC in the plow layer. The stratification of SOC under NT may confer a long-term influence on carbon sequestration.     

秸秆还田量对黑土区土壤及团聚体有机碳变化特征和固碳效率的影响

【目的】探讨不同秸秆还田量下土壤及团聚体有机碳的变化特征,阐明土壤及团聚体有机碳储量变化对外源有机碳累积投入的响应关系,揭示黑钙土土壤及团聚体固碳效应和土壤有机碳定量提升机理。【方法】于2012年4月在吉林省农安县玉米主产区设置了玉米秸秆还田量田间定位试验,共设计4个处理:秸秆还田量0(SA0)、秸秆还田量4 500 kg·hm^-2(SA300)、秸秆还田量9 000 kg·hm^-2(SA600)、秸秆还田量13 500 kg·hm^-2(SA900)。利用多年试验土壤有机碳储量与外源有机碳投入的数据分析其量化关系和固碳效率。通过湿筛法筛分>2 mm、2—0.25 mm、0.25—0.053 mm和<0.053 mm粒级团聚体,分析不同粒级团聚体有机碳储量变化特征及固碳效应。【结果】长期秸秆还田能显著提高土壤有机碳含量,秸秆还田SA600和SA900两处理土壤有机碳含量均显著高于秸秆不还田(SAO)、低量秸秆还田(SA300)(P<0.05),并且后3年SA900和SA600两处理土壤有机碳含量差异达显著...     

不同施肥方式对农田有机碳含量的影响

[目的]研究不同施肥方式对农田有机碳（SOC）含量的影响,为制定农田管理措施以减少碳排放提供科学依据。[方法]收集我国37个试验站资料,分析不同施肥处理下SOC变化。[结果]对照（CK）、有机肥（M）、无机肥（NPK）、无机肥＋秸秆（NPKS）和无机肥＋厩肥施肥（NPKM）处理方式下,SOC含量上升的样本比例分别为37.86%、89.96%、72.24%、97.87%和94.43%。不同施肥处理下SOC的增长量与施肥时间呈显著正相关（P〈0.01）。SOC初始值与不同施肥方式下的SOC含量呈极显著正相关（P〈0.01）,但与SOC年增长率呈明显或极显著负相关（P〈0.05,P〈0.01）。[结论]有机肥和无机肥配施,有助于提高SOC含量,增强土壤养分供贮能力,有利于维持土壤有机质的平衡。     

潮土区小麦、玉米残体对土壤有机碳的贡献——基于改进的RothC模型

【目的】为进一步了解秸秆还田对土壤有机碳(SOC)的提升效果,探究作物残体(根系与秸秆)对潮土区SOC的贡献,为华北冬小麦-夏玉米区SOC提升提供理论依据。【方法】基于腐解试验的有机物料碳残留率数据,获得4种有机物料在RothC-26.3模型最优时对应的DPM/RPM参数值(易分解植物残体和难分解植物残体的比值)。利用修订的DPM/RPM参数,获得了改进的RothC-26.3模型,并用郑州潮土区短期腐解试验(2012年11月至2013年11月)和长期定位试验数据(1990—2008年)进行验证,模拟出郑州潮土区冬小麦-夏玉米轮作系统中小麦、玉米残体在3种不同施肥处理下(不施肥CK,平衡施肥NPK和秸秆还田NPKS)对新形成SOC的贡献。【结果】在模型达到最优时,小麦根系(wheat root,WR)、小麦秸秆(wheat straw,WS)、玉米根系(corn root,CR)和玉米秸秆(corn straw,CS)的DPM/RPM值分别为0.89、3.04、4.35和3.25。模型结果显示,CK处理小麦根系、玉米根系的碳投入占碳投入的比例均为50%,而来源于小麦根系、玉米根系的SOC(0—20 cm)占新形成的SOC比例分别为60%、40%;小麦根和玉米根固碳效率分别为15.5%、10.8%;NPK处理小麦根系、玉米根系的碳投入占碳投入的比例分别为60%、40%,而来源于小麦根系、玉米根系的SOC(0—20 cm)占新形成SOC的比例分别为71%、29%;小麦根和玉米根固碳效率分别为17.5%、11.4%;NPKS处理小麦根系、玉米根系、玉米秸秆的碳投入的比例分别为47%、21%、32%,而小麦根系、玉米根系、玉米秸秆对新形成的SOC(0—20 cm)贡献分别为50%、22%、28%;小麦根系、玉米根系、玉米秸秆的固碳效率分别为16.9%、11.2%、11.4%。总之,冬小麦-夏玉米轮作系统中无论是不施肥、平衡施肥还是秸秆还田处理,小麦根系对新形成SOC的贡献率(50%—71%)大于玉米根系和玉米秸秆对新形成SOC贡献率(22%—40%)。源自小麦的SOC占新形成SOC的比例均分别大于源自小麦的碳投入占总碳投入的比例,而源自玉米的投入及其对新形成SOC的贡献则反之。小麦根系的固碳效率(15.5%—17.5%)大于玉米根系和玉米秸秆的固碳效率(10.8%—11.4%)。【结论】改进后的RothC模型可用来探究潮土区冬小麦-夏玉米轮作系统中小麦、玉米残体对新形成SOC的贡献。郑州潮土区冬小麦-夏玉米轮作系统中小麦根系对新形成SOC的贡献率均大于玉米根系和玉米秸秆的贡献率。根茬还田(尤其是小麦根茬还田)更有利于提升土壤有机碳含量。     

不同农作管理措施对东北地区农田土壤有机碳未来变化的模拟研究

【目的】研究与探索不同农作管理措施对东北农业土壤有机碳的影响,为东北地区高产高效低碳农业及可持续发展提供科学依据。【方法】不同农作管理措施能够影响土壤有机碳（soil organic carbon,SOC）的未来变化,该研究基于东北地区4个长期定位试验站点（黑龙江省哈尔滨站点、吉林省公主岭站点、吉林省德惠站点、辽宁省沈阳站点）的试验数据,用站点的实测作物产量和SOC双标准对DAYCENT模型进行校验。DAYCENT模型调整的相关参数包括作物参数、耕作方式参数、施肥参数、收获参数和有机肥参数等,在对所选试验站点的长期定位试验结果校验后,利用已校验的各项参数,对模型模拟情况进行验证,发现模型模拟值与实测值吻合良好,表明DAYCENT模型适用于这4个地区的作物产量和SOC模拟,可以较好地模拟SOC的动态变化。进而研究在未来气候变化情景下（representative concentration pathway 4.5,RCP 4.5）,用校验了的DAYCENT模型对这4个站点在4种不同管理情景（施用化肥、增施有机肥、秸秆还田、免耕）下的SOC变化情况进行模拟。【结果】模拟结果显示,对于哈尔滨站点,采用有机肥和氮磷钾化肥配施处理（MNPK）在短时间内使SOC升高较快,而从长远来看,配施低量有机肥与单施用化肥对SOC增加的斜率基本一致,但由于化肥和有机肥配施（MNPK）处理的初始SOC含量高,其SOC未来含量的绝对值也比较高;对于德惠站点,虽然短时间内,免耕处理SOC低于常耕处理,但长期看来,免耕更有利于增加SOC,其SOC涨幅逐渐高于常耕处理,40年间相对增加了11.88%;公主岭站点有机肥氮磷钾化肥配施和氮磷钾化肥结合秸秆还田措施较单施化肥可显著提高农田SOC;沈阳站点的未来有机碳模拟发现,在单施化肥情况下,未来的42年内SOC呈略微下降趋势,相对降低2.83%,从长远看来,单施化肥并不能使该地区SOC增加,因此,可以考虑采用有机肥和氮磷钾化肥配施等措施来提高该地区的农田SOC。【结论】DAYCENT模型可以有效地模拟作物产量和土壤有机碳的动态变化,模型适应性较强,同时DAYCENT模型可用于模拟站点未来SOC的动态变化。在东北地区农田土壤管理方面,可通过合理的有机肥化肥配施、推广免耕和秸秆还田技术来固定土壤碳,最终达到提高土壤有机碳库和促进农业可持续发展的目标。     

Long-term organic and inorganic fertilizations enhanced basic soil productivity in a fluvo-aquic soil

The improvement of soil productivity depends on a rational input of water and nutrients, optimal field management, and the increase of basic soil productivity(BSP). In this study, BSP is defined as the productive capacity of a farmland soil with its own physical and chemical properties for a specific crop season under local field management. Based on 19-yr data of the long-term agronomic experiments(1989–2008) on a fluvo-aquic soil in Zhengzhou, Henan Province, China, the decision support system for agrotechnology transfer(DSSAT ver. 4.0) crop growth model was used to simulate yields by BSP of winter wheat(Triticum aestivium L.) and summer maize(Zea mays L.) to examine the relationship between BSP and soil organic carbon(SOC) under long-term fertilization. Five treatments were included:(1) no fertilization(control),(2) nitrogen, phosphorus and potassium fertilizers(NPK),(3) NPK plus manure(NPKM),(4) 1.5 times of NPKM(1.5NPKM), and(5) NPK plus straw(NPKS). After 19 yr of treatments, the SOC stock increased 16.7, 44.2, 69.9, and 25.2% under the NPK, NPKM, 1.5NPKM, and NPKS, respectively, compared to the initial value. Among various nutrient factors affecting contribution percentage of BSP to winter wheat and summer maize, SOC was a major affecting factor for BSP in the fluvo-aquic soil. There were significant positive correlations between SOC stock and yields by BSP of winter wheat and summer maize(P0.01), and yields by BSP of winter wheat and summer maize increased 154 and 132 kg ha~(–1) when SOC stock increased 1 t C ha~(–1). Thus, increased SOC accumulation is a crucial way for increasing BSP in fluvo-aquic soil. The manure or straw combined application with chemical fertilizers significantly enhanced BSP compared to the application of chemical fertilizers alone.     

Microbial community structure and functional metabolic diversity are associated with organic carbon availability in an agricultural soil

Exploration of soil environmental characteristics governing soil microbial community structure and activity may improve our understanding of biogeochemical processes and soil quality. The impact of soil environmental characteristics especially organic carbon availability after 15-yr different organic and inorganic fertilizer inputs on soil bacterial community structure and functional metabolic diversity of soil microbial communities were evaluated in a 15-yr fertilizer experiment in Changping County, Beijing, China. The experiment was a wheat-maize rotation system which was established in 1991 including four different fertilizer treatments. These treatments included: a non-amended control(CK), a commonly used application rate of inorganic fertilizer treatment(NPK); a commonly used application rate of inorganic fertilizer with swine manure incorporated treatment(NPKM), and a commonly used application rate of inorganic fertilizer with maize straw incorporated treatment(NPKS). Denaturing gradient gel electrophoresis(DGGE) of the 16 S r RNA gene was used to determine the bacterial community structure and single carbon source utilization profiles were determined to characterize the microbial community functional metabolic diversity of different fertilizer treatments using Biolog Eco plates. The results indicated that long-term fertilized treatments significantly increased soil bacterial community structure compared to CK. The use of inorganic fertilizer with organic amendments incorporated for long term(NPKM, NPKS) significantly promoted soil bacterial structure than the application of inorganic fertilizer only(NPK), and NPKM treatment was the most important driver for increases in the soil microbial community richness(S) and structural diversity(H). Overall utilization of carbon sources by soil microbial communities(average well color development, AWCD) and microbial substrate utilization diversity and evenness indices(H' and E) indicated that long-term inorganic fertilizer with organic amendments incorporated(NPKM, NPKS) could significantly stimulate soil microbial metabolic activity and functional diversity relative to CK, while no differences of them were found between NPKS and NPK treatments. Principal component analysis(PCA) based on carbon source utilization profiles also showed significant separation of soil microbial community under long-term fertilization regimes and NPKM treatment was significantly separated from the other three treatments primarily according to the higher microbial utilization of carbohydrates, carboxylic acids, polymers, phenolic compounds, and amino acid, while higher utilization of amines/amides differed soil microbial community in NPKS treatment from those in the other three treatments. Redundancy analysis(RDA) indicated that soil organic carbon(SOC) availability, especially soil microbial biomass carbon(Cmic) and Cmic/SOC ratio are the key factors of soil environmental characteristics contributing to the increase of both soil microbial community structure and functional metabolic diversity in the long-term fertilization trial. Our results showed that long-term inorganic fertilizer and swine manure application could significantly improve soil bacterial community structure and soil microbial metabolic activity through the increases in SOC availability, which could provide insights into the sustainable management of China's soil resource.     

Effects of long-term straw return on soil organic carbon fractions and enzyme activities in a double-cropped rice paddy in South China

Long-term straw return is an important carbon source for improving soil organic carbon(SOC) stocks in croplands, and straw removal through burning is also a common practice in open fields in South China. However, the specific effects of long-term rice straw management on SOC fractions, the related enzyme activities and their relationships, and whether these effects differ between crop growing seasons remain unknown. Three treatments with equal nitrogen, phosphorus, and potassium nutrient inputs, including straw/ash and chemical nutrients, were established to compare the effects of straw removal(CK), straw return(SR), and straw burned return(SBR). Compared to CK, long-term SR tended to improve the yield of early season rice(P=0.057), and significantly increased total organic carbon(TOC) and microbial biomass carbon(MBC) in double-cropped rice paddies. While SBR had no effect on TOC, it decreased light fraction organic carbon(LFOC) in early rice and easily oxidizable organic carbon(EOC) in late rice, significantly increased dissolved organic carbon(DOC), and significantly decreased soil p H. These results showed that MBC was the most sensitive indicator for assessing changes of SOC in the double-cropped rice system due to long-term straw return. In addition, the different effects on SOC fraction sizes between SR and SBR were attributed to the divergent trends in most of the soil enzyme activities in the early and late rice that mainly altered DOC, while DOC was positively affected by β-xylosidase in both early and late rice. We concluded that straw return was superior to straw burned return for improving SOC fractions, but the negative effects on soil enzyme activities in late rice require further research.     

Carbon cycle in response to residue management and fertilizer application in a cotton field in arid Northwest China

Understanding the influence of farming practices on carbon(C) cycling is important for maintaining soil quality and mitigating climate change, especially in arid regions where soil infertility, water deficiency, and climate change had significantly influenced on agroecosystem. A field experiment was set up in 2009 to examine the influence of residue management and fertilizer application on the C cycle in a cotton field in the Xinjiang Uygur Autonomous Region of Northwest China. The study included two residue management practices(residue incorporation(S) and residue removal(NS)) and four fertilizer treatments(no fertilizer(CK), organic manure(OM), chemical fertilizer(NPK), chemical fertilizer plus organic manure(NPK+OM)). Soil organic carbon(SOC) and some of its labile fractions, soil CO_2 flux, and canopy apparent photosynthesis were measured during the cotton growing seasons in 2015 and 2016. The results showed that SOC, labile SOC fractions, canopy apparent photosynthesis, and soil CO_2 emission were significantly greater in S+NPK+OM(residue incorporation+chemical fertilizer) than in the other treatments. Analysis of all data showed that canopy apparent photosynthesis and soil CO_2 emission increased as SOC increased. The S+OM(residue incorporation+organic manure) and S+NPK+OM treatments were greater for soil C sequestration, whereas the other treatments resulted in soil C loss. The S+NPK treatment is currently the standard management practice in Xinjiang. The results of this study indicate that S+NPK cannot offset soil C losses due to organic matter decomposition and autotrophic respiration. Residue return combined with NPK fertilizer and organic manure application is the preferred strategy in arid regions for increasing soil C sequestration.     

The effects of co-utilizing green manure and rice straw on soil aggregates and soil carbon stability in a paddy soil in southern China

The co-utilization of green manure (GM) and rice straw (RS) in paddy fields has been widely applied as an effective practice in southern China. However, its effects on soil aggregate and soil organic carbon (SOC) stability remain unclear. In the present study, the effect of GM, RS, and co-utilization of GM and RS on particle size distribution of soil aggregates and SOC density fractions were measured in a field experiment. The experiment included six treatments, i.e., winter fallow (WF) without RS return (Ctrl), WF with 50% RS return (1/2RS), WF with 100% RS return (RS), GM without RS return (GM), GM with 50% RS return (GM1/2RS) and GM with 100% RS return (GMRS). The results showed that the proportion of small macro-aggregates (0.25–2 mm) and the mean weight diameter (MWD) of aggregates in the GMRS treatment was greater (by 18.9 and 3.41%, respectively) than in the RS treatment, while the proportion of silt+clay particles (<0.053 mm) was lower (by 14.4%). The concentration of SOC in microaggregates (0.053–0.25 mm) and silt+clay particles was higher in the GMRS treatment than in GM and RS treatments individually. The concentration and proportion of free light organic carbon (fLOC) in aggregates of various particle sizes and bulk soil was greater in the GMRS treatment than the RS treatment, whereas the concentration and proportion of mineral-associated organic carbon in small macroaggregates, microaggregates, and bulk was lower in the GMRS treatment than in the RS treatment. The proportion of intra-aggregate particulate organic carbon (iPOC) was greater in the GMRS treatment than in GM treatment. The GMRS treatment had strong positive effects on iPOC in small macroaggregates, suggesting that SOC was transferred from fLOC to iPOC. In conclusion, co-utilizing green manure and rice straw cultivated the SOC pool by increasing the concentration of fLOC and improved soil carbon stability by promoting the sequestration of organic carbon in iPOC as a form of physical protection.     

Discrepancy in Response of Rice Yield and Soil Fertility to Long-Term Chemical Fertilization and Organic Amendments in Paddy Soils Cultivated from Infertile Upland in Subtropical China

From 1990, over 17 years field experiment was carried out in paddy field cultivated from infertile upland to evaluate the response of rice productivity, soil organic carbon (SOC), and total N to long-term NPK fertilization or NPK combined with organic amendments. The field trials included NPK (N, P, K fertilizer), NPKRS (NPK combined with rice straw), NPK2RS (NPK combined with double amount of rice straw), NPKPM (NPK combined with pig manure) and NPKGM (NPK combined with green manure) and the cropping system was rice-rice {Oryza sativa L.) rotation. Annual rice yield, straw biomass, and harvesting index increased steadily with cultivation time in all treatments. Average annual rice yield from 1991 to 2006 was ranged from 7 795 to 8 572 kg ha-1 among treatments. Rice yields in treatments with organic amendments were usually higher than that in treatment with NPK. Contents of SOC and total N also increased gradually in the cultivation years and reached the level of 7.82 to 9.45 and 0.85 to 1.03 g kg-1, respectively, in 2006. Soil fertilities in treatments with chemical fertilization combined with organic amendments were relatively appropriate than those in treatment with NPK. There was obvious discrepancy between cumulative characters of rice yield and soil organic fertility in newly formed paddy field. Compared with relatively high rate of crop productivity improvement, cumulative rates of SOC and total N were much lower in our study. SOC and total N contents were still less than half of those in local highly productive paddy soils after 17 years cultivation in subtropical China. Present work helps to better understand the development of infertile paddy soils and to estimate the potential of yield improvement in this region.     

长期施肥对中国3种典型农田土壤活性有机碳库变化的影响

 【目的】观测分析了中国3种典型农田土壤——黑土、灰漠土和红壤有机碳在时间与空间上对长期不同施肥措施的响应特征,为农田土壤培肥提供理论依据。【方法】通过有机碳分组对比分析了长期施肥后土壤总有机碳与活性有机碳的含量与比例变化。【结果】16年后,不施肥（CK）灰漠土总有机碳、活性有机碳含量均呈显著下降趋势,下降幅度分别为11.7%和34.9%,且活性有机碳占总有机碳的比例也显著下降了5.4个百分点;长期施用氮肥（N）3种土壤总有机碳含量基本保持不变,但活性有机碳所占比例显著下降,其中黑土下降幅度高达9.5个百分点;化肥配施（NP,NPK）后,黑土和灰漠土活性有机碳占总有机碳的比例仍显著下降,红壤则略呈上升趋势;有机无机配施（NPKM、1.5NPKM）,3种土壤的总有机碳、活性有机碳及活性有机碳占总有机碳的比例均显著提高,其中红壤上升幅度最大,NPKM处理提高幅度分别为80.6%、146.2%和7.5个百分点,其次是灰漠土,分别提高了64.4%、138.0%和5.0个百分点;实施秸秆还田（NPKS）后,红壤的总有机碳、活性有机碳及活性有机碳占总有机碳的比例分别增加了21.6%、59.0%和7.5个百分点,黑土和灰漠土则相对较稳定。【结论】活性有机碳占总有机碳比例对施肥措施反应敏感,长期不施肥或只施氮肥多数导致土壤总有机碳含量和活性有机碳所占比例下降,有机无机配施能维持和提高土壤有机碳含量和活性有机碳所占比例,且效果优于秸秆还田,优于化肥（NPK）配施。     

用RothC-26.3模型模拟玉米连作下长期施肥对黑土有机碳的影响

 用RothC (Version 2 6 .3)模型模拟研究东北地区黑土长期定位施肥试验中玉米连作下土壤有机碳 (SOC)含量的变化。从 2 4个施肥处理中选取了无肥 (对照 )、氮肥、氮肥配施厩肥、氮磷钾肥配施、厩肥 5个处理 ,对耕层土壤SOC的模拟值与实际测定值进行了比较。模型预测值与实测值之间吻合较好 ,说明RothC模型可以很好的用来模拟东北温带气候区现有耕作管理条件下黑土SOC的动态变化。结果表明 ,在当前常规耕作秸秆不还田条件下 ,整个试验期间不施肥 ,SOC含量持续下降 ;单施氮或施氮磷钾不能维持耕层 (2 0cm)SOC含量 ;厩肥配合施用化肥 ,则会增加SOC含量。保持这种管理方式不变 ,SOC将持续下降至新的平衡点。模拟结果表明 ,如果实施秸秆还田 ,到 2 0 2 2年时无肥、氮肥、氮磷钾肥、氮肥配施厩肥和氮磷钾配施厩肥等处理区的SOC较 2 0 0 2年将分别增加 2 6 %、4 0 %、4 5 %、38%和 4 6 %。RothC模型可用来评价不同管理方式下黑土SOC变化趋势 ,秸秆还田将显著增加研究区黑土的SOC含量     

长期增施有机肥/秸秆还田对土壤氮素淋失风险的影响

【目的】研究长期增施有机肥/秸秆还田对作物产量及土壤氮素淋失风险的影响,旨在为华北平原冬小麦-夏玉米轮作区增强土壤肥力、提高作物产量及降低农业面源污染风险提供依据。【方法】以国家褐潮土肥力与肥料效益监测基地的长期肥料试验为平台,研究长达27年不同施肥处理对冬小麦-夏玉米产量、土壤肥力、氮素淋失风险和土壤氮素剖面分布的影响,试验共设置5个施肥处理,即：对照（CK）;氮磷钾（NPK）;氮磷钾+有机肥（NPKM）;氮磷钾+过量有机肥（NPKM+）;氮磷钾+秸秆还田（NPKS）。【结果】（1）在27年的不同施肥处理中,长期增施有机肥/秸秆还田均能使作物增产,改善土壤肥力。其中,增施有机肥处理尤为显著,与NPK相比,NPKM、NPKM+处理提高小麦和玉米产量分别为41%-50%和30%-32%;增加0-20 cm表层土壤有机碳（SOC）和全氮（TN）含量分别为62%-121%、107%-187%;但降低小麦、玉米氮肥偏生产力（PFP_N）分别达22%-32%、27%-41%。而NPKS处理对作物增产及提升土壤肥力的作用低于增施有机肥处理,对小麦产量、玉米产量、SOC、TN含量的增幅分别为24%、6%、9%、97%,但提高小麦季PFP_N为216%、降低玉米季PFP_N为40%。（2）长期增施有机肥/秸秆还田处理中,0-20 cm表层土壤SOC、TN、硝态氮（NO₃^--N）、可溶性碳氮等养分含量以及氮矿化速率、硝化潜势等微生物学过程显著高于20-200 cm,说明长期增施有机肥/秸秆还田等外源碳的添加对土壤养分及微生物学过程的影响主要发生在表层。（3）与NPK相比,NPKM处理能够显著增加100-200 cm深层土壤中NO₃^--N含量,NO₃^--N平均含量为17.8-26.1 mg·kg^-1;而NPKS处理在一定程度上能够增加0-100 cm土层NO₃^--N含量,NO₃^--N平均含量为3.6-13.4 mg·kg^-1,表明增施有机肥会促进土壤NO₃^--N的向下迁移,而秸秆还田对土壤NO₃^--N具有一定的固持作用。此外,由于有机肥和秸秆带入的氮素, NPKM、NPKM+、NPKS处理氮盈余比NPK处理增加312%、1 037%、953%,大大增加了土壤氮素淋失风险。【结论】在氮磷钾化肥基础上增施有机肥/秸秆还田会提高作物产量、增强土壤肥力,但会提高土壤氮盈余量,提高氮素淋失风险,尤其是增施有机肥会大大增加氮素淋失风险。     

Substituting nitrogen and phosphorus fertilizer with optimal amount of crop straw improves rice grain yield,nutrient use efficiency and soil carbon sequestration

Crop straw return after harvest is considered an important way to achieve both agronomic and environmental benefits.  However, the appropriate amount of straw to substitute for fertilizer remains unclear.  A field experiment was performed from 2016 to 2018 to explore the effect of different amounts of straw to substitute for fertilizer on soil properties, soil organic carbon (SOC) storage, grain yield, yield components, nitrogen (N) use efficiency, phosphorus (P) use efficiency, N surplus, and P surplus after rice harvesting.  Relative to mineral fertilization alone, straw substitution at 5 t ha^–1 improved the number of spikelets per panicle, effective panicle, seed setting rate, 1 000-grain weight, and grain yield, and also increased the aboveground N and P uptake in rice.  Straw substitution exceeding 2.5 t ha^–1 increased the soil available N, P, and K concentrations as compared with mineral fertilization, and different amounts of straw substitution improved SOC storage compared with mineral fertilization.  Furthermore, straw substitution at 5 t ha^–1 decreased the N surplus and P surplus by up to 68.3 and 28.9%, respectively, compared to mineral fertilization.  Rice aboveground N and P uptake and soil properties together contributed 19.3% to the variation in rice grain yield and yield components.  Straw substitution at 5 t ha^–1, an optimal fertilization regime, improved soil properties, SOC storage, grain yield, yield components, N use efficiency (NUE), and P use efficiency (PUE) while simultaneously decreasing the risk of environmental contamination.