长期梨树种植土壤团聚体组成及有机碳分布特征

为探究长期梨树种植土壤团聚体结构及其对土壤有机碳的影响，以砀山县良梨镇共12个年限的梨树土壤为研究对象，以果园附近农田土壤为对照，分析不同梨树种植年限土壤(0～20 cm)的团聚体粒级分布、土壤及各团聚体组分有机碳含量的动态特征。研究结果表明：随着种植年限的增加，土壤大团聚体(>0.25 mm)含量呈先上升后略有下降并趋于稳定的趋势，种植150 a处取得最大值达到798.8 g/kg。梨园土壤总有机碳含量、大团聚体有机碳含量相较对照农田土壤显著提高(P<0.05)，分别提高了1.45倍和2.24倍，而微团聚体(<0.25mm)有机碳含量显著下降。各个年限梨园土壤有机碳主要由大团聚体贡献，贡献率为68.06%～98.78%，相较农田土壤(39.76%)贡献率提高28.3%～59.02%；微团聚体的贡献率随着年限的增加而下降，表明梨园的长期种植促使有机碳从微团聚体向大团聚体分配。土壤大团聚体含量与有机碳含量呈极显著正相关(P<0.01)，均随着种植年限的增加先上升后下降至稳定趋势。表明梨园种植有利于改善土壤结构，增加土壤的固碳潜力。     

苜蓿作物轮作模式对土壤团聚体稳定性及有机碳的影响

本研究以苜蓿?作物轮作试验为研究对象,探讨了苜蓿?苜蓿(L-L)、苜蓿?休闲(L-F)、苜蓿?小麦(L-W)、苜蓿?玉米(L-C)、苜蓿?马铃薯(L-P)和苜蓿?谷子(L-M)6种轮作模式对陇中黄土高原雨养农田苜蓿土壤团聚体稳定性以及土壤总有机碳含量的影响。结果表明:不同轮作模式下土壤机械稳定性团聚体以≥0.25 mm团聚体为优势团聚体,均占72.17%以上,而土壤水稳性团聚体以0.25 mm团聚体为优势团聚体,均占95.18%以上。随着土层深度的增加,各处理≥0.25 mm的团聚体数量及平均重量直径(MWD)均随之增加,而水稳性大团聚体数量及MWD值无明显规律性。与L-L处理相比,L-C和L-P处理0~30 cm耕层土壤≥0.25 mm的团聚体含量分别增加5.94%和1.12%,L-C处理的MWD表现为最高,而其他轮作处理则不同程度降低了≥0.25 mm团聚体含量及MWD;随着土层深度的增加,6种不同轮作模式的土壤有机碳含量均呈现逐渐降低的趋势,在0~30 cm的耕层土壤,较之L-L处理,L-W、L-C、L-P和L-M处理均从不同程度上降低了土壤有机碳含量,其中L-P处理有机碳含量最低,降低了18.68%。相关性分析表明,土壤总有机碳分别与2~5 mm、1~2 mm、0.5~1 mm和0.25~0.5 mm粒径的水稳性团聚体比例以及MWD表现出极显著正相关,而与0.25 mm粒径的水稳性团聚体呈极显著负相关。综上所述,苜蓿?玉米轮作模式能明显增加土壤团聚体机械稳定性,而不同苜蓿?作物轮作模式对土壤团聚体的水稳性影响较小,土壤有机碳含量在很大程度上影响着土壤水稳性团粒结构的形成与稳定性,二者密切相关。     

农田和果园土壤有机碳氧化稳定性和储量差异

不同土地利用方式下有机碳的含量和性质变化越来越受到人们的关注。以黄土高原南部高原沟壑区(长武地区)塬面上农田以及不同树龄的果园为对象,研究了土壤总有机碳、易氧化有机碳和难氧化有机碳含量,比较了不同利用方式下土壤有机碳的氧化稳定系数(Kos)和有机碳密度差异。结果显示,该区域果园表层土壤总有机碳的整体水平与农田相当,但果园总有机碳、易氧化有机碳随果园年限增长有降低的趋势。在土壤剖面中,总有机碳、易氧化有机碳及难氧化有机碳都随深度下降而下降的趋势;而Kos值随剖面深度和果园年限增长而呈升高的趋势。0～2 m土壤剖面有机碳储量从高到底顺序是:农田>新果园(小于5年果园)>盛果期果园(10～15年果园)>老果园(15年以上果园)。以农田为基准,在0～200 cm厚度土层中,新果园有机碳储量下降了6.1%,盛果期果园下降了9.3%,老果园有机碳储量下降了22.4%。说明随着果园年限的增长,土壤有机碳储量降低。     

民勤绿洲区苜蓿地土壤有机碳组分分布特征

为了解西北民勤绿洲区紫花苜蓿种植后土壤有机碳组分的变化趋势及影响因素,以民勤绿洲区3a(A3)、14a(A14)和22a(A22)苜蓿种植地为研究对象,以棉花种植地(CK)为对照,通过野外调查取样以及室内测试分析,对土壤中的全部有机碳(TOC)、重组有机碳(HFOC)、轻组有机碳(LFOC)、颗粒有机碳(POC)和微生物量碳(MBC)的含量进行测定,分析变化趋势并对其规律进行研究。结果表明:相对于棉花种植地,22a苜蓿地土壤容重和电导率分别降低了13.9%和95.4%。3~22a苜蓿地较棉花种植地(CK)的TOC、LFOC、HFOC和MBC分别表现出175.0%,1 416.0%,47.8%和216.0%的增长幅度,变化差异较为显著。在垂直剖面上,棉花种植地(CK)显著低于苜蓿地LFOC、POC、MBC含量,并随土层加深而不断降低。逐步回归分析表明LFOC与TOC显著正相关(p0.05)。苜蓿种植年限、土层以及这两个变量的交互作用对POC/TOC产生显著影响(p0.01),对TOC、LFOC、HFOC、POC、MBC、LFOC/TOC、HFOC/TOC和MBC/TOC均产生极显著影响(p0.001)。苜蓿种植提高了土壤质量,降低了土壤容重和盐碱性,连续种植14a是苜蓿最为合理的种植年限,同时苜蓿种植有利于0—60cm垂直土层有机碳组分的累积,尤其对TOC、LFOC和MBC的增长效果极其显著。     

黄土高原吕梁山不同撂荒年限土壤团聚体稳定性及有机碳分布特征

为探究不同撂荒年限土壤结构及有机碳分布特征,试验选取黄土高原吕梁山自然撂荒1、2、3、5、10、15、20 a枣园土壤为研究对象,以清耕作业下的枣园土壤为对照(CK),利用干筛和湿筛法测定并分析各样地0～20 cm土层中土壤团聚体稳定性、团聚体有机碳与土壤总有机碳含量及其相关性。结果表明:撂荒初期,土壤团聚体含量呈波动变化趋势,撂荒3 a后土壤水稳性大团聚体含量(0.25 mm团聚体含量,R_(0.25))及团聚体平均重量直径(MWD)、几何平均直径(GMD)随撂荒年限的增加逐步提高。20 a撂荒地土壤水稳性大团聚体含量占团聚体总量的69.6%,较CK提高了55.2个百分点。土壤总有机碳、团聚体有机碳含量随撂荒年限的延长均呈先降低后增加的趋势,撂荒20 a土壤总有机碳含量达最大值7.88 g/kg;团聚体有机碳含量随团聚体粒径的减小呈先增加后降低的特点,主要集中于1～0.25 mm团聚体内。不同撂荒年限土壤中机械稳定性大团聚体有机碳对土壤总有机碳的贡献率为54.3%～82.2%,较CK(29.3%)提高25.0～52.9个百分点;水稳性大团聚体有机碳对土壤总有机碳的贡献率为17.7%～71.8%,除撂荒1 a和3 a土壤外,其他样地均高于CK (21.1%)。水稳性团聚体MWD、R_(0.25)与土壤总有机碳含量极显著相关(P0.01);水稳性团聚体GMD与土壤总有机碳含量显著相关(P0.05);水稳性团聚体R_(0.25)与2～1、1～0.25和0.25 mm水稳性团聚体有机碳含量极显著相关(P0.01),与5～2 mm团聚体有机碳含量显著相关(P0.05)。可见,撂荒恢复促进了土壤有机碳及水稳性团聚体有机碳含量的提高,从而提高了团聚体的稳定性。     

不同生长年限紫花苜蓿草地土壤团聚体有机碳分布特征

对黄土高原地区不同生长年限紫花苜蓿(Medicago sativa L.)草地土壤团聚体0~40 cm土层的分布及其有机碳含量特征进行研究。结果表明:土壤总有机碳随着生长年限的增加而呈先增加后减小的趋势,各年限0~10 cm土壤有机碳含量均最高,呈表聚现象。不同生长年限紫花苜蓿湿筛处理下土壤团聚体均以0.106 mm粒级团聚体为主,约为40%~90%,随土层深度增加而减小;0.25 mm粒级团聚体在4年时含量最高,并随生长年限的增加呈先增加后减小的趋势。不同年限紫花苜蓿土壤团聚体有机碳以0.106 mm粒级团聚体含量最高,随粒级的减小而增加;不同年限紫花苜蓿土壤20~40 cm团聚体有机碳含量高于0~20 cm土层,并随生长年限增加呈先增加后减小的趋势。     

黄土丘陵区植被恢复中不同粒级土壤团聚体有机碳分布特征

对黄土丘陵区土壤有机碳在不同粒级团聚体中的分布特征及其对植被恢复的响应进行了研究。结果表明:(1)黄土丘陵区不同植被覆盖条件下,土壤有机碳的分布具有一定的表聚性,0~20 cm土层中有机碳的含量均高于20~40 cm中有机碳的含量,不同植被群落下有机碳的含量大小为:大针茅群落>长芒草群落>铁杆蒿群落>百里香群落;(2)同一深度土壤各粒级团聚体中有机碳的分布特征是:0.5~0.25 mm与1~0.5 mm两个粒级中有机碳的含量最高,>1 mm的团聚体中有机碳的含量有随粒级增大而减小的趋势;(3)恢复年限对不同粒级土壤团聚体中有机碳的含量影响很大,有机碳的含量随恢复年限的增加总体呈上升趋势。黄土高原沟壑区土壤有机碳的积累与土壤团聚体的粒级和植被恢复的类型、年限等有明显的关系。     

黄土丘陵区刺槐林土壤团聚体稳定性和土壤可蚀性动态变化

退耕还林工程是黄土高原控制水土流失的主要措施之一,探讨退耕还林对土壤团聚体稳定性与土壤可蚀性的影响,可为黄土高原地区生态恢复和水土保持效益评价提供科学依据。以农田为对照,选取不同退耕年限(5,10,15,20,25,30年)刺槐林为研究对象,研究退耕还林后0—30 cm土层土壤团聚体稳定性和土壤可蚀性动态变化,并探讨土壤可蚀性与土壤团聚体稳定性之间的关系。结果表明:(1)＞0.25 mm水稳性团聚体含量、平均重量直径、几何平均直径随着退耕年限增加呈递增趋势,三者相比退耕前(农田)分别增加32%~79%,32%~98%,2%~60%。(2)土壤团聚体分形维数随着退耕年限增加呈递减趋势,较退耕前减少0.6%~6.0%;土壤有机质随着退耕年限增加呈递增趋势,较退耕前增加8.4%~38.9%。(3)土壤可蚀性因子(K)随着土层增加而增加,但随退耕年限增加呈递减趋势,随退耕年限递增(K)分别减少1.0%,2.7%,3.6%,3.9%,5.0%,7.9%。(4)退耕还林后,＞0.25 mm水稳性团聚体含量和土壤团聚体分形维数是土壤可蚀性变化的主要驱动因子; 地上生物量通过影响＞0.25 mm水稳性团聚体含量和土壤团聚体分形维数间接影响土壤可蚀性因子(K),且总效应最大。退耕还林后地上生物量增加对土壤团聚体的形成与稳定,以及土壤可蚀性降低起着重要作用,且退耕还林可显著提高团聚体稳定性,降低土壤可蚀性。     

耕作措施对旱作农田土壤颗粒态有机碳的影响

为了探明耕作措施对陇中黄土高原旱作农田土壤有机碳的影响,以连续进行17年的不同耕作措施长期定位试验为研究对象,利用碘化钠重液分组法,探索了传统耕作(T)、传统耕作+秸秆还田(TS)、免耕(NT)、免耕+秸秆覆盖(NTS)4种耕作措施对陇中黄土高原旱作农田土壤游离态颗粒有机碳、闭蓄态颗粒有机碳、颗粒态有机碳和矿质结合态有机碳的影响。结果表明:土壤总有机碳含量随土层加深而降低,游离态颗粒有机碳、闭蓄态颗粒有机碳、颗粒态有机碳的含量和占土壤总有机碳的比例均随土层加深而降低,而矿质结合态有机碳含量和占土壤总有机碳比例则随土层加深而增加。在0~40 cm各土层,各处理土壤颗粒态有机碳占总有机碳的比例(54.02%~76.78%)均高于矿质结合态有机碳占总有机碳的比例(31.78%~46.11%)。较之T处理,TS和NTS处理均不同程度提升土壤游离态颗粒有机碳、闭蓄态颗粒有机碳、颗粒态有机碳的含量和占土壤总有机碳的比例,其中NTS处理的提升效果最显著,TS处理次之。虽然NT、TS、NTS处理可提升土壤矿质结合态有机碳含量,但T处理下的矿质结合态有机碳占总有机碳的比例高于NT、TS和NTS处理。耕作模式和秸秆添加模式均对土壤总有机碳、游离态颗粒有机碳、闭蓄态颗粒有机碳、颗粒态有机碳和矿质结合态有机碳的提升具有显著效应,但秸秆添加模式的效应高于耕作模式。同时,免耕模式仅对0~10 cm各土层土壤总有机碳的提升效应达到显著水平,对0~20 cm各土层土壤碳组分的提升效应均达显著水平,而添加秸秆对0~40 cm各土层土壤总有机碳和各组分均发挥着显著提升效应。综合来看,免耕配合秸秆还田可以提升土壤活力,促进土壤固碳,有利于该区构建环境友好型和可持续发展型农业生产模式。     

不同秸秆还田年限对稻麦轮作土壤团聚体和有机碳的影响

为了揭示稻麦轮作不同秸秆还田年限下土壤团聚体稳定性以及有机碳组分的变化特征及其响应机制,采用大田小区试验,考察不同秸秆还田年限(0,3,4,5,6,7,8,9a)对土壤团聚体分布特征和团聚体稳定性指数(平均重量直径MWD、几何平均直径GMD、分形维数D)的影响,并研究其与土壤有机碳组分的相关性。结果表明,秸秆还田条件下土壤大团聚体数量R_(0.25)、MWD和GMD均显著提升,分形维数D则显著降低,随还田年限越长趋势越明显,但短期秸秆还田(5a以内)对土壤MWD和分形维数D的改善效果不显著;长期秸秆还田显著提升了土壤总有机碳TOC,但短期秸秆还田(5a以内)与不还田处理差异不显著,长期和短期秸秆还田均对活性有机碳AC的提升效果显著;多元回归分析显示,相比AC,土壤团聚体结构稳定更能促进TOC的增长,GWD与土壤有机碳组分的拟合度最高,更适合用于揭示团聚体与有机碳组分之间的关系。     

半干旱区草粮轮作田土壤水分恢复效应

采用野外实地观测和作物模型模拟相结合的方法,研究了不同轮作模式黄土高原半干旱区长期种植苜蓿地农田土壤水分恢复状况。结果表明：长期连作苜蓿地土壤干燥化进程与不同轮作模式下土壤湿度恢复的进程均表现为前期快后期慢;8～10 m深层土壤湿度恢复困难,6～8年生苜蓿草地翻耕后适宜采用PPW轮作模式（马铃薯→马铃薯→春小麦）以恢复土壤水分,种植16～20 a粮食作物后可以再次种植苜蓿。该研究结果可为黄土高原半干旱区苜蓿草地的土壤水分利用和恢复提供参考。     

长期保护性耕作对黄绵土总有机碳和易氧化有机碳动态的影响

长期定位试验研究了黄土高原西部旱农区不同耕作措施(传统耕作T、免耕+秸秆覆盖NTS、免耕NT、传统耕作+秸秆翻埋TS、传统耕作+地膜覆盖TP和免耕+地膜覆盖NTP)对黄绵土土壤总有机碳和易氧化有机碳的影响。结果表明, 土壤有机碳含量随土壤深度的增加而降低, 10~30 cm土层土壤有机碳含量的下降较为明显, 并且在0~5 cm、5~10 cm和10~30 cm土层中, 均表现为由研究初期各处理相对差异较小到试验中后期各处理出现显著差异的变化。不同耕作措施下0~30 cm土壤总有机碳和易氧化有机碳在2002-2012年的平均含量均为NTS>TS>NTP>NT>T>TP。与传统耕作相比, 免耕各处理和传统耕作秸秆翻埋处理可增加1.2%~7.2%的土壤总有机碳, 5.3%~16.6%的土壤易氧化有机碳含量, 而传统耕作覆膜处理分别降低4.3%和2.7%。免耕和秸秆覆盖处理均有利于黄绵土土壤有机碳和易氧化有机碳的积累, 免耕结合秸秆覆盖效果最佳, 而多年传统耕作覆盖地膜后有机碳明显降低。免耕秸秆覆盖处理土壤总有机碳和易氧化有机碳含量平均值在2004年、2006年、2008年、2010年及2012年分别较2002年提高9.5%和42.9%、13.2%和67.6%、21.5%和71.5%、1.1%和15.9%、2.7%和12.6%。因此, 在西部黄土高原黄绵土区, 采用免耕结合秸秆覆盖的保护性耕作措施有利于土壤总有机碳和易氧化有机碳含量的提高, 从而有利于土壤质量的持续改善。易氧化有机碳对不同耕作措施的响应比总有机碳更灵敏, 可以将其作为指示黄绵土有机碳变化的早期指标。     

黄土高原半干旱偏旱区苜蓿-粮食轮作土壤水分恢复效应

该文测定和分析了黄土高原半干旱偏旱区不同生长年限苜蓿草地以及轮作不同年限粮食作物后0～1000 cm深层土壤水分变化规律.结果表明:随着苜蓿生长年限的延长,苜蓿草地土壤干层厚度逐渐增加,3年生苜蓿草地土壤干层深度达到760 cm,6、7、10年生苜蓿草地土壤干层深度均超过1000 cm,6年生苜蓿地1000～1500 cm土层仍为干燥层,土壤平均湿度为9.68%;采用草粮轮作能明显减小苜蓿草地干层的厚度和范围,0～1000 cm土壤水分较10年生苜蓿草地都有不同程度的恢复,轮作2、6、8、12和18 a粮田平均土壤水分恢复速率25.2 mm/a,年均累积恢复土层厚度123.1 cm,0～300 cm土层水分恢复程度较高,且轮作年限愈长,土壤水分恢复效果越好,轮作18 a粮食作物后0～660 cm土层土壤水分恢复量达到了531.1 mm;苜蓿草地适宜翻耕年限为5～6 a,且6年生苜蓿草地0～1000 cm土壤水分恢复到当地土壤稳定湿度值需要23.8 a,该地区适宜的苜蓿-粮食轮作模式为"5～6年生苜蓿→24年粮食作物".     

陇东黄土高原苜蓿草地土壤水分消耗及水分生态效应（英）

黄土高原地区土壤干化导致林草植被大面积衰退,研究苜蓿草地土壤水分消耗规律对该区农业持续发展及生态环境恢复具有重要的理论意义。该文研究了黄土高原地区不同生长年限苜蓿草地1 000 cm土层土壤水分的变化特征及其对土壤水分生态环境的影响。结果表明：在0～1 000 cm土层,4年、6年生苜蓿草地土壤水分条件最好;12年、18年、26年生苜蓿草地土壤水分条件最差。在黄土高原地区,苜蓿地土壤干层出现的区域及发生的程度不同。4年、6年、8年生苜蓿草地,对土壤水分生态环境不会产生不利影响;12年、18年、26年生苜蓿草地,对土壤水分生态环境产生深刻负面影响。研究表明在陇东黄土高原地区苜蓿生长6 a后,应实施粮草轮作,以恢复土壤水分,持续提高土地生产力水平。     

Soil carbon pool and effects of soil fertility in seeded alfalfa fields on the semi-arid Loess Plateau in China

The dynamics of the soil organic carbon pool and soil fertility were studied in soils with different number of growing years of alfalfa (Medicago sativa L.) in the semiarid Loess Plateau of China. The soil water content and soil water potential decreased and the depth of desiccated layers grew with the number of growing years of alfalfa. The soil organic C (SOC) cannot be enhanced on short timescales in these unfertilized and mowed-alfalfa grasslands in the topsoil, but the light fraction of organic C (LFOC), soil microbial biomass C (MBC) and microbial biomass N (MBN) all increased with the number of growing years. When alfalfa had been growing for more than 13 yr, the soil MBC increased slowly, suggesting that the MBC value is likely to reach a constant level. SOC, soil total P (STP), available P (AvaiP) and the ratio of SOC to soil total N (C/N) all decreased monotonically with the growing years of alfalfa up to 13 yr and then increased. SOC was significantly positively correlated with STP, AvaiP, soil total C (STC) and soil total N (STN) (R=0.627**, 0.691**, 0.497*, 0.546*, respectively). MBC and LFOC were significantly positively correlated with the number of growing years of alfalfa (R=0.873*** and 0.521*, respectively), and LFOC was more sensitive to vegetation components, degree of cover and landform than to the number of years of growth. SOC showed a significant negative correlation with LFOC/SOC and MBC/SOC (R=−0.689**, −0.693**, respectively). A significant positive correlation exists between MBC and soil inorganic C (SIC). LFOC, MBC, LFOC/SOC and MBC/SOC were all significantly positively correlated with each other. Therefore, practices that involve water-harvesting technologies and add residues and phosphate fertilizer to soils should be promoted to improve soil nutrients and hydration and to postpone the degradation of alfalfa grasslands under long-term alfalfa production.     

Crop management effects on soil carbon sequestration on selected farmers’ fields in northeastern Ohio

Soil organic carbon (SOC) pool is the largest among terrestrial pools. The restoration of SOC pool in arable lands represents a potential sink for atmospheric CO₂. Restorative management of SOC includes using organic manures, adopting legume-based crop rotations, and converting plow till to a conservation till system. A field study was conducted to analyze soil properties on two farms located in Geauga and Stark Counties in northeastern Ohio, USA. Soil bulk density decreased with increase in SOC pool for a wide range of management systems. In comparison with wooded control, agricultural fields had a lower SOC pool in the 0–30 cm depth. In Geauga County, the SOC pool decreased by 34% in alfalfa (Medicago sativa L.) grown in a complex rotation with manuring and 51% in unmanured continuous corn (Zea mays L.). In Stark County, the SOC pool decreased by 32% in a field systematically amended with poultry manure and 40% in the field receiving only chemical fertilizers. In comparison with continuous corn, the rate of SOC sequestration in Geauga County was 379 kg C ha⁻¹ year⁻¹ in no-till corn (2 years) previously in hay (12 years), 760 kg C ha⁻¹ year⁻¹ in a complex crop rotation receiving manure and chemical fertilizers, and 355 kg C ha⁻¹ year⁻¹ without manuring. The rate of SOC sequestration was 392 kg C ha⁻¹ year⁻¹ on manured field in Stark County.     

轮作模式与周期对黄土高原旱地小麦产量、养分吸收和土壤肥力的影响

【目的】粮草轮作、粮豆轮作是黄土高原旱地区常见种植制度,本文利用长期定位试验探索该地区轮作制度和茬口年限对小麦产量、养分吸收和土壤肥力的影响,以期优化旱地作物种植制度。【方法】长期定位试验始于1984年,试验设8个处理:对照(小麦连作,CK),粮草长周期轮作(3组种植方式:2茬小麦→4茬苜蓿→1茬马铃薯→小麦,WAT1;小麦→4茬苜蓿→1茬马铃薯→2茬小麦,WAT2;4茬苜蓿→马铃薯→3茬小麦,WAT3),粮草短周期轮作(2组种植方式:小麦+红豆草→红豆草→小麦,WST1;红豆草→小麦→小麦+红豆草,WST2),粮豆轮作(2组种植方式:小麦+糜子→豌豆→小麦,WPT1;豌豆→小麦→小麦+糜子,WPT2)。小区面积66.69 m2,每个处理重复3次,随机区组排列。小麦收获后采集植物及土壤样品,测定小麦产量、籽粒和秸秆养分含量、土壤肥力性质。【结果】与小麦连作相比,轮作小麦籽粒增产1.47%~29.66%,秸秆增产2.17%~29.77%,粮草轮作增产效果更显著,轮作优势在豆科牧草后第二年最高,第三年减弱。粮草长周期轮作有利于小麦对N、K、Fe、Cu、Zn的吸收,吸收量在苜蓿茬后第三年第二年第一年;粮草短周期轮作可提高小麦对N、K、Fe的吸收量,红豆草茬后第1年吸收量稍高于后第二年;粮豆轮作有利于小麦吸收N、K、Fe、Mn,豌豆茬后第二年吸收量大于第一年。轮作制度和茬口年限对小麦微量元素养分收获指数的影响程度大于大量元素,粮豆轮作有利于N、P、Cu向籽粒转移,3种轮作制度下小麦K收获指数均低于连作小麦,粮草轮作中小麦Fe收获指数低于连作小麦。轮作后,土壤全氮增加11.54%~20.51%,碱解氮提高9.66%~21.56%;粮草短周期轮作对土壤有机质、氮素和速效钾的提升作用突出,但有效磷亏缺23.97%;粮豆轮作对土壤磷素累积和有效化作用明显,其有效磷比小麦连作增加45.52%。【结论】黄土高原旱地区增加小麦产量、改善籽粒矿质营养,实现土壤培肥的较优轮作模式为红豆草(2~4年)→小麦(2年),以4~6年为一个轮作周期,同时注意增施磷肥。     

Effects of vegetation restoration on soil organic carbon sequestration at multiple scales in semi-arid Loess Plateau,China

Soil organic carbon (SOC) sequestration by vegetation restoration is the theme of much current research. Since 1999, the program of “Grain for Green”has been implemented in the semi-arid Loess Plateau, China. Its scope represents the largest vegetation restoration activity in China. However, it is still unclear for the SOC sequestration effects of vegetation cover change or natural succession promoted by the revegetation efforts at different scales under the semi-arid conditions. In this study, the changes in SOC stocks due to the vegetation restoration in the middle of Loess Plateau were estimated at patch, hill slope transect and small watershed scale from 1998 to 2006. Soil samples were taken from field for the determination of cesium-137 (¹³⁷Cs) and SOC contents. Vegetation cover change from 1998 to 2006 at the small watershed scale was assessed using Geographic Information System. The results showed that cropland transforming to grassland or shrubland significantly increased SOC at patch scale. Immature woodland, however, has no significant effect. When vegetation cover has no transformation for mature woodland (25 years old), SOC has no significant increase implying that SOC has come to a stable level. At hill slope scale, three typical vegetation cover patterns showed different SOC sequestration effects of 8.6%, 24.6%, and 21.4% from 1998 to 2006, and these SOC increases mainly resulted from revegetation. At the small watershed scale, SOC stocks increased by 19% in the surface soil layer at 0–20 cm soil depth from 1998 to 2006, which was equivalent to an average SOC sequestration rate of 19.92 t C y^− 1 km^− 2. Meanwhile, SOC contents showed a significant positive correlation (P < 0.001) with the ¹³⁷Cs inventory at every soil depth interval. This implied significant negative impacts of soil erosion on SOC sequestration. The results have demonstrated general positive effects of vegetation restoration on SOC sequestration at multiple scales. However, soil erosion under rugged topography modified the spatial distribution of the SOC sequestration effects. Therefore, vegetation restoration was proved to be a significant carbon sink, whereas, erosion could be a carbon source in high erosion sensitive regions. This research can contribute to the performance assessment of ecological rehabilitation projects such as “Grain to Green” and the scientific understanding of the impacts of vegetation restoration and soil erosion on soil carbon dynamics in semi-arid environments.     

Crop rotation with plastic mulching increased soil organic carbon and water sustainability: A field trial on the Loess Plateau

Appropriate crop rotations are beneficial for food security and carbon sequestration. In cool and semiarid rain-fed areas, however, the effect on carbon sequestration in soil and the soil–crop system is not clear. In this study, a crop rotation field experiment was carried out on the Loess Plateau, China, involving (1) wheat continuous cropping (WCC), (2) maize continuous cropping (MCC), (3) potato continuous cropping (PCC) and (4) wheat–maize–potato rotating cropping (RC). All treatments were tilled once, and then, plastic mulched immediately to inhibit evaporation. We found that the rotating cropping system improved water storage in the 0–300 cm soil profile by 65.8 mm through the 6 years, while MCC depleted deep soil moisture. In a drought year, total dry matter (DM) for the rotating cropping was greater by 23.9% and 79.3% and harvested carbon quantity (HCQ) by 0.6 and 1.8 Mg ha⁻¹ compared with WCC and MCC systems, respectively. Total evapotranspiration significantly decreased by 14.5% compared with MCC, with no significant change compared with WCC and PCC. The soil organic carbon (SOC) concentration at 20–30 cm depth in the rotating cropping system was 36.0%, 28.0% and 30.3% greater than those of WCC, MCC and PCC, respectively. Similarly, the SOC sequestration rate at this depth was higher by 3.8, 3.2 and 3.4 Mg ha⁻¹, respectively. The pure carbon accumulation (PCA) of the rotating cropping system significantly increased compared with WCC and PCC, resulting in increased water use efficiency of pure carbon accumulation (WCP) by 11.1, 2.2 and 3.1 Mg ha⁻¹ mm⁻¹ compared with the WCC, MCC and PCC systems, respectively. Overall, the rotating cropping (RC) system maintained better soil water conditions, sustained crop development and SOC sequestration, especially optimizing the relationship between crop water utilization and SOC sequestration in soil–crop system in the cool semiarid rain-fed area.