农业耕作措施对非点源污染的影响

美国1987年的国土资源调查提供了伊利诺斯州100块随机抽取的玉米和大豆作物样地,在传统耕作和免耕耕作方式下分别实行了玉米连续种植和玉米—大豆轮作种植。结果表明,每种作物产量均接近水土保持局所估算的产量,但免耕法可大大减少土壤侵蚀速率和营养物质N、P的流失。作物根系周围的渗透流中的硝酸盐N的含量较高,超过了饮用水标准值(10mg/1),因此这里亦是地下水污染区。玉米—大豆轮作种植样地的地表径流、亚地表径流和渗透流中与玉米连续种植样地的相比能减少10%~30%的可溶性氮肥流失。因免耕法撒播到土壤表面的磷肥不能立即与土壤混合,其地表径流中磷肥的流失量较大,但从淤积泥沙中流失的磷肥,传统耕作法高于免耕法。     

横垄耕作的面源污染截留效应研究

为了解横垄耕作的面源污染截留效应,选取吉林省长春市莫家沟小流域横垄耕作坡耕地为研究区,应用210Pbex核素示踪技术得到研究区土壤侵蚀模数为2 268 t/(km2.a),吸附态氮、磷流失负荷分别为4 889、2 022 kg/a;运用RU-SLE2.0模型,模拟在同等立地条件下顺坡耕作土壤侵蚀模数约为6 200 t/(km2.a)。对比结果表明:横垄耕作较顺坡耕作可减少约63%的土壤流失量及随土壤流失的吸附态氮磷负荷。     

东北黑土有机碳的分布及其损失量研究

为了分析东北黑土土壤有机碳(SOC)的分布特征及其开垦以来黑土SOC的损失程度,我们于2004～2005年在黑龙江和吉林两省采集了32个自然黑土剖面样品,在每个自然黑土样品附近对应采集32个景观条件相似的耕作黑土样品。结果表明,自然黑土样品0～30cm土层SOC含量平均为32.20 g kg-1,最高可达63.46 g kg-1,黑龙江省自然黑土SOC含量(34.55 g kg-1)高于吉林省(23.80 g kg-1)。耕作土壤SOC平均含量为22.71 g kg-1,远低于自然土壤。受温度的影响,随着纬度的增加,自然黑土与耕作黑土SOC含量逐渐递增。由于土壤侵蚀以及耕垦和去除作物残留物等农业管理措施的综合作用,使得耕作黑土表层SOC含量小于自然黑土。与自然黑土相比,耕作黑土0～10cm土层SOC损失量在26.84%～46.57%之间,亚表层损失相对较少。黑土SOC含量下降也是土壤水土流失致使黑土层变薄的一个直接表现。耕作黑土表层流失厚度可以通过自然与耕作黑土剖面SOC含量的分异差值来估算。通过对土壤剖面上SOC的分布进行校正剔除土壤侵蚀的影响后得到的同等深度SOC含量的差值才可视为由耕作以及有机质输入量差异等因素造成的SOC损失量。未经校正而进行的自然黑土和耕作黑土同一深度SOC含量的比较可能过高估计了农业管理措施对土壤SOC损失量的影响。     

三峡库区小流域旱坡地氮磷流失特征研究

为探讨三峡库区小流域旱坡地氮磷流失特征,采用标准径流小区对重庆市涪陵区珍溪镇王家沟小流域常规耕作方式(顺坡耕作)以及水土保持耕作方式(常规顺坡耕作+PAM土壤调节剂、免耕+顺坡种植+稻草覆盖、常规顺坡耕作+植物篱、免耕+横坡垄作、常规横坡耕作)下土壤氮素和磷素的流失量及形态特征进行分析。结果表明:(1)就旱坡地土壤氮素的流失特征而言,径流中氮素的流失量相对较小,最大值仅为53.63mg/m2;而泥沙中所携带的氮素流失量相对较大,其最大值达131.25mg/m2;整个观测期内,氮素的流失主要以颗粒态为主,颗粒态氮的流失量占总氮流失量的53.0%～62.0%。(2)就旱坡地土壤磷素的流失特征而言,各处理径流中磷素的总体规律基本表现为:常规顺坡耕作>常规横坡耕作>免耕+顺坡种植+稻草覆盖>常规顺坡耕作+PAM土壤调节剂>免耕+横坡垄作>常规顺坡耕作+植物篱;泥沙中所携带的磷素流失量相对于径流中的磷素流失量而言较大,最大值为58.14mg/m2;整个观测期内,颗粒态总磷流失量为水溶态总磷流失量的1.75～2.15倍,流失方式同样以颗粒态为主。总体而言,水土保持耕作方式下的氮磷流失量均小于常规耕作处理,能有效减少径流及泥沙中各形态氮磷的流失。     

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。     

东北薄层黑土区作物轮作防治坡面侵蚀的效果与C值研究

作物轮作通过影响通用土壤流失方程(USLE)中作物覆盖和管理因子C值的变化和改良土壤性质而减少坡面土壤侵蚀。基于东北薄层黑土区连续6年大豆—红小豆轮作和裸露休闲坡面小区的径流泥沙和降雨资料,分析了2011—2016年研究区侵蚀性降雨特征,探讨了作物轮作防治坡面土壤侵蚀的效果,研究了作物轮作C值的年内和年际动态变化。结果表明:研究区所有侵蚀性降雨皆发生在5—10月,其降雨量占全年降水量的32.5%～68.1%,且年内和年际分布不均。对于5°坡度的裸露小区,土壤侵蚀主要发生在6—8月,坡面径流量和土壤流失量分别为48.4mm和1 388.2t/(km~2·a);对于5°坡度的作物轮作小区,土壤侵蚀主要发生在5—7月,坡面径流量和土壤流失量分别为19.5mm和166.7t/(km~2·a)。与裸露休闲小区相比,作物轮作小区可使黑土坡面年径流量和土壤流失量减少59.7%和88.0%。大豆—红小豆轮作措施的多年平均C值为0.12,其中大豆作物的C值为0.04,变化范围0.007～0.080;红小豆作物的C值为0.38,变化范围0.28～0.46。大豆和红小豆作物的C值月变化分别为0.01～0.24和0.01～0.80,呈先减少后增加的变化趋势。大豆—红小豆轮作对东北薄层黑土区坡面土壤侵蚀防治有明显效果,研究结果可为薄层黑土区土壤侵蚀定量评价和预报模型的建立提供基础数据。     

不同利用方式及施肥对黑土地表磷素养分流失的影响

本文针对黑土利用现状,在吉林农业大学教学试验场黑土区选择不同利用方式的玉米地、休闲地、果园、草地,并在玉米区进行了不同数量的施肥。通过野外试验,采集2002年度5~10月历次自然降雨(共7次)产流及泥沙样品,同时采集降雨前后的耕层土壤样品,研究了黑土区地表径流对磷素养分特征及肥力退化的影响。结果表明:径流TP流失比和DP流失比随覆盖度都表现为先增加后逐渐降低;不同利用方式表层土壤的TP和DP相差很大,就全磷富积表现为果园>草地>玉米地>休闲地,可溶性磷的富积却表现为:休闲地>玉米>果园>草地;随P肥用量的增加而径流磷素(TP、DP)浓度及径流磷素流失量也增加;流失泥沙TP浓度随着磷素施入的增加而增加;泥沙磷素浓度、泥沙磷素流失量均比CK大,但泥沙流失量均比CK小;增施氮磷虽能增加作物的产量,但N、P施用量必须适度,从试验期间径流、泥沙的TP、DP流失量观测,可以初步得出黑土氮磷配合施肥的宜于选配的方案是B5区N98P44N570。     

窄草篱对径流及土壤流失的影响

采用降雨模拟试验 ,研究了设在小区基部 0 72m宽的牛尾梢草篱在免耕和耕作状态下对径流及土壤流失的作用。供试地块坡度为 8%～ 16 % ,已种植玉米 33a,建草篱 6a。通过对保留玉米秸秆和除去玉米秸秆的不同小区(3 7m宽 ,10 7m长 )进行 2h的模拟降雨 (6 4mm/h) ,结果发现 ,窄草篱可以大幅度减少径流量及土壤流失量。在免耕状态下 ,保留秸秆并设有草篱的小区与相应未设草篱的小区相比 ,径流平均减少 5 2 % ,土壤流失量平均减少5 3 %。而在耕作状态下 ,保留秸秆并设有草篱的小区与对照小区相比 ,径流平均减少 2 2 % ,土壤流失量减少 5 7% ;除去秸秆但设有草篱的小区比相应未设草篱的小区径流平均减少 41% ,土壤流失量平均减少 6 3%。由此可见 ,种植窄草篱是一项有效的水土保持措施 ,尤其在与其它耕作措施 (如免耕或少耕 )配合应用时 ,效果更佳。     

基于WEPP模型的土地整理对长期土壤侵蚀的影响

针对典型丘陵区土地整理项目,利用坡面土壤侵蚀WEPP机理模型,模拟不同坡地梯田改造后土壤流失量和产沙量的长期变化,及土地利用和耕作措施的影响。结果表明,随着坡度增加,坡地的梯田整理对于减少土壤流失量的作用减弱,但对于减少总产沙量作用增加。土地利用方式影响土壤流失量和产沙量,由高到低为常规耕作的农田、草地和灌丛。对于耕作措施来说,小麦玉米轮作条件下,免耕措施与传统的耕作措施相比,可以明显降低土壤流失量和产沙量。土壤流失量受降雨的影响制约,休闲地日降雨量超过12mm时产生土壤流失,而农田日降雨量超过20mm时才产生土壤流失,降雨量越大,梯田减少土壤流失的效应越明显。长期模拟结果表明,土壤流失的年际变化受降雨量变化主导,土壤流失量变化趋势与降雨量变化一致。     

不同土地利用方式对黑土胶散复合体的影响及与酸度的关系

以吉林省黑土玉米带区域内10对长期定位采样点的2种土地利用方式土壤(耕作黑土和防护林带黑土)为研究对象,采用胶散分组法提取土壤胶散复合体,探究长期不同利用方式对黑土胶散复合体和酸度的影响。结果表明:耕作黑土与防护林带黑土均表现为G_0与G_2组的绝对含量增加,G_1组的绝对含量下降,复合体总量分别下降了3.88%和0.28%。耕作黑土和防护林带黑土pH分别平均下降12.12%和3.77%,有机碳含量在耕作黑土和防护林带黑土中分别平均下降23.17%和9.00%,2种利用方式土壤的胡敏酸、富里酸、交换性钙离子和碳酸钙均出现下降;耕作黑土分别平均下降12.18%,3.53%,16.29%,31.53%;防护林带黑土分别平均下降20.07%,13.14%,2.81%,7.81%。G_1组与pH、HA、Ca~(2+)和CaCO_3呈极显著正相关,与FA呈显著负相关;G_2组与pH、HA、Ca~(2+)和CaCO_3呈极显著负相关。pH与HA、Ca~(2+)和CaCO_3呈极显著正相关,与FA呈显著负相关。经过11年的变化,黑土胶散复合体稳定性下降,相比非耕作状态下黑土,耕作模式下的黑土胶散复合体稳定性下降更为严重,胶散复合体总量下降的更多,酸度下降更为明显。Ca~(2+)和HA的变化是影响黑土土壤酸化和土壤团聚体稳定性的主要驱动因素。土壤酸化的结果使土壤胶散复合体数量减少,稳定性变差。     

Black soil degradation by rainfall erosion in Jilin,China

Black soils, originally characterized by a deep, dark A‐horizon, are widespread in the Northeast Plain of China and have been one of the most fertile agricultural resources in the country. However, more than a half‐century of intensified management degraded its productivity, mainly with the loss of the dark‐coloured A‐horizon by rainfall erosion. Using the Revised Universal Soil Loss Equation (RUSLE), the rainfall erosion losses of black soils in YuShu and DeHui counties of Jilin Province were estimated. The rate of loss of thickness of the A‐horizon of black soils and the time over which the A‐horizons of some black soils in the region might be lost were evaluated. The results showed that about 4–45 t ha⁻¹ topsoil could have been lost each year under corn (Zea mays L.) production. Soybean (Glycine max L. Merr) production would double the losses. Soil losses were directly related to soil type, tillage practices and crop grain yields. The thickness of the A‐horizon of black soils in the region decreased at rates of 0ċ5–4ċ5 mm yr⁻¹, depending on soil type and management practices. Corn production may have resulted in an annual loss of 8ċ3 million tonnes of topsoil from black soils alone in Jilin Province; soybean production could have greatly increased this loss. Traditional intensified farming can accelerate the degradation of black soils; conservation tillage has great potential to prevent rainfall erosion losses for the same soils. Accordingly, to preserve and restore the productivity of black soils, conservation tillage is appropriate and should be adopted in Jilin. Copyright © 2003 John Wiley & Sons, Ltd.     

基于最小数据集的吉林省黑土耕层土壤质量评价

黑土作为吉林中部平原粮食主产区主要土壤类型,其质量的优劣直接影响区域生态安全和农业可持续发展。该研究以吉林省典型黑土耕层土壤作为研究对象,采集1 401个土壤样本,测定8项土壤理化指标及玉米产量。采用最小数据集法筛选评价指标,对于黑土耕层土壤进行质量评价,并综合土壤质量指数和产量提出评价指标的适宜范围。结果表明:吉林省黑土耕层土壤质量评价最小数据集由耕层容重、有机质、速效磷、pH构成,由全量数据集(Total Data Set,TDS)、重要数据集(ImportantDataSet,IDS)和最小数据集(MinimumDataSet,MDS)分别计算的土壤质量指数之间存在显著正相关关系,R~2分别为0.716、0.771,表明MDS可以替代TDS对黑土耕层土壤质量进行评价。黑土玉米种植区耕层土壤质量指数分布在0.22～0.75之间,均值为0.53,呈现东部高西部低的趋势。土壤质量指数随产量先增加后降低。黑土耕层保持较高土壤质量及产量的评价指标适宜范围分别为:容重为1.23～1.43 g/cm3,酸碱度(pH值)为4.74～6.96,有机质为33.14～35.81 g/kg,有效磷为122.46～136.06 mg/kg。该研究结果可为吉林省黑土耕层土壤质量诊断、提高黑土肥力及选择适合农田管理措施提供理论及参数支撑。     

Effects of agricultural management systems on soil organic carbon in aggregates of Ustolls and Usterts

Soil erosion contributes to the removal and redistribution of soil organic C from cultivated fields. The soil organic C content of wind erodible and water unstable aggregates is an important factor in determining the amount of carbon loss occurring in erosion processes. The relative distribution of organic carbon among aggregate size fractions may also affect the response of soils to erosion. Soil organic C distribution is dependent on the chosen management system. The effects of no-till, till, and grassland management systems on organic C content of erodible and non-erodible aggregates were examined in six Ustolls and two Usterts of central South Dakota. Organic C contents were related to dry- and wet-sieving to represent the potential influence of wind and water erosion on C loss in the absence of vegetative cover. Loss of aggregate stability in cultivated soils was associated with organic C loss. Most structural characteristics developed under tilled systems persisted after 6–16 years of no-till. Changes in distribution of organic C due to management systems were most evident in Ustolls where cultivation resulted in net soil C losses. Soil organic C was not significantly increased by the no-tillage practices applied in this on-farm study (in Ustolls 49 Mg ha⁻¹ in no-till versus 41 Mg ha⁻¹ in till, for 0–0.20 m depth). Soil properties of Usterts were less affected by land use and management practices due to the high shrink swell action and self-mixing. In both soil orders the greater concentration of organic C in the wind erodible (<1 mm) dry aggregate size fraction implies a high potential for organic C loss by erosion in addition to organic C loss from mineralization after tillage. Grassland when compared to cultivated topsoil showed the largest amounts of organic carbon stored and the minimal potential for erosion loss of soil organic C.     

Tillage and crop management effects on soil erosion in central Croatia

Soil erosion continues to be a primary cause for soil degradation and the loss of soil quality throughout the world. Our objectives were to quantify soil erosion (referred to as erosional drift) and to assign erosion risk to six tillage and crop management treatments evaluated from 1995 to 1999 for a 5-year maize (Zea mays L.), soybean (Glycine hyspida L.), winter wheat (Triticum aestivum L.), oil-seed rape (Brassica napus var. oleifera L.), and spring barley (Hordeum vulgare L.) plus double-crop soybean rotation on Stagnic Luvisols in central Croatia. Standard black fallow (tilled, unsown, and without any vegetative cover) Universal Soil Loss Equation (USLE) plots were used to establish the erosion potential associated with the rainfall pattern for each year. Soil loss from the check plots was several times greater than the T value, which is estimated to be 10 t ha⁻¹ per year. During the 2 years when spring seeded maize or soybean were grown (1995 and 1996) erosion risk was extremely high, especially for treatments where tillage and planting (row direction) were up and down the slope. When autumn seeded winter wheat or oil-seed rape were grown (1996/1997 or 1997/1998), soil erosion was insignificant. Also, except when plowing and sowing were up and down slope, erosion loss for the spring barley plus double-crop soybean crops in 1999 was insignificant. With no-tillage, soil erosion from the maize and soybean crops was reduced 40 and 65% compared to plowing up and down slope, even though the planting direction was still up and down the slope. With the exception of maize in 1995, erosion losses were moderate to insignificant when plowing and planting were performed across the slope. We conclude that erosion risk can be used as a reliable indicator of sustainable land management and that using no-tillage or plowing and planting perpendicular to the predominant slope are effective soil conservation practices for this region.     

土壤有机质含量与玉米生产力的关系

土壤有机质是土壤肥力的重要指标。本文通过空间移位的方法,将东北黑土带由南向北5个点有机质含量为18.1g kg-1、31.1g kg-1、54.6g kg-1、103.9g kg-1、53.6g kg-1的农田黑土,分别移至黑龙江省的海伦市和吉林省的德惠市的两种气候下,通过田间试验的方法,研究了黑土有机质含量与玉米生产力的关系。结果表明,在相同的施肥条件下,土壤有机质含量与玉米产量间不存在显著相关关系,产量差异不显著;施肥对各种有机质含量的黑土均有显著增产作用,增产幅度在12.3%～64.1%,黑土带的南部区域德惠市的施肥增产作用要明显高于北部区域海伦市的增产作用。     

Soil microbial communities under different soybean cropping systems: Characterization of microbial population dynamics, soil microbial activity, microbial biomass, and fatty acid profiles

This work analyzes the direct effect of soil management practices on soil microbial communities, which may affect soil productivity and sustainability. The experimental design consisted of two tillage treatments: reduced tillage (RT) and zero tillage (ZT), and three crop rotation treatments: continuous soybean (SS), corn–soybean (CS), and soybean–corn (SC). Soil samples were taken at soybean planting and harvest. The following quantifications were performed: soil microbial populations by soil dilution plate technique on selective and semi-selective culture media; microbial respiration and microbial biomass by chloroform fumigation-extraction; microbial activity by fluorescein diacetate hydrolysis; and fatty acid methyl ester (FAME) profiles. Soil chemical parameters were also quantified. Soil organic matter content was significantly lower in RT and SS sequence crops, whereas soil pH and total N were significantly higher in CS and SC sequence crops. Trichoderma and Gliocladium populations were lower under RTSS and ZTSS treatments. Except in a few cases, soil microbial respiration, biomass and activity were higher under zero tillage than under reduced tillage, both at planting and harvest sampling times. Multivariate analyses of FAMEs clearly separated both RT and ZT management practices at each sampling time; however, separation of sequence crops was less evident. In our experiments ZT treatment had highest proportion of 10Me 16:0, an actinomycetes biomarker, and 16:1ω9 and 18:1ω7, two fatty acids associated with organic matter content and substrate availability. In contrast, RT treatment had highest content of branched biomarkers (i15:0 and i16:0) and of cy19:0, fatty acids associated with cell stasis and/or stress. As cultural practices can influence soil microbial populations, it is important to analyze the effect that they produce on biological parameters, with the aim of conserving soil richness over time. Thus, in a soybean-based cropping system, appropriate crop management is necessary for a sustainable productivity without reducing soil quality.     

不同农田植被条件下黑土坡耕地产流和产沙特征

[目的]研究不同农田植被条件下的水土侵蚀特征,为该区作物种类选择提供参考。[方法]2013年在位于东北典型黑土带上的黑龙江省红星农场径流小区内,开展了玉米、大豆、大豆—玉米间作3种农田植被条件下的地表径流和土壤侵蚀特征研究。[结果]玉米的径流拦蓄和土壤侵蚀控制的效果最好,间作次之,大豆位居最后;玉米和间作模式的地表径流分别较大豆减少了15.8%和10.7%,土壤侵蚀量亦分别减少了10.47%和5.35%。[结论]在较低降雨强度下玉米和间作的减流减沙效果差别不甚明显,在较高强度下玉米和间作减流减沙效果明显好于大豆。     

红壤坡地不同树种林下水土流失特征研究

利用浙江省兰溪水土保持综合试验站不同树种的7个径流小区连续9 a(1985-1997年)的监测资料,分析了不同树种林下水土流失的动态过程.结果表明:(1)在树木栽培的前2 a内水土流失较为严重,前2 a内水土流失除茶园地和松树林地外,占9 a水土流失总量的90％以上.随着树龄的增长,林木水土保持功能增加,小区水土流失趋于减缓,部分树种林下的侵蚀产沙接近于零.(2)前2 a内各林地小区水土流失强度排序为:杉树林＞密柑林＞稀柑林＞毛竹林＞混交林.林灌混交林地小区的水土保持功能最为明显.(3)茶园地在生产管理中,由于施肥和采茶等人为的干扰,水土流失没有表现出随树龄的增加而减缓的趋势,其水土流失年际间波动明显.研究表明,在培育水土保持林时,最初2 a内是加强林下水土保持的重要时段,茶园地加强施肥采茶等生产过程的人为干扰更是减少水土流失的关键.     

Overwinter soil denitrification activity and mineral nitrogen pools as affected by management practices

During freeze-thaw events, biophysical changes occurring in soils can affect processes such as mineralization, nitrification and denitrification which control inorganic N balances in agro-ecosystems. To evaluate the impact of these climatic events on soil biochemical properties, a study was conducted comparing soil denitrification enzyme activity (DEA), dissolved organic C (DOC) and inorganic N levels before and after the winter season in plots under: (1) continuous corn (Zea mays L.) (CC) with annual chisel plow and disking, (2) corn-soybean (Glycine max L.) (CS) rotation with chisel plow every other year prior to planting soybean, and (3) corn-soybean-wheat (Triticum aestivum L.)/hairy vetch (Vicia villosa Roth) (CSW-V) with ridge tillage during the corn and soybean crops, and dairy manure application during the corn year. Soil cores were collected in late autumn and immediately after spring thaw at 0-5, 5-10, 10-15, and 15-30 cm depths. Regardless of management practices, freeze-thaw events resulted in significant (2-10 times) increases in NH₄⁺-N, NO₃^--N (P<0.001) and DOC (P<0.01) levels at all soil depths. Following freeze-thaw, DEA remained unchanged in the 5-30 cm depth but dropped significantly (P<0.01) in the 0-5 cm soil layer. In that layer, soils which had been chisel plowed during the previous growing season lost 78-84% of the DEA recorded during the fall, whereas in the plots amended with manure during the previous season, the loss of activity was 40-45%. These data indicate that frequent tillage, compared with manure additions, is more conducive to overwinter loss of DEA in surface layers of soils subject to freeze-thaw cycles.     

Contrasting grain crop and grassland management effects on soil quality properties for a north-central Missouri claypan soil landscape

Abstract

Crop management has the potential to either enhance or degrade soil quality, which in turn impacts on crop production and the environment. Few studies have investigated how crop management affects soil quality over different landscape positions. The objective of the present study was to investigate how 12 years of annual cropping system (ACS) and conservation reserve program (CRP) practices impacted soil quality indicators at summit, backslope and footslope landscape positions of a claypan soil in north-central Missouri. Claypan soils are particularly poorly drained because of a restrictive high-clay subsoil layer and are vulnerable to high water erosion. Three replicates of four management systems were established in 1991 in a randomized complete block design, with landscape position as a split-block treatment. The management systems were investigated: (1) annual cropping system 1 (ACS1) was a mulch tillage (typically ≥ 30% of soil covered with residue after tillage operations) corn (Zea mays L.)–soybean (Glycine max (L.) Merr.) rotation system, (2) annual cropping system 2 (ACS2) was a no-till corn–soybean rotation system, (3) annual cropping system 3 (ACS3) was a no-till corn–soybean–wheat (Triticum aestivum L.) rotation system, with a cover crop following wheat, (4) CRP was a continuous cool-season grass and legume system. In 2002, soil cores (at depths of 0–7.5, 7.5–15 and 15–30 cm) were collected by landscape position and analyzed for physical, chemical and biological soil quality properties. No interactions were observed between landscape and crop management. Relative to management effects, soil organic carbon (SOC) significantly increased with 12 years of CRP management, but not with the other management systems. At the 0–7.5-cm soil depth in the CRP system, SOC increased over this period by 33% and soil total nitrogen storage increased by 34%. Soil aggregate stability was approximately 40% higher in the no-till management systems (ACS2 and ACS3) than in the tilled system (ACS1). Soil aggregation under CRP management was more than double that of the three grain-cropping systems. Soil bulk density at the shallow sampling depth was greater in ACS3 than in ACS1 and ACS2. In contrast to studies on other soil types, these results indicate only minor changes to claypan soil quality after 12 years of no-till management. The landscape had minor effects on the soil properties. Of note, SOC was significantly lower in the 7.5–15-cm soil depth at the footslope compared with the other landscape positions. We attribute this to wetter and more humid conditions at this position and extended periods of high microbial activity and SOC mineralization. We conclude that claypan soils degraded by historical cropping practices will benefit most from the adoption of CRP or CRP-like management.