Soil quality effects on regeneration of annual Medicago pastures in the Swartland of South Africa

Annual medic (Medicago spp.) pastures are widely used as the forage component of crop rotation systems in the Mediterranean region of South Africa. Reliable establishment of medics can be challenging. This may be related to poor soil quality, an inherent problem of soils in the region often aggravated by poor management. The aim of this study was to determine the underlying soil quality factors that result in classifying soils as having low, medium and high medic pasture production potential. The study was carried out on two farms that have followed crop/pasture rotation systems for the past 20 years. Two growing seasons (2015 and 2016) were evaluated on areas within fields that were identified to have poor, medium and high production potential. Soil samples were taken to evaluate soil quality and to determine the medic seed density in soil. Above-ground seed production and herbage production were monitored during the growing season. The low productivity soils had the lowest below-and above-ground seed density, medic seedlings establishment and medic herbage yield. Soil sodicity was one of the main factors decreasing pasture productivity. In a production system where medics need to regenerate effectively following good seed production, soil sodicity may be especially detrimental.     

放牧改变了藏北高原高寒草甸土壤微生物群落

本研究基于2008年7月布设的3个围栏与自由放牧样地(一个高寒草原化草甸,冬季牧场;一个高寒草原化草甸,夏季牧场;一个典型高寒草甸,夏季牧场),开展了藏北高原高寒草甸土壤微生物群落组成对放牧的响应研究。土壤微生物群落组成采用磷脂脂肪酸方法(phospholipid fatty-acid,PLFA)测定。结果表明,冬季放牧显著降低了高寒草原化草甸的土壤真菌、革兰氏阴性细菌、放线菌和原生动物。夏季放牧显著降低了典型高寒草甸的土壤总PLFA、真菌、细菌、革兰氏阳性细菌、革兰氏阴性细菌、放线菌、丛枝菌根真菌和原生动物。基于冗余度分析,3个放牧与围栏条件下的土壤微生物群落组成都存在显著差异。土壤无机氮和水溶性有机氮显著影响着高寒草原化草甸冬季牧场的土壤微生物群落组成,而硝态氮和水溶性有机碳显著影响着高寒草原化草甸夏季牧场和典型高寒草甸夏季牧场的土壤微生物群落组成。因此,放牧对高寒草甸土壤微生物群落的影响与放牧季节和草地类型有关。     

内蒙古苏尼特右旗草原土壤营养元素有效态含量分析

本研究选择内蒙古苏尼特右旗天然草场主要6个草场类,8个草场型,分析了0~30 cm土壤营养元素(全N、P、K、Ca、Mg、S、Fe、Mn、Cu、Zn、B和Mo)有效态含量及与土壤有机质、pH值之间的相互关系。结果表明,1)研究区土壤pH(8.84±0.23),均为碱性土壤;土壤有机质含量与全N含量均较低,平均分别为(9.92±4.65) g/kg和(0.46±0.25) g/kg;营养元素有效态含量积累顺序为:河泛地、湖盆低地盐生草甸草场类>荒漠草原草场区“小针茅+无芒隐子草+葱属”植被型>沙丘植被草场类,河泛地、湖盆低地盐生草甸草场类土壤矿质元素有效态含量显著高于其他草场类。2)土壤富含K元素,B和Mo处于严重缺乏状态;除了河泛地、湖盆低地盐生草甸草场类以外草场类微量元素含量均处于轻度缺乏或缺乏状态。3)土壤pH与土壤N、P、Ca、Mn和Cu元素有效量存在显著负相关性关系;土壤有机质则与土壤N、P、Ca、S、Fe、Mn和Cu元素有效量存在极显著正相关性关系。     

干旱区盐碱地不同栽培草地土壤理化性质及微生物数量

对宁夏干旱区盐碱地6种栽培草地0-20、20-40 cm土层土壤理化性质、土壤养分含量及微生物数量进行比较,旨在筛选出改善干旱区盐碱地土壤品质的优良草地。结果表明,各栽培草地0-20 cm土壤含水量、容重、pH值均低于20-40 cm,土壤养分及全盐含量均高于20-40 cm;豆科栽培草地改善两层土壤有机质、全氮、速效氮及降低20-40 cm全盐的效果强于禾本科,禾本科栽培草地保水蓄水、降低土壤容重及增加20-40 cm土层速效磷的效果强于豆科;豆科、禾本科栽培草地改善土壤品质的效果大小分别为紫花苜蓿(Medicago sativa)＞沙打旺(Astragalus adsurgens)＞黄花草木樨(Melilotus offcinalia)和圆柱披碱草(Elymus cylindricus)＞扁穗冰草(Agropyron cristatum)＞蒙杂冰草(A.cristatum×A.mongolicum);各栽培草地0-20 cm土层细菌、放线菌及真菌数量远大于20-40 cm土层,豆科、禾本科栽培草地两层土壤中3种微生物数量大小分别为紫花苜蓿＞沙打旺＞黄花草木樨和圆柱披碱草＞扁穗冰草＞蒙杂冰草;0-20 cm土壤含水量与真菌数量呈显著正相关(P0.05),20-40 cm土壤pH值与放线菌、真菌数量呈显著负相关(P0.05);两层土壤的全盐含量与细菌、放线菌及真菌数量均呈负相关,有机质、全氮、速效氮和速效钾与细菌、放线菌数量均呈极显著正相关(P0.01),速效磷、速效钾与真菌数量呈极显著正相关(P0.01)。     

矿区排土场人工草地土壤水分及入渗特征效应

本研究以露天煤矿排土场新土体上建植的不同人工草地为对象,分析了不同人工草地地上生物量、土壤水分及土壤入渗性能。结果表明,不同人工草地地上生物量之间差异显著(P<0.05),灌木和草灌混播草地的地上生物量比单一草种草地高,冰草+沙蒿和沙打旺+沙蒿草地地上生物量分别比单一种植冰草和沙打旺的草地高40.84%~47.88%和27.31%~53.49%;不同人工草地土壤含水量随深度增加而增大,20~30 cm层土壤含水量花棒草地最高;不同人工草地地上生物量和土壤水分的累加值呈负相关关系;草灌混播草地的平均土壤初始入渗速率比单一草种草地高44.25%。本研究结果表明,在矿区排土场新土体改良和植被恢复建设中应以草灌混播人工草地为主,可有效提高草地生产力,改善土壤的水分状况和入渗性能,利于植被生长的可持续。     

Nutrition of intensive pastures in the summer rainfall areas of southern Africa

Consideration is given to the current state of knowledge regarding the nutrition of cultivated pastures in the summer rainfall areas of southern Africa. Research efforts over the years have concentrated on the nitrogen (N) requirements of pastures, with relatively little significant work being undertaken on phosphorus (P), potassium (K) and lime. The numerous N response curves derived in cutting trials provide a useful basis for predicting N requirements under cutting‐and‐removal type utilization, but are of little value in predicting N requirements under grazing. The critical roles of P, K and lime in pasture productivity and persistence have been demonstrated in field trials undertaken in the Natal Midlands and south‐eastern Transvaal. Soil test calibrations, established for several important pasture species on Natal soils, have been found to provide a sound basis for predicting P, K and lime requirements of pastures. In considering the direction of future research, it is suggested that considerable potential exists for more efficient fertilizer and lime usage; research efforts should therefore be channelled in that direction.     

不同高寒草甸土壤碳氮稳定同位素和密度的差异

为了解不同类型高寒草甸土壤碳氮稳定同位素和密度的差异,采用稳定同位素质谱仪Isoprime100对采自黄河源区不同高寒草甸覆被条件下0~30 cm土壤进行了碳氮稳定同位素组成特征和密度分析。结果表明,高寒草甸土壤δ¹³C值介于-25.42‰~-24.20‰之间,δ¹⁵N值介于3.37‰~4.69‰之间,显著高于大气δ¹⁵N值。δ¹³C值和δ¹⁵N值均随土壤深度加深而增大。人工草地土壤δ¹³C值显著低于轻度和重度退化草甸(P<0.05),而δ¹⁵N值显著高于轻度和重度退化草甸(P<0.05)。土壤碳氮比最小值为7.89,最大值为9.97,平均碳氮比为8.71。土壤有机碳含量和全氮含量呈正相关(P<0.01),二者的回归方程为y=0.0963x+0.0336(R²=0.9619)。轻度退化草甸、严重退化草甸和人工草地0~30 cm土壤碳密度依次为7.14、6.67和6.46 kg/m²;全氮密度依次为0.83、0.77和0.75 kg/m²。植物吸收、生长有利于¹²C和¹⁴N的输出,而将较重的¹³C和¹⁵N留在了土壤中。人工草地植物生长势强,形成的地上生物量多,吸收了较多的土壤氮素¹⁴N,导致土壤¹⁵N升高。植被退化或种植人工草地均可导致土壤碳氮密度的显著降低,这种变化主要发生在0~20 cm土层。     

Grazing Management,Season, and Drought Contributions to Near-Surface Soil Property Dynamics in Semiarid Rangeland

Grazing management effects on soil property dynamics are poorly understood. A study was conducted to assess effects of grazing management and season on soil property dynamics and greenhouse gas flux within semiarid rangeland. Grazing management treatments evaluated in the study included two permanent pastures differing in stocking rate (moderately and heavily grazed pastures) and a fertilized, heavily grazed crested wheatgrass (Agropyron desertorum [Fisch. ex. Link] Schult.) pasture near Mandan, North Dakota. Over a period of 3 yr, soil properties were measured in the spring, summer, and fall at 0–5 cm and 5–10 cm. Concurrent to soil-based measurements, fluxes of carbon dioxide, methane, and nitrous oxidewere measured on 1-wk to 2-wk intervals and related to soil properties via stepwise regression. High stocking rate and fertilizer nitrogen (N) application within the crested wheatgrass pasture contributed to increased soil bulk density and extractable N, and decreased soil pH and microbial biomass compared to permanent pastures. Soil nitrate nitrogen tended to be greatest at peak aboveground biomass, whereas soil ammonium nitrogen was greatest in early spring. Drought conditions during the third year of the study contributed to nearly two-fold increases in extractable N under the crested wheatgrass pasture and the heavily grazed permanent pasture, but not the moderately grazed permanent pasture. Stepwise regression found select soil properties to be modestly related to soil–atmosphere greenhouse gas fluxes, with model r² ranging from 0.09 to 0.76. Electrical conductivity was included most frequently in stepwise regressions and, accordingly, may serve as a useful screening indicator for greenhouse gas “hot spots” in grazing land.     

Grazing Protection Influences Soil Mesofauna in Ungrazed and Grazed Riparian and Upland Pastures

The influence of grazing protection caused by streambank fencing on soil mesofauna density is unknown. Our objective was to determine if grazing protection (ungrazed vs. grazed), location (upland vs. riparian pasture), and seasonal (spring vs. fall) treatment effects associated with streambank fencing had a significant influence on soil mesofauna distribution and density. We collected five intact soil cores (0–5 cm depth) in June and October of 2012 from within four treatments consisting of ungrazed and grazed riparian and upland pastures associated with streambank fencing along an 800-m reach of the Lower Little Bow River in southern Alberta, Canada. Soil mesofauna were extracted and densities of Acari (mites) taxa, Collembola (springtails) taxa, and other mesofauna were determined. Grazing protection resulted in a significant (P ≤ 0.05) negative response of Astigmata mite densities for the upland pasture, and a positive response for Oribatida mites and total Collembola, and Hypogastruridae and Onychiuridae springtails for both pastures. Location and season had a significant influence on Acari and Collembola taxa, but the effects were dependent on interaction effects. We conclude that grazing protection influenced certain soil mesofauna in pastures associated with streambank fencing, and this may influence decomposition of soil organic matter, nutrient cycling, and soil structure in associated pastures.     

河西走廊盐渍土不同种植年限苜蓿根际磷含量变异特征

盐渍土的改良利用已有大量研究,但在盐碱地种植牧草的报道并不多.试验以河西盐渍地2、3、4、5、8龄苜蓿Medicago sativa的根际和非根际土壤为材料,研究土壤全磷及有效磷含量变异特征,结果表明,所有株龄苜蓿根际与非根际土壤全磷含量差异不显著,有效磷含量根际高于非根际土壤.在种植苜蓿的前5年,有效磷在根际与非根际均显著增加,种植8年开始降低,而全磷无显著变化规律.根际pH值低于非根际,但根际酸化不明显.根际与非根际土壤有效磷和全磷含量,根际pH值和有效磷含量相关性不显著.     

安太堡露天矿不同复垦年限苜蓿地土壤养分化学计量特征

对山西安太堡露天矿排土场不同复垦年限苜蓿地（3年、8年、20年）,自然恢复地和耕地不同深度土壤总有机碳（C）、全氮（N）、全磷（P）及其化学计量比进行分析,结果表明：土壤C、N随复垦年限延长递增,P相对稳定;耕地和20年苜蓿地,C、N随土层深度增加递减。20年苜蓿地0～10 cm土壤C、N分别较耕地提高30.1%和28.8%;0～40 cm与耕地接近,说明复垦能提高,特别是提高表层土壤C、N质量分数。C∶P,N∶P随复垦年限增加而上升,C∶N呈先增加、后降低的趋势;20年苜蓿地0～40 cm土壤C∶N,C∶P,N∶P均与耕地接近。土壤C和N极显著相关,C∶P,N∶P与C、N极显著相关,C∶N与C、N相关性不显著,说明C∶P,N∶P分别由碳、氮控制,C∶N受碳、氮共同控制,生物措施对复垦土壤C、N的提升作用比P明显。     

不同刈割频度对大针茅草原土壤呼吸及其土壤因子的影响

通过对大针茅草原土壤呼吸特性及影响因子的测定,研究3种不同刈割方式天然草地土壤呼吸特性及其影响因子,为典型草原刈割对碳收支研究提供基础理论依据。大针茅草原是亚洲中部草原亚区特有的一种草原类型。研究区设置在内蒙古锡林浩特市东部以大针茅建群的典型草原;在2009-2013年进行不同频度的刈割处理,一年两次、一年一次、两年一次(割一年休一年)、围封,在2013年8月采集测定土壤养分样品,在2013年生长季的6、7、8月进行土壤呼吸速率的测定及土壤微生物数量的测定。结果表明,围封处理下土壤含水量要高于其他刈割处理。6与8月时,围封处理下的细菌和微生物总数均显著高于刈割处理。不同频度刈割下群落的土壤呼吸速率有显著的差异,割一年休一年与围封处理显著高于其他刈割处理,且不同处理的土壤呼吸速率均在7月初为最低;土壤呼吸速率在内蒙古干旱半干旱地区与土壤含水量呈极显著正相关关系,受土壤含水量影响显著。结合生物多样性及生产利用的角度,割一年休一年为最合理的刈割频度。     

Performance of simple irrigation scheduling calendars based on average weather data for annual ryegrass

Poor irrigation management in pastures can lead to yield and quality reduction as well as loss of income through extra pumping and leaching of nitrate fertiliser. A number of irrigation scheduling techniques of varying levels of sophistication have been developed over the years to address limited irrigation water availability and maximise productivity. Despite this, the adoption of irrigation scheduling tools by farmers remains low. The objective of this study was to assess the use of simple irrigation scheduling calendars based on average weather data to improve irrigation management in ryegrass. The calibrated Soil Water Balance (SWB) model was used to generate simple irrigation calendars and assess effectiveness for different scenarios by mechanistically simulating water dynamics and pasture growth. Scheduling irrigation using the calendars gave similar irrigation applications, water losses and yields compared to a more scientific real-time scheduling (in response to soil water depletion by the crop). While site-specific irrigation scheduling calendars can easily be generated by consultants and irrigators, even simpler monthly estimates of average daily water use can also be useful. Application of calendars by farmers is encouraged to improve water and nutrient use efficiency of irrigated pastures, if real-time irrigation scheduling is not employed.     

黄河源区不同退化程度高寒草地土壤特征研究

研究了不同退化梯度的高寒草地不同层次（0～10cm,10-20cm和20-30cm）土壤理化性状变化特征。结果表明：随草地退化程度的加重,土壤含水量下降,土壤容重和pH值增加;土壤有机碳含量亦随退化程度加剧而降低,以0-10cm土层的降低最明显,轻度,中度和重度退化的“黑土滩”草地该土层有机碳含量与未退化草地相比,分别下降36．1％,66．79／6和73．5％;草地0-10cm土壤全氮、全磷含量大小顺序为轻度退化〉未退化〉中度退化〉“黑土滩”退化草地,全钾变化趋势不明显。轻度、中度、“黑土滩”退化草地0～10cm土层速效氮分别比未退化草地降低了21％,54％和64％,10-20cm土层中度退化草地和“黑土滩”分别降低了37％和21％;随草地退化程度加大,速效钾含量在各土层的变化趋势不同,但不同土层的最大速效钾含量均出现在轻度退化草地。     

Soil fertility management in pasture small-plot trials: potential pitfalls

Small-plot cutting trials are of particular importance in research relating to intensive pastures. Undetected changes in soil fertility during the course of experimentation may detract from the validity of results in trials of this kind. Information from field trials conducted in KwaZulu-Natal during the past two decades are used to illustrate the potential impact of soil fertility aspects in small-plot cutting trials. A major potential pitfall is the underestimation of potassium (K) depletion accompanying the removal of herbage at harvesting. In an Italian ryegrass trial 518 kg K ha^?1 was removed in harvested material in a single season. Failure to compensate (by fertilizer topdressings) for removals of K may result in growth, particularly in the more favourable treatments, being inadvertently restricted. Soil acidification during the course of experimentation is a second factor which may threaten the usefulness of data from cutting trials. Acidification is promoted by the application of relatively high rates of N fertilizers; in this context, variable acidification where N fertilization is a factor in trials warrants particular attention. Removals, immobilization and leaching of phosphorus and sulphur as well as inherent soil heterogeneity on the trial site are additional important considerations in small-plot trials. The only effective means of dealing with these problems is through the testing of soil samples drawn from individual treatments at suitably regular intervals.     

刈割对羊草草原土壤酶活性和养分含量的影响

土壤酶是土壤生态系统中最活跃的组分之一,是土壤中重要的生物活性物质,草地土壤酶活性与草地土壤养分含量关系密切。本文研究了刈割制度对呼伦贝尔羊草草原土壤酶活性和养分的影响,主要结果为:土壤脲酶、碱性磷酸酶对刈割制度的响应较为敏感,与逐年刈割相比,刈割间隔2年到6年草地0~30 cm土壤的脲酶活性提高了0.34~0.64倍,碱性磷酸酶活性降低了28.9%~44.2%。刈割对草地30~60 cm土壤养分含量影响更大,表现为土壤全氮、速效氮、全磷、速效钾和速效磷含量在各处理间0~30 cm土壤中没有显著的变化,仅6年1割样地较逐年刈割样地土壤有机质含量增加了10.5%;随刈割间隔年限的增加,30~60 cm土壤全氮和有机质含量变化范围分别为0.36~0.66 g/kg和12.26~17.73 g/kg,并且速效钾和速效磷含量都有降低的趋势。不同刈割制度下草地土壤养分含量与土壤酶活性的关系不尽相同,正负兼有。研究结果表明逐年刈割对土壤养分的影响有限,逐年刈割适用于该研究区的草地管理。     

黄土丘陵区不同撂荒年限自然恢复的退化草地土壤养分及酶活性特征

黄土丘陵区不同撂荒年限的自然恢复草地土壤中有机质、全N、有效N和速效P以及土壤蔗糖酶、脲酶、中性磷酸酶活性在剖面的分布均为上高下低,并随着土层的加深而降低。随着草地利用时间的增长,土壤有机质等养分和三种酶活性含量增高,活性增强。土壤养分及酶活性均以永久草地最高,三种酶活性与有机质和全N都呈明显的正相关,与有效N和速效P的相关不明显。人工草地不能增加土壤养分含量和酶活性,反而会大量消耗土壤养分使其肥力逐渐降低。     

利用方式对盐渍化土壤中有机质和盐分的影响

在河西盐渍化土地区选择了天然草地、小麦地、1年生苜蓿地、2年生苜蓿地和3年生苜蓿地,就不同利用方式对盐渍化土有机质和盐分的影响进行了研究.结果表明,种植农作物后,土壤的有机质含量明显下降;种植苜蓿后,前2年土壤有机质含量减少,3年后显著增加.土壤盐分在开垦种植后显著下降,苜蓿地的降盐效果更好.可溶性阳离子中,Mg2 含量的下降趋势最大,其变化曲线与全盐相同;Na 向土壤下层迁移,Ca2 含量随土壤深度的增加而降低, K 含量下降.     

不同恢复模式对草甸草原带土壤碳积累的影响

以科尔沁沙地南缘的果-草、果-田、林地、栽培草地、天然草地及农田6种不同恢复模式的风沙土为研究对象,利用土壤有机碳密度指标分析不同利用模式对风沙土土壤碳积累的影响.结果表明,在6种恢复模式中,1m深土层农田模式的有机碳密度极显著高于其他模式的有机碳密度(P＜0.01).6种恢复模式的碳积累呈3种特点:其一,果-草和林地...     

不同生长年限苜蓿栽培草地CO2通量的初步研究

以种植第1年、第2年、第3年和第5年的紫花苜蓿阿尔冈金（Medicago sativa cv. Algonquin）为对象,通过研究其光合生理特性、土壤呼吸以及土壤有机碳的净通量等分析不同生长年限苜蓿草地碳通量的变化规律。结果表明,不同生长年限的苜蓿草地净光合速率呈单峰曲线,第1年和第5年在盛花期达到最大,分别为50和69 μmol/(m2·s),第2年和第3年在结荚期达到最大值,分别为60和72 μmol/(m2·s),与叶绿素a和b的含量不相关（P＞0.05）。苜蓿草地土壤呼吸的动态变化呈不规则单峰曲线变化,6月24日达到最小值,7月达到最大值,平均值为第5年＞第2年＞第3年＞第1年。土壤呼吸速率与土壤温度无明显的相关性（P＞0.05）;除第1年外,与土壤湿度显著相关（P＜0.05）,其中,第3年和第5年极显著相关（P＜0.01）。第1年、第2年、第3年和第5年的苜蓿土壤有机碳的净通量分别为3.71、-1.71、12.17和12.53 g/kg。