Characterizing farming systems around Kakamega Forest,Western Kenya,for targeting soil fertility–enhancing technologies

Kakamega district in Western Kenya represents the smallholder farming systems typical for much of the densely populated humid highlands in East Africa. A specific feature, however, is the presence of a protected forest reserve (Kakamega Forest National Park), covering some 20% of the district area. Year‐round crop production with little use of external inputs is resulting in declining soil fertility and crop yields. Technologies to counteract fertility constraints are rarely implemented, as they do not consider system diversity or farm‐specific characteristics. We surmised that farm type–specific targeting of technology options to address soil fertility–related production constraints would reduce the anthropogenic pressure on the resources of the adjacent Kakamega rainforest reserve. Based on Kenyan national census data, we selected 168 farms in physical proximity of the Kakamega forest and characterized them regarding production system and soil attributes. Cluster and principal component analyses identified five distinct farm categories. Three representative farms from each cluster group were subsequently selected to establish labor‐use patterns, draw resource‐flow maps, and determine NPK balances. Small subsistence‐oriented farms were most common (> 50%), with maize yields of 0.9 t ha^–1 (Cluster 1). Most farmers relied on the forest to provide fire wood, animal feed, and medicinal plants. Mixed farms, combining subsistence maize with industrial crops, were differentiated by soil type, with tea being grown on Ferralsol (Cluster 3), and sugar cane being grown on Acrisol (cluster 4). The dependence on forest resources was limited to animal grazing and the collection of feed stuff (Cluster 3), or the extraction of medicinal plants (Cluster 4). Only few farms showed a high degree of market orientation of the food‐crop production. These comprised either small farms with high investments in fertilizer and maize yields close to 2 t ha^–1 (Cluster 2), or larger farms (1.6–3.9 ha) with low fertilizer but high hired‐labor use (Cluster 5). Their reliance on forest resources was generally low. Resource flows showed mainly patterns of nutrient export in subsistence farms, and more complex flow patterns, involving several farm compartments, in the diversified farms. Partial nutrient balances were strongly negative for N and K, irrespective of soil or farm type. Soil‐fertility characteristics reflected the nutrient balances with generally low C and N in all farms on Acrisol, and low P in farms not applying mineral fertilizers or farmyard manure. The proposed typology is expected to improve the targeting of technologies addressing soil fertility–related production constraints, and to reduce the pressure on forest resources. This is of particular importance in the case of small‐scale subsistence and mixed farms close to the forest margin.     

Effect of tillage,cropping, and mulching pattern on crop yield,soil C and N accumulation,and carbon footprint in a desert oasis farmland

The desert oasis is one of the major grain production areas in arid land, and many intensive farming practices have been adopted to improve the land utilization in the agriculture system. However, there remains little consensus on how to improve such farming practices for increasing both productivity and environment benefits in this system. A 4-year experiment was conducted in a typical desert oasis farmland to determine the effects of the farming practices on crop yield, soil carbon (C) and nitrogen (N) accumulation, and carbon footprint (CF). The farming practices included two tillage patterns: conventional (CT) and reduced tillage (RT), two cropping patterns: continuous (Con) and rotation cropping (Rot), and two mulching pattern: film (F) and straw mulching (S) with eight combined treatments. The RT did not significant decrease crop yield but increase soil C and N accumulation rate by 59% and 130%, and thus decrease CF for crop production compared with the CT. S can also improve soil C and N accumulation, and cause low CF for crop production, but leading to 14–41% decrease in maize yield compared with F. Rot result in a 14% increase on maize yield also has extra benefit to decrease CF for crop production, but no significant effect on soil C and N accumulation compared with Con. Our study adds a reasonable perspective on how to improve the conventional farming systems in desert oasis, the information about RT, straw mulching, and maize–soybean rotation have positive effect on improving soil quality and decreasing CF for crop production in this desert soil area is critical to develop the sustainable agriculture system in this desert oasis farmland, which both maintaining crop productivity and minimizing negative environmental impacts.     

吉林省农田黑土肥力变化趋势及评价

通过吉林省3个典型黑土实验点(15年玉米和水稻连作)的长期测定,对土壤养分变化进行了分析,并采用数值化的方法对其综合肥力进行了评价。研究结果表明,土壤有机质含量3个实验点均呈增加趋势;土壤全氮、碱解氮和速效钾含量平原玉米地呈下降趋势,而坡地玉米地和平原水稻田呈上升趋势;近年来,速效磷含量3个实验点均下降明显。肥力综合评价表明,平原玉米地的综合肥力略呈下降趋势,而坡地玉米地和平原水稻田的综合肥力呈现上升趋势,总体反映出在常规管理条件下,典型地块肥力15年来没有严重的退化现象。     

玉米残体分解对不同肥力棕壤团聚体组成及有机碳分布的影响

以棕壤肥料长期定位试验(29 a)形成的高、低两种肥力水平棕壤为研究对象,采用不同部位玉米残体为试验试材,分别向两种土壤中加入玉米根茬和茎叶,进行田间原位培养试验,试验设置6个处理:低肥力土壤添加玉米根茬(LF+R)、低肥力土壤添加玉米茎叶(LF+S)、高肥力土壤添加玉米根茬(HF+R)、高肥力土壤添加玉米茎叶(HF+S)和未添加玉米残体的对照处理(LF,HF)。本研究旨在探明玉米根茬、茎叶添加后不同肥力土壤团聚体组成及有机碳分布的变化规律,为构建合理的秸秆还田与施肥措施,减少土壤侵蚀提供理论依据。结果表明:1)添加玉米残体后低肥力棕壤团聚体稳定性、较大级别团聚体(2 mm和1~2 mm)有机碳贡献率的提升幅度比高肥力棕壤大,说明低肥力土壤对外源有机质的响应更敏感,向大团聚体转化的速率更快。2)培养结束时,高肥力棕壤添加茎叶处理团聚体稳定性显著高于添加根茬处理,而添加根茬处理各粒级团聚体有机碳含量显著高于添加茎叶处理;低肥力棕壤中根茬和茎叶添加处理团聚体稳定性及有机碳含量之间差异不明显。3)在田间原位培养过程中,棕壤2 mm和1~2 mm团聚体所占比例和团聚体稳定性呈现出前期(0~360 d)快速增加,后期(360~720 d)趋于稳定的趋势。可以看出,玉米残体对土壤团聚体团聚化过程的作用强度逐渐减弱。以上结果表明,作物残体输入对棕壤团聚体组成及有机碳分布的影响与棕壤肥力水平和不同残体部位间的差异关系密切。     

燕沟流域农田基础肥力分析与培肥途径

黄土丘陵区燕沟流域农田基础肥力水平低下,特别是近几年新修的梯田,土壤有机质、全Ｎ、水解Ｎ,速效Ｐ和阳离子量代换量都处于很低和低等水平,速效Ｋ为中低程度,土壤酶活性也很低。坝地土壤养分和酶生相对梯田较高,但大多也只处于中低水平,是影响农作物产量和限制农业发展的主要因素。土壤肥力水平提高的根本途径在于大量有机肥力的投入、农作物秸秆还田和增加养地作物种植面积来增加土壤有机质的含量。     

COMPARING FARMERS' PERCEPTION OF SOIL FERTILITY CHANGE WITH SOIL PROPERTIES AND CROP PERFORMANCE IN BESEKU,ETHIOPIA

Farmers' perceptions of soil fertility change were compared with observations on soil quality changes and crop performance in soils from a chronosequence representing a range of soil ages since conversion from forest to cropland (0 to 57 years). A majority of the farmers, 92 per cent, had observed a decline in soil fertility on their land. Farmers use crop yield, indicator plants, soil softness and soil colour to judge soil fertility. They identified 11 plants that they used to indicate high soil fertility and four plants that they used to indicate low soil fertility. There was a strong correlation (r = 0·96) between soil organic matter content (loss on ignition) and farmers' ranking of soil fertility based on colour and softness of soil samples from the chronosequence. The biotest experiment with maize showed an exponential decline in biomass production along the chronosequence, confirming the results of farmers' soil fertility ranking. In the biotest, total soil N predicted produced biomass well (r² = 0·95), whereas the relationship with soil available P (Olsen) was less obvious. Among the eight analysed plant nutrients in the maize leaves, N content was found to correlate best with biomass production (r² = 0·94). We conclude (i) that there is good agreement between farmers' knowledge and scientific indicators of soil fertility and (ii) that the major reason for declining soil fertility in Beseku is the decrease in N mineralization over time. Interventions should focus on supporting farmers to implement a diversified nutrient management strategy that can maintain or increase long‐term productivity of the soil. Copyright © 2011 John Wiley & Sons, Ltd.     

Effects of crop-slope interaction on slope runoff and erosion in the Loess Plateau

Crops are the most important ground cover on slope farmland and have a significant impact on the soil erosion. But soil erosion on slope farmland is also affected by many other factors, such as topography and rainfall. In order to explore the effect of crop growth on soil erosion on different slope gradient of slope farmland, and analyze the interaction of crop growth and slope gradient on soil erosion, this study used artificial simulated rainfall to observe the runoff rates and soil loss amounts under different slope gradients for maize, soybeans, and winter wheat in different growth stages. Results showed that crops and slope gradient both significantly affected production and development of slope runoff. Compared with bare land, mean runoff rate on slopes was reduced by 24%, 32%, and 94% respectively, and sediment yield was decreased by 44%, 55%, and 99% respectively on maize, soybean, and winter wheat fields. Inhibitory effects of crops on slope runoff rate and sediment yield were enhanced with crop growth and decreased with increasing slope gradient. Crop growth and coverage could offset the impact of increasing slope gradient on runoff and sediment to some extent and reduced water and soil loss on slopes. Sediment yield was produced largely when the slope gradient was greater than 10 degrees on maize and soybean fields, but soil erosion was effectively inhibited when the slope gradient was less than 15 degrees on winter wheat fields. Crop planting can effectively reduce the impact of slope gradient on soil erosion, especially during the flourishing period of crop growth.     

轮作休耕模式对土壤团聚体及有机碳含量的影响

为探究轮作休耕模式对红壤坡耕地团聚体稳定性及有机碳含量的影响,通过田间试验设置了休闲地、玉米单作、玉米-豌豆-玉米和玉米-苕子-玉米4个处理,分析了不同种植模式下土壤团聚体稳定性及有机碳含量,结果表明:(1)不同种植模式下土壤机械稳定性和水稳定性团聚体组成均以≥0.25 mm粒径占比最高,机械稳定性团聚体占比在80.68%以上,水稳定性团聚体达到了77.05%以上,且≥0.25 mm团聚体所占比例大小顺序为:休闲地>玉米-豌豆-玉米>玉米-苕子-玉米>玉米单作。(2)根据不同团聚体稳定指数(MWD,GMD,R_0.25和PAD)显示,休闲地的团聚体稳定性最好,与玉米单作之间差异显著,且休闲地和玉米轮作两种模式下团聚体稳定性均优于玉米单作。(3)玉米单作土壤团聚体有机碳含量最低,玉米轮作和休闲地能显著提高有机碳含量,并且玉米-苕子-玉米轮作效果最优; ≥0.25 mm粒径范围的团聚体储存的有机碳含量最高。(4)通过对土壤水稳性团聚体稳定指数与有机碳含量的相关性分析表明,4个不同团聚体稳定指数与有机碳含量都呈极显著正相关关系,与R_0.25相关程度最高。研究结果可为试验区域坡耕地水土流失防治提供理论依据。     

A decision support framework for identifying soil constraints to the agricultural productivity of tropical upland soils

Sustainable agricultural systems are based on managing soils according to their capabilities and constraints. To facilitate the identification of constraints and appropriate management strategies for upland soils, a decision support framework ‘Soil Constraints and Management Package’ (SCAMP) has been developed. Basic soil data (both field and laboratory) are entered into an Access database and are processed to output reports that identify soil constraints to productivity and that tabulate appropriate management strategies. Where spatially referenced soil data are available, maps of constraints can be readily produced in a Geographic Information System. To demonstrate the ability of SCAMP to identify soil constraints at plot scale, it was applied to soil data sets from the two major soil types (Ferralsols and Acrisols) of Gia Lai Province, Vietnam. Phosphorus (P) fixation, aluminium toxicity and low cation exchange capacity (CEC) were identified as common constraints to productivity on Ferralsols, and low plant available water capacity, compaction and low K status as common constraints to productivity on Acrisols. Field experiments were undertaken on a Ferralsol and an Acrisol to assess management strategies for minimizing these constraints in the presence of adequate N, P and K. Maize (Zea mays) yields from the Ferralsol were increased by applying a plant amendment (Tithonia diversifolia) (selected to increase soil pH and decrease P fixation) and high activity clay (selected to increase CEC). Water‐soluble P fertiliser recovery was increased in this high P‐fixing soil by placing the fertiliser in a sub‐surface band. For the Acrisol, maize was grown in mounded rows and yields were maximized by applying a super‐absorbent material (selected to increase soil water holding capacity) or a high activity clay (selected to increase the low CEC of this soil). To demonstrate the usefulness of SCAMP on a catchment/regional scale, spatially referenced soil survey data of the Herbert River catchment, Queensland, Australia, were used to produce a map identifying areas of low pH, high acidification hazard and low CEC. These applications demonstrate the usefulness of SCAMP for linking soil data to management strategies for sustainable productivity at both plot and catchment scale.     

Soil quality and other factors influencing maize yield in northern Ghana

Food security is a crucial issue in sub‐Saharan Africa as a consequence of unreliable rainfall, marginal soil fertility and a low level of inputs leading to declining crop yields. As a case study, we investigated the most important variables affecting maize yield in northern Ghana. We combined a soil quality index on a continuous scale with a social data set to model maize yield using linear multiple regression. Five significant variables have been identified (P < 0.05): soil quality index, fertilizer use, household size, distance from main market, and the interaction between fallow length and soil quality index. The effect of the interaction between soil quality and fallow on maize yield is negative, suggesting the influence of litter quality and N immobilization in the soils. Research and policy should focus on the development of site‐specific, legume‐based cropping, and the integration of crop and livestock farming in Northern Ghana and similar areas in sub‐Saharan Africa.     

生物炭对紫色土农田土壤NO排放的影响

为探明生物炭对紫色土农田土壤NO排放的影响,利用静态箱-化学发光氮氧化物分析法对夏玉米-冬小麦轮作土壤施用生物炭后的NO排放进行了为期一年(2013年6月至2014年5月)的原位观测,比较了生物炭与化肥混施处理(BCNPK)和常规施肥处理(NPK)的紫色土NO排放特征,无肥(CK)作为计算排放系数的对照。结果表明,玉米生长季,NPK处理下的土壤NO排放速率、累积排放通量及排放系数与BCNPK处理下相应参数之间均呈极显著差异(P0.01)。施用生物炭后,NO排放速率、累积通量及排放系数分别降低了73.1%、77.4%和85.5%,但在小麦季两种处理之间的差异均不显著(P0.05)。此外,在玉米季和小麦季,BCNPK处理单位产量的综合温室效应(yield-scale GWP)分别比NPK处理降低了79.4%和26.4%。因此,在同等氮肥施用量的条件下配施生物炭既能保证紫色土农田土壤作物不减产又能降低NO的排放。     

Soil Fertility,Mineral Nitrogen,and Microbial Biomass in Upland Soils of the Central Amazon under Different Plant Covers

Amazon is the largest state in Brazil and majority of the state is covered by the largest tropical rainforest of the world. Most soils of the Amazon region soils are acidic and infertile. When the Amazon forest land is cleared for agricultural use by burning the vegetation, the efficient nutrient recycling mechanisms are disrupted. However, nutrient contents in the deforested burn land increased temporarily. The objective of this study was to evaluate the soil fertility, mineral nitrogen (N), and microbial activity of carbon (C), N, and phosphorus (P) resulting from the replacement of the primary forest with pasture (Brachiaria brizantha) and commercial plantations of rubber (Hevea spp.), cupuaçu (Theobroma grandiflorum), and citrus trees (Citrus sinensis) cultivated in Xanthic Ferralsol and secondary forest under Acrisols Dystric Nitosols. The results showed that ammonium-N predominates in the 0- to 10-cm soil depth in both primary forest and areas with secondary forest, citrus plantation, and pasture. There was no increase in soil fertility with management of the cultivated areas under the secondary forest, but in the pasture there was a significant increase in the stock of organic C and total N and high C/N ratios, the inverse of what occurred with the C of the microbial biomass. The primary forest had the greatest values of C and P of the microbial biomass and the lowest metabolic quotient. Of the successions studied, the rubber trees were the plant cover with the smallest changes in terms of quality of the organic matter in the soil.     

田间条件下小麦和玉米秸秆腐解过程中微生物群落的变化——BIOLOG分析

对秸秆分解微生物演变机理的研究是调控秸秆还田、提高农田地力的理论基础。本试验基于土壤置换试验平台,利用BIOLOG方法研究在寒温带、中温带和中亚热带气候下,埋于黑土、潮土和红壤中的小麦和玉米秸秆在腐解过程中微生物对碳源利用的变化规律。试验中利用网袋法区分直接分解秸秆微生物。试验结果发现秸秆腐解微生物的碳源代谢活性(Average Well Color Development AWCD值表示)在腐解0.5 a和1 a后表现出一定的随气候变化规律,即随温度和降雨量的增加而降低。其中0.5 a为海伦(0.765±0.060)>封丘(0.737±0.165)>鹰潭(0.326±0.076),1 a为海伦(0.630±0.092)>封丘(0.319±0.096)>鹰潭(0.291±0.029),但这种趋势在腐解2 a后减弱。气候条件是影响秸秆腐解微生物碳源代谢活性的主要因素,其次是腐解时间和土壤类型。主成分分析表明在腐解0.5 a后海伦、封丘地区的微生物群落代谢特征与鹰潭差异较大,而1 a后封丘和鹰潭的微生物群落代谢特征与海伦的差异较大,腐解2 a后不同气候条件下的秸秆腐解微生物对碳源的利用趋于一致,均对含氮化合物利用较多。     

土地利用方式和栽培措施对农田土壤不同组分有机碳的影响

以河北曲周县原状草地土壤和农田土壤为研究对象,分析了土地利用方式、秸秆还田、耕作方式和施肥水平对土壤有机碳特性的影响。研究表明,华北原状草地改变为农田后（34年）,土壤砂粒、颗粒有机碳的含量和总有机碳的比例、轻组土壤和轻组土壤有机碳都显著降低,且以秸秆还田影响最大。经过8年的耕作,施加底肥、免耕和秸秆整株还田等农艺措施,明显提高了土壤颗粒有机碳含量。秸秆还田使得0～20cm土壤颗粒有机碳含量明显增加,且整株还田比粉碎还田更能增加10～20cm土壤颗粒的有机碳含量,而免耕对土壤颗粒有机碳的增加主要表现在0～10cm。土壤非保护性有机碳的比例也会显著降低,且非保护性有机碳主要分布在0～5cm土层。     

Soil C and N dynamics and maize (Zea may L.) yield as affected by cropping systems and residue management in North-western Pakistan

This paper presents the results of irrigated rotation experiment, conducted in the North West Frontier Province (NWFP), Pakistan, during 1999–2002 to evaluate effects of residues retention, fertilizer N and legumes in crop rotation on yield of maize (Zea mays L.) and soil organic fertility. Chickpea (Cicer arietinum L) and wheat (Triticum aestivum L) were grown in the winters and mungbean (Vigna radiata) and maize in the summers. Immediately after grain harvest, above-ground residues of all crops were either completely removed (−residue), or spread across the plots and incorporated by chisel plough by disc harrow and rotavator (+residue). Fertlizer N rates were nil or 120 kg ha⁻¹ for wheat and nil or 160 kg ha⁻¹ for maize. Our results indicated that post-harvest incorporation of crop residues significantly (p < 0.05) increased the grain and stover yields of maize during both 2000 and 2001. On average, grain yield was increased by 23.7% and stover yield by 26.7% due to residue incorporation. Residue retention also enhanced N uptake by 28.3% in grain and 45.1% in stover of maize. The soil N fertility was improved by 29.2% due to residue retention. The maize grain and stover yields also responded significantly to the previous legume (chickpea) compared with the previous cereal (wheat) treatment. The legume treatment boosted grain yield of maize by 112% and stover yield by 133% with 64.4% increase in soil N fertility. Similarly, fertilizer N applied to previous wheat showed considerable carry over effect on grain (8.9%) and stover (40.7%) yields of the following maize. Application of fertilizer N to current maize substantially increased grain yield of maize by 110%, stover yield by 167% and soil N fertility by 9.8% over the nil N fertilizer treatment. We concluded from these experiments that returning of crop residues, application of fertilizer N and involvement of legumes in crop rotation greatly improves the N economy of the cropping systems and enhances crop productivity through additional N and other benefits in low N soils. The farmers who traditionally remove residues for fodder and fuel will require demonstration of the relative benefits of residues return to soil for sustainable crop productivity.     

Compost,Manure and Synthetic Fertilizer Influences Crop Yields,Soil Properties,Nitrate Leaching and Crop Nutrient Content

From 1993 to 2001, a maize-vegetable-wheat rotation was compared using either 1) composts, 2) manure, or 3) synthetic fertilizer for nitrogen nutrient input. From 1993 to 1998, red clover (Trifolium pratense L.) and crimson clover (Trifolium incarnatum L.) were used as an annual winter legume cover crop prior to maize production. From 1999 to 2001, hairy vetch (Vicia villosa Roth.) served as the legume green manure nitrogen (N) source for maize. In this rotation, wheat depended entirely on residual N that remained in the soil after maize and vegetable (pepper and potato) production. Vegetables received either compost, manure, or fertilizer N inputs. Raw dairy manure stimulated the highest overall maize yields of 7,395 kg/ha (approximately 140 bushels per acre). This exceeded the Berks County mean yield of about 107 bushels per acre from 1994 to 2001. When hairy vetch replaced clover as the winter green manure cover crop, maize yields rose in three of the four treatments (approximately 500-1,300 kg/ha, or 10-24 bu/a). Hairy vetch cover cropping also resulted in a 9-25 % increase in wheat yields in the compost treatments compared to clover cover cropping. Hairy vetch cover crops increased both maize and wheat grain protein contents about 16 to 20% compared to the clover cover crop. Compost was superior to conventional synthetic fertilizer and raw dairy manure in 1) building soil nutrient levels, 2) providing residual nutrient support to wheat production, and 3) reducing nutrient losses to ground and surface waters. After 9 years, soil carbon (C) and soil N remained unchanged or declined slightly in the synthetic fertilizer treatment, but increased with use of compost amendments by 16-27% for C and by 13-16% for N. However, with hairy vetch cover crops, N leaching increased 4 times when compared to clover cover crops. September was the highest month for nitrate leaching, combining high rainfall with a lack of active cash crop or cover crop growth to use residual N. Broiler litter leaf compost (BLLC) showed the lowest nitrate leaching of all the nutrient amendments tested (P= 0.05).     

Short-term effects of biochar amendment on soil microbial community in humid tropics

Biochar is known to ameliorate soil fertility and improve crop production but information regarding soil microbiota responses on biochar amendment remains limited. The experiment was conducted to study the effect of biochars from palm kernel (pyrolysed at 400°C) and rice husk (gasified at 800°C) in a sandy loam Acrisol from Peninsular Malaysia. The soil was amended with palm kernel shell biochar (PK), rice husk biochar (RH), palm kernel biochar with fertilizer (FPK), rice husk biochar with fertilizer (FRH), fertilizer and control soil. Soil samples were taken during maize harvesting and were analysed for physico-chemical properties, microbial biomass, microbial abundance and microbial diversity. Increase in pH, moisture content, CEC, organic C, and labile C were recorded in all biochar amended soils. Microbial biomass C was 65% and 36% higher in RH and FRH, respectively, than control. Microbial biomass N was greatest in FPK and FRH with respective increment of 359% and 341% than control. β-glucosidase and xylanase activities were significantly increased in all biochar treated soils than control. A shift in microbial diversity was not detected. The biochar affects the microbial community by altering the soil environment and increasing labile active carbon sources in the short-term amendment.     

风沙区雨养耕地水分与养分动态及其对作物产量的影响

风沙区由于林带的缺少,雨养耕地风蚀现象严重,就地起沙,形成了风蚀地以及风积地在短距离内交错分布的特点。通过对风沙区雨养耕地土壤水养状况的定位研究得出:没有防护林带保护的雨养耕地有3种类型,即风蚀地、积沙地、过渡地段。沿主害风方向,上风地段为风蚀沙地,下风地段为风积沙地。风蚀沙地水分状况最好,风积沙地最差;表层土壤(0~20cm)养分状况比下层(20~60cm)差,风积沙地肥力最低,过渡地段最好。沙区雨养耕地特点明显,一年中土壤含水率变幅比降水量小得多,水养同步作物生产力水平高;农作物产量与土壤中全N、全P、全K含量关系不密切,与土壤表层有机质、有效P、K含量及下层有效N的含量呈明显的正相关。     

等高反坡阶对坡耕地土壤碳库的影响

[目的]研究坡耕地等高反坡阶措施的蓄水保土和固碳减排效应,为改善云南山区红壤坡耕地土壤侵蚀状况提供科学依据。[方法]自然降雨条件下,通过松花坝迤者小流域1a的野外径流小区定位观测,对有、无等高反坡阶措施条件下的坡面产流产沙和土壤有机碳流失进行对比分析。[结果](1)泥沙作为土壤有机碳流失的重要载体,因其流失所致的流失量占总有机碳流失量的85%以上,最高达95.38%;(2)等高反坡阶具有显著的蓄水减流和保土减沙效应,其减流率在5.56%~53.91%,减沙率在18.84%~83.11%,产沙调控作用更优;(3)雨季前后,原状坡面小区土壤碳储量减少率达9.90%,明显高于等高反坡阶小区土壤碳储量的减少率3.99%;(4)通过相关分析发现,2个小区土壤有机碳的流失率与降雨量均未达到显著相关,但与降雨侵蚀力显著相关(p0.05)。径流、泥沙与2个小区有机碳的流失率均达到了显著正相关(p0.05)。[结论]等高反坡阶通过改变地表微地形,减少了坡耕地有机碳的输出。     

Effects of trefoil cover crop and earthworm inoculation on maize crop and soil organisms in Reunion Island

 Traditional tree fallows have been abandoned on the western coast of the Reunion Island because of the increasing need for cultivated land. Soil fertility is no longer restored and crop yields have decreased drastically. The leguminous plant, Lotus uliginosus (trefoil), used as a cover crop, has made possible the control of erosion, the restoration of soil macrofauna, especially earthworms, and the increase in crop yields. When trefoil was associated with earthworms (Amynthas corticis), the densities of maize, the yields of maize stalk and dry matter, the yield of trefoil fodder dry matter, and the biomass and respiratory activity of soil microflora were considerably increased. The combined effects of their association led to a significant decrease in populations of the plant-parasitic nematode, Pratylenchus vulnus, in maize roots, and in the population of borers. Some soil chemical features were modified. Received: 10 September 1997