稻作系统有机肥替代部分化肥的土壤氮循环特征及增产机制

采用有机肥替代部分化肥是实现化肥使用零增长和作物稳产增产的重要途径。基于近年来的研究进展,探讨了稻作系统有机肥替代部分化肥对水稻产量、氮素利用效率、土壤氮库组分和微生物固氮、氨化、硝化和反硝化等氮循环关键过程的影响。同时,就单施化肥与有机肥替代部分化肥的氮素循环特征进行了比较。有机肥替代部分化肥通过改变稻田土壤氮素循环多个环节(增强氨化过程、协调硝化和反硝化过程、降低氨挥发和减少氮素损失等),改善土壤氮素供给状态(提高小分子有机氮供给、协调无机氮组分与比例、提高土壤微生物量氮和总氮固持),进而促进水稻氮素吸收并协调植株氮素分配过程,最终实现水稻稳产增产。     

Carbohydrates in water-stable aggregates and particle size fractions of forested and cultivated soils in two contrasting tropical ecosystems

Information on changes in storage and loss of soil organic carbon (SOC) when tropical forests are converted to cropland is needed for evaluating soil structural degradation and for selecting appropriate sustainable soil management practices. We evaluated changes in SOC storage of organic carbon and acid-hydrolyzable carbohydrates content of aggregated classes and particle size fractions of adjacent forested and cultivated soils in eight agroecosystems from Ethiopian highlands and Nigerian lowlands. In all agroecosystems, SOC content was two to four times higher in the forested than the cultivated soils. Higher SOC content was found in Ethiopian (20.2–47.3 g.kg^–1) than Nigerian (12.0–24.0 g.kg^–1) forested soils. The magnitude of reduction in SOC and total carbohydrates with cultivation was soil-specific, being generally higher in the sandy than the clayey soils. The smaller aggregate classes (< 1.00 mm) and the sand-sized particles (2000–63 µm) of the forested soils were preferentially enriched in carbohydrates relative to larger aggregates (4.75–1.00 mm). Carbohydrates were more concentrated in the clay-size fraction of the forested than in that of the cultivated soils. Cultivation reduced aggregate stability, increased the proportions of the smaller size aggregates and their associated carbohydrates relative to the forested soils. The susceptibility of the cultivated soils to loss in structural stability reflected this initial aggregation which was greater in the more stable clayey than the fragile sandy soils. The aggregate stability of either the forested or the cultivated soil could not be accounted for by the levels of OC or total carbohydrates in the soil.     

宁南山区植被恢复对土壤团聚体水稳定及有机碳粒径分布的影响

土壤团聚作用和土壤有机碳固定之间密切相关.对宁南山区不同植被恢复措施和年限下土壤团聚体粒径分布及稳定性、土壤团聚体中有机碳及其组分分布进行了研究,探讨了有机碳及其组分对植被恢复的响应.结果表明,不同植被恢复措施下,土壤团聚体粒径分布表现为“V”字分布:＞5 mm和＜0.25 mm这两个粒径的团聚体含量最多,5-2 mm、1-0.25 mm团聚体的含量次之,2-1 mm粒径的团聚体含量最少.坡耕地的平均重量直径(MWD)最低,为1.4,其他植被恢复措施下土壤的平均重量直径MWD在1.9-3.1之间.不同的植被恢复措施下,0-20 cm土层和20-40 cm土层全土有机碳含量在7.4-17.7 g/kg之间、微生物碳含量分布在50.3-664.7 mg/kg之间、腐殖质碳含量在0.9-2.5g/kg之间.胡敏酸碳含量分布在0.2-0.6 g/kg,富里酸碳含量在0.6-1.9 g/kg之间.全土有机碳、微生物碳、腐殖质碳、富里酸碳均为坡耕地最低,其他植被恢复措施的有机碳、微生物碳、腐殖质碳、富里酸碳含量分别是坡耕地的1.1-2.3倍、2.0-8.4倍、1.0-2.0倍、1.2-2.4倍.不同粒径团聚体有机碳相比较,大多呈现中间高两边低的变化趋势,最大值出现在中间粒径,即5-2 mm、2-1 mm、1-0.25 mm这3个粒径.逐步回归表明,5-2 mm团聚体和1-0.25 mm团聚体有机碳含量的提高有助于土壤水稳性团聚体的形成.研究结果表明,植被恢复提高了土壤团聚体有机碳含量,在碳形态上,富里酸碳和微生物生物量碳对不同植被恢复措施的敏感度较高,胡敏酸碳含量则相对稳定.     

不同栽培管理模式对农田土壤团聚体组成及其碳、氮分布的影响

在两种肥力条件下设置超高产栽培模式(SH)、高产高效栽培模式(HH)、农民习惯处理(FP)和不施肥对照处理(CK)4种栽培管理模式的定位试验,研究了以肥料投入为主要影响因素的不同栽培管理模式对黄淮海区域不同肥力农田耕层土壤团聚体组成及其碳、氮分布的影响,为通过培肥土壤实现小麦-玉米周年可持续增产增效提供技术支持.结果表明: 与低肥力田块(LSF)相比,高肥力田块(HSF)耕层土壤团聚体的平均质量直径和几何平均直径高、分形维数低,有利于大团聚体的形成与稳定,各级团聚体的有机碳和全氮含量较高.优化施用氮磷钾肥、配施有机肥可增加耕层土壤团聚体的粒径、降低其分形维数,促进大团聚体的形成与稳定,对高肥力田块的影响大于低肥力田块;二者亦可提高有机碳和全氮在大团聚体中的含量与分布,其中,对＞5 mm团聚体的贡献率的影响在低肥力田块大于高肥力田块,对5～0.5 mm的各粒级团聚体的贡献率的影响在高肥力田块优于低肥力田块.     

种植模式和施肥对黄土旱塬农田土壤团聚体及其碳分布的影响

本研究以长武黄土高原农业生态试验站33年长期定位试验处理为研究对象,选取撂荒(R)、小麦连作(CK/W)、小麦玉米轮作(L),小麦连作选取单施氮肥(N)、单施磷肥(P)、施氮磷肥(NP)、单施有机肥(M)、氮肥配施有机肥(NM)、磷肥配施有机肥(PM)、氮磷肥配施有机肥(NPM)共10种不同种植模式和施肥田间处理,运用...     

生物炭配施氮肥对典型黄河故道区土壤理化性质和冬小麦产量的影响

探讨典型黄河故道区生物炭配施氮肥对耕层土壤理化性质和作物产量的影响,阐明生物炭配施氮肥后土壤碳氮含量和理化性质的变化规律,可为合理培肥土壤、提升耕地质量、提高冬小麦产量提供科学依据。本研究以黄河故道典型区域潮土和中性生物炭为供试材料,连续两年进行田间定位试验,开展不同生物炭用量(0、15、30 t·hm^-2)配施氮肥(N 270、330 kg·hm^-2)对土壤理化性质的影响研究。结果表明: 生物炭施入2年后,土壤广义土壤结构指数(GSSI)增大、土壤三相结构距离指数(STPSD)减小,显著改善了土壤三相比,其中在30 t·hm^-2施炭量条件下土壤三相比最接近理想状态;土壤紧实度和容重降低,土壤总孔隙度和毛管孔隙度增加,田间持水量和透水透气性增大,土壤板结状况得到缓解;>0.25 mm粒径团聚体显著增加(增幅70.6%～94.4%),团聚体平均重量直径(MWD)增大(增幅24.0%～48.0%),土壤团聚体结构得到改善。施加生物炭可显著增加土壤有机碳含量(增幅15.8%～67.0%),并可调节土壤C/N,降低氮素释放强度,提高氮肥利用率,显著增加土壤肥力,但未提高土壤pH值,其中10～20 cm土层土壤pH值呈显著下降趋势。在相同施氮条件下,施用生物炭比不施用处理的冬小麦产量2年平均增加9.6%～25.6%,增产效果显著;在相同生物炭施用量下,高氮处理比常规氮处理的冬小麦平均增产2.5%～4.4%,但差异不显著。综上,生物炭配施氮肥能够改善土壤微生态环境,提高土壤肥力,增加作物产量。从改善土壤理化性质、作物增产效果和投入成本等方面综合考虑,推荐在黄河故道区耕作层施入生物炭30 t·hm^-2并配施氮肥330 kg·hm^-2较为适宜。     

Surface soil chemical and physical patterns in a brigalow–Dawson gum forest,central Queensland

Brigalow (Acacia harpophylla)–Dawson gum (Eucalyptus cambageana) open forests are predominantly supported by solodic soils in central Queensland. This report describes relations between some physical, chemical and morphological properties of surface soils (0–0.10 m) within a virgin brigalow–Dawson gum forest. Soil property gradients were found to radiate horizontally from tree-dominated to non-vegetated areas, indicative of a vegetation-induction process. These reflect the importance of litterfall organic matter in determining soil fertility and soil physical conditions at this site. The decomposition of litterfall is probably responsible for significant increases in soil organic carbon (C), total nitrogen (N) and total sulphur (S) concentrations with increasing vegetation canopy cover. The composition of soil organic matter appears constant across the study area, as similar soil C:N:S ratios were recorded across all vegetation canopy classes. Soil salinity, total phosphorus, mineral nitrogen, cation exchange capacity, exchangeable calcium and exchangeable potassium levels also increased with increasing vegetation canopy cover. Surface soil physical properties were also related to vegetation canopy cover. Bulk density and the < 20 μm dispersion ratio decreased while soil micro-relief and A hor?izon depth increased with increasing vegetation canopy cover. Organic C, through inverse relations with bulk density and the < 20 μm dispersion ratio, appears to enhance soil porosity and aggregate stability, indicating the role of organic matter in the stabilization of larger virgin soil aggregates. The close association between virgin forest and surface soil fertility is seen to have implications for changes in land-use, with a decline in nutrient availability, soil aggregate stability and productivity following forest clearing.     

Effects of the nematofauna on microbial energy and matter transformation rates in European grassland soils

The effect of the nematofauna on the microbiology and soil nitrogen status was studied in 6 major European grassland types (Northern tundra (Abisko, Sweden), Atlantic heath (Otterburn, UK), wet grassland (Wageningen, Netherlands), semi-natural temperate grassland (Linden, Germany), East European steppe (Pusztaszer, Hungary) and Mediterranean garigue (Mt. Vermion, Greece). To extend the range of temperature and humidity experienced locally during the investigation period, soil microclimates were manipulated, and at each site 14 plots were established representing selected combinations of 6 temperature and 6 moisture levels. The investigated soils divided into two groups: mineral grassland soils that were precipitation fed (garigue, wet grassland, seminatural grassland, steppe), and wet organic soils that were groundwater fed (heath, tundra). Effects of the nematofauna on the microflora were found in the mineral soils, where correlations among nematode metabolic activity as calculated from a metabolic model, and microbial activity parameters as indicated by Biolog and ergosterol measurements, were significantly positive. Correlations with bacterial activity were stronger and more consistent. Microbial parameters, in turn, were significantly correlated with the size of the soil nitrogen pools NH4, NO3, and Norganic. Furthermore, model results suggested that there were remarkable direct effects of nematodes on soil nitrogen status. Calculated monthly nematode excretion contributed temporarily up to 27% of soluble soil nitrogen, depending on the site and the microclimate. No significant correlation among nematodes and microbial parameters, or nitrogen pools, were found in the wet organic soils. The data show that the nematofauna can under favourable conditions affect soil nitrogen status in mineral grassland soils both directly by excretion of N, and indirectly by regulating microbial activity. This suggests that the differences in nitrogen availability observed in such natural grasslands partly reflect differences in the activity of their indigenous nematofauna. This revised version was published online in June 2006 with corrections to the Cover Date.     

Effects of forest conversion into grassland on soil aggregate structure and carbon storage in Panama: evidence from soil carbon fractionation and stable isotopes

Land-use and land-cover strongly influence soil properties such as the amount of soil organic carbon (SOC), aggregate structure and SOC turnover processes. We studied the effects of a vegetation shift from forest to grassland 90 years ago in soils derived from andesite material on Barro Colorado Island (BCI), Panama. We quantified the amount of carbon (C) and nitrogen (N) and determined the turnover of C in bulk soil, water stable aggregates (WSA) of different size classes (<53 μm, 53–250 μm, 250–2000 μm and 2000–8000 μm) and density fractions (free light fraction, intra-aggregate particulate organic matter and mineral associated soil organic C). Total SOC stocks (0–50 cm) under forest (84 Mg C ha⁻¹) and grassland (64 Mg C ha⁻¹) did not differ significantly. Our results revealed that vegetation type did not have an effect on aggregate structure and stability. The investigated soils at BCI did not show higher C and N concentrations in larger aggregates, indicating that organic material is not the major binding agent in these soils to form aggregates. Based on δ¹³C values and treating bulk soil as a single, homogenous C pool we estimated a mean residence time (MRT) of 69 years for the surface layer (0–5 cm). The MRT varied among the different SOC fractions and among depth. In 0–5 cm, MRT of intra-aggregate particulate organic matter (iPOM) was 29 years; whereas mineral associated soil organic C (mSOC) had a MRT of 124 years. These soils have substantial resilience to C and N losses because the >90% of C and N is associated with mSOC, which has a comparatively long MRT.     

鼎湖山亚热带常绿针阔叶混交林凋落物及矿质氮输入对土壤有机碳分解的影响

2010年7-12月,选取鼎湖山国家级自然保护区亚热带针阔叶混交林,采用全因子控制试验,研究不同类型的凋落物(针叶和阔叶凋落物)添加及氮处理(加氮模拟氮饱和、减氮模拟根吸收)对表层(0～10 cm)和下层(20～30 cm)土壤有机质分解(呼吸)的影响.结果表明： 2010年7-11月间,两种凋落物的添加使土壤-凋落物系统的呼吸速率显著增加,但这种影响在12月消失.减氮和加氮处理均显著增加了土壤-凋落物系统的呼吸.叶凋落物短期内完全分解,对土壤碳分解和积累的影响十分有限,可能不是该系统中土壤有机质的主要来源.通过减少土壤可利用氮模拟根系对氮的吸收能够明显促进土壤有机质的分解.     

有机无机肥配施提高麦-稻轮作系统中水稻氮肥利用率的机制

采用盆栽试验,研究了有机无机肥配施对麦-稻轮作系统中水稻氮素累积动态和土壤氮素供应动态的影响,并从微生物学角度探讨了有机无机肥协同提高水稻氮肥利用率的机制.结果表明：有机无机肥配施处理的土壤微生物生物量碳、氮和矿质态氮在水稻分蘖期前低于化肥处理,而在抽穗期至灌浆期显著高于其他处理.土壤氮素供应动态与水稻吸收利用氮素规律吻合程度最高,促进了水稻产量、生物量和氮素累积量的增加,显著提高了水稻的氮肥利用率.其主要机制是有机无机肥配施促进了土壤微生物繁殖,使其在水稻生育前期固持了较多的矿质氮,在水稻生育中、后期这些氮素逐渐被释放以供水稻吸收利用,较好地满足了水稻各阶段生长发育对氮素养分的需求.     

冻融季帽儿山森林改变有机碳输入方式对土壤活性氮含量的影响

根系与凋落物有机碳输入变化对土壤碳氮循环的影响已成为当前学界关注的热点,但冻融季不同有机碳输入方式将对土壤活性氮含量产生何种影响尚不明确。为此在春季具有明显冻融作用的温带森林设立凋落物去除、根系去除处理以代表仅根系有机碳输入方式、仅凋落物有机碳输入方式,并设置自然条件有机碳输入方式即保留根系及凋落物作为对照,多角度探究土壤微生物量氮、矿质氮动态变化。结果表明：(1)有机碳输入方式对土壤活性氮含量有重要影响：与自然条件下有机碳输入方式相比,仅根系输入处理使土壤微生物氮、总矿质氮含量升高10.5%、12.3%。(2)输入时长改变了有机碳输入方式对土壤活性氮含量的作用效果：长期单一有机碳输入使土壤微生物量氮含量下降,反应率值为0.451、0.422。(3)季节差异是影响有机碳输入方式对土壤活性氮含量作用效果的关键因素：仅根系有机碳输入在冻融季使总矿质氮含量上升,反应率值为0.404,生长季相反,呈下降趋势,其值为0.121。以上结果表明,有机碳输入方式对土壤活性氮含量有重要调控作用,且作用效果会受季节、输入时长等因素影响。     

喀斯特山区土地利用对土壤团聚体有机碳和活性有机碳特征的影响

通过选取喀斯特山区火龙果园、草丛、花椒林、乔木林和灌草丛为研究对象,对其土壤团聚有机碳和团聚体活性有机碳分布与积累特征进行研究,结果表明:各土地利用方式下的团聚体组成均以＞0.5 mm团聚体为主,其含量可占团聚体总量的82.57％-94.79％;各粒级团聚体中有机碳和活性有机碳的含量均以乔木林最高,花椒林和火龙果园相对居中,而以草丛和灌草丛较低,随土壤团聚体粒径降低,有机碳和活性有机碳的峰值基本出现在＜0.25 mm粒级团聚体,但该粒径对土壤有机碳和活性有机碳的贡献率却不足6％和4％;土壤有机碳和活性有机碳的累积均受5-1 mm团聚体中有机碳和活性有机碳含量增加的影响,该粒级团聚体对有机碳和活性有机碳的贡献率也分别达28.70％-49.47％和34.13％-47.47％,可将5-1 mm粒径团聚体作为喀斯特山区的土壤有机碳固定的特征团聚体;土壤团聚体活性有机碳含量与土壤团聚体总有机碳含量呈极显著正相关关系(r=O.8768),表明团聚体活性有机碳可以作为衡量喀斯特山区土壤团聚体有机碳动态的一个敏感性指标.     

The legacy of stockless organic conversion strategies

Legume‐containing leys are commonly used to improve soil fertility in the 2‐year conversion period from conventional to organic production. While in‐conversion land may be grazed, in stockless farming systems, land is effectively out of production, leading to a reduction in income and pressure on cash flow. The impacts of seven organic conversion strategies on the first organic crop (winter wheat) were previously reported. This study investigates the effect of the conversion strategies on the second (winter beans) and third (winter oats) organic crops, thereby extending the analysis throughout the first complete rotation. The strategies were (a) 2‐years’ red clover–ryegrass green manure, (b) 2‐years’ hairy vetch green manure, (c) red clover for seed production then a red clover–ryegrass green manure, (d) spring wheat undersown with red clover, then a red clover green manure, (e) spring oats, then winter beans, (f) spring wheat, then winter beans and (g) spring wheat undersown with red clover, then a barley–pea intercrop. Conversion strategy had a significant impact on organic bean yield, which ranged from 2.78 to 3.62 t ha^?1, and organic oat yield, which ranged from 3.24 to 4.17 t ha^?1. In the organic bean crop, weed abundance prior to harvest, along with soil texture, accounted for 70% of yield variation. For the oats, soil mineral nitrogen in November together with weed abundance in April accounted for 72% of the variation in yield. The impacts of conversion strategies on soil mineral nitrogen levels were still detectable 3 years after conversion. The results from this study indicate that the choice of conversion crop has important long‐term implications. More exploitative conversion strategies, that is those with a higher proportion of cash cropping, had an increased weed burden and decreased levels of soil mineral nitrogen, leading to reduced yields of beans and oats, 2 and 3 years after conversion.     

The nitrogen fertilization of spring barley

Summary From 1971 to 1979 field trials with increasing rates of fertilizer nitrogen on spring barley with sugar beet as the preceding crop were conducted on a farm on sandy loam in the south western part of The Netherlands. Prior to sowing and fertilizing soil samples were taken and analysed for mineral nitrogen (N_min). The average yield increase through application of fertilizer nitrogen was only 750 kg of grain per ha per year, the maximum yield being about 5 tonnes per ha. In the case of a fixed rate of fertilizer nitrogen per annum it can be derived from the response curves that 60 kg of N would have given the smallest average yield deficit (170 kg grain per ha) in comparison with maximum yields. With an N-advisory system based on soil analysis the average yield deficit would be at a minimum (163 kg of grain per ha) with a value for mineral soil nitrogen+fertilizer nitrogen totalling 120 kg N per ha.No relationship was found between optimum rate of fertilizer nitrogen and the amount of mineral soil nitrogen at the end of the winter. This was ascribed to the relatively small variation in mineral soil nitrogen and the weak response of the crop to fertilizer nitrogen.Promising results from nitrogen fertilizing systems based on soil analysis can be expected from more responsive crops like winter wheat, sugar beets and potatoes.With the average yield deficit compared with maximum yield as a characteristic, the usefulness of any N-advisory system can be compared, taking a fixed rate of nitrogen system as a standard.Seconded by the Agricultural Bureau of the Netherlands Fertilizer Industry (LBNM).     

川西高山林线土壤活性碳、氮对短期增温的响应

随着温室效应的加剧,受低温限制的高山林线生态系统对全球气候变暖较为敏感,可能直接影响到植物的生长和土壤碳氮过程.本研究假设气候变暖会改变高山生态系统土壤活性碳氮含量,在四川省理县米亚罗高山生态系统定位站,采用开顶式模拟增温装置(OTC)模拟增温对土壤活性碳、氮的短期影响.分别于2017年4、7和10月,采集OTC以及对照样地(CK)内土壤有机层和矿质土壤层的原状土壤,测定土壤可溶性有机碳(DOC)、土壤微生物生物量碳(MBC)、土壤可溶性有机氮(DON)和土壤微生物生物量氮(MBN)含量.结果表明: 模拟增温使年均气温升高0.88 ℃,土壤有机层和矿质土壤层的年均温度分别提高0.48和0.23 ℃.模拟增温没有显著改变土壤有机质和含水量,但显著提高了矿质土壤层的pH值,同时显著降低了非生长季矿质土壤层的DOC、DON含量;季节变化对两个层次的DOC、DON和MBN含量有极显著影响,而MBC没有明显的季节动态;增温和季节交互作用对矿质土壤层的DOC和DON有显著影响.土壤有机层的MBC、MBN含量显著高于矿质土壤层.土壤活性碳、氮与土壤有机质和含水量呈极显著正相关,MBC、MBN与土壤pH呈极显著正相关,MBN与土壤温度呈显著负相关.     

Aggregate formation and organo-mineral association affect characteristics of soil organic matter across soil horizons and parent materials in temperate broadleaf forest

Precise assessment of soil organic carbon (OC) storage requires understanding of soil type and depth specific differences in organic matter (OM) stabilization. Therefore, we aimed to analyze OC dynamics down the soil profile and to clarify the effect of depth on the importance of aggregate formation and mineral adsorption for OC storage in mature beech forest soils developed from different parent materials. Aggregate size and density fractions were separated from samples of top and subsoil horizons, which were quantified and analyzed by infrared spectroscopy. We also determined the microbial biomass C (C_mic) and the amount of C decomposed within incubation experiments (CO₂-C) for the bulk soil samples. OC stabilized via aggregate formation and mineral association significantly increased with soil depth. However, this stabilized pool seemed to fuel the labile OM stronger in the subsoil than in the topsoil because the CO₂-C/SOC and CO₂-C/C_mic ratios increased with depth. Measured differences in the magnitude of the detected stabilization and destabilization patterns were attributed to parent material and soil horizon, indicating pronounced spatial and vertical heterogeneity in the contribution of soils under temperate broadleaf forest to terrestrial C sequestration. Considering such site and depth specific differences will improve assessment and modelling of soil OC storage for areas covered with the same forest type but with high pedogenetic diversity.

     

开垦对绿洲农田碳氮累积及其与作物产量关系的影响

以新疆策勒绿洲近百年来不同开垦年限农田为研究对象,采用空间序列换算时间序列的方法,研究绿洲农田开垦过程中土壤有机碳和全氮密度、碳氮比(C/N)及速效氮含量的垂直变化特征,并探讨了农田土壤碳氮变化与作物产量的关系。结果表明:荒漠土壤开垦后,显著增加了表层土壤(0-20 cm)有机碳和全氮密度,随开垦年限延长对深层土壤(40-200 cm)有机碳密度也有一定的影响,如在开垦30 a左右时下降了36.4%,但在100 a左右时则增加了52.0%。耕层土壤C/N随开垦年限延长而明显增加,深层土壤除100 a农田外其它均有不同程度下降;不同土层C/N与速效氮含量呈负相关关系,仅在开垦初期(0-10 a)达到显著水平。不同年限农田的玉米产量存在显著差异,且和有机碳及全氮密度(0-200 cm)均呈显著正相关;棉花除100和10 a农田产量差异较小外,在其它农田间均达显著水平,但和有机碳及全氮密度无明显相关性。由此可见,在现有投入条件下,提高土壤碳氮累积量对增加玉米产量仍有十分重要作用,但对棉花产量的影响不明显。     

Soil organic matter and yield of forest and tree crops

Summary Three hundred and sixty eight soil samples collected from the surface layers of plantations of coffee (Coffea robusta) andGmelina arborea (a forest tree crop) were analyzed for organic carbon, total nitrogen and loss-on-ignition as the case might be. The aim was to investigate the direct influence of soil organic matter on the yield of tree crops in different ecological zones of Nigeria. Coffee yield collected at different harvests and total coffee yield were seperately regressed on soil organic carbon content. In most cases, positive regressions of coffee yield on soil organic carbon were recorded. Consistent positive correlations between each of indicators of soil organic matter and girth ofGmelina arborea were recorded in the order of organic carbon, nitrogen and loss-on-ignition. The relationship between C: N ratio and the performance of Gmelina depended on which of organic carbon and soil nitrogen was more influential at a particular location.     

干旱区典型盐生植物群落土壤团聚体组成及有机碳分布

以干旱区玛纳斯河流域扇缘带为研究区,分析了花花柴(Karelinia caspia)、雾冰藜(Bassia dasyphylla)、梭梭(Haloxylon ammodendron)和柽柳(Tamarix ramosissima)4个典型盐生植物群落土壤团聚体的组成及有机碳分布。研究表明:不同植物群落土壤团聚体均以0.25—0.053 mm粒径为主,占了46.7%—74.6%,且与其他粒径差异显著(P0.05),0.25 mm和0.053mm粒径土壤团聚体含量较少,仅占7.8%—43%。梭梭群落0.25 mm团聚体平均含量较高,达32%。不同植被群落土壤总有机碳介于2.01—8.73 g/kg之间,不同粒径团聚体有机碳介于1.70—13.68 g/kg之间。不同群落之间,梭梭和柽柳群落总有机碳和团聚体有机碳含量均相对较高,且随着土层深度下降而下降。不同粒径之间,有机碳含量在0.25—0.053 mm粒径最低,在0.25 mm和0.053 mm粒径中最高,呈现"V"型分布且差异显著(P0.05)。0.25—0.053 mm团聚体中有机碳含量的贡献率最高,达43.43%,而0.053 mm粒级贡献率较低,但有机碳含量较高,说明了小粒径团聚体对有机碳保护能力较强。土壤有机碳含量与0.25—0.053 mm团聚体含量呈显著负相关(P0.05)。而从整体来看,梭梭群落0.25 mm团聚体比例较高,且土壤有机碳和团聚体有机碳含量也较高,说明了在该研究区,梭梭群落聚集土壤养分能力较强,相对其他群落更有利于土壤有机碳的积累。