强度耕作对^137Cs、^210Pbex和有机质剖面分布的影响

很少有关于直接测定强度耕作侵蚀引起土壤退化过程的报道。我们的目的是确定应用137Cs和210Pbex直接定量评价耕作侵蚀对土壤有机质(SOM)坡面运移影响的可能性。我们在黄土高原陡坡耕地上进行了50次犁耕活动,并将与其相临的另一块陡坡耕地作为对照。在对照坡地不同坡位,137Cs浓度均匀分布于上部0～30cm土层,而210Pbex浓度在坡上部和坡中部随土层深度增加呈现线性递减,在坡下部呈指数函数递减。0～30cm土层中土壤有机质含量显著大于30cm深度以下土层,并在坡中部和坡下部呈现与210Pbex类似的土壤剖面分布特征。与对照坡地比较,50次犁耕活动导致坡上部、坡中部0～45cm土层的SOM含量分别降低了38%和47%,坡下部0～100cm土层中的SOM含量却提高了18%。坡上部土壤剖面中137Cs浓度的加权平均值从1.48Bq/kg降低到0.29Bq/kg,坡中部从2.53Bq/kg减少到0.33Bq/kg,坡下部从1.48Bq/kg提高到2.81Bq/kg。210Pbex浓度的剖面加权平均值在坡上部从27.71Bq/kg下降到6.15Bq/kg,在坡中部和坡下部分别从35.46Bq/kg和25.53Bq/kg降低到1.57Bq/kg和19.40Bq/kg。137Cs和210Pbex的剖面分布与SOM在p<0.001水平呈显著相关,相关系数R2值在对照坡地为0.81～0.86,在犁耕实验坡地为0.86～0.91。实验结果表明,环境放射性核素137Cs和210Pbex在黄     

土壤中钙键和铁/铝键结合的有机碳差异的比较

为研究矿质元素在有机碳矿化中所起的作用,以棕壤、黄棕壤、红壤为供试土壤,比较了不同利用方式和施肥处理土壤中钙键、铁/铝键结合的有机碳的差异。结果表明,从北至南的地带性土壤(棕壤、黄棕壤和红壤)系列中,全钙及与有机碳结合的钙依次降低,钙键结合的有机碳占有机碳总量的比值依次升高;铁/铝键结合的有机碳及其占全碳的比值依次升高。与自然土壤相比,耕作土壤在不施肥条件下,钙键有机碳、铁/铝键有机碳占有机碳总量的比值增加,且铁/铝键有机碳占有机碳总量比值的增加率始终比钙键有机碳占有机碳总量比值的增加率要高;覆膜比不覆膜时铁/铝键有机碳占有机碳总量比值的增加率比钙键有机碳占有机碳总量比值的增加率高得多。这表明,与全土有机碳相比,有机碳矿化稳定性由高到低依次是铁/铝键有机碳、钙键有机碳、全土有机碳。     

不同耕作方式下黑土有机无机复合体变化及有机碳分布特征

研究了不同耕作方式下黑土有机无机复合体组成及有机碳在各级复合体中的分布特征。结果表明:黑土有机无机复合体组成以粉粒复合体为主;黑土有机碳主要存在于小粒级复合体中,开垦有使有机碳向小粒级复合体中聚集的趋势。随着复合体粒径的增大,有机碳各组分的含量趋于减少,HA/FA比值趋于增加;腐殖质碳主要集中在粉砂粒以下的复合体中,且复合体的粒径越小,HA所占比重越大。开垦可导致土壤复合体分散,不利于HA类胶结物质向小粒级复合体中分配,轮作有利于土壤有机碳的累积,土壤物理性状的改善及土壤肥力的提高。     

Effects of nitrogen and intensive mixing on decomposition of C-labelled maize (Zea mays L.) residue in soils of different land use types

This study investigated the effects of mineral-N addition and intensive mixing (analogous to disturbance by plowing) on decomposition of ¹⁴C-labelled maize (Zea mays L.) residue and soil organic matter (SOM). Soils were collected from the upper 5 cm of three land use types at Edelweiler, Germany: plow tillage (PT), reduced tillage (RT), and grassland (GL). Soils were incubated for 112 days at 20 °C, with or without ¹⁴C-labelled maize residue (4 g DM kg⁻¹ soil), with or without nitrogen (100 mg N kg⁻¹ soil as NH₄NO₃) and with or without intensive mixing.

The effect of mineral-N on maize residue decomposition differed depending on the stage of decomposition and land use type. Nitrogen accelerated residue decomposition rates in the first 5 days in RT and GL soils, but not in PT soil, and decreased residue decomposition rate in all three land use types after 11 days. At the end of the incubation, N suppressed ¹⁴CO₂ efflux in RT and PT soils, but not in GL soil. Mineral-N did not increase SOM decomposition independently on the land use types.

Intensive mixing stimulated decomposition of both plant residue and SOM in all three land use types. However, effects were smaller in GL soil than in RT or PT soil, presumably because stronger soil aggregates in GL would have been less affected by mixing and allowed greater protection of SOM and plant residue against decomposition.     

The Influence of pH and Organic Matter from Sugarcane By-products on Soil Cadmium Fractionation

ABSTRACT

Crop wastes or by-products can have the potential to be used as effective amendments to improve agricultural soil quality and/or crop yields subject to appropriate screening and testing. Sugarcane (Saccharum officinarum L.) waste by-products from an ethanol production plant, including boiler ash, filter cake, and vinasse, were applied as soil amendments at 5%, 10%, 20%, and 40% (w/w) to study the relationship between pH and organic matter (OM) on cadmium (Cd) bioavailability and adsorption via organic matter using the Cd sequential extraction procedure. Soil pH was significantly affected by aging of the treatment with boiler ash, filter cake, and vinasse. At the end of the experiment, the Cd concentrations with all treatments were mainly released in the first two extraction steps of the sequential procedure, i.e., most mobile and easily mobilized fractions. Pearson correlation analyses revealed a negative relationship between pH and bioavailable Cd and between OM and oxidizable Cd. The pH reduction induced by the amendments was a major factor affecting soil Cd bioavailability. The effect of OM on Cd fractionation could not be clearly observed and interpreted in this study.     

不同有机材料覆盖对土壤保水效果的影响

[目的]研究不同有机材料覆盖对土壤水分蒸发量、土壤含水量的影响,并筛选出保水效果最佳的材料。[方法]以木片、树皮及经过堆腐的园林废弃物为研究对象,进行模拟蒸发及桶装控制试验。[结果]不同粒径的园林废弃物覆盖均能降低土壤水分日蒸发量,日蒸发量从大到小依次为CK,3～5 cm粒径(M_3)、0～1 cm粒径(M_1)、1～3 cm粒径(M_2)。在连续蒸发14 d后,M_2,M_1,M_3和CK的土壤水分累积蒸发量分别为193.0,269.5,304.0和1 037.0 g,与CK相比,分别减少了81.4%,74.0%,70.7%;不同有机材料覆盖均能提高土壤含水量。除了雨季之外,不同土层土壤含水量从高到低依次表现为:木片覆盖(M_4)树皮覆盖(M_5)1～3 cm粒径园林废弃物覆盖(M_2)CK。土壤含水量的年变化整体呈现出双峰趋势,一年中4—5月含水量较低,6—8月含水量较高,不同土层土壤含水量的年变化趋势基本一致。M_4,M_5,M_2和CK的0—40 cm土层土壤年平均含水量分别为32.9%,30.3%,27.4%,26.8%。[结论]木片为保水效果最好的有机材料,其次是树皮和园林废弃物。     

Determination of phospholipid- and lipopolysaccharide-derived fatty acids as an estimate of microbial biomass and community structures in soils

Several soils subject to different cultivation and management practices were examined by analysis of fatty acid profiles derived from phospholipids and lipopolysaccharides, using an improved sequential method which is capable of measuring ester-linked and non-ester-linked phospholipid fatty acids (EL-PLFA, NEL-PLFA, respectively) and the hydroxy fatty acids in lipopolysaccharides. A good correlation was obtained (r>0.90) between the soil biomass and total EL-PLFA in the soils investigated, which ranged from forest soils to a variety of agricultural soils. Elucidation of the composition of the community structure was an additional task. Eukaryotes can be differentiated from bacteria by the presence of polyunsaturated and -hydroxy fatty acids, both of which were much more abundant in the OF layer of the forest soil than in the remaining samples. A relatively low proportion of monomethyl branched-chain saturated fatty acids was obtained in the forest OF horizon, these being indicators for Gram-positive bacteria and actinomycetes. Various subclasses of proteobacteria produce and mid-chain hydroxy fatty acids, which occur primarily in agricultural soils. The ratios between monounsaturated fatty acids and saturated fatty acids seem to be very useful parameters of soil environmental conditions. In addition, on the basis of the differences in composition of the NEL-PLFA and hydroxy fatty acids of lipopolysaccharides, clear indications for the community structure of various soils were obtained. In the forest soils much more abundant anaerobic micro-organisms and relatively less abundant proteobacteria were present than in the other soils. In the cultivated soils, however, the proportion of Gram-negative bacteria was considerably higher. Furthermore, eukaryotes appeared to be pre-dominant in the soils once used for a manure deposit site.     

Simultaneous effects of plants and earthworms on mineralisation of 15N-labelled organic compounds adsorbed onto soil size fractions

 The simultaneous impact of three successive crops of wheat (Triticum aestivum L.) and of the earthworm (Lumbricus terrestris L.) on the mineralisation of ¹⁵N-labelled organic compounds adsorbed to different soil size fractions (sand and organic residues >50 μm; silt 50–2 μm; coarse clay 2–0.2 μm and fine clay <0.2 μm) was studied under controlled conditions in the greenhouse. Unplanted soils (UPS) were used as controls. In planted soils without earthworm (PS) total plant biomass decreased with each cropping by up to 50%. However, in planted soils with earthworms (PES) the total plant biomass loss was only 17%. This pattern was explained by the earthworm effect. Compared to the unplanted soils, the planted soils had an increased (mean +37%) mineralisation of ¹⁵N adsorbed onto fine clays and a partial transfer of ¹⁵N to silt and coarse clay. The quantities of ¹⁵N mineralised and transferred were higher in the planted soils with earthworms, indicating an amplification of the phenomenon in the presence of earthworms. The simultaneous effect of the rhizosphere and the drilosphere did not lead to increased mineralisation of N adsorbed onto coarse clays and silts but instead a greater transfer of N associated with the fine fractions towards the coarser fractions. Received: 25 April 2000     

Effect of water and nitrogen management on aggregate size and carbon enrichment of soil in rice‐wheat cropping system

A study was carried out on a silty clay loam soil (Typic Haplustept) to evaluate the effect of farmyard manure (FYM) vis‐à‐vis fertilizer and irrigation application on the soil organic C content and soil structure. The fertilizer treatments comprised of eight different combinations of N and FYM and three water regimes. The results indicated that the application of FYM and increasing N rate increased soil organic carbon (SOC) content. Addition of FYM also increased the percentage of large sized water stable aggregates (> 5 mm) and reduced the percentage of smaller size aggregates. This was reflected in an increase in the mean weight diameter (MWD) and improved soil structure. The organic carbon content in macroaggregates (> 1 mm) was greater compared to microaggregates, and it declined with decrease in size of microaggregates. This difference in organic C content between macro‐ and microaggregates was more with higher N dose and FYM treated plots. The effect of residual FYM on MWD and organic C content of the soil after wheat harvest was not significant. The effect was less in deeper layers compared to surface layers of the soil. MWD was significantly correlated with the SOC content for the top two layers.