A yield-independent, 15N-isotope dilution method to estimate legume symbiotic dependence without a non-N2-fixing reference plant

The proportional contribution of atmospheric N₂ to the N nutrition of lupin (P _atm) was estimated in a field experiment following addition of NH₄Cl of KNO₃ to unconfined microplots (1.5 m²) at 2.5 g N m^-2 (10 atom% ¹⁵N). The integrated ¹⁵N enrichment, or mean pool abundance, of nitrate extracted from 0- to 15-cm samples taken under the lupin crop on eight occasion between 28 and 190 days after sowing was used as the reference criterion to estimate P _atm by the ¹⁵N-isotope dilution technique. Estimates of P _atm were similar to those obtained using canola as a non-fixing reference plant, but were higher than estimates obtained using a yield-dependent model. Use of mean pool abundance obviates the need for a non-fixing reference plant, and the frequent sampling and isotope-ratio analysis of the legume biomass required with the yield-dependent model is unnecessary. However, further work is needed to validate a sampling strategy commensurate with the growth of the legume roots.     

土壤磷扩散规律及其能量特征的研究──Ⅰ．水分、质地、温度及其相互作用对磷扩散的影响

用＾３２Ｐ示踪扩散池和扩散管法测定了４种不同质地土壤在不同含水量和温度下的磷自扩散系数。结果表明，非饱和土壤磷扩散系数随土壤水分含量增加或土壤水吸力减小而增大，符合幂函 数Ｄａ＝ａＷ＾ｂ＝ａＳ＾－ｂ关系；质地对磷扩散的影响与土壤水分条件密切相关，在同一含水量下，轻质土壤Ｄａ值大于粘质土，Ｄａ与粘粒含量呈显著负相关，而同吸力下与此恰好相反。饱和土壤磷扩散系数比Ｄａ值通常大２－３个数量级，但不同土壤之     

黄丘五副区降雨和地形因素与坡面水土流失关系研究

本项研究依据６年来在黄丘五副区定西试验区径流场所取得的观测资料，探讨了降雨物征值和地形中坡度、坡长、坡形三个因子对坡面水土流失的影响规律及其相互关系．提出了表征降雨侵蚀力、坡面产流的指标均为ＰＩ３０，依次建立了相应的数学模型群。此项研究不但从理论上揭示了坡面水土流失发生发展过程及机制，而且在实践上为有效地进行坡面水土流失的治理和水土保持措施的优化配置提供了科学依据。     

Earthworm channels in cultivated clayey and loamy Norwegian soils

Studies of earthworm species and their activity, expressed as channels, on cultivated loamy (Humic Cryaquept) and clayey soils (Typic Endoaqualf and Typic Cryaquept) were conducted in southern and central Norway before conversion from conventional to organic cropping systems. At all the three study areas: Landvik (Grimstad), Voll (Ås) and Kvithamar (Stjørdal), the earthworm species Aporrectodea caliginosa, Aporrectodea rosea, Allolobophora chlorotica and Lumbricus rubellus were found. At Landvik, where the deep-burrowing species Aporrectodea longa, A. caliginosa and Lumbricus terrestris dominated, medium (4–6 mm) and coarse (>6 mm) earthworm channels were most numerous below the plough layer. Almost no coarse pores were found at Voll and Kvithamar. The volume of earthworm channels below the plough layer was 0.6–0.8% of total soil volume at Landvik and Voll and 0.3–0.4% at Kvithamar. Earthworm channels >6 mm below the plough layer were useful to identify present and previous activity of deep-burrowing earthworms such as L. terrestris. Below the plough layer, roots were almost entirely restricted to earthworm channels and interaggregate spaces.     

水土流失定量遥感方法及其应用的研究

本文介绍了水土流失定量遥感方法，应用实验和结果，并讨论了它的实质和应用前景等。该法的监测模型虽有与ＵＳＬＥ和ＲＵＳＬＥ相同的表达形式，但其因子琥式算法系由我国实测资料所建，故有更人合我国实际的应用效果，尤其它适用于遥感和ＧＩＳ数据的微机处理。     

耕作管理措施对残茬覆盖及其分解的影响

The effects of tillage methods on percent surface residue cover remaining and decomposition rates of crop residues were evaluated in this study. The line transect method was used to measure residue cover percentage on continuous corn (Zea mays L.) plots under no tillage (NT), conventional tillage (CT), chisel plow (CH), and disk tillage (DT). Samples of rye (Secale cereale L.) and hairy vetch (Vicia villosa Roth) were used for residue decomposition study. Results showed that the percentage of residue cover remaining was significantly higher for NT than for CH and DT and that for CT was the lowest (< 10%). For the same tillage system, the percent residue cover remaining was significantly higher in the higher fertilizer N rate treatments relative to the lower fertilizer N treatments. Weight losses of rye and vetch residues followed a similar pattern under CT and DT, and they were significantly faster in CT and DT than in NT system. Also, the amounts of residue N remaining during the first 16 weeks were always higher under NT than under CT and DT.     

The effect of urban refuse compost and different tractors tyres on soil physical properties, soil erosion and maize yield

Application of urban refuse compost to agricultural soil could help to solve municipalities' problems related to the increasing production of waste only if soil property improvement and environmental conservation can be demonstrated. The use of low-pressure tractor tyres is another proposal in modern agriculture for reducing soil compaction. This study thus aimed to detect the effects of both compost and low-pressure tractor tyres on soil loss, runoff, aggregate stability, bulk density, penetrometer resistance and maize (Zea mays L.) yield. A 3-year field experiment was carried out on a hilly (15% slope) clay loam soil in central Italy. Twelve plots (200 m² each) were monitored with tipping-pot devices for runoff and soil erosion measurement. Treatments were: compost addition (64 Mg ha⁻¹), mineral fertilisation, use of low-pressure tyres, use of traditional tyres, with three replicates, in a fully randomised block design. Compost was applied once at the beginning of the experiment. Runoff reduction due to compost ranged between 7 and 399 m³ ha⁻¹ during seasons, while soil erosion was reduced between 0.2 and 2.4 Mg ha⁻¹. Mean weight diameter (MWD) of stable aggregates, measured on wheel tracks, increased by 2.19 mm, then progressively decreased. Compost significantly increased bulk density by 0.08 Mg m⁻³ due to its inert fraction content. This effect was less evident in the second and third year, probably due to harrowing. Maize yields were slightly, but significantly, reduced in composted plots by 1.72 Mg ha⁻¹ in the third year. Low-pressure tyres significantly reduced soil loss in the third year by 1 Mg ha⁻¹. Furthermore, they did not significantly influence runoff volumes and soil structural stability. Low-pressure tyres or compost addition were singly able to prevent an increase in penetrometer resistance due to agricultural machinery traffic. Low-pressure tyres increased the maize yield during the 3 years and the difference (0.4 Mg ha⁻¹) became significant in the third year. In conclusion, results show the positive lasting effect of compost in ameliorating soil physical properties and reducing runoff and soil erosion. Low-pressure tyres appear justifiable both for the observed increase of grain production and reduction of soil compaction. This latter effect is, nevertheless, masked by compost addition which is also able to reduce penetrometer resistance. Further research is required to explain the causes of the slight inhibition of grain yield observed when compost was compared with mineral fertilisation.     

Carbon distribution and losses: erosion and deposition effects

Because of concerns about the eventual impact of atmospheric CO₂ accumulations, there is growing interest in reducing net CO₂ emissions from soil and increasing C storage in soil. This review presents a framework to assess soil erosion and deposition processes on the distribution and loss of C in soils. The physical processes of erosion and deposition affect soil C distribution in two main ways and should be considered when evaluating the impact of agriculture on C storage. First, these processes redistribute considerable amounts of soil C, within a toposequence or a field, or to a distant site. Accurate estimates of soil redistribution in the landscape or field are needed to quantify the relative magnitude of soil lost by erosion and accumulated by deposition. Secondly, erosion and deposition drastically alter the biological process of C mineralization in soil landscapes. Whereas erosion and deposition only redistribute soil and organic C, mineralization results in a net loss of C from the soil system to the atmosphere. Little is known about the magnitude of organic C losses by mineralization and those due to erosion, but the limited data available suggest that mineralization predominates in the first years after the initial cultivation of the soil, and that erosion becomes a major factor in later years. Soils in depositional sites usually contain a larger proportion of the total organic C in labile fractions of soil C because this material can be easily transported. If the accumulation of soil in depositional areas is extensive, the net result of the burial (and subsequent reduction in decomposition) of this active soil organic matter would be increased C storage. Soil erosion is the most widespread form of soil degradation. At regional or global levels its greatest impact on C storage may be in affecting soil productivity. Erosion usually results in decreased primary productivity, which in turn adversely affects C storage in soil because of the reduced quantity of organic C returned to the soil as plant residues. Thus the use of management practices that prevent or reduce soil erosion may be the best strategy to maintain, or possibly increase, the worlds soil C storage.     

Analysis of soil-vegetation systems' sensitivity to changes of climate-dependent carbon turnover parameters

 The nonlinear model of the carbon cycle in soils (NAMSOM) was used to analyze the sensitivity of soil organic matter levels to variations in carbon turnover parameters. We were able to predict the sensitivity of soil organic matter levels to variations of climate-dependent carbon turnover parameters, which allowed us to compare the sensitivity of soil organic matter levels to net primary productivity of plant communities and plant debris decomposition rate constants across the range of soils in the European part of Russia. The results indicate that meadow steppes show the lowest sensitivity to variations of these parameters. In passing from meadow steppes to the northern taiga and to semideserts, the sensitivity increases. In general, soil organic matter levels of boreal forest ecosystems are about 2–3 times more sensitive to input and decomposition of plant debris than to decomposition of humus. In subboreal grassland ecosystems the sensitivity to humus decomposition increases and becomes closer to the degree of sensitivity shown by soil organic matter levels to variations of productivity and decomposition of plant debris. The proposed method may be useful for predicting the response of ecosystems to climatic change. Received: 1 December 1997     

土壤生物在土壤磷有效化中的作用

本文概述了磷被土壤组分固定的机制,详述了土壤微生物,根,菌根和蚯蚓在提高土壤磷植物有效性中起的作用。土壤生物对磷的活化作用主要机制为;通过产生质子和有机酸溶解不溶态无机磷,通过分泌磷酸酶水解有机磷,这种作用受土壤供磷与植物对磷需求间平衡的调控。