Evaluation of the selective respiratory inhibition method for measuring the ratio of fungal:bacterial activity in acid agricultural soils

A procedure for the measurement of the fungal and bacterial contribution to substrate-induced respiration was tested in three arable soils. Glucose and different amounts of cycloheximide (eukaryote inhibitor) and streptomycin sulfate (prokaryote inhibitor) were added to soil suspensions, and respiration (CO₂ evolution) was measured. Streptomycin sulfate concentrations from 10 to 120 mg ml^–1 soil solution caused a stable inhibition of respiration. Amounts of cycloheximide ranging from 5 to 35 mg ml^–1 showed an increasing inhibition. In a test with separate and combined addition of the antibiotics at maximum inhibitory concentrations, inhibition by streptomycin was completely overlapped by cycloheximide. This indicated non-target inhibition which may lead to overestimation of fungal respiration. Experiments with sterilized soils inoculated with either fungi or bacteria confirmed that streptomycin selectively inhibited bacteria. Cycloheximide, however, did not only inhibit fungal respiration already at 2 mg ml^–1, but also increasingly inhibited bacterial respiration at increasing concentrations. Only at less than 5 mg cycloheximide ml^–1 was the condition of selective fungal inhibition fulfilled. When 2 mg cycloheximide and 10 mg streptomycin sulfate ml^–1 were applied, the sum of the separate inhibitions almost equalled the combined inhibition by the mix of both inhibitors in field samples. This method yielded fungal:bacterial respiration ratios of 0.50 to 0.60, and confirmed the dominance of bacteria in Dutch arable soils. The ratios obtained by the selective inhibitors were not correlated with, and were higher than, ratios of fungal:bacterial biovolume (0.19 to 0.46) as determined by microscopy and image analysis. Similar measurements in a forest soil (A-horizon) raised doubts on the reliability of the fungal inhibition by cycloheximide in this soil. It is concluded that the separate:combined inhibition ratio should always be checked, and comparison with other approaches is recommended. Received: 17 September 1996     

耕作白浆土有机无机复合体腐殖质组成及类型

本文用Ｋｕｍａｄａ法研究了耕作白浆土各粒径级分中有机质的特征。结果表明，土壤及各粒径级分中有机碳含量多是高肥土壤大于低肥，并随复合体粒径增大而下降，下降的比例是高肥小于低肥；土壤有机质及粘粒含量影响有机碳贮量曲线与各粒径级分含量曲线的关系，高肥土壤中粉粒或细砂级分中的有机碳贮量明显高于低肥。土壤及各粒径级分的腐殖质以能被０．１ｍｏｌ／Ｌ ＮａＯＨ提取的游离态为主，其故敏酸（ＨＡ）含量、ＰＱ１值等多     

河北省太行山区域耕地资源空间分布特征研究

文根据遥感影像资料, 在对河北省境内太行山区域耕地资源进行解译的基础上, 应用GIS技术和空间分析方法, 对其空间分布特征从海拔高度、坡度及地形类型3个方面进行了分析研究。结果表明, 河北省太行山区域耕地的80.9%分布于海拔500 m以下, 93.7%分布于坡度15°以下, 70.3%分布于平地和U型谷地。由此可以看出, 目前河北省太行山区域耕地资源开发利用比较合理。本文对河北省太行山区域耕地资源空间分布特征的分析可为太行山区域耕地质量评估和合理利用提供科学依据和支持。     

Earthworms of different functional groups affect the fate of the Bt-toxin Cry1Ab from transgenic maize in soil

The fate of the insecticidal Cry1Ab protein from crop residues (leaves and roots) of the transgenic maize variety MON810 was studied in the presence and absence of two earthworm species (Lumbricus terrestris, Aporrectodea caliginosa; separate incubations) in soil microcosms. The recombinant Cry1Ab protein was quantified using a highly sensitive ELISA. Control microcosms received corresponding non-transgenic plant material. All earthworms survived in the microcosms over a period of 5 weeks, irrespective of whether they received MON810 or non-transgenic plant material. Weight loss was observed for both earthworm species, independent of the plant material or transgenic modification. A strong decline of immunoreactive Cry1Ab in plant residues (mean initial concentration approx. 5000 ng g⁻¹) of MON810 was observed in all treatments, but in microcosms with earthworms this decline was significantly higher with less than 10% of the initial Cry1Ab concentration remaining after 5 weeks. Cry1Ab concentrations in casts were only 0.1% of those found in remaining plant material of the respective microcosms. No immunoreactive Cry1Ab proteins were found in earthworm tissues (threshold of detection: 0.58 ng g⁻¹ fresh weight). No further decline was found for Cry1Ab concentrations in casts of A. caliginosa during a subsequent period of 3 months of incubation in bulk soil (<0.1 ng g⁻¹) after removal of the earthworms from the microcosms, while in casts of L. terrestris the concentration decreased from 0.4 to below 0.1 ng g⁻¹. In conclusion, this study demonstrates that earthworms enhance the decline of immunoreactive Cry1Ab proteins from maize residues.     

Application of Dolostone Powder as Industrial Residual on Magnesium‐Deficient Arable Soils in Estonia

About 60% (678,000 ha) of Estonian arable soils have a deficiency of plant‐available magnesium (Mg). The soils formed from dolostone (or dolomite rock) till are considerably richer in Mg than those formed from limestone‐rich and noncalcareous tills. Formerly, ground dolostone rock with a high content of mineral dolomite was used only as a soil liming material. Later, dolostone powder (DSP), received in the course of industrial manufacturing of dolostone rubble, was also applied for the mitigation of Mg deficiency in soil. The easily accessible resources of DSP as an industrial waste may also qualify as an Mg fertilizer. It soon became apparent, however, that with the application of DSP to the soil, an excessive quantity of Mg could be accumulated. This Mg surplus in soil destroys the equilibrium in plants' assimilation of nutrition elements and inhibits the normal development of agricultural crops. In our research, the influence of different DSP doses on the yield of red clover (Trifolium pratense L.), lucerne (Medicago sativa L.), barley (Hordeum vulgare L.), wheat (Triticum aestivum L.), and oil rape (Brassica napus L. var. Oleifera subvar. Annua) was studied on arable soils formed from different parent materials. We elucidated from the 2‐year experiment the high efficiency of DSP application in increasing the yields of Mg‐philic crops such as clover, lucerne, and oil rape. The negative influence of excessive Mg application on crop yields, especially in the first year of DSP application, is more clearly visible on soils that are calcium deficient for plant production. For the amendment of deficiency in Mg acid arable soils, 1–1.5 t ha^?1 of DSP should be used every 2 to 3 years. The broad application of industrial‐origin DSP is useful from at least three points of view: (1) industrially produced Mg fertilizers may be replaced by a readily available local industrial (mining) by‐product, (2) managing costs and territories for the disposal of industrial wastes will be reduced, and (3) it will be possible to attain complex and environmentally friendly utilization of local mineral resources.     

A new method for analyzing agricultural land-use efficiency,and its application in organic and conventional farming systems in southern Germany

Improving the land-use efficiency (LUE) of farming systems could satisfy increasing global food, feed, biomass and bioenergy demand in a sustainable manner. This study presents a new method for calculating LUE, beginning with an overview of different approaches to assessing agricultural LUE. This new method takes into account the quality and function of agricultural products and the relationship between the yield of the assessed farm and the average yield of the reference region with comparable soils, climate and socio-economic conditions.The new approach was tested using data from long-term experiments at the Scheyern Research Farm in southern Germany, which include different farming systems (organic mixed farming, arable farming, and agroforestry; conventional arable farming and agroforestry). In our case studies, the LUE of conventional systems (arable farming: 1.00; improved arable farming: 1.06; agroforestry: 0.98) was higher than those of the organic systems (mixed farming: 0.69; arable farming: 0.33; agroforestry: 0.43) due to different crop rotations, dry matter yields, and biomass usage (harvest ratio). The conversion of high-input arable farming systems (conventional farming) to agroforestry systems is an extensification with negative effects on the dry matter yield and land-use efficiency. Nevertheless, the conversion to agroforestry systems can increase dry matter yield and land-use efficiency in low-input arable farming systems (organic farming). LUE should be used in combination with agri-environmental indicators, in order to ensure both efficient and sustainable land use.     

决策树在耕地地力等级评价中的应用

在介绍数据挖掘技术的基本概念、决策树方法的基础上,结合牡丹江市地力等级数据样本,采用决策树ID3分类算法建立了耕地地力等级决策树分级图。通过该分级图可以预测各地区耕地地力等级,为该领域的数据挖掘提供了合理的挖掘方式。     

农村青壮年劳动力流失引起的耕地撂荒及留守人群问题探究

以四川省三台县为例,介绍了农村留守人群遇到的困难及土地撂荒现状,分析了农村青壮年大量流失及耕地出现大面积撂荒的原因,最后,提出了相关对策建议。     

我国耕地保护制度现状及发展方向分析

回顾了我国耕地保护制度发展的过程,并将其划分为启动阶段、确立阶段、发展阶段和完善阶段;并从耕地承包经营、基本农田保护、耕地占补平衡、土地用途管制和土地整治制度对现有耕地保护制度体系进行了分析;最后,从耕地保护的目标、制度、模式、主体和监管方式等方面对我国耕地保护制度的未来发展方向进行了讨论。     

农用地分等中几种β值计算方法的比较

[目的]在农用地分等工作中需要把不同作物折算到同一基础上进行比较,不同折算方法会给结果带来多大差异是值得关注的问题。[方法]总结目前常见的5种折算方法,在全国随机抽取样点进行产量折算,对折算结果进行统计分析。[结果]5种折算方法间的差异并不十分显著,但不同折算方法在地域上的误差表现会有所不同。[结论]选择β时不仅要考虑研究目的,还要考虑研究地域的影响,用蛋白质含量折算也许是目前适宜于大部分研究领域的方法。