Fungi,bacteria and protozoa in soil from four arable cropping systems

Summary The effects of four cropping systems on soil microorganisms were investigated during 3 years. The cropping systems were B0, barley without nitrogen fertilizers; B120, barley with 120 kg N ha^–1 year^–1; GL, grass ley receiving 200 kg N ha^–1 year^–1; and LL, lucerne ley without nitrogen fertilizer additions. At samplings in September during three consecutive years no differences were found between treatments. Total fungal lengths ranged between 0.7 and 2.0 × 10³ m and bacterial numbers between 3.5 and 7.2 × 10⁹ g^–1 dry wt. soil.Twenty samplings over 3 years in B120 and in GL indicated higher numbers of bacteria and protozoa during the growing season, except for periods with moisture stress. No clear seasonal trends were found for the fungi. When comparing mean values for the 20 samplings, the grass ley contained significantly (P < 0.05) higher numbers of amoebae. Means of the bacterial numbers and biomass, total and FDA-active hyphal lengths were also higher or equal (FDA-active hyphae) but not significantly so.Seventy-nine per cent of the bacterial biomass and 73% of the total fungal lengths were found in the top soil, where also 85% of the oxygen was consumed.     

Ammonium oxidizer numbers,potential and actual oxidation rates in two swedish arable soils

Summary The number of ammonium-oxidizing bacteria was measured with the most probable number (MPN) method while potential ammonium oxidation rates were determined with a chlorate inhibition technique in two arable soils. A new method for measuring actual in situ ammonium oxidation in soil cores is presented.One soil was cropped for 4 years with one of four crop-fertilizer combinations: Unfertilized lucerne ley, unfertilized barley, nitrate-fertilized grass ley, or nitrate-fertilized barley. The highest ammonium oxidizer numbers and potential rates were found in the grass ley. The unfertilized barley had one-third the number and activity of the grass ley. Actual rates were in general 5–25 times lower than potential rates.The other soil was that undergoing a 27-year-old field trial with a fallow and four different cropping treatments: No addition, nitrate, nitrate + straw, or manure. Ammonium oxidizer numbers were highest in the manure and straw treatments. MPN numbers and potential rates were lowest in the fallow treatment. Typical specific potential rates were 30 ng N oxidized cell^–1 h^–1. Actual rates were in general 40 times lower than potential rates.Actual ammonium oxidation measurements seem to correspond to actual in situ activity at the moment of sampling, whereas the MPN technique and the potential measurements reflect events that occurred weeks to months before the sampling.     

Seasonal aspects of sciarid emergence in arable land (Diptera: Sciaridae)

In April-October 1990-95 soil sciarids emerging in two Danish barley fields were recorded by means of emergence traps. In 1990-92 the fields were conventionally tilled, in the autumn of 1992 one of the fields was abandoned as annual set-aside (1993) and in 1994-95 most of the field was recropped. In the cropped and uncropped fields 480-527 ind. m⁻² and 369-433 ind. m⁻² emerged, respectively. Ten sciarid species were recorded, eight of which are well-known farmland inhabitants. Apparently, abandonment affected Scatopsciara atomaria negatively, whereas Corynoptera perpusilla was encouraged. The predominant species were probably bivoltine or trivoltine. In Lycoriella castanescens, Scatopsciara atomaria, Corynoptera perpusilla and Bradysia trivittata the female proportion increased significantly during the season. It is assumed that the primary sex ratio of the species is spanandrous. The seasonal change in sex ratio might arise from the unusual modes of reproduction demonstrated in Sciaridae. In Lycoriella castanescens, Bradysia trivittata and Corynoptera perpusilla a significant seasonal increase in wing length was recorded, whereas the wing length of Scatopsciara atomaria and Bradysia rufescens decreased significantly during the season. This suggests a seasonality in the production of large, potentially migrant females. In arable fields sciarid life history traits such as sex ratio, adult biometry and fecundity might be facultative.     

陕西省城镇化进程及其对耕地资源的影响

城镇化是工业化和现代化发展的必然结果,也是衡量一个国家或地区经济社会发展水平的重要标志。陕西省在城镇化水平不断提高的同时,也给耕地带来了严重的影响,尤其是减少了耕地的面积。本文通过运用权重法和综合指数法来计算陕西省2000年到2011年城镇化指数,确认城镇化发展的速度,通过对陕西省2000年到2011年年末常用耕地面积、房屋建筑施工面积、农业占总产值比重和公路里程数据进行分析,进而对城镇化与耕地资源的各项指标进行相关性分析。结果表明陕西省城镇化进程的加快对耕地造成了很大的影响,呈现高度负相关。我们应减少城镇化对土地的依赖,更好地合理利用和配置土地资源。     

我国热带山区耕地土壤养分分布特征

[目的]明确海南山区耕地土壤养分空间分布特征,为热带山区耕地土壤养分管理提供思路.[方法]以海南五指山市耕地为研究对象,采用野外调查、采样和室内分析相结合的方法,在分析土壤养分含量基础上,阐述土壤养分现状,探讨其土壤养分分布规律.[结果]五指山耕地土壤总体呈酸性,其pH为5.1;土壤养分含量分布不均,土壤有机质、有效磷、速效钾和中量元素(钙、镁、硫)含量均为中等或偏下水平,土壤有效铜和有效锌含量较为丰富.五指山耕地土壤酸化和养分含量分布不均主要与气候、母质分布和施肥不平衡有关.[结论]根据五指山市耕地土壤养分分布状况,可采取适宜措施以促进土壤养分平衡,如推广秸秆还田,采用测土配方施肥技术进行施肥指导.     

贵州铅锌冶炼区农田土壤镉铅有效性评价与预测模型研究

农田土壤重金属的不同活性库分布和土壤-溶液分配模型能够提供重金属的生物有效性和浸出能力等信息,因而在风险评价和修复实践中非常重要。本研究采集毕节铅锌冶炼区30个历史污染农田土壤,同时在贵州省范围内采集5种类型背景土壤制成不同浓度Pb/Cd单一污染土壤;经3个月老化,分别测定由0.43 mol/L HNO_3、0.1 mol/L HCl和0.005 mol/L DTPA提取态表征的重金属反应活性库以及由0.01 mol/L CaCl_2提取态表征的直接有效库;分析铅锌冶炼区农田土壤Cd、Pb不同有效库的分布特征,建立土壤-溶液分配模型,并讨论土壤理化性质的影响。结果表明:历史污染土壤中Cd和Pb的直接有效库占全量比例分别比人工污染土壤低4倍和223倍,然而历史污染土壤Cd和Pb的反应活性库(0.43 mol/L HNO_3提取态)占全量比例要高于相应人工污染土壤中的比例。拓展Freundlich形式吸附方程能够准确描述各提取态表征的Cd和Pb活性库与土壤全量Cd和Pb的关系,尤其0.43 mol/L HNO_3提取方法能够克服土壤理化性质对土壤Cd和Pb提取的影响而与总量建立极显著的相关关系。pH依附性Freundlich吸附方程准确描述了Cd和Pb的总反应活性库分别与土壤溶液Cd和Pb的关系,对于Pb而言,还要考虑土壤有机质和有效磷的影响。本研究可为矿区农田土壤重金属污染评价、修复以及农田有效态标准的推导提供参考。     

辽宁省耕地质量与环境保障问题及其体系建设

本文通过分析我省当前耕地质量与环境保障体系建设的有关问题,探讨建设我省耕地质量及其环境预测预警监测体系、无公害农产品生产基地环境评价系统、主要农作物平衡施肥技术体系模式,并提出我省整个耕地质量及其环境保障体系的各项保障措施。     

Loss‐on‐Ignition in the Determination of Pools of Organic Carbon in Soils of Forests and Afforested Arable Fields

Abstract

Loss‐on‐ignition (LOI) and concentration of organic carbon (Cc) were determined on pristine forest soils and soils from afforested arable fields. The objectives were to investigate the relation between the Cc of soil estimated indirectly from LOI and true Cc from dry combustion (C_LECO) and further to evaluate how the applied analytical method affects the carbon pool estimates. According to results, LOI was a good indicator of Cc in the organic layer. As regards mineral soil, however, C_LECO/LOI ratio significantly decreased with increasing depth, and the ratio changed differently in soils underlying forest sites as opposed to the soils from former fields. The results indicate that estimation of carbon pools from conversion factors would lead to considerable bias and that direct measurement of Cc is preferable to the use of any Cc/LOI ratio. The results also emphasize the need for elimination of carbonate carbon when measuring Cc from the soil of arable fields.     

西藏山南浪卡子县卡热乡耕地利用现状调查

以西藏山南浪卡子县卡热乡2006年和2009年的总耕地面积、粮食耕地面积、油菜耕地面积、菜类耕地面积为调查对象,通过查阅该乡政府基本情况统计表,调查了该乡2006年和2009年耕地数量及各耕地类型的分布状况。结果表明：2006～2009年该乡总耕地面积没有发生变化,但各耕地利用类型所占面积变化较大,其中,粮食耕地面积呈减少趋势,油菜耕地面积和菜类耕地面积有所增加,特别是油菜耕地面积比例增加了1倍以上。进一步提出了耕地开发利用的新思路：合理利用耕地,加强基础建设,培植龙头企业及开拓和完善区内外农牧产品市场。     

基于粮食安全需求的耕地需求量多情景预测研究——以湖北省咸宁市为例

基于粮食的安全需求,根据粮食的调出率高、中、低3种情景,预测了咸宁市3种情景2020年的耕地面积分别为166.32、178.41、190.51 kg/hm2。