固磷基质(无定形铁)淋失特征及其与磷素淋失的关系

采用淋洗试验研究了水田土壤固磷基质（无定形铁）淋失特征及其与磷素淋失的关系。结果表明,添加柠檬酸和葡萄糖培养处理对无定形铁、络合态铁的淋失具有极显著效应,水分和温度等因素对无定形铁和络合态铁的淋失交互效应显著;相关分析表明,固磷基质（无定形铁）淋失与磷素淋失的相关关系显著,说明对磷素淋失有一定的影响。     

酶浸提取方法对士的宁产率的影响

目的：研究了纤维素酶在提取生物碱过程中的应用。方法：采用酶浸法和氯仿法两种不同的工艺提取马钱子生物总碱,高效液相色谱法（HPLC）测定了马钱子生物总碱中士的宁的含量。结果：酶浸法提取士的宁和氯仿法提取士的宁的含量分别为1．83％、1．32％;酶浸法和氯仿法提取马钱子生物总碱的产率分别为：2．85％、1．86％。     

酸雨作用下的森林冠层盐基离子(Ca2+,Mg2+,K+)淋洗

在韶山针阔叶混交林中设立了10个30 m×30 m的样方,对1年中各个季节的森林截留沉降、降雨后树冠层总滤出量、盐基离子滤出量以及树冠层对H+和NH4+的摄入量进行了分析和估算.韶山森林湿沉降成分中以Ca2+为主,Mg2+,K+含量较低.树冠层盐基离子总滤出量中Ca2+最高,达到155.34 mmo1 m-2a-1,Mg2+最低,为30.74mmol m-2a-1,K+居中,为84.13 mmol m-2a-1.Ca2+的大量滤出表明它是树冠层缓冲降水酸度的主要介质,同时也表明酸雨对韶山森林的潜在危害,其在总滤出量中的比重的季节变化是夏(58.4%)＞春(54.1%)＞冬(51.4%)＞秋(32.5%).盐基离子的滤出量以冬→春→夏→秋依次递减,但是树冠层季节摄入NH4的量在30-100mmo1 m-2而对H+的摄入量则在30-180 mmol m-2.     

Global assessment of nitrogen fertilizer: The SCOPE/IGBP Nitrogen Fertilizer Rapid Assessment Project

Nitrogen (N) availability is a key role in food and fiber production. Providing plant-available N through synthetic fertilizer in the 20th and early 21st century has been a major contributor to the increased production required to feed and clothe the growing human population. To continue to meet the global demands and to minimize environmental problems, significant improvements are needed in the efficiency with which fertilizer N is utilized within production systems. There are still major uncertainties regarding the fate of fertilizer N added to agricultural soils and the potential for reducing losses to the environment. Enhancing the technical and economic efficiency of fertilizer N is seen to promote a favorable situation for both agricultural production and the environment, and this has provided much of the impetus for a new N fertilizer project. To address this important issue, a rapid assessment project on N fertilizer (NFRAP) was conducted by SCOPE (the Scientific Committee on Problems of the Environment) during late 2003 and early 2004. This was the first formal project of the International Nitrogen Initiative (INI). As part of this assessment, a successful international workshop was held in Kampala, Uganda on 12 - 16 January, 2004. This workshop brought together scientists from around the world to assess the fate of synthetic fertilizer N in the context of overall N inputs to agricultural systems, with a view to enhancing the efficiency of N use and reducing negative impacts on the environment. Regionalization of the assessment highlighted the problems of too little N for crop production to meet the nutrient requirements of sub-Saharan Africa and the oversupply of N in the major rice-growing areas of China. The results of the assessment are presented in a book (SCOPE 65) which is now available to provide a basis for further discussions on N fertilizer.     

Are differences in root growth of nitrogen catch crops important for their ability to reduce soil nitrate-N content,and how can this be measured?

An experiment was made to measure root growth of nitrogen catch crops, to investigate whether differences in root growth among plant species are related to their ability to deplete the soil nitrate-N pool. Large differences were observed in root growth parameters. Monocot species had rooting depth penetration rates in the range of 1.0 to 1.2 mm d^–1 °C^–1, whereas the non-legume dicot species had rates between 1.5 and 2.3 mm d^–1 °C^–1. Substantial differences were also found in the lag time from sowing until significant root growth was observed. The estimated temperature sum needed for the crops to reach a rooting depth of 1.0 m varied from 750 d °C for fodder radish to 1375 d °C for Italian ryegrass. The depth distribution of the root system varied strongly, and at a depth of 1.0 m the non-legume dicot species generally had root intensities (number of root intersections m^–1 line on the minirhizotrons) 12 times as high as the monocot species.The amount of nitrate left in the topsoil (0–0.5 m) was only weakly correlated to a few of the measured plant and root parameters, whereas nitrate left in the subsoil (0.5–1.0 m) was clearly correlated to several root parameters. Subsoil nitrate residues were well correlated to root intensity, but showed even stronger correlations to more simple estimates of rooting depth. In the deepest soil layer measured (1.0–1.5 m), the soil water nitrate concentration was reduced from 119 g L^–1 without a catch crop to 61 g L^–1 under Italian ryegrass and to only 1.5 g L^–1 under fodder radish.The results show that to identify the important differences in root growth among catch crops, root growth must be measured in deep soil layers. In this study, none of the measurements made aboveground or in the upper soil layers were well related to subsoil nitrate depletion.     

Plant uptake and leaching of copper during EDTA-enhanced phytoremediation of repacked and undisturbed soil

EDTA-enhanced phytoremediation of copper contaminated soil was evaluated. Up to 740 g g^–1 of Na₂H₂ EDTA in solution was added to repacked soil columns, and intact cores of a sandy loam of volcanic origin, that was growing Agrostis tenuis. The soil contained up to 400 g g^–1 of copper due to a history of fungicide spraying. EDTA application increased the herbage copper concentration of the grass growing in repacked soil from 30 to 300 g g^–1, but the same application to an intact core only brought about an increase from 10 to 60 g g^–1. More copper accumulated in the herbage when the EDTA was applied in numerous small doses than in just one or two larger amounts. Calculation of the concentration of copper in the water taken up by the grass revealed this to be two orders of magnitude lower than that in the soil solution. As a result of the EDTA applications, about 100 times more copper was leached than was taken up by the herbage. This means that a strategy for managing leaching losses needs to be part of any plan for EDTA-enhanced phytoremediation.     

Earthworms Increase Nitrogen Leaching to Greater Soil Depths in Row Crop Agroecosystems

Many biological functions of soil organisms are replaced in intensive agricultural systems, but earthworms and other soil invertebrates may continue to have significant effects on nutrient cycling in these disturbed systems. We investigated the influence of earthworms on leaching of water and nitrogen in corn (Zea mays L.) agroecosystems in a long-term (6-year) field experiment in Wooster, Ohio, USA. We employed a split-plot experimental design in which main plots received one of three nutrient treatments (cow manure, legume–grass mixture, inorganic fertilizer) and contained three 4.5 × 4.5-m field enclosures in which earthworm populations were increased, decreased, or unmodified. We installed zero-tension lysimeters beneath enclosures with increased or decreased populations and collected leachates regularly in 1996, analyzing them for water volume and concentrations of NH₄⁺, NO₃^–, and dissolved organic nitrogen (DON). Earthworms did not influence concentrations of inorganic N or DON but greatly increased leachate volume. The total flux of N in soil leachates was 2.5-fold greater in plots with increased earthworm populations than in those with decreased populations. Earthworm population density was positively correlated with total N leaching flux (r² = 0.49). Leaching losses of N to a depth of 45 cm were greater in the inorganically fertilized than in the organically fertilized plots, possibly due to greater inorganic N concentrations and lower immobilization potential in inorganically fertilized systems. Our results indicate that earthworms can increase the leaching of water and nitrogen to greater soil depths, potentially increasing N leaching from the system.Present address: Departamento de Ecoloxia e Bioloxía Animal, Universidade de Vigo, E-36200, Spain. Present address: Archbold Biological Station, 300 Buck Island Ranch Rd., Lake Placid, Florida 33852, USA. ¶Present address: P.O. Box 303, Yucca Valley, California 92286, USA.     

The role of <Emphasis Type="Italic">Calamagrostis</Emphasis> communities in preventing soil acidification and base cation losses in a deforested mountain area affected by acid deposition

The effects of grass growth and N deposition on the leaching of nutrients from forest soil were studied in a lysimeter experiment performed in the Moravian-Silesian Beskydy Mts. (the Czech Republic). It was assumed that the grass sward formed on sites deforested due to forest decline would improve the soil environment. Lysimeters with growing acidophilous grasses (Calamagrostis arundinacea and C. villosa), common on clear-cut areas, and with unplanted bare forest soil were installed in the deforested area affected by air pollution. Wet bulk deposition of sulphur in SO₄^2– corresponded to 21.6–40.1 kg ha^–1 and nitrogen in NH₄⁺ and NO₃^– to 8.9–17.4 kg N ha^–1, with a rain water pH of 4.39–4.59 and conductivity of 18.6–36.4 S cm^–1 during the growing seasons 1997–1999. In addition, the lysimeters were treated with 50 kg N ha^–1 yr^–1 as ammonium nitrate during the 3 years of the experiment. Rapid growth of planted grasses resulted in a very fast formation of both above- and below-ground biomass and a large accumulation of nitrogen in the tissue of growing grasses. The greatest differences in N accumulation in aboveground biomass were observed at the end of the third growing season; in C. villosa and C. arundinacea, respectively, 2.66 and 3.44 g N m^–2 after addition of nitrogen and 1.34 and 2.39 g N m^–2 in control. Greater amounts of nitrogen were assessed in below-ground plant parts (9.93–12.97 g N m^–2 in C. villosa and 4.29–4.39 g N m^–2 in C. arundinacea). During the second and third year of experiment, the following effects were the most pronounced: the presence of growing grasses resulted in a decrease of both the acidity and conductivity of lysimetric water and in a lower amount of leached nitrogen, especially of nitrates. Leaching of base cations (Ca²⁺ and Mg²⁺) was two to three times lower than from bare soil without grasses. An excess of labile Al³⁺ was substantially eliminated in treatments with grasses. Enhanced N input increased significantly the acidity and losses of nutrients only in unplanted lysimeters. The leaching of N from treatments with grasses (3.9–5.6 kg N ha^–1) was 31–46% of the amount of N in wet deposition. However, the amount of leached N (4.2–6.0 kg N ha^–1) after N application was only 7.1–8.9% of total N input. After a short three year period, the features of soil with planted grasses indicated a slight improvement: higher pH values and Ca²⁺ and Mg²⁺ contents. The ability of these grass stands to reduce the excess nitrogen in soil is the principal mechanism modifying the negative impact on sites deforested by acid depositions. Thus it is suggested that grass sward formation partly eliminates negative processes associated with soil acidification and has a positive effect on the reduction of nutrient losses from the soil.     

Immobilization, stabilization and remobilization of nitrogen in forest soils at elevated CO2: a 15N and 13C tracer study

The fate of immobilized N in soils is one of the great uncertainties in predicting C sequestration at increased CO₂ and N deposition. In a dual isotope tracer experiment (¹³C, ¹⁵N) within a 4‐year CO₂ enrichment (+200 ppm_v) study with forest model ecosystems, we (i) quantified the effects of elevated CO₂ on the partitioning of N; (ii) traced immobilized N into physically separated pools of soil organic matter (SOM) with turnover rates known from their ¹³C signals; and (iii) estimated the remobilization and thus, the bio‐availability of newly sequestered C and N. (1) CO₂ enrichment significantly decreased NO₃^? concentrations in soil waters and export from 1.5 m deep lysimeters by 30–80%. Consequently, elevated CO₂ increased the overall retention of N in the model ecosystems. (2) About 60–80% of added ¹⁵NH₄¹⁵NO₃ were retained in soils. The clay fraction was the greatest sink for the immobilized ¹⁵N sequestering 50–60% of the total new soil N. SOM associated with clay contained only 25% of the total new soil C pool and had small C/N ratios (<13), indicating that it consists of humified organic matter with a relatively slow turn over rate. This implies that added ¹⁵N was mainly immobilized in stable mineral‐bound SOM pools. (3) Incubation of soils for 1 year showed that the remobilization of newly sequestered N was three to nine times smaller than that of newly sequestered C. Thus, inorganic inputs of N were stabilized more effectively in soils than C. Significantly less newly sequestered N was remobilized from soils previously exposed to elevated CO₂. In summary, our results show firstly that a large fraction of inorganic N inputs becomes effectively immobilized in relative stable SOM pools and secondly that elevated CO₂ can increase N retention in soils and hence it may tighten N cycling and diminish the risk of nitrate leaching to groundwater.     

Global assessment of nitrogen fertilizer: The SCOPE/IGBP Nitrogen Fertilizer Rapid Assessment Project

Nitrogen (N) availability is a key role in food and fiber production. Providing plant-available N through synthetic fertilizer in the 20th and early 21st century has been a major contributor to the increased production required to feed and clothe the growing human population.To continue to meet the global demands and to minimize environmental problems, significant improvements are needed in the efficiency with which fertilizer N is utilized within production systems. There are still major uncertainties regarding the fate of fertilizer N added to agricultural soils and the potential for reducing losses to the environment. Enhancing the technical and economic efficiency of fertilizer N is seen to promote a favorable situation for both agricultural production and the environment, and this has provided much of the impetus for a new N fertilizer project.To address this important issue, a rapid assessment project on N fertilizer (NFRAP) was conducted by SCOPE (the Scientific Committee on Problems of the Environment) during late 2003 and early 2004. This was the first formal project of the International Nitrogen Initiative (INI). As part of this assessment, a successful international workshop was held in Kampala, Uganda on 12 -16 January, 2004. This workshop brought together scientists from around the world to assess the fate of synthetic fertilizer N in the context of overall N inputs to agricultural systems, with a view to enhancing the efficiency of N use and reducing negative impacts on the environment.Regionalization of the assessment highlighted the problems of too little N for crop production to meet the nutrient requirements of sub-Saharan Africa and the oversupply of N in the major rice-growing areas of China. The results of the assessment are presented in a book (SCOPE 65)which is now available to provide a basis for further discussions on N fertilizer.