丁子香酚在番茄和土壤中的残留动态

采用田间试验的方法,研究了0.3%丁子香酚可溶液剂在番茄上的残留动态和最终残留,用带紫外检测器的液相色谱测定了丁子香酚的残留量。丁子香酚的最低检出量为3×10-10g,在番茄和土壤中的最低检出浓度均为0.003mg/kg。在番茄和土壤中的平均回收率为93.2%￣112.5%,变异系数为1.2%￣14.0%,符合农药残留分析的要求。试验结果表明:丁子香酚在番茄和土壤中的消解很快,其半衰期分别为9.5h和16.5h;0.3%丁子香酚可溶液剂按推荐剂量5.3ga.i./hm2和推荐剂量的1.5倍8.0ga.i./hm2使用3、4次,末次施药距收获间隔1、2、3d,丁子香酚在番茄中的残留量为0.012￣0.028mg/kg,土壤中为ND(<0.003)-0.084mg/kg;该农药属易分解农药(T1/230d),按推荐剂量使用是安全的。     

Effect of human activities on forest ecosystems: N cycle and soil fertility

Forests are important terrestrial ecosystems, with particular nutrient cycling mechanisms to maintain structure and functions. Nitrogen is essential for forest growth and development, and commonly limited for the forest productivity. N cycles in forest ecosystems are frequently disturbed by intensive human activities. Based on a variety of research results, some potentially important human disturbances are discussed and their effects on forest ecosystems are reviewed. Precipitation is a considerable N input to forest ecosystems. However acid precipitation is detrimental to the ecosystems in the long run. Acidification causes remarkable reduction in forest productivity in the world, due to the harmful effect of acid on plant physiology and more importantly to the reduction in soil fertility by lowering mineralization and increasing N loss by runoff and leaching. The most important nutrient cycling mechanism in forest ecosystems is litterfall. Removal of trunks only for commercial use will not affect N cycle in forest ecosystems significantly, but attention on the intensity and rotation times of harvest should be paid. Clear-cutting should be prevented in forest harvesting. It deserves more attention that the change of environment after clear-cutting will affect the N cycling processes in forest ecosystems, which substantially influence soil fertility and forest productivity. Ammonification and nitrification processes are stimulated after harvesting, by which N is becoming more moveable. Unfortunately in the situation of no assimilation after clear-cutting, much of N will be lost out of the ecosystems and soil fertility will be diminished. The N pool in forest floor and underlying mineral soil is big, but forest productivity is generally low in natural conditions. Forest management is needed to meet the increasing demand for forest products. Optimization of stands structure is the most economic way to increase soil fertility and forest productivity. Mixed coniferous-broad leaved forest is recommended for plantation practice. Addition of fertilizer N effectively promotes forest productivity and may compensate for the N loss from the systems by harvesting.     

Effect of source and nest size of N fertilizers and temperature on nitrification in a coarse textured, alkaline soil

Nitrification occurring in an alkaline sandy loam soil fertilized with urea, ammonium sulphate (AS) and ammonium chloride (AC) was studied in the laboratory at 20°C and 40°C for 30 days. Nitrogen fertilizers were applied as nest of sizes 0.2, 0.5, 1.0 and 2.0 g. Unfertilized control and soil mixed with 50 mg N kg^-1 were also included as treatments.Nitrification in all the fertilizer treatments decreased markedly with increasing nest size. At 20°C, differences among the three N sources were not significant at 5 days after incubation but marked differences appeared thereafter. All the N was nitrified by 30 days in case of fertilizers mixed into the soil. In nest placement, nitrification ranged from 30.1 to 75.5%, 28.3 to 74.6% and 35.3 to 88.7% for urea, AC and AS, respectively. When equal amounts of fertilizers were placed in a nest, nitrification occurred at a slower rate with urea than with AC and AS. Rates of nitrification were significantly higher at 40°C than at 20°C. At 20 days, nitrification from different nest sizes ranged from 8.4 to 64.9% and from 24.9 to 87.0% at 20°C and 40°C, respectively. The difference in nitrification at two temperatures were more pronounced at higher nest sizes than at smaller nest sizes. While nitrification with the three N sources decreased linearly with increase in N concentration (nest size) in soil at 40°C, it showed a quadratic relationship at 20°C. At equal N concentration, the highest rate of nitrification occurred with urea and the lowest with AC. At the same rate of applied N (50–2000 mg kg^-1), AC and AS increased electrical conductivity of soil by 1.3–9 times that of urea. Apparent mineral N recovery of applied N decreased with the increase in nest size.     

Technique for determining effects of banded fertilizer on soil solution composition and root growth

A technique is described whereby fertilizer, equivalent on an area basis to that applied in a band, diffuses into a soil-filled column of stacked rings. By recovering individual rings, 5 mm sections of soil are obtained at different distances from the fertilizer source. These soil sections are enclosed in an assembly which allows short term (48 h) root growth experiments to be undertaken. Following these experiments, sufficient soil solution can be extracted from each soil section to enable multi-element analyses.     

Effects of lanthanum on nitrification and ammonification in three Chinese soils

The effects of lanthanum on nitrification and ammonification in three Chinese soils were evaluated through an incubation experiment. Soils were collected from experimental plots under rice/rape rotation in Yingtan, Jiangxi province (red soil), under rice/wheat rotation in Wuxi, Jiangsu province (paddy soil), and under corn/wheat rotation in Fengqiu, Henan province (Fluvo-aquic soil). Soil nitrification was stimulated slightly by La at lower concentrations, and the stimulation rate reached about 20% in red soil at 150 mg La kg^–1 dry soil, and 14% in fluvo-aquic soil at 300 mg La kg^–1 dry soil. When more La was added in soils, nitrification was inhibited, with a maximum inhibition rate of 42, 44 and 66% in red soil, fluvo-aquic soil, and paddy soil, respectively. Soil ammonification was not significantly different between control and up to 600 mg La kg^–1 dry soil in red soil, but it was significantly reduced in doses of 900 and 1200 mg La kg^–1 dry soil. Significant reduction in soil ammonification was also found in doses from 60 to 1200 mg La kg^–1 dry soil except for 600 mg La kg^–1 dry soil in fluvo-aquic soil. In contrast the ammonification in paddy soil was strongly stimulated by La, reaching about 25 times that of control at 900 mg La kg^–1 dry soil. We assumed that application of La accelerates the transformation of nitrogen in soils at low dosage, and the currently applied dosage in agriculture in China cannot inhibit soil nitrification and ammonification even after long term successive application.     

Effects of soil solution on the dynamics of N2O emissions: a review

In this review, which consists of two parts, major interactions between nitrous oxide (N₂>O) and soil solution are described. In the first part, as an introduction, concentrations of dissolved N₂>O in different aqueous systems are summarized. An inventory of data on maximal N₂>O concentrations in soil solution (up to 9984 g N₂>O-N l^–1>) and in soil air (up to 8300 ppm) from literature is presented. The peak N₂>O concentrations represent a N₂>O supersaturation in the soil solution up to 30000 times with respect to ambient air and a soil air N₂>O concentration about 25000 times higher than in the atmosphere. The main physico–chemical parameters (solubility, diffusion) controlling N₂>O distribution between soil solution and soil air are outlined. The influences of cultivation practice, nitrogen turnover, water content and temperature on N₂>O a ccumulation in soil solution and soil air are reviewed. In the second part some models of N₂>O dynamics in soils are discussed with emphasis on N₂>O transport processes. A simple qualitative scheme is developed to categorize the effects of the soil solution on N₂>O dynamics in soils. In this scheme the temporary, intensive N₂>O oversaturation of the soil solution is interpreted as a result of gas diffusion inhibition by water (barrier function of soil solution) resulting in an accumulation of N₂>O. In addition, N₂>O supersaturation is an indication that transitory much N₂>O can be stored in the soil solution (storage function of soil solution). Where the soil solution flows up-, down- or sidewards it can act as a relevant transport medium for dissolved N₂>O (transport function of soil solution). This scheme is applied to examples from the literature.     

腐植酸物质对盐碱化中低产田土壤理化性质及玉米影响的研究

通过田间试验探讨了复合改良制剂、草炭、风化煤等腐植酸类物质施用对盐碱化中低产田土壤理化性质及生长作物的影响，结果表明：复合改良制剂、草炭、风化煤施用对土壤理化性质均有积极的影响，与对照相比达到显著水平。玉米产量的方差分析表明，复合改良制剂处理与草炭、风化煤等处理差异显著，与对照差异极显著，增产率均达到30．67％以上。     

唑螨酯对土壤呼吸作用和过氧化氢酶活性的影响

通过模拟实验研究了杀螨剂唑螨酯对土壤呼吸作用和土壤巾过氧化氢酶活性的影响。结果表明,唑螨酯对土壤的呼吸作用有一定的影响,用1mg/kg剂量处理,初期土壤呼吸作用表现为轻微的抑制,到第15d则恢复到与对照一致。用5、10mg／kg剂量处理,则在培养期间内一直处于被抑制状态。唑螨酯对土壤中过氧化氢酶的活性有一定影响但不显著,在试验期间内,低浓度处理（1、10mg／kg）呈现出轻微的抑制-激活-恢复过程,而高浓度处理（40、80mg／kg）则呈现出抑制-激活-抑制-恢复过程。实验结果表明,唑螨酯对土壤微生物影响较小,属于低毒或无实际危害的农药。     

腐植酸对土壤中无机磷活化效应的研究

通过磷的吸附—解吸试验,大豆盆栽和大田试验,研究了在石灰性土壤上施用风化煤、泥炭、膨润土对土壤中不同形态无机磷的影响和生物效应。试验结果表明:施用风化煤、泥炭对磷的活化作用比较明显,而膨润土的效果相对较弱;在与磷肥配合中也是风化煤、泥炭的效果最好,膨润土的效果略差。在单施风化煤、泥炭的处理中,土壤中对植物有效性较高的Ca2-P等都有增加,而植物难利用的Ca10-P则降低了,施泥炭的土壤中有效磷增量比较明显;施磷处理中,泥炭加磷肥比其他处理高,而风化煤、膨润土的效应比泥炭略差。就各指标进行综合评价,3种材料活化磷的效果依次是:风化煤>泥炭>膨润土。     

Nitrification and denitrification derived N2O production from a grassland soil under application of DCD and Actilith F2

The relative contribution of nitrification and denitrification to N₂O production was investigated by means of soil incubations with acetylene in a mixed clover/ryegrass sown sward 5 days after application of a mineral fertiliser (calcium ammonium nitrate) or an organic one (cattle slurry) with and without the addition of the nitrification inhibitor dicyandiamide (DCD) and the commercial slurry additive Actilith-F2. At this time, maximum field N₂O emissions were taking place. N₂O production by the slurry amended soil was twice as high as that of the mineral amended one. N₂O came in a greater proportion from nitrification rather than from denitrification in the slurry treatment, while for the mineral fertilisation most N₂O came from denitrification. The addition of DCD to slurry produced a decrease in N₂O production both from nitrification and denitrification. No reduction in N₂O losses was observed from addition of DCD to the mineral fertilisation, although DCD resulted effective in reducing the nitrification rate by 53% both in the slurry and the mineral fertilisation. Actilith F2 induced a high nitrification rate and N₂O production from denitrification was reduced while that from nitrification was not. This revised version was published online in August 2006 with corrections to the Cover Date.     

The role of inorganic fertilizers and their management practices

Nutrient management is the key issue in sustainable soil fertility. N, P, K fertilization aims not only for a high economic return of the investment through optimized yield and quality, but also for minimum environmental hazards. The basic concept underlying integrated plant nutrition systems, is the maintenance and possible increase of soil fertility for sustaining enhanced crop productivity through optimal use of all sources of plant nutrients, particularly inorganic fertilizer, in an integrated manner and as appropriate to each specific ecological, social and economic situation. Much research has established the importance of fertilizers in increasing the fertility of soil and in influencing its productivity. It has been observed that applying fertilizers causes many changes in the soil, including chemical changes, that can positively or negatively influence its productiveness. Only a fraction of the fertilizer applied to the soil is taken up by the crop, the rest either remains in the soil or is lost through leaching, physical wash-off, fixation by the soil, or release to the atmosphere through chemical and microbiological processes. The critical information on the relative merits of different fertilization practices such as method of fertilizer placement, time and rate of application and type of fertilizers, is essential. Results from different field and laboratory experiments which helped to achieve maximum efficiency, in the most economical and sustainable way of fertilizer use to reduce the nutrient losses and production costs to the farmers and prevent environmental pollution are presented in the paper.     

Response of tomato to nitrogen fertilization and irrigation frequencies in a semi-arid tropical soil

The effect of different irrigation frequencies (5, 7 and 9 days interval) and N rates (0, 50, 100 and 150 kg N ha^–1) on applied N in tomato was studied in a field experiment during 3 growing seasons. The application of 100 kg N ha^–1 with irriga tion scheduled at 7 days interal resulted in significantly higher N uptake and recovery rate than the other combinations of N rate and irrigation frequencies studied.     

The effect of direct application of phosphate rock on increasing crop yield and improving properties of red soil

Field experiments, designed to evaluate the effect of direct application of phosphate rock, were carried out on red soil (Ultisol) uplands at three different places. The results indicated: (1) for the first year's crop, the rapeseed yields with phosphate rock treatment and triple superphosphate treatment were almost identical when their rate of phosphorus application was the same; (2) when the same level of phosphorus fertilizer was applied, the residual effect of phosphate rock was better than that of triple superphosphate, and the residual effect of all phosphorus fertilizers on winter crop yields increased with the increase of the amount of Phosphorus applied; (3) with the application of phosphate rock, the pH value, the amount of available phosphorus and exchangeable Ca and Mg of soils went up, whereas the content of active Al in soils decreased. Therefore, the direct application of phosphate rock to red soil also has an important role in improving soil properties.The project was financially supported by American Phosphate Foundation, PPI/PPIC and National Natural Science Foundation of China.     

Effects of various hydrocarbons on micellar growth

The effect of aliphatic and aromatic hydrocarbons on surfactant micellar growth has been investigated by viscosity measurements at 40°C. Aqueous and aqueous KBr (0.1 M) solutions of 0.1 M cetylpyridinium bromide (CPB) showed that the viscosity behavior changed substantially in the presence of KBr. This is attributed to favorable conditions produced by KBr that assist micellar growth by addition of hydrocarbons. Reasons for the effectiveness of the solubilized hydrocarbons are suggested and supported by theoretical arguments. The causes of viscosity decrease at higher aromatic hydrocarbon concentrations are also explained. Micellar growth with soluble aromatic/aliphatic hydrocarbons could also be initiated if a moderate salt concentration is present in CPB micellar solutions. The chainlength, solubilization site, and molar volume of the soluble hydrocarbons all affect the bulk viscosity of the solution. Such surfactant and hydrocarbon combinations may find use in micellar-enhanced ultrafiltration of benzene and its derivatives, but it should be kept in mind that micellar shape may change and be more curved at higher benzene derivative concentrations.     

The effects of superphosphate and potassium fertilizer and salts on the nitrogen mineralization of incubated meadow soil

Three experiments were carried out to study the effect of superphosphate, potassium fertilizer salts on the extent of N mineralization and on the nitrification rate with increasing time of incubation of soil samples from a meadow. Experiment 1: Increasing amounts of superphosphate, up to 96 mg per 30 g soil (equivalent to 174 kg P per ha) had only a small effect on the N mineralization. The samples treated with potassic fertilizer, up to 126 mg per 30 g soil (equivalent to 996 kg K per ha), reached values up to 65% higher than the control without any fertilizer. There was a positive and significant P × K interaction. The nitrification decreased with applications of any fertilizer. Experiment 2: The addition of potassium as chloride, sulfate and carbonate increased the amount of mineralized N to the same extent. Chloride and sulfate reduced the nitrification rate, whereas carbonate promoted it. Experiment 3: The addition of potassium chloride to soil sterilized with thimerosal had no effect on the amount of N released. With increasing time of incubation the content of mineral N in the samples increased. The abiotical release of N without K addition amounted to nearly 1.9 mg N per 100 g soil after 3 days of incubation and 15 days later to 6.0 mg N per 100 g soil.     

Farmer's view on soil organic matter depletion and its management in Bangladesh

Bangladesh is an agricultural country. About 80% of the total population live in rural areas. The contribution of agriculture to the gross domestic product is 30%. Rice is the major food crop while jute, sugarcane and tea are the main cash crops. Other important crops are wheat, tobacco, pulses, vegetables and fruits. Overall productivity in Bangladesh is stagnating or declining. The implication of yield stagnation or declining productivity is severe, since these trends have occurred despite rapid growth in the use of chemical fertilisers. Depletion of soil organic matter is the main cause of low productivity, which is considered one of the most serious threats to the sustainability of agriculture in Bangladesh. In Bangladesh, most soils have less than 17 g/kg and some soils have less than 10 g/kg organic matter. Farmers realise that there is a problem with soil fertility related to organic matter depletion. Farmers say that organic matter increases yield, reduces the production cost, improves crop growth and the economy, increases water-holding capacity and improves the soil structure. They recognise soil with higher organic matter content by darker brownish to black in colour. Some farmers are using fast-growing trees such as Flemingia macrophyla, Ipilipil (Leucaen leucophala), Glyricidia sepium, Boga Medula (Tephrosia candida), Dhol Kolmi (Ipomoea fistulosa), etc., as living fences, which can be used as fuel, fertiliser and fodder. To increase the soil organic matter, farmers use green manure crops, compost, quick compost, cow dung, azolla, etc. However, fuel for cooking purposes is limited and cow dung and crop residues are largely used as fuel. Crop residues are also used as fodder for livestock. Farmers expressed the wish to learn more about organic fertilizer management. However, sufficient food should be produced to keep pace with population growth. To alleviate the hunger and poverty is to increase the intensity of agricultural production and maintain favorable ecological conditions. Therefore, more organic matter should be used in the farmers' fields to sustain the soil fertility in an intensive farming system. This revised version was published online in June 2006 with corrections to the Cover Date.     

Effects of excreta return on properties of a grazed pasture soil

The long term impact of excreta return on some chemical and biological properties of a pasture soil fertilised with sulphur and phosphate was studied in a system that had been with or without excreta for 23 years. Excreta free areas that had developed under electric fencelines, and parallel transects in the paddocks, were sampled to provide this comparison. Sampling was to 300 mm depth in 0–75, 75–150 and 150–300 mm sections. Total carbon and nitrogen were 20% higher in the 0–150 mm soil layer of areas receiving excreta but did not differ in the 150–300 mm layer. Carbon:nitrogen ratios were similar in both systems as was mineralisable nitrogen, both absolutely and as a percentage of total in the 0–75 mm layer. Significantly more N was mineralised in the 75–150 mm layers of the areas receiving excreta but this was reversed in the 150–300 mm layer. Nitrification rate was higher in all layers of the excreta areas. Inorganic and organic P fractions did not differ significantly. Total P was significantly higher in the 0–75 mm layer and significantly lower in the 150–300 mm layer of the excreta areas. Exchangeable potassium was much higher throughout the excreta areas while this was offset by calcium. The sum of the cations was similar in both areas. Excreta affected most of the diagnostic soil tests used for fertiliser recommendations. The soil properties measured did not reflect clearly the differences in productivity that were obvious in the two areas. It is concluded that excreta return has a impact resulting in increased organic matter storage. Short-term effects of urine have a greater impact on productivity. The major effect is on the disposition of cations and available P.     

Effects of N management on growth, N2 fixation and yield of soybean

Soybean (Glycine max) is one of the most importantfood and cash crops in China. Although soybean has the capacity to obtain alarge proportion of its N from N₂ fixation, it is commonfarmer's practice to apply an N top dressing to maximize grain yield. Afield experiment was conducted to study the effects of N application as urea atvarious stages during the vegetative and reproductive phases on crop biomass,N₂ fixation and yield of two soybean genotypes, Luyuebao and Jufeng.Starter N at 25 kg ha^–1 resulted in minimumbiomass and pod yield while starter N at 75 kgha^–1 had no significant effect and N top dressing, ateither the R1 or R5 stage, resulted in increased biomass and pod yield. Maximumbiomass and pod yield were obtained when a top dressing of 50 kgha^–1 was applied at the flowering stage. The effects oftop dressing on the capacity to fix N₂ were complex. The proportionof plant N derived from N₂ fixation (Pfix) was highest when onlystarter N at 25 kg ha^–1 was applied. Any topdressing reduced nodulation and Pfix, but increased biomass, so that totalN₂ fixed increased for top dressing at the flowering or pod fillingstage. Common farmer's practice of applying 75 kg Nha^–1 at the V4 stage, resulted in a significantreduction in N₂ fixation. To evaluate the application of Nfertilization at various stages ofdevelopment on growth, nodulation and N₂ fixation in more detail, anexperiment in nutrient solution with or without 20 mMNO₃ ^– was conducted with genotype Tidar. The N-freetreatment gave the lowest biomass and total N accumulation, as in the fieldexperiment. A continuous nitrate supply resulted in the highest biomass,associated with an increase in total leaf area per plant, maximum individualleaf area, branch and node number per plant, shoot/root ratio and leaf arearatio, compared to the N-free treatment. R1 was the most responsive stage fornitrate supply as well as for interruption of the nitrate supply. Since theresults from the field experiment were in agreement with thosefrom the experiment in nutrient solution in a greenhouse, the latter can beusedto predict crop performance in the field.     

Turnover of15N ammonium sulfate with dicyandiamide under aerobic and anaerobic soil conditions

The influence of the nitrification inhibitor dicyandiamide (DCD) on the turnover of¹⁵N-labelled ammonium sulfate (AS) was investigated in two soils under aerobic and waterlogged conditions. Nitrification of ammonium sulfate was markedly inhibited by addition of DCD in both soils. Up to 45% of the supplied N was transformed into a non-extractable N form, which only slowly released nitrogen over 147 or 264 days. This immobilization was higher in the presence of DCD than without DCD. In all aerobic experiments, the recovery was 100% ± max. 2.4%, indicating that no gaseous losses of N occurred.If aerobic preincubation of 28 or 42 days was followed by water-logging with H₂O or a solution of glucose, considerable N losses occurred only in presence of the carbohydrate. DCD retarded nitrification and thus reduced losses by denitrification from 61 to 15%.DCD application resulted in an increased immobilization of labelled N into the non-exchangeable soil N fraction. This amounted to more than 50% of the applied N, compared to 39% without DCD.The late Dr. Klaus Vilsmeier, a very dedicated and talented young scientist, died before he was able to finish completely the revised version of this article. We will always keep him in our minds and kindly remember his kind personality as well as his sense of humour and justice. Prof. Dr. Heiner Goldbach on behalf of all members of the department.     

Effect of soil water contents in the non-rice growth season on CH4 emission during the following rice-growing period

A pot experiment was carried out to investigate the effect of soil water content in the non-rice growth season (winter season) on CH₄ emission during the following rice-growing period. The results showed that CH₄ fluxes increased significantly with the increase of soil water content in the winter season, except air-dry water condition. The mean CH₄ fluxes of treatments with soil water contents in the winter of 3.89–5.37% (air-dry), 25–35%, 50–60%, 75–85% and 107% (flooded) of field water capacity (FWC) were 13.04, 4.04, 8.61, 13.26 and 20.47 mg m^–2 h^–1, respectively. Antecedent soil water contents also markedly affected temporal variation patterns of CH₄ fluxes and soil redox potential (E_h) during the rice-growing period. The higher soil water contents in the winter season were, the quicker soil E_h decreased, and the earlier CH₄ emission occurred after rice transplanting, except air-dry water condition. Though the seasonal mean CH₄ flux was significantly correlated with the seasonal mean soil E_h, the seasonal variation of CH₄ fluxes was not always significantly correlated with soil E_h. For the treatment flooded in the fallow season, there was no significant correlation between CH₄ flux and soil E_h, but there was significant correlation between CH₄ flux and soil temperature during rice growth season. In contrast, for the other four treatments, it was soil E_h, not soil temperature that significantly affected the temporal variation of CH₄ emissions. Soil water contents in the fallow season significantly influenced concentrations of soil labile organic carbon (including undecomposed plant debris), active Fe and Mn immediately before rice transplanting. The mean CH₄ fluxes during rice-growing period were significantly correlated with soil labile organic carbon contents (positively) and contents of soil active Fe and Mn (negatively).