大豆-玉米轮作区适宜NPK用量试验研究

通过连续多年的小区定位试验,采用NPK三因素多水平的不完全设计,在12个不同NPK用量的配方中筛选出适合本地区大豆-玉米轮作条件下的适宜肥料用量。由于每小区包含有连续多年的肥料效应,理论上可提供更多的养分信息,生产实践上更为实用。初步研究结果表明:大豆施氮不同用量之间,增产效果有明显的不同,大豆对氮的需求量增高,目前黑土区大豆生产需要有更多的氮素供应。大豆适宜施氮量为45 kg hm-2~60 kg hm-2;玉米适宜施氮量为166 kghm-2。施磷不同用量之间,增产效果无明显差别。由于磷素的土壤积累,磷肥增产作用已经明显低于上世纪80年代,大豆、玉米对施磷的需求量降低,但氮素对磷素有显著的协助作用,施氮能显著促进作物对磷的吸收。     

Effect of Baythroid on nitrogen transformations in soil

Laboratory incubation experiments were conducted in soil to study the influence of the insecticide Baythroid on immobilization-remineralization of added inorganic N, mineralization of organic N, and nitrification of added NH _inf4 ^su+ -N. Baythroid was applied at 0, 0.4, 0.8, 1.6, 3.2, and 6.4 g g^-1 soil (active ingredient basis). The treated soils were incubated at 30°C for different time intervals depending upon the experiment. The immobilization and mineralization of N were significantly increased in the presence of Baythroid, the effect being greater with higher doses of the insecticide. Conversely, nitrification was retarded at lower doses of Baythroid and significantly inhibited at higher doses. The results of these studies suggest that excessive amonts of insecticide residues affect different microbial populations differently, leading to changes in nutrient cycling.     

上海地区不同施肥方式氮磷随地表径流流失研究

选择上海宝山罗店镇具有代表性的旱地蔬菜农田生态系统,在从2004年3月到8月的近半年时间里,通过对径流及径流中侵蚀泥沙的氮磷流失情况的连续监测与实验分析,研究了旱地农田施肥与氮磷流失污染之间的关系,探讨了农田氮磷的迁移特征及环境效应,主要结果表明:随地表径流流失的总氮、总磷,流失形态以沉积相为主,大部分是当季施用的化肥,随径流排出农田的氮素中有37.7%是当季施用的氮素化肥,磷素中有26.9%是当季施用的磷素化肥。     

Recovery of cover-crop-N in the soil-plant system in the Guinea savannah zone of Ghana

In order to understand the efficiency of residue-N use and to estimate the minimum input required to obtain a reasonable level of crop response, it is important to quantify the fate of the applied organic-N. The recovery of N from ¹⁵N-labelled Crotalaria juncea was followed in the soil and the succeeding maize crop. Apparent N recovery (ANR) by maize from unlabelled Crotalaria juncea, Crotalaria retusa, Calopogonium mucunoides, Mucuna pruriens and mineral fertilizer at three locations were also evaluated. The maize crop recovered 4.7% and 7.3% of the ¹⁵N-labelled C. juncea-N at 42 days after sowing (DAS) and at final harvest, respectively. The corresponding ¹⁵N recovery from the soil was 92.4% and 58.5%. The highest mean ANR of 57.4% was with mineral fertilizer, whereas the mean ANR of 14.3% from C. retusa was the lowest. A large pool substitution and added-N interaction effect was observed when comparing N recovery from the labelled and unlabelled C. juncea. The amount of residue-N accounted for by the isotope dilution method at 42 DAS was 97.1% and at final harvest 65.8%. The large residue-N recovery in the soil organic-N pool explains the residual effect usually observed with organic residue application.     

Soil freeze-thaw cycle experiments: Trends, methodological weaknesses and suggested improvements

Although freeze-thaw cycles can alter soil physical properties and microbial activity, their overall impact on soil functioning remains unclear. This review addresses the effects of freeze-thaw cycles on soil physical properties, microorganisms, carbon and nutrient dynamics, trace gas losses and higher organisms associated with soil. I discuss how the controlled manipulation of freeze-thaw cycles has varied widely among studies and propose that, despite their value in demonstrating the mechanisms of freeze-thaw action in soils, many studies of soil freeze-thaw cycles have used cycle amplitudes, freezing rates and minimum temperatures that are not relevant to temperature changes across much of the soil profile in situ. The lack of coordination between the timing of soil collection and the season for which freeze-thaw cycles are being simulated is also discussed. Suggested improvements to future studies of soil freeze-thaw cycles include the maintenance of realistic temperature fluctuations across the soil profile, soil collection in the appropriate season and the inclusion of relevant surface factors such as plant litter in the fall or excess water in the spring. The implications of climate change for soil freeze-thaw cycles are addressed, along with the need to directly assess how changes in soil freeze-thaw cycle dynamics alter primary production.     

Denitrification losses from puddled rice soils in the tropics

Summary Although denitrification has long been considered a major loss mechanism for N fertilizer applied to lowland rice (Oryza sativa L.) soils, direct field measurements of denitrification losses from puddled rice soils in the tropics have only been made recently. This paper summarizes the results of direct measurement and indirect estimation of denitrification losses from puddled rice fields and reviews the status of research methodology for measurement of denitrification in rice fields. The direct recovery of (N₂+N₂O)-¹⁵N from ¹⁵N-enriched urea has recently been measured at sites in the Philippines, Thailand, and Indonesia. In all 12 studies, recoveries of (N₂+N₂O)-¹⁵N ranged from less than 0.1 to 2.2% of the applied N. Total gaseous N losses, estimated by the ¹⁵N-balance technique, were much greater, ranging from 10 to 56% of the applied urea-N. Denitrification was limited by the nitrate supply rather than by available C, as indicated by the values for water-soluble soil organic C, floodwater (nitrate+nitrite)-N, and evolved (N₂+N₂O)-¹⁵N from added nitrate. In the absence of runoff and leaching losses, the amount of (N₂+N₂O)-¹⁵N evolved from ¹⁵N-labeled nitrate was consistently less than the unrecovered ¹⁵N in ¹⁵N balances with labeled nitrate, which presumably represented total denitrification losses. This finding indicates that the measured recoveries of (N₂+N₂O)-¹⁵N had underestimated the denitrification losses from urea. Even with a probable two-or threefold underestimation, direct measurements of (N₂+N₂O)-¹⁵N failed to confirm the appreciable denitrification losses often estimated by the indirect difference method. This method, which determines denitrification losses by the difference between total ¹⁵N loss and determined ammonia loss, is prone to high variability. Measurements of nitrate disappearance and ¹⁵N-balance studies suggest that nitrification-denitrification occurs under alternate soil drying and wetting conditions both during the rice cropping period and between rice crops. Research is needed to determine the magnitude of denitrification losses when soils are flooded and puddled for production of rice.     

Nitrogen fixation,biomass production,and nutrient uptake by annual Sesbania species in an alkaline soil

Summary In three field trials conducted during the summer season of 1986, 1987 and 1989 in an alkaline soil, 17 accessions of annual Sesbania spp. were evaluated for nodulation, N₂ fixation (acetylene reduction assay), dry weight of roots and shoots, woody biomass production, and nutrient uptake. At 50 days after sowing all the accessions were effectively nodulated (average 36.4 root nodules plant^-1) with a high nodule score (3.4). There was a lot of variation in nodule volume and mass and in acetylene reduction activity but not in N content (5.2%). N uptake in shoots, roots and nodules averaged 639, 31, and 13 mg plant^-1, respectively, and much of the fixed N remained in shoots. Accessions of S. cannabina complex performed better than others. S. rostrata had poor root nodulation but exhibited excellent stem nodulation (300 nodules plant^-1) even though not inoculated with Azorhizobium sp. Average concentrations of N, P, K, S, Ca, and Mg in the shoots were high, at 3.2, 0.28, 1.5, 0.28, 1.5, and 0.4% respectively, and Na was low (0.15%), reflecting the usefulness of Sesbania spp. as an integrated biofertilizer source. Green matter production was 26.0 Mg ha^-1 (5.9 Mg dry matter) and N uptake was 158 kg ha^-1, 54 days after sowing. Average woody biomass of six accessions at maturity, 200 days after sowing, was high (19.9 Mg ha^-1), showing its potential for shortterm firewood production. Total nutrient uptake for production of woody biomass (200 days of growth) was no more demanding than growing the plant to the green-manuring stage of 50–60 days' growth.     

我国水土保持宏观规划初探

通过对土壤侵蚀环境及侵蚀类型空间特征的分析，划分了我国水土保持类型区，依据土壤侵蚀强度、危害性及水保效益等进行了水土保持评价并编制了《１：１５００万中国水土保持图》，在些基础上对我国水土保持的宏观规划进行了讨论。     

Litter decomposition and nitrogen mineralization in newly formed gaps in a Danish beech (Fagus sylvatica) forest

Gap formation is suggested as an alternative forest management approach to avoid extreme changes in the N cycle of forest ecosystems caused by traditional management practises. The present study aimed to investigate the effect of gap formation on N availability in beech litter and mineral soil on sites, which experienced only little soil disturbance during tree harvest. N pools, litter decomposition, and N mineralization rates in mineral soil were studied in two gaps (17 and 30 m in diameter) in a 75-year-old managed European beech (Fagus sylvatica L.) forest in Denmark and related to soil temperature (5 cm depth) and soil moisture (15 cm depth). Investigations were carried out during the first 2 years after gap formation in measurement plots located along the north-south transect running through the centre of each gap and into the surrounding forest.An effect of gap size was found only for soil temperatures and litter mass loss: soil temperatures were significantly increased in the northern part of the large gap during the first year after gap formation, and litter mass loss was significantly higher in the smaller gap. All other parameters investigated revealed no effect of gap size. Nitrification, net mineralization, and soil N concentrations tended to be increased in the gaps. Cumulative rates of net mineralization were two fold higher in the gaps during the growing season (June-October), but a statistically significant increase was found only for soil NH₄-N concentrations during this period. Forest floor parameters (C:N ratios, mass loss, N release) were not significantly modified during the first year after gap formation, neither were the total C content nor the C:N ratio in mineral soil at 0-10 cm depth.     

不同氮肥及肥料组合对芹菜生长和硝酸盐含量的影响

通过田间试验研究了氮肥品种组合及不同肥料配施对芹菜生长和硝酸盐含量的影响.结果表明氮肥中的氯化铵、硫酸铵及其配合施用有利于降低芹菜体内硝酸盐含量,减少土壤NO3--N积累;肥料组合正交试验结果表明几种肥料对芹菜产量影响的主次关系为尿素＞硫酸钾＞石灰＞油枯,对芹菜硝酸盐积累影响的主次关系为尿素＞油枯＞硫酸钾＞石灰.施用油枯和石灰,芹菜硝酸盐显著积累,但其用量水平间差异不显著.随着尿素施用量的增加,芹菜硝酸盐含量大幅度增加.钾肥能提高芹菜的产量并降低硝酸盐含量.统计分析表明油枯1125 kg/hm2,尿素495 kg/hm2,硫酸钾600 kg/hm2,石灰0 kg/hm2的配合施用在促进芹菜高产方面最为适宜.