Outlook on fertilizer use efficiency in the tropics

In this paper efficiency of applied fertilizers under tropical conditions is examined. Understanding of the fertilizer efficiency is particularly important for the developing countries mainly because there is need for enhancement of crop yields at a reduced cost. Many of the soil, plant and climatic factors of the tropical regions that contribute to the efficiency of the applied fertilizers have been discussed. Many of the tropical soils are acidic in nature and in these soils efficiency of applied fertilizer is relatively poor, mainly because plant roots are unable to grow and function to their fullest extent in utilizing the soils available nutrients. To enhance yield potentials there is need for understanding of interaction between crop species and soil and climatic variables. Incorporation and adoptation of a suitable application time can greatly enhance efficiency of urea form of nitrogen. Research findings in tropical soils have shown that an initial broadcast application of P and subsequent band treatment is more effective than either method of application alone. Current crop yields in tropical countries are far below the known yield potentials. Such low production potentials are attributed to the lack of suitable crop germplasms and understanding of improved agronomic practices. Intensification of research activities in fertilizer use efficiency in tropical countries is suggested.Senior author formerly was a Research Advisor to EMBRAPA/IICA/World Bank Program in Brazil.     

An easy pot incubation method for measuring nitrogen mineralization from easily decomposable organic material under well defined conditions

A pot incubation method for measuring mineralization dynamics from fresh plant material was tested. The aim was to develop a method which under well-defined conditions could produce mineralization data suited for estimating model input parameters for nitrogen prediction models. The results showed that the water tension of the soil could be controlled easily and precisely by diffusion through porous ceramic cups, and that nitrogen mineralization or immobilization could be measured already after 15 days at 15°C. The results showed that for the incubated catch crop residues carbon, nitrogen and nitrate-N contents were the most important factors determining mineralization. No significant effects ould be ascribed to other parameters measured.     

A comprehensive approach to evaluating watershed models for predicting river flow regimes critical to downstream ecosystem services

Selection of strategies that help reduce riverine inputs requires numerical models that accurately quantify hydrologic processes. While numerous models exist, information on how to evaluate and select the most robust models is limited. Toward this end, we developed a comprehensive approach that helps evaluate watershed models in their ability to simulate flow regimes critical to downstream ecosystem services. We demonstrated the method using the Soil and Water Assessment Tool (SWAT), the Hydrological Simulation Program–FORTRAN (HSPF) model, and Distributed Large Basin Runoff Model (DLBRM) applied to the Maumee River Basin (USA). The approach helped in identifying that each model simulated flows within acceptable ranges. However, each was limited in its ability to simulate flows triggered by extreme weather events, owing to algorithms not being optimized for such events and mismatched physiographic watershed conditions. Ultimately, we found HSPF to best predict river flow, whereas SWAT offered the most flexibility for evaluating agricultural management practices.     

Bauxite residue (red mud) increases phosphorus retention in sandy soil catchments in Western Australia

The Peel-Harvey estuary on the Swan Coastal Plain, Western Australia has become eutrophic partly because of the leaching of fertiliser phosphorus from sandy soils. The acid, coarse textured sandy soils are predominantly quartz, have a low iron and aluminium content and do not retain phosphorus. Red mud, derived from bauxite, is a by-product of the alumina industry and has the ability to retain phosphorus. Retention of phosphorus is enhanced when the red mud is neutralised with gypsum. Red mud has been suggested as a soil amendment to reduce phosphorus leaching.To investigate the reduction in the leaching of phosphorus from soils amended with red mud, weirs were constructed at the outlets from a pair of catchments to quantify the amount of phosphorus in the streamflow. Both catchments were deep grey Bassendean sand. One of the catchments was treated with 80 t/ha of red mud which had been neutralised with waste gypsum from the phosphate industry. The red mud was applied to the soil surface using conventional fertiliser spreading equipment. The other catchment was untreated.The red mud reduced phosphorus loss by 70% from 13.8 kg/ha on the untreated catchment, to 4.2 kg/ha on the treated catchment. Both catchments were treated with 20.4 kg/ha of phosphorus as superphosphate. The catchment treated with red mud also received a further 41.5 kg/ha of phosphorus from the phosphogypsum that was used to neutralise the red mud.Our results show that red mud reduces phosphorus leaching and is potentially a nutrient management option in sandy soils. Red mud has the potential to reduce the impact of agriculture on the estuarine environment and has implications for the continued expansion and intensification of agriculture in the Peel-Harvey catchment.     

计算机网络安全与防护技术研究

本文主要对计算机网络安全产生的根源和存在的风险进行了初步分析,对目前常用的网络安全技术进行了较为深入的研究,并阐述了防火墙技术与入侵检测技术在计算机网路中联合部署的方法和步骤.     

Fate of nitrogen fertilizer applied to lowland rice on a Sulfic Tropaquept

A field experiment was conducted on an acid sulfate soil in Thailand to determine the effect of N fertilization practices on the fate of fertilizer-N and yield of lowland rice (Oryza sativa L.). A delayed broadcast application of ammonium phosphate sulfate (16-20-0) or urea was compared with basal incorporation of urea, deep placement of urea as urea supergranules (USG), and amendment of urea with a urease inhibitor. Deep placement of urea as USG significantly reduced floodwater urea- and ammoniacal-N concentrations following N application but did not reduce N loss, as determined from an¹⁵N balance, in this experiment where runoff loss was prevented. The urease inhibitor, phenyl phosphorodiamidate (PPD), had little effect on floodwater urea- and ammoniacal-N, and it did not reduce N loss. The floodwater pH never exceeded 4.5 in the 7 days following the first N applications, and application of 16-20-0 reduced floodwater pH by 0.1 to 0.3 units below the no-N control. The low floodwater pH indicated that ammonia volatilization was unimportant for all the N fertilization practices. Floodwater ammoniacal-N concentrations following application of urea or 16-20-0 were greater on this Sulfic Tropaquept than on an Andaqueptic Haplaquoll with near neutral pH and alkaline floodwater. The prolonged, high floodwater N concentrations on this Sulfic Tropaquept suggested that runoff loss of applied N might be a potentially serious problem when heavy rainfall or poor water control follow N fertilization. The unaccounted-for¹⁵N in the¹⁵N balances, which presumably represented gaseous N losses, ranged from 20 to 26% of the applied N and was unaffected by urea fertilization practice. Grain yield and N uptake were significantly increased with applied N, but grain yield was not significantly affected by urea fertilization practice. Yield was significantly lower (P = 0.05) for 16-20-0 than for urea; however, this difference in yield might be due to later application of P and hence delayed availability of P in the 16-20-0 treatment.     

Available nitrogen in soils and its determination by the ‘Nmin-method’ and by electroultrafiltration (EUF)

Excess nitrogen fertilizer rates are an environmental hazard. To avoid excess rates, the level of available nitrogen in the soil must be known and considered for assessing the nitrogen fertilizer rate. In arable soils nitrate and exchangeable ammonium in the rooting depth of a crop are directly available to plant roots. These two nitrogen forms are recovered with the Nmin method and they are considered in assessing the nitrogen fertilizer rate for arable crops.Besides nitrate and ammonium recovered by the Nmin method from soil samples taken in early spring, a considerable amount of organic soil nitrogen may be mineralized during the growth period and contribute to crop nutrition. The nitrogen mineralization potential can be determined in incubation tests. The absolute quantities of mineralized nitrogen thus obtained, however, are much higher than the mineralization rates under field conditions. It is for this reason that incubation tests have not obtained a major importance for assessing nitrogen fertilizer rates.With the electro-ultrafiltration (EUF) method nitrate, ammonium, and a minor portion of organic soil nitrogen are extracted from a soil suspension. There is experimental evidence that this organic nitrogen (=Norg) is easily mineralizable. Based on field experiments with cereals and maize formulae were established by which the nitrogen fertilizer rate can be calculated. In these formulae nitrate, ammonium and organic nitrogen extracted by EUF are considered.Advantages and drawbacks of the Nmin method and EUF method are discussed.     

型钢翼缘狗骨式削弱在型钢混凝土节点的作用

为了防止地震时型钢混凝土节点核心区发生剪切破坏以及梁柱连接焊缝发生脆性断裂,提出对型钢混凝土节点核心区附近梁端型钢的上、下翼缘采取狗骨式削弱,并系统研究翼缘削弱对提高型钢混凝土节点抗震性能的作用.研究表明,由于在梁端型钢翼缘采取狗骨式削弱,不仅能够将塑性铰控制在梁型钢削弱的位置,从而有效地降低了节点核心区所受的剪力以及梁柱连接焊缝的应力;而且能够改善节点塑性铰区的转动能力和抗剪性能,提高节点的延性和耗能能力.     

确定土壤背景值的Hazen概率法——以铜陵矿区Pb为例

本文选取已知土壤背景含量的铜陵矿区,基于Hazen概率曲线,探讨了土壤污染重金属元素Pb背景含量与污染叠加含量的区分方法.得到Pb元素的背景含量为28.5μg/g,与该区深层土壤样中Pb元素含量的平均值(34μg/g)比较接近.还得到了Pb元素污染叠加含量与背景含量的界线点51μg/g.基于Hazen概率曲线区分铜陵矿区土壤Pb元素背景含量与污染叠加含量的方法是有效的,有必要将该方法推广到土壤中其它重金属污染元素、其它地区作进一步研究.     

双洞口配筋砌块砌体框支墙梁试验

为研究双洞口配筋砌块砌体框支墙梁地震前后的受力模式,在拟动力子试验前后进行了底层框架配筋砌块短肢砌体剪力墙结构三层足尺模型的竖向力静载试验.试验结果表明:托梁与上部墙体表现出良好的协同工作能力,其工作模式为拉杆拱.通过对其在拟动力试验前后的受力模式进行了比较,可知带洞口配筋砌块砌体框支墙梁结构体系在墙体受到一定损伤时,并不会使墙梁的受力机理发生明显改变.