Modeling Irrigation with Gypsiferous Mine Water: A Case Study in Botswana

The possible use of mine effluent for irrigation of agricultural crops was investigated for BCL Ltd. nickel mine (Selebi Phikwe, Botswana). The aims were to estimate the long-term water and salt balance under irrigation with gypsiferous mine water, as well as to make recommendations on cropping and management options. A simple but mechanistic edynamic soil water-salt balance generic crop growth model (SWB, Soil Water Balance) and a weather data generator (CLIMGEN) were used for long-term predictions. Eleven years of irrigation with BCL effluent were simulated for different cropping systems and irrigation management practices, followed by 39 years of irrigation with freshwater or dry land cropping. The long-term simulations indicated that between 661 and 2017 mm of mine effluent could be used annually through irrigation, depending on crop choice and irrigation management. Between 18% and 32% ot the total amount of salt added through irrigation was predicted to leach in 11 years, the remainder being precipitated in the 1.1 m deep soil profile in the form of gypsum. The rate of gypsum dissolution and leaching after 11 years of irrigation with mine water depended on management. Simulated root density-weighted electrical conductivities at saturation indicated favorable conditions for growth of summer crops, but a leaching fraction is recommended in winter. A lucerne perennial pasture was the most suitable cropping system from the point of view of mine water utilization and salt precipitation in the soil profile. Deficit irrigation (room for rain) followed by dry land cropping was the most suitable management strategy in order to limit salt leaching and possible ground water contamination. The acceptability of the proposed strategies will depend on Botswana's standards for environmental protection, as well as social and economic issues.     

Miniature ultra-broad-band voltage probe

A miniature voltage probe giving a good response over 2?18 GHz is described. It is constructed from standard OSSM line of approximately 2 mm diameter, and has been used in a miniature l.s.a. circuit for measuring Gunn-diode l.s.a. waveforms with harmonics up to 14 GHz.     

The Sustainability of Irrigation with Gypsiferous Mine Water and Implications for the Mining Industry in South Africa

The sustainability of irrigation with gypsiferous mine water and different irrigation management practices was evaluated using a milti-disciplinary approach, where crop response was investigated along with the impact on soil and groundwater resources. Field trials carried out at two mines (Landau and Kleinkopje Colliery, Mpumalanga Province, South Africa) indicated that a wide range of species can be cropped for commercial purposes under irrigation with this water. Chemical analyses of groundwater underlying irrigated areas indicated that contamination of groundwater did not occur after three years. The results of a glasshouse trial indicated that the inclusion of NH₄ ⁺ for N-fertilization in a NO₃ ⁻-NH₄ ⁺ ratio of 2:1 to 1:1 is advantageous to root and top growth of wheat. According to simulations run with the Soil Water Balance (SWB) model and the CLIMGEN weather data generator, soil chemical and physical properties will not be irreparably damaged after thirty years of irrigation. Perennial pastures, irrigated at high frequency, provided the highest net farm income and water utilization.     

Sampling in non-experimental research

The importance of choosing an appropriate sample in non-experimental research studies is undisputed, but it is an area which causes problems for researchers from many fields, including nursing. The authors illustrate the decisions which must be made when selecting a sample by considering a hypothetical study of the socialisation of student nurses.     

Predicting Impact Velocities of Developed Jets

Abstract

Dam overtopping often results in the erosion of foundation and abutment materials. To quantify erosion potential, the jet impact velocity at the plunge pool interface must be estimated. Regións of the overtopping jet trajectory through free-fall are termed undeveloped (compact) and developed (individual particles). A physical model was constructed to simulate the developed region of a free-falling jet and to measure the impact velocity of developed jets. The equation derived for estimating the impact velocity of an undeveloped jet (Ervine and Falvey, 1987) was applied to the developed portion. The undeveloped jet estimation equation significantly overestimated the impact velocity of the developed jet. A drag expression was formulated and appended to the undeveloped equation resulting in a new equation, referred to as the Dimensional Equation Technique. The Dimensional Equation Technique was used to estimate developed jet impact velocities to within ± 4 percent.     

Policy SEA: lessons from development co-operation

This professional practice report reflects upon lessons learned from piloting and evaluating an innovative approach to policy strategic environmental assessment (SEA) in developing countries. The primary analytical focuses of the approach are institutions and governance characteristics, plus it places strong emphasis on learning. The piloting provides valuable insights about the conduct of SEA at the policy level and in socio-political where there is limited experience with SEA. From our observations we reflect upon the importance of appropriate ownership of an SEA; the practical implications of working in contested political environments; the challenges in using SEA as a tool to promote good governance; and the centrality of a long-term perspective to environmental and social mainstreaming.     

Influence of plant density on variability of soil fertility and nutrient budgets in low input East African highland banana (Musa spp. AAA-EA) cropping systems

The productivity of East African highland (EAH) banana cropping systems is declining, particularly in areas with low inherent soil fertility. Soil fertility management requires knowledge of nutrient flows at the interface between the soil surface and the soil system. The magnitude of soil fertility dynamics and nutrient depletion was studied for a short-term banana plant density trial in three contrasting agro-ecological sites of Rwanda (Kibungo low rainfall with medium soil fertility, Rubona high rainfall with low soil fertility and Ruhengeri high rainfall with high soil fertility) using nutrient stock and partial nutrient balance calculations. Plant density did not influence significantly nutrient mass fractions in plant parts (fruit, leaves and pseudostems) but nutrients contained through shredded leaves and pseudostems and those removed through bunch dry matter increased with plant density. Plant density responses to variation in soil fertility and partial nutrient balances seemed to depend on diversity in climate and soil type. Partial N and K balances (kg ha^?1 year^?1) were estimated to be strongly negative at Rubona and Ruhengeri while Ca and Mg were positive at Kibungo and Ruhengeri but negative at Rubona. This study showed that partial nutrient balances associated with soil nutrient stocks can provide the first order of magnitude of nutrient depletion in low input EAH banana cropping systems. This brings attention from agricultural researchers and farmers to develop options that can improve the productivity of these systems, where resource availability for improved nutrient management is scarce.     

Assessment of the Impact of Irrigation with Low-quality Mine Water on Virgin and Rehabilitated Soils in the Upper Olifants Basin

Low-quality mine water from collieries may be used in large quantities to irrigate agricultural crops on virgin (unmined) and rehabilitated soils in South Africa. Such a use could enhance crop production and allow environmentally sustainable mine water disposal. In this study, the volume and qualities of the runoff from two centre pivots irrigated with moderately saline mine water, as well as their soil water salinities, were monitored and used to determine water and salt balances, using the modified ACRU agrohydrological model, ACRU2000, and its salinity module, ACRUSalinity. At both sites, much of the water evaporated, while a significant part of the salt input either precipitated or remained with the water in the soil horizons. A higher percentage of drainage water (and salinity) were retained as ground water storage and a lower percentage of runoff occurred in the rehabilitated sandy loam soil, while a higher percentage of salts accompanied runoff in the virgin clayey soils. Simulated salt saturation values indicate that many crops could be successfully irrigated at 100% yield potential at either site. Electrical resistivity surveys were carried out at both sites. A general decrease in resistivities with depth in both the virgin and rehabilitated soils reflected the decreasing influence of the mine water used for irrigation with depth and the precipitation of salts in the soils close to the ground surface. The occurrence of a thicker, low-resistivity, near-surface layer near the exit of each pivot area indicates that the water and salt content of the subsurface increased in the direction that the surface and near-surface irrigation water flowed. An erratum to this article can be found at