Proceedings of the International Symposium on Forest Seed Problems in Africa, Harare, Zimbabwe, Aug. 23 - Sept. 2, 1987

Meeting: International Symposium on Forest Seed Problems in Africa, 23 Aug.-2 sept. 1987, Harare, ZWPublished in cooperation with IDRC, EARO and Forest Research Centre, Harar

Applications of electrified dust and dust devil electrodynamics to Martian atmospheric electricity

Atmospheric transport and suspension of dust frequently brings electrification, which may be substantial. Electric fields of 10 kVm-1 to 100 kVm-1 have been observed at the surface beneath suspended dust in the terrestrial atmosphere, and some electrification has been observed to persist in dust at levels to 5 km, as well as in volcanic plumes. The interaction between individual particles which causes the electrification is incompletely understood, and multiple processes are thought to be acting. A variation in particle charge with particle size, and the effect of gravitational separation explains to, some extent, the charge structures observed in terrestrial dust storms. More extensive flow-based modelling demonstrates that bulk electric fields in excess of 10 kV m-1 can be obtained rapidly (in less than 10 s) from rotating dust systems (dust devils) and that terrestrial breakdown fields can be obtained. Modelled profiles of electrical conductivity in the Martian atmosphere suggest the possibility of dust electrification, and dust devils have been suggested as a mechanism of charge separation able to maintain current flow between one region of the atmosphere and another, through a global circuit. Fundamental new understanding of Martian atmospheric electricity will result from the ExoMars mission, which carries the DREAMS (Dust characterization, Risk Assessment, and Environment Analyser on the Martian Surface)-MicroARES (Atmospheric Radiation and Electricity Sensor) instrumentation to Mars in 2016 for the first in situ measurements

Prediction of Long-Term Drainage-Water Salinity of Pipe Drains

Long term drainage water salinity of pipe drains is modeled with the advection-dispersion equation for the zone above drain level and stream functions for the zone below drain level. Steady-state water flow is assumed. The model is applied to two experimental pipe drainage sites in Haryana State, India. Calculations are conducted for different values of leaching fraction and drain spacing. On average, comparison between measured and predicted drainage water salinity is satisfactory for both the Sampla site and the Hisar site. Calculations show that it may take 15-50 years before drainage water salinity has reduced to equilibrium levels. Leaching fraction has considerable influence on the drainage water salinity. An increase in the leaching fraction from 0.2 to 0.4 will reduce the time to reach equilibrium drainage water salinity levels by about 50%. Drain spacing has little influence on drainage water salinity, provided the hydraulic properties below drain level are uniform (Sampla). Some influence of drain spacing might be expected if the zone below drain level consists of a less conductive layer underlain by a more conductive layer (Hisar). In the latter case, the larger the drain spacing, the longer the time to achieve equilibrium drainage water salinity levels. (C) 2000 Elsevier Science B.V

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Not AvailableIn many parts of the country there is sodic groundwater with high residual sodium carbonate (RSC), which is considered unsuitable for agricultural crops and aquaculture purposes. In present investigation a case study was undertaken on farmer’s field utilizing high RSC water in a aquaculture based farming system. A pond of 0.4ha (water area of 0.3ha and 2.0m depth) having sodic water, along with the adjoining 500 m2 nursery pond located in the village Lotani, Kurukshetra District was renovated. A platform of 2.0 m width with an area of 0.1 ha was made along the inner periphery of the pond for growing field crops. Gypsum treatment was given for neutralizing the RSC effect in the pond water. The pond was filled with pumped water from a 50 m deep tube well that had RSC ranging from 2.5-4.1 meq l-1 and also supplemented with rainwater. Normal pond management practices were followed which included application of raw buffalo dung. Pond water was used for irrigation. Gypsum treatment and application of raw buffalo dung in the pond created RSC neutralizing effect. In general, pond water had an electrical conductivity (EC) of 0.4dS m-1, RSC of < 0.8meq l-1 and dissolved oxygen of 4.0-8.2 mg l-1 during fish culture operation. Fish growth in the adopted pond was found to be 625-1150g in 12 months, depending on species of Indian major carps and exotic carps. Fish production was recorded to be at the level of 6000 kg ha-1yr-1. Production of field crop per ha were 1000 kg potato, 400 kg onion, 200 kg maize (bhutta),100 kg garlic, 40 kg pigeon pea and 100 kg turmeric beside considerable quantity of consumable vegetables (cauliflower, chillies, radish, methi, palak, ladies’finger, brinjal, banana) and green fodder from the dyke (inner platform of the pond), during the year of observation. The study demonstrated that sodic water with certain chemical and organic remediation can be used for aquaculture-led integrated farming practices with success.Not Availabl

Effect of punping on temporal changes in groundwater quality

Pumping studies were conducted at five sites distributed over a 3000 ha area in the Gohana block in Haryana state of India. The project area is a part of the Indo-Gangetic plain and lies in a topographical depression susceptible to waterlogging, soil salinity and groundwater pollution from surrounding industrial towns. The crop productivity of irrigated lands in the project area is declining due to secondary salinization and shortage of surface irrigation supplies forcing farmers to depend on groundwater abstraction through shallow tubewells. Three wells of 30 m depth and two of 60 m depth were developed in the project area and the effect of pumping on temporal changes in groundwater depths and quality was studied over a period of 72 h. Groundwater samples, collected from different depths up to 30 m at each site while installing piezometers and at different times during pumping tests, were analyzed for electrical conductivity (EC), pH, ionic composition and heavy metals like arsenic (As), copper (Cu), zinc (Zn), manganese (Mn), cadmium (Cd), nickel (Ni), lead (Pb) and chromium (Cr). The results indicated varying values of EC, pH, sodium adsorption ratio (SAR) and residual sodium carbonate (RSC) which, in an average sense, were much above the limits prescribed for use of water for irrigation. Of the heavy metals, groundwater was heavily contaminated with As, Pb, Cd and Ni having maximum concentrations of 27.5, 1.53, 0.12 and 1.46 mg/l, respectively, which are much higher than maximum permissible limits. Contaminants had variable times of peak concentration, some with multiple peaks, denoting non-uniform contaminant concentrations and possibly different adsorption characteristics. The results emphasize that groundwater in the project area needs to be analyzed not only in respect of conventional quality parameters but also for heavy metal contamination for their safe use in agriculture. The source or the cause of such serious groundwater pollution problems in the region must be identified to minimize the hazardous effects of using such waters on a long-term basis

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Not AvailableFresh water scarcity is the main problem for growing crops in the coastal West Bengal beyond the rainy season. To alleviate the water scarcity during the non-monsoon period, augmentation of capacity of ground water through artificial recharge during the rainy season was experimented at ICAR-CSSRI, RRS, Canning Town farm. A recharge tube well of 12.7 cm diameter and 40.5 m depth was installed in the year 2011. As the water table came up very close to the surface (< 1 m bgl) during the rainy season, an experiment was carried out for lowering the water table by pumping during summer and artificial recharge of runoff water during the rainy season. For pumping out the ground water, 1 HP electrical pump with discharge of 0.64 lps was used. In spite of 30 days (6 hours per day) of pumping in the summer season, the pumping water level was not lowered below 6 m depth. There was depletion of the water table due to pumping till 27th week from January, 2012. Later the water table moved up due to recharge in the monsoon period. The rising of water table near to the surface was similar to previous year when tube well was installed during July/August, 2011 and there was no artificial recharge. Therefore, the present situations are not conducive for artificial recharge in the Canning area. However, if at any location the water table in post monsoon season depletes regularly beyond 3m bgl, there artificial recharge may be done.Not Availabl