Abstract Residual soil N following maize ( Zea mays L.) harvest is susceptible to leaching over winter. There is no available information regarding the combination of intercropping system and water table control to conserve soil N in maize production systems. A 2‐yr study was conducted to examine the effects of cropping systems (monocrop maize, and maize intercropped with annual Italian ryegrass [ Lolium multiflorum Lam.]) and water table controls (free drainage, or subirrigation to establish water table depths at 70 and 80 cm below the soil surface) on conserving soil N, under climatic and soil conditions of southwestern Québec. The resulting six treatments were fertilized in the spring with 270 kg N ha −1 . The effects of adding fertilizer at 0, 180, and 270 kg N ha −1 on monocrop maize with free drainage were also investigated. Soil cores of 1 m in depth were collected in the spring and fall of 1993 and 1994. In 1993, intercropping decreased the amount of NO − 3 ‐N in the top 1 m of the soil profile by 47% (92.3 kg N ha −1 ) relative to monocropped maize at harvest time. Water table depth had less effect on soil NO − 3 ‐N content than cropping system. Both increasing water table depth and monocrop maize enhanced downward movement of NO − 3 ‐N during the growing season and following spring. More NO − 3 ‐N was present in freely drained subsoil under maize given 270 kg N ha −1 than under maize given 180 kg N ha −1 .
Earth as a building material has been used over the years in the construction industry. However its strength characteristics have been inadequate. Therefore, stabilizers are used to enhance its strength. Where conventional stabilizing agents like cement and lime have been used, they have considerably increased the cost of construction. It is with this backdrop that this paper describes the pozzolanic characteristics of municipal solid waste ash (MSWA) and its use as a stabilizing agent. The total elemental concentration in the MSWA was determined by use of Total X‐ray Florescence method, while the laser particle analysis method was used to determine the particle size distribution of the ash. X‐ray Diffractometer method was used to measure the level of molecular compounds including the oxides of silicon, aluminium and iron. The Total X‐Ray Florescence (TXRF) analysis indicated that the ash contained high levels of calcium (220,240 mg/kg) and mercury (23.76 mg/kg). According to the Canadian Public Health guidelines, this concentration of mercury exceeded the acceptable limit of 23 mg/kg. Calcite was the main oxide (57.6%) with its glass halos occurring between 20° to 50° two‐theta. The total amounts of SiO2, Al2O3, and Fe2O3 were less than 70%, categorising the ash as Class F pozzolana meaning that MSWA was not self‐cementing. Laser diffraction particle size analysis showed that the ash was mainly composed of particles finer than 0.002 mm (55.82%), with its probability distribution function depicting a bimodal curve. The municipal solid waste (MSW) had a high loss of ignition (83.49%), an indication that it contained high amounts of un‐burnt carbon. Despite the low quartz (SiO2) content as compared to that of pozzolana cement, MSWA had high calcite (CaCO3) content enabling it to contribute to bonding effect of the ash. From the study, it is recommended that MSWA has to be used as a bonding agent and not as a cementing ash. Also the ash has to be finely ground prior to use as a pozzolanic material in soil stabilization, so as to increase both its filler and bonding effect.
Accurate evaluation of nitrate leaching potential in agricultural fields is a major challenge. Field data are expensive to gather and use of existing prediction models is limited by inadequate understanding of the physical and chemical processes underlying nitrate leaching. A neural network model was developed to acquire the inherent characteristics of an experimental data set, and successfully used to simulate nitrate leaching in agricultural drainage effluent under various management systems. Simulation results indicated that: (i) sub-irrigation with a 0.5 m water table depth could reduce nitrate leaching to negligible levels, (ii) intercropping corn with ryegrass could reduce nitrate leaching by 50%, and (iii) the application of more than 180 kg N ha−1 of fertilizer may cause excessive nitrate leaching.
This study included collection of field data using questionnaires and analysis of secondary data from Kenya’s Directorate of occupational safety and Health (DOSH) covering the period between 2010 and 2014. Perhaps due to inadequate training in safety and lack of experience, 74% of the workers who were injured or killed when accidents occurred in construction sites were below 40years old. Some 26% of the accidents occurred during the busiest months of the year, June and July, a period which coincides with the closure of financial year. Also, about a third of construction site accidents occur during the busiest hours of the day (10-11 am, and 3-4 pm). Falling from height and being hit by falling objects contributes towards about 64% of all construction site accidents. The majority of construction companies in Nairobi allocate less than 1% of project budget to health and safety. This could be because most companies do not have a clear accident prevention policy. Five administrative factors rated on a scaled of 0-5, were thought to contribute to accidents: (1) reluctance to provide resources for safety (4.10 ± 0.2); (2) lack of staff training (4.07 ± 0.2); (3) safety regulations not enforced (3.98 ± 0.2); (4) workers not safety conscious (3.83 ± 0.2); and (5) top leaders not being safety aware (3.71 ± 0.2). It is recommended that investment in Occupational Health and Safety (OSH) and also in health and safety training should be prioritized in construction industry. DOSH should be empowered to provide customized safety training, workshops and seminars to enable construction workers minimize accident occurrence.
The maturity method has been successfully used to predict the strength of concrete prepared according to Americanstandards (ASTM). This study investigated the applicability of the method to concrete prepared according to British standards(BS), and also assessed the effect of a plasticizer on the strength and maturity of concrete. Three mixes were prepared, oneaccording to American standards (mix A) and two according to British standards (mixes B and C). Modified lignosulphonate(Sika Plastiment BV-40) was used to increase the workability of mix C. Although concrete mix proportioning according toBritish standards resulted in a denser mix (2400 kg/m 3 ) than American standards (2342 kg/m 3 ), a water-cement (w/c) ratio of 0.5was used for all mixes. Cylindrical specimens (each measuring 150 mm in diameter by 300 mm deep) and beam specimens (eachmeasuring 150 mm wide by 530 mm long by 150 mm deep) were made andcured at 23 oC. The compressive and splitting tensilestrengths of the cylinders and the flexural strength of the beams were approximately equal for the three mixes. Also, the internaltemperature (and hence the calculated maturity) of concrete was the same for all mixes. The effect of using different standardswas negligible, as was the addition of a plasticizer. These findings indicate that: (1) concrete mixes with identical w/c ratiosprovide the same strength regardless of composition; and (2) although ASTM C 1074 is based on the assumption that concrete isprepared according to American standards and without admixtures, the maturity method provides a satisfactory estimate of thestrength of concrete prepared according to British standards, and concrete prepared usinga plasticizer.
Nitrate leaching from corn production systems and the subsequent contamination of ground and surface waters is a major environmental problem. In field plots 75 m long by 15 m wide, the writers tested the hypothesis that subirrigation and intercropping will reduce leaching losses from cultivated corn and minimize water pollution. Nitrate leaching under subirrigation at a depth of either 0.7 m or 0.8 m below the soil surface was compared with leaching under free drainage. The cropping systems investigated were corn (Zea mays L.) monoculture and corn intercropped with annual Italian ryegrass (Lolium multiflorum Lam. cv. Barmultra). The effects of three fertilizer application rates (0, 180, and 270 kg N ha−1) on leaching were investigated in the freely drained plots. The greatest annual loss of NO3--N in tile drainage water (21.9 kg N ha−1) occurred in freely draining, monocropped plots fertilized with 270 kg N ha−1. Monocropped plots fertilized with 270 kg N ha−1, with subirrigation at 0.7 m depth, resulted in annual nitrate losses into tile drainage of 6.6 kg N ha−1, 70% less than under free drainage. Annual soil denitrification rates (60 kg N ha−1) with subirrigation at 0.7 m were about three-fold greater than under free drainage. Intercropping under free drainage resulted in a 50% reduction in tile drainage loss of NO3--N compared with monocropping. Off-season (November 1, 1993, to May 31, 1994) tile drainage losses of NO3--N (7.8 kg N ha−1) from freely draining monocropped plots accounted for 30% of the annual tile drainage losses.
Pavement construction tends to be relatively expensive in areas where expansive clay forms the bulk of the alignment soil. The common practice in Kenya is to remove the undesirable material and fill the space with more stable materials. The present study has developed a method for stabilizing expansive clay for Subgrade Class S2 pavement construction. A combination of 20% by weight of rice husk ash (RHA) and approximately 2% by weight of natural lime improved the California bearing ratio (CBR) of expansive clay soil by 800%, reduced the soil plasticity by approximately 90%, and decreased free swell by approximately 70%. It has been shown that use of RHA as a stabilizer is not only an affordable green technology, but also gives expansive clays the strength required for the Subgrade Class S2 pavement layer.
Concrete pavements are expected to have a long structural life. The present study considered a jointed plain concretepavement (JPCP) road in Kenya that developed surface cracks within the first 2 years of construction. With a CBR of 10-17%, thesubgrade layer was ruled out as a possible cause of cracking. However, the subbase layer did not meet the minimum CBR value,and 24% of the pavement did not attain the recommended minimum layer modulus value of 345 MPa for neat gravel construction.Furthermore, the concrete strength was below the design strength of 30 KN/mm 2 . None of the saw-cut joints met the recommendeddepth and only 5% of the slabs met the design slab thickness. Inadequate slab thickness, inadequate depth of cut joints, andinadequate strength of subbase layer could have been responsible for the development of surface cracks. These shortcomingsshould be interrogated further to establish the true combination of factors that were responsible for the cracking of the JPCPFurthermore, there is need for a deliberate effort to assess the capacity and competencies of the construction industry in Kenya tohandle new technologies in road construction.
Consumption of contaminated water is a major cause of illness in the world and particularly in rural communities, especially in developing countries like Kenya. The objectives of this cross-sectional study were to evaluate access to safe drinking water, water purification techniques and water-borne disease incidence in Masaba North District. Some 100 households were randomly selected with structured interview questions being administered to 25 households in each of the four divisions in the District. Water testing was carried out in a make-shift laboratory using the Oxfam DelAgua kit to determine the number of E. coli colony forming unity (CFU) per 100ml while a hach turbidimeter was used to measure water turbidity. It was found that a high percentage of the households had access to ‘improved’ water sources including protected springs (79%) with 64% of the households boiling their water before consumption.. Only 17% of the households had access to water free from fecal contamination. The most effective method of purification was Biosand filtration which provided 57% reduction in turbidity and 92% reduction in E. coli. Out of the 100 households, 20% households indicated that at least one member of the household had suffered from water-borne diseases in the past year. Whereas many households can easily access improved water sources, access to safe drinking water was still a major challenge. Further more, water from “protected sources” was not necessarily safe for drinking. There was inconsistent and inadequate utilization of water purification techniques leading to consumption of contaminated water even after purification had been carried out.
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