Southern African Center for Cooperation in Agriculrural and Natural Resources Research and Training
Centro de cooperacao para investigacao, agraria, recursos naturais e formacao na Africa Austral

No. 38 June 1997

Regional Msc programmes: Thesis Abstracts

J.E.R. Tarimo, 1995. Soils of Mtibwa Sugar Estate: some physical and chemical properties and their effect on crop performance under sprinkler irrigation. Department of Agricultural Engineering and Land Planning; Sokoine University of Agriculture, Tanzania.

A study was conducted at Mtibwa Sugar Estate, Morogoro, to investigate the causes of the observed decline in sugarcane production. The study involved detailed soil physical characterization of affected areas and that of a bare area. The quality of the irrigation water was also studied.

The results showed that the salt affected blocks have a sandy loam topsoil overlying a sandy clay subsoil of low permeability (0.5 - 0.9 m/day). The electrical conductivity of the saturation extract is low to medium (1.15 - 3.7 dS/m); the level of sodium is very high throughout the profiles of affected blocks (above 2.0 cmol (+)/kg); the calcium content is very low to low (1.10-3.39 cmol (+)/kg) while that of magnesium is moderate (1.5 - 2.39 cmol (+)/kg).

It was concluded that the soil of the affected fields is Gleyic Cambisol according to the FAO-UNESCO (1989) Classification. It was classified as Typic Tropaquept according to the United States Department of Agriculture Soil Classification System (Soil Survey Staff, 1990).

The soil of the non-affected field was found to be in the subgroup Typic Ustipsamment (USDA Soil Taxonomy). It was classified as Umbric Regosol (FAO-UNESCO Classification). According to the FAO (1976) land suitability classification, the affected fields studied are marginally suitable while the non-affected field is moderately suitable.

The electrical conductivity of the irrigation water is low (0.09 dS/m) and that of the groundwater of field 10E is medium (0.55 dS/m). The sodium content in the irrigation water is low (0.2 meq/1) but very high (56.35 - 71.04 meq/1) in the groundwater of the affected fields. It was also noted that the chloride content of the groundwater of the affected fields is very high (145.0 - 236.0 meq/1).

It was concluded that salinity, sodium and chloride toxicity are the main problems responsible for the decline in sugarcane production at Mtibwa Sugar Estate. The Mtibwa Sugar Company is therefore urged to investigate means of correcting the observed problems for example, by establishing a drainage system for the Estate. The adoption of this recommendation will of course be determined by the economics involved, as will be reflected in the drainage plans and designs.

B.H. Magongo, 1995. Evaluation of sprinkler irrigation performance at Simunye Sugar Estate in Swaziland. Department of Agricultural Engineering and Land Planning; Sokoine University of Agriculture, Tanzania.

The study evaluated the performance of the sprinkler irrigation system at Simunye in Swaziland. The specific objectives were: (1) to identify the original design parameters, (2) to investigate performance parameters so as to establish whether the system is operating as designed, and (3) to recommend suitable changes in the operation and system configurations that can be implemented to improve the irrigation efficiency.

The results showed that there were no available design parameters on which the system of Simunye Sugar Estate was designed. The system showed a uniformity coefficient (Cu) of 76%, which is within the recommended Cu range for design market acceptance. The distribution uniformity obtained was 61% and the potential application efficiency for the low-quarter (PELQ) was found to be 54%. Both of these parameters were lower than the recommended values, and they were significantly different when compared with the recommended values of at least 67% and 75 - 85%, respectively. The actual application efficiency for the lower-quarter (AELQ) was found to be 45%, which is too low when compared with the PELQ. The minimum basic infiltration rate of the soils irrigated by the sprinkler system was 5 mm/h.

Factors which contributed to the non-uniformity of the system were wind velocity and wind direction, the operating pressure (which was too high or lower than that recommended for the system), evaporation losses, and the sprinkler spacing. From the results it was shown that improper management of the irrigation system had a negative effect on the performance of the system.

R. Masinja, 1995. Sustainability of irrigation schemes for small scale farmers: A case study of furrow irrigation scheme at Buleya Malima, Gwembe Valley, Zambia. Department of Agricultural Engineering and Land Planning; Sokoine University of Agriculture, Tanzania

This study was carried out to determine the factors that influence sustainability of smallholder irrigation schemes in Zambia. This was against the background that many schemes have been established by the government to resettle people and have operated smoothly under its management. However, upon government withdrawal, farmers have failed to manage these schemes.

The study was carried out at Buleya Malima smallholder irrigation scheme. The objectives of study were: (a) to evaluate the scheme using technical and socio-economic parameters inherent in the scheme, (b) to assess the current practices and, (c) to make recommendations for improving the performance of the scheme and management practices.

The average results for the technical study were: 26.4%, 64.5% and 9.2% for application efficiency, tailwater ratio and deep percolation ratio, respectively. The results showed that there was a waste of water by farmers through tailwater runoff. Therefore, the system was performing poorly and could not be sustained at these levels of water loss.

The study on the socio-economic aspects revealed that irrigated farming can be sustainable if it is properly designed and planned with the involvement of the farmers. The main problem was lack of managerial ability and innovativeness by the scheme management to provide farmers with an enabling environment to form their own viable organisations which could see to the continuity of the scheme, even after the government had withdrawn.

Farmer participation in planning, decision-making and implementation of these decisions is advisable in order to sustain the scheme operations. Management should create an enabling environment to enable the farmers to form viable associations through which they and management can coordinate their operations. Formal and informal training in the technical aspects of irrigation infrastructure and new agricultural practices should be provided so that farmers can operate the irrigation system with minimum dependence on management. Therefore, provision of well trained management personnel to impart appropriate knowledge on the operations and maintenance of the irrigation system is advisable.

T.N. Mashinga, 1996. Adoption of modified Pandey Bioeconomic model for evaluating the economic feasibility of rain water harvesting (RWH) for supplementary irrigation in semi-arid areas of Tanzania. Department of Agricultural Engineering and Land Planning; Sokoine University of Agriculture, Tanzania.

A weather driven simulation model was developed to evaluate the economic feasibility of rain water harvesting (RWH) in the farming system. The biophysical parameters were incorporated with the economic parameters to determine the net benefits of RWH system to a farmer.

The model is composed of the biophysical component which consists of the following submodels, rainfall-runoff, soil water balance, evapotranspiration, and the economic submodel which consists of the input-output prices relationship component. When the two components were incorporated, they facilitated decision making regarding the prospects of RWH technology of reference.

The model was calibrated using historical climatic data obtained from meteorological stations at experimental site. The data collected were for three seasons (1991/92 - 1994/95). The model validation was performed by correlating observed and predicted data. The observed data were obtained from the field trials and historical data, while the predicted data were estimated using the simulation model.

A regression analysis was applied to test the performance of the model. A 1:1 graph was produced in which a straight line passing through the origin was fitted to the data. A perfect prediction would lead all points lying along 450 line passing through the origin to a correlation coefficient of 1. The slope of the regression line was taken as a correlation factor for calibrating the predicted data.

The model revealed that, the returns accrued to the resources invested could be recovered, particularly in years proceeding the initial year of investment. This is because the storage tank is a long term asset which generates a stream of benefits for several years in future. This can be reflected by the high yield harvested under RWH storage, comparing with the yield produced without RWH storage. Whereas the yields produced under catchment area ratio (CA:CF) of 4:1 and 2:1 with RWH storage were 3.92 and 2.53 t/ha, respectively, the yields produced under catchment area ratio (CA:CF) of 4:1 and 2:1 without RWH storage were 1.92 and 2.4t/ha, respectively.

Basing on the findings of one growing season data, it is shown that RWH system could be a breakthrough to the long term problem of erratic and unreliable rainfall in semi-arid areas of Tanzania. In view of this, it is recommended that RWH techniques be advocated for adopting by smallholder farmers in Tanzania.

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