Browsing by Author "Stewart, J.I."
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Item Crop Yields and Returns under Different Soil Moisture Regimes(1983) Stewart, J.I.; Kenya Agricultural Research Institute, Nairobi, KenyaReserch begun in Kenya in 1977 under the Dryland Cropping Systems Research Project is described. In Machakos District, intercropping of maize and beans [Phaseolus vulgaris] was studied under line source irrigation. Yields of both spp. increased linearly with applied water until requirements were satisfied at 250 mm for beans; maize water requirements were not satisfied at 438 mm and the estimated water requirement for max. yield was 589 mm. With 450 mm water yields were 5.92 and 2.5 t/ha for pure strands of maize and beans, resp., compared with 4.98 + 0.7 t in the intercrop. Intercropping was only advantageous when rainfall was more than 325 mm with an early onset of rains. In a 2nd trial at Katumani maize yields increased with application of 40 kg N/ha, but higher rates did not increase yields further. In fertile conditions, grain production began when water use was 218 mm, but without N fertilizer 298 mm was required. Grain production also depended on plant density; with 154 mm rainfall plots of 20 000 plants/ha produced grain but higher density plots did not. In better rainfall seasons 40 000 or even 60 000 plants/ha produced max. grain yields.Item Effective Rainfall Analysis to Guide Farm and Predict Yields(1980) Stewart, J.I.Kenya is presently acknowledged as the world leader in population growth rate. Consequently, the traditionally rich agricultural lands with high rainfall, but which are less than 15% of the nation's area, have for some time been overcrowded. The result is a fast-moving process of expansion of smallholder crop farming into ever drier historical grazing areas.Item Impact of Weather Analysis on Agricultural Production and Planning Decisions for the Semiarid Areas of Kenya(1982) Stewart, J.I.; Hash, C.T.; United States Department of Agriculture/United States Agency for International Development, Kenya Agriculture Research Institute, Muguga, Kenya. United States Agency for International Development, Nairobi, Kenya.Requirements for effective rainfall analysis and crop yield estimation are outlined. A case study is presented in which effective rainfall for maize at Katumani, Machakos District, was evaluated for each of the 48 wet seasons in a 24-yr period. The analysis takes into account rainfall, evaporation, soil depth and water holding capacity and growth characteristics of the crop influencing water uptake and yield. Dates of onset of rains were sortable into early (high-medium water adequacy for maize production), late (medium-low expectation) and too late for sowing. These expectations determined recommendations for sowing and fertilizer rates. Although unpredictable earlier, the rainfall pattern after onset fell into categories of high, medium or low adequacy for maize. Recommendations for final plant densities and N side dressing rates were based on these categories. Total season effective rainfall could be estimated 2 months before harvest, allowing final yield predictions.Item Lysimeter Water Balance for Bare and Cropped Soil(1979) Stewart, J.I.; Mugah, J.O.Water balance is the algebraic sum of the\total accretion and removal of water within a defined hydrological unit such as a lake a basin, a 1ysimeter, etc., taking into account net changes of storage. Accretion comes mostly from rainfall and irrigation (at least within the tropics), although in extra-tropical areas snow and other forms of precipitation such as dew may be appreciable. Upward movement of water by capillarity from a water table, and lateral seepage from adjacent areas are also possible sources of accretion.Item Predicting Effects Of Water Shortage On Crop Yield(1969) Robert, M.H.; Stewart, J.I.Years of less than normal water supply have always meant disaster in varying degree to those engaged in agriculture, and in many instances to those dependent on their produce. Now, with the worldwide acceleration of population growth, irrigation project development is going forward at an unprecedented rate, utilizing water supplies which are less and less reliable while ever more costly. At the same time people are becoming increasingly dependent on these projects for their well-being-in the USA, for their continuing financial success, abroad, for the very food they require to maintain life. Put somewhat differently, water shortage in irrigated agriculture is becoming more commonplace, and simultaneously more serious in its consequences.Item Rainfall Criteria to enable Response Farming through Crop-based Climate Analysis(1983) Stewart, J.I.; Kashasha, D.A.R.; USAID, Kenya Agricultural Research Institute, Muguga, KenyaThe correlation between effective rainfall during the growing season, onset of rains and early season rainfall is considered and recommendations are given for cultivation of maize, beans [Phaseolus vulgaris] and intercropped maize + beans or alternative more drought-resistant crops according to predicted rainfall. Correlations are confirmed with reference to data from 10 sites in Machakos, Kitui and Kajiado districts for up to 55 years.Item Research on Rainfall Prediction and Yield Responses to Water and Nitrogen in Different Environment for Cutting Crop Selection and Farm Practices in Semiarid Areas in Kenya(1982) Stewart, J.I.; KARI, Muguga, KenyaThe semiarid areas of Kenya are peopled by small holders, farming mostly at the subsistence level. Their numbers are burgeoning, not only due to the Latiomrice 49 population growth rate, but to migration from the well wavered highlands. This is a rather recent develop, and experience in coping with the problems of limited and highly variable rainfall is lacking. One facet of the Kenya Government's response to this growing problem is the USAID/Kenya Agriculture Research Institute "Dryland Cropping Systems Research Project".Item Water-Yield Response of a Maize and Bean Intercrop(1982) Lenga, F.K.; Stewart, J.I.; Kenya Agricultural Research Institute, P.O. Box 30148, NairobiFor many years models for water balance accounting have been used in irrigation (Pereira, 1957; Wallis, 1963; Blore, 1966; Stewart et al., 1974), hydrologic investigation (Pereira and Hosegood, 1962) and in general descriptive climatology (Woodhead, 1970). Their use for assessing crop or pasture performance has not been fully exploited although such models do have broad Agro climatological utility. This has been demonstrated in regional case studies aimed at evaluating crop yield drought response (Stewart and Wangati, 1980; Steward and Hash, 1982). Determining length of growing season (Dowker, 1971) assessing climatic suitability for various crops (Dagg. 1965) and defining intermittent growth behaviour in arid zones (Fitzpatrick et al., 1967; Nix and Fitzpatrick, 1969; Salter and Good, 1967).
