School of Agriculture, Food and Ecosystem Sciences - Theses
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ItemPhysiological and morphological responses of several genotypes of tropical and sub-tropical maize (Zea mays L.) to water and nitrogen deficit during the early vegetative phase( 1997)Intermittent drought combined with nitrogen stress during early growth of maize crops in the tropics limits maize production in developing countries. Plant morphological and physiological responses of different maize genotypes to two aspects of stress, water deficit and nitrogen stress, were examined during the growth of several maize genotypes. Eight maize genotypes including three inbred lines (Gn 160, Gn 106, Gn 175), three single crosses (Gn 160 x Gn 175, Gn 106 x Gn 175, Gn 106 x Gn 160) and two open pollinated cultivars (Tuxpeno Sequla Cycle 0, drought sensitive; Cycle 8, drought resistant) were examined for drought tolerance during early growth. Variables used for assessing tolerance were dry weight of shoot and root, leaf area, relative water content, water potential and stomatal conductance which were measured in both well-watered and the respective droughted treatments for each genotype. Under growth room conditions, the level of severe drought imposed caused a substantial reduction in growth of eight maize genotypes, relative to the respective well-watered conditions. The single cross Gn106 x Gn160 revealed drought tolerance traits in shoot and total biomass, which were higher than the other single crosses. It is concluded that this single cross is more drought-tolerant than the other single crosses during early growth stages. Tuxpeno Sequla Cycle 0 and Cycle 8 had similar shoot and total biomass under both water regimes, and did not show differences in drought tolerance during early growth. There was no clear indication of transmissability of drought tolerance from parent lines to their respective single crosses. The combined effects of drought and timing of N stress during early growth on morphological and physiological traits, which were altered during later growth and yield components, were investigated in two related tropical maize cultivars, Tuxpeno Sequla Cycle 0 (Tux. CO) and Cycle 8 (Tux. C8), which were selected for drought sensitivity (Tux. CO) and tolerance (Tux. C8), during flowering under glasshouse conditions. Total biomass at maturity and green leaf number below the ear at grain filling were similar between Tux. CO and C. 8 under different water regimes. Increased grain yield and harvest index in Tux. C8, compared with Tux. CO, resulted mainly from increased kernel number per row and rows per ear. Tux. C8 was not only higher in yield but also higher in N use efficiency than Tux. CO when experiencing moisture and N stress during early growth. Shoot biomass under moderate drought versus well-watered conditions was found to be more sensitive than root biomass in both Tux. CO and C8. Under drought compared with well-watered conditions, stem biomass was more sensitive than leaf biomass. Leaf area in the high-N treatments was more sensitive to water deficit than in low N treatments, as indicated by the fact that droughted plants in the early N application (NE) and split (NS) treatment produced lower leaf areas than well-watered plants, while in the control (NO) and late N (NL) treatments there was no significant difference in leaf area between drought and well-watered conditions. Early N application resulted in a shorter time from sowing to anthesis than later N application. Clearly N stress is the main limiting factor for growth and yield of maize under moderate level of water deficit. This study revealed that maize plants require N for growth and dry matter accumulation as early as immediately after seedling emergence even under low N input conditions (75 kg N per hectare). Increased grain N content and nitrogen harvest index for a split N application resulted from increased N content in the stem and leaf Even under low N input conditions i.e. the application equivalent to 75 kg N/ha in this experiment, N still needed to be supplied as a split application, in order to increase N use efficiency. Nitrogen harvest index under well-watered conditions was higher than that under drought, indicating that water deficit also had an effect on nitrogen harvest index of both cultivars (CO and C8) under different level of N treatments.
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ItemInfluence of socio-economic factors on adoption of maize related technology : the case of smallholder farmers in Hamisi division, Kenya( 1993)Although new technologies continue to be developed for the farming community in low income countries, relatively few are ever adopted. This study uses the results of a survey among 145 farmers in Kenya to determine the extent to which they had adopted high yielding varieties (HYV) seeds, chemical fertilisers and pesticides as envisaged in the "Green Revolution" and identify the reasons for adoption and non-adoption. The study analyses some of the socio-economic factors influencing the acceptance of these technologies and progresses to outline some of the constraints limiting the adoption process. Relationships between adoption of HYV and awareness of technology, farmers' level of income, level of education and information seeking tendency were significant, as were adoption of pesticide and information seeking tendency, and adoption of chemical fertilisers in relation to both use of hired labour and frequency of attendance at meetings on financial matters. This implies that there is an increased probability of farmers adopting innovations when they are aware of the existence of technology that is appropriate, have higher levels of income and education, have higher propensity to seek for information, hire labour to assist in carrying out farm activities and regularly attend meetings on financial issues. Various constraints which act as deterrents to increased adoption of improved technologies included costly inputs, lack of credit, lack of pertinent information and knowledge about farm inputs, non-availability of inputs, unfavourable attitudes towards some technologies, and lack of resources. A change in extension and research strategy is emphasised towards one recognising smallholder farmers as equally deserving as large commercial farmers as clients for extension and marketing services, and being part of the research process to facilitate technology transfer.
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ItemImprovement of utilization of white clover by supplementing with maize silage for lactating cows( 1991)In a 10 day cross over design experiment, six Friesian cows, in late lactation, were fed either white clover or white clover plus maize silage on a 50:50 DM basis in metabolism cages from continuous feeders. Data for intake, digestibility, nitrogen balance, milk production and rumen pH, volatile fatty acids (VFA), ammonia, fluid flow rate, pool sizes and protozoa population were collected. Replacing 50 % of white clover with maize silage reduced nitrogen intake significantly (P<0.001) and increased neutral detergent fibre (NDF) intake (P<0.01) and acid detergent fibre (ADF) intake (P<0.05). Digestibility was reduced significantly as follows: dry matter digestibility (P<0.05), organic matter, NDF, and ADF digestibilities (P<0.01) and crude protein digestibility (P<0.001). There was no significant difference between diets for dry matter intake (DMI), organic matter intake (OMI) or digestible organic matter intake (DOMI). Milk yield and composition were similar for both diets. Rumen fluid ammonia concentration and urea nitrogen in urine were reduced significantly (both at P<0.001) by adding maize silage to white clover. There was no significant difference in nitrogen in milk or nitrogen balance. Rumen protozoa population increased significantly in the cows fed white clover plus maize silage diet due to an increase in Entodinium, No/ml (P<0.05) and total protozoa No/ml (P<0.01). There was no significant difference in rumen fluid VFA, pH, or fluid flow rate. It was concluded that feeding white clover with maize silage improves the efficiency of utilization of nitrogen in white clover which potentially can increase milk production per cow and/or per hectare without changing the milk composition or altering the rumen environment.
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ItemThe nutritive value of white clover pasture for cows in mid-lactation when supplemented with maize silage( 1992)In a completely randomised grazing trial, 8 cows in mid-lactation were offered white clover pasture (35kg DM/cow/day) with 4 of the cows given a supplement of maize silage (8 kg DM/cow/day). Factors evaluated over a 28 day period were total DMI, pasture DM/maize silage DM substitution rate, herbage selection in the pasture, milk yield, fat and protein concentration. Supplementing cows with maize silage increased total DMI by 22% and lowered pasture herbage DMI by 21%; equivalent to a substitution rate of 0.5 kg pasture DM /kg of maize silage DM. Selection of herbage in the pasture was not affected by supplementation, but cows on both treatments selectively grazed the white clover. Supplementing cows with maize silage increased milk yield by 34%, fat yield by 35% and protein yield by 35% (P<0.05), but did not affect milk fat and protein concentration. In a metabolism trial, 6 rumen fistulated cows in mid-lactation were fed similar diets in a crossover experiment but with white clover fed ad libitum. Digestibility, nitrogen balance, milk yield, fat and protein concentration were evaluated over a 7 day period. Maize silage DM and white clover DM digestion in the rumen were evaluated by DM disappearance rates from nylon bags over a 96 hr period. Measurments of rumen fluid volume, fluid mean retention time, fluid outflow, pH, ammonia and VFA concentration and the acetate/propionate ratio were estimated over a 24 hr period. Supplementing cows with maize silage increased total DMI by 34%, without affecting DM digestibility (DMD). However, OMD was reduced by 5% and fibre digestion by 18% (P<0.05). Supplementing cows with maize silage did not affect the rate of digestion of maize silage DM or white clover DM in nylon bags, but white clover was digested at a faster rate than maize silage (P<0.05). The increased DOMI by cows supplemented with maize silage was highly correlated with a 24% increase in milk yield (P<0.05; iI=61 ) but had no effect on milk fat and protein concentration. At similar nitrogen intakes cows supplemented with maize silage produced 2.3 kg more milk (P<0.050='66) but there was no effect on milk fat and protein concentration. Rumen fluid volume, mean retention time and fluid outflow rate were not significantly altered by the maize silage supplement, although rumen pH and ammonia concentration were significantly lower (P<0.05). Total VFA concentration was not significantly different between the two diets, but acetate concentration was significantly lower (P<0.05), while propionate concentration was significantly higher (P<0.05) in supplemented cows. The reduction in acetate and the corresponding increase in propionate, lowered the acetate/propionate ratio. Butyrate concentration was not affected. It was concluded that for cows in mid-lactation fed on good quality white clover dominant pasture, maize silage supplementation can increase milk yield, without affecting milk fat and protein concentration. The increase in milk yield was attributed to increased apparent energy intake as nitrogen intake did not change markedly. However further work is required to quantify whether increased nitrogen utilization occurred and whether the lower ammonia concentration in maize silage supplemented cows were due to improved rumen microbial synthesis. The possibility also exists that improved milk yields were due to by-pass rumen starch, thereby providing glucose to the animal, after enzymatic digestion in the small intestine.