https://hdl.handle.net/13049/505 2026-04-29T04:33:41Z https://hdl.handle.net/13049/522 Effect of phloem sap deposition on properties of sapwood in Pterocarpus angolensis (Mukwa) following bark stripping by elephants in Chobe forests reserves in northern Botswana Mmolotsi, R.; Lumbile, A.; Kwerepe, B.C.; Kopong, I.; Rampart, M.; Segwagwe, A.; Sebolai, B.; Lekorwe, L.; Maphane, T. An investigation was carried out to assess properties of sapwood in Pterocarpus angolensis following debarking by elephants in Botswana. The objective of this study was to assess the effect of phloem sap deposition on properties of P. angolensis wood in northern Botswana. Wood samples were obtained from bark stripped trees in the Chobe district. Ten samples were obtained for the different woods types each for assessing density, compression and modulus of elasticity (MOE) and wood colour. Wood colour was evaluated using the Munsell Color chart Wood density was derived by dividing wood sample weight by its volume. Compression and elastic properties were determined using a Llyods intrumentslO kN materials testing system according to British Standard 373 for testing small clear wood samples. Debarked stems yielded red discoloured sapwood. The discoloured sapwood yielded the highest density at 537.7± 17.26 kg m’3 where the lowest density was recorded in the sapwood (F=25.98 and P<0.05). Compression stress was highest in phloem sap discoloured wood of 59.38±2.46 MPa, followed by the heartwood at 55.67±1.87 MPa and the lowest in sapwood at 39.66±l.61 MPa (F=30.64 and P<0.05). Modulus of elasticity showed no significant differences in between samples obtained from the different parts. The discoloured sapwood however yielded the higher MOE values. Overall, the wood with bark stripped by elephants and discolouration showed superior properties. It is therefore recommended that phloem sap discoloured wood be used for structural timber. 2011-01-01T00:00:00Z https://hdl.handle.net/13049/521 Effect of fire burning interval on species composition, herbage yield and bush control in the savanna of eastern Botswana Mphinyane, W.N.; Moleele, N.M.; Sebego, S.J. The purposes of this study were to examine the effects of various fire burning intervals on the dynamics of woodland structure and the resultant herb layer in the savanna vegetation of eastern Botswana. Plots of 1.2 ha were burnt at the interval of 0, 1, 2, 3, 4, and 5 years, using head fires from 1958 to 2003 in an Acacia nigrescens/Combretum apiculatum tree vegetation. In 1982 and 2003 the first and second evaluations, were assessed for bush density, grass basal cover, grass yield, composition and for soil properties when all burning treatments coincided for the first and second time, respectively. The data were analyzed using ANOVA procedure in Statistical Analysis System and means were separated using the Fisher’s test. Annual burning revealed an increase in the vigour and abundance of Eragrostis regidior and Bracharia nigropedata while Digitaria eriantha and litter accumulation increased with less burning frequency. Total grass basal cover was increased although not significantly (p>0.05) from 2.43±2.25% in 1982 to 3.08±0.52% in 2003. Fire was successful in opening up woodland structure by shifting large trees to smaller size classes. Total woody plant density declined although not significantly in 2003 (1498±154 plants per ha) compared to 1982 (1623±285 pants per ha). The changes in soil properties resulting from low frequency of burning were small to account for any differences in vegetation composition. In the semi-arid savanna, once fire is used to control bush, it should not be a one time activity, but should be continued in order to control the re-growth of recruited seedlings and preventing their recruitment to adulthood. 2011-01-01T00:00:00Z https://hdl.handle.net/13049/520 Evaluation of relative resistance of four cowpea (Vigna unguiculata (L.) Walp) varieties to the black cowpea aphid (Aphis Craccivora) in South-eastern Botswana Munthali, D.C.; Lenamile, K. Cowpea (Vigna unguiculala (L.) Walp) is an important food legume in many tropical countries, but its production is seriously constrained by insect pests. Aphis craccivora is one of the major pests of cowpea worldwide. Abundance of the pest was assessed on four cowpea varieties, Black eye, B359, IT18 and Tswana in field cages in order to determine their relative resistance to the pest in southeastern Botswana. The data was analysed using MSTAT-C programme package. Aphid abundance varied significantly between varieties (P < 0.05). Overall abundance was greatest (95.4 aphids per plant) on Black eye and least (17.7 aphids per plant) on IT18 plants. Therefore, cowpea variety IT 18 was 5.3 times more resistant to the black cowpea aphid than variety Black eye. Using relative resistance to A. craccivora., the varieties were ranked in the order: IT18 > B359 > Tswana > Black eye. A relatively higher proportion (53%) of alates than apterae was produced on variety IT 18. Variety IT 18 showed a combination of antibiosis and antixenosis mechanisms of resistance against the pest. This variety would be the most suitable for use in breeding programmes aimed at developing more resistant cultivars to the cowpea aphid. 2011-01-01T00:00:00Z https://hdl.handle.net/13049/519 Effects of original source of dairy cows, season and age on milk production in Botswana Mpapho, G.S.; Dambe, L.; Nsoso, Shalaulani James The objective of the study was to determine the effects of animal and environmental factors on milk yield of Holstein dairy cows kept under intensive system in Botswana. A total of 768 monthly records of 27 Holstein cows of different parities were recorded over 5 years (2004- 2008) at Botswana College of Agriculture (BCA) dairy farm were used. The data was analyzed using General Linear Model of Statistical Analysis System. Higher (p<0.05) higher milk yield was recorded in spring (14.42±0.36 kg/d) than in winter (11.27±0.35 kg/d) with other seasons being intermediate. Third parity cows produced more milk (14.65±1.03 kg/d) than first calvers (11.60±0.66 kg/d). Although not significantly (p>0.05) different, the third parity corresponded with greater lactation yield than the others. Lactation length for third parity was 369.91±57.20days. Milk yield was significantly higher at 4 years of age (16.02±0.51 kg/d) than at 9 years (10.96±0.79 kg/d) and 10 years of age (5.85± 1.15 kg/d). Although the amount of milk produced by cows that were sourced from South African farms (15.26±1.52 kg/d) was higher than those sourced from Botswana College of Agriculture (11.89±1.16 kg/d) and Animal Production Research Unit (11.19. ±1.20 kg/d), these did not differ significantly. Farms should have more cows lactating in spring and at parities and ages that maximize milk yield. 2011-01-01T00:00:00Z