Abstract A field experiment involving two plant densities (83,333 and 166,666 plants per hectare), two cropping systems (monoculture and mixed culture) and five cowpea (Vigna unguiculata L. Walp.) genotypes (3 farmer-selected varieties: Bensogla, Sanzie and Omondaw, and 2 breeder-improved cultivars: ITH98-46 and TVuI509) was conducted for two years in 2005 and 2006 at Nietvoorbij (33°54S, 18°14E), Stellenbosch, South Africa, to evaluate the effect of these treatments on the growth and symbiotic performance of cowpea. The results showed that, of the five cowpea genotypes, plant growth and N2 fixation were significantly greater in the three farmer-selected varieties (Sanzie, Bensogla and Omondaw) relative to the two improved cultivars (ITH98-46 and TVuI509). Furthermore, plant growth and symbiotic performance (measured as tissue N concentration, plant N content, 15N natural abundance and N-fixed) were significantly (P:50.05) decreased by both high plant density and mixed culture (intercropping). However, the %Ndfa values were significantly (P:S0.05) increased by both high plant density and mixed culture compared to low plant density or monoculture (or monocropping). Whether under low or high plant density, the cv. Sanzie was found to accumulate significantly greater total N per plant in both 2005 and 2006, followed by the other two farmer varieties relative to the improved cultivars. Similarly, the actual amount ofN-fixed was much greater in cv. Sanzie, followed by the other farmer varieties, under both low and high plant density. The data also showed better growth and greater symbiotic N yield in cowpea plants cultivated in monoculture (or low plant density) relative to those in mixed culture (or high plant density). Our data suggest that optimising legume density in cropping systems could potentially increase N2 fixation in cowpea, and significantly contribute to the N economy of agricultural soils in Africa.

Abstract A field experiment involving two plant densities (83,333 and 166,666 plants per hectare), two cropping systems (monoculture and mixed culture) and five cowpea (Vigna unguiculata L. Walp.) genotypes (3 farmer-selected varieties: Bensogla, Sanzie and Omondaw, and 2 breeder-improved cultivars: ITH98-46 and TVuI509) was conducted for two years in 2005 and 2006 at Nietvoorbij (33°54S, 18°14E), Stellenbosch, South Africa, to evaluate the effect of these treatments on the growth and symbiotic performance of cowpea. The results showed that, of the five cowpea genotypes, plant growth and N2 fixation were significantly greater in the three farmer-selected varieties (Sanzie, Bensogla and Omondaw) relative to the two improved cultivars (ITH98-46 and TVuI509). Furthermore, plant growth and symbiotic performance (measured as tissue N concentration, plant N content, 15N natural abundance and N-fixed) were significantly (P:50.05) decreased by both high plant density and mixed culture (intercropping). However, the %Ndfa values were significantly (P:S0.05) increased by both high plant density and mixed culture compared to low plant density or monoculture (or monocropping). Whether under low or high plant density, the cv. Sanzie was found to accumulate significantly greater total N per plant in both 2005 and 2006, followed by the other two farmer varieties relative to the improved cultivars. Similarly, the actual amount ofN-fixed was much greater in cv. Sanzie, followed by the other farmer varieties, under both low and high plant density. The data also showed better growth and greater symbiotic N yield in cowpea plants cultivated in monoculture (or low plant density) relative to those in mixed culture (or high plant density). Our data suggest that optimising legume density in cropping systems could potentially increase N2 fixation in cowpea, and significantly contribute to the N economy of agricultural soils in Africa.

Abstract In 2005 and 2006, 30 and 15 cowpea genotypes were respectively evaluated for plant growth and symbiotic performance at Manga in Northern Ghana, in order to identify Nz-fixing potential of these cowpea genotypes as source of N for cropping systems. The results showed differences in biomass production by the 30 or 15 cowpea genotypes. In 2005, cultivars Fahari, Mchanganyiko, IT97K-499-39, IT93K-2045-29 and IT84S-2246 produced the most shoot biomass, while Apagbaala, Brown Eye, ITH98-46, Vita 7 and Iron Grey produced the least. Of the 15 genotypes tested in 2006, cv. TVu1l424 produced the largest amount of biomass, and ITH98-46, the least. Isotopic analysis of 15N in plant parts also revealed significant differences in 1)15N of the cowpea genotypes studied. As a result, the percent N derived from fixation (% Ndfa) also differed among the cowpea genotypes tested in 2005, with only 5 out of the 30 cultivars obtaining over 50% of their N from symbiotic fixation. Whether expressed as mg Nplant' or kg N.ha-I , the levels of Nz fixation by the cowpea genotypes varied considerably during 2005 and 2006, with values ofN contribution ranging from 14.1 kg N.ha-1 by cv. TVul509 to 157.0 kg N.ha-1by IT84S-2246 in 2005. The amounts ofN-fixed in 2006 ranged from 16.7 kg N.ha-1 by cv. ITH98-46 to 171.2 kg N.ha-1 by TVu11424, clearly indicating genotypic differences in symbiotic N yield. Re-evaluating 15 out of the 30 cowpea genotypes for Nz fixation in 2006, revealed higher % Ndfa values (>50%) in all (15 cowpea genotypes) relative to those tested in 2005, indicating greater dependence on Nz fixation for their N nutrition even though, the actual amounts of fixed-N were lower in 2006. This was due, in part, to reduced plant biomass as a result of very late sampling in 2006, close to physiological maturity (72 DAP in 2006 vs. 46 DAP in 2005) when considerable leaf matter was lost. The amount ofNfixed in 2006 can therefore be considered as being under-estimated.

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Orchard profitability and sustainability are largely dependent on the proportion of crop that can be marketed as first quality (pack-out). While pack-out is directly related to average fruit quality, the visual components of quality, i.e. colour, size and skin finish, predominantly determine whether a premium price is achieved. Fruit quality is the result of a complex interaction of management and environmental factors. By understanding the impact of environment, culture, harvesting, handling and storage on fruit quality, growers should be able to improve both average quality in their crop as well as improving the proportion of fruit in the highest quality grade. Whilst management practices such as pruning, shading, and crop regulation methods have been widely studied as individual or isolated issues, the role of each in commercial orchard systems is less well understood. From the literature, it was concluded that available information was conflicting in relation to the impact of practices such as pruning and chemical thinning on fruit quality, while the impact of crop load on fruit quality was often confounded by the effect of chemicals used to manage crop load. The impact of time and level of pruning, protection of fruit from direct sunlight, and crop regulation was studied in a series of field experiments in orchards managed to local commercial standards. An examination of level and time of fruit thinning on a range of cultivars is included along with an assessment of two new generation blossom thinners (desiccants). As these desiccants frequently cause varying degrees of foliar damage, the impact of various levels of simulated foliar damage on both crop load and fruit quality was assessed. The blossom desiccant ammonium thiosulphate (ATS) showed positive effects on fruit quality with an increase in both fruit firmness and sugar content. Potassium thiosulphate showed similar promise to ATS in terms of both fruit quality and as a method of managing crop load. Low levels of foliar damage during the flowering period had little effect on fruit quality but, where 75% or more of the leaf surface was lost, fruit quality was affected and fruit set was reduced. This study confirmed that loss of leaf area affects fruit quality but it also showed differences between the two cultivars studied. It has been demonstrated by this study that both the degree and timing of pruning can affect crop load, fruit size, and fruit quality. Pruning during the dormant winter period resulted in better fruit quality than when pruning was delayed until after fruit set. Summer pruning adversely affected fruit size, sugar content and fruit skin finish. Both crop load and fruit size were reduced by overall shading of trees during early fruit development. Covering individual fruit with commercial paper ‘apple bags’ improved fruit skin finish with the effectiveness related to time of application. The earlier in the season fruit is covered, the more likely that fruit skin damage will be prevented. Early thinning had a positive effect on fruit quality, resulting in larger, firmer fruit with higher sugar levels. Evidence also showed that early thinning caused fruit to mature earlier than later thinning. In addition, positive relationships were demonstrated between fruit sugar content and weight, between fruit firmness and weight, and between fruit sugar content and fruit firmness. These relationships have not been reported previously and demonstrate that early thinning is a valuable tool in improving fruit quality. Overall results were consistent with the established view that major aspects of fruit quality are determined in the first few weeks of development when cell division is dependent on carbohydrates derived from storage or limited current photosynthate. This study has demonstrated that by increasing awareness of the impact of orchard management practices on fruit quality and making appropriate adjustments, the base level of fruit pack-out can be increased with minimal or no additional cost to growers.

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Thesis (M.S.)--University of Wisconsin--Madison, 1960. / Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 47-49).

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