Efficient agronomic practices are vital for achieving sustainable management of water resources and N for producing highly nutritious leafy vegetables to curb malnutrition and poverty. The importance of proper N and irrigation of sustainable crop production is well recognised in literature, although irrigation and N application rate guidelines for ALV’s might not be sufficient for advisory purposes, especially for smallholder and commercial farmers. The limited access is attributed by factors such as the lack of commercialisation as a result of limited agronomic information describing optimum management options for S. retroflexum. Availability of such information would contribute to successful commercialisation of this crop. The primary objective of this study was to establish optimum agronomic management practices for S. retroflexum for smallholder farmer as well as commercial production in South Africa. This project consists of three main components with the overall objective to evaluate agronomic management practices of irrigation and N application on the marketable yield, nutritional water productivity and 1H-NMR metabolic profiling under a rainshelter. The results suggested that S. retroflexum responded positively to N application rates until an optimum marketable yield was obtained at 150 kg N·ha-1 with I66%FC, followed by the I100%FC with 150 kg N·ha-1,while, the lowest biomass was recorded in the I33%FC irrespective of the N application rate. This also indicates of how S. retroflexum is affected by insufficient irrigation, even at sufficient N application rates. N and irrigation are key factors limiting plant survival and growth and low applications has adverse effects on the marketable yield of S. retroflexum. Dry matter production increased with the higher N application and a linear increase was observed with N application having a significant effect on the dry matter production. Maximum irrigation use efficiency (IUE), was obtained in the moderately irrigated treatment (I66%FC) and the 150 kg N·ha-1, followed by the I100%FC and 150 kg N·ha-1. The stressed irrigation and N treatments showed sustainably low irrigation use efficiency as compared to the well irrigated treatment. This suggests the competitive capacity of S. retroflexum roots to draw water from deeper parts of the soil profile, during stressed conditions to maintain the turgor pressure, indicating that production of S. retroflexum is possible in arid areas where water could be a limiting input, but might not be profitable for farmers. However, the biomass yields obtained under the less irrigated soil water conditions may lack the quality needed to market the produce. The NWP for Zn and Fe showed significant differences among the irrigation and N treatments. Although the NWP of Mg in S. retroflexum was neither influenced by irrigation nor N application, with no statistical differences between the irrigation and N application observed. Among the different irrigation and N treatments evaluated, I33%FC obtained the lowest NWP irrespective of the N application rate, followed by I100%FC. The NWP increased linearly with an increase in N application. Optimum Fe NWP was obtained with 150 kg N ha-1, but declined significantly at application 225 kg N ha-1 in I33%FC and I100%FC. Maximum Fe NWP was obtained with I66%FC with 150 kg N ha-1. The NWP Fe for S. retroflexum in this study, are acceptable when compared to those obtained in literature. Therefore a significant interaction between N and irrigation application exist, with respect to Fe and Zn availability of S. retroflexum, which could be ideal for Fe and Zn malnutrition alleviation in resource poor households. 1H-NMR based metabolomic profiling was utilized for compound annotation as effected by irrigation and N. Chlorogenic acid, proline, sucrose and trigonelline were associated with separation in the irrigation treatments. Since no separation of the irrigation or N treatments was observed with the PCA, an OPLS-DA plot was constructed. A pairwise comparison of the I33%FC and I100%FC samples was done, which provided better separation between the clusters for the first harvest. Even better separations were observed with a pairwise OPLSDA analysis of the I33%FC and I100%FC samples for the second harvest. Primary metabolites such as sucrose, and proline and secondary metabolites trigonelline and chlorogenic acid were responsible for grouping of the stressed irrigation treatment as compared to the well irrigated treatment. Main findings of the study suggest that S. retroflexum is highly nutritious in Fe, Zn and Mg, which might play a significant role in malnutrition alleviation. Solanum retroflexum requires sufficient soil water content, for achieving high nutrient yield and nutritional water productivity. The results clearly illustrate that the perception that S. retroflexum grow well on low soil fertility mostly practised in rural and smallholder farming is incorrect and misleading. Moreover, S. retroflexum can be an ideal cropping system for smallholder and commercial farmers in water scarce areas such as South Africa, although marketable yield is severely affected. / Agriculture and  Animal Health / M. Sc. (Agriculture)

Diss. (sammanfattning) Uppsala : Sveriges lantbruksuniv., 2009. / Härtill 4 uppsatser.

The contamination of process pea (Pisum sativum L.) crops by the immature fruit of black nightshade (Solanum nigrum L.) and hairy nightshade (S. physalifolium Rusby var. nitidibaccatum (Bitter.) Edmonds) causes income losses to pea farmers in Canterbury, New Zealand. This thesis investigates the questions of whether seed dormancy, germination requirements, plant growth, reproductive phenology, or fruit growth of either nightshade species reveal specific management practices that could reduce the contamination of process peas by the fruit of these two weeds. The seed dormancy status of these weeds indicated that both species are capable of germinating to high levels (> 90%) throughout the pea sowing season when tested at an optimum germination temperature of 20/30 °C (16/8 h). However, light was required at this temperature regime to obtain maximum germination of S. nigrum. The levels of germination in the dark at 20/30 °C and at 5/20 °C, and in light at 5/20 °C, and day to 50 % germination analyses indicated that this species cycled from nondormancy to conditional dormancy throughout the period of investigation (July to December 2002). For S. physalifolium, light was not a germination requirement, and dormancy inhibited germination at 5/20 °C early in the pea sowing season (July and August). However, by October, 100% of the population was non-dormant at this test temperature. Two field trials showed that dark cultivation did not reduce the germination of either species. Growth trials with S. nigrum and S. physalifolium indicated that S. physalifolium, in a non-competitive environment, accumulated dry matter at a faster rate than S. nigrum. However, when the two species were grown with peas there was no difference in dry matter accumulation. Investigation of the flowering phenology and fruit growth of both species showed that S. physalifolium flowered (509 °Cd, base temperature (Tb) 6 °C) approximately 120 °Cd prior to S. nigrum (633 °Cd). The fruit growth rate of S. nigrum (0.62 mm/d) was significantly faster than the growth rate of S. physalifolium (0.36 mm/d). Because of the earlier flowering of S. physalifolium it was estimated that for seedlings of both species emerging on the same date that S. physalifolium could produce a fruit with a maximum diameter of 3 mm ~ 60 °Cd before S. nigrum. Overlaps in flowering between peas and nightshade were examined in four pea cultivars, of varying time to maturity, sown on six dates. Solanum physalifolium had the potential to contaminate more pea crops than S. nigrum. In particular, late sown peas were more prone to nightshade contamination, especially late sowings using mid to long duration pea cultivars (777-839 °Cd, Tb 4.5 °C). This comparison was supported by factory data, which indicated that contamination of crops sown in October and November was more common than in crops sown in August and September. Also, cultivars sown in the later two months had an ~ 100 °Cd greater maturity value than cultivars sown in August and September. Nightshade flowering and pea maturity comparisons indicated that the use of the thermal time values for the flowering of S. nigrum and S. physalifolium can be used to calculate the necessary weed free period required from pea sowing in order to prevent the flowering of these species. The earlier flowering of S. physalifolium indicates that this species is more likely to contaminate pea crops than is S. nigrum. Therefore, extra attention may be required where this species is present in process pea crops. The prevention of the flowering of both species, by the maintenance of the appropriate weed free period following pea sowing or crop emergence, was identified as potentially, the most useful means of reducing nightshade contamination in peas.