Maximizing dry bean (Phaseolus vulgaris L.) production through selected agronomic practices

Abstract

Dry bean production in South Africa is lower than required for human consumption. Dry beans are rich in protein and thus an ideal replacement for expensive meat protein, especially for rural and poor communities in South Africa. To meet local demand, efforts to improve the yields obtained by small scale and subsistence farmers are needed. Therefore a series of experiments were conducted to investigate how dry bean production can be improved or optimized using selected agronomic practices. The objectives of the study were to determine the stability of dry bean varieties under the climatic conditions of Limpopo, to determine the impact of planting dry bean at lower or higher than recommended planting populations, to determine the effect of deficit irrigation and drought stress on dry bean production and to calibrate and validate SWB model in dry bean. The latter is of huge importance in South Africa where water resources are limited. The desirable genotype in terms of high mean yield was OPS-RS1 and the desirable environment in terms of high mean yield was Tshiombo irrigation scheme. The GGE biplot analysis resulted in meaningful and useful summary of GE interaction data and assisted in examining natural relationships and variations in genotype performance across tested environments. According to GGE biplot OPS-RS1 can be characterized as the genotype with the highest mean yield and high in stability. The results revealed that the interaction relationship between dry bean varieties and plant populations significantly influenced the grain yield per area, grain yield per plant, chlorophyll content, and plant height at 62 and 98 DAP (days after planting), while it affected dry matter production at 30, 62 and 98 DAP. The highest grain yield was achieved with OPS-RS2 at 150 000 plants per hectare (3.802 t ha-1) in 2012. The number of seeds per plant was influenced by plant population and dry bean variety. The number of pods per plant was only influenced by plant population. A plant population of 150 000 plants per hectare was found to be the most suitable for both determinate and indeterminate dry bean varieties. The introduction of deficit irrigation resulted in a significant reduction in plant height, number of seeds per plant and number of pods per plant. The reduction in number of seeds per plant and number of pods per plant resulted in a significant reduction in grain yield. The shelling % and 100 seed mass were not significantly influenced by deficit irrigation. Treatment S3 resulted in the poorest results throughout. The results revealed that deficit irrigation can result in substantial yield reduction in dry beans. There is thus a need for further research to develop drought tolerant varieties of dry beans. The introduction of drought stress resulted in a reduction in dry matter production, leaf area index, number of seeds per plant, number of pods per plant, seed size and finally grain yield. The treatments S2 and S3 performed poorly throughout. The results also revealed that 100 seed mass, number of pods per plant, number of seeds per plant, total dry matter yield at 92 DAP and leaf area were all positively correlated to grain yield. Water use efficiency was significantly affected by drought stress. The results suggest that drought stress towards the end of the growing season may not cause serious harm in grain yield. The results of the study indicate that drought stress effects on photosynthetic rate were highly significant, with a reduction of up to 45%. The reduction of photosynthesis at 63 and 105 DAP was greatly due to reduced stomatal conductance. Drought stress resulted in a reduction in intercellular carbon dioxide concentration, stomatal conductance and transpiration. Chlorophyll fluorescence was also affected by drought stress. The minimal chlorophyll fluorescence (F0) was increased by drought stress, accompanied by a reduction in the maximal chlorophyll fluorescence (Fm) and Fv/Fm. Drought stress can have serious effects on leaf gaseous exchange rate and chlorophyll fluorescence, depending on the growth stage of the plant and the duration of drought stress. The SWB model was successfully calibrated and validated for dry beans. The results revealed that the model can be used for scenario simulation for future planning.