The effect of plant population, spatial arrangement and weed competition on growth and yield of dwarf beans (Phaseolus vulgaris L.) : a thesis submitted in partial fulfilment of the requirements for the degree of Master of Agricultural Science in the University of Canterbury [Lincoln College]

Abstract

During the 1980-81 season, a field experiment was conducted at Lincoln College to study the effect of plant population and spatial arrangement on growth, green bean yield and yield of dry seed of the standard commercial green bean (Phaseolus vulgaris L., Cv. 'Gallatin 50'). The crop was grown in all combinations of 15, 30, 38 and 45 cm row widths and 7.0 and 14.0 cm intra-row spacing giving a population of 22 to 73 plants m⁻² at green bean harvest. Within this population range, the maximum yield of processable green beans was 3.64 kg m⁻² obtained at a plant population of 53 plants m⁻². This was at an almost square planting of 15 cm x 14 cm. Total DM yield for all treatments increased up to a maximum, 72 days after sowing with a peak LAI of 5.2 being attained in 15 cm rows. Total plant height, flowering and maturity were not influenced by either population or arrangement but branch number and pods per plant declined with increasing population and with a decrease in inter-row and intra-row widths. There was no significant treatment effect on pod size distribution, greenness of pods or weight of individual pods.

The population at dry bean harvest ranged from 17 to 63 plants m⁻². Within this range, the relationship between seed yield and population was asymptotic. The optimum population was 47 plants m⁻² at which a yield of 386 gm⁻² of dry seed was obtained. This was at a spacing of 30 cm x 7 cm. Seed yield per plant and pods per plant declined with increasing population, but the harvest index, seeds per pod and 1000-seeds weight were not significantly affected.

In the same season, a supplementary experiment was carried out to determine the extent to which competition between weeds and a bean crop at constant spacing influenced yield of both green beans and dry seed. Plots were kept free of weeds for 0, 3, 6, and 9 weeks after emergence. A continuous weeding treatment was also included. Considerable reduction in green bean yield was observed when competition between weeds and the bean crop exceeded a period of 7 weeks. Reduction in yield was caused mostly by weeds emerging soon after planting. Later emerging weeds were effectively suppressed by the bean crop canopy. It is suggested that weed control for at least 3 weeks after emergence is necessary to ensure good yields of both green and dry beans.