The effect of plant arrangement and population on the growth and seed yield of Phaseolus vulgaris cv. ’Sanilac’

Less than 10% of New Zealand's annual requirement for dry seed of Phaseolus vulgaris is grown in the country, the remainder being imported from North America. In a population trial in Canterbury in 1976, Goulden obtained a maximum seed yield of 6.2 t ha⁻¹ at a population of 104 plants m⁻². Little work has been carried out on this crop in New Zealand since then. The field trial reported here was conducted in an attempt to define the optimum population and plant arrangement to maximize the seed yield of Phaseolus vulgaris cv, 'Sanilac' in Canterbury. Decreasing row width from 30 cm to 15 cm had several apparent practical advantages. Plant height was increased, flowering started slightly earlier, weed infestation from pod fill until maturity was suppressed, and canopy structure was more open and thus less favourable for the development and spread of fungal pathogens. Maximum seed yield of 248 gm⁻² was obtained at near equidistant plant spacing of 15 x 13 cm. This was at a population of 49 plants m⁻², and with a harvest index of 0.52. Branch numbers and pod numbers per plant decreased with increased population and with decreased row width. Pod production per unit area appeared to be the major factor determining yield. In a pot trial which compared five strains of Rhizobium phaseoli, a strain from Rothamsted, RCR 3622, and also the two other isolates from the temperate regions, RCR 3644 and NZP 5232 were effective in forming active nodules on phaseolus vulgaris cv. 'Sanilac'. Inoculation also appeared to promote root growth. Results from these trials indicate that good seed yields of Phaseolus vulgaris can be obtained in Canterbury when sown in 15 cm rows. The optimum population for yield was 49 plants m⁻², at 15 x 13 cm spacing. Good nodulation with active bacteria was also achieved in a pot trial. Further work is needed to determine the best time of sowing and of irrigating, the most suitable cultivar of Phaseolus vulgaris and strain of Rhizobium phaseoli, a successful method of field inoculating the seed, and the optimum rate of starter N fertilizer for the crop. An apparent response in plant height to shelter could also be further investigated.