Plant population and spatial arrangement effects on productivity, nutrient status, and microclimate relationships of snap beans (Phaseolus vulgaris L.)

During 1974 the large-leaved Early Gallatin snap bean cultivar was observed for growth and yield relationships under varied population and spacing systems. The spacings and relative densities employed were 91 by 4 cm (100 per cent), 12 by 3 and 15 by 15 cm (150 per cent), and 46 by 4 and 23 by 8 cm (200 per cent). Three crops were included which were subject to extremes in moisture and disease conditions. Competitional influences were not indicated until about the flowering stage which coincided generally with early canopy closure in the higher densities. Additions of leaf area and dry weight per plant were favored by greater available space, but on a land area basis the higher densities had productivity exceeding the conventional row spacing. Competitional pressure in the highest density suppressed productivity increases over the middle density except under very favorable growing conditions. In only one case were growth differences noted between spacings within densities. No consistent trends in mean CGR, RGR, or NAR were associated with the different populations. Pod maturities and numbers per unit area were little affected by treatment. The exception was under very favorable growing conditions where vegetative growth encroached on the reproductive period. Over all crops yield improvements were obtained with higher populations, but only the square, middle density and wide row, high density spacings were consistently highest. Fertilizer was broadcast at rates 1.5 times that recommended for normal populations. Petiole analysis throughout the growth periods indicated this rate was fully sufficient for the highest density. At harvest the leaf, stem, and pod contents of N, P, K, Ca, and Mg were also unaffected by spacing. Conventional rows left 20 to 30 per cent of the inter-row space exposed at harvest. Attenuation of light was a direct function of the LAI and canopy continuity, and intra-canopy air temperatures were generally lowered 1 to 2°C by increasing canopy densities. Surface soil moisture levels did not differ between open and closed canopies, and differences in diffusion resistance related to higher population use of moisture rather than canopy density and were very small. No dense canopy-depletion of CO₂ was observed as soil and ambient air replenishment was apparently quite rapid in this relatively low growing crop. Shading effects from closer spacing on stomatal densities and chlorophyll contents of basal leaves were not observed. With equal biological and economic productivity to the highest density studied, the square, middle density spacing exhibited better efficiency. Depending on development of a planter commercially acceptable, this square spacing with less seed investment presents a viable option to currently employed "double-conventional" high density planting systems.