Optimizing plant spacing for commercial snap bean production

A study was conducted at The University of Tennessee Plateau Experiment Station to determine optimum row spacing and in-row plant density for commercial production of snap beans (Phaseolus vulgaris L.). The field tests, arranged in a split plot experimental design, were replicated twice at each of five planting dates. Whole plot treatments were two fertilizer application rates, 350 and 700 pounds per acre of 8-12-6 analysis granular fertilizer. The sub-plot treatments were a factorial arrangement of three plant densities (6, 9, and 12 plants per foot) and three row spacings (12, 24, and 36 inches). The plots were hand seeded in a conventionally prepared seedbed. Plots were thinned to the desired stand when the plants were fully emerged. The beans were hand harvested at maturity, approximately 55 days after seeding. Performance of the various treatments was compared by evaluating parameters describing plant growth characteristics, plant and pod yields, and pod quality. Decreasing the spacing between rows resulted in smaller plants. Moreover, plants in the narrow rows yielded fewer pods per plant than those in the 36-inch rows. However, pod yields per unit area from the 12-inch rows were 29 percent greater than yields from 36-inch rows. Pod set was higher above the ground surface in the narrow rows compared to the 36-inch rows. Increasing the plant density within the row from six to twelve plants per foot increased the average width of the plant canopy by 1.6 inches. The average per acre pod yield was increased by 15 percent when the planting density was increased from six to nine plants per foot of row. Increasing the plant density to twelve plants per foot further increased average yields by only 2.5 percent over the nine plants per foot rate. Fertilizing at the 700 pounds per acre rate increased plant lodging by 14 percent compared to the 350 pound rate. The higher fertilizer rate increased the average canopy width by 2.1 inches, but decreased the median height of pod set by 1.2 inches. Application of fertilizer at the higher rate did not increase the number of pods produced, total weight of pods harvested, or total plant and pod weight.