Effect of plant density on growth and yields of six soybean (Glycine max L. Merril) cultivars grown at three localities in South Africa

Abstract

Agronomic field trials were conducted at Potchefstroom, Rustenburg and Bethlehem during the 2013/4 planting season to investigate the effect of plant density on growth and productivity of six commercial soybean cultivars. Treatments consisted of six plant densities (200 000, 250 000, 300 000, 350 000, 400 000 and 450 000 plants ha-1) planted at three inter-row spacing (90, 75, and 45 cm) for the six different roundup ready soybean cultivars (LS 6240R, PAN1454R, PAN 1654R, PAN 1500R, LS 6164R, and PAN 1614R). The trial at each locality was laid out in a split-split plot arrangement and fitted into a randomized complete block design (RCBD). Growth and phenological data were collected from the trials and data collected were tested for comparable magnitude using Shapiro-Wilk's test for assessment of deviation from the normality. Weighted combined analysis of variance and pair-wise comparisons were also carried out using the Fishers least square means of significant (LSD) test at a probability level of 5%. Soybean grain yield was significantly affected by plant density, locality x density, locality x cultivar, and density x cultivar interaction effects. Grain yield at Potchefstroom was higher ( 4 389.5 kg ha-1) than either Rustenburg (3 553.1 kg ha-1) or Bethlehem (3 409.5 kg ha- 1). The cultivar that performed the best at Potchefstroom was PAN 1500R (5 820.2 kg ha- 1) at a plant density of 400 000 plants ha-1 and a row spacing of 45 cm. The protein content of soybean grains was significantly affected by plant density, cultivar variation, locality x density and locality x cultivar interaction effects. Grains harvested from Rustenburg had the highest protein content (44.1 %) than either Bethlehem (41.1 %) or Potchefstroom (40.9%). The plant density that gave the highest grain protein (44.5%) content was 400 000 plants ha-1 at 75 cm row spacing. The cultivar LS 6164R had grain with the highest protein content (45.3%) at Rustenburg. The oil content of soybean grain trial was significantly affected by plant density, cultivar and locality x cultivar interaction effects. Grain harvested from Potchefstroom had the highest oil content (21.0%). The highest seed oil content of 21.9% was obtained in cultivar LS 6240R grain harvested at Potchefstroom while cultivar PAN 1664R at Bethlehem had the least oil content of 19.3%.