The effects of density and foliar nitrogen on yield of Fiskeby V soybeans

Abstract

Previous research on soybeans showed that United States cultivars in Maturity Groups I and II suited to latitudes 40-45°N were not highly productive in Canterbury, New Zealand, at 43-44°S because of the cool maritime summers. Two trials were carried out during 1978-79 and 1979-80 to investigate the effects of density and foliar nitrogen on the seed yield of cold tolerant, short season cultivar Fiskeby V (Maturity Group 00) bred in Sweden at 58°N. The first trial in 1978-79 was a 6 x 2 factorial with 6 established plant populations of 16, 20, 35, 42, 57, and 69 plants m⁻² and two nitrogen levels of 0 and 60 kg N ha⁻¹, using a foliar spray of urea at 20 kg N ha⁻¹ at flowering, pod filling and grain maturity. Increases in plant density and nitrogen application both increased seed yields. At the highest plant density, nitrogen treated plots averaged a seed yield of 304 g m⁻² while N plots averaged 278 g m⁻² Nitrogen increased seed yields due to an increase in number of seeds per pod and 100-seed weight. Increasing plant density decreased all other components of yield except number of seeds per pod and 100-seed weight which were relatively stable. Changes in plant density had little effect on seed protein which averaged 43.4 per cent. There were no density x nitrogen interactions. Yields from the two lowest densities in the 1978-79 season were poor, so these were omitted in the 1979-80 trial. To determine the optimum time of application of foliar N, the number of N treatments was increased. The second trial was a 4 x 2³ factorial experiment. On established plant populations of 25, 42, 58, and 76 plants m⁻², foliar nitrogen was applied either at flowering, pod filling or grain maturity, each at two levels, 0 and 20 kg N ha⁻¹ in all combinations to give eight foliar nitrogen treatments. Seed yield increased with increases in plant density. At the highest density, seed yield was 312 g m⁻². Seed yields and average seed protein per cent of 47.9 were higher than those for the 1978-79 trial. All components of yield decreased with increase in plant density except 100 seed weight which increased. Nitrogen had no effect on seed yield or its components. The differences in yield between the two seasons are discussed in relation to soil, climate and nodulation. Seed yields from these two trials were satisfactory when compared to world soybean yields. Still better yields can be obtained if more effective pre-emergence herbicides than trifluralin are used for better weed control in late summer. The major drawback to growing the cultivar Fiskeby V commercially is the short stature of the cultivar with pods near ground level which makes machine harvesting difficult.