Relationship of seed boron concentration to germination and growth of soybean (t Glycine max)

Abstract

Soybean seeds with B concentrations ≤ 10 mg B kg-¹ have been reported to have deformed cotyledons. This paper examines the relationship of seed B concentration to seed germination, seedling normality, and plant growth of soybean (Glycine max) cv. NW1 sown in soil with a range of B levels. Seed with 7 mg B kg-¹ performed poorly, with 80% failing to germinate. Moreover, 70% of the seedlings which emerged were abnormal when sown on a low B soil. Increasing soil B had no effect on germination but decreased the percentage of abnormal seedlings by one third. Seed with 10 mg B kg-¹ germinated as well as seed with 14 or 20 mg B kg-¹, but when sown on a low B soil, 80% of the seedlings were abnormal compared with 50 and 20%, respectively. Increasing soil B almost eliminated the incidence of seedling abnormality when seed contained 10 – 20 mg B kg-¹. When grown to maturity on the lowest soil B, plants from seed with 10 mg B kg-¹ produced less than half the seed yield of plants from seed with 14 or 20 mg B kg-¹. They had fewer pods per plant and fewer seeds per pod. They responded strongly to increasing soil B, so that in soil with higher B levels, plants from seed with 10, 14 or 20 mg B kg-¹ gave the same yield.

The results suggested that soybean seed with a low concentration of B have permanently damaged seed embryos, preventing their germination or producing defective seedlings. At slightly higher concentrations, embryos are not permanently damaged, but require a higher level of external B for their normal development than do those with higher concentrations of seed B. In the present experiments, the critical concentration of B in soybean seed for permanent damage was between 7 and 10 mg B kg-¹, and for normal seedling development in low B soils was between 14 and 20.