Influence of boron in organic red clover (Trifolium pratense L.) seed production

The effect of boron (B) on flower development, nectar production, seed yield and germination in organic red clover was investigated in soils with <1 mg B kg(-1). Different techniques for application of a liquid B product were studied in four field experiments in 2009-2011. The treatments were as follows: control (no B); three rates of B application to the soil at sowing; and three rates of B as foliar application in the harvest year. The effects of B application varied between the fields and included increased seed yield, seed weight of fifty inflorescences (IFs), number of florets IF-1 and nectar volume IF-1. The greatest effects on seed yield were found in treatments with low B rates. Boron application increased seed B concentration in only one experiment and had no effect on shoot B concentration. The percentage of seeds with normal germination increased with increasing seed B concentration (R-2=0.73). Seed weight of fifty IFs and number of IFs m(-2) increased with increasing shoot B concentration. Boron is therefore an important element for red clover seed production. Further knowledge on improving the B uptake of red clover plants is required to improve seed yield and quality.