Boron in rockwool grown sweet pepper (capsicum annuum L.)

Symptoms of B deficiency are often found in rockwool grown sweet pepper crops the cause of which is obscure since it is common practice that the concentrations supplied as well in the root environment are higher than the standards. Plant stage and pH might affect B uptake and translocation in the plant. Investigations were carried out to gather background information. At first, data on B in the supply, in the root environment and in plant tissue were monitored at commercial holdings. Secondly four commercial sweet pepper crops were followed by sampling subsequent leaf layers during 25 weeks. An experiment was set up to investigate the effect of B application, pH and fruit load; pH levels were 4.5, 5.5 and 6.5, Boron at 25 and 60 µmol L-1 and fruit load was reduced from standard (100%) to 66 and 50%. The results showed that in the first 15 weeks of the growing period, which coincides with the increasing fruit load period, the boron content in young leaves decreases dramatically. Moreover, in ageing leaves the B content does not accumulate. After this period, B tends to accumulate easily, especially in old transpiring leaves. This indicates that in the period of heavy fruit load, B uptake is restricted. pH had no clear effects