Boron nutrition of cowpea

Abstract

Cowpea (Vigna sinensis L.) cv. Rituraj was grown in refined sand at graded levels of boron ranging from 0·0033 to 6·6 mg l⁻¹. Maximum biomass and seed weight were obtained at 0·33 mg B l⁻¹ supply. In acute deficiency of boron (0·0033 and 0·033 mg l⁻¹), its deficiency symptoms were pronounced, the biomass was depressed markedly and neither pods nor seeds were formed. At moderate deficiency of boron, deficiency symptoms were mild and the number and weight of seeds were reduced by about 40% and 50% respectively. Marked boron toxicity symptoms were observed at 6·6 mg B l⁻¹ supply where not only biomass and seed yield but also the concentration of starch and non-reducing sugars and the activity of starch phosphorylase and ribonuclease were depressed. In the latter treatment reducing sugars were increased so also the activity of polyphenol oxidase and peroxidase. In acute boron deficiency, the concentration of reducing sugars and non-reducing sugars were increased so also the activity of peroxidase, ribonuclease and polyphenol oxidase but the activity of starch phosphorylase was depressed only at 0·0033 mg B l⁻¹ supply. As the concentration of boron in seeds was markedly less than in leaves, the values of deficiency, threshold of deficiency and threshold of toxicity in leaves was higher than in seeds.