The effects of sulphur fertilisers on the content of sulpho‐amino acids in seeds of cowpea (Vigna unguiculata)

Abstract

AbstractSeed meals of three cowpea (Vigna unguiculata) cultivars, grown in pots containing sulphur‐deficient soil supplemented with 0, 0.2, 0.6, 1.8, 5, 15 and 45 parts/106 sulphate‐S levels in the soil solution, were examined for total nitrogen, total sulphur and sulpho‐amino acid contents. The sulphur content and the ratio of sulphur to nitrogen were found to increase with the increasing level of sulphate‐S fertilisation up to ca 5 parts/106. Compared with the control the sulpho‐amino acid content in seeds of cowpea TVu 76 increased with S‐supplementation up to 5 parts/106 and that of cowpea Sitao Pole increased with S up to 1.8 parts/106. Similar levels (7 and 2 parts/106 respectively) of sulphate‐S were required in the soil solution to obtain 95% of the maximum yields of cowpea seeds. The content of sulpho‐amino acids in the seeds from 5 parts/106 treatments were similar to those reported for cowpeas grown under field conditions at IITA and elsewhere with adequate levels of soil sulphur for maximum yield.