Many Asian Brassica crops, for example, often contain high concentrations of glucosinolates and vitamins.
The experiments reported here investigated the effects of different sources of nitrogen on the growth of two such crops. Seeds of Brassica rapa subsp. nipposinica var. chinoleifera 'Mibuna Early' and of Brassica juncea 'Red Giant' were sown in rockwool cubes and germinated in a glasshouse at 15 degsC.
The young plants were then transferred to gullies, where they were supplied continuously with one of three nutrient solutions. Each solution had the same total nitrogen concentration. Edible plants must not contain high nitrate concentrations and in these experiments the lowest tissue nitrate concentration occurred when nitrogen was supplied as 100 per cent NH4.
However, this treatment also reduced the shoot fresh weight of both species, although their dry matter content was enhanced. Three experiments were done at different times of year and the highest shoot fresh weight with the lowest nitrogen content was usually obtained when the plants grew at a medium level of solar radiation.
Effects of Nitrogen Form and Radiation on Growth and Mineral Concentration of Two Brassica Species by Fallovo, Colla, Schreiner, Krumbein and Schwarz (2009). Scientia Horticulturae 123 (2): 170-177. The contents of issues of Scientia Horticulturae and abstracts of papers are provided at www.elsevier.com/locate/scihorti.