1. Acta Horticulturae 1972, No. 26, p. 81.
2. Acta Horticulturae 1971, No. 18, p. 66.
3. Acta Horticulturae 1972, No. 26, p. 129.
4. Evaluation of fritted trace elements on peat substrates. Rapport 1, 1971, Institute for Soil Fertility, Haren-Groningen, The Netherlands.