Ettala, Terttu, Matti Kreula, and Hilkka Tähtinen. “The Effect of Sulphur Deficiency and Sulphur Fertilisation on the Nitrogen Compounds of Timothy”. Agricultural and Food Science 50, no. 2 (March 1, 1978): 137–146. Accessed December 25, 2024. https://journal.fi/afs/article/view/71966.