Predicting economic optimum and nitrogen balance in the ley - ruminant system / B.W.R. Torssell, B. Fagerberg. -- Uppsala : Swedish university of agricultural sciences, 1990. -- 48 s. : 14 obr. -- (Crop production science 10). metabolizmus dusíka * hnojenie dusíkom * pasienky * prežúvavce * dusík