The effect of nitrogen fertilizing on root and above-ground mass ratio during the growth of spring cereals

abonos nitrogenados ammonium sulphate biomasa biomass biomasse contenido de materia seca cultivos de primavera culture de printemps dry matter content hordeum vulgare leaf area nitrogen content nitrogen fertilizers partie souterraine racine roots spring crops stems sulfate d'ammonium sulfato de amonio superficie foliar surface foliaire tallo teneur en azote tige triticum aestivum underground parts