EFFECTS OF SODIUM FERTILIZER ON THE CHEMICAL-COMPOSITION OF GRASS ANDCLOVER LEAVES, STEMS AND INFLORESCENCES

Sodium fertiliser was applied to dairy cow pasture to investigate the effects on the chemical composition of grass and clover leaves, stems and inflorescences. The effect of sodium fertiliser varied between fra ctions, with grass leaves and stems generally being more responsive th an grass fluorescences or clover fractions. The sodium content of all fractions was already high in the control treatment, and was increased to an excessive level by sodium fertiliser in all fractions except gr ass stems. Grass leaves were most affected. Potassium content was redu ced in grass leaves and stems, but not in other fractions. The effects on calcium and magnesium varied between fractions but the K:(Ca + Mg) ratio, the most sensitive index of susceptibility to hypomagnesaemia, was reduced in grass leaves, but increased in other fractions. DM dig estibility was decreased in grass and clover leaves by sodium, probabl y because of the high sodium content. MAD fibre content was also incre ased in these fractions. Crude protein content was decreased by sodium fertiliser in grass leaves, in particular. Therefore, when applied to pasture which is naturally high in sodium, sodium fertiliser had detr imental effects on pasture macronutrient content. However, beneficial effects were still observed on mineral ratios for plant and animal nut rition. It is concluded that if sodium fertiliser increases herbage so dium concentrations above 5 g kg(-1) DM, improvements in mineral ratio s that could affect ruminant health may be offset by reductions in the nutritive value of the herbage. It is therefore recommended that the herbage sodium concentration should be known before sodium fertiliser is applied.