| Abstract: | Fertilisation of herbage with Na can increase acceptability to cows, but the influence of fertiliser rate and fertilisation by K is unknown. In experiment 1, ten cows were grazed on pasture plots that had just been fertilised with 0–132 kg-Na ha−1 (current Na) and had received 0–64 kg-Na ha−1 in the previous grazing season (residual Na). Herbage Na concentration increased in proportion to current Na from 2·7 to 4·9 g-Na kg−1 dry matter (DM) and also increased with increasing residual Na from 2·2 to 4·5 g-Na kg−1 DM. Herbage K concentrations were low (10 g kg−1 DM at 0 kg-Na ha−1) and were only slightly reduced by Na fertiliser. Herbage Mg and Ca concentrations and DM digestibility were maximum at 66–99 kg-current-Na ha−1. Cows grazed current-Na-fertilised plots to a lower height and spent more time grazing them. In experiment 2, pasture plots received no fertiliser, low and high isomolar and independent applications of Na and K or a combination of the two. The herbage was more mature than in experiment 1 and Na concentration of the herbage without Na fertilizer was high (5 g kg−1 DM). Na fertiliser, therefore, only slightly increased Na concentration, more in clover than in grass, and had little effect on K concentration. K fertiliser increased K concentration from 16 to 20 g kg−1 DM and reduced Na concentration to 3·5 g kg−1 DM. Sodium fertiliser, therefore, only increased the acceptability of herbage to cattle when herbage Na concentrations were initially low (less than 5 g kg−1 DM) and were increased substantially by the application of the fertiliser. © 1998 SCI. |
