Root distribution in a deep sand and its relationship to the uptake of added potassium by pasture plants

Abstract

The distribution of roots and the uptake of 42K from various depths in soil were studied in glasshouse and field experiments on 12 temperate annual pasture species. Root/top weight ratios were mostly higher in grasses than in legumes or herbs. This ratio decreased with increasing maturity of the plants. The concentration of roots under field swards decreased exponentially with depth, from 10 cm downwards. Large differences in root distribution were noted between species. The most shallow-rooted were lotus, subterranean clover, and silver grass. The deep-rooted species were cape-weed, erodium, oats, lupins, and serradella. Some ecological implications of these differences in rooting depth are discussed. The effective rooting depth in the field was correlated with root penetration rates measured on young plants. The possibility of using root penetration rate as a means of predicting potential rooting depth is discussed. All species had a high proportion of their roots in the top 10 cm of soil and took up most 42K from this layer. As the depth increased, both the concentration of roots in the soil and the amount of potassium absorption decreased. The amount of roots at the sites of 42K placement was closely related to both the concentration and the total amount of 42K in the tops.