Effects of foliar and root applied nitrogen on nitrogen uptake and movement in white clover at low temperature

Abstract

‘Grasslands Huia’ white clover plants were grown at a constant root and shoot temperature of 8°C in a controlled environment room. Nitrate or urea labelled with 15N was applied to the foliage, foliage plus the roots, or to the roots only. After 21 days, plants supplied with foliar nitrogen (N) or with N to the foliage plus roots, produced significantly (P < 0.05) more lamina dry weight than plants supplied with N to the roots only. Plants supplied with N to the foliage contained significantly (P < 0.05) more lamina 15N than plants supplied with N to the foliage plus the roots or to the roots only. From 14 days onwards, plants supplied with foliar N, or N to the foliage plus the roots, had significantly (P < 0.05) higher leaf areas than plants supplied with N to the roots only, irrespective of the form of N applied. By 21 days, plants supplied with foliar nitrate or urea had significantly (P < 0.05) higher photosynthesis, transpiration, stomatal conductance rates, and lamina sucrose concentrations, than plants supplied with N to the roots. The experiment demonstrated the importance of N availability as a rate‐limiting factor on starch and sucrose synthesis and, in turn, on foliage growth at low temperatures in white clover.