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

'Grasslands Huia' white clover plants were grown at a constant root and shoot temperature of 8 degrees C in a controlled environment room. Nitrate or urea labelled with N-15 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 15 N 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.