a1 Macaulay Institute for Soil Research, Craigiebuckler, Aberdeen, AB9 2QJ
a2 Scottish Crop Research Institute, Invergowrie, Dundee, DD2 5DA
The effects of nitrogen applications, ranging from 0 to 25 g N/m2, on the nitrogen uptake and growth of the potato crop was studied in an experiment in both 1983 and 1984. Nitrogen uptake was substantially increased by fertilizer application. At high rates of nitrogen application, the crops took up more than was needed to satisfy their immediate requirements for growth. Initially, this extra nitrogen appeared predominantly in the form of soluble protein in the leaves and nitrate in the stem, with reduced-nitrogen in the tubers becoming a large component during tuber bulking. Application of 25 g N/m2 increased the partitioning of nitrogen to the foliage compared with the tubers.
Tuber yield was considered to be a product of four processes: radiation interception, conversion of intercepted radiation to dry matter, partitioning of dry matter between tubers and the rest of the plant and regulation of tuber dry-matter contents. Maximum tuber yields at final harvest were achieved with 15 g N/m2 in both years. Yield increases were due to increased radiation interception, while the photosynthetic efficiency of the canopy and the dry-matter contents of the tubers were little affected. Increases in light interception, in response to nitrogen, were partially offset by a concomitant decrease in the proportion of the dry weight partitioned to the tubers, particularly during the initial period of tuber bulking. The effect of nitrogen application on tuber yield was, therefore, dependent on the date of harvest.
(Received April 18 1986)
(Revised April 18 1986)