In a 2-year field experiment with potatoes measurements were made at successive harvests of the dry-matter yield of leaves and tubers and of the length of the root system. Experimental treatments were 150 kg N/ha, control plots receiving no N, and each with or without irrigation.In both years the crop gave increased yields with fertilizer N and irrigation. Fertilizer N increased the weight of leaves and embryonic tubers as early as 6 weeks after planting; it had little effect on water use. Irrigation, which was applied only in the mid-season after water deficits of about 100 mm had developed, increased yields and water use. Highest uptake rates of N, P and K (g/m 2 /day) occurred 4-6 weeks after crop emergence when they reached 0-62, 0-071 and 0-88 respectively. At harvest the tubers contained (g/m 2 ) N: 8-7-211, P: 1-5-2-8 and K: 11-7-27-2. Uptake of all three nutrients was increased by application of N fertilizer and by irrigation.The average root length for all treatments throughout the season in both years was 12 km/m 2 of soil surface, with 84% in the top 30 cm of soil.

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