Growth, mineral nutrition and water use by potato crops

Abstract

SUMMARY: 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/m²/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/m²) N: 8·7–21·1, 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/m² of soil surface, with 84% in the top 30 cm of soil. From values of inflow of water and NO₃–-N₁ calculated from depletion of successive 15 cm deep soil horizons, roots below 30 cm depth were substantially more active than those nearer the soil surface. During most of the growing season about half the nitrate reached the roots by mass flow.During crop growth NO₃–-N concentration in the soil decreased to less than 10 μg/cm³ to 30 cm depth. Summation of crop N and soil NO₃·N indicated net mineralization rates of soil N of between 0·07 and 0·17 g/W/day (average 012 g/m²/day). At final harvest the residue of N of about 9–10 g/m² on plots that received N fertilizer, included crop residues, NO₃–·N left in the soil and leaf fall.