Växtnäringsstyrning i potatis

During 1991-1993 an investigation concerning application of optimal amounts of nutrients to potatoes was carried out. The trials were situated at two locations, Hedemora in Dalarna at latitude 60° N and Halmstad in Halland at latitude 56° N. The research plan included 3 table potato varieties, Bintje, Matilda and Ukama, and 5 different ways to apply the nutrients. l. Broadcasting before planting. 2. Placing all nutrients in connection with planting. 3. Placing 1/2 of the nutrients at planting and placing 1/2 at the last hilling. 4. Placing half of NPK at planting + K to full rate + spraying 2 times with 1/4 N + 1/4 P. 5. Placing half the amount of NPK at planting + PK to full rate + spraying 2 times with 1/4 N. The result shows that placing at planting of the whole nutrient rate gave, on average, 9 percent higher yield than broadcasting before planting. Placing of 1/2 the rate at planting and 1/2 the rate at the last hilling gave, on average, 3 percent higher yield than broadcasting. Spraying with nitrogen and phosphorus gave lower yields than broad-casting. The dry matter content showed small differences between different treatments and were not statistically significant. The difference in cooking quality between different treat-ments was not statistically significant but a slight increase in sogginess in comparison with other treatments was observed when the nutrients had been placed. The highest contents of nitrogen and phosphorus were found in treatments where the fertilizers had been placed. The contents of potassium did not seem to be affected by different treatments. The contents of calcium, magnesium and sulphur were highest in tubers from the broadcast treatment. The method of analyzing nitrate in potato leaves in the field with "Nitrachek" showed very good correlation with methods in laboratory. This rapid method may therefore be of good help in following the nitrate content in the potato leaves during growth.