NITRATE ESTIMATES USING THE NITRACHEK TEST FOR PRECISE N-FERTILIZATION DURING PLANT-GROWTH AND, AFTER HARVEST, FOR QUALITY TESTING POTATO-TUBERS

The effect of various levels, timing, and form of inorganic and organic nitrogenous fertilizers on the variation in nitrate content of stem bases over time was measured by means of the Nitrachek test in experiments carried out on sandy soils in Bremervorde, Germany (1985-7) and Helsinki, Finland (1987). There were good correlations between fertilizer use and nitrate content in the stem sap, and it was shown to be feasible to derive standard nitrate values which varied with growth stage. Splitting the application of N gave higher yields than applying all the N in the seedbed. The nitrate contents of tubers at harvest were correlated with the intensity of fertilizer use and was influenced by season. Soil N balances showed that splitting the N dressings reduced the soil N content more than applying all the nitrogen at the time of planting.