AbstractDepression of percentage emergence of vegetable seedlings was linearly related to the quantity of nitrogen fertiliser applied when the fertiliser was broadcast and worked into the seed bed. Placement of fertiliser at a depth of 8 cm avoided depression of emergence. The extent to which emergence was affected depended on the weather, and on the crop, some species (e.g. lettuce) being sensitive, others (e.g. red beet) being resistant to the effects of nitrogen fertilisers. A computer program was used to calculate the effects of rainfall, evaporation and soil temperatures on the concentration of nitrate in the top 5 cm of soil in a series of 45 field experiments, and this was compared with the seedling emergence records. According to the program this concentration varied widely over short periods. Red beet and radish achieved a high percentage emergence after very brief periods of low nitrate concentration. For most crops, however, transient short periods of low nitrate concentration were insufficient for satisfactory emergence, and most crops exposed to high nitrate concentrations, even if these were not continuous, suffered some reduction of emergence. Spinach was able to resist a high concentration of nitrate during the 3 days after sowing, but not at later periods. The sensitivity of crops varied, and the period of sensitivity was also different for different crops. Methods of application of nitrogen fertilisers likely to avoid depression of seedling emergence are briefly discussed.