Temperature sum is considered inaccurate for the optimal application time of nitrogen fertilizer. Possibly soil temperature is a better estimate for this. On peat soil (KTC Zegveld) a field trial has been carried out, in which fertilizer was applied with or without slurry at different soil temperatures. The total period, which according to the temperature sum is regarded as optimal for spreading, was even six weeks. The spreading moments in this period gave the smallest differences in grass yield and the (relatively) highest grass yields. The hypothesis that taking into account soil temperature leads to a higher Nitrogen utilization, and therefore dry matter yield, was not confirmed by the trial in 2018.