During the first days after harvest of Lolium perenne L., low N uptake from the soil may lead to N loss if N fertilizer is applied too soon. Furthermore, temporary N deprivation has been found to stimulate root growth. We therefore hypothesized that a strategic delay in N application after harvest may improve N use efficiency of L. perenne grassland by increasing root biomass and reducing N loss. In a laboratory and field experiment, we delayed N fertilizer application for 0, 3, 6, 9 and 12 days after harvest, and determined effects on herbage yield, herbage N uptake and root biomass of L. perenne. In both experiments, delaying N application with up to 12 days had no significant effect on root biFomass or total herbage N uptake. In the field experiment, total yield tended to be highest with a 3-day delay. For two harvests in the field experiment there was a significantly higher N uptake when N application was delayed, possibly due to rainfall-induced N losses in the treatments with shorter delay. Therefore, timing of N fertilizer application based on rainfall forecasts can contribute to improve N use efficiency by reducing N losses.
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Keywords in English: N fertilization, delayed N application, root biomass, N use efficiency, nitrogen, Lolium perenne