ABSTRACT
Summary With most of the grasses grown for seed in Denmark, a series of trials has been carried out on increasing nitrogen rates in the autumn combined with increasing rates in the spring. The results of these trials show that an autumn application of nitrogen is very important to most of the grasses and necessary if the optimum yield of seed is to be achieved. In order to find the best time to apply nitrogen in the spring when producing grass seed, a number of trials have been carried out in recent years with various grasses. Up to and including 1980, the following trials have been carried out: 29 with Festuca rubra, 28 with Dactylis glomerata, 4 with Poa pratensis, 13 with Lolium perenne, 23 with Festuca pratensis, 22 with Phleum pratense, and 6 with Phleum bertolinii. The first application was made as soon as winter was over and it was possible to drive in the field; the second was made when growth had started; the third application was made when the new tillers were about 15 cm long, with the average dates of application to Festuca rubra being 2 March, 1 April, 30 April (these are very near the averages for the other grasses). The results showed that time of nitrogen application in the spring is of great importance for development of the grass. Delays in nitrogen application to most of the species resulted in negative effects of varying magnitudes on the number of fertile tillers/unit area but positive effects on seed weight and number of seeds/fertile tiller. The result of these effects on the yield components was a decrease in seed yield of Festuca rubra, Dactylis glomerata, and Poa pratensis but an increase in yield of Phleum pratense and Phleum bertolinii. As for Lolium perenne and Festuca pratensis, the positive and negative effects on yield cancelled each other out, and the seed yield did not depend on time of nitrogen application. On the basis of these results it is recommended that nitrogen be applied in the spring to Festuca rubra, Dactylis glomerata, and Poa pratensis as soon as winter is over and to Festuca pratensis and Lolium perenne as soon as growth has started but to Phleum pratense and P. bertolinii (which ripen late) only when growth is well under way and the grass has tillers about 10 cm long.
