Nitrogen studies in Lolium perenne grown for seed. IV. Response of amenity types and influence of a growth regulator

Abstract

Abstract In field trials in 1979–81, perennial ryegrass cultivars Royal and Majestic (amenity) and Morenne (agricultural) produced maximum seed yields at levels of applied N ranging from 40 kg ha −1 to 160 kg ha −1 . Available soil N levels were estimated at 55 kg ha −1 ; hence maximum seed yields were obtained at total nitrogen levels of 95–135 kg ha −1 in Royal, 95–215 kg ha −1 in Morenne, and 175–215 kg ha −1 in Majestic. Applied N at rates above 120 kg ha −1 either reduced or did not significantly increase seed yield, decreased seed numbers per unit area and decreased spikelets per tiller and seeds per spikelet. The use of a growth regulator increased seed yields by preventing lodging, but did so irrespective of nitrogen application rate. It is suggested that failure to increase seed yield at high N rates is a result not of poor pollination because of lodging, but seed abortion as a consequence of competition for assimilate supply by secondary vegetative tillers.