Influence of time and level of urea application on seed production of Paspalum plicatulum at Mt. Cotton, south-eastern Queensland

Abstract

Five levels of urea were applied as single or split dressings in early summer, at floral initiation (about Febraury 14), or at inflorescence exsertion to Paspalum plicatulum cv. Rodds Bay grown in rows on a red-yellow podzolic soil. All components of seed yield-tiller density, tiller fertility, raceme number and seed number, and seed size-were influenced by external nitrogen supply. The effects of adequate nitrogen supply during one development phase usually persisted subsequently when differences in plant nitrogen concentration had disappeared. Nitrogen applications during the vegetative and floral initiation stages were most influential. The efficiency of response varied from 5.6 kg additional crude seed produced per kg N at the 50 kg N ha-1 level to 1.2 at the 400 kg N ha -1 level. High levels of urea (200 or 400 kg N ha-1) induced lodging and poor recovery of seed at harvest during a wet year, accentuated moisture stress during a dry year, but improved seed viability.