Nitrogen shows a strong influence on oat growth and development, mainly on early stages of plant cycle. Oat tiller number and survival and grain yield as affected by nitrogen supply was studied in five field experiments at Estação Experimental Agronômica/UFRGS (Eldorado do Sul, RS), from 1993 through 1998, with cultivars UFRGS 10 and UFRGS 15. Treatments consisted in applying N in different plant stages (emergence to booting) or in different levels at plant emergence. In all situations, treatments received or not an extra N-supply at the 7th leaf stage. Tillering was stimulated mainly by N applied at plant emergence for tiller emission and by N applied at the 7th leaf stage which reduced tiller mortality and mantained synchrony between main stem and tiller development. The best grain yields were obtained when N was available from emergence up to 7th leaf stage. Late N application (booting stage) resulted in no yield increase. When soil nitrogen supply is restricted, N should be applied at sowing and 7th leaf emission.
top dressing; Avena sativa
