EFFECT OF SOIL-MANAGEMENT SYSTEM AND FERTILIZATION LEVEL ON SUNFLOWERCULTIVATED AFTER AVENA-STRIGOSA

Direct seeding and the planting of winter crops for soil cover are tec hniques which have acquired importance in maintaining or increasing pr oductivity of summer crops. The objective of this study was to determi ne the effect of soil management systems (conventional and direct plan ting), and fertilization levels (zero, half and recommended doses of N , P2O5, K2O and B) in sunflower (Helianthus annuus L.) culture in two cultivation systems preceeding the culture (with Avena strigosa or in fallow). The experiment was carried out in the 1990/91 and 1991/92 gro wing seasons, in the EEA/UFRGS, in the Central Depression of Rio Grand e do Sul. Grain yield of sunflower and the leaf nitrogen content were affected by the fertilization level, being smaller in the treatments w ithout fertilization. Data relative to stem diameter, plant stature an d root length showed that the sunflower plants presented greater growt h in the conventional soil management system, and in succession to Ave na strigosa.