POTENTIAL USE OF WINTER GREEN MANURE SPECIES FOR NITROGEN RECYCLING BY 'NIAGARA ROSADA' GRAPEVINES

Green manures have become an important option for recycling nutrients in organic cropping. However, its benefits are often not obtained in the short term. In this context, the study aimed to determine whether the use of cover crops during winter can contribute to N provision in the following spring, in the beginning of the growth of young grapevines. The winter green manure species white lupin (Lupinus albus), forage pea (Pisum arvense), common vetch (Vicia saliva), hairy vetch (Vicia villosa), triticale (Triticale hexaploide), oat (Arena saliva). rycgrass (Lollium multiflorum) and forage turnip (Brassica rapa) were grown until flowering in 4 L pots and fertilized with ammonium sulfate enriched at 10% with 131 1 atoms. In the following spring, grapevines cv. Niagara Rosada (Vitis labrusca) grafted on two different rootstocks (IAC-572 'Jales' and IAC 766 'Campinas') were planted in 14 L pots where it was superficially applied one of the five different sources of N. The green manure species employed as N source were forage pea (Pisum arvense), common vetch (Vicia saliva), hairy vetch (Vicia villoan) and oat (Arena sativa). The soil surface was covered with the dry matter from the green manure species (38 dry matter pot(-1)) or fertilized with ammonium sulfate enriched at 2% with N-15 atoms. The results demonstrated that the oat plants showed the highest dry matter content (11.68 g pot(-1)). The species forage pea, hairy vetch and common vetch had the lowest C/N ratios, with values of 16, 16 and 18, respectively. Hairy vetch was the most efficient (255.1 mg pot(-1)) for the accumulation of N and oat plants showed the highest N uptake from the mineral fertilizer. The N uptake and accumulation by the 'Niagara Rosada' grapevines varied according to N source and rootstock. Grapevines accumulated N in higher amounts from mineral fertilizer, followed by the N from leguminous species and then lower quantities from the oat plants. Grapevines grafted on the IAC-572 'Jales' rootstock accumulated higher amounts of N than those grafted on IAC-766 'Campinas', probably due its higher vigor and, consequently, better soil exploration by the roots. Despite of the rootstock, between the green manure species, the N from forage peas was the most recovered by the grapevines cv. Niagara Rosada, attaining 30.8%, while common vetch 23.1%, hairy vetch 19.0%, and oat only 5.2%.