Blackberry cultivars, nitrogen and potassium fertilization under drastic summer pruning in a subtropical area

The expansion of blackberry cropping in subtropical regions is recent, requiring adaptability studies and the development of new cultivars, as well as suitable plant management. Aiming to study adaptability and agronomic performance of blackberry (Rubus spp.) under drastic summer pruning in a subtropical region, the response of four blackberry cultivars ('BRS Tupy', 'Guarani', 'Brazos and 'Choctaw') to N and K fertilization was evaluated during two growing seasons in Jundiai (Brazil). The experiment used split-plots in a randomized complete block design with four replicates. The plots consisted of combinations of three N rates (75,150 and 300 kg.ha(-1).year(-1)) and three K rates (50, 100 and 200 kg.ha(-1).year(-1 ) of K2O) in factorial arrangement and an additional control treatment without fertilizer application. In the subplots, four cultivars of blackberry were studied. Considering fruit yield, accumulation of phytomass and mineral elements, as well as the nutrient efficiency use, the cultivars that showed greater adaptation to cultivation in a subtropical area under drastic summer pruning management are 'Brazos', 'Guarani', 'BRS Tupy' and 'Choctaw', in that order. An annual application of 120 and 67 kg.ha(-1) of N and K2O, respectively, is expected to be sufficient to achieve maximum economic yield.