FERTILIZATION AND PLANT POPULATION DENSITY EFFECTS ON THE PRODUCTIVITY OF OPUNTIA FICUS-INDICA IN NORTHEAST BRAZIL

The arid and semi-arid region occupies 89.3% of Northeast Brazil, with livestock farming as one of the most important activities in this region. The lack of forage during the dry season, however, is hampering the expansion of this activity. Cactus forage is an important option to feed the animals during drought, having an estimated planted area of 400,000 ha in NE Brazil. This experiment was carried out from 1998 to 2002 at the Caruaru Experimental Research Station (IPA) and aimed to study N (0; 75; 150; 225; 300 kg N ha^-1 yr^-1) and P fertilization (0 and 75 kg P₂O₅ ha^-1 yr^-1) at two planting densities (5,000 and 40,000 plants ha^-1) of Opuntia ficus-indica ‘Clone 20’. A split-split plot arrangement was used in a completely randomized block design, with five replications per treatment. The main plot was formed by harvests, the split-plot by the factorial arrangement of N and P levels and the split-split plot by the plant populations. The results showed higher (P<0.05) yields when P was added (12.6 vs. 10 T DM ha^-1 2 yrs^-1). Higher plant populations also increased forage yield (13.4 vs. 9.2 T DM ha^-1 2 yrs^-1). Productivity increased at the second harvest (16.2 T DM ha^-1 2 yrs^-1) when compared to the first harvest (6.4 T DM ha^-1 2 yrs^-1). A triple interaction among N x plant population x harvest was observed. In the first harvest, a quadratic response was detected for the N levels, for both plant populations. In the second harvest, a linear response was observed for the higher population whereas a quadratic response was associated to the lower population. Increasing plant population and fertilizing with N and P resulted in positive DMY response of ‘Clone 20’ in NE Brazil.