RESPONSE STABILITY OF SIGNAL GRASS (BRACHIARIA-DECUMBENS, STAPF) WITH INCREASING NITROGEN AND PHOSPHORUS LEVELS

The study was carried out at the Itambe Experimental Station of the Pernambuco Agricultural Research Enterprise (IPA). Data from nine harvests was used during an experiment in which was studied the effect of three levels of N (0; 60 and 120 kg/ha of P2O5 at every three cuttings) and of four levels of N (0; 20; 40 and 60 kg/ha of N after each cutting), on dry matter yield of signal grass (Brachiaria decumbens Stapf.) was studied. For each nutrient level, correlation analyses, linear regression and regression deviation were made, considering the growth index as an independent variable, and the dry matter productivity as a dependent variable. The was a significant interaction between N and P in the fertilization of B. decumbens. Fertilization with 20 kg of N after each cutting, associated to 60 kg of P2O5 after each three cuttings, increased the dry matter yield from 2.3 to 4.2 t/ha cut, respectively. Stability analysis revealed that the intermediate levels of fertilization may be utilized with greater security, since the responses at these levels were more stable.