LEAF DIAGNOSIS AND PRODUCTIVITY OF FORAGE SORGHUM FERTIGATED WITH NITROGEN DOSES IN TWO HARVESTS

The aim of the present study was to evaluate the degrees of macronutrients in the diagnostic leaf and the productivity of forage sorghum IPA 467, submitted to fertigation with nitrogen doses, during two harvests (summer and winter), both without regrowth. From January 20 to May 18 and from June 17 and October 14, 2016, two experiments were conducted in Caninde de Sao Francisco, State of Sergipe, in the Brazilian semi-arid. The experimental design was randomized complete blocks, with four replications. The treatments consisted of four doses of N (0; 80; 160 and 240 kg ha-1). Joint analysis of variance was carried out, considering each different harvest as a new factor. The characteristics evaluated were the content of nitrogen (N), phosphorus (P), potassium (K), calcium (Ca) and magnesium (Mg) in the leaves, height of the plant, diameter of the stem,green mass productivity, dry mass productivity and percentage of dry mass. The macronutrient content in the leaves was incremented with increasing doses of N, except Ca which presented no influence. The winter crop promoted the highest content of K, while the summer crop presented an elevated absorption of Mg. The varying dosage of N or the harvests season did not influence dry mass productivity (average of 17,386 ton/ha-1). The content of N (23.16-26.68 g kg-1), P (3.16-4.11 g kg-1), K (10.98-33.36 g kg-1), Ca (3.61 g kg-1) and Mg (4.78-9.64 g kg-1) can be considered enough for the full development of the plant.