Nitrogen is the mineral nutrient required most by plants. There are, however, no studies on N fertilization calibration for rooted cocoa tree cutting production on substrate and frequent irrigation. The objective of this study was to compare the efficiency of urea fertilization on substrate and leaves for rooted cocoa tree cutting and to define N recommendable doses and foliar critical N level. The experiment was set up in a rooted cutting breeding nursery of the Cocoa Biofactory Institute, in Ilheus, Bahia, in July 2006, involving 10 treatments (two fertilization treatments and five urea doses), in random blocks with four repetitions. Each plot consisted of 12 rooted cocoa cuttings in plastic tubes, containing 288 cm³ substrate (50 % coconut fiber and 50 % Plantmax®). The substrate was limed with 3.20 kg m-3 and fertilized with 2.68 kg m-3 of single superphosphate. The treatments were applied between the 82nd and 138th day, with the following weekly N doses to the substrate (0, 20, 40, 60 and 80 mg dm-3) and to the leaves (0.0, 2.25, 4.5, 9.0 and 13.5 g L-1). For all treatments, fertilization was supplemented with P, K, S, Zn and B via substrate. On the 145th day, the plants were harvested to evaluate diameter, height, leaf area, shoot dry matter (SDM), nutrient concentration in the diagnostic leaf and nutrient content in the shoot. The biometric and nutrient variables responded to treatments. Adding urea to the substrate led to the maximum yield, exceeding foliar fertilization for SDM, height and leaf area. The N doses recommended to obtain 99 % of the maximum yield varied, according to the biometric variable, from 43 to 76 mg dm-3 for fertilization on substrate and from 9.1 to 11.7 g L-1 for foliar fertilization. The critical foliar N level to obtain 99 % of the maximum yield of SDM by foliar fertilization was 23.1 g kg-1 N.
Theobroma cacao; nutrition; foliar fertilizer; critical level; soilless crop; nitrogen
