CRESCIMENTO, QUALIDADE INDUSTRIAL E BALANÇO DE NUTRIENTES DE CULTIVARES DE CANA-DE-AÇÚCAR SOB ADUBAÇÃO NO CERRADO

Abstract

The fertilizer application must be done in a planned manner to ensure an appropriate nutrient supply. This paper aimed to evaluate the response of sugarcane cultivars to the addition of increasing NPK doses in Oxisol in Ceres municipality, Goiás State (GO), Brazil. Two experimental designs were used. The first experiment related to the sugarcane growth phase was at completely randomized design (CRD), in a 2x4x7 split-plot scheme, being two cultivars (RB92579 and SP801816), four NPK 05-25-25 fertilizer doses (0, 250, 500, and 750 kg ha-1), seven evaluation periods, (every two months) with four replicates. In the second experiment (end-cycle), there was no period factor, setting a 2x4 factorial arrangement, also with four replicates. The growth variables were: (a) number of profiles (NP); (b) plant height (PH); (c) culm diameter (CD); (d) number of green leaves (GL); and (e) number of buds (NB). The end-cycle variables were: (a) ton of culms per hectare (TCH); (b) °Brix; (c) apparent sucrose content in the broth (Pol); (d) fiber content (FC); and (e) total recoverable sugars (TRS). Phosphorus and potassium nutrient balance in the soil and crops was also evaluated. The growth variables of NP and PH showed significant interaction between cultivar and fertilization. All growth variables had significant interactions between cultivar/period and fertilization/period. The RB92579 cultivar responded linearly to NPK doses for NP and PH. The SP801816 cultivar had quadratic adjustment for PH and had not adjustment to the models tested for NP, CD, and NB. GL and NB showed adjustment for doses (isolated factor) to the quadratic model. In the cultivar/period interaction, the RB92579 cultivar had adjustment to the linear model for PH and NB, to the cubic model for NP and GL, and to the quadratic model for CD. The SP801816 cultivar responded in a linear way to NP, PH, and GL, in a quadratic way to CD, and in a cubic way to GL. For end-cycle variables, only TCH has not showed significant interaction between cultivar/fertilization, as well as for isolated factors. For end-cycle variables, fertilization influenced the ºBrix, Pol, FC, and total reducing sugar (TRS). For RB92579 cultivar, the response was linear for oBrix, Pol, and TRS with no adjustment for FC. The SP801816 cultivar was adjusted (in a linear way) only for FC. Maximum tillering occurred at 150th day after planting (DAP) in the RB92579 cultivar and was linear for the SP801816 cultivar. The P extraction by the culms increased up to the 500 kg ha-1 dose for4 both cultivars, and potassium extraction by the culms increased up to the 500 and 750 kg ha-1 of NPK 5-25-25 doses for the SP801816 and RB92579 cultivars, respectively. The maximum technical efficiency of NPK 05-25-25 doses for the RB92579 and SP801816 cultivars vary from 455.6 to 750 and 442.7 to 750 kg ha-1, respectively. The RB92579 cultivar showed higher yield (9.7%-TCH) than the SP801816 cultivar. Doses from 500 kg ha-1 showed a positive balance for K and P, respectively, for sugarcane plant, not affecting the reserves of these nutrients in the soil under this study conditions.