Adubação de cobertura com nitrogênio, potássio e cálcio na producão de cenoura

Abstract

Carrot is the major vegetable with a commercial root. This study evaluated root yield, number and quality of carrot cultivar Brasília - RL, under different top-dressing fertilizations. The experiment was done on a Red-Yellow Latosol (Latossolo Vermelho- Amarelo), at Fazenda Olhos D Água, in São Gotardo - MG, from January to April 2006. The experimental design was randomized blocks with nine treatments (T0 = no topdressing control; T1 = 100 kg 20-00-20 ha-1 at 30 and 45 days after sowing; T2 = 200 kg 20-00-20 ha-1 at 30 and 45 days after sowing; T3 = 300 kg 20-00-20 ha-1at 30 and 45 days after sowing; T4 = 200 Kg 20-00-20 at 30 days after sowing; T5 = 200 kg 20-00-20 ha-1 at 45 days after sowing; T6 = 300 kg 20-00-20 ha-1 at 45 days after sowing; T7 = 130 kg Nitrocalcium ha-1 at 30 and 45 days after sowing; T8 = 130 kg Nitrocalcium ha-1 at 30 days after sowing and 133 kg 15-00-14 ha-1 at 45 days after sowing) and five repetitions. The root number and weight in each commercial class was evaluated: 10 (>10 < 14 cm), 14 (> 14 < 18 cm), 18 (>18 < 22 cm), 22 (> 22 < 26 cm), 26 (> 26 cm), the commercial (C), the non commercial (NC) and total (T) root number and weight were also evaluated. The total number of carrot roots (T) did not present significant differences with the top-dressing fertilizations. However, the total number of commercial roots (C) varied significantly with the top-dressing with increasing doses of the 20-00-20 (N-P2O5-K2O) fertilizer and the additional treatments. Root yield (kg ha-1) presented, in general, results similar to those observed for root number, with the exception of total (T) root yield (kg ha-1), which presented a significant change with topdressing fertilization and the increasing doses of the 20-00-20 fertilizers vs. additional treatments. Total yield of commercial roots (C) changed significantly with increasing doses of the fertilizer 20-00-20. Maximum root yield (27,505.1 kg ha-1) was obtained with the fertilization with 229.1 kg ha-1 of 20-00-20. However, this result is not significantly different from the yield of commercial roots obtained with the use of the additional treatments. No significant differences were observed among the treatments in the experiment, nor in the interaction of increasing doses of the 20-00-20 fertilizer in vs. additional treatments. The joint application of nitrogen, potassium and calcium sources increased commercial root yield, especially of those classified as C-18, which is the major commercial class, presenting greatest economical value, demand and is the most accepted in the market.