A long term trial of boron fertilization was conducted with cotton in a latin square design, firstly installed in 1983 on a low fertility Dusky Red Latosol, limed and frequently fertilized without boron. Rates of 0, 0.2, 0.4, 0.8, 1.6 and 3.2 kg/ha of B as borax (11% of B), were applied annually at planting time. The cotton variety used was the IAC-20. The plots were limed in the fourth, sixth and nineth years. In the seventh year Canajus indicus was cultivated, in crop rotation, to control the increasing incidence of nemathodes. After the eighth year, there was intense attack of Anthonomus grandis Boheman. Thus, cotton yield diminished from the first period, of three years, to the last, while the effect of boron accumulation increased in this sense. In the first period, there was an enchance of yield at rate of 0.4 kg/ha of B, but after lime reaction the best responses were obtained with 0.8 kg/ha of B. The plants were more sensitives to fertilization in terms of boron concentration in the leaf blade, specially after liming. Rates of 1.6 and 3.2 kg/ha of B were injurious starting from the beginning of the study. After liming, yield decreases were related with B concentration higher than 50 mg/kg in leaf blades. Results of soil analysis in the nineth year, indicated a great residual effect of boron accumulation in the 0-20 cm soil layer, as well as leaching of the micronutrient at least down to 40-60 cm deep, in proportion to the rates applied.
long term trial; boron accumulation; yield and foliar analysis of cotton; soil analysis; correlations