ABSTRACT
The experiments were conducted to verify the effect of doses and application time of boron (B) in the grain yield of maize and to study different plant tissues as a nutritional diagnosis tool for B. Six doses of B (0, 1, 2, 3, 4 and 12 kg ha−1) and two application times (before at sowing and V6 growth stage) were tested. In the first growing season, the B doses and application time did not influence yield components of maize. While the second growing season, B application reached maximum grain yield with 5.0 kg ha−1 at sowing, but at a high dose provided toxicity causing injuries in the cobs. In general, the B content in the leaf at flowering stage was higher with the application at V6 growth stage. B content and distribution in the leaves close to the cob vary with the rainfall that occurs before to the collection, harming the definition of the critical leaf level. The B content in the silk can be a reliable alternative for checking the deficiency or toxicity of this nutrient in the plant, presenting critical level for deficiency (calculated) of 23.2 mg kg−1 while values above 31.5 mg kg−1 can be considered toxic.