Response to Application and Tissue Diagnosis of Boron Deficiency and Toxicity in Maize

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.