Five greenhouse experiments were conducted to determine adequate and toxic levels of boron in upland rice, common bean, corn, soybean and wheat. The boron treatments were 0, 1, 2, 3, 6, 12 and 24 mg B kg-1 of soil for rice and corn and 0, 1, 2, 3, 6 and 12 mg B kg-1 of soil for common bean, soybean and wheat crops. Maximum dry matter yield of the tops of rice, common bean, corn, soybean, and wheat was obtained with the application of 0.4, 2.0, 4.7, 3.4, and 0.4 mg B kg-1 of soil, respectively. Toxic levels of B, responsible for a 10% yield reduction were 3.0, 4.4, 8.7, 6.8, and 7.4 B kg-1, respectively for the same crops and, based on soil analysis, the adequate levels of B were found to be 0.4, 0.9, 1.3, 2.6 and 0.4 mg B kg-1 of soil. Similarly, the toxic levels of B in the soil for these crops were 2.3, 2.8, 5.7, 5.2, and 4.3 mg B kg-1 of soil, respectively. Adequate levels of B in the plant tissues varied from 10 to 75 mg B kg-1 and toxic levels varied from 20 to 153 mg B kg-1 of dry tissue depending on crops.
dry matter yield; root length; B concentration in plant; B concentration in soil
