Critical and toxic boron levels in corn plants and soils of Pernambuco, Brazil

Research on B availability in soils is essential to assess the crops response to different concentrations of available B in soils. A greenhouse experiment was carried out aiming at studying the corn plant (Zea mays) response to B doses (0, 2, 4, 6, and 12 mg dm(-3)) applied to ten soils from the state of Pernambuco, Brazil. Available B was assessed by three extractants: hot water, HCl 0.05 mol L-1, and Mehlich-1. The critical and toxic levels were determined in soils and plants. Additionally, B toxicity symptoms in corn plants were recorded. Results showed that the critical and toxic B levels in soils ranged from 0.4 to 2.3 mg kg(-1) and from 1.8 to 8.3 mg kg(-1), respectively. For corn plants, the critical levels varied from 13.8 to 129.6 mg kg(-1) and the toxic levels from 43.3 to 372.2 mg kg(-1). HCl 0.05 mol L-1 was the extractant that best correlated with the B plant content, followed by Mehlich-1 and hot water. Both available B assessed by HCl and B plant contents were inversely related to clay and organic matter concentrations in soils. Soils on which plants with highest B contents grew presented the most acute B toxicity symptoms. This was associated with sandy and low organic matter soils.