The Boron Problem on Guatemalan South Coast Soils.

Boron (B) availability in Guatemalan south coast soils is known to be low, and the main crops (sugarcane and bananas) grown in the area show B deficiency symptoms with little response to B fertilizer applications to the soil at normal rates. The outputs from a chain of volcanoes forming the backbone of the country influence the properties of the soils in the region, although the soils are not all classified as Andisols. Previous studies on Mexican and Hawaiian volcanic soils have revealed high capacities for B adsorption due to the presence of large amounts of amorphous minerals and organic matter. A group of representative soils with economic importance on the south coast region of Guatemala have been selected for a detailed laboratory study of B adsorption in relation to their physicochemical properties. The study includes the determination of clay content and surface area, identification of minerals in the clay fraction with X-ray diffraction (XRD) and thermal analysis, and quantification of the andic character of the soils based on pH in fluoride and the Al, Fe, and Si extracted from amorphous minerals by acid oxalate solution. Preliminary results show that the B adsorption capacities these soils range from 3 mg B kg^-1 for a loamy sand soil with a surface area of 16 m² g^-1, to 90 mg B kg^-1 for a loam soil with a surface area of 98 m² g^-1. B adsorption was positively correlated with the andic character of the soils, suggesting that the high adsorption capacities were the reason for the lack of response to B fertilizer applied to soil at low rates.