Nickel Analysis in Soils

A large number of approaches, including diethyltriaminepentaacetic acid (DTPA), BaCl₂, Sr(NO₃)₂, and ammonium acetate among others (48,65) are used to extract metals from soils in an attempt to predict nickel availability to plants. The DTPA method, however, is probably the most commonly used (48,66,67) and has been shown to be quite effective for a variety of soils to define Ni excess. The DTPA method is improved significantly if factors such as soil pH and soil bulk density are incorporated into the resulting regression equation (65). Many authors (48,65), however, observe that plant species and soil environment (water, oxygen content, and temperature) can markedly affect the relationship between soil-extractable and plant-nickel concentrations (2). These results suggest that the condition under which the soil is collected and tested can significantly influence the interpretation of results. Nickel deficiency is also known to be exacerbated by environmental conditions that limit uptake (cold, wet weather) and by the oversupply of apparently competing elements such as Cu, Mn, Mg, Fe, Ca, and Zn (2). Nickel bioavailability can also be determined by the ion-exchange resin (IER) method, which has been used quite successfully in a limited number of soil types and facilitates the in situ assessment of exchangeable nickel (68).