Prediction of plant available copper, zinc and phosphorus in arable soils : comparison of diffusive gradients in thin film (DGT) technique with soil extraction methods

Abstract: Nutrient deficiencies in crop production are today a worldwide problem. To maximize fertilizer efficiency and crop yields it is important to be able to assess the accurate amount of available nutrients in the soil (Mason et al., 2005). There are different methods to assess plant available nutrients in the soil and asses the risk of nutrient deficiency. Soil extraction analyses like Aqua regia (HNO3 + HCl), HNO3, EDTA, DTPA, CaCl2 and P-AL are often used in purpose to assess available nutrients (Tandy et al., 2011). Copper, zinc and phosphorus are all essential nutrients which the plant requires. Diffusive gradients in thin films (DGT) is a fairly new method, a gel tech-nique which accumulates metals and phosphates in soil (Zhang, 2003). This study was carried out in the middle to Southern part of Sweden, fourteen different soils from agricultural fields were chosen with cultivated wheat (Triticum aestivum). All the laboratory work was done at Swedish universi-ty of agriculture sciences (SLU) in Uppsala. The objective with this study was to investigate and compare the DGT technique with three conventional extraction methods: HNO3, CaCl2 and P-AL. The concentration of copper (Cu), phosphorus (P) and zinc (Zn) was measured by all methods and was then compared with the plant Cu, P and Zn concentration, to see which method that correlated best with the plant uptake. All methods predicted Cu concentration significantly but DGT technique was the most accurate meth-od (R2=0.64). Extracted Zn and P were not significantly correlated to the Zn or P concentration in the plant, or of DGT or any other extraction method. Copper and phosphorus concentration measured by the DGT technique showed significant correlation between the extracted Cu and P by P-AL, HNO3 and CaCl2. Zinc measured by DGT did neither prove significant cor-relations to the Zn plant concentration or to extracted Zn concentrations by HNO3 and CaCl2. It was concluded that DGT was found to be the most accurate method for predicting plant available Cu but not for P or Zn. Further research has to be done before DGT can become one of the conventional trustworthy methods.