Mehlich III predicts that soils in Wisconsin and Illinois may cause nickel deficiency in crops

Background and aims Nickel (Ni) is essential to plants and Ni deficiencies have been proven in Oxisols of Brazil and scattered crops and soils in the US. However, little research has been conducted to assess the spatial variability and Ni deficiency more widely. By adding Ni to the analysis suite at a commercial soil testing lab, extractable Ni data was collected on a larger scale than any survey to date. The data were compared to published critical soil test levels to estimate to what, if any, extent Ni deficiencies exist. The large area from which the samples originated allowed for a preliminary assessment of spatial variability, and the suite of other tests performed by the lab allowed for correlations between Ni and other soil parameters to be explored. Methods 37,504 soil samples were collected using generally accepted soil sampling procedures from a region representing approximately 45,600 ha across Wisconsin and Northern Illinois and submitted to a commercial lab for fertility analysis. Samples were dried at 53 °C, pulverized, and sieved to 2 mm. Available Ni was extracted with Mehlich III (M3) solution and analyzed by ICP-OES. Results The M3-extractable Ni results correlate with estimated CEC and M3-extractable Ca and Mg. Nickel results show distinct population differences between soils of Wisconsin and Illinois. Interpreting Ni levels by existing published criteria suggests that Ni supplementation could cause perennial ryegrass yield responses in 2.4 to 99.9% of soil samples, depending upon the geographic origin of the samples and which of three critical Ni levels was used. Conclusions Soils of the U.S. are likely to cause Ni deficiency. This study will lay the groundwork for a fuller understanding of soil Ni availability and concentrations and justify further efforts to develop critical soil test levels for M3-extractable Ni under a variety of cropping systems.