Effects of limestone applications on soil pH and extractable elements in a cauliflower field study

Abstract

The pH and Mehlich-3 extractable concentrations of a variety of elements including those that were study treatments (Ca, Mn and Zn) and those that were expected to be influenced by the treatments (Mg, Sr, K, Rb, Na, Al, Fe, Si and Cu) were determined in soil samples from a cauliflower field trial conducted between 1979 and 1985. The treatments were limestone applied to the soil at three rates (0, 9 and 19 Mg ha-1) and Zn and Mn foliar applications. The pH of air-dried samples varied only slightly when analysed within each year of sampling versus as one batch after the trial was completed, which showed that the samples were stable over the long time the samples had to be stored through the field trial period and until the samples were analysed. Being able to do all the analyses in one batch also facilitated the application of quality control to ensure comparability of results. There were differences in the soil measurements of most of the elements taken pre-plant versus post-harvest, showing that the time of sampling must be consistent for experimental and soil test interpretations. Post-harvest samples (i.e., focusing on residual effects of limestone application) were selected to examine the treatment effects. Limestone application had wide-ranging and variable effects on extractable elements in the soil. Soil pH and extractable Ca increased with increased limestone rate as expected, while the amount of extractable Mn, Zn, K, Mg, Na, Al and Fe decreased. Extractable Sr, Si and Cu increased with limestone applications. Extractable Ca, Zn, Mg, Al and Si were affected to 15-30 cm depth, and pH and extractable Mn, Rb and Fe were affected to 30-60 cm. Subsurface (>15 cm depth) Sr, K, Na and Cu were not influenced by the limestone treatments. The effect of limestone on the elements tended to correspond to the effect previously observed on the contents of these elements in cauliflower plants. The ability of Mehlich-3 extract solution to reflect the availability of elements to plants and the effect of limestone applications on other elements simultaneously showed the potential for this soil test solution to predict the need for nutrient amendments to prevent lime-induced deficiencies.