Amelioration of soil pH and magnesium concentration with sulfur application

Abstract

Base saturation of magnesium (Mg) in northern Illinois soils is excessive leading to high soil pH. Magnesium has a high influence on soil pH. Lowering the magnesium concentration in soils would lower soil pH. When considering sulfur in crop production, sulfur in the plant and its effect on crop yield increases are commonly studied. In calcareous soils, the addition of elemental sulfur can reduce soil pH. However, the addition of larger amounts of sulfur has been deemed economically unfeasible to lower soil pH. The goal of this creative component was to ascertain if elemental sulfur application is an economically viable practice to lower soil pH. The specific objectives of the project were to 1) show that specific sulfur treatments can lower soil pH, 2) demonstrate a change in base saturation of cations, specifically by reducing Mg with S application, 3) compare changes in total amount of cations in the soil profile, 4) compare yields in those areas over the study period, and 5) analyze cations in comparison with the total CEC of the soil to understand the effects different rates of sulfur application have on base saturations. Soil samples were taken from fields identified as “Field 1,” “Field 21,” and “Field 22” from the Prairie Lane Farms. Initial soil samples were collected in 2016 and compared with soil samples from 2021. Sulfur treatments were AMS, MESZ, or elemental sulfur. For Fields 1, 21, and 22, AMS was applied in December 2017 at rates of 200 or 400 pounds (lbs.) per acre (ac). MESZ was applied at a rate of 100 lbs. ac-1. For comparison, control plots had 0 lbs. ac-1 of sulfur. This study was an on-farm study with naturally unbalanced treatments in the experimental design where each field was considered a “block.” The Generalized Linear Model (GML) was used for statistical analysis with SAS version SAS 9.4M8 to analyze all treatment effects collectively, rather than individually. Results showed an average soil pH of 7.1 in Field 1 from 2016 to 2021 in the range of 7.0 to 7.5 with an average change in pH units of 0.3. In Field 21, the average soil pH was 7.4 in the range from 7.1 to 7.9 from 2016 to 2021 with an average change in pH units of -1.0. In Field 22, the average soil pH from 7.4 in the range from 7.1 to 7.8 from 2016 to 2021 with an average change of -0.1 in pH units. Across the three fields, the average soil pH was 7.4 from 2016 to 2021. The results showed changes in magnesium in all the three fields between 2016 and 2021. In Field 1, Field 21, and Field 22, magnesium decreased by 6.5% or 145.9 pounds per acre, 7.9% or 267.2 pounds per acre, and 5.9% or 438.1 pounds per acre, respectively. Corn and soybean yield between 2016 and 2021 across all three fields showed yield decreases. The results from this study showed that sulfur applications can be an effective soil management strategy to reduce soil pH and the magnesium in high magnesium content soils. However, it will be difficult to link any changes in corn and soybean yields directly to any one change in soil fertility management, including the application of sulfur as a soil amendment. Experimentation with soil management practices that seek to enhance soil fertility and quality should not be included in a soil fertility program if soil nutrient levels are lower than sufficiency levels to achieve production goals.