Manganese Geochemistry and Plant Availability in Response to Agricultural Practices

Manganese (Mn) is an essential micronutrient for all organisms. In soils, Mn forms determine availability to plants. Most Mn research has been conducted in forest ecosystems and Mn cycling in agricultural systems is understudied. Therefore, the objective of the experiment is to understand the effect of different agricultural management strategies on Mn cycling and plant availability. First, a greenhouse experiment was conducted to determine the effect of different application rates of two Mn fertilizers (MnSO₄ and MnEDTA) on soil geochemical properties and growth of corn (Zea mays) and soybean (Glycine max). The fertilizers were applied to soil at three different rates (Recommended, 10x, and 50x). Second, a field experiment was conducted to investigate the effects of contrasting land-use systems (Organic and Conventional Agriculture, Unmanaged Forest) on soil geochemical properties and Mn availability. For both experiments, soil analysis included a sequential extraction to understand the distribution of plant available and stabilized Mn. Plant uptake of Mn and other nutrients was measured in the greenhouse experiment. In the greenhouse experiment, both fertilizer types increased available Mn in the soybean group. However, there was only an increase in plant uptake in the MnSO₄ treatment. The MnEDTA treatment decreased Mn uptake with increased Mn application, likely due to competition with Fe. Overall, MnSO₄ has a stronger effect on plant Mn uptake and Mn cycling than MnEDTA. The field experiment showed depleted available Mn levels in the agricultural systems relative to the unmanaged system. Additionally, available Mn forms had a positive relationship with SOC, while unavailable forms had a negative relationship.