Effect of Water Logging Conditions on Solubility of Soil Nutrients.

The wide use of herbicides, fungicides, fertilizers, and soil amendments affect the rhizosphere biochemistry and ecology. Soils in the Midwest of the US tend to be saturated in the early spring when snow and ice melt, and frequent rain occurs. This saturation causes the soil to go trough oxidation and reduction cycles. Oxygen enters the soil system through oxygenated rainwater infiltration or by diffusion; after the soil is water logged the O₂ supply is curtailed. Plants and microbes use the O₂, and soil system moves toward being anaerobic. Under these conditions soil nutrient losses are believed to change due to a modification of the soil solution pe and pH. An experiment was designed in order to evaluate the change in solubility of soil nutrients, in a soil subjected to water logging. Four different treatments were evaluated: 1) untreated soil; and surface added 2) glyphosate, 3) gypsum, and 4) glyphosate + gypsum. The soil used was a Toronto-Millbrook complex (fine, silty, mesic Udollic Ochraqualf). Three replicates of each treatment were incubated for 1, 3, 7 and 14 days. The incubations were purged using nitrogen gas with 380ppm of CO₂ at a rate of 15 cm³ min^-1. Hourly readings of pe and pH were measured, and concentrations of NO₃, NH₄, PO₄, and redox-sensitive species were measured for 1, 3, 7, and 14 days. We observed that after 24 hours the soil samples were under sub-oxic conditions, and close to the third day anoxic conditions were achieved. The results of this research showed that the amounts of soluble nitrate and orthophosphate remaining in solution after a 24-hour incubation period increased by the addition of gypsum, indicating that its addition inhibited nitrate and phosphate reduction. The results of this research are important in understanding nutrient losses in periodically saturated soil and its impact on water quality.