Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/29/2011
Publication Date: N/A
Citation: Interpretive Summary: Water quality from the downward movement of nitrogen and phosphorous into ground or drainage water is a major environmental concern from addition of fertilizers in agriculture. We conducted a laboratory study on a typical midwestern USA cornbelt soil to determine the if adding gypsum to the soil or increasing the amount of calcium in the soil could reduce the amount nitrogen of phosphorous leached. Addition of gypsum to the surface of the soil significantly decreased the amount of phosphorous leached from applied fertilizer, increased the amount of ammonium nitrogen lost but had no effect on nitrate leaching. The amount of calcium level compared to magnesium in the soil did not affect the leaching results except the high calcium content decreased clay dispersion and lowered the amount of particulate phosphorous in the leachate compared to the high magnesium soil which favored dispersion. The floculation effect from the electrolyte from gypsum was more effective at reducing clay dispersion than just increasing the calcium content alone. The practical impact from this research is that fertilizers can be co-applied with gypsum to reduce the loss of soluble phosphorous and potentially make amonium nitrogen more available for plants. Changing the calcium level in the soils does not seem to effect the leaching of either nitrogen or phosphorous.
Technical Abstract: The movement of N and P from the soil by leaching contributes to losses from agricultural land and represents an important environmental and human health concern. The objective of this study was to evaluate the effect of gypsum amendment and the resultant impact of different levels of exchangeable Ca and Mg in the soil on movement of P, NH4-N, and NO3-N movement in infiltrated water and soil. A column experiment was carried out using a Miami silt loam soil (fine-loamy, mixed, mesic Oxyaquic Hapludalf) with the following treatments: control; gypsum applied at the surface; gypsum mixed at 2.5-cm depth; and five different soil exchangeable Ca/Mg ratios (90/10, 80/20, 50/50, 20/80, 10/90). Calcium and Mg ratio on the soil exchange complex was modified by saturation with CaCl2/MgCl2 solutions according to the target ratio followed by washing with CaSO4/MgSO4 solutions to adjust the electrolyte concentration similar to that of the control. A clear plexiglass cylinder was filled with a 15-cm layer of soil, and N, P, and K were applied all together in solution at the surface after the soil had been wetted and drained. Deionized water at a flow of 0.5 ml per min was applied and eight leachate fractions, totaling about 5 pore volumes, were collected. Gypsum (5000 kg ha-1) applied at the surface and mixed in a 2.5-cm depth significantly decreased P and increased NH4-N, but did not affect NO3-N concentration in leaching. Exchangeable Ca/Mg treatments did not affect soluble nutrient losses; however, particulate P was significantly less in the Ca-treated soil when compared with the Mg-treated soil as a result of a decrease in clay dispersion. Electrolyte concentration (gypsum) was more efficient than exchangeable Ca on controlling clay dispersion, but this difference did not affect P-sediment transport. Soil P and NH4-N mobility was decreased and increased, respectively, by gypsum amendment.