Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/28/2006
Publication Date: 8/22/2006
Citation: Favaretto, N., Norton, L.D., Joern, B.C., Brouder, S.M. 2006. Gypsum amendment and exchangeable calcium and magnesium affecting phosphorus and nitrogen in runoff. Soil Science Society of America Journal. 70(5)1788-1796.
Interpretive Summary: Loss of nutrients through surface runoff and soil erosion is a major environmental concern. Phosphorous (P) loss from agricultural systems is mainly associated with runoff whereas nitrogen loss can result from both runoff and leaching. We studied the effect of adding gypsum (a common amendment to control erosion) on the amount of N, P, and sediment in runoff and the amount of runoff. We studied small runoff plots using a soil typical of the Midwestern corn-belt treated with gypsum or having differing calcium (Ca) and magnesium (Mg) ratios and a non-treated soil. All plots were amended with N, P, and potassium (K) based of soil tests with amounts according to standard recommendations for corn. Rainfall simulation was applied with two intensities and runoff and infiltrating water were measure every five minutes over two hours. We found that addition of gypsum compared to the untreated soil decreased the amount of soluble P, total P, soluble ammonium-N and total N in runoff. Nitrate-N in runoff was not affect by gypsum amending. Gypsum also reduced the amount of sediment runoff and water soluble P in soil. The difference between Ca/Mg treated soils were that high Ca soils reduced the amount of P compared to high Mg soil. The impact of this research is that gypsum application in addition to decreasing soil erosion can also reduce the amount of N and P in runoff and help control a major environmental water quality concern.
Technical Abstract: The beneficial effect of gypsum and high Ca on the exchangeable complex in controlling erosion by improving soil structure and increasing water infiltration has been demonstrated. Phosphorus loss in agricultural systems is strongly associated with runoff and erosion while N loss is more related to subsurface leaching. The main objective of this study was to evaluate the effect of gypsum amendment and soil exchangeable Ca on the concentration and loss of nutrients in runoff, sediment, and soil. The experiment was carried out in the laboratory using a programmable rainfall simulator and erosion pans (32-cm wide, 45-cm long, and 20-cm deep). The soil was a Miami silt loam (fine-loamy, mixed, mesic Oxyaquic Hapludalf) and treatments were: gypsum (5000 kg ha-1); five exchangeable target Ca/Mg ratios (90/10, 80/20, 50/50, 20/80, 10/90); and a control. 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 solution to adjust the electrolyte concentration similar to the control. Nitrogen, P and K were applied in all seven treatments based on soil test results and standard recommendations for corn (Zea mays L.). The fertilizers were mixed to a 2.5-cm depth before prewetting the soil. Gypsum was applied to the surface just before the rain. Two rainfall intensities were simulated, and infiltrated water and runoff samples were taken every 5 min over 2 h. Nitrate N, NH4-N, and P in runoff, sediment, and soil were determined. The results showed that gypsum as compared to the control significantly decreased the concentration and loss of dissolved reactive P, total P, soluble NH4-N, and total N in runoff. Nitrate N in runoff was not affected by gypsum. Gypsum also affected sediment and soil water extractable P. The only significant effect of exchangeable Ca/Mg ratios was observed in the sediment water extractable P, where Ca-treated soil decreased the concentration of P compared to Mg-treated soil. The results of this study demonstrated the important potential of gypsum in decreasing transport of total N and total P as well as the importance of Ca in the soil solution on decreasing P solubility.