Empirical analysis and prediction of nitrate loading and crop yield for corn-soybean rotations

Nitrate nitrogen losses through subsurface drainage and crop yield are determined by multiple climatic and management variables. The combined and interactive effects of these variables, however, are poorly understood. Our objective is to predict crop yield, nitrate concentration, drainage volume, and nitrate loss in subsurface drainage from a corn (Zea mays L.) and soybean (Glycine max (L.) Merr.) rotation as a function of rainfall amount, soybean yield for the year before the corn-soybean sequence being evaluated, N source, N rate, and timing of N application in northeastern Iowa, U.S.A. Ten years of data (1994-2003) from a long-term study near Nashua, Iowa were used to develop multivariate polynomial regression equations describing these variables. The regression equations described over 87, 85, 94, 76, and 95% of variation in soybean yield, corn yield, subsurface drainage, nitrate concentration, and nitrate loss in subsurface drainage, respectively. A two-year rotation under average soil, average climatic conditions, and 125 kg N/ha application was predicted to loose 29, 37, 36, and 30 kg N/ha in subsurface drainage for early-spring swine manure, fall-applied swine manure, early-spring UAN fertilizer, and late-spring split UAN fertilizer (urea ammonium nitrate), respectively. Predicted corn yields were 10.0 and 9.7 Mg/ha for the swine manure and UAN sources applied at 125 kg N/ha. Timing of application (i.e., fall or spring) did not significantly affect corn yield. These results confirm other research suggesting that manure application can result in less nitrate leaching than UAN (e.g., 29 vs. 36 kg N/ha), and that spring application reduces nitrate leaching compared to fall application (e.g., 29 vs. 37 kg N/ha). The regression equations improve our understanding of nitrate leaching; offer a simple method to quantify potential N losses from Midwestern corn-soybean rotations under the climate, soil, and management conditions of the Nashua field experiment; and are a step toward development of easy to use N management tools.     

Synchrotron Infrared Absorbance Measurements of Hydrogen in MgSiO3 Perovskite

Micro-infrared spectroscopic measurements on single crystals of MgSiO(3) perovskite document two pleochroic hydroxyl absorbance peaks at 3483 and 3423 centimeter(-1). These measurements were obtained with the use of a synchrotron infrared source for spectroscopy. These data are consistent with a trace hydrogen content of 700 +/- 170 hydrogen atoms per 10(6) silicon atoms in the nominally anhydrous MgSiO(3) perovskite. When integrated over the volume of the lower mantle, this concentration is comparable to 12 percent of the mass of hydrogen in the Earth's hydrosphere.     

An evaluation of the combined usage of separated liquid pig manure and inorganic fertiliser in nutrient programmes for winter wheat production

The effect of spring application of separated liquid pig manure (LPM) in combination with medium to high levels of inorganic nitrogen (N) to winter wheat was investigated in a field trial study at two sites in two successive growing seasons (2007–2008). The key crop parameters examined were crop N uptake (CNU), N use efficiency and grain yield. The LPM product (3.5–4.0 g/kg total N) was applied at three application rates: 15, 30 and 45 m³/ha using a band spread application technique. The LPM was used in combination with reduced and recommended inorganic N levels; a zero N control was also included. Weather conditions in both seasons were similar with below average rainfall levels in spring followed by above average summer rainfall levels. The zero N control gave lowest CNU levels in both growing seasons (70–88 kg N/ha). Inorganic N application at the reduced and recommended N rates increased CNU levels by approximately 100 kgN/ha and 112 kgN/ha, respectively compared to the untreated control. Liquid pig manure application resulted in an additional crop uptake of 58 kgN/ha. Nitrogen use efficiencies for LPM ranged from 23 to 56% while inorganic N use efficiency levels were higher ranging from 58 to 73%. Lowest grain yield levels were measured from the zero N control (range 3.95–5.01 t/ha). The application of inorganic N increased grain yield levels by a minimum of 4.05 t/ha with LPM usage increasing grain yield levels by an additional 0.2–1.09 t/ha. This study showed that LPM could be successfully used in combination with inorganic fertilisers for the improved N nutrition of winter wheat in spring as part of an integrated nutrient programme.