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Fluid Journal : Fall 2014
8 The Fluid Journal Fall 2014 applied at rates of 0, 11.2, 22.4, and 33.6 kg N/ha and ATS applied at rates of 16.8 and 33.6 kg S/ha, which also contained 7.7 and 15.5 kg/ha N with a flat fan spray tip. Timing. UAN/ATS were applied at two different timings to separate plots, making a total of 13 treatments (Table 1). The first timing occurred in September after wheat harvest. The second timing took place in February, the second year before temperatures increased to favor microbial decomposition. Residue samples were collected from every research plot in a 0.61 by 0.61 meter area in the summer of 2012, in June and October of 2013 from all three sites. We tried to conduct the sampling at these times when cultivation is commonly in process to simulate the situation cultivator experiences. The residue was sieved to remove any soil and material that may have been collected from the field. It was dried and weighed to calculate total surface residue. A subsample was then ground and sent to the laboratory for total N and total carbon analysis. Shear box A double shear-using shear box was applied to test the shear stress and specific energy required to cut wheat- straw. The shear box consists of two parallel aluminum plates (channel) 6 mm apart (Figure 1). Between them, the third plate (blade) can move up and down along the central axis freely. Five holes with diameters ranging from 2 mm to 6 mm were drilled on all three plates to accommodate different wheat straw sizes. The shear box was then attached to the load cell of a tension/ compression testing machine (Figure 2). The blade was set to move at 10 mm/ min velocity and the applied force was recorded by a strain-gauge load cell. The shear stress was then calculated as: F rs=-- 2A where r2 is the shear stress (MPa), F is the shear force at failure (N), and A is the wheat straw wall area at failure cross section (mm2). The specific energy was then calculated as: Figure 1. Design of shear box through AutoCAD2010 and manufactured shear box. Table 1.Treatments of decomposition experiment and their application time. Treatment N rate (kgGha) S rate (kgGha) Fertilizer application timing 1 Control 0 0 Sept. 2011 Sept. 2012 2 Urea20 11.2 0 3 Urea40 22.4 0 4 Urea60 33.6 0 5 ATS15 7.7 16.8 6 ATS30 15.5 33.6 7 Mixed 49.1 33.6 8 Urea20 11.2 0 Feb. 2012 Feb. 2013 9 Urea40 22.4 0 10 Urea60 33.6 0 11 ATS15 7.7 16.8 12 ATS30 15.5 33.6 13 Mixed 49.1 33.6