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Fluid Journal : Fluid Journal 1999-2001
2 Fluid Journal Summer 2000 The study produced very positive changes that promise to enhance the performance of disk drills in NT envi- ronments. Nine years The second N study examined a dry- land, NT crop rotation (winter wheat- corn-fallow, and winter wheat-sorghum- fallow or 3 complete rotation cycles over 9 years), again at Akron. Total above-ground crop residue (averaged over both rotations) increased with in- creasing N rate (Figure 2). This trans- lated into increasing SOM levels with increasing N rates in the 0 to 6-inch soil 80 25 50 75 100 9 10 11 12 13 14 15 16 WCF and WSF Study - Akron Y = 12.48 + 0.024X - 0.000061X R=0.57 2 2 SOM (after 9 years) Crop Residue Refurned (6 crops, 9 years) Y = 9.02 + 0.113X - 0.0007X R=0.99 2 2 Nitrogen Rate (lb N/A) Residue or SOM (t/acre) 2.60 50100150200250300350400 2.7 2.8 2.9 3.0 3.1 3.2 3.3 3.4 Sept. 1953 (Study Inititation) June 1983 Y = 2.66 + 0.00026X + 0.000016X R = 0.986 2 2 N Added To Sugarbeet Crop (lb N/A) Soil Organic Matter (%) depth for both crop rotations. Demon- strated was the positive influence that N fertilization can have on SOM in an NT, dryland cropping environment. Thirty years The third N study involved a small grain/sugar beet rotation conducted under an irrigated, intensive tillage en- vironment (moldboard plowing, disking, mulching, leveling) for seed- bed preparation. The study began the fall of 1953 at Sidney, MT, and contin- ued until 1983. From 1954 through 1959, all crop residues were removed from the plot area. From 1960 through 1980, above- ground crop residues were returned to the soil. In 1981, the study was con- verted to a continuous corn rotation using a reduced tillage, ridge-till sys- tem. Corn stalks were removed in 1981 and 1982. Soil samples were collected in June 1983 to assess SOM levels. The estimated quantity (dry weight basis) of spring wheat straw and sugar beet tops returned to the soil increased with in- creasing N rate. Wheat grain yields, however, were near maximum with re- sidual N remaining from the applica- tions of 200 lbs/A of N to sugar beets. Sugar beet sucrose yields peaked at N rates of about 100 lbs/A. In September 1953, SOM concentra- tion was 3.3 percent for all N treatments (Figure 3). In June 1983, SOM concen- trations in the 0 to 6-inch soil depth were lower than in 1953, with increas- ing SOM concentrations with increas- ing N rate. Soil bulk densities were not measured in 1953 or 1983, therefore we cannot accurately calculate the tons per acre of SOM present for each N rate. The apparent loss of SOM from 1953 to 1983 probably resulted from the inten- sive tillage operations performed to prepare a seedbed for sugar beets. In this study, all surface residue was Figure 3. Changes in SOM as function of N rate in 21 crops over 30 years, Halvorson, et al., Sidney MT. Figure 2. Above-ground crop residue returned to soil and changes in SOM as function of N rate in annual cropping rotation, Halvorson, et al. , 9 years, Akron, CO.
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