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Fluid Journal : Fluid Journal 1999-2001
3 Fluid Journal Summer 2000 Sod 0 5 10 15 20 SOM (t/acre) 25 30 35 40 Dryland Farm, Grant, NE 0-6" depth 6-12" depth NT CT buried by tillage from 1953 until 1981. Tillage mixed the crop residue with soil, putting it in direct contact with soil microbes that break down the resi- due, releasing CO2 and nutrients. Till- age provides aeration to the soil, which accelerates residue decomposition. Even though tillage was more intensive in this irrigated environment, the quan- tity of crop residue returned to the soil increased with increasing N rate, which had a positive effect on SOM concen- tration. Advantage no-till The influence of tillage system on SOM is vividly demonstrated in the samples collected from a dryland farm near Grant, NE, in June 1999. Soil samples were taken from four separate locations in each field and analyzed separately. The NT field had previously been in a crop-fallow CT environment for 25+ years before conversion to an NT more intensive cropping system. The SOM levels shown in Figure 4 reflect the positive influence of NT and an intensive crop rotation after 27 years (winter wheat, corn, millet being the predominant crops in rotation with no fallow). The SOM in the NT field is contrasted with that from an adjacent field, on a similar soil and slope. The field was maintained in a CT environ- ment with a predominantly crop-fallow farming system during the same time period of the NT field. For comparison, we also sampled a native sod area in the adjacent farmstead, which its owner claimed had never been tilled. As you can see, the NT system had much higher levels of SOM than the CT field. After 27 years, SOM level in the NT system was 85 percent of the native sod SOM level in the 0 to 6-inch soil depth, whereas the SOM level of the CT field was only 40 percent of the native sod level. In the 6- to 12-inch soil depth, SOM levels of NT and CT fields were 82 and 35 percent, respectively, of the native sod SOM level. Dr. Halvorson and Mr. Reule are soil scientists, USDA/ARS, Ft. Collins, CO; Dr. Murphy is president of the Fluid Fertilizer Foundation, Manhattan, KS. Figure 4. Comparison of SOM levels between an NT system after 27 years, a CT system after 50+years, and native sod, Halvorson, et al., Grant, NE.
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