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Fluid Journal : Fluid Journal 2005-2007
Winter 2005 Soil Organic Carbon Levels Increase in Texas Trials Dr. Ardell Halvorson, Dr. Arvin Mosier, and Curtis Reule Summary: Corn grain yields have varied due to climatic variation between years and site differences in Texas. At Texline they have averaged 213 bu/A and at Dalhart 217 bu/A. Total residue biomass and residue carbon (C) returned to the soil has been slightly greater at the Texline site (clay loam) than at the Dalhart site (fine sandy loam). Four-year trends in soil organic carbon (SOC) and total soil nitrogen (TSN) show that SOC and TSN levels are increasing at both sites. The SOC and TSN levels of the cropped fields have equaled or exceeded those of native sod. Several more years of data collection will be needed to ascertain whether or not the addition of liquid N fertilizer in the fall to the corn residue before tillage will benefit SOC sequestration. Residual soil NO3-N levels were very low under native sod at both sites compared with the cropped areas. Residual soil NO3-N levels at both cropped sites have increased since 1999. Residual soil NO3-N at both sites was greater where N fertilizer was applied to corn residue after harvest (N2) than with the (N1) fertilizer management treatment. Farmers need to apply nitrogen (N) to optimize yields and economic returns, but should take care to use only that amount of N fertilizer needed for optimal yield in order to minimize NO3- N leaching potential and nitrous oxide (N2O) emissions (a greenhouse gas influencing global warming) in irrigated systems. N2O emissions increase with increasing N fertilizer rate; therefore, avoiding excess N application helps preserve environmental quality. Ongoing study so far shows that maximizing soil productivity in a reduced-till, irrigated contiuous corn production system benefits soil organic carbon sequestration. Fluid Journal 1 Two observation sites in northwest Texas, located near Dalhart and Texline, were initiated in April 1999. Following the 1998 cropping season, two N fertility management levels were established at each location on center- pivot irrigated fields that were being continuously cropped to corn by Jim Poole and business associates. Each pivot received a normal fertilization program (N1) sufficient to produce greater than 250 bu/A corn. Half of each pivot received additional liquid N fertilizer, applied to the corn stalks prior to fall tillage operations to aid in corn residue decomposition (N2) and possibly enhance SOC sequestration. A DMI Ecotiller, a heavy-duty combination disk/chisel plow/ripper implement with a tillage depth of about 12 to 14 inches was used in the fall after harvest. A tandem disk was used in the spring for seedbed preparation. When the corn was about 2 feet tall, an inter-row ripper- dammer/diker machine was used to control weeds between the rows and create small dams between corn rows to reduce water runoff from the field. Herbicides were also applied. The corn planter was equipped with a coulter and residue managers in front of the seed opener. Plant populations have aver- aged 29,222 plants/A at Dalhart and 32,932 plants/A at Texline from 1999 through 2002. Available information on the long- term effects of N fertility and tillage system on crop residue production and its subsequent effects of SOC in irrigated cropping systems in the Great Plains is limited. Therefore, in 1999 the authors, in cooperation with Mr. Poole and the Fluid fertilizer Foundation (FFF), selected two irrigated continuous corn fields in north Texas that had been broken out of native sod in 1995. Our objective was to monitor changes in SOC and residual soil NO3-N over time. Mr. Poole and the FFF were also interested in evaluating the effects of maximum soil productivity (high level of plant nutrient and water) on SOC sequestration.
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