SOIL ORGANIC CARBON LEVELS INCREASE IN TEXAS TRIALS.

Authors: Halvorson, Ardell; Mosier, Arvin; Reule, Curtis

Submitted to: Fluid Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/20/2004
Publication Date: 1/1/2005
Citation: Halvorson, A.D., Mosier, A.R., Reule, C.A. 2005. Soil organic carbon levels increase in texas trials. Fluid Journal. Vol. 13(1): 8-11.

Interpretive Summary: Carbon sequestration in agricultural soils can help offset greenhouse gas emissions from agricultural practices used in food and fiber production. Studies were conducted in Texas and Colorado to determine the effects of crop management practices on soil organic carbon (SOC) sequestration and greenhouse gas emissions in irrigated continuous corn production systems. At the two Texas sites, reduced tillage (RT) systems were used with two N fertilization treatments (N1 and N2). The N1 treatment had N fertilizer rates sufficient to achieve >250 bu/A corn yield. The N2 treatment received the same N fertilizer as for N1 plus additional liquid N applied to the corn residue after harvest and before fall tillage to aid in residue decomposition. Corn grain yields, residue yields, and residue C levels were similar for both N treatments at the Texas sites. SOC increased linearly with each additional corn crop from 1999 through 2002 at both Texas sites, but SOC levels were similar for both N treatments after 4 years. At the Colorado site, two tillage treatments [conventional plow tillage (CT) and no-till (NT)] with N rates from 0 to 180 lb N/A were used. Corn grain yields, crop residue production and residue C increased with increasing N rate for both NT and CT systems. Corn residue and residue C amounts did not vary with tillage system. SOC increased linearly with each crop year in the NT system, but showed no increase in the CT system. Trends were for N fertilization to be increasing SOC when compared to plots with no N fertilizer applied in the NT system. At the Colorado site, nitrous oxide (N2O) emissions increased with increasing N rate, but were similar for both tillage systems. Carbon dioxide emissions were not affected by N fertilization, but were higher with the CT system than with the NT system. The soil was a small source of methane under irrigated conditions, but methane emissions did not vary with N fertilization or tillage system. Farmers need to apply N to optimize yields and economic returns, but should take care to use only that amount of N fertilizer needed for optimum yield in order to minimize NO3-N leaching potential and N2O emissions in irrigated systems.

Technical Abstract: Carbon sequestration in agricultural soils can help offset greenhouse gas emissions from agricultural practices used in food and fiber production. Studies were conducted in Texas and Colorado to determine the effects of crop management practices on soil organic carbon (SOC) sequestration and greenhouse gas emissions in irrigated continuous corn production systems. At the two Texas sites, reduced tillage (RT) systems were used with two N fertilization treatments (N1 and N2). The N1 treatment had N fertilizer rates sufficient to achieve >250 bu/A corn yield. The N2 treatment received the same N fertilizer as for N1 plus additional liquid N applied to the corn residue after harvest and before fall tillage to aid in residue decomposition. Corn grain yields, residue yields, and residue C levels were similar for both N treatments at the Texas sites. SOC increased linearly with each additional corn crop from 1999 through 2002 at both Texas sites, but SOC levels were similar for both N treatments after 4 years. At the Colorado site, two tillage treatments [conventional plow tillage (CT) and no-till (NT)] with N rates from 0 to 180 lb N/A were used. Corn grain yields, crop residue production and residue C increased with increasing N rate for both NT and CT systems. Corn residue and residue C amounts did not vary with tillage system. SOC increased linearly with each crop year in the NT system, but showed no increase in the CT system. Trends were for N fertilization to be increasing SOC when compared to plots with no N fertilizer applied in the NT system. At the Colorado site, nitrous oxide (N2O) emissions increased with increasing N rate, but were similar for both tillage systems. Carbon dioxide emissions were not affected by N fertilization, but were higher with the CT system than with the NT system. The soil was a small source of methane under irrigated conditions, but methane emissions did not vary with N fertilization or tillage system. Farmers need to apply N to optimize yields and economic returns, but should take care to use only that amount of N fertilizer needed for optimum yield in order to minimize NO3-N leaching potential and N2O emissions in irrigated systems.