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Title: LONG-TERM NITROGEN FERTILIZATION BENEFITS SOIL CARBON SEQUESTRATION

Author
item Halvorson, Ardell
item Reule, Curtis

Submitted to: Better Crops
Publication Type: Popular Publication
Publication Acceptance Date: 11/10/1999
Publication Date: N/A
Citation: Halvorson, A.D., Reule, C.A. 1999. Long-term nitrogen fertilization benefits soil carbon sequestration. Better Crops with Plant Food. 83(4): 16-20.

Interpretive Summary: Nitrogen fertilization is essential to assure economic yields from annual dryland cropping systems. We studied N fertilization effects on crop residue production and its subsequent effects on soil organic C (SOC) and total soil N (TSN) within a dryland no-till (NT) annual cropping system. Six N fertilizer rates (0, 20, 40, 60, 80, and 120lb N/a) were applied to the same plots cropped to either spring barley, corn, winter wheat, or oat/pea hay each year from 1984 through 1994. Phosphorus, 69 lb P2O5/a, was applied to half of each plot in 1984. Barley responded to the P application in 1984 with a resulting increase in SOC due to P fertilization. Crop residue returned to the soil (excluding hay years) averaged for the above respective N rates. Increasing residue production with increasing N rate increased SOC and TSN in the 0- to 3-inch soil depth after 11 crops and decreased soil bulk density. Nitrogen fertilization increased C sequestered in the soil. This study demonstrates that C-seque on can be enhanced by increasing crop residue returned to the soil through improved N fertility in a no-till system. Increasing the level of SOC and TSN through N fertilization will enhance soil productivity.

Technical Abstract: No-till in the Great Plains has increased the potential to crop more frequently than with the traditional conventional-till crop-fallow system of farming. More intensive cropping requires N input to maintain economical yields. This study evaluated the effects of N fertilization rates on crop residue production and its subsequent effects on soil organic cC (SOC) and total soil N (TSN) in a dryland no-till (NT) annual cropping system. The study included six N fertilizer rates (0, 20, 40, 60, 80, and 120lb N/a) that were applied to the same plots from 1984 through 1994 for crops grown on a Weld silt loam. Phosphorus fertilizer was also applied to half of each plot in 1984. Spring barley, corn, winter wheat, and oat/pea hay were grown in rotation. Phosphorus fertilization increased barley yields and SOC in 1984. Although crop residue production varied with crop and year, estimated average annual amount of above-ground residue returned to the soil (excluding hay years) was 2612, 3433, 3888, 3897, 3903, and 4121 lb/a for the above N rates, respectively. The positive effects of the increased return of crop residues to the soil with increasing N rate on SOC and TSN were significant in the 0- to 3-inch soil depth, but not at the 3-6 inch soil depth after 11 crops. The increase in SOC with increasing N fertilization rate significantly decreased the soil bulk density in the 0- to 3-inch soil depth, contributed toward improved soil quality, improved residue levels for soil erosion control, and increased the efficiency of C- stration into the soil. This study shows that C-sequestration can be enhanced by increasing crop residue returned to soil through improved N fertility in a no-till system.