SOIL ORGANIC CARBON AND NITROGEN CHANGES UNDER IRRIGATION IN NORTHERN TEXAS.

Authors: Halvorson, Ardell; Reule, Curtis; POOLE, JIM - POOLE CHEM & POOLE FARMS

Submitted to: Fluid Fertilizer Foundation Symposium Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 1/15/2005
Publication Date: 2/13/2005
Citation: Halvorson, A.D., Reule, C.A., Poole, J. 2005. Soil organic carbon and nitrogen changes under irrigation in northern texas. Fluid Fertilizer Foundation Symposium Proceedings. Scottsdale, AZ. 22:154-159 and CD-ROM.

Interpretive Summary: The influence of N fertility management on grain yields, residue C inputs to the soil, SOC sequestration, and NO3-N leaching potential under irrigated, continuous crop production in northern Texas was evaluated. Two N fertility management levels were established in 1999 on separate halves of center-pivot irrigated fields located near Dalhart (Dallam fine sandy loam soil) and Texline, TX (Conlen and Dumas clay loam soils) employing reduced-till (RT), continuous corn production systems. The normal fertility program (N1) had corn yield goals of >250 bu/A. The higher N fertility treatment (N2) received the same fertilizer rate as the N1 treatment plus an additional application of liquid N fertilizer to the corn residue after harvest and prior to fall tillage to aid the decomposition of the residue. Addition of N to the crop residue was discontinued in 2003 at Dalhart and in 2002 at Texline due to a large increase in residual NO3-N. Grain yields and crop residue C inputs to the soil were similar for both N treatments. Total soil N (TSN) and SOC levels in the 0-6 inch soil depth have increased linearly with each additional crop year (1999-2003). Differences in SOC sequestration have not been observed between N treatments. Root zone soil NO3-N levels at both sites have increased more with the N2 than the N1 treatment. Nitrogen needs to be applied to optimize irrigated crop yields and economic returns, but only the amount needed for optimum yield should be applied to minimize NO3-N leaching potential.

Technical Abstract: Crop management practices that optimize crop yields and reduce soil erosion tend to have positive effects on soil organic carbon (SOC) sequestration. The influence of N fertility management on grain yields, residue C inputs to the soil, SOC sequestration, and NO3-N leaching potential under irrigated, continuous crop production in northern Texas was evaluated. Two N fertility management levels were established in 1999 on separate halves of center-pivot irrigated fields located near Dalhart (Dallam fine sandy loam soil) and Texline, TX (Conlen and Dumas clay loam soils) employing reduced-till (RT), continuous corn production systems. The normal fertility program (N1) had corn yield goals of >250 bu/A. The higher N fertility treatment (N2) received the same fertilizer rate as the N1 treatment plus an additional application of liquid N fertilizer to the corn residue after harvest and prior to fall tillage to aid the decomposition of the residue. Addition of N to the crop residue was discontinued in 2003 at Dalhart and in 2002 at Texline due to a large increase in residual NO3-N. Grain yields and residue C inputs to the soil were similar for both N treatments. Total soil N (TSN) and SOC levels in the 0-6 inch soil depth have increased linearly with each additional crop year (1999-2003). Differences in SOC sequestration have not been observed between N treatments. Root zone soil NO3-N levels at both sites have increased more with the N2 than the N1 treatment. Nitrogen needs to be applied to optimize irrigated crop yields and economic returns, but only the amount needed for optimum yield should be applied to minimize NO3-N leaching potential.