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

Authors: Halvorson, Ardell; Reule, Curtis; POOLE, JIM - POOLE FARMS, TEXLINE, TX

Submitted to: Symposium Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 1/15/2004
Publication Date: 2/1/2004
Citation: Halvorson, A.D., Reule, C.A., Poole, J. 2004. Changes in soil organic carbon and soil nitrogen under irrigation in northern texas. Symposium Proceedings. 21:112-118.

Interpretive Summary: The influence of N fertility management on corn grain yields, residue C inputs to the soil, soil organic C (SOC) sequestration, and NO3-N leaching potential under irrigated, continuous crop production in northern Texas was evaluated. Two N fertility management levels were established on separate halves of center-pivot irrigation systems located near Dalhart (Dallam fine sandy loam) 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 corn residues. Grain yields and residue C inputs to the soil have been 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 (1999-2002) and are now greater than the 1999 native sod SOC levels. Addition of liquid N to the corn residue after harvest (N2) has not significantly influenced SOC levels after 4 years at either site. Root zone soil NO3-N levels have increased in the cropped area compared to native grass at both sites and have increased more with the N2 than the N1 treatment. Several more cropping seasons will be needed to detect changes in SOC caused by differences in N fertility management. 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 in irrigated systems.

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 corn 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 on separate halves of center-pivot irrigation systems located near Dalhart (Dallam fine sandy loam) 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 corn residues. Grain yields and residue C inputs to the soil have been 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 (1999-2002) and are now greater than the 1999 native sod SOC levels. Addition of liquid N to the corn residue after harvest (N2) has not significantly influenced SOC levels after 4 years at either site. Root zone soil NO3-N levels have increased in the cropped area compared to native grass at both sites and have increased more with the N2 than the N1 treatment. Several more cropping seasons will be needed to detect changes in SOC caused by N fertility management. 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 in irrigated systems.