Crop Management Effects on Soil Carbon and Nitrogen in Northern Texas

Authors: Halvorson, Ardell; Reule, Curtis; POOLE, J - POOLE CHEM., TEXLINE, TX

Submitted to: Fluid Fertilizer Foundation Symposium Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 1/8/2007
Publication Date: 2/18/2007
Citation: Halvorson, A.D., Reule, C.A., Poole, J. 2007. Crop Management Effects on Soil Carbon and Nitrogen in Northern Texas. Fluid Fertilizer Foundation Symposium Proceedings. 24:67-74. Also a CD ROM publication.

Interpretive Summary: The influence of management practices on crop residue C and N inputs to the soil, SOC sequestration, and NO3-N leaching potential under irrigated, continuous crop production in northern Texas was evaluated for 8 years. Two N management levels (N1 and N2) were established in 1999 in irrigated fields located near Dalhart (Dallam fine sandy loam soil) and Texline, TX (Conlen and Dumas clay loam soils) using reduced-till (RT), continuous corn production systems. The N1 site received the normal fertility program for a corn yield goal of >250 bu/A. The N2 site received the same fertilizer program as the N1 site plus an additional application of liquid N to the corn residue after harvest to aid crop residue decomposition. Application of N to the residue at the N2 sites was discontinued in 2002 at Dalhart and 2001 at Texline due to a buildup of residual soil NO3-N. At Dalhart, winter wheat was inserted into the rotation in 2003, with a corn-wheat rotation followed in 2004 – 2006, with dryland corn rather than wheat on the N2 site in 2006. At Texline, cattle have grazed the corn stalks after grain harvest since 2001. Grain yields and residue C inputs to the soil were similar for both sampling sites at both locations. Total soil N (TSN) and SOC levels increased linearly from 1999 through 2003 in the 0-6 inch soil depth with linear SOC sequestration rates of about 1122 lb C/A per year at Dalhart and 1464 lb C/A per year at Texline, then leveled off or declined from 2004 through 2006 with cropping system changes at Dalhart and extensive corn residue removal by livestock at Texline. Differences in SOC sequestration rates between the N1 and N2 sites were not significant. SOC analyses suggest that the water stress and change in cropping system at Dalhart and the cattle grazing corn stalks at Texline caused reduction in SOC sequestration rate. Root zone soil NO3-N levels declined with a reduction in N rates and discontinued application of N to the crop residue. The study shows that under irrigated, high fertility conditions, SOC sequestration is possible while using reduced tillage and continuous corn production, when corn residues are not removed.

Technical Abstract: Optimizing crop yields and reducing soil erosion can enhance soil organic carbon (SOC) sequestration. The influence of management practices on crop residue C and N inputs to the soil, SOC sequestration, and NO3-N leaching potential under irrigated, continuous crop production in northern Texas was evaluated for 8 years. Two N management levels (N1 and N2) were established in 1999 in irrigated fields located near Dalhart (Dallam fine sandy loam soil) and Texline, TX (Conlen and Dumas clay loam soils) using reduced-till (RT), continuous corn production systems. The N1 site received the normal fertility program for a corn yield goal of >250 bu/A. The N2 site received the same fertilizer program as the N1 site plus an additional application of liquid N to the corn residue after harvest to aid crop residue decomposition. Application of N to the residue at the N2 sites was discontinued in 2002 at Dalhart and 2001 at Texline due to a buildup of residual soil NO3-N. At Dalhart, winter wheat was inserted into the rotation in 2003, with a corn-wheat rotation followed in 2004 – 2006, with dryland corn rather than wheat on the N2 site in 2006. At Texline, cattle have grazed the corn stalks after grain harvest since 2001. Grain yields and residue C inputs to the soil were similar for both sampling sites at both locations. Due to drought at Dalhart and severe hail at Texline in 2006, biomass samples were not collected. Total soil N (TSN) and SOC levels increased linearly from 1999 through 2003 in the 0-6 inch soil depth with linear SOC sequestration rates of about 1122 lb C/A per year at Dalhart and 1464 lb C/A per year at Texline, then leveled off or declined from 2004 through 2006 with cropping system changes at Dalhart and extensive corn residue removal by livestock at Texline. Differences in SOC sequestration rates between the N1 and N2 sites were not significant at either location. The SOC analyses suggest that the water stress and change in cropping system at Dalhart and the cattle grazing corn stalks at Texline caused reduction in SOC sequestration rate. Root zone soil NO3-N levels declined with a reduction in N rates and discontinued application of N to the crop residue at the N2 sites. 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. The study shows that under irrigated, high fertility conditions, SOC sequestration is possible while using reduced tillage and continuous corn production, when corn residues are not removed.