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Title: Development and evaluation of the carbon-nitrogen cycle module for the GPFARM-Range model

Author
item QI, ZHIMING - Colorado State University
item Bartling, Patricia
item Ahuja, Lajpat
item Derner, Justin
item Dunn, Gale
item Ma, Liwang

Submitted to: Computers and Electronics in Agriculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/10/2012
Publication Date: 7/1/2012
Citation: Qi, Z., Bartling, P.N., Ahuja, L.R., Derner, J.D., Dunn, G.H., Ma, L. 2012. Development and evaluation of the carbon-nitrogen cycle module for the GPFARM-Range model. Computers and Electronics in Agriculture. 83:1-10.

Interpretive Summary: Carbon and nitrogen cycle in the pedosphere has raised an increasing concern with a changing climate. Rangeland accounts for approximately 50% of the terrestrial surface of the earth. However, few decision support tools for rangeland management include a sufficient carbon-nitrogen cycle component. In this study, a carbon-nitrogen cycle module was incorporated into GPFARM Great Plains Farm and Ranch)-Range model and was tested along with the forage module against field data obtained from 1993-2006 in Cheyenne, WY under various grazing treatments. The results indicated that the peak standing crop and changes in soil organic carbon and total nitrogen were simulated reasonably well. The GPFARM-Range model can be used as a tool to evaluate the impacts of rangeland management on carbon sequestration and nitrogen dynamics. To further test the model, a data set with longer term measurement in soil carbon and nitrogen and root growth of range plants over a longer term is needed.

Technical Abstract: Rangelands cover approximately 50% of the terrestrial surface of the earth. The soil carbon and nitrogen storage and turnover in rangeland systems are becoming increasingly important for sustainable grazing management and adaptations to climate change. In this study, a carbon-nitrogen (C-N) cycle module from NLEAP (Nitrate Leaching and Economic Analysis) was added into the GPFARM (Great Plains Farm and Ranch)-Range model. This linkage was tested against a 14-year forage dataset with 3 yearly measurements of C and N near Cheyenne, WY. The results showed that the peak standing crop (PSC), and changes in soil organic carbon (SOC) and total nitrogen (TN) in the rangeland were simulated by the GPFARM-Range model reasonably. For the simulation of PSC, the indices of agreement (d) were greater than 0.85 and the mean bias errors (MBE) were less than 130 kg per ha. The SOC and TN in the soil profile were simulated with root mean square error (RMSE) less than 5% for the calibration treatment without grazing and less than 20% for the validation treatments with grazing, both showing no significant bias or error from the observed values. A long-term dataset with more frequent soil carbon and nitrogen measurement events is needed to further test the model. Further investigation is needed into the adequacy of root to shoot ratio approaches to simulate root growth for forage groups in these systems particularly where root dynamics and their partitioning to soil carbon pools are critical to the native productivity of the system.