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Estimating Carbon Stocks at the Field-Management Scale

Estimating Carbon Stocks at the Field-Management Scale Michael L. Thompson 1 , Teresita Chua-Ona 1 , Jessica Hutchison 2 , and Ya-Fang Wu 3 1 Iowa State University, Agronomy Department, Ames, IA 50011-1010 2 Cameron University, Biology Department, Lawton, OK 73505

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Estimating Carbon Stocks at the Field-Management Scale

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  1. Estimating Carbon Stocks at the Field-Management Scale Michael L. Thompson1, Teresita Chua-Ona1, Jessica Hutchison2, and Ya-Fang Wu3 1Iowa State University, Agronomy Department, Ames, IA 50011-1010 2Cameron University, Biology Department, Lawton, OK 73505 3University of Connecticut, Statistics Department, Storrs, CT 06269 Topographic Map Elevation (m) Rationale Both the concentrations and the stocks of soil organic carbon vary across the landscape. Area = 17.3 ha Relief = ~10 m Length = 585 m Width = 275 m An estimate of the quantity of the soil organic carbon stock and the precision of that estimate are both important. Why? Block Kriging Estimate of Carbon Stocks Carbon stock based on sum of values estimated by block kriging: 1614 Mg of C per 30 cm depth Error based on the sum of variances: 5 Mg of C per 30 cm depth • To decrease risk for parties who contract for soil carbon storage • To target carbon payments where they will be most effective at changing soil carbon storage • To meet expectations of international accords • To improve accuracy and precision of dynamic carbon models that must eventually be calibrated on real carbon values Summary Objectives • To identify alternative methods to assess the total stock of organic carbon in an agriculturally managed field • To compare the values of stocks estimated by multiple techniques and the precision of the estimated values Using ISPAID • Multiply ISPAID values of organic carbon and bulk density by depth and map unit area to predict stock of C to 30 cm depth Methods • Two sites: representative till-derived and loess-derived soils in Iowa: 14.7 ha and 17.3 ha • Grid-based sampling designs: 124 and 143 points with a variety of lag distances • Sample 7.5-cm-diameter cores to 30-cm depth • Determine bulk density and organic C in depth increments of 0-5, 5-15, and 15-30 cm • Calculate carbon stocks to depth of 30 cm • Only one site is described here 2 Stock of organic C estimated from the mean of 143 samples kg m-2 30 cm-1 Concentration Stock of carbon Relative of carbon in field uncertainty - 2 kg m to 0.3 m Mg to 0.3 m depth % 1430 Mean 8.27 Standard Variability in the 201 14 1.16 Deviation population Precision of the Standard Error of 17 1 0.10 estimate of the the Mean mean value N = 143 Area of field = 172,810 m 2 This project was supported by CASMGS and by the National Research Initiative of the USDA Cooperative State Research, Education and Extension Service, Grant Number 2005-35107-16128.

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