Calculate SOC change

Monitoring:

A project that off-sets CO₂ by carbon sequestration should be able to prove that significant carbon gains have occurred following a given land management practice compared to the pre-treatment baseline (Olson, 2013).

Calculating change in SOC stocks

Change in SOC= SOC_t+1 – SOC_t

Suppose that a 664.5 ha watershed consists of Crop land (252 ha), forest land (197.9 ha), and Grazing land (214 ha) (Figure 1).

Based on the baseline and SOC measurement after 5 years (Table 1) the mean SOC stock in the study area has increased by 1.44 ± 0.79 over 5 years with 95% confidence level. The CO₂ equivalent is calculated by multiplying SOC stock by 44/12.

Table 1. Example data on changes in SOC stocks between time measurements (click HERE for a spreadsheet example)

Land use	Plot		SOC stocks (t ha^-1)
		T0 (baseline)	T1 (after 5 years)	Change (T1- T0)
Crop land (252 ha)	1	35	36	1
	2	22	24	2
	3	33	32	-1
	4	25	26	1
	5	19	22	3
	6	27	30	3
Forest land (197.9 ha)	1	35	38	3
	2	22	21	-1
	3	33	33	0
	4	25	27	2
	5	19	19	0
Grazing land (214 ha)	1	35	37	2
	2	22	26	4
	3	33	34	1
	4	25	26	1
	5	19	21	2
Summary
Mean SOC	t ha^-1	26.81	28.25	1.44
Standard deviation SOC	t ha^-1	6.21	6.16	1.46
Standard error of mean	t ha^-1	1.55	1.54	0.37
t value (α = 0.05, n-1)		2.13	2.13	2.13
95% confidence level of the mean		3.30	3.28	0.79
95% CI of mean, lower	t ha^-1	23.51	24.97	0.65
95% CI of mean, upper	t ha^-1	30.11	31.53	2.23
Total SOC stocks	t	17815.28	18772.16	956.88
95% confidence level of total SOC		2193.85	2179.56	524.96
95% CI of total, lower		15621.43	16592.60	431.92
95% CI of total, upper		20009.13	20951.72	1481.84
CO2 equivalent total		65322.69	68831.25	3508.56
95% confidence level of total CO2 equivalent		8044.12	7991.72	1924.85
CO2 equivalent CI total, lower	t	57278.57	60839.53	1583.71
CO2 equivalent CI total, upper	t	73366.81	76822.97	5433.41
Report
Mean SOC ± 95% confidence level	t ha^-1	26.81 ± 3.3015	28.25 ± 3.28	1.44 ± 0.79
Total SOC ± 95% confidence level	t	17815.28 ± 2193.85	18772.16 ± 2179.56	956.88 ± 524.96
Total CO2 equivalent	CO2 e	65322.69 ± 8044.12	68831.25 ± 7991.72	3508.56 ± 1924.85

Both the mean and total carbon stocks could change with change in land use. In Figure 2, for instance, part of the forest land is converted into cultivated and grazing lands.

Refer Donovan (2013) for more information on calculating SOC change.

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Donovan, P. 2013. Measuring soil carbon change: A flexible, practical, local method.