Table 3. Estimates of SOC (soil organic carbon) stocks and SOC density values of various Soil Groups using the mean, median, SPS (soil profile statistic), and PKB (pedological professional knowledge based) methods.

Soil Group	Areaa	PKB		Mean			Median			SPS
	(km2)	SOC density(kg m−2)	SOC stock(106 t)	SOC density(kg m−2)	SOC stock(106 t)	%b	SOC density(kg m−2)	SOC stock(106 t)	%b	SOC density(kg m−2)	SOC stock(106 t)	%b
Red soils	39681.3	6.53	259.10	6.73	266.96	3.0	6.24	247.71	−4.4	6.50	258.11	−0.4
Yellow soils	10013.5	16.92	169.45	14.00	140.15	−17.3	12.24	122.54	−27.7	16.72	167.44	−1.2
Purple soils	3597.7	5.73	20.60	5.00	18.01	−12.6	4.77	17.15	−16.7	5.65	20.34	−1.2
Limestone soils	1571.0	10.18	16.00	8.56	13.45	−15.9	9.43	14.82	−7.4	10.47	16.45	2.8
Skel soils	13736.8	5.11	70.20	5.26	72.30	3.0	4.29	58.99	−16.0	5.09	69.95	−0.4
Red clay soils	29.1	5.45	0.16	5.45	0.16	0.0	5.45	0.16	0.0	5.45	0.16	0.0
Mountain meadow soils	3.3	45.30	0.15	104.32	0.34	130.3	49.89	0.16	10.1	45.30	0.15	0.0
Fluvio-aquic soils	4318.3	7.43	32.10	7.33	31.66	−1.4	7.17	30.98	−3.5	7.44	32.13	0.1
Coastal saline soils	2793.3	7.79	21.75	7.58	21.19	−2.6	7.50	20.95	−3.7	7.80	21.78	0.1
Paddy soils	24995.8	9.68	241.98	9.67	241.66	−0.1	9.20	229.86	−5.0	9.64	241.06	−0.4
Total soils	100740.1	8.25	831.49	8.00	805.88	−3.1	7.38	743.32	−10.6	8.21	827.57	−0.5

^aArea used for the four methods in this study was from the 1∶50,000 digital soil map.

^bPercentage of difference of estimated SOC stocks between the mean, median, or SPS method and the PKB method.