Using different versions of the Rothamsted Carbon model to simulate soil carbon in long-term experimental plots subjected to paddy–upland rotation in Japan

Figures & data

Table 1. Summary of two long-term experimental sites

Site	Experimental period (years)	Depth† (cm)	Clay (%)	Initial SOC‡ (t C ha^–1)	IOM§ (t C ha^−1)	Carbon input for equilibrium¶ (t C ha^−1 year^−1)
A	1968–2007 (40)	13	14.4	33.05	2.63	1.01 (3.07)
B	1970–2007 (38)	13	24.0	27.05	2.10	0.76 (2.30)
Values were obtained from Sumida et al. (2005) and Nishida et al. (2007).
†Depth of topsoil used for simulation.
‡Soil organic carbon.
§Inert organic matter calculated from Falloon et al. (1998): IOM = 0.049 × SOC^1.139.
¶Value in simulation with paddy soil version followed by value in simulation with original Rothamsted Carbon (RothC) model in parentheses.

Table 2. Crop rotations of two long-term experimental sites

Site	Rotation	Until 1981	82–89	1990	1991	1992	1993	1994	1995	1996	1997	1998	1999	2000	2001	2002	2003	2004	2005	2006	2007
A	Continuous paddy	R	R	R	R	R	R	R	R	R	R	R	R	R	R	R	R	R	R	R	R
	Short-term upland conversion	R	R	S	R	R	R	S	R	S	R	R	S	R	S	S	R	R	S	R	R
	Mid-term upland conversion	R	R	S	S	S	R	S	S	S	R	R	S	S	S	S	R	S	S	S	R
B	Continuous paddy	R	R	R	R	R	R	R	R	R	R	R	R	R	R	R	R	R	R	R	R
	Long-term upland conversion	R	S	S	S	S	S	S	S	S	S	S	S	R	R	R	S	S	R	R	R
R and S shows paddy rice and soybean, respectively.

Table 3. The amount of carbon input to soils from crop residue and applied rice straw in each plot of Site A

		Average carbon input during experimental period (t C ha^−1 year^−1)
Rotation	Rice straw	Residue of rice†	Residue of soybean‡	Average of rice and soybean residue	Applied rice straw
Continuous paddy	+ straw	0.561	–	0.561	1.938
	− straw	0.553	–	0.553	–
Short-term upland conversion	+ straw	0.572	0.975	0.643	1.938
	− straw	0.565	1.011	0.643	–
Mid-term upland conversion	+ straw	0.584	0.928	0.696	1.938
	− straw	0.583	0.930	0.696	–
†Roots + stubble.
‡Roots + stubble + fallen leaves.

Table 4. The amount of carbon input to soils from crop residue and applied compost in each plot of Site B

			Average carbon input during experimental period (t C ha^−1 year^−1)
Rotation	Rice straw compost	Chemical fertilizer†	Residue of rice‡	Residue of soybean§	Average of rice and soybean residue	Rice straw compost¶
Continuous paddy	+ compost	+ N	0.621	–	0.621	1.505
		− N	0.490	–	0.490	1.505
	− compost	+ N	0.577	–	0.577	–
		− N	0.395	–	0.395	–
Long-term upland conversion	+ compost	+ N	0.592	2.208	1.443	1.505
		− N	0.555	2.210	1.426	1.505
	− compost	+ N	0.553	1.898	1.261	–
		− N	0.475	1.973	1.264	–
†Nitrogen, phosphorous and potassium (NPK) were applied in +N plots. Phosphorous and potassium (PK) were applied in –N plots.
‡Roots + stubble.
§Roots + stubble + all leaves + stems.
¶1.796 t C ha^−1 year^−1 from 1970 to 1987 and 1.244 t C ha^−1 year^−1 from 1988 to 2007 (1.505 t C ha^−1 year^−1 is average). Rice straw compost was treated as farmyard manure (FYM) in the Rothamsted Carbon (RothC) model simulation.

Table 5. Monthly factors used in the Rothamsted Carbon (RothC) simulations to correct the decomposition rate of carbon based on whether paddy rice or upland crops were used

		Year for paddy rice			Year for upland crop
	Month	January– April	May– September	October– December	January– April	May– September	October– December
Simulation pattern	Crop	No crop	Paddy rice	No crop	No crop	Soybean	No crop
(A) Original model†		1	1	1	1	1	1
(B) Paddy soil version		0.6	0.2	0.6	0.6	0.6	0.6
(C) Alternate use of paddy and upland versions		0.6	0.2	0.6	1	1	1
†Developed for upland soils.

Figure 1. Comparison of simulation results for Site A. (A) Original model, (B) paddy–soil version, and (C) alternate use of the two versions. Solid and dashed lines show predicted changes in soil organic carbon (SOC) in plot with and without straw application, respectively. Closed and open triangles show observed SOC in plot with and without straw, respectively. P, continuous paddy; SU, short-term upland conversion; MU, medium-term upland conversion.

Figure 2. Comparison of simulation results for Site B. (A) Original model, (B) paddy–soil version, and (C) alternate use of the two versions. Thick solid and dotted lines show predicted soil organic carbon (SOC) in –compost plots with and without nitrogen (N) fertilizer application, respectively. Thin solid and dotted lines show predicted changes in SOC in +compost plot with and without N fertilizer application, respectively. Closed and open circles show observed SOC in –compost plot with and without N fertilizer application, respectively. Closed and open triangles show observed SOC in +compost plot with and without N fertilizer application, respectively. P, continuous paddy; LU, long-term upland conversion.

Figure 3. Comparison of root mean square error (RMSE) and mean difference (M) among the three model simulations. Open, closed and gray bars show original model, paddy–soil version and alternate use of two versions, respectively. P, continuous paddy; SU, short-term upland conversion; MU, medium-term upland conversion; LU, long-term upland conversion.

Figure 4. Comparisons of model performances of our study (A), previous studies (B) and (C) from Shirato and Yokozawa (2005), and (D) and (E) from Shirato et al. (2004). Closed and open bars show averages of root mean square error (RMSE) and absolute value of mean difference (M), respectively. Numbers above bars are values of the average. Numbers in parentheses in the labels on the x-axis indicate the number of plots.

Shirato, Y , and Yokozawa, M , 2005. Applying the Rothamsted Carbon Model for long-term experiments on Japanese paddy soils and modifying it by simple tuning of the decomposition rate , Soil Sci. Plant Nutr. 51 (2005), pp. 405–415.

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Shirato, Y , Hakamata, T , and Taniyama, I , 2004. Modified Rothamsted Carbon Model for Andosols and its validation: changing humus decomposition rate constant with pyrophosphate-extractable Al , Soil Sci. Plant Nutr. 50 (2004), pp. 149–158.

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