Page 74 - Read online

Cui et al. Carbon Footprints 2026, 5, 19 Page 7 of 16

Table 1. Changes in the SOC stocks across the 0-100 cm soil profile under different farming treatments over the 16-year experimental
period

SOC stock in 2008 (Mg C ha ) SOC stock in 2024 (Mg C ha ) Annual change (Mg C ha yr )
-1
-1
-1
-1
0-20 cm CK 28.4 ± 1.60 28.2 ± 2.00c -0.01 ± 0.06c
FRM 34.0 ± 0.58b 0.35 ± 0.07b
OPT 38.5 ± 3.04a 0.63 ± 0.11a
NoT 35.7 ± 1.17ab 0.46 ± 0.06b
0-40 cm CK 42.7 ± 3.56 45.5 ± 4.75b 0.17 ± 0.14c
FRM 52.5 ± 2.46ab 0.61 ± 0.08b
OPT 59.9 ± 8.25a 1.07 ± 0.36a
NoT 55.4 ± 4.40ab 0.79 ± 0.14ab
0-70 cm CK 57.1 ± 4.08 62.1 ± 5.32b 0.31 ± 0.09c
FRM 73.9 ± 4.95a 1.05 ± 0.11b
OPT 82.8 ± 6.89a 1.61 ± 0.18a
NoT 76.5 ± 3.25a 1.21 ± 0.06b
0-100 cm CK 64.3 ± 4.96 84.6 ± 6.75b 1.27 ± 0.22c
FRM 92.1 ± 6.67ab 1.74 ± 0.21b
OPT 104 ± 9.82a 2.48 ± 0.43a
NoT 94.3 ± 4.96ab 1.88 ± 0.09b

The data shown are the mean ± SD (n = 4). Different letters for the same crop indicate significant differences at P < 0.05 among the four
treatments. CK represents the control treatment, FRM represents the local farmer operation treatment, OPT represents the optimized farming
operation treatment, and NoT represents the no-tillage treatment. SOC: Soil organic carbon.

In contrast to the SOC stocks, the SIC stocks in the four experimental treatments decreased as the duration
of the long-term experiment increased [Table 2]. For the 0-20 cm layer, the SIC stocks decreased annually by
0.27 ± 0.12 (CK), 0.71 ± 0.11 (FRM), 0.46 ± 0.11, and 0.53 ± 0.11 (NoT) Mg C hm yr . As the soil depth
-2
-1
increased, the SIC stock losses also increased. For the 0-100 cm layer, the increases were 1.62 ± 0.17 (CK),
1.88 ± 0.13 (FRM), 2.31 ± 0.11 (OPT), and 2.42 ± 0.46 (NoT) Mg C hm yr , respectively. Both OPT and NoT
-2
-1
resulted in higher SIC loss rates, followed by FRM and CK.
Given that the SOC and SIC pools were considered together, we found that after the 16-year experimental
period, the net C sequestration rates in the different soil layers were 0.17 ± 0.14 Mg C hm yr at 0-20 cm,
-2
-1
0.14 ± 0.47 Mg C hm yr at 0-40 cm, and 0.17 ± 0.64 Mg C hm yr at the 0-100 cm layer (Table 3). With
-1
-2
-1
-2
respect to the other experimental treatments, i.e., FRM, NoT, and CK, the net C losses were similar across
the 16-year experimental period, and the loss rates were similar across the three treatments, except for higher
loss rates in the 0-20 cm layer in the CK and CON treatments.
Effects of farming practices on soil organic carbon conversion efficiency
During the 16-year experimental period, the CK, FRM, OPT, and NoT treatments received OC inputs of
59.6, 58.1, 130, and 115 Mg C ha , respectively [Table 4]. The conversion efficiencies of the organic material
-1
inputs for the four experimental treatments were calculated. In the 0-20 cm layer, some of the SOC stock in
the CK treatment decreased as the experiment progressed, and its CE was negative. Nevertheless, the CE
values of the other three treatments were 9.53% (FRM), 7.75% (OPT), and 6.35% (NoT). For the 0-40 cm soil
layer, the CE nearly doubled; for the 0-100 cm layer, the CE quadrupled and was highest in FRM (47.9%),
followed by CK (34.1%), OPT (30.4%), and NoT (26.2%).