Sediment amendment with paddy straw biochar: effects on greenhouse gas fluxes, sediment characteristics, and enzymatic dynamics in inland saline shrimp ponds

Aquaculture, particularly shrimp farming, contributes to GHG emissions due to protein-rich feed inputs and reduced enzymatic activity in saline sediments, which affects soil health. A 75-day field study evaluated the role of PSB in reducing GHG emissions and improving sediment enzyme activity. PSB was applied at two rates: 20 kg/200 m 2 (1 ton ha -1 , T1) and 40 kg/200 m 2 (2-ton ha -1 , T2). Biochar application significantly ( p < 0.05) increased SMBC levels, reaching 452.43 ± 1.71 mg kg -1 (9.68%) in T1 and 487.99 ± 2.13 mg kg -1 (13.73%) in T2, compared with the control (429.14 ± 1.32 mg kg -1 ). Bacterial plate counts increased by 32.22% in T1(59.50 ± 1.50 CFU g -1 ) and 52.22% in T2 (68.50 ± 3 CFU g -1 ), relative to the control (45.00 ± 2 CFU g -1 ). Sediment enzymatic activities improved significantly ( p < 0.05): FDA activity increased by 9.66% in T1 (25.96 ± 1.78 μg g -1 h -1 ) and 24.49% in T2 (33.13 ± 2.05 μg g -1 h -1 ), while DHA and ALP increased by 25.55% (40.10 ± 2.88 µg TPF g -1 24 h -1 ) and 63.18% (52.11 ± 2.20 µg TPF g -1 24 h -1 ), and 9.70% (63.89 ± 1.18 µg PNP g -1 h -1 ) and 24.48% (72.50 ± 2.36 µg PNP g -1 h -1 ) in T1 and T2, respectively but only T2 showed statistically significant increases in DHA and ALP ( p < 0.05). Biochar application significantly influenced sediment characteristics ( p < 0.05). By day 75, sediment organic carbon in T2 was 77.9% (1.21%) higher than the control (0.68%). Similarly, available phosphorus increased by 2.22% in T1 (7.36 mg kg -1 ) and 2.08% in T2 (7.35 mg kg -1 ), while total nitrogen increased by 50.2% and 101.7% in T1 (0.1750%) and T2 (0.2350%), respectively, compared to the control (0.1165%). CH 4 flux declined by 3.05% in T1 (613.69 ± 12.33 g h -1 d -1 ) and 9.72% in T2 (571.45 ± 7.72 g h -1 d -1 ) on day 60, with further reductions of 9.37% (464.91 ± 10.91 g h -1 d -1 ) and 19.36% (413.67 ± 18.08 g h -1 d -1 ) by day 75, respectively. N 2 O flux dropped by 7.62% in T1 (1.843 ± 0.043 g h -1 d -1 ) and 21.83% in T2 (1.560 ± 0.034 g h -1 d -1 ) compared to control (1.996 ± 0.037 g h -1 d -1 ) on day 75, with no significant effect on CO 2 . These findings highlight the potential of biochar in reducing CH 4 and N 2 O emissions while enhancing sediment quality in inland saline aquaculture.