Simulating long-term soil carbon sequestration and wheat productivity under biochar amendments in saline-irrigated sandy soils

Improving carbon sequestration in sandy soils under saline irrigation is essential for sustaining agricultural productivity in marginal environments. This study addressed two key questions: (i) can biochar, alone or combined with organic amendments, enhance soil carbon storage and fertility under saline irrigated? and (ii) What are the long-term impacts of biochar application on soil organic carbon (SOC) dynamics and wheat (Triticum aestivum L) productivity? A field experiment was conducted using three treatments: compost-only, biochar at 20 t ha⁻¹ (+B), and biochar (20 t ha⁻¹) combined with chicken manure (40 t ha⁻¹) (B+M). The Decision Support System for Agrotechnology Transfer (DSSAT) model was further employed to simulate long-term (20-year) effects. Results showed that biochar amendments significantly enhanced soil carbon storage, with total organic carbon increasing from 9.29 g kg⁻¹ (compost-only) to 15.87 g kg⁻¹ (+B) and 23.72 g kg⁻¹ (B+M). Relative to compost treatment, SOC increased by 117.66% and 208.98%, and inorganic carbon by 126.95% and 368.79% under +B and B+M, respectively. Biochar also significantly increased microbial biomass carbon (by 132.29% in +B and 187.68% in B+M) and improved nutrient availability (N: 77.78%–145.19%, P: 167.14%–354.23%, K: 80.70%–141.10%). In addition, water-use efficiency increased from 4.70 to 6.67 kg mm⁻¹ ha⁻¹ under B+M, indicating improved soil water retention and plant uptake. Model validation demonstrated high predictive accuracy (R² = 0.93) between observed and simulated yields. Long-term DSSAT simulations projected SOC increases of 26.4% (+B) and 30.57% (B+M) over 20 years, along with reduced nutrient leaching and wheat yield improvements of 58.18% and 85.4%, respectively. Although short-term CO₂ fluxes increased following biochar, long-term simulations indicate substantial benefits for carbon sequestration and crop productivity. These findings demonstrate that integrating biochar with organic amendments is an effective strategy for improving soil carbon storage and sustaining wheat production in saline-irrigated sandy soils.