Article ID: 040304
The objective of this field experiment was to quantify changes in total carbon (TC), total organic carbon (TOC), total inorganic carbon (TIC), residual oxidizable carbon (ROC), and dissolved organic carbon (DOC) in perennial pasture soils planted with white clover (Trifolium repens) and tall fescue (Festuca arundinacea). Treatments included ammonium sulfate (AS), and urea (U) fertilizers applied with rice husk biochar (700 °C) at 5 t ha⁻¹ (B5) and 10 t ha⁻¹ (B10). Biochar–N treatments increased TOC, TIC, and ROC more than sole N treatments, with exceptions for TIC in ASB5 (white clover) and UB5 and ASB10 (tall fescue). In white clover, TC increased more under biochar-N treatments, particularly ASB10 and UB10, which also showed the least TOC reductions and the highest ROC increases. In white clover, UB5 and UB10 increased DOC losses more than U alone, likely due to increased microbial activity and DOC mineralization. In tall fescue, ASB5 and ASB10 reduced DOC losses more than AS, likely due to biochar's DOC sorptive potential and reduced microbial decomposition. U treatment resulted in higher TC, TOC, ROC TIC, and DOC percentage changes than AS treatment in both pastures. TC correlated positively with TIC, TOC, ROC, DOC, soil nitrogen, exchangeable calcium, and pH. Overall, U with high-rate biochar improved carbon stabilization in white clover, while AS with biochar reduced DOC losses in tall fescue
