Optimising Soil Hydraulic Behaviour Through Combined Cellulose and Biochar Amendments: Implications for Climate-Smart Agriculture

Soil hydraulic functioning plays an important role in soil water management under increasingly variable climatic conditions. Total water storage alone, however, does not necessarily reflect the stability of retained water after drainage. This study evaluated the effects of waste paper cellulose and biochar, applied individually and in combination, on soil hydraulic behaviour across contrasting soil types. Water-holding capacity (WHC), maximum capillary water capacity (WMCC), water retention capacity after 24 h drainage (WRCC24), soil texture, and organic matter were determined in 64 soil and soil-related samples. Retention efficiency (RE = WRCC24/WMCC) was used as an indicator of water retention stability. WHC was strongly associated with soil organic matter, whereas RE was primarily related to soil texture and likely reflected differences in pore-system characteristics. Cellulose markedly increased WHC, particularly in soils with initially low hydraulic performance, but changes in WHC were not directly related to changes in RE, indicating partly independent hydraulic responses. Combined cellulose–biochar treatments showed complementary effects: cellulose primarily enhanced total water storage, while biochar improved retention stability. The results demonstrate that total water storage and retention stability may respond differently to soil amendments and should therefore be evaluated together when assessing amendment performance. The findings also highlight the potential of combined cellulose–biochar amendments for improving water retention stability under water-limited conditions.