Nitrogen Availability in Biochar-Amended Soils with Excessive Compost Application

Adding biochar to excessive compost amendments may affect compost mineralization rate and nitrogen (N) availability. The objective of this 371-day incubation study was to evaluate the effects of four proportions of woody biochar (0%, 0.5%, 1.0%, and 2.0%) from lead tree (Leucaena leucocephala (Lam.) de. Wit) biochar produced at 750 °C through dynamic mineral N and N mineralization rates in three rural soils (one Oxisol and two Inceptisols). In each treatment, 5% poultry–livestock manure compost was added to serve as an excessive application. The results indicated that the biochar decreased available total inorganic nitrogen (TIN) (NO₃⁻-N+NH₄⁺-N) by on average 6%, 9% and 19% for 0.5%, 1.0% and 2.0% treatments, respectively. The soil type strongly influenced the impact of the biochar addition on the soil nitrogen mineralization potential, especially the soil pH and clay content. This study showed that the co-application of biochar and excessive compost benefited the agricultural soils by improving NO₃⁻-N retention in agroecosystems. The application of biochar to these soils to combine it with excessive compost appeared to be an effective method of utilizing these soil amendments, as it diminished the net N mineralization potential and reduced the nitrate loss of the excessive added compost.