Application of rice straw and corn straw compost for enhancing phosphorus availability in ultisol and corn plants

Ultisol, a widely distributed soil in tropical regions, remains underutilized in agriculture due to its inherently low phosphorus (P) availability, with substantial amounts bound in recalcitrant Al-P, Fe-P, and Ca-P fractions, limiting plant uptake. However, limited understanding exists regarding how different compost sources can more effectively mobilize these P fractions to enhance crop performance in field-relevant tropical conditions. This study addressed this problem by evaluating the efficacy of rice straw and corn stover composts in transforming these key P fractions into more available forms for corn (Zea mays) growth. A two-phase experimental design was employed, including a six-week soil incubation where Ultisol was amended at 20 tons/ha to assess shifts in Al-P, Fe-P, Ca-P, and available P, and a subsequent greenhouse experiment examining corn growth responses to varying compost rates (10, 20, 30 tons/ha). Compared to rice straw compost, corn stover compost, which contained higher levels of humic and fulvic acids, more effectively reduced P bound in Al-P, Fe-P, and Ca-P complexes by up to 67 %, thereby significantly enhancing P availability. These results align with previous findings on organic amendments but further demonstrate the pivotal role of higher humic and fulvic acid content in boosting P release from multiple soil-bound fractions. Enhanced P availability translated into improved crop performance, as evidenced by increased ear length, diameter, and grain weight. The implications of this study suggest a cost-effective and environmentally friendly approach to overcoming P limitations in acidic, highly weathered soils. Nonetheless, the greenhouse-scale scope represents a limitation, highlighting the need for longer-term field evaluations to assess broader impacts on soil health and nutrient cycling. These findings highlight that the superior capacity of corn stover compost to chelate metal ions, release bound P, and increase its bioavailability offers a sustainable strategy to overcome P limitation in Ultisol. Future research should explore multi-season field trials and in-depth microbial assessments of compost impacts on P dynamics, soil health, and crop resilience, ultimately optimizing sustainable soil management in tropical agriculture.