Biochar, Mineral P and Their Co-Application Affects Chemical Fractions of P and Mung Bean Growth in Two Tropical Soils

Abstract

ABSTRACT Phosphorus fixation reduces P availability and affects crop yields in tropical soils. The ameliorative effect of biochar and its co-application with mineral P fertilizer on the soil labile inorganic P fractions and crop growth are unknown and hence studied in two soils with contrasting properties. Soils were applied with kunai grass (Imperata cylindrica) biochar at 15 t ha−1, mineral P fertilizer at 64 mg P kg−1 either together or solely to the potted soils under greenhouse conditions and mung bean (Vigna radiata) seeds were planted. Treatments were replicated 3 times and pots were arranged in complete randomized design. Soil samples were collected from the rhizosphere on days 30 and 90 and analyzed for pH, soluble P, inorganic Fe, Al and Ca-bound P fractions. Dry matter content and P uptake by the mung bean was also assessed. Soil pH was unaffected by fertilization regimes in both soils. Sole biochar application as well as co-application with mineral P increased the amount of P in Ca-P, Al-P and Fe-P fractions in both soils. However, co-application of kunai grass biochar with 64 mg P kg−1 of fertilizer significantly (p < .05) increased mung bean crop dry matter in acidic (78.8%) as well as alkaline soil (23.1%). The usage of kunai grass biochar should be combined with mineral P for reaping the synergistic agronomic benefits in the tropical acidic and slightly alkaline soils.