Plant-available phosphorus in young volcanic soils developed on pyroclasts from the 1991 eruption of Mt. Pinatubo, Philippines

Phosphorus (P) is an essential nutrient for crop growth but its availability in soils is often limited due to precipitation in secondary minerals, adsorption to clays, or fixation/immobilization with organic matter. Plant available P (Pavail) in young volcanic soils may be high due to rapid weathering of primary minerals. This study assesses the content of plant-available P in agricultural and nonagricultural soils after 26 years of pyroclastic (ash and lahar) deposition from 1991 Mt. Pinatubo eruption. Pavail concentrations of modern soils (56-152 mg/kg) under different land-use types did not differ significantly (Fig. 4). Buried soils from high altitude forest and grassland have deficient Pavail concentration at 5 and 2 mg/kg, respectively. Buried soil of IR-Lahar has significantly higher Pavail (136 mg/kg) even with minimal inorganic fertilizer application compared to IR-Ash (24 mg/kg) applied with 18-27 kg P/ha/yr (as per comm. with farm owners).