Soil microbial biomass phosphorus as an indicator of phosphorus availability in a Gleyic Andosol

Abstract The relationship between plant phosphorus (P) uptake and soil microbial biomass phosphorus (biomass P) or available phosphorus (Truog P) was estimated in a Gleyic Andosol in Sapporo, Hokkaido, in a 4-year field trial (2004–2007). Every year, the soil was treated in duplicate (each plot 36 m2) or triplicate (each plot 24 m2) with chemical fertilizer, cow manure compost or sewage sludge compost, and then kidney beans (Phaseolus vulgaris) were planted. Pooled data of the shoot content of P at harvest over the 4 years was significantly correlated with biomass P determined 1 month after the application of fertilizer (P < 0.01). A multivariate analysis revealed that the grain yield was significantly positively correlated with the shoot content of P (P < 0.01) and significantly negatively correlated with the shoot content of calcium (P < 0.05), but not correlated with the shoot content of either nitrogen or potassium. These results suggest that P is the most limiting element to affect the productivity of kidney bean plants in this trial and that biomass P is an important P source that explains the differences in P availability among soil amendments. Biomass P is a better indicator of P availability for kidney beans grown in Gleyic Andosols compared with Truog P, which is widely used in Japan.