Distribution of Inorganic and Organic Phosphorus Fractions in Two Phosphorus-Deficient Soils as Affected by Crop Species and Nitrogen Applications

Abstract

It is desirable to know the distribution of phosphorus (P) fractions in soil so that plants may use P efficiently. Here we report the dynamics of inorganic and organic P in P-deficient black and rice soil cropped by soybean, white lupin, and maize supplied with nitrogen (N) inputs by N fixation and urea fertilizer. Inorganic P fractions of the three cropped soils could be ranked as O-P (organic phosphorus) > Al-P (aluminum phosphorus) > Fe-P (iron phosphorus) > Ca10-P (calcium-10 phosphorus) > Ca8-P (calcium-8 phosphorus) > Ca2-P (calcium-2 phosphorus), irrespective of soil type. The potential of various inorganic P fractions to plant nutrition differed between soybean and white lupin. The percentage of total P present as inorganic P was affected by crop, soil type, and N source. In black soil, the change of organic P fraction induced by N fixation was larger than by urea application. The moderately labile organic P (MLOP) concentration was not affected significantly by soil type and crop species, and it was probably the main P source to the inorganic P fraction because the correlation between the two pools was high (r = 0.945; P < 0.05). Crop species differed in their uptake of inorganic and organic P from soil. Though P fraction concentrations varied between black soil and rice soil, their response to crop species and N source was similar. The amounts of P removed from soil were affected by N source. The right choice of crop species and the application a suitable N source may increase crop yield and P uptake by plant in P-deficient soils.