Adding intercropped maize and faba bean root residues increases phosphorus bioavailability in a calcareous soil due to organic phosphorus mineralization

Background and aims Root residues are an important factor influencing soil phosphorus (P) availability for crop uptake, but how the residues from different species combinations in sole cropping or intercropping systems affect soil P pools remains unclear. Methods Maize and faba bean were planted as either sole crops or intercrops in a P-deficient calcareous soil in cycle 1, and the same cropping systems were added with and without root residues of single or both species in the 2(nd) and 3(rd) cycles in a greenhouse experiment. Biomass and P concentration were determined after each cycle, and soil P fractions were measured after final cycle. Results Addition of a mixture of intercrop root residues increased biomass, total P content, microbial biomass P concentration and soil acid phosphatase activity, compared with addition of root residues of a single crop. Changes in Hedley soil P fractions varied with root residue sources. Sole maize root residue with high C/P ratio caused a considerable depletion of inorganic P (NaHCO3-P-i, NaOH-P-i and 1 M HCl-P-i), and sole faba bean root residue with lower C/P ratio caused a large depletion in Resin-P and NaHCO3-P-o fractions, and the root residue of intercrops with an intermediate C/P ratio depleted more of the NaHCO3-P-o and conc. HCl-P-o fractions. Without adding root residues, sole faba bean depleted more of the Resin-P, NaHCO3-P-i, NaOH-P-i and NaHCO3-P-o fractions than the other two cropping systems did, because it acquired more P from the soil than other crops did. Conclusions Adding a root residue mixture of maize and faba bean accelerated soil organic P mineralization (NaHCO3-P-o and conc. HCl-P-o) by increasing microbial biomass P concentrations and acid phosphatase activities, and thus enhanced the intercropping advantage in terms of biomass and total P content in a P-deficient soil.