Compost amendment enhances population and composition of phosphate solubilizing bacteria and improves phosphorus availability in granitic regosols

Abstract

This study was conducted to investigate the relationship between available phosphorus (P) in granitic regosols and the population and composition of phosphate solubilizing bacteria (PSB) enhanced by compost amendments. Enrichment of soil with rock phosphate (RP) or no enrichment was combined with poultry manure (PM), cattle manure (CM), sewage sludge (SS), or P-adjusted sawdust (PSD) compost amendments at a rate equivalent to 5 mg P kg⁻¹ soil, or without compost amendment. Soil was enriched with RP at 0.25 or 0.5 g kg⁻¹ soil in the pot experiment and 0.5 g kg⁻¹ soil in the incubation experiment. The amended soils were used to grow African millet (Eleusine coracana Gaertn, cv. Yukijirushi) for 30 days in Wagner's pots (200 cm²). Plant P uptake in RP-enriched soil at 0.25 g RP kg⁻¹ soil was 2- 3-fold greater with compost addition than without compost. The results of the incubation experiment showed that compost amendments significantly enhanced microbial biomass P and population density of PSB, which showed significant positive correlation with the available P in soil. The dominant isolates of PSB in all the compost treatments were closest to Burkholderia fungorum. The treatment-specific isolates of PSB with the type of compost amendment were closely related to Burkholderia phytofirmans in PM treatment, Burkholderia caledonica or Arthrobacter ramosus in SS treatment and Burkholderia phenazinium in PSD treatment. The enhanced available P in RP-enriched treatments could be related to specific isolates of PSB in each compost treatment.

Keywords:

• compost
• microbial biomass phosphorus
• phosphate-solubilizing bacteria
• granitic regosols
• rock phosphate.

Acknowledgments

The authors would like to acknowledge the financial support of the Ministry of Education, Sports, Culture, Science and Technology, Japan.