Abstract
Phosphate rocks (PR), the primary source of phosphorus (P), are often co-composted with organic materials to enhance P availability. However, the mechanisms of P solubilization in PR-enriched composts are not well elucidated. This study investigated such mechanisms by monitoring the changes in P fractions during composting and by determining the relationships between the physicochemical and biological parameters. Sorghum straw residues were composted alone (Comp), or with 10% PR (P-Comp), or with 10% PR and 10% rhizosphere soil (P-Comp-Soil), and samples were collected at 45, 60, and 180 days for analysis. The labile-P composed of H2O- and NaHCO3-extractable inorganic P (Pi) and organic P (Po), the moderately labile-P extracted by NaOH (Pi + Po), and the unavailable P formed of the HCl-P and residual-P, increased with the progress of the composting. At 180 days, P-Comp-Soil contained the highest amount of labile-P. There were strong and positive correlations between labile-P and the abundance of total fungi, phosphate-solubilizing fungi (PSF), alkaline phosphatase phoD, phosphonatase phnX, acid phosphatase aphA. Although total fungi were much fewer than total bacteria, the PSF mainly triggered the mineral P solubilization. The alkaline phosphatase phoD was the main enzyme leading the organic P mineralization, while the contribution of phosphonatase phnX, acid phosphatase aphA, and siderophore entA to the organic P solubilization was minor. Besides, the bacterial specific-transporter (pstS) gene increased with the increase of labile-P, allowing for immobilization of little fractions of P in microbial cells. This study highlighted the significant role of phosphate-solubilizing fungi and alkaline phosphatase in the P solubilization of PR-enriched composts. Furthermore, it showed the benefit of supplementing the PR-enriched composts with rhizosphere soil, a niche of ecologically important source of beneficial microbes.
Highlights
The rapid increase in the world’s human population expected to reach 9.1 billion by 2050 requires to increase food production by 70% (Krishnaraj and Dahale, 2014)
We observed an increase of each P fraction’s concentration from 45 to 180 days (Table 2), which was more pronounced in Burkina phosphate rock (BPR)-enriched composts
This study evaluated the mechanisms of P solubilization of Burkina Faso phosphate rock-enriched composts, using sorghum straw as organic material
Summary
The rapid increase in the world’s human population expected to reach 9.1 billion by 2050 requires to increase food production by 70% (Krishnaraj and Dahale, 2014). Phosphorus (P), the second most essential nutrient after nitrogen for plant growth, is, present at deficient low levels of available fractions in many ecosystems (Barber et al, 1963) This P deficiency has become a threat to soil fertility and crop production throughout the world (Ochwoh et al, 2005), and in the humid tropics and subtropics, and sandy soils of the semi-arid tropics (Sanchez et al, 1997). The high price of chemical fertilizers and phosphate rock (Sharma et al, 2013) added to the severe environmental threat due to the exploitation of phosphate rock reserves require to consider alternative strategies to sustain soil fertility and crop production In this perspective, animal manures, straw, and other solid wastes are used as substrates for PR-enriched composts
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