Bioactivation of Legacy Phosphorus in Calcareous Soil by P-Activators and Its Effect on Maize Growth

ABSTRACT

Soil legacy phosphorus (P) accumulated due to the long-term continuous application of P fertilizers in agricultural fields accumulated in the soil for years, as sparingly soluble forms. This can be made as a possible soil P source using P-activators. In this study, a laboratory incubation and a pot experiment were conducted to evaluate the potential of some P activators (Phosphorus solubilizing bacteria, phytase, humic acid, oxalic acid) in increasing the availability of residual phosphorus in calcareous soil. For the incubation experiment, the P activators were applied alone and in combination. Soil samples were analyzed at subsequent intervals for soil available P, alkaline phosphatase activity, and sequential P fractions. The results showed that phytase application with humic acid (HA) increased the available soil P (12.4 kg ha⁻¹) and alkaline phosphatase activity (47.42 µg p-nitrophenol released g⁻¹ soil hr⁻¹) followed by phosphorus solubilizing Bacteria (PSB) with humic acid and PSB with phytase treatments. All treatments have a significant effect on different soil P-fractions. A greater reduction in calcium phosphate fraction was noted in phytase and humic acid application. The combined application of P-activators performed better than their sole application. The best three treatments selected from the laboratory incubated experiment were used for the pot experiment with maize, along with the different dosages of P fertilizer. The morphological parameters were observed on the 30th and 60th days of the maize crop. The results of plant height, chlorophyll index, and dry matter production showed that the application of phytase and HA with 100% recommended dose of P was statistically comparable with phytase and HA with 75% recommended dose of P. The findings have illustrated the extent of P release by different P activators in increasing the legacy P availability. The application of phytase and HA with 25% reduced dose of P fertilizers will promote the availability of legacy P in calcareous soils through solubilization.

KEYWORDS:

• Calcareous soil
• humic acid
• legacy p
• p activators
• phosphorus
• phytase

Acknowledgements

I would like to thank my chairperson and members of my advisory committee for their valuable suggestions during my research work. Also I wish to thank the Department of Soil Science and Agricultural Chemistry, Tamil Nadu Agricultural University, Coimbatore–641003, Tamil Nadu, India.

Disclosure statement

No potential conflict of interest was reported by the author(s).