Negative interactive effects between biochar and phosphorus fertilization on phosphorus availability and plant yield in saline sodic soil

Little is known about the interactive effects between biochar application and phosphorus (P) fertilization on plant growth and P uptake. For this purpose, five wheat straw biochars (produced at 25 °C, 300 °C, 400 °C, 500 °C and 600 °C for 4 h) with equal P (36 mg kg− 1) amount, with and without additional P fertilization (100 mg kg− 1) were applied in a pot experiment to investigate the growth of Suaeda salsa and their uptake of P from biochar and P fertilization amended saline sodic soil. Soil P fractions, dry matter yield, and plant P concentrations were determined after harvesting 90 days. Our results confirmed that relatively lower pyrolysis temperature (< 400 °C) biochar retained P availability and increased plant growth. The plant P concentration was significantly correlated with NaHCO3-Pi (P < 0.05), and NaOH-Pi (P < 0.1) during early incubation time (4 days) for biochar amended soil. As revealed by statistical analysis, a significant (P < 0.05) negative (antagonistic) interaction occurred between biochar and P fertilization on the biomass production and plant P concentration. For plant biomass, the effects size of biochar (B), P, and their interaction followed the order of B × P (0.819) > B (0.569) ≈ P (0.568) based on the partial Eta squared values whereas the order changed as P (0.782) > B (0.562) > B × P (0.515) for plant P concentration. When biochar and P fertilization applied together, phosphate precipitation/sorption reaction occurred in saline sodic soil which explained the decreased plant P availability and plant yield in saline sodic soil. The negative interaction effects between biochar and P fertilization indicated limited utility value of biochar application in saline sodic soil.