Acquisition of rock phosphate by combined application of ammonium fertilizers and Bacillus amyloliquefaciens FZB42 in maize as affected by soil pH

Aims The use of plant growth-promoting micro-organisms (PGPMs) to improve plant-nutrient acquisition has a long history but reproducibility remains a challenge. Recent findings suggest an important role of suitable inoculant-fertilizer combinations for the expression of PGPM-effects, particularly with respect to nitrogen (N) supply. In face of the well-documented N form effects on rhizosphere pH, this study addressed the impact of ammonium-assisted PGPM-interactions on the acquisition of sparingly soluble calcium-phosphates as affected by soil pH. Methods and Results The effects of stabilized ammonium fertilization combined with the PGPM inoculant Bacillus amyloliquefaciens FZB42 on the acquisition of rock phosphate in maize were examined on two soils (moderately acidic-pH 5 center dot 6 and alkaline-pH 7 center dot 8). On the two contrasting soils, FZB42 improved the P status and promoted plant growth by different mechanisms. On the acidic soil, a combination of ammonium-fertilization with FZB42 increased P-acquisition by Rock P solubilization via rhizosphere acidification but P-supply in the noninoculated control was already sufficient to meet the plant demands. By contrast, on the alkaline soil, plant growth-promotion was associated with FZB42-induced root growth stimulation. Conclusion The results suggest a significant impact of soil pH on performance and the mode of action of PGPM inoculants, to be considered for practical applications. Significance and Impact of the Study The study advanced existing knowledge on PGPM-assisted P solubilization as affected by different soil properties. The results suggest perspectives for management options to be considered for efficient use of PGPMs in terms of selecting application strategies with compatible PGPM-fertilizer combinations, depending on soil pH conditions.