I. K. Mpanga
University of Hohenheim, Germany
Isaac Kwadwo Mpanga is currently a PhD student at the University of Hohenheim, Germany, where he obtained his MSc. in Crop Sciences. His work focuses on fertilization strategies to improve plant-growth promotion of microorganisms which is under the just ended European Union project called BIOFECTOR chaired by Prof. Dr Guenther Neumann at University of Hohenheim, Germany.
The use of soil microorganisms as inoculants (bioeffectors, BEs) for nutrient mobilization and plant growth promotion has gained increasing interest as a potential tool to reduce the input of agrochemicals with their negative impacts on the environment. However, their use is challenged due to variable performance and efficiency under practical conditions. This study demonstrates that the form of nitrogen fertilization (nitrate or ammonium) is one factor with an impact on the efficiency of beneficial interactions between plants and microbial BEs. Combination of ammonium fertilizers (stabilized by nitrification inhibitors) instead of nitrate fertilization, with BEs of fungal and bacterial origin, resulted in a stimulation of plant growth promotion. Ammonium-fertilized maize plants with BE inoculation showed a more intense rhizosphere acidification associated with improved mobilization of sparingly soluble soil P sources and micronutrients (Zn, Mn), increased root concentrations of hormonal growth regulators (auxin, cytokinins, gibberellic acids), increased root surface area, a higher auxin production potential of various bacterial inoculants (Pseudomonas sp., Bacillus sp.), and increased root colonization by BEs (Trichoderma harzianum). The activities of both, acid and alkaline phosphatases, involved in mineralization of organic P forms in the rhizosphere, were increased in response to BE inoculation, but not affected by the different forms of N fertilization. However, the effectiveness of the fertilization strategy was, dependent on the soil pH and the P-nutritional status of the soil. These findings underline the importance of considering compatible BE-fertilizer combinations for further development of BE-assisted fertilization strategies.