Nitrification inhibitor differentially regulates manganese and phosphorus shoot concentrations in maize : The pros and cons of rhizosphere acidification
High soil pH can lead to Mn2+ and P deficiency, and crop yield losses. NH4 +-N fertilization can increase soil Mn2+ availability and shoot concentration. Nitrification inhibitors (NIs) such as DMPP, can lower rhizosphere soil pH, and improve plant P uptake and prevent P deficiency. It is unknown if it is nitrification-induced acidification of bulk soil or NI-induced rhizosphere acidification, that is effective in enhancing Mn2+ and P availability and shoot concentrations. Experiments were done under liming, soil textures and drought stress with the aim of investigating differential effect of rhizosphere acidification in regulating maize Mn2+ and P shoot concentrations. Chapter two indicates acidification of bulk soil increased Mn2+ shoot concentration. Rhizosphere acidification promoted P shoot concentration, but not at high soil pH due to high buffering capacity. Chapter three informs on effectiveness of rhizosphere acidification in improving Mn2+ availability and shoot concentration in loamy sand but not in other soil textures. Moreover, rhizosphere acidification promotes P availability and shoot concentration in silt loam and loamy sand. Finally, in Chapter four, DMPP is effective in alleviating Mn2+ and P deficiencies in silt loam, rather than in sand under drought conditions considering the effect being soil-texture dependent. In conclusion, DMPP-use in promoting P uptake should be recommended for increasing yield in high-pH soil. Except for neutral pH loamy sand, DMPP is not beneficial in increasing Mn2+ uptake in maize, and so Mn2+ deficiency be considered on DMPP-use to augment P uptake. Finally, DMPP-use in attenuating drought impacts on Mn2+ and P deficiencies amidst climate change scenario, may build resilience in crops, leading to high yield. Future focus be on mechanisms of NI-induced antagonistic effect of NH4 + uptake on Mn2+, NI impact on plant species’ Mn2+ uptake, and response of Mn2+ and P deficiencies to NI under increasing drought regimes.
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