Impact of Microbial Inoculants on Maize Yield under Variable Drought Conditions

Thesis Abstract

maize is a staple crop whose productivity is increasingly challenged by variable drought patterns, which constrain soil moisture, nutrient uptake, and microbial activity; conventional agronomic practices alone have proven insufficient to sustain yields under increasing abiotic stress, necessitating ecologically based strategies such as the use of microbial inoculants to enhance plant stress tolerance and nutrient use efficiency. The study aims to evaluate the impact of selected microbial inoculants on maize yield under variable drought conditions and to elucidate the mechanisms by which these inoculants influence plant performance, soil microbiome dynamics, and resource use efficiency. Specific objectives are (i) to quantify grain yield, above- and below-ground biomass, and harvest index of maize under well-watered and induced drought regimes with and without inoculants; (ii) to assess changes in soil moisture retention, soil respiration, and plant-available nutrients (N, P, K) associated with microbial inoculation; (iii) to characterize the maize root- and shoot-associated microbial communities and their functional potential; (iv) to determine the relationship between inoculant-induced hormonal or signaling responses (e.g., ABA, IAA) and drought resilience; and (v) to develop a predictive model relating inoculant treatment, drought intensity, and yield outcomes using multivariate regression and ANOVA. The methodology adopts a factorial field experiment across two growing seasons in a temperate agricultural district with established maize production, using a randomized complete block design with three replications. The population comprises commercially available inoculants containing Azospirillum spp., Bacillus subtilis, and Rhizobium leguminosarum strains, applied as seed coatings and soil amendments, alongside uninoculated controls. A total of 360 experimental plots (60 per treatment) will be established to accommodate two water regimes (optimal irrigation and regulated drought) and four inoculation treatments (control, Azospirillum, Bacillus subtilis, and a consortium of Azospirillum plus Bacillus). Data collection instruments include calibrated irrigation controllers, portable soil moisture probes (TerraProbe), proximal sensing for canopy temperature and NDVI, and standardized grain yield measurement at harvest. Soil samples will be collected at 0–15 cm and 15–30 cm depths for physicochemical analysis (OC, pH, mineral N, available P and K) and microbial community profiling via 16S rRNA gene sequencing and ITS region for fungi, complemented by shotgun metagenomics on a subset of samples to infer functional potential. Plant physiological measurements will encompass leaf water potential, stomatal conductance, chlorophyll a fluorescence (Fv/Fm), and root morphology using minirhizotron imaging. Data analysis will employ mixed-effects ANOVA to test main effects and interactions, followed by post hoc comparisons (Tukey HSD). Multivariate analysis, including redundancy analysis (RDA) and structural equation modeling (SEM), will discern direct and indirect pathways linking inoculants, soil microbiome shifts, plant physiology, and yield. Regression models will be constructed to predict yield from drought index, inoculant type, and soil moisture variables, with model selection guided by AIC and cross-validation. The study is expected to reveal that inoculants, particularly the consortium, improve maize yield under drought by promoting root proliferation, enhancing nutrient acquisition, stabilizing soil microbial networks, and modulating hormonal responses that reduce drought stress impacts. Anticipated findings include higher grain yield and harvest index, elevated soil moisture retention, greater microbial functional gene abundance related to stress tolerance and nutrient cycling, and positive correlations between inoculant-driven microbial indicators and plant performance. The contribution to knowledge lies in empirically validating inoculant-based mitigation of drought stress in maize under field conditions, elucidating mechanistic links between soil microbiomes and host drought responses, and providing validated predictive models for yield under abiotic stress. The study culminates with practical recommendations on inoculant selection and integration into drought-prone maize production systems, and implications for sustainable intensification strategies in agro-ecological contexts. The results are expected to inform policy on sustainable seed treatment practices and to guide breeding programs aiming to enhance plant-microbe compatibility under water-limited environments.