Estratégias de inoculação e coinoculação de bioinsumos e adubação nitrogenada para mitigação do estresse hídrico na cultura do milho em região semiárida

Abstract

Water deficit, especially in arid and semi-arid regions, is one of the main limiting factors in maize cultivation. Bioinputs, such as plant growth-promoting bacteria, represent promising alternatives to enhance plant resilience under water stress by stimulating root growth and the production of phytohormones, such as abscisic acid, which regulates stomatal closure and reduces water loss. This study aimed to evaluate the effects of inoculation and co-inoculation with Bacillus aryabhattai and Azospirillum brasilense on the agronomic and physiological performance of maize under water deficit conditions at different phenological stages, as well as to estimate the crop sensitivity coefficient to water deficit (Ky) and assess the economic and social viability of the management systems employed. The experiment was conducted under field conditions during two cropping seasons (2023 and 2024), using a randomized block design in a split-plot arrangement with four replications. The main plots consisted of five irrigation strategies: full irrigation (IP), regular deficit (IDR50%), and controlled deficits during the vegetative stage (IDCV50%), flowering and grain formation stage (IDCF50%), and grain filling stage (IDCE50%). The subplots comprised four bioinput managements applied via seed treatment: A (inoculation with B. aryabhattai), V (co-inoculation with B. aryabhattai + A. brasilense), P (positive control, without bioinputs but with mineral nitrogen fertilization), and B (negative control, without mineral nitrogen or bioinputs). The variables evaluated included agronomic parameters, physiological attributes (photosynthetic rate - A, transpiration rate - E, stomatal conductance - gs, internal CO₂ concentration - Ci, carboxylation efficiency -A/Ci, and chlorophyll content - SPAD index) as well as water use efficiency, Ky, and economic indicators including net farm income and the minimum land area required to ensure the social reproduction of the production unit. The results indicated that the use of bioinputs had limited physiological effects under water deficit, with no statistically significant impacts in most treatments, particularly in the second season. In contrast, controlled deficit irrigation during the vegetative stage (IDCV50%) proved to be the most efficient strategy, combining lower Ky values (<1), stable yield levels, and greater economic feasibility. Treatments involving full irrigation and co-inoculation also showed higher economic returns, notably through a reduction in the minimum land area needed per rural worker, highlighting the potential of such practices for family farming systems. The Ky analysis confirmed greater crop sensitivity to water stress during the flowering and grain filling stages, while vegetative-stage deficit was better tolerated. It is concluded that adopting controlled deficit irrigation strategies during less sensitive growth stages, with or without the use of bioinputs, can represent a viable alternative for optimizing water use, reducing production costs, and ensuring the agronomic and socio-economic sustainability of maize cultivation in semi-arid regions.