Quinoa (Chenopodium quinoa Willd.) is a crop of global significance due to its high nutritional value and remarkable adaptability to adverse agroclimatic conditions (Zurita-Silva et al., 2014; Fuentes et al., 2009). These attributes have driven its increasing agronomic importance, positioning it as a key contributor to food security (Ruiz et al., 2014). Since the 1980s, quinoa exports from South America have increased, and its cultivation has expanded to various countries worldwide (Bazile et al., 2016; Ruiz et al., 2014). In Peru, quinoa has become one of the most important Andean grains, with a steadily growing production and export value that reflects its increasing global demand (MIDAGRI, 2025).

Nationally, 97.5% of quinoa production is concentrated in eight departments: Puno, Ayacucho, Apurímac, Cusco, Arequipa, Junín, Huancavelica, and La Libertad (MIDAGRI, 2023). In the Arequipa department, the cultivated area has expanded significantly in recent years. Notably, the Majes, Santa Rita, and La Joya irrigation systems account for 60% of this area (Zegarra Alarcon, 2018). However, these irrigation systems are located along the Peruvian coast, where agricultural production is constrained by water scarcity and soil limitations. Coastal soils are often characterized by high salinity, low organic matter content, and poor humidity retention capacity, which hinder optimal crop development. To overcome these challenges, the adoption of efficient irrigation technologies, such as drip irrigation, and sustainable soil management practices are essential for maintaining agricultural productivity.

Due to these soil limitations, Peruvian coastal agriculture relies heavily on synthetic chemical fertilizers as the primary source of nutrients, which are indispensable in conventional farming (Krasilnikov et al., 2022). Over the past decade, disruptions in global supply chains—including natural disasters, geopolitical conflicts (such as the war in Ukraine), and the COVID-19 pandemic—have impacted the production and distribution of fertilizers, thereby threatening food security (Ben Hassen and El Bilali, 2022; Penuelas et al., 2023). Additionally, climate change has introduced new challenges, including rising annual and seasonal temperatures, shifts in precipitation patterns, and an increased frequency of extreme weather events, all of which significantly impact agricultural productivity (Grigorieva et al., 2023). Changes in key agroclimatic indexes—such as Growing Degree-Days, the Temperature-Humidity Index, and variations in the growing season length—have been observed, further influencing crop yields and production stability (Mu et al., 2013; Kipriyanov and Savinykh, 2019). Addressing these challenges necessitates adaptive strategies, including the development of more resilient crop varieties and the optimization of sowing schedules. In this context, implementing multiple sowing cycles or year-round cultivation has been proposed as a viable approach to sustaining food production in the face of changing climatic conditions (Gao et al., 2023; Zou et al., 2024).

Additionally, plant growth-promoting rhizobacteria (PGPR) have emerged as an innovative, natural, and environmentally sustainable technology for optimizing fertilizer use and mitigating abiotic stress (Ikiz et al., 2024; Shah et al., 2021). PGPR enhances plant growth through multiple mechanisms, including biological nitrogen fixation, nutrient solubilization, siderophore production, and phytohormone synthesis. Furthermore, PGPR improves plant resilience to abiotic stress by promoting the accumulation of specific osmolytes and by reducing ethylene levels in roots through the activity of 1-aminocyclopropane-1-carboxylate (ACC) deaminase (Ahemad and Kibret, 2014; Vurukonda et al., 2016; Braud et al., 2009; Hayat et al., 2010; Hartman and Tringe, 2019; Etesami and Adl, 2020). Among the diverse soil bacterial taxa, species belonging to the genera Pseudomonas and Bacillus are particularly abundant in strains with well-documented PGPR effects (Zahir et al., 2003; Shah et al., 2021; Hasan et al., 2024).

The growth-promoting effects of Pseudomonas putida include nitrogen fixation, siderophore production, and phosphate solubilization (Sah et al., 2021). Similarly, Bacillus subtilis enhances plant nutrition through nitrogen fixation, phosphate solubilization, and the production of key phytohormones such as auxins, cytokinins, and gibberellic acid (Arkhipova et al., 2005; Gutiérrez-Mañero et al., 2001; Přikryl et al., 1985; Testen et al., 2022). Studies have identified P. putida and B. subtilis in the rhizosphere of quinoa plants, with functional capacities associated with biological nitrogen fixation, phosphorus solubilization, and indole-3-acetic acid biosynthesis (Ortuño Castro et al., 2014; Rafique et al., 2025). Furthermore, Bacillus isolates associated with Chenopodium species have been shown to possess plant growth-promoting traits (Testen et al., 2022).

PGPR applications can be tailored to different crops and agricultural practices. Standard inoculation methods include seed treatment, soil drenching, foliar spraying, and root dipping (Yang et al., 2024). However, current PGPR research in quinoa is largely limited to conventional growing seasons, highland or rainfed systems, and non-fertigation inoculation methods, which restricts its applicability to intensive coastal agriculture. Although previous studies have demonstrated the beneficial effects of P. putida and B. subtilis on quinoa growth and nutrient acquisition (Ortuño Castro et al., 2014), no studies have explicitly evaluated their co-application via fertigation under arid, off-season coastal conditions in Peru. This lack of evidence represents a clear research gap, particularly in regions such as the Peruvian coast, where drip irrigation is essential and quinoa production is increasingly expanding into non-traditional sowing periods. Fertigation-based PGPR delivery offers several agronomic advantages, including targeted inoculum placement in the rhizosphere, enhanced root colonization, and compatibility with reduced fertilizer inputs. Nevertheless, the effectiveness of fertigation-applied PGPR in improving quinoa performance under arid and off-season conditions remains unknown.

Therefore, a critical knowledge gap exists regarding whether fertigation-based co-inoculation with P. putida and B. subtilis can sustain quinoa growth and yield under reduced NPK fertilization in arid coastal environments. Addressing this gap is essential for developing sustainable microbial-based management strategies adapted to climate variability and resource-limited agroecosystems.

The objective of this study was to evaluate the effect of fertigation-based co-inoculation with Pseudomonas putida (P3 strain) and Bacillus subtilis (BacF strain) on quinoa growth and yield under arid, off-season coastal conditions in Peru, in combination with reduced synthetic NPK fertilization, in order to assess its potential as a sustainable strategy to optimize fertilizer use and improve productivity.

This study evaluated the fertigation-based application of a microbial inoculant composed of rhizobacteria from the genera Pseudomonas and Bacillus in the Salcedo INIA quinoa variety, cultivated out of season. The inoculant’s effect was analyzed as a growth and yield promoter under arid climatic conditions with persistent moisture deficiency (SENAMHI, 2020). The beneficial effects of plant growth-promoting rhizobacteria (PGPR) are well-documented and include enhanced nutrient uptake, phytohormone production, and the release of substances that improve resistance to abiotic stress through the accumulation of specific solutes (Sarti et al., 2023; Sarti and Miyazaki, 2013; Wang et al., 2024).

In line with these findings, plants treated with microbial inoculant and 75% NPK fertilization exhibited greater height than those without inoculation. Additionally, PGPR application led to a higher accumulation of dry biomass (12%). Solórzano-Acosta and Quispe (2024) reported that the Bacillus subtilis strain used in their study enhances soil NPK extraction and improves nitrogen uptake efficiency. Likewise, Pseudomonas putida can solubilize poorly soluble phosphate compounds by releasing low-molecular-weight organic acids, such as gluconic acid, and producing phosphatases and phytases, which break down organic phosphate compounds. This process acidifies the external environment, chelates phosphate-bound cations, and increases phosphate availability (Khoso et al., 2024; Rafique et al., 2022).

Based on these mechanisms, microbial inoculation can induce vegetative development, including increased root biomass (Rafique et al., 2022; Solórzano-Acosta and Quispe, 2024). However, in contrast to the findings of Solórzano-Acosta and Quispe (2024), our results did not show significant differences in root dry biomass despite a tendency toward higher values in inoculated treatments (Figure 4C). This discrepancy may be related to the characteristics of the Salcedo INIA quinoa variety, which prioritizes biomass development under stress conditions (Antezana, 2019). Temperature effects may also have influenced vegetative development, as quinoa’s adaptability to high temperatures without water deficit has been linked to the development of larger stomata and an increased number and length of lateral branches, often at the expense of better root development (Becker et al., 2017; Hinojosa et al., 2019; Serrat et al., 2024).

This thermal effect was reflected in the leaf area index (LAI), which showed the highest values in treatments receiving full fertilization, whereas microbial inoculant treatments did not exhibit significant differences (Figure 5A). This suggests that optimal leaf distribution was favored under conditions of sufficient water and nutrient availability (Becker et al., 2017). Additionally, studies such as those by Kakabouki et al. (2019) indicate that increasing nitrogen doses to 200 kg ha^-¹ in quinoa cultivation can enhance LAI, thereby improving yield. The resulting increase in LAI may facilitate greater light capture, potentially boosting photosynthesis and ensuring an adequate supply of assimilates to the developing organs of the quinoa plant. Plant chlorophyll content is closely linked to photosynthetic capacity and nutritional status, as nitrogen is a fundamental component of this biomolecule (Su et al., 2017). The SPAD chlorophyll index serves as an indicator of plant nitrogen status, demonstrating a positive correlation with nitrogen availability (Ribeiro Da Cunha et al., 2015). Accordingly, the values recorded for the 75% fertilization treatments tended to be lower than those for full fertilization. However, under fertilization stress conditions, microbial inoculation enabled chlorophyll content to remain statistically comparable to treatments receiving full NPK doses, with an average increase of 10% (Figure 5B).

Studies such as that by Ferioun et al. (2024) reported increases of 13–30% in SPAD values following the application of formulations containing Achromobacter insolitus, Pseudomonas putida, Providencia rettgeri, and Alcaligenes sp. Similarly, Li J. et al. (2023) observed higher chlorophyll levels in quinoa crops treated with Bacillus-based inoculants. This trend has also been documented in maize, tomato, strawberry, oats, alfalfa, and cucumber using Bacillus and Pseudomonas as microbial inoculants (Abbasi et al., 2011; Chebotar et al., 2022; Li et al., 2020; El hjouji et al., 2025). Similar to plant height, once the crop’s nutritional requirements were met, microbial inoculation did not lead to further significant increases in chlorophyll content. This suggests that quinoa has an upper limit for nutrient uptake, beyond which additional inputs do not further enhance its physiological potential (Cárdenas-Castillo et al., 2021).

The capacity of Pseudomonas putida (P3 strain) and Bacillus subtilis (BacF strain) to enhance yield-related traits is evident in the Figure 6, where microbial inoculation led to increased panicle dry weight at both fertilization levels, as well as higher thousand-grain weight. These findings demonstrate that these inoculants positively influence grain yield, a key agronomic trait, possibly through the production of growth hormones and/or nutrient mobilization (Rafique et al., 2025). Solórzano-Acosta and Quispe (2024) reported that the Pseudomonas putida strains used in their study can solubilize phosphates and produce siderophores, while Bacillus subtilis enhances nitrogen uptake efficiency—mechanisms that align with their potential to improve crop yields. Similarly, Castillo et al. (2022) highlighted the ability of Bacillus sp. to enhance nitrogen fixation and phosphorus solubilization in quinoa, resulting in improvements in growth parameters, including length, weight, diameter of the panicle, and grain yield. Additionally, Rafique et al. (2022) reported that Pseudomonas spp. significantly enhance quinoa growth and yield by improving relative water content, quantum flux, diffusive resistance, and crop transpiration rate.

Despite a general trend toward higher yields through microbial inoculation, this did not translate into significant improvements in commercial yield. However, the positive effect of full fertilization on commercial yields was confirmed, reflecting quinoa’s strong ability to assimilate fertilizers at the proposed doses. Cárdenas-Castillo et al. (2021) suggested that quinoa grown in low-fertility areas, such as the Peruvian coast, can achieve yields exceeding 3.6 t ha^-¹ after assimilating approximately 240 kg ha^-¹ of nitrogen. Furthermore, fertilization rates of 90 kg ha^-¹ phosphorus and 105 kg ha^-¹ potassium have been reported to enhance both yield and nutritional content in quinoa (Kakabouki et al., 2019; Taaime et al., 2023; Van Minh et al., 2022).

Despite improvements in vegetative development and a positive trend in yield potential (i.e., greater panicle and thousand-seed weights), the obtained commercial yields were lower than the typical 4 t ha^-¹ reported for the Salcedo INIA quinoa variety in coastal production areas (INIA, 2014). This outcome may be primarily attributed to the atypical sowing season, which coincided with high temperatures (33 °C) during the flowering stage. Such conditions have been reported to reduce quinoa grain-setting efficiency by altering the final number of grains per abortion (Bertero and Ruiz, 2008; Lesjak and Calderini, 2017). Given that the Salcedo INIA variety is adapted for coastal environments with average temperatures of 24–25 °C (FAO, 2015), it is likely that heat stress during flowering negatively impacted grain set efficiency. Similarly, Hinojosa et al. (2019) investigated quinoa growth and pollen morphology in response to high temperatures, reporting a 30–70% reduction in pollen viability under heat stress. However, they found that seed size and leaf greenness were unaffected, while photosynthesis rates increased, demonstrating quinoa’s high plasticity in response to elevated temperatures and environmental stresses (Alzahrani et al., 2024).

Based on these findings, the use of microbial inoculants Pseudomonas putida (P3 strain) and Bacillus subtilis (BacF strain) has a positive effect on quinoa cultivation in low-fertility, arid environments such as the Peruvian coast. This effect is particularly significant under reduced fertilization conditions, suggesting a potential strategy to lower production costs without compromising biomass, especially in fields that employ drip irrigation systems. On one hand, microbial inoculants enhance nutrient uptake efficiency; on the other, they represent an underutilized technology in the country that could be integrated with more widely adopted practices in coastal agriculture, such as pressurized irrigation systems.

However, careful management of sowing seasons is crucial for this variety, as its ability to tolerate temperatures above 30 °C during the full flowering and grain-setting stages is limited, which ultimately compromises commercial yield. In this context, beyond the use of PGPR, it may also be necessary to incorporate varietal selection or breeding programs aimed at improving heat tolerance, so that microbial strategies are complemented by greater crop resilience.

It should be acknowledged that the application of SERENADE SOIL (Bacillus subtilis QST 713 strain) to all treatments, including the non-inoculated controls, represents a methodological limitation of this study. Its use was necessary to prevent severe phytosanitary losses and ensure uniform plant survival. Therefore, the non-inoculated treatment cannot be considered a completely Bacillus-free control. Importantly, this experimental condition implies that the treatment comparisons should not be interpreted as “PGPR versus no PGPR”, but rather as “BacF + B. subtilis QST 713” versus “B. subtilis QST 713 alone”. Although B. subtilis QST 713 is primarily recognized for its antifungal activity, its presence may have partially masked or attenuated the exclusive effects of the BacF PGPR strain. Therefore, the physiological and agronomic responses observed in this study reflect the additional or synergistic contribution of BacF under a baseline biofungicide application, rather than its isolated effect. Despite this limitation, the consistent differences between inoculated and non-inoculated treatments indicate that BacF exerted functional effects beyond those provided by B. subtilis QST 713 alone. Future studies should include treatments without Bacillus-based fungicides and, where possible, monitor microbial populations to more precisely distinguish the individual contributions of biocontrol agents and PGPR inoculants.

This study demonstrates that the integration of Pseudomonas putida (P3 strain) and Bacillus subtilis (BacF strain) through fertigation promotes quinoa growth and biomass accumulation, particularly under reduced fertilization in arid coastal environments. Microbial inoculation enhanced nutrient uptake and yield components such as panicle weight and thousand-grain weight, highlighting its potential to optimize production while reducing dependence on chemical fertilizers. However, commercial yield was constrained by heat stress during flowering ((+)100%: 2.20 ± 0.30 t ha^-1, (+)75%: 1.42 ± 0.19 t ha^-1, (-)100%: 1.50 ± 0.30 t ha^-1, (+)75%: 1.02 ± 0.13 t ha^-1), underscoring the importance of proper sowing date management and the need to complement microbial strategies with variety selection or breeding for heat tolerance.

From a sustainability perspective, fertigation with microbial inoculants represents an environmentally friendly alternative that can reduce fertilizer use, improve soil health, and strengthen the resilience of agroecosystems. Broader validation across different environments, cost–benefit evaluations, and assessments of grain nutritional quality are required to confirm its broader applicability. Extending this approach to other regional crops such as maize and rice could further increase agricultural productivity while safeguarding natural resources in Peru.