# Effectiveness of Streptomyces enissocaesilis and chitosan on agronomic, biochemical, and quality traits of soybean under different irrigation intervals

## TL;DR

This study shows that using Streptomyces enissocaesilis and chitosan with frequent irrigation improves soybean growth, yield, and quality.

## Contribution

The novel contribution is the synergistic effect of Streptomyces and chitosan on soybean under different irrigation regimes.

## Key findings

- Combined Streptomyces and chitosan under well-watered conditions significantly increased chlorophyll and seed yield.
- Water stress reduced oil and protein content, but bio-stimulants helped preserve seed quality.
- Hierarchical clustering and PCA confirmed the distinct benefits of bio-stimulants under optimal irrigation.

## Abstract

This study evaluated the growth, biochemical, yield-related, and chemical traits of soybean under different irrigation intervals (8, 13, and 18 days), seed inoculation with Streptomyces enissocaesilis, and foliar application of chitosan (0, 0.25, and 0.50 g.L-1) during two successive seasons in 2023 and 2024. A split-split plot design arranged in randomized complete blocks with three replications was employed. Analysis of variance indicated that irrigation interval was the most influential factor, exhibiting a highly significant effect (p < 0.001) on most assessed traits. Additionally, Streptomyces inoculation and chitosan application interacted synergistically, significantly improving all yield-related and chemical parameters compared to their individual effects. Under well-watered conditions (8-day interval), the combined application of seed inoculation with 0.50 g.L-1 chitosan resulted in the highest concentrations of chlorophyll a and b, more than doubling the levels observed in the stressed, untreated control. Conversely, the longest irrigation interval (18 days) combined with the same dual treatment triggered the strongest biochemical stress response, maximizing key markers including proline content, peroxidase, and polyphenol oxidase activities. Most notably, the highest 100-seed weight (23.33 g), pod number per plant (60.67), and pod weight per plant (38.00 g) were achieved under well-watered conditions with inoculation and 0.50 g.L-1 chitosan, resulting in the highest seed yield (3220.93 kg.ha-1). In contrast, water stress substantially compromised nutritional components, as evidenced by the significant reduction in oil and protein content, highlighting the critical role of inoculation and chitosan in preserving seed quality under such stress. These results were further validated by hierarchical clustering, principal component analysis, and radar plot visualization, confirming that the application of bio-stimulants (inoculation and chitosan) under well-watered conditions produced a distinct and favorable profile for soybean growth, biochemical, yield-related, and chemical traits. Therefore, the current findings provide valuable recommendations for the integrated application of S. enissocaesilis inoculation and chitosan under short-interval irrigation as a sustainable and effective strategy to maximize soybean productivity and quality.