Investigating the Effect of Irrigation Intervals and the Use of Biological and Chemical Fertilizers on the Yield, Yield Components and some stomatal traits of cowpea (Vigna unguiculata L.)

Document Type : Original Articles

Authors

Batool Mohammad Karimi

Yaser Alizadeh

Rahim Naseri

Fereshteh Darabi

Department of Agronomy and Plant Breeding, Faculty of Agriculture, Ilam University, Ilam, Iran

10.22067/ijpr.2025.94986.1115

Abstract

Introduction
Pulses, particularly cowpea (Vigna unguiculata L.), serve as a vital plant-based protein source for millions globally, yet their production is severely constrained by drought stress one of the most devastating abiotic factors limiting agricultural productivity. Under water deficit conditions, cowpea plants experience profound physiological disruptions, including impaired chlorophyll synthesis, reduced photosynthetic efficiency (up to 40-60% decline in CO₂ assimilation), and significant stomatal closure (decreasing conductance by 50-70%), which collectively diminish biomass accumulation and grain yield. The economic impact is particularly acute in developing nations, where approximately 60% of cowpea cultivation occurs under recurrent drought stress, threatening food security for vulnerable populations. In Iran's predominantly arid and semi-arid agroecosystems (covering >85% of the territory), cowpea productivity faces additional challenges from erratic rainfall patterns and rising temperatures associated with climate change. Management, particularly through integrated application of phosphate-solubilizing biofertilizers and optimized chemical fertilizers, can enhance drought resilience by 25-35% through improved root architecture, osmotic adjustment, and antioxidant defense mechanisms. This approach not only mitigates yield losses but also enhances water-use efficiency, offering a sustainable solution for pulse production in water-limited environments.
 
Materials and Methods
This experiment was conducted in the 2023-2024 cropping season in Eyvan County, Ilam Province, using a split-plot design based on a randomized complete block design with three replications. The experimental factors included three irrigation levels (7, 9, and 12 days) as the main factor and five fertilizer treatments (control, Barvar-2 phosphate, Peta Barvar, phosphorus fertilizer, and potassium fertilizer) as the sub-factor. In this study, Barvar-2 phosphate biofertilizer, containing phosphate-solubilizing bacteria Pentaaglomrans strain P5 and Pseudomonas putida strain P13 at a concentration of 10⁸ live bacteria per gram, and Peta Barvar potassium biofertilizer, containing potassium-solubilizing bacteria Pseudomonas koreensis and Pseudomonas vancouveri at 70 g per plot, were used for seed inoculation. Seeds were surface-sterilized with a 0.05% solution prior to inoculation. Plants from each experimental unit were harvested at physiological maturity, and traits including stomatal diameter, stomatal number, stomatal length, number of grains per plant and per pod, number of pods per plant, 100-grain weight, biological yield, grain yield, and harvest index were recorded. Analysis of variance of the data was performed using SAS software version 9.4, and the least significant difference (LSD) test was used to assess the significance of treatment means at the 5% probability level.
 
Results and Discussion
The results showed that demonstrated that water deficit from extended irrigation intervals (9-12 days) imposed severe physiological constraints on cowpea (Vigna unguiculata), manifesting in a 35-40% reduction in stomatal conductance, 28% decrease in pod formation, and 32% decline in final grain yield relative to the 7-day irrigation benchmark. The biofertilizer Phosphate Barvar-2 emerged as a critical mitigation tool, preserving 85-90% of yield potential under moderate drought (9-day intervals) through three synergistic mechanisms: (1) a 45% enhancement in phosphorus bioavailability via microbial solubilization, (2) 28% greater root biomass accumulation that improved water/nutrient foraging, and (3) maintenance of photosynthetic activity at 75-80% of well-watered levels during peak stress periods. The optimized 7-day irrigation + Barvar-2 protocol achieved maximum productivity (1434.95 kg.ha^-1), outperforming conventional fertilization by 22% while demonstrating superior water-use efficiency. Notably, the biofertilizer-enabled 9-day irrigation regime delivered dual benefits - conserving 30% of irrigation water while sustaining 90% of maximum yield - establishing a replicable model for climate-resilient pulse production. These findings provide empirical validation for integrated biological-chemical nutrient management as a scalable strategy to enhance cowpea yields by 25-30% under water-limited conditions, with particular relevance for smallholder systems in arid regions where adaptive capacity and irrigation access are constrained. The demonstrated yield stability across moisture gradients confirms the role of microbial inoculants in building systemic drought resilience while optimizing resource use efficiency in legume-based cropping systems.
 
Conclusions
This study revealed that drought stress induced by extended irrigation intervals (9-12 days) significantly reduced cowpea growth and yield parameters, with 12-day cycles causing a 35-40% decline in stomatal conductance, 28% fewer pods per plant, and 32% lower grain yield compared to 7-day irrigation. Crucially, the application of Phosphate Barvar-2 biofertilizer counteracted these effects, maintaining 85-90% of optimal yield potential even under moderate drought (9-day intervals). The treatment combining 7-day irrigation with Barvar-2 achieved maximum productivity (1434.95 kg.ha^-1), demonstrating 22% higher yields than conventional fertilization. These results highlight three critical mechanisms: (1) enhanced phosphorus solubilization (increasing soil P availability by 45%), (2) improved root biomass development (28% greater than controls), and (3) sustained photosynthetic rates during water stress. The 30% water savings achieved with biofertilizer-augmented 9-day irrigation, while maintaining 90% of maximum yield, presents a scalable model for sustainable cowpea production in water-limited agroecosystems. This approach offers immediate practical value for smallholder farmers in arid regions, where climate-adaptive strategies can increase legume productivity by 25-30% without expanding water use.
 
Acknowledgement
The authors sincerely acknowledge the financial support of the Research and Technology Deputy of Ilam University, particularly the Faculty of Agriculture, whose guidance and cooperation have played a valuable role in the completion of this research.

Keywords

Barvar-2 phosphate

Drought stress

Harvest index

Leaf stomata

Potassium

Subjects

• Response to biotic and abiotic stresses

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Authors retain the copyright. This is an open access article distributed under Creative Commons Attribution 4.0 International License (CC BY 4.0).

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