Introduction

Intercropping is defined as the simultaneous cultivation of two or more crop species in the same location during a growing season. Climate change in recent years has led to more regions facing drought stress. In this context, water management in agricultural systems has gained greater importance. Partial root-zone irrigation, involves irrigating half of the root system while leaving the other half in dry soil. This method has been studied in various intercropping systems and, in most cases, has led to improved water use efficiency. Partial root-zone irrigation can be an effective management strategy for water conservation in farming systems. Accordingly, the present study aimed to evaluate the yield and seed quality of cowpea and roselle under partial root-zone irrigation in both sole cropping and different intercropping patterns



Materials and Methods

A two-factor RCBD factorial experiment (5×3) with three replications was conducting during 2023-2024 in Shadegan county, Khuzestan, Iran. Two irrigation methods included full irrigation and partial root-zone irrigation and five planting patterns consisted of two sole cropping treatments (cowpea and roselle) and three intercropping patterns (75% cowpea + 25% roselle, 50% cowpea + 50% roselle, and 25% cowpea + 75% roselle), were evaluated in this research. The partial irrigation treatment was applied after the establishment of cowpea plants in the field. To calculate the competitive ability of cowpea relative to roselle, as well as the complementarity of the intercropping components in using environmental resources, the competitive ratio index and the relative yield total index were calculated, respectively.



Results and Discussion

The intercropping pattern of 25% cowpea + 75% roselle under partial root zone irrigation resulted in lower 1000-seed weight (41.4% reduction) and seed yield (64.8% reduction) of cowpea. Full irrigated sole cropped plots of cowpea had the highest protein yield (446 kg per hectare). The highest water productivity for seed production of cowpea (approximately 330 grams of seed per cubic meter of water consumed) was achieved under partial root-zone irrigation in both sole cropping and the intercropping pattern of 75% cowpea + 25% roselle. Under partial root-zone irrigation, the seed yield of roselle decreased by 37.1%. Roselle had the highest seed yield in sole cropping, and the lowest roselle seed yield recorded in the 75% cowpea + 25% roselle intercropping pattern, which was 42.4% lower than sole cropping. Under partial root-zone irrigation sole cropped roselle exhibited the highest water productivity, producing approximately 165 grams of seed per cubic meter of water consumed. The relative yield total under full irrigation conditions was significantly higher than partial root-zone irrigation. No significant difference was observed in the relative yield total among different planting patterns, and the average of this index across various intercropping systems was 1.39. The highest competitive ratio of cowpea to roselle under both irrigation conditions (full and partial root-zone irrigation) was achieved in the 75% cowpea + 25% roselle intercropping pattern. No statistical difference was found between any intercropping pattern under both full and partial root-zone irrigation conditions.



Conclusion

Since the relative yield total in all intercropping patterns was greater than one, cowpea and roselle acted complementarily in using environmental resources. Therefore, the intercropping of cowpea and roselle has advantages over their sole cropping. The selection of the intercropping pattern depends on the target crop. Accordingly, depending on the target crop (cowpea or roselle), the highest density of the corresponding plant in the intercropping system can be selected. Based on this, if the target crop is cowpea for seed production, the intercropping pattern of 75% cowpea + 25% roselle under full irrigation conditions is recommendable. However, partial root-zone irrigation, despite an approximately 29% reduction in seed yield, results in the highest protein yield. If the target crop is roselle for seed production, the intercropping pattern of 25% cowpea + 75% roselle can be recommended.