Evaluation of the Performance and Growth Indices of Green Bean (Phaseolus vulgaris L.) and Black Cumin (Nigella sativa L.) in a Replacement Intercropping System

IntroductionDue to rapid population growth and the reduction of arable land, the most effective way to increase crop yields is by boosting production per unit area. So far, many studies have shown the positive effect of intercropping on LAI (Leaf area index), TDM (Total dry matter) (g.m-2), CGR (Crop growth rate) (g.m-2.day-1), RGR (Relative growth rate) (g.g-1.d-1), and NAR (Assimilation rate) (g.m-2Leaf.day-1) growth indices, and so on. Therefore, this study aimed to evaluate and compare the yield and growth indices of green bean and black seed in sole culture and replacement intercropping ratios. Materials and MethodsThe experiment was conducted based on RCBD design during the growing season 2018-19. Treatments included replacement intercropping ratios including 25% green bean + 75% black seed (P1N3), 50% green bean + 50% black seed (P2N2), 75% green bean + 25% black seed (P3N1), and sole culture of green bean (P) and black seed (N). Irrigation was done once a week, and sampling was performed once every 10 days. The effect of different replacement intercropping ratios on growth indices during the growth period was investigated. The curve function was fitted using Slide Write ver 2.0 software, and Excel 2016 was used to draw figures. Results and DiscussionThe results showed that the treatments affected the growth indices of green bean and black seed. The highest LAI of bean and the black seed (3.53 and 0.5) were observed in the sole culture of these crops. The lowest LAI of green bean (1.14) and black seed (0.2) were obtained in P2N2 and P3N1 treatments. The sole cultures had the highest TDM for green bean (973.34 g.m-2) and black seed (339.55 g.m-2). The lowest TDM of green bean and black seed were observed in P1N3 (164.25 g.m-2) and P3N1 (91.18 g.m-2) treatments, respectively. The highest crop growth rate (CGR) of green bean (10.83 g·m⁻²·d⁻¹) and black seed (25.71 g·m⁻²·d⁻¹) were recorded in their respective sole cropping systems at 73 and 82 days after planting. P3N1 and P2N2 treatments had the highest RGR of green bean (0.1 g.g-1 d-1) and black seed (0.13 g.g-1.d-1), respectively. The highest NAR of green bean (14.95 g.m-2.d-1) and black seed (48.24 g.m-2.d-1) were recorded at 72 days after planting in P2N2 and 63 days after the planting in sole culture of black seed, respectively. The highest yields of green bean and black seed were obtained in P3N1 and P2N2 treatments, respectively, which did not differ significantly from their sole culture. The land equivalent ratio (LER) for the P1N3 treatment was close to one, while the LER values for the P2N2 and P3N1 treatments were greater than one. This suggests that the P2N2 and P3N1 treatments utilized arable land more effectively and ecologically compared to the P1N3 treatment. The findings can be considered as a reason for improving crop yields due to improving ecological efficiency in the intercropping.Conclusion The results revealed that the intercropping of black seed with green bean improved the growth of this medicinal plant. In both crops, the Leaf area index, total dry matter, and crop growth rate in sole culture were higher than in other treatments due to their higher plant density; however, the relative growth rate and assimilation rate were also improved in the intercropping treatments. Thus, the intercropping of green bean and black seed would be beneficial from the perspective of ecological management. In general, the replacement of half of the black seed planting density with green bean can be considered beneficial in terms of productivity in crop production.