Evaluation of yield and financial advantage of intercropping of poplar (Populus nigra 62/154) with alfalfa (Medicago sativa L.) at Saatlou poplar research station of Urmia

Background and Objective: Due to the increasing demand for wood in the country's timber industries and the implementation of the forest breathing plan, which prohibits logging in northern forests, combined with the challenges of importing wood because of costly and unstable currency exchange rates, there is a need to expand poplar plantations in appropriate areas. Although extensive poplar plantations exist in West Azerbaijan province, the lack of economic justification, particularly in the early years of tree growth, highlights the importance of integrating mixed-cropping systems in the northwest's climatic zone. The combination of poplar with alfalfa is especially beneficial, given alfalfa’s role in livestock feed and West Azerbaijan's position as the second-largest alfalfa producer in the country. Additionally, mixed cropping is recognized for its ability to enhance productivity, serve as a primary income source for farmers, and improve soil fertility and resource utilization efficiency, making it a promising strategy for agroforestry. This study aims to evaluate the benefits of poplar-alfalfa intercropping in Urmia County’s climatic conditions.
Material and Methods: The study was conducted at the Saatlui Poplar Research Station in Urmia, situated at 1338 meters above sea level and affiliated with the Agricultural and Natural Resources Research Center of West Azerbaijan Province, from 2019 (when cutting propagation began) to 2023. The Populus nigra 62/154 clone, which has demonstrated high wood production performance in compatibility tests, was selected as the tree component. Alfalfa (Medicago sativa L.), the Hamdani variety, was planted between poplar saplings in March 2021 (the year of planting), with a spacing of 2×4 meters (4 meters between rows and 2 meters within rows). Measurements for alfalfa characteristics were taken at harvest after each of the three cuts, and poplar tree measurements were recorded at the end of the growing season over three consecutive years: fall 2021, 2022, and 2023. Economic assessments and profitability comparisons for pure and mixed cropping systems were conducted using land equivalent ratio (LER), relative value total index (RVT), actual yield increase (AYL), and agroforestry utility index (IA).
Results: The results showed that the diameter at breast height, height, and volume stock of poplar trees were significantly different at the 5% probability level only in 2023, with the highest growth occurring in pure poplar plantations. Regarding alfalfa, significant differences in plant height were observed between pure and mixed cropping types and across three cuts for the years 2021-2023. In 2021 and 2022, plant height differences were significant at the 5% level, and in 2023, at the 1% level. Additionally, in 2021, plant height differences were significant at the 5% level, and in 2022, at the 1% level, under the interaction of cropping type and cut, while dry weight showed no significant differences. Alfalfa yield per hectare was higher in mixed cropping across all three harvest years, though no significant difference was found between pure and mixed cropping over the three years. The total relative value (RVT) was 1.80, 1.27, and 1.07 for 2021, 2022, and 2023, respectively, indicating that mixed cropping of poplar and alfalfa generated 1.80, 1.27, and 1.07 times more income than pure poplar and alfalfa cultivation in each respective year. The agroforestry utility index (IA) values were 4.80, 2.67, and 1.83 for 2021, 2022, and 2023, respectively, all greater than one and positive. Economic analysis for 2023 showed that pure poplar cultivation resulted in a negative profit (−18.75 million IRR), while mixed poplar and alfalfa cultivation generated a positive net profit of 14.16 million IRR per hectare.
Conclusion: This study demonstrates that mixed cropping was economically more beneficial than monoculture in all three years, with RVT values exceeding one and positive net profits. Overall, the research suggests that, despite traditional agroforestry systems in the region, these mixed systems offer higher profitability and economic returns compared to monoculture farming. If properly managed, such systems could have a positive impact on rural economies.