Introduction
The pressing need for global food security, particularly concerning strategic oilseeds like canola (Brassica napus L.), underscores the importance of increasing agricultural productivity. Mazandaran province, though a major producer, exhibits an average yield (1715 kg.ha^-1) even below the national figure, with Behshahr County being a critical area within the province for production. Closing the gap between actual and potential yield remains the most effective pathway to enhanced national oilseed production. This study was specifically undertaken to quantify the yield gap and precisely identify the key managerial constraints responsible for this shortfall in irrigated canola farms within the Miankaleh district of Behshahr County, Mazandaran Province, Iran.
Materials and Methods
The research employed the Comparative Performance Analysis (CPA) methodology across two consecutive cropping seasons (2021-2022 and 2022-2023). The study involved a comprehensive field survey and detailed interviews conducted on 100 canola farms in the Miankaleh region, characterized by a moderate and humid climate. Data collection covered farmer demographics, field characteristics, and intricate details of all agronomic management practices, including land preparation, variety selection, sowing date, fertilization (base and top-dressing), pest and weed control, irrigation, and final yield. The collected data allowed for a thorough analysis, which began with the development of a yield function using stepwise multiple regression. This statistical model linked various management variables (both quantitative and qualitative) directly to grain yield, enabling the estimation of the average observed yield and the attainable potential yield by substituting average and optimal managerial values into the final, predictive model.
Results and Discussion
The average yield achieved by the surveyed farmers was calculated at 2247 kg.ha^-1, whereas the estimated potential yield for the region stood at 4798 kg.ha^-1. This disparity resulted in a considerable total yield gap of 2551 kg.ha^-1. Importantly, the stepwise regression analysis successfully isolated and quantified the influence of six distinct managerial factors that collectively accounted for a substantial 89% of this observed yield gap, thereby providing clear targets for intervention. The single largest contributor to the yield loss was identified as the suboptimal management of plant nutrition. A detailed breakdown showed that the most significant individual constraint was the inadequate application of phosphorus (P) fertilizer, contributing a major 43 percent to the total yield gap. Following this, the insufficient or complete lack of amino acid supplements accounted for a further 16 percent reduction in yield, indicating a gap in adopting advanced nutritional practices. Additionally, a deficiency in sulfur (S) fertilizer usage contributed another 6 percent of the gap. Collectively, these nutritional deficiencies highlight that nutrient management is the dominant factor limiting current production. Beyond nutritional issues, pest control emerged as the second principal area of concern. Specifically, inadequate and untimely control of snails during the crucial early stages of the growing season was quantified as contributing a significant 22 percent to the total yield gap. Finally, poor weed management practices also played a role. This was reflected by the high frequency of herbicide application (11 percent contribution) and the need for supplementary hand weeding (1 percent contribution), both of which signal sub-optimal control strategies and increased weed competition that negatively impacts yield.
Conclusion
The results unequivocally demonstrate that the most efficient pathway to closing the existing 2551 kg.ha^-1 yield gap lies in the optimization of the nutritional management program. Priority must be given to ensuring adequate and timely application of key fertilizers, particularly phosphorus and sulfur, alongside the integration of beneficial supplements such as amino acids. Furthermore, the establishment of an immediate and highly effective strategy for controlling early-season pests, especially snails, is crucial. By focusing resources and efforts on these specifically quantified managerial factors, a significant portion of the current yield shortfall can be practically addressed, leading to enhanced farm profitability and a vital step towards achieving national self-sufficiency in oilseed production.
Acknowledgements
The authors would like to express their sincere gratitude to the respected farmers of the Miankaleh region for their valuable cooperation in data collection. We also acknowledge the support from the faculty and staff at Gorgan University of Agricultural Sciences and Natural Resources for their guidance and assistance during this research project.