Introduction: Soybean (Glycine max) is one of the important food crops, which is rich in protein and vegetable oil. Soybean is the only legume with ample amount of essential omega-3 fatty acid and alpha-linolenic acid. One of the primary challenges in soybean production in the central region of Mazandaran province, Iran, is the substantial difference between actual and attainable yields, referred to as the yield gap. In recent years, this gap has been noteworthy. Closing the disparity between actual and potential yield, achievable through proper management, necessitates a detailed investigation and analysis of its underlying causes. Thus, identifying soybean yield-limiting factors is crucial. This study was conducted in Babolsar, located in the central region of Mazandaran province, Iran, to simultaneously recognize the best management practices, assess the percentage of affected fields, and estimate soybean yield potential and gaps using the Comparative Performance Analysis (CPA) method.
Materials and Methods: This study aimed to evaluate the factors limiting wheat yield in Babolsar County using the CPA method during the 2019-2020 period. Information collection, including planting dates, cultivation and harvesting activities, and soil physicochemical properties, was carried out through fieldwork and personal interviews with farmers. A total of 120 soybean fields within the geographical scope of the study area were monitored each crop year. Information related to soil characteristics, including EC, pH, percentage of organic carbon, absorbable phosphorus, absorbable potassium, percentage of clay, percentage of silt, percentage of sand, and soil texture class was obtained using soil tests and digital maps available in the agriculture organization of Babolsar. In the Comparative Performance Analysis method, stepwise regression was employed to examine the relationship between variables and yield. The yield gap rate, its causal factors, and the contribution of each factor to the yield gap creation were estimated.
Results and Discussion: Among the investigated variables, a model with seven independent variables (farmer experience, plant density, frequency of nitrogen fertilization use, starter fertilizer, frequency of pesticides, and herbicides) was selected as the final regression equation. The results of the yield model indicated a difference of 1736 kg/ha between attainable (4059 kg/ha) and actual yield (2323 kg/ha). Notably, farmer experience, plant density, frequency of nitrogen fertilization use, starter fertilizer, frequency of pesticides, and herbicides use had the most significant influence on soybean yield gap in the study area, contributing 15.6% (261.71 kg/ha), 24.6% (426.58 kg/ha), 8.3% (143.4 kg/ha), 3.3% (57.97 kg/ha), 16.7% (288.79 kg/ha), and 31.5% (545.79 kg/ha) respectively. Every plant needs the right time for fertilization for more yield. If the best fertilization time is not chosen for the plant, later or earlier fertilization will cause harmful effects in the plant. Weed control emerged as a crucial factor for increasing crop yield, emphasizing the importance of selecting optimal plant density based on regional climatic and soil conditions. Pesticide use played a vital role in pest control, contributing to a considerable reduction in pest damage and increased yield. Although farmers' experience had a significant role in the yield gap (15.6%), it was underscored that experience alone, without scientific knowledge, might be insufficient. The study emphasized the need for farmers to adopt scientific principles to enhance productivity. Additionally, the proper use of fertilizers at the plant's critical stages was highlighted to increase soil nutrient levels and improve nutrient efficiency.
Conclusion: This study employed the Comparative Performance Analysis to determine optimal requirements for various management factors in soybean cultivation, aiming to achieve the highest yield. Through proper agricultural management and modification of influencing factors, the study suggests that it is possible to reduce the disparity between attainable and actual yields, ultimately achieving desired results.