عنوان مقاله [English]
Food security is one of the most important challenges facing humankind. Therefore improving crop yields are essential to meet the increasing pressure of global food demands. The loss of high-quality lands, increasing fertilizer use, and its effect on the environment indicate that we need to develop new strategies to increase grain yields with less impact on the environment. One strategy that could help address this concern is by narrowing the yield gaps using improved management. Comparative Performance Analysis (CPA) is an approach for studying yield gaps; it defines quantified yield-gap functions. Assessing the yield gaps in major field crops can help us understand yield variability and potential. Rapeseed is one of the world’s most important oilseeds, and its production has economic and agronomic advantages. Rapeseed oil is considered a healthy ingredient and the third most used oil in foods. There is a difference between the average yield and the maximum expected yield of rapeseed in Khorramshahr. There are potential lands in this region that, by investigating the reasons for low yield, farmers can be encouraged to cultivate rapeseed on their farms. Therefore, this study aimed to determine the yield gap and the limiting management factors in rapeseed cultivation of Khorramshahr.
Materials and Methods
This study was carried out to investigate management factors causing the rapeseed yield gap in Khorramshahr during the 2018-2019 growing season. This study recorded information from 57 farms with variation in the area under cultivation, farm management and yield based on information from local experts and field studies. The comparative performance analysis (CPA) method was used to evaluate the yield gap. All information related to management practices was either measured or recorded. From the relationship between all measured variables (quantitative and qualitative) yield model was obtained through stepwise regression. By putting the best-observed value of the variables in the model, the maximum attainable yield was calculated, and the difference between them was considered a yield gap.
Results and Discussion
The yield observed in the surveyed farms, and the yield predicted by the model show a significant relationship. In this regard, the correlation coefficient was 93%, which indicates the high accuracy of the model for predicting the yield gap of the studied rapeseed fields. Based on the model, nine independent variables were selected from all studied variables. Then actual and attainable yield and contribution of each variable to the yield gap were determined by using the model. Results showed that the average yield, achievable yield, and yield gap of rapeseed were 1663, 3197, and 1533 kg.ha-1, respectively. The most important variables in the rapeseed yield gap were the use of the leveler, farmer’s education level, phosphate fertilizer application, time and amount of potassium fertilizer application and method of removing crop residues of the previous year, irrigation frequency, and sowing machinery. Factors that had the highest share of yield gap were potassium application time (27.14%), application of superphosphate (26.85%), potassium rate (25. 9%), crop residues removing method (9.63%), and use of lever (9.13%). According to the findings, the highest contribution to the yield gap was related to potassium fertilizer application time and superphosphate fertilizer application. These variables caused a yield gap of 416 and 411 kg.ha-1, respectively.
This study showed a difference between the actual yield and potential yield of rapeseed fields in Khorramshahr, which can be reduced by modifying crop management. The observed yield gap was 1533 kg.ha-1 (48%). The results of this study indicate that fertilizer management of Khorramshahr rapeseed fields, especially potassium and phosphorus fertilizers, is important and should be considered by farmers in the region. More than half of the rapeseed yield gap can be reduced by using phosphorus fertilizer and changing the time and rate of potassium application in Khorramshahr.