Investigating the rapeseed yield gap in Dehloran

As suitable agricultural land for increasing crop production is decreasing, while the expansion of agricultural land is associated with irreparable damage to the environmen, intensifying sustainability in existing agricultural land is the only way to increase production to meet the increasing demand for food resources. Therefore, investigating the biophysical limitations on yield and estimating yield gaps  in the cultivated lands, as well as reducing this gap, is one of the ways to increase the yield per unit area. After soybean, rapeseed is the world's second produced oilseed. Ilam province is one of the most important oilseeds producer regions of the country, including rapeseed, and about 80% of the rapeseed crop of this province is produced in the border city of Dehloran, and this city is one of the pioneer cities and the main pole of rapeseed production in the province. Therefore, according to the importance of rapeseed in Deholran city, this study was conducted with the aim of determining the limiting factors of rapeseed production in Dehloran.

In the present study, all the management operations were performed from seedbed preparation to harvesting in 51 farms were recorded through field studies during the years 2021 to 2022. In this study, the yield gap was estimated by the method of yield comparison analysis and borderline analysis, and to determine the yield model, the relationship between quantitative and qualitative variables was measured and yield was evaluated by step-by-step regression method.

Determining the limiting factors on rapeseed production in the studied area showed that there was a gap between the actual yield of farmers and the yield predicted by the model of about 833.54 kgha-1, which was the contribution of the variables of potash fertilizer consumption, sulfur consumption, and the number of irrigations. The consumption of micronutrients from this yield interval was equal to 102.99, 118.56, 442.20 and 169.79 kgha-1, which is equivalent to 12.36, 14.22, 53.05 and 37, respectively. 20% of the total yield gap was observed. Gap analysis of rapeseed yield showed that the number of irrigations alone accounts for 53% of yield reduction compared to attainable yields.

As, there is a need to irrigate the field in the very early planting date in October, it seems that with better management of rapeseed for this planting date in the region, the occurrence of drought stress can be reduced to the plant and to some extent fill the gap in the existing yield. In addition, 57% of the yield gaps in the region were related to the use of potash, sulfur and micronutrient fertilizers, which can be easily removed this limitations in the fields.