Investigating the yield gap and it's influencing factors in irrigated wheat fields of Azna county, Lorestan province, Iran, using comparative performance analysis (CPA)

Introduction
Wheat is one of the most important plant affecting human life due to various application. This plant is planted and harvested almost year-round across the globe due to high adaptability to various environmental conditions. Diverse management practices of farmers is caused the potential of the agricultural lands are often not optimally utilized, resulting in low yields per unit area. This issue is a significant problem in wheat fields that needs to be examined through field methods. The comparative performance analysis (CPA) method effectively estimates yield differences based on the potential of the land and the yield resulting from farmer’s management. This study was planned and implemented to investigate the yield gap and its contributing factors in the irrigated wheat fields of Azna county, Lorestan province, Iran, using the CPA method.

Materials and methods
In this study, data from 74 irrigated wheat farms in Azna county were used to estimate the yield gap and its contributing factors through the CPA method. The data from the wheat fields were collected using a questionnaire including farm characteristics (rural area, farmer experience and literacy, field area and rotation), planting operations (planting date, plowing, subsoiler, cultivator and trowel, disk and its number, planting method, fungicide, variety, seed quantity, amount, type, method and time of spreading nitrogen, phosphorus and potash fertilizers, amount and type of livestock manure), maintenance operations (type, irrigation frequency, irrigation in autumn and its number, first irrigation in spring, amount, time and method of top-dress nitrogen fertilizer, pest and weed control), and harvesting operations ((harvest date and length of wheat growth period). Topographic (aspect, slope and elevation of wheat fields) and soil information (organic matter, pH, available phosphorus and potassium, total nitrogen and soil texture) for each wheat field were also obtained from the GIS-prepared layers based on their geographical locations. To determine the yield model (output), the relationship between all measured variables and yield was examined using stepwise regression analysis with SAS software. Finally, using the derived production equation, the yield gap and its contributing factors, along with the share of each, were identified.

Research findings
The results of this study showed that the minimum and maximum observed yield of wheat fields were 2500 and 8500 kg.ha^-1, respectively, with the average of 5943 kg.ha^-1. Also, the average, minimum and maximum yield estimated by the model were 5906.62, 3248.22 and 11289.24 kg.ha^-1, respectively, and the total yield gap was 5382.62 kg.ha^-1. The correlation coefficient between the estimated yield and the actual yield of farmers was 0.81, and the residual root mean square (RMSE) and the coefficient of variation (CV) of the model were obtained 842.71 kg.ha^-1 and 14.27%, respectively. The analysis of the factors contributing to the yield gap indicated the role of six variables, including low organic matter content in the soil (26.8%), lack of row planting (3.60%), low seed usage (10.96%), reduced number of irrigations in the fall (18.88%), reduced amounts of nitrogen applied as Top-dressing fertilizer (17.28%), and untimely harvesting (22.43%) in creating the yield gap in the irrigated wheat fields in Azna county.

Conclusion
This study confirms the acceptable capability of the CPA method in estimating the yield gap and the factors affecting it in the wheat fields of Azna County. The results showed that with timely, targeted, and intelligent management, the yield gap can be reduced by approximately 48%, thereby significantly increasing wheat production. Implementing appropriate crop rotation, managing wheat and other crop residues, using animal manure, promoting the use of row planters and providing them to farmers, managing seedbed preparation, selecting suitable varieties, and strongly recommending fall irrigation, soil testing to determine appropriate nitrogen fertilizer levels, and distributing it according to the growth stages of wheat, along with precise planning to avoid overlap in spring crop cultivation with wheat harvesting and timely entry of harvesting machinery into wheat fields are recommended to reduce the yield gap based on the influencing factors.