Identification of production constraints and yield gap monitoring of local rice (Oryza sativa L.) cultivars in Mazandaran province

One of the main problems for rice production is the large difference between farmers' actual yields and attainable yields. Therefore, it is important to identify the limiting factors on yield and yield gap. In this research, all performed management practices from seedbed preparation to harvesting in 228 paddy fields of local rice cultivars in the east, central and west parts of Mazandaran province, Iran were surveyed through field monitoring in 2015 and 2016. The results showed that the variables of certified seed, seedling age, and potassium application, nitrogen application after flowering, harvest time and pest problem were introduced into the comparative performance analysis (CPA) equation. The actual yield of the field and the calculated yield potential were estimated 4456 and 6642 kg.ha-1, respectively, hence the yield gap was estimated 2186 kg.ha-1. In the boundary line analysis (BLA), by fitting one line on the upper edge of the data, it was determined that the response function as a dependent variable to independent variables on seed rate, transplanting date, planting density, nitrogen application. Moreover, basal nitrogen application, nitrogen application in vegetative and after flowering stages had a positive piecewise function. The seedling age variable, phosphorus and potassium application and the number of seedling per hill followed a negative piecewise function. However,, four variables including the lodging, pests, diseases and weeds problems followed a linear function. According to BLA, the average yield was 5755 kg.ha-1 with a yield gap of 1207 kg.ha-1. An average relative yield and relative yield gap were estimated 79.8% and 20.90%, respectively. Given that the calculated yield potential in this analysis in three regions was obtained from the actual data of each field, it can be concluded that the yield potential is dependent on the region and is attainable.