Application of regionalism method based on cropped ecology for determining yield gap of irrigated wheat in the climate groups of Iran

By calculating the potential yield of crops, the yield gap can be determined. Also, the management of water and soil resources can be done based on effective factors in production. Attending to limitations in agricultural programs, for increasing the wheat yield, applying a predictive model of yield potential rate could be effective in the yield management based on various parameters including climate factors. A suitable model for this goal is regionalism method based on cropped ecology, in which it is assumed the climatic requirements are prepared and water, nutrients, salinity, pests and diseases do not effect on growth and yield potential. In this study, with the goal of estimating the yield potential in 30 province centers in Iran, by using factor and cluster analysis and considering nine climate factors, the stations were classified. Then, climate data was collected for a period of 30 years (up to 2010) from synoptic stations of province's centers. Also, the average values of actual yield for winter wheat were collected from the site of Centre for Information and Communication Technology, Ministry of Agriculture Jahad, in each province. Then the potential yield and gap yield (kilograms per hectare) were determined, using the regionalism method based on cropped ecology.
According to the variance percentage and special values of effective factors, KMO value was equal to 0.598; forwhich, four climatic parameters including mean temperature, relative humidity, wind speed and precipitation were selected in classifying process. Therefore, nine provinces were categorized in dry climate including Birjand, Kerman, Yazd, Zahedan, Qom, Isfahan, Shiraz, Tehran and Semnan. In semi-arid and semi-humid climate there were 15 provinces including Mashhad, Qazvin, Bojnoord, Sanandaj, Kermanshah, Tabriz, Arak, Shahrekord, Zanjan, Hamedan, Orumieh, Ilam, Khorramabad, Yasooj and Ardebil. Three provinces were in humid with low precipitation climate including Busheher, Bandarabbas and Ahvaz. Also, three provinces were in humid-rainy climate including Rasht, Sari and Gorgan. Then, the estimated values of parameters in regionalism method based on cropped ecology and the actual and potential of wheat yield were determined in four regional groups. Also, the percentage of yield gap which caused by the difference between the actual and potential yield due to the lack of climatic requirements was determined in each group.
As a result, regionalism method based on cropped ecology in arid -low precipitation regions of the country could not estimate potential yield of wheat. In the region with semi-arid and semi-humid climate, the lowest and highest amount of yield gap was 30.9 and 53.5 percent in Ardebil and Ilam stations, respectively. Also, the average percentage of yield gap in this group was 43.2 percent. In regions with arid climate, the minimum and maximum of yield gap percentage were in Semnan and Zahedan stations with 10.2 and 52.1 percent, respectivelyand the average percentage of yield gap in this group was 27.5 percent. In humid-rainy region, including the stations of the northern coasts of Iran, the percentage of yield gap was very high. In this group, the maximum yield gap was in the Rasht station with 68.9 percent and the minimum was in Gorgan station with 41.2 percent. Also, the average percentage of yield gap in this group was 55.8 percent. Among the four regional groups, in terms of required climatic parameters, the maximum of yield gap occurred in humid-rainy regions and the lowest was in low precipitation humid climate. Furthermore, among 30 provinces which were studied, the Rasht station from humid-rainy regions had the highest yield gap and the Semnan station from dry regions had the lowest. The results of factor analysis showed that temperature was important for classifying the provinces by climate. Also, the results showed that model had the greatest sensitivity to the average temperature, comparing to the other climatic factors. This caused the lowest yield gap occured in the regions with low precipitation and dry climates with 15 and 27.5 percent, respectively. Also, the moderate climate in rainy climate condition caused more growing and a longer season of growth in the most species. Therefore, the difference between average yield and potential yield has been occcured which caused the average of yield gap in the northern coastal provinces of the country to be 55.8 percent. The conclusion of results represented that the regionalism method based on cropped ecology is one of the appropriate tools for predicting wheat yield and determining yield gap in different climatic regions.