Long term weather data including temperature and radiation in Northern, Razavi and Southern
Khorasan provinces were collected and used for agroecological zonation of wheat over the whole
province. Weather data after spatial interpolation between stations and generation of daily values were used as inputs of a model for simulation of wheat growth and yield. The WOFOST model that showed acceptable performance during validation for predicting yield and development stages of wheat cultivars under favourable growth conditions, was used for estimation of potential (climatic) yield of wheat. The results showed that in spite of inter annual variations, mean potential yield of wheat was 6.2, 6.9 and 4.8 t ha-1 for Northern, Razavi and Southern Khorasan provinces, respectively. Actual wheat yield (harvestable yield) during a 10-year period from 1375 to 1385 was calculated as the average of the whole period and mean of the last 3 years of time series in each province. On this basis yield gap was estimated as the difference between potential and actual wheat yield. A regional yield factor was also calculated from the ratio of actual: potential yields. Yield data was stored in a GIS package and zonation maps were produced. Results indicated that mean actual wheat yield during the
3-year period of 1383-1385 compared to the 10-year period of 1375-1385 was increased by 28, 34 and 30% in Northern, Razavi and Southern Khorasan provinces, respectively which could be mainly due to improved management practices and introducing new cultivars. However, a relatively high yield gap of 3.7, 4.3 and 3.8 t ha-1 was estimated for Northern, Razavi and Southern Khorasan provinces, respectively. Regions with higher yield potential showed a higher yield gap and regional yield factor of wheat in Razavai and Southern Khoransan provinces with the highest and the lowest yield potentials was estimated as 0.37 and 0.42, respectively. During the period of 1383-85 in all 3 provinces the actual yield reached to the 50% of the potential yield indicating that the yield gap of wheat has been bridged due to improved management practices. |
