Temporal and Spatial Variation of Wheat and Bean Yields, Case Study: Khorasan-e Razavi province

The impact of climate on crop yield is mediated through the interaction of temperature, carbon dioxide, humidity, rainfall and the other factors. In general, temperature, solar radiation and precipitation are the most important environmental parameters affecting growth and development of plants and their fluctuations will affect crop yields.
In this research, three cities located in Khorasan-e Razavi province were studied. 17-years interval data (77-82) of wheat and bean yields and climate parameters was collected from agriculture (Jahad-e Keshavarzi) and meteorological (IRIMO) organizations of Iran, respectively. To investigate temporal variation of wheat and bean yields, time series method and Mankendal test was used. In case of spatial variation of yields, two methods consist of inverse distance weighted (IDW) and Kriging was utilized. To investigate yield correlation among different regions, the thirteen-year climatic variables including monthly rainfall and minimum, maximum and optimum temperatures was obtained from whether center of Khorasan-e Razavi province. The correlation between yield and climatic variables was evaluated via simple and multivariate regression.
The trend of yield changes over 17 years across Mashhad city showed that yield reduction was 2900, 2200 and 1900 kg during 1374, 1378 and 1386, respectively, and the highest wheat yield was recorded 4100 kg during 1387. In Mashhad city, the highest correlation between wheat yield and climatic variables was obtained in January minimum temperature, so that 40% of wheat yield changes in Mashhad can be described by this variable. The 17-year trend of wheat yield showed a linear increase. Over 17 years, the low yield was 1700, 1400 and 1500 kg in 1372, 1378 and 1386, respectively, and the highest yield was recorded 3749 kg in 1387. In Nishabour county, wheat yield showed the highest correlation, among climatic variables, with March rain and April maximum temperature (r=70.0). Yield was reduced to 2181 kg ha-1 in 1999 and in 2009 the highest yield was 4050 kg ha-1. Torbat-e-heydarieh was stable in the final model after regression analysis between yield and climate variables maximum and minimum temperatures in May and March respectively. There was no relationship between climate variables and yield in bean for Neyshabur and Torbat-e-heydarieh. Variations in bean yield may be due to non-climatic factors such as soil, management, pest and disease, weed and etc. In general, according to Mankendal test, minimum temperatures had a more increasing rate compared to maximum temperatures. Among 17 years of wheat yield in three research sites, the least yield was obtained in the year 1999 , therefore this year was compared with 2009; the last year of research. Wheat yield was high in many Khorasan-e Razavi province cities in 2009, because rainfall and minimum temperatures were lower during 2009. In the other words, the wheat performance of Khorasan Razavi in 2009 was between 2200 and 4200 kgha-1 and rainfall lay in the range of 100-400 mm and the minimum temperature varied from 5 to 13.5°C, while the wheat performance in 1999 ranged from 1200 to 2200 kg ha-1 and rainfall varied from 110 to 340 mm (rainfall was less than 160 mm in most cities) and the minimum temperature was within the range of 5-13°C (the minimum temperature was less than 7°C in most cities). Consequently, the wheat performance in 2009 was nearly two times higher than that in 1999. Bean had the best performance (1900 kg ha-1) in Mashhad in 1999. At the same time, it had the best performance (1500 kg ha-1) in Torbat Heidrieh in 2009, because in 1999, the maximum and minimum temperatures in Torbat Heidarieh were 20.4 and 7.3°C, respectively which were less than the maximum (22°C) and minimum (8.4°C) temperatures in Mashhad. Therefore, the performance of Torbat Heidarieh was less than that of Mashhad in 1999. In 2009, the minimum temperature of Mashhad (9.5°C) was higher than that of Torbat Heidarieh (8.5°C); as a result, the bean performance of Mashhad was less than that of Torbat Heidarieh in 2009. The kriging method showed the best results in terms of spatial accuracy.
In this study, wheat and bean yields in three locations in Khorasan-e Razavi province were studied over a period of 17 years. The impact of rainfall compared with monthly temperature as irrigation, has been very low and insignificant. There was a meaningful relationship between bean yield changes and climatic variables only in Mashhad station. . From the view point of spatial variation, in year 2010, wheat yield decreased from East to the West and bean yield showed the maximum amount in the center of Khorasan province (Torbat Heydaryieh).