Application of two measures of adaptation to climate change for assessment on the yield of wheat, corn and sunflower by the aquacrop model

Frequent occurrence of droughts over the last two decades, as well as increases in the air temperature increase have led to the rise farmers' concerns that field crop production would not be possible without irrigation. The aim of this research is to assess how two adaptation measures, sowing dates and irrigation and water excess impacts the yields of wheat, maize and sunflower in Serbia. In order to assess the future of climatic condition five representative locations have been selected for the analysis (Novi Sad, Valjevo, Kragujevac, Negotic and Leskovac). For the analysis of future climatic conditions, results of the ensemble of nine regional climate models from the Euro-CORDEX database were used. The period between 1986 and 2005 was used as a reference, while time slices in the future are: 2016-2035 (near future), 2046-2065 (mid-century) and 2081-2100 (end of the century). Analyses were made for the scenario of GHG emmisions RCP8.5. Aquacrop model v.6.1 was used for the yield, sowing period, and irrigation requirement assessment. The analysis and the results have indicated that earlier start of the growing season of maize and sunflower for 5, 11 and 19 days in near future, mid and end of the century, respectively, whereas optimal sowing period for rainfed wheat will vary from September 20 to November 30, depending on rainfall occurrence, and for irrigated one in optimal sowing period (beginning of October). The warmer climate will shorten the growing cycle of all studied crops. However, the shortening significantly differs among locations. The growing cycle of maize shortened from 34 up to 48 days in Valjevo in near future through the end of the century, while in Negotin it could be less only for 6 days. The increase in air temperature and earlier start of the growing season will enable the most sensitive phenophases, flowering and fruit formation, to appear in a period of more favorable weather conditions, together with the increase in CO2 concentration, can help mitigate the negative impact of the climate change, so that there will be no reduction in sunflower yields. Slight increment of sunflower yields could be expected by the end of century (2.3 - 13.8%), whereas yield of maize will remain on the present level. The increase of wheat yield could be expected only in the near future (up to 8.3 %), but also it can be reduced at some locations by the end of the century. Irrigation water requirements of all studied crops will remain at the same level the same level as the present, but only if sowing applied in the optimal period. Although it is known that irrigation changes microclimatic conditions, ie., the air humidity increases, and the air temperature decreases (the so-called oasis effect), which can affect the extension of the vegetation period, and thus the increase in yield. Such subtle changes in the microclimate cannot be "recognized" by models, so even simulated yields cannot be fully (accurately) predicted. This research come to the conclusion that in addition to irrigation, shifting the sowing dates earlier can have an impact on mitigating the consequences of climate change in crop production, which is of great importance for areas where there is not enough water for irrigation. The risk of drought will exist on shallow and sandy soils as well as on overwetted lands that cannot be plowed until drained to be sown in optimal terms and all crops sown in the late spring.