Conclusions

According to the climate change selected scenario (that stabilizes radiative forcing at 4.5 W.m-2 in the year 2100), potential yield of winter wheat will grow, both with and without irrigation. Irrigation effect is particularly significant for the cultivated areas on saline (black alkalized and natric) soils in the recent time while in the prognosis period the effect is relatively lower. Whilst the climate change has smaller effect on maize productivity, in particular: potential yields of the maize will remain quite stable from year to year, both for rainfed and irrigated agriculture and changes between the investigated periods is are insignificant (+4%), amounting, in average, to 2–2.5 t.ha-1. Also, by the end of the century, the areas favourable for growing cereals will increase significantly

For winter wheat cultivation by about 40% will extend zones with suitable climate conditions will extend by about 40%, but for maize, growth is expected to increase by almost 2 times areas requiring additional water supply.

Irrigation effect is particularly significant for winter wheat cultivated on saline (black alkalized and natric) soils in the current period while in the prognosis period the effect is relatively lower.

For winter wheat that belongs to the crops moderately sensitive to soil water stress, effect of precipitation reduction is apparent only for the plantations on saline (black alkalized and natric) soils. On the rest of territory, water deficiency caused by reduction of precipitation is compensated by reduction of evapotranspiration and improvement of crop water productivity. According to the future projection, this trend will be maintained at least up to the middle of the century and in the Dedoplistskaro district, even in case of rainfed cultivation, growth of the yields could be expected. Hence, during prognosis period, to maintain maximal yields, water requirement will be 40–60% lower, compared with the current period. At the same time, it should be considered that by the end of the century, against the background of a significant decrease in precipitation overall country territory would increase areas, where additional water will be needed to grow cereals.

For the maize that belongs to the crops sensitive to soil water stress, effect of precipitation reduction was not apparent due to high moisture content in the studied territory. Due to this, no any significant effect of irrigation on yields was identified.

Increases in air temperature and CO2 are considered as being one of the main components of changing climate, that climate that would have significant impact on agriculture crop productivity by the means of increased crop water effectiveness and through the biomass production. The modeling results indicate that the increased concentration of the CO2 will have a positive effect on biomass production of winter wheat, however, CO2 fertilization effect in some cases overlaps with the unfavourable changes of climatic parameters during growing season and is specific depending on the soil type common in the study area. For maize, the above effect and yield increase are relatively small, which is explained by the high ability of carbon fixation by maize. [Emphasis added.]

By default, the AquaCrop model discusses agro-technical measures taken against agricultural crops (such as pest and disease control, weed control, etc.) at the optimal level, which is largely inconsistent with the real situation. Such influences are involved in the model through soil fertility stress. Such stress was not taken into account when simulating the model, as accurate information about the above measures was not available. Thus, the real decline in wheat yields should not only be due to changes in climatic conditions and is likely to be the result of improper exploitation of land and agro-technical measures and inconsistent management. As for maize, it seems that in the studied region, conditions favourable for maize growing exist now, will exist in the future and low average yields (compared with the global figures) are supposedly caused by the crop varieties or some other reasons (vermin, diseases, ineffective management).

One should also bear in mind that nor neither model not nor agro-climatic zoning approach does do not take into consideration impact of such significant factors as extreme phenomena, like floods, hail, strong winds etc. on agricultural crop spatial distribution and productivity. In addition, raised temperature and more frequent heat waves results in increase of the fire risks, vermin propagation and frequency of diseases.

This article appeared on the Acta Horticulturae et Regiotecturae website at
https://www.jahr.sk/uploads/10.2478_ahr-2021-0005.pdf