New Trends for Crop Evapotranspiration and Irrigation Water Requirements in Orchards during the First Decade of the Twenty-First Century in Southern Romania

This paper deals with the trend for Penman-Monteith reference evapotranspiration (ETo), crop evapotranspiration (ETc) and irrigation water requirements (IWRs) of some fruit tree species during the first decade of the 21st century in Southern Romania. These indices were calculated for three weather stations in various relief regions of southern Romania: Pitesti, Bucharest-Baneasa and Constanta. Monthly distribution of ETo for the three locations studied showed that for the first half of the year, monthly values were higher for the first decade of the 21st century versus the means of the 20th century. The mean ETo values ranged between 3.34 and 3.39 mm/day during the growing season and between 4.38 and 4.52 mm/day in the summer time. In the first decade of century XXI versus century XX, ETc specifically increased in May, June and July, while in August the increase was negligible, and in September ETc decreased. Remarkable high ETc values were especially met for mowed sod treatments of orchards: apple, cherry, pear or peach, apricot and plum. IWRs have not shown a clear pattern with regard to the trend in the first decade of the XXI century versus century XX. For the peak month, July, IWRs reached as much as 110 mm in Constanta, 80 mm in Bucharest-Baneasa and 45 mm in Pitesti, respectively, for the clean cultivation system while for apple, pear and cherry-mowed sod the values ranged between 145 mm in Constanta, 115 mm in Bucharest-Baneasa and 80 mm in Pitesti, respectively. For peach, apricot and plum, these values were slightly lower. IWRs increased in May and June and this latter month was the month showing the maximum increase in IWRs versus century XX. The following months: July and August had practically the same IWRs values, whereas September was the month where irrigation application decreased by about 50-70% versus last century. Because this study only refers to one decade from a new century, and this decade showed high dynamics in global warming versus century XX, these changes could also have either a cyclic or a long term character, and this finding should be confirmed by further studies.