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Climate changes, especially precipitation and temperature regimes, have often adverse influences on field crop yields. Based on 5-year data maize for grain is main field crop in Croatia (302 406 ha) and Bosnia and Herzegovina (B&H: 189 557 ha) and covering 34% (Croatia) and 42% (B&H) of used (882 752 ha and 447 181 ha, respectively) arable lands. The harvested areas of maize among years are mainly similar, while yield variation is considerable and in range from 4.3 t/ha to 8.0 t/ha (Croatia) and from 3.75 t/ha to 5.12 t/ha (B&H). The lower precipitation and the higher air temperatures, particularly in July and August, are in close connection with the lower yields. In both countries the lowest maize yields were realized in 2012 (4.30 and 2.90 t/ha in Croatia and B&H, respectively) and they were lower for 48% (Croatia) and 40% (B&H) than in 2008. Precipitation and mean air temperature in July + August of 2012 in Osijek were 52 mm and 24.5 oC (average 1961-1990: 123 mm and 20.7 oC), while in 2008 these values were 145 mm and 21.8 oC. The data for Tuzla (average 1961-1990: 138 mm and 22.4 oC) were 8 mm and 23.5 oC (2012), 156 mm and 20.8 oC (2008). The western parts of both countries had the higher precipitation and the lower air temperatures (July + August 1961-1990: 178 mm and 19.7oC in Zagreb, 159 and 21.5 oC in Banja Luka) and this trend was found also in the 2008-2012 period

The used arable land covering in Croatia 882752 ha and in Bosnia and Herzegovina (B&H) 447181 ha (average 2008-2012) or 15.60% (Croatia) and 8.75% (B&H) of the state territory. Main field crops (average 2008-2012) are maize for grain (302266 ha and 189 557 ha and winter wheat (168433 ha and 57480 ha). Annual yields of wheat in the mentioned period were from 4.00 to 5.50 t/ha (Croatia) and from 2.63 to 3.80 t/ha (B&H). Global warming and increasingly experiencing with extreme weather conditions around the globe affecting often adversely on field crop yields. Annual temperature over Europe increased between 0.1 and 0.4% /decade. In our study, average air temperature in 2008- 2012 (October-June) were higher from average (1961-1990) for 0.9 oC (Osijek), 1.5 oC (Zagreb), 0.8 oC (Tuzla) and 1.2 oC (Banja Luka). As both in Croatia and B&H are dominant less permeable soils, the low yields of wheat in the growing season 2009/2010 (4.00 t/ha in Croatia and 2.63 t/ha in B&H: average of the remaining four years 5.30 t/ha and 3.74 t/ha, respectively) are in close connection with excessive precipitation. Precipitation in December-February (mm) were 244 (Osijek), 230 (Zagreb), 296 (Tuzla) and 414 (Banja Luka) or the higher for the referent values (1961-1990) for 76%, 57%, 59% and 90%, respectively. Also, loss of yield is partly caused by excess of precipitation in May and June (350 mm in Osijek, 434 mm in Tuzla and 383 mm in Banja Luka (average 1961-1990: 147 mm, 203 mm and 209 mm, respectively).