DEFICIT IRRIGATION OF SOYBEAN (GLYCINE MAX. (L.) Merr.) BASED ON MONITORING OF SOIL MOISTURE, IN SUB-HUMID AREA OF EASTERN CROATIA

Deficit irrigation of soybean was induced by irrigation at 60-100% field water capacity (FWC) during three different climatic years in sub-humid area. Crop evapotranspiration (ETc) was measured for each irrigation plots, dry-land (al), deficit irrigation (a2) and full irrigated plots (a3). Average across years ETc totalled 46.05 mm/dec from initial to late stage. Kc values ranged from 0.35 at vegetative stage, 1.0 at reproductive stage after what it declines to 0.82. In deficit irrigated plots grain yield of soybean was increased as compared to control plots by 7.5% (2006), 1.15% (2007) and 7.3% (2008). In average climate years (2006 and 2008), by increasing soil water content at full irrigated plots (80-100% FWC), grain yield of soybean was reduced by 1.9% (2006) and 5.8% (2008) in comparison to deficit irrigated plots. This was in contrast to results obtained in extremely warm and very dry year 2007, when the highest yield was at full irrigated plots (3.68 t ha(-1)). Averaged across years, the highest irrigation water use efficiency was at deficit irrigated plots (0.3 to 3.3 kg m(-3)). Results obtained from this research showed that deficit irrigation management is an efficient measure for preserving water resources and achieving high yields in average climate years.