A three-year field trial was conducted to study the effect of plant population and harvesting dates on the yield of cleaned 2.0-6.0 mm seed and the seed yield (g) per plant. The highest seed yield was obtained with a spacing of 50 × 12 cm, or 160,000 plants/ha. A decrease in the plant-to-plant spacing to 9 cm decreased the yield by an average of 70 kg/ha over the three study years. The seed yield decreased to an even greater extent when the plant-to-plant spacing was 16 or 24 cm. The seed yields increased the most between the first and second harvesting dates: 400 kg/ha, or 50 kg/ha a day. On the last harvesting date, the seed yield was as low as 5-8 kg/ha. The yield loss was somewhat higher in the most densely sown treatment. The effect of spacing and harvesting date on seed yield per plant was similar to that on total seed yield.

Research was carried out at Rimski Šančevi experiment field of Institute of Field and Vegetable Crops in Novi Sad in the period 1993-2004. The experiment included an irrigated and non-irrigated control treatment. Irrigation water use efficiency (I wue ) and evapotranspiration water use efficiency (ET wue ) were determined in order to assess the effectiveness of irrigation on soybean yield. The average yield increases of soybean due to irrigation practice was 0.82 t ha -1 , ranging from 2.465 t ha -1 in years with limited precipitation and higher than average seasonal temperatures (2000) to 0 t ha -1 in rainy years (1996, 1997, 1999). Evapotranspiration water use efficiency (ET wue ) of soybean ranged from 0.11 kg m -3 to 1.36 kg m -3 with an average value of 0.66 kg m -3 , while irrigation water use efficiency (I wue ) varied from 0.11 kg m -3 to 1.04 kg m -3 with an average value of 0.56 kg m -3 . Effect of irrigation on yield of soybean and results of both ET wue and I wue which were similar to those obtained from the literature indicate that irrigation schedule of soybean in the study period was properly adapted to plant water requirements and water-physical soil properties. Determined values of ET wue and I wue could be used for the planning, design and operation of irrigation systems, as well as for improving the production technology of soybean in the region.

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