The water balance of chernozem soil and its correlation with maize yield was examined in a 28-year-long long-term experiment in three crop years with different precipitation supply: drought (2007), rainy (2008) and dry (2009); two crop rotation systems (mono- and biculture); and two different crop densities (60 000 and 80 000 plants per hectare). The examined soil layer was divided into three levels (0–60 cm, 61–120 cm, 121–200 cm) in which soil moisture content was examined throughout the growing season. Based on the obtained results, the change in the upper (0–60 cm) and middle (61–120 cm) layer was the most intensive, these are the layers where the direct impact of precipitation is the most obvious. Maize yield was compared to the amount of yield obtained by one millimeter of precipitation. It can be seen from the obtained findings of the comparison of mono- and biculture, that the water conversion rate of maize is the most favourable in the case of biculture and at a crop density of 60 000 plants per hectare.

Keywords: long-term experiment, moisture stock, crop year, WUE, crop rotation, monoculture, maize