Rotational set-aside preceding sugar beet – Effect of set-aside position in the rotation and cover crop on soil nitrogen leaching risk and sugar beet yield and quality

In the frame of the common agricultural policy reform in the early 90th rotational set-aside was introduced into crop rotations. Several field trials were conducted to study the influence of annual catch crops grown on set-aside land on the risk of nitrate leaching during the following winter period and yield and quality of sugar beet. For comparison, perennial fodder crops and cereals were included. Cumulated nitrogen yield in above ground plant mass was highest with alfalfa, followed by oil radish, phacelia, mixtures of these with Egyptian clover, perennial ryegrass, tumble down and winter wheat straw. The risk of nitrate leaching was high after phacelia, winter wheat and alfalfa, and smallest after perennial ryegrass. After legumes (alfalfa, oil ra-dish/clover, phacelia/clover) maximum white sugar yield was obtained without mineral nitrogen application. Against this, follo-wing tumble down resp. perennial ryegrass similar resp. more fertilizer N was required compared to wheat. Maximum yields did not differ between the tested forecrops. With regard to an efficient ground water protection it is concluded that legumes should not be grown on set-aside land. Furthermore, before winter crops should grow actively as long as possible. To avoid sugar beet quality losses, nitrogen fertilizer application must be adopted to the crop grown during the set-aside period.