Nitrate leaching and residual effect in dairy crop rotations with grass–clover leys as influenced by sward age, grazing, cutting and fertilizer regimes

Abstract Intensive dairy farming, with grass-arable crop rotations is challenged by low N use efficiency that may have adverse environmental consequences. We investigated nitrate leaching and N fertility effects of grass–clover leys for five years in two organic crop rotations with different grassland proportions (33 and 67%) and five grassland managements in terms of cutting, grazing, fertilization and combinations thereof. In grass–clover, the combination of fertilization and grazing caused excessive leaching (average 60 kg N ha −1 ) but leaving out either fertilization or full-time grazing substantially reduced leaching losses to on average 23 kg N ha −1 . There was no linear relationship between sward age and nitrate leaching. The annual N surplus of the grasslands was only weakly related to nitrate leaching ( R 2  = 0.05, P −1 ) consisting of the barley wholecrop undersown with Italian ryegrass, (2) medium–low leaching (10–20 kg N ha −1 ) consisting of barley with grass–clover undersown and the 1-yr-old grasslands, (3) medium leaching (25–50 kg N ha −1 ) consisting of barley–pea and 2-4-yr-old grasslands with the 2-yr-old leaching the most (36–46 kg N ha −1 ), and (4) high leaching (>50 kg N ha −1 ) with lupin and maize, where especially maize was consistently high in all five years (average 81 kg N ha −1 ). Great care should be taken during all phases of the dairy crop rotation where grasslands cause considerable build-up of fertility. With due care and the best management practice, nitrate leaching losses may be reduced to low levels.