Nitrate leaching from an organic dairy crop rotation: the effects of manure type, nitrogen input and improved crop rotation

Four management systems combining high and low livestock densities (0.7 and 1.4 livestock units ha(-1)) and different types of organic manure (slurry and straw based FYM) were applied to an organic dairy crop rotation (undersown barley - grass-clover - grass-clover - barley/pea - oats - fodder beet) between 1998 and 2001. The effects of the management systems on crop yields and nitrate leaching were measured. In all four years, nitrate leaching, as determined using ceramic suction cups, was higher in the three crops following ploughing of grass-clover than under the barley or grass-clover. Overall, no significant differences in nitrate leaching were observed between the management systems. However, the replacement of the winter wheat crop used in the earlier experimental period (1994-97) by spring oats with catch crops in both the preceding and succeeding winters reduced nitrate leaching compared with the earlier rotation. Increasing the livestock density, which increased manure application by c. 60 kg total N ha(-1), increased crop yields by 7 and 9% on average for FYM and slurry, respectively. Yields were 3-5% lower where FYM was used instead of slurry. The experiment confirmed the overriding importance of grassland N management, particularly the cultivation of the ley, in organic dairy crop rotations.