These quantities can be high (up to 100 kg ha-1) at the beginning even at the end of the winter. It is present mainly in the first horizon (0-30 cm). Analyses have been made for all samples but interpretation need some more work.
* UFU: Utilised feed units -1 feed unit = 1 kg barley
Despite various conditions, nitrate leaching risks under grazed white clover swards seem to be lower than under pure grass swards receiving 300 mineral N.
However when the herbage production is similar in two traitments, because of a high clover content (over 50% of the DM) on one side and a haevy N dressing on the other side, the nitrate leaching risk seem to be about the same and high in both case. To be save in most condition it will probably advocate for a moderate level of clover (20-35%) or a moderate level of nitrogen (150 to 200 N) when the paddock are only grazed.
Further research is needed to clarify the factors influencing the optimum level of clover or mineral N in relation to soil type, climate, grazing animals and grazing systems.
Figure 1: TREVAREZ
Figure 2: TREVAREZ
Figure 3: KERLAVIC