Catch crops vary in their efficiency to prevent losses of nitrogen (N) by nitrate leaching. However, little is known about the relevance of rooting patterns on N leaching. In the present study Phacelia, sunflower and a cruciferous catch crop were grown in drainage lysimeters following spring wheat, which was supplied or not with 250 kg N ha-1, in a three year study with the aim to evaluate the spatial and temporal characteristics of their root development and to relate these to N leaching. N off-take (g m-2) was estimated from shoots sampled shortly after frost killing, while N leaching was estimated from samples of drainage water. Observations from horizontal minirhizotron were used to assess root counts (root cm-2) at seven soil depths between 0.10 and 1.00 m. Root counts were fitted to a logistic growth equation using growing degree days as the time scale. Although Phacelia took off significantly higher amounts of N, its ability to reduce N leaching was worst among the tested catch crops. Shoot N off-take was a weak indicator of the ability of catch crops in preventing N leaching. The quantity of roots formed only differed among the catch crops in the deep soil layers (0.80 and 1.00 m), resulting in different mean rooting depths from 680 ºC days. The main difference among the catch crops, however, was found in the temporal pattern of root development in deep soil layers. At 0.80 and 1.00 m, it took 78 and 88 °C day less to the cruciferous species to produce 50 % of the total root system, when compared to sunflower and Phacelia. We conclude that the superior ability of cruciferous crops to reduce N leaching is at least partially a consequence of its faster exploration of the soil profile.
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