Abstract: | Cover crops grown as green manure or for other purposes will affect nitrogen (N) distribution in the soil, and may thereby
alter root growth of a succeeding crop. During two years, experiments were performed to study effects of nitrogen supply by
green manure on root development of carrots (Daucus carota L). Total root intensity (roots cm−2 on minirhizotrons) was significantly affected by the green manures, and was highest in the control plots where no green manure
had been grown. Spread of the root system into the interrow soil was also affected by green manure treatments, as the spread
was reduced where spring topsoil Nmin was high. Although N supply and distribution in the soil profile differed strongly among the treatments, no effect was observed
on the rooting depth of the carrot crops. Across all treatments the rooting front penetrated at a rate of 0.82 and 0.68 mm
day−1 °C−1 beneath the crop rows and in the interrow soil, respectively. The minirhizotrons only allowed measurements down to 1 m, and
the roots reached this depth before harvest. Extrapolating the linear relationship between temperature sum and rooting depth
until harvest would lead to rooting depths of 1.59 and 1.18 m under the crop rows and in the interrow soil respectively. Soil
analysis showed that the carrot crop was able to reduce Nmin to very low levels even in the 0.75 to 1.0 m soil layer, which is in accordance with the root measurements. Still, where
well supplied, the carrots left up 90 kg N ha−1 in the soil at harvest. This seemed to be related to a limited N uptake capacity of the carrots rather than to insufficient
root growth in the top metre of the soil.
This revised version was published online in June 2006 with corrections to the Cover Date. |