K. Thorup-kristensen et R. Van Den Boogaard, Vertical and horizontal development of the root system of carrots following green manure, PLANT SOIL, 212(2), 1999, pp. 145-153
Cover crops grown as green manure or for other purposes will affect nitroge
n (N) distribution in the soil, and may thereby alter root growth of a succ
eeding crop. During two years, experiments were performed to study effects
of nitrogen supply by green manure on root development of carrots (Daucus c
arota L). Total root intensity (roots cm(-2) on minirhizotrons) was signifi
cantly 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 in
terrow soil was also affected by green manure treatments, as the spread was
reduced where spring topsoil N-min was high. Although N supply and distrib
ution in the soil profile differed strongly among the treatments, no effect
was observed on the rooting depth of the carrot crops. Across all treatmen
ts the rooting front penetrated at a rate of 0.82 and 0.68 mm day(-1) degre
es C-1 beneath the crop rows and in the interrow soil, respectively. The mi
nirhizotrons only allowed measurements down to 1 m, and the roots reached t
his depth before harvest. Extrapolating the linear relationship between tem
perature sum and rooting depth until harvest would lead to rooting depths o
f 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 N-min to ver
y low levels even in the 0.75 to 1.0 m soil layer, which is in accordance w
ith 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 limit
ed N uptake capacity of the carrots rather than to insufficient root growth
in the top metre of the soil.