Fig. 3. Average root depth development versus (a) date and (b) accumulated daily temperature including regression outputs, from sowing of catch crops on 8 August. In (a) the horizontal bar on the x-axis indicates the 6-d period of the ¹⁵N injection experiment and the error bars indicate standard errors (n = 4). In (b) the two last data points were deleted from the regression analysis for fodder radish due to root depth exceeding measuring depth of minirhizotrons.