Root growth and Nitrate uptake of three different catch crops in deep soil layers

Catch crops can reduce NO3 losses from leaching, but little is known about the importance of deep rooting for the efficiency of NO3 depletion. In a field experiment, we investigated the N uptake and root growth of three types of catch crops using minirhizotrons (glass tubes of 70-mm o.d.) reaching 2.4 m. Our purpose was to evaluate minirhizotron methodology and the importance of deep rooting in the ability of catch crops to take up NO3 from deep soil layers. Nitrogen uptake was studied over a 6-d period at the end of October by injection of (NO3)-N-15 at four depths in the ranges: 0.4 to 1, 0.5 to 1.4, and 1 to 2.5 m under Italian ryegrass (Lolium multifloram Lam.), winter rye (Secale cereale L.), and fodder radish (Raphanus sativus L. var. oleiformis Pers.), respectively. The root depth of the three species were 0.6, 1.1, and more than 2.4 m, respectively. No (IN)-I-15 was taken up from placements below root depth, and linear relationships were found between root density and (IN)-I-15 uptake from different depths. Residual soil NO3 of 18, 59, and 87 kg N ha(-1) was left under fodder radish, winter rye, and ryegrass, respectively. The measurements obtained with the minirhizotron method were highly relevant for evaluating N uptake from different soil layers, and root depths of the catch crops were important for N depletion. Knowledge about root growth and N uptake in deep soil layers may he utilized when designing crop rotations with improved N use efficiency. Where N has been left by a preceding crop and leached to deeper soil layers, it may be recycled by deep-rooted catch crops.