THE EFFECT OF NITROGEN CATCH CROPS ON THE NITROGEN NUTRITION OF A SUCCEEDING CROP

The effects of catch crops on the nitrogen nutrition of a succeeding carrot crop were investigated. An attempt was made to distinguish the effects of growth and nitrogen uptake by the catch crop from the effect of mineralization of its residues. It was found that growth and nitrogen uptake by catch crops could reduce the nitrogen supply to the succeeding carrot crop through pre-emptive competition, whereas mineralization of nitrogen from the catch crop residues increased the nitrogen supply to the carrot crop. Nitrogen uptake by the carrots was thus highest where catch crop residues were incorporated on plots where no catch crop had been grown. The effect of the mineralization was found mainly to influence topsoil mineral nitrogen contents and the early nitrogen uptake by carrots, whereas the effect of pre-emptive competition was to reduce subsoil mineral nitrogen content and the nitrogen uptake by carrots late in the growing season. The apparent recovery of catch crop nitrogen by carrots was between 8 and 33%.