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

Ten widely different plant species were compared for their ability to reduce soil mineral nitrogen levels in the autumn and their ability to improve the nitrogen nutrition of the succeeding crop. The species in cluded monocots and dicots, crops that survived the winter (persistent ) or were winter killed (non-persistent) as well as legumes and non le gumes. Their ability to reduce soil mineral nitrogen content was depen dent on both root depth and persistency of the crops in the autumn. Fo r non-persistent catch crops most of the mineralization of plant nitro gen occurred during the winter, and for some of these so early as to a llow leaching of some mineralized nitrogen. For persistent crops most of the mineralization occurred shortly after incorporation in the spri ng. The effect of the catch crops on nitrogen uptake by the succeeding barley crop varied from 13 to 66 kg N ha-1 and the differences betwee n the crops could not be related to any single character, but to a com bination of root depth, persistency, plant nitrate accumulation, and d epletion of the soil mineral nitrogen pool in spring.