Role of Fine Roots in the Nitrogen Economy of Sugar Beet

In 31 field experiments with sugar beet, carried out in 1982–84 in Scania, southern Sweden, fertilizer nitrogen recovery in tops and beets, calculated with the difference method, amounted to 73%. To elucidate the role of the fine lateral roots in the fate of the nitrogen not accounted for, the lateral roots within depths of 0–25 and 25–60 cm were sampled at harvest in late September, 1984 in five sugar beet experiments. Irrespective of differences in nitrogen fertilization and plant-available soil nitrogen, a mean of ca. 3 kg/ha^?1 of nitrogen was found in the fine lateral roots. This corresponded to only ca. 2% of the nitrogen in the whole crop at harvest, whereas the beets and tops contained 43 and 55%, respectively. Using the difference method, calculations with, as well as without, fine roots therefore yielded the same recover (75%) of fertilizer nitrogen in the beet crop. The increase of residual mineral nitrogen in the soil at harvest caused by the fertilization corresponded to 2% of the fertilizer nitrogen applied. This means a total recovery of 77%.