Field experiments on uptake of nitrogen from leaf sprays by sugar beet

Abstract

When the leaves of sugar-beet crops were sprayed on six occasions in late September and early October with 100 gal./acre of a 3% solution of ammonium nitrate or equivalent urea, in two experiments about 70% of the nitrogen was recovered in the plants in mid-October, compared with 40% recovered from applications of the same amounts of fertilizer to the soil at the same times. In a third experiment the recovery from similar sprayings with urea solution was less than 40%, but very little nitrogen was absorbed from soil dressings, so that the difference between the recoveries from spray and soil applications was nearly the same as in the other experiments.Nitrogen per cent of dry matter in all parts of the plant was increased by the sprays. More than half of the nitrogen absorbed from the sprays was in the leaf laminae, and the remainder was equally divided between petioles (including crowns) and roots. Between 20 and 30% of the nitrogen supplied in spray in the first two experiments was converted to protein in the leaf laminae, and half of this was present as soluble protein precipitable by trichloracetic acid, a fraction that is extracted in the largescale preparation of leaf protein.Spraying slightly increased the dry-matter yield of the tops, but not of the roots. It reduced the sugar content of the roots by about 1% of fresh weight. In one experiment it had no effect on sugar yield; in the others it caused losses of 2 and 5 cwt./acre.The recovery of nitrogen in the tops from a single low-volume spraying (12½ or 25 gal./acre) with nearly saturated urea solution was about the same as from repeated high-volume sprays supplying the same total amount of nitrogen, but in the roots it was higher from the single than from the repeated sprays.