Foliar applications of nitrogen to slash pine seedlings

Summary The absorption of N from foliar applications of various N sources by pine seedlings was studied under greenhouse conditions. Needles dipped into solutions of 4,000 ppm N from Ca(NO₃)₂ were burned slightly at the tips at two weeks. Although higher concentrations of (NH₂)₂CO and (NH₄)₂SO₄ could be used without plant damage, a uniform concentration of 3,000 ppm was used in all comparative tests of sources. The level of tissue N, brought about by soil fertilization 6 weeks previously, did not significantly influence absorption of foliarly applied N¹⁵. Soil moisture maintained at near 100, 60 to 70, and 25 to 35 per cent of water-holding capacity of the Leon fs did not significantly affect the absorption of tagged N. Greater quantities of N¹⁵ were absorbed as urea than as Ca(NO₃)₂ or (NH₄)₂SO₄. The use of a spreader-sticker increased the N¹⁵ uptake, regardless of the N compound used. However, the magnitude of the increased absorption associated with use as a sticker varied from 490 per cent with (NH₄)₂SO₄ to 260 per cent with urea. It was calculated that approximately 71, 45, and 39 per cent of foliar applied N was absorbed into needles within 24 hours from urea, Ca(NO₃)₂, and (NH₄)₂SO₄, respectively. Journal Paper No3588 of the Florida Agricultural Experiment Station, Gainesville, Florida.