Urea and Biuret Stimulate Growth of Douglas-fir and Western Hemlock Seedlings
- Richard E. Miller ,
- Harry W. Anderson and
- Donald C. Young
Two experiments were conducted in a greenhouse to test a theory that biuret in urea fertilizer reduces growth of Douglas-fir [Pseudotsuga menziesii (Mirb.) Franco] or western hemlock [Tsuga heterophylla (Raf.) Sarg.]. Newly germinated seedlings in 2.5-L pots were treated with 0, 0.224, 2.24, or 22.4 kg biuret ha−1 (40% N) in factorial combinations with 0, 84, or 168 kg N ha−1 as reagent-grade urea (46% N). The biuret was applied as a solution to either the sandy loam soil or the foliage. Four of the eight replicates were harvested 203 d after treatment. For Exp. 2, the remaining seedlings were retreated as they were initially and harvested 305 d later. In both experiments, the two species responded strongly to urea; moreover, seedling dry weight increased with increasing biuret (P = 0.003). Averaged over all other factors, weight of seedlings treated with the highest biuret dosage was 14% more than the weight of seedlings with no biuret. Unfertilized hemlock responded as much to 0.2 kg biuret ha−1 (0.08 kg N ha−1) as to 84 kg N ha−1 as urea; this suggests that biuret functions as a hormone. The results indicated that biuret is unlikely to reduce growth of seedlings of either species even when urea heavily contaminated with biuret is applied at high dosage.
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