Gaseous Loss of Ammonia from Prilled Urea Applied to Slash Pine

Abstract

Abstract Gaseous loss of NH 3 from prilled urea, surface applied at 100 kg N/ha to undisturbed dry organic residue over moist soil under slash pine ( Pinus elliottii Engelm. var. elliottii ), averaged 4% in 7 days as compared with 2% for an area that was control‐burned 5 weeks previous, and 5% for one from which loose debris had been removed. This was approximately equivalent to removal by burning. Residual urea recovery of 41% for the burned area as compared with 16 and 12% for the undisturbed and cleaned areas, indicated urease inactivation and partial soil sterilization by burning. Where urea had been applied to moist undisturbed organic residue, hydrolysis approached completion in 3 days and was accompanied by 9% N loss as NH 3 . Various types and orientations of needle‐bearing portions of branches of slash pine were submitted to a 75–100 cm drop of prilled urea at 100 kg N/ha. From 0.32–0.87 g of pellets were retained per meter of branch. Aspiration tests under typical alternating night and day humidities and native urease activity showed only 3% loss of this retained urea‐N as NH 3 in 4 days. At 8 days an average of 52% of the initially retained N was still dilute‐acid soluble from macerated bark plus needle stubs, with a ratio of seven parts urea N to three parts NH 4 + ‐N. The remainder, except for the small gaseous loss, probably was assimilated.