The tolerance of a grass forage, grown in pots, to urea applied to calcareous soils under very hot, dry conditions

Abstract

Proso grass was grown in pots in calcareous soils that received different levels of urea applied at seeding under very hot, dry conditions. Urea applications greater than 83 mg N kg/1 in one experiment and 130 mg N kg/1 in another caused severe toxicity to the grass seedlings. The toxicity corresponded to the period of active urea hydrolsis, 3–5 days from germination. At this time detectable NH4 in a low-and a high carbonate soil was equally far below that applied. A level of 40 mg NH4-N per kg soil appeared critical to seedling toxicity.