Transport of ammonium- and nitrate-nitrogen in surface runoff from pasture as influenced by urea application

Sharpley, A.N.; Syers, J.K.; Tillman, R.W.

Transport of ammonium- and nitrate-nitrogen in surface runoff from pasture as influenced by urea application

1983

Sharpley, A.N. | Syers, J.K. | Tillman, R.W.

The effect of a surface application of urea on the transport of N in surface runoff from permanent pasture in New Zealand was investigated under natural rainfall conditions. Maximum concentrations of NH4- N(3.6 mg l-1) and NO3-N(4.5 mg l-1) in surface runoff were attained 3 and 1 week, respectively, following urea application (60 kg N ha-1). Amounts of NH4-N, NO3-N, and total N transported in surface runoff from unfertilized (1.58, 0.52, and 4.73 kg ha-1 yr-1, respectively) and fertilized pasture (1.74, 1.09, and 8.96 kg ha-1 yr-1)were less than inputs in precipitation (2.09, 3.63, and 10.9 kg ha-1 yr-1), respectively. Amounts of NH4-N, NO3-N, and total N transported in surface runoff were only 0.3, 1.0, and 7.1 % of that applied. The mean annual concentration of NH4-N (0.9 mg l-1) in surface runoff from unfertilized pasture was above the recommended levels for drinking water (0.5 mg l-1) and the mean concentration of NO3-N (0.5 mg l-1) was greater than levels associated with accelerated cutrophication (0.3 mg l-1 ). The practicality of attaining or maintaining N concentrations in surface runoff from fertilized agricultural land below recommended levels is questioned.

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