, Volume 26, Issue 1-3, pp 341-357

Efficiency and future potential of urea for temperate grassland

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The efficacy of urea as a grassland fertilizer under temperate conditions has been assessed in a wide variety of comparisons with either ammonium nitrate or calcium ammonium nitrate (CAN). Data from the British Isles have been evaluated and compared to results mainly from continental Europe.

In general urea is as good as CAN early in the growing season, but less-effective in summer. There is no evidence to indicate that urea is significantly more variable that CAN for spring grass production. Maximum yields with urea are lower than those with CAN.

The principal reason for inefficiency of urea is volatilization loss of ammonia. Chemodenitrification is also likely to be important but has not been quantified satisfactorily. In contrast, leaching and denitrification are the principal loss processes with ammonium nitrate. The translation of nitrogen uptake into dry matter yield may be less effective with urea than with CAN.

A wide variety of strategies have potential for improving the efficiency of urea and these have been reviewed. Recent developments with urease inhibitors offer the promise of an effective compound in the near future. Such a development could lead to urea displacing ammonium nitrate as the dominant N fertilizer on temperate grassland.