The physiological basis and consequences for nitrate leaching of novel fertiliser strategies involving foliar fertilisation of wheat
Supplying a proportion of the N requirement of a wheat crop via the foliage would potentially reduce immobilisation of fertiliser N in the soil organic matter and losses by leaching or denitrification. A field experiment to investigate the effects on crop yield, N recovery and nitrate leaching of supplying the main spring N application to winter wheat as different proportions of foliar urea rather than as soil applied ammonium nitrate was repeated on the same site over three years. In year two,
... years. In year two, for selected treatments in the main experiment, recovery of 15N-labelled nitrogen in the plant and soil was recorded. Experiments were conducted to investigate interception by the foliage, and the effect of timing and rate of N applied.N as foliar urea produced similar yields to N applied conventionally to the soil as solid ammonium nitrate or urea over a range of rates of N applied. Early application of foliar urea increased above ground dry matter production and had little effect on harvest index, later applications reduced above ground dry matter production and increased harvest index. The effect of foliar urea on above ground dry matter production was due to increased green area index at anthesis, owing to increased leaf expansion.Apparent recoveries indicated that gaseous losses, most likely by volatilisation, can be im portant for high rates of N applied as foliar urea under warm windy conditions. Applied under cooler conditions likely to inhibit gaseous losses however, true recovery o f fertiliser N in the crop-soil system was similar to that for N applied to the soil as solid ammonium nitrate or urea.Exploiting the potential for increased physiological N use efficiency as indicated and controlling gaseous losses would potentially reduce N losses.