Dry Weather & Fertiliser Nitrogen

In very dry weather it is best to hold fertiliser N applications until rain is forecast/occurs, particularly on bare dry soils with little cover. Soil moisture deficits (SMD) of >50 mm increasingly limit grass growth and therefore N demand and uptake. The Figure below produced using the SMD model developed at Johnstown Castle shows that many soils in the south and east particularly have much higher soil moisture deficits and therefore limited growth rates.

Source: https://www.met.ie/forecasts/farming

Fertiliser N Type (CAN / Protected Urea)

Where fertiliser is applied to dry soils and rain remains absent – points to know:

• CAN based fertilisers: the forms of N in CAN are relatively safe.
• Protected Urea (urea+NBPT): the protection of the urease inhibitor NBPT will breakdown over time, if rain has not arrived to melt the fertiliser into the soil after 4 to 7 days some N loss through volatilisation is likely. Usually this is not an issue in Ireland with regular rainfall and heavy dew being more typical.

During a protracted drought such as the current period it is best to hold off applying fertiliser N until rain is forecast/arrives and grass growth rates begin to recover.