Fate of 15N-nitrogen fertiliser applied in high rainfall zone dairy pastures

Understanding soil and fertiliser contributions to pasture nitrogen (N) uptake over more than one growth period can help improve N use efficiency in dairy pastures.

A field experiment using 15N isotope techniques found that pasture utilised between 34 and 42% of applied urea-N over an 8-13 month period on dryland and irrigated pastures in a temperate zone. Greatest uptake of applied N occurred in the first two harvests post fertilisation. However > 77% of the pasture N came from the soil. These findings suggest that utilising soil N reserves combined with lower fertiliser inputs could improve N use efficiency in dairy systems.