In years with high precipitation early in the growing season, there may be a need for supplementary fertilisa-tion in maize. Nitrogen (N) is leached as nitrite, which is retained poorly in the soil – particularly in coarse sandy soils, where water easily percolates. The need for supplementary fertilisation further depends on when the previous fertiliser was applied. The earlier a slurry is applied, the more the leaching and the higher the need for supplementary fertilisation. It is thus not recommended to apply slurry on coarse sandy maize fields before 1 April. Nitrification from ammonium to nitrate in animal manure may be slowed by nitrification inhibitors, which reduces N leaching and thus the need for supplementary fertilisers. Plant analysis showing an N-content below 3.3 % of the plant dry matter, indicates that N might be a yield limiting factor and reveals a need for supplementary fertilisation, which should be applied as soon as possible. A yield effect is possible until the end of July but recedes with time. To prevent ammonia volatilisation, supplementary fertilisation with slurry may be injected, trail hose applied after weeding and/or acidified.