Danish Institute of Agricultural Sciences Department of Agroecology N-management in grass-arable crop rotations Jørgen Eriksen 96 Tools for reducing N-losses

Build-up in grassland Years of grassland % N Source: Johnston 1991

Loss after ploughing N (t/ha) Years after ploughing Source: Whitmore et al. 1992

What effects nitrate leaching? Fertilizer application Feeding Use (grazing/ cutting) Composition (grass/clover) Duration Grazing time Animal density

Leaching from grassland

Why lower leaching from grass-clover? Explanation 1: Reduced N-fixation leading to lower input

Nitrate leaching from grassland Unfertilized grass-clover Fertilized grass-clover Fertilized grass Total N input Nitrate leaching kg N/ha/yr Source: Ledgard

Grassland yields Why less leaching from grass-clover? Explanation 1: Reduced N-fixation resulting in lower input Explanation 2: Lower yields resulting in less grazing

Utilizing N in urine spots Source: Cuttle and Bourne

Crop rotation Time of ploughing Fertilizer application History What effects nitrate leaching?

Nitrate leaching – crop rotation

Winter wheat -> catch crop Bare soil -> catch crop Nitrate leaching – crop rotation

Utilizing the residual effect ”Old” pastures on coarse sandy soil 3-yr-old grass-clover far from the farm 5-yr-old grass-clover close to the farm Cultivation followed by: Green barley – Ital. ryegrass Barley maturity – per. Ryegrass Barley maturity – bare soil

N-uptake – cereals after grassland

Leaching – cereals after grassland

Management in grass-arable rotations During grazing Fertilizer in grassland Time of grazing (day/year) Grazing/cutting Following cultivation Time of ploughing Choice of crop (incl. catch crop) Fertilizer application year 1 and 2 Crop rotation Grassland age at ploughing Grassland frequency in rotation

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