|Authors: ||H. Riley, G. BÝrtnes|
|Keywords: ||leaching, fertilizer, gross margin, model, nitrogen|
Most vegetables require high N-fertilization, and have associated risks of leaching as they are grown in intensive rotations on light soils with large amounts of crop residue.
In order to assess leaching risks in relation to economic output of some of the vegetables grown in Norway, simulations were performed with the EU-Rotate_N model (Rahn et al., 2007) for commonly used rotations of varying intensity in inland and coastal areas.
All simulations were performed over six years using weather data for the period 2000-2005.
In the inland area, with moderate annual precipitation and loam soil, rotations with up to 50% vegetables were compared with a rotation with five cereals and one potato crop.
Simulations were performed at both recommended and assumed grower fertilizer levels.
The model predicted ca. 25% increase in leaching when one cabbage or onion crop was included, whereas the inclusion of swedes or carrots decreased it.
The inclusion of both cabbage and onions in the same rotation increased leaching by almost 50%, and it was almost doubled if cauliflower was included as well.
Despite these large increases in leaching, the gross margins of vegetable rotations were high in relation to the amounts of N applied.
Leaching from similar rotations simulated on sandy loam in a coastal area with milder winters and slightly more precipitation was ca. 10-20% higher than that inland.
In a comparison of early and late vegetable crops in this coastal area, early crops showed the same or slightly more N leaching than late crops, despite having lower N fertilizer levels.
The use of catch crops is therefore recommended in such cases.
Simulations with more intensive rotations, with 67% vegetables including early potatoes, indicated that such rotations have the highest leaching losses, especially in coastal areas of South and South-West Norway, where precipitation is high.
The simulations with assumed grower levels of fertilizer showed 20-60% higher leaching losses than with the use of recommended N fertilizer rates, but seldom appeared to give any economic benefit.
An exception was found for cauliflower in one coastal area.
In this case, better economy was predicted by increasing the number of split fertilizer applications.
This had, however, little effect on overall leaching.
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