The Long-term Nutrient Depletion Trial (Udpiningsmarken)

Field testing of crop response to P and K application generally requires an experimental site with low available soil P or K status. However, many arable soils are high in available P and K due to generous fertilisation with inorganic fertilisers and animal manures for decades.

At the University of Copenhagen the Long-term Nutrient Depletion Trial was established back in 1964 by staff at the Department of Plant Nutrition on 8.5 ha of a sandy clay loam. The site did not receive any P or K containing fertilizers or manures in the period up to 1995 and in this period the field was managed with continuous cereal production. The available P and K levels decreased to relatively low values over these more than 30 years of depletion (Olsen-P of 11 mg kg-1 and exchangeable K of 55 mg kg-1).

In 1996 a new experimental design was applied in the majority of the field, with two more varied crop rotations and seven nutrient application treatments, including both mineral fertilizers and animal manures. The overall objectives of the new experimental design were to study how soil biology, physics, chemistry and crop physiological response and yield for different crop species and cultivars react when an arable soil low in P and K receives variable combinations of N, P and/or K in mineral fertilizers or animal manures.

Crop biomass production, yield and nutrient uptake results are available for most years. The experiment has also accommodated related studies on e.g. the relationship of root hair promoted P uptake of selected barley genotypes to the grain yields in P limiting soil (Gahoonia and Nielsen, 2004) and the ability of different catch crop species to mobilise and take up P and K from soils of low availability, as well as their ability to deliver P and K to the subsequent main crop (Jensen et al., 2005).

The field trial comprises the following permanent treatments (incomplete combinations:

  • N: 50% or 100% of crop max N norm (120-160 kg N/ha
  • P: 0, 10, 20 or 40 kg P/ha
  • K: 0, 60, 120, 240 kg K/ha
  • Slurry: 0, 15, 30 t/ha

Period: The trial was initiated in 1964 with no P and K application until 1996 and is an ongoing activity with the current design was implemented in 2010.

Project head: Lars Stoumann Jensen

Funding: various sources

Danish website:


  • Gahoonia, T. S. ; Nielsen, N. E.. 2004 Barley genotypes with long root hairs sustain high grain yields in low-P field. Plant and Soil. 262, 55-62
  • Jensen LS, Pedersen A, Magid J, Nielsen NE. 2005 Catch crops have little effect on P and K availability of depleted soils. DARCOF e-news 2, 1-7.