1. Avril P 1987 Légende de la carte des sols des Belgique. Faculté des Sciences Agronomiques de l’Etat, Gembloux, Service de la Science du Sol, 26 p.
2. Blanchar R W and Caldwell A C 1966 Phosphate-ammonium-moisture relationship in soils. II. Ion concentrations in leached fertilizer and effect on plants. Soil Sci. Soc. Am. Proc. 30, 43–48.
3. Chalmeres A G, Church B M, Dyer C J and Leech P K 1991 Fertilizer use on farm crops, England and Wales 1990. Survey of Fertilizer Practice. MAFF Publications, London, 16 p.
4. Chamberes B J and Smith K A 1992 Soil mineral nitrogen arising from organic manure applications. In Nitrate and Farming Systems. Eds. J R Archer, K W T Goulding, S C Jarvis, C M Knott, E Lord, S E Ogilvy, J Orson, K A Smith and B Wilson. Asp. Appl. Biol. 30, 135–143.
5. Christian D G, Goodlass G and Powlson D S 1992 Nitrogen uptake by cover crops. In Nitrate and Farming Systems. Eds. J R Archer, K W T Goulding, S C Jarvis, C M Knott, E Lord, S E Ogilvy, J Orson, K A Smith and B Wilson. Asp. Appl. Biol. 30, 291–300.