The contribution of dairy farming on peat soil to N and P loading of
surface water
C.L. van Beek
1,
*
, G.A.P.H. van den Eertwegh
2
, F.H. van Schaik
2
, G.L. Velthof
1
and
O. Oenema
1
1
Alterra, P.O. Box 47, 6700 AA Wageningen, The Netherlands;
2
Rijnland Water Board, P.O. Box 156, 2300
AD Leiden, The Netherlands;
*
Author for correspondence (e-mail: christy.vanbeek@wur.nl)
Received 2 March 2004; accepted in revised form 24 May 2004
Key words: Denitrification, Leaching, Mineralization, Nitrogen, Peat, Phosphorus, Polder, Slush
Abstract
In agriculturally used peat land areas, surface water quality standards for nitrogen N and phosphorus P are
frequently exceeded, but it is unclear to what extent agriculture is responsible for nutrient loading of the surface
water. We quantified the contribution of different sources to the N and P loading of a ditch draining a grassland
on peat soil Terric Histosol used for dairy farming in the Netherlands. Measurements were performed on N and
P discharge at the end of the ditch, supply of N and P via inlet water, mineralization of soil organic matter, slush
application, composition of the soil solution, and on N losses through denitrification in the ditch for 2 years
September 2000 to September 2002. Discharge rates at the end of the ditch were 32 kg N ha
–1
y
–1
and 4.7 kg P
ha
–1
y
–1
. For N, 43 to 50% of the discharge was accounted for by applications of fertilizers, manure and cattle
droppings, 17 to 31% by mineralization of soil organic matter, 8 to 27% by nutrient-rich deeper peat layers, 8 to
9% by atmospheric deposition and 3 to 4% by inlet water. For P, these numbers were 10 to 48% for applications
of fertilizers, manure and cattle droppings, 2 to 14% mineralization of soil organic matter, 33 to 82% nutrient-
rich peat layers and 5 to 6% inlet water. The results of this paper demonstrate that nutrient loading of surface
water in peat land areas involves several sources of nutrients, and therefore, reducing one source to reduce nu-
trient inputs to surface water is likely to result in modest effectiveness.
Introduction
In agriculturally used peat land areas PLA, surface
water quality standards are frequently exceeded, re-
sulting in a general increase of water impairment in
these areas Best et al. 1993; Klapwijk 1988. In ad-
dition to agriculture, other sources of nutrients, e.g.,
seepage and mineralization of peat, may also contrib-
ute nutrients to surface waters in PLA. The contribu-
tions of different sources of nutrients to the total
nutrient loading of the surface water in PLA are often
unknown, which leads to variable results of similar
measures in different PLA to improve the surface wa-
ter quality.
In the western part of the Netherlands, a large part
of the grasslands on peat soils is located in polders,
which are commonly used for dairy farming grazing
and foraging. Typically, the fields are long and nar-
row e.g., 55 1250 m
2
and are separated by ditches
to improve drainage. Most peat land polders have
been cultivated since around 1000 AD and, due to ar-
tificial drainage, flow pathways to the surface water
are shallow 0–1 m below soil surface; Schothorst
1982. When precipitation exceeds evapotranspiration
most often during winter, water is pumped out of
the polder. When evapotranspiration exceeds precipi-
tation most often during summer, water is supplied
to the polder from the surrounding lakes and chan-
Nutrient Cycling in Agroecosystems 70: 85–95, 2004.
© 2004 Kluwer Academic Publishers. Printed in the Netherlands.
85