Sustainable Nitrogen Management in Agriculture: An Action Programme towards Protecting Water Resources in Walloon Region (Belgium) - Water and Agriculture: Sustainability, Markets and Policies - page 400

and the derogation is no longer granted. As the programme was only launched in 2004,
this situation has not yet occurred, but exclusions have already been decided on the basis
of the poor quality of the collaboration between the excluded farm and the coaching
structure Nitrawal.

Figure 3. Reference values for nitrogen residues
in soil profiles

100

80

Class C1
Class C2
Class C3
Class P

60

40

20

0

October November December
Automn 2004, Walloon region (Belgium)

Source: Nitraw al, 2005

This programme has the advantage of assessing the performance of a farm towards
water pollution directly on the result of its practices and thus on objective criteria. It is a
very good pedagogic tool as the farmer can directly 'see' the effect of his/her practices on
water pollution. On the other hand, it requires a substantial amount of work and
dedication from Nitrawal to prepare the reference curves for each year, analyse the results
and explain them to the farmer. The price of the dosages themselves is paid by the farmer
enrolled in the programme. The sampling is done by the laboratory performing the
dosage.

N balance
In addition to this nitrate residues control in soil profile, a complete nitrogen balance
of each farm is carried out every year, both at farm gate and soil surface level. The farm
gate balance tries to show if and where improvements can be made to the system, without
taking into account the type of speculation present on the farm. The soil surface balance
on the other hand focuses more on the pollution risk : it tries to determine whether the
speculations chosen by the farmer and his management present a risk of nitrate pollution.
As every balance, the calculation aims to determine the difference between nitrogen
entering in the system and nitrogen leaving it. The result is either nitrogen stored or
nitrogen lost in the environment.
Having regard to the many different speculations existing in the region, the
interpretation of the result is difficult without reference values:

The reference value used in the farm gate balance is calculated on the basis of the
nitrogen production of each speculation multiplied by an efficiency factor specific to
the speculation. The nitrogen efficiency of manure is also taken into account. The
comparison between the surplus of the farm and the reference value is an indicator of
the potential progress in nitrogen management to be made, taking into account the
N efficiency specific to each speculation in optimal management conditions.