Agriculture Reference
In-Depth Information
Manures are the second in nutrient inputs to agricultural land. The nu-
trient content of manure varies from one country to another and from one
region to another within the same country. It depends on the type of farm-
ing, grazing systems and nutrient content of different foods and fodder for
livestock. There is evidence that at least 50% of manure is lost in storage and
transport and another 25% of manure is lost after application [58,59]. An in-
cubation study with composted poultry manure showed a gradual release of
inorganic N, mineralizing 0.4 to 5.8% of the total N over 56 days compared
to 25.4-39.8% of the total N in uncomposted poultry manure [60].
The application of manure with different level of humifi cation, (i.e com-
posted), has frequently been shown to increase soil fertility [61] and to stimu-
late soil microbial activity through the improvement of soil structure [62].
Additionally, it has been demonstrated that humic substances have auxin-like
activity and positive effects on plant physiology by infl uencing nutrient uptake
and root architecture [63,64]. Simultaneously, it has been shown that through
the use of fl ow-through colorimetry that there is and adsorption of nitrate on to
humic substances, thus improving N availability to the plant [65].
From information on N inputs to agricultural soils and estimates of N
uptake by crops and grass, a calculation of the excess amounts of N ap-
plied to agricultural land can be established. This method of calculating the
excess N is known as N balance at the surface [66]. The surface balance
can be used as an indicator that highlights areas potentially threatened by
N pollution under various environmental scenarios [67,68]. In addition,
monitoring the evolution of these surpluses over several years can be used
to evaluate the effectiveness of agri-environmental measures to avoid pol-
lution by nitrates. The calculation of the surplus cannot however be imme-
diately interpreted as an indicator of N loss in water. The balance between
inputs and outputs for a system includes all potential losses described in
the above sections, and inventory changes of N, mainly in the soil.
15.3 NITROGEN FERTILIZATION USING GREEN MANURE AND
COVER CROPS
Green manure fertilization (see [69] for a review) aims to improve soil fer-
tility and quality by incorporation into the soil of any field or forage crop
