Digestate as Fertilizer

Legal requirements in Germany and Europe
Finally, considering the 11 component
material categories of which the fertilizers
may consist, they are classified into one of
the 7 Product Function Categories (PFC):
Fertilizer, liming material, soil improver,
growing medium, agronomic additive, plant
biostimulants and fertilizing product blend.
Heavy metal contents are defined for all
PFC limits, for example cadmium (Cd),
chromium (Cr), mercury (Hg), nickel (Ni),
lead (Pb), arsenic (As), copper (Cu), and
zinc (Zn), and are formulated depending
on PFC minimum requirements for hygiene
(salmonella, e. coli), dry matter content or
carbon and nutrient content.
Cd CrVI Hg Ni Pb As Cu Zn
[mg / kg DM]
Limit value 1,5 2 1 50 120 40 300 800
Furthermore, the absence of salmonella
spp. has to be guaranteed for organic fertilizer,
and the value of escherichia coli or
enterococcacae is limited by a maximum of
1000 colony forming units (CFU)/g.
There are two possible product function categories
that digestate can be assigned to:
on the one hand, it can be assigned to the
PFC “fertilizer” and, on the other hand, to
PFC “soil improver”. All nutrient contents
are related on the fresh matter content. In
most cases, digestate does not reach the
required nutrient contents and, therefore,
cannot be classified as “organic fertilizer”.
Additionally, digestate will not fulfil the dry
matter content in order to be part of solid
fertilizers or soil improver unless the digestate
is further upgraded. Specifically,
this means the exclusion of the majority
of digestate from the EU Fertilizer Regulation.
This leads to a big disadvantage for
the digestate market and, in the best case,
should be changed.
This inevitably results in the necessity of
upgrading for most liquid digestate (see
Chapter 6: “Digestate upgrading techniques”)
if they are to be marketed freely
within the European Union. Of course, the
requirements for national law remain unaffected
by this, if the fertilizer is only to be
marketed and applied inside one member
state for which it meets the requirements.
However, once the EU Fertilizer Regulation
enters into force, national guidelines
Suggested heavy metal contents for organic fertilizer in [mg/kg dm]
Solid Organic
Fertilizer
Liquid Organic
Fertilizer
Organic
Soil Improver
DM-Content [%FM] ≥40 ≤40 ≥40 6
Nitrogen (N) [%FM] 2,5 2 - 0,3
Phosphorus (P 2
O 5
) [%FM] 2 1 - 0,1
Potassium (K 2
O) [%FM] 2 2 - 0,14
Organ. Carbon (C org) [%FM] ≥15 ≥5 ≥7,5 1,5
may also have to be amended and existing
national standards adapted if necessary.
The EU Fertilizer Regulation is not
expected to come into force before the end
of 2019.
In the Federal Republic of Germany,
the Fertilizer Ordinance
complies with the EU Fertilizer
Regulation at the national level.
It specifies constitution of the fertilizer,
e.g. which substances can be used, limit
values on heavy metals and other pollutants,
relevant nutrient contents as well as
requirements on labelling and marketing.
The planned application determines the
classification as fertilizer, soil improver or
growing media.
Application of digestate with drag hose
Average of
liquid digestate
As a second requirement, the Fertilization
Ordinance regulates good professional
practice in the application of fertilizers on
agricultural land. The requirements for
upper application limits, determination
of nutrient demand of the plant, nutrient
surpluses, blocking periods, and storage
capacity for storing organic fertilizers were
significantly tightened by the last amendment
for agricultural holdings. In doing so,
the main aim is to implement the requirements
of the European Nitrates Directive,
which intends to avoid nitrate contamination
of groundwater and surface water by
agriculture. Restrictions on the application
of nitrogen and phosphate-containing fertilizers
depending on location and soil conditions
are also laid down in the Fertilization
Ordinance. The farmer must determine the
nutrient demand for each crop or management
unit before applying the digestate
containing significant quantities of nitrogen
and phosphate.
Probably the strongest intervention by
the amended Fertilization Ordinance is
the increase of the average upper limit of
170 kg N / ha to all organic and organicmineral
fertilizers, which means that digestate
is now also affected independently of
the input materials to produce it. This limit
applies irrespective of the actual nutrient
demand of the crop and regional characteristics,
such as soil quality, yield expectations
and the proportion of grassland. This
regulation thus undermines the sustainable
nutrient cycles and promotes the use
of mineral fertilizers, as this is not limited
across the board. In contrast, organic fertilizers
have to be transported to other regions
or to other distribution channels.
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