Distribution via tanker
The tanker is filled at the slurry storage and pulled to the field for distribution. Below are the
principal distribution systems ex-tanker:
With reflection plate
The slurry is squirted through a nozzle against a reflection plate which, by it’s special
form, diverts and broadens the squirt. An improvement of the simple reflection-plate-
distribution is a swiveling plate which leads to a more even distribution.
Direct application through sliding hoses
The slurry is pumped into a distribution system which feeds a number of hoses which
move closely to the ground. The slurry is applied directly on the soil surface, therefore
reducing nutrient losses. Distances between the hoses can be adjusted to suit different
plant cultures.
Hoses with drill coulters
The soil is opened with two disks (drill coulters) in a v-shape. The slurry is applied with
sliding hoses into the v-furrows, which are closed behind the hose. This application
method could be labeled ’sub-surface application’. It is the most advanced in terms of
avoiding nutrient losses. Similar to the hose application, distances between application
rows are adjustable. Alternatively to the hose application, the slurry can be positioned by a
metal injector.
The application methods close to the soil surface, in contrast to the broadcasting methods,
have the advantage of a higher degree of exactness and less nutrient losses to the
atmosphere. Fertilization can be better adjusted to plant needs. In contrast to broadcast-
spraying, direct application is possible even at later stages of plant growth without damaging
the leaves. Disadvantages are the rather sophisticated machinery necessary and the high
costs involved. Direct application methods are, therefore, mostly used as inter-farm
operation.
Separation of slurry and drying of the moist sludge
In industrialized countries, the slurry is usually separated by means of separators and sieves.
The water is re-fed into the digestion process or distributed as liquid manure while the moist
sludge is dried or composted. As a simple technology for separation, slow sand-filters can be
used.
The moist sludge can be heaped on drying beds, filled in flat pits or simply placed on paved
surfaces near the biogas plant for drying. Depending on climatic conditions, large drying
areas may be necessary. Drying times and nutrient losses can be reduced by mixing dry
substances with the moist sludge. A disadvantage of all drying methods, again depending on
the climate, is the high loss of nutrients. In particular heavy rains can wash out the soluble
nutrients. Losses of nitrogen, for example, can amount to 50% of the overall nitrogen and up
to 90% of the mineral nitrogen. Drying of the moist sludge can only be recommended where
long distances and difficult terrain hampers transport to the fields or if composting is difficult
for lack of manpower and lack of dry biomass.
Composting of slurry
Dry plant material is heaped in rows and the liquid slurry is poured over the rows. Ideally,
plant material and slurry are mixed. The mixing ration depends on the dry matter content of
plant material and slurry. The main advantage is the low nutrient loss. Compost, containing
plant nutrients in a mainly biologically fixed form, is a fertilizer with long-term effects. It’s
value for improving soil structure is an additional positive effect of importance.
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