1 On Farm Biogas production with solid manure in organic farming Evaluation of the two stage dry anaerobic biogas plant production and recycling on Skilleby experimental farm in Järna 2004 -2010 Final report December 2011 Artur Granstedt Biodynamic Research Institute Skilleby, 153 91 Järna, Sweden
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On Farm Biogas production with solid
manure in organic farming
Evaluation of the two stage dry anaerobic biogas plant production and recycling on Skilleby experimental farm in Järna 2004 -2010
Final report December 2011
Artur Granstedt Biodynamic Research Institute Skilleby, 153 91 Järna, Sweden
2
Evaluation of the two stage dry anaerobic biogas plant and the influence on production and recycling on Skilleby experimental farm in Järna 2004 -2010
Background European countries are committed to reduce CO2 emissions originating from fossil fuels.
Additional changes in policy priorities as well as the development of agricultural technology
are important driving forces. Organic farming principles for their part include the use of
renewable energy resources and the minimisation of nutrient losses on-farm as far as possible.
On-farm produced biogas may replace fossil fuels and thereby contribute to achieve the target
of reduced green house gas emissions. Losses of nitrogen are also reduced by dry anaerobic
digestion of organic material. In accordance with the EU-regulation (EU 1774/2002) animal
by-products can also be used for biogas production.
Most on-farm biogas plants in Europe use slurry and co-substrate for biogas production. This
technology is reasonable only on farms, where slurry technology is already in use. Slurry
based biogas plants are well developed in those European countries where investment
subsidies for biogas plants are granted and prices for electric power production are low. Such
favourable conditions prevail mainly in Germany. Farms, which use a dry manure chain
technology, and farms without livestock are not able to use the prevailing on-farm biogas
technology.
The top 10 benefits of dry anaerobic-digestion biogas plants are clearly in line with organic
farming principles and strengthen sustainable agriculture (Hoffmann, 2002, quote from
Schäfer, Lehto and Teye, 2006):
1. Dry anaerobic digestion is suitable for nearly all farm residues like manure, plant
residues, and household organic wastes. Higher energy density compared to slurry
digestion requires reduced reactor capacity and reduces construction costs.
2. High dry matter content reduces transport costs due to reduced mass transfer in
respect of the produced biogas quantity per mass unit.
3. Mobile digester modules allow batch production and continuous, easily controllable
gas production.
4. Dry anaerobic digestion residues can be composted and in this way fertilisers, also suitable
for off-farm use, are produced. Composted manure may also be better for food quality
compared to liquid manure.
5. Dry anaerobic batch digestion does not need special techniques like slurry pumps,
mixers, shredders, and liquid manure injectors for distribution. Most of the machinery
needed for filling and discharging the digester like front loaders and manure
spreaders are often already available on-farm.
6. The amount of energy required for heating the process is lower than in slurry reactors
because of
reduced reactor size. Process energy of dry anaerobic batch digestion is not
required because continuous homogenisation is not needed.
7. There is improved process stability and reliability. There occur no problems like foam or
sedimentation. Possible digestion breakdowns are easily dealt with in batch
3
digesters by exchanging the module.
8.There are reduced odour emissions because there is no slurry involved.
9. There is reduced nutrient run-off during storage and distribution of digester residues
because there is no liquid mass transfer.
10. The process is suitable for farms without slurry technology, especially farms using deep
litter
systems e.g. chicken production. 50% of Swedish manure originates from farms
handling solid dung.
Figure 1. The two stage dry anaerobic-digestion biogas plant in Järna build on the biodynamic
farm Yttereneby Järna by the Biodynamic Research Institute (Photo 2003, Wienfried
Schäfer).
The Biogas plant on the Biodynamic experimental farm Skilleby - Yttereneby in Järna and the aim of this study.
Figure 1. The two stage dry anaerobic-digestion biogas plant in Järna build on the biodynamic
farm Yttereneby Järna by the Biodynamic Research Institute (Photo 2003, Wienfried
Schäfer).
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One of the world's first large scale on-farm dry anaerobic-digestion biogas plants has been
built on the mainly self-supporting farm organism, Skilleby-Yttereneby by the Biodynamic
Research Institute in Järna. This on-farm biogas plant is integrated into the farming system
and employs a new process technique: Dairy cattle manure and organic residues originating
from the farm and nearby food processing units are digested in two different reactors.
The first reactor is continuously filled with solid manure from a stanchion barn. The organic
matter contains 17.7 to 19.6 % total solids. After digestion the residue is discharged and
separated into a liquid and a solid fraction. The liquid fraction is further digested in a methane
reactor and the effluent is used as liquid fertiliser. The solid fraction is composted and used as
manure on the winter wheat in the five year crop rotation. The use of the composted manure
has been evaluated as part of the long term study during 2006 – 2010.
The Biogas plant is build on the farm YtterEneby which functions as a unit with Skilleby
experimental farm. The purpose of the plant is to evaluate and demonstrate the possibility to
achieve ecological recycling agriculture which is fully based on the local renewable resources,
is environmentally sustainable and with the best possible productivity and food quality.
The following goals were formulated:
1. To make agriculture production self sufficient in energy
2. To reduce the negative impact on the environment compared to traditional manure
management with respect to green house gas emissions, leaching of plant nutrients,
and ammoniac emissions.
3. To increase the efficiency in agriculture production through effective internal
recycling of plant nutrients in manure and liquid manure and with reduced losses
from the farming system in line with ecological recycling agriculture (ERA)
principles (Granstedt, et al 2008).
The objective of this study is to evaluate the extent to which these goals have been reached
and identify possible improvements. In addition this study will evaluate:
4. the capacity of manure to improve the fertility of and humus content in soil thereby
improving yields and food quality .
The evaluation includes the technical evaluation of the biogas plant, the material and nutrient
flows on the whole Skilleby/Yttereneby farm unit and field studies over many years.
The two-stage fermentation process results in the production of two fractions of manure , one
solid fraction and one liquid fraction. The solid fraction has been composted and compared
with non-fermented manure. The liquid manure has been used like urine. The evaluation has
been done as an integrated part of the long-term on-farm study of manure recycling and
utilisation on Skilleby- Yttereneby .
The technical evaluation of the biogas plant covers the period between 2003 - 2005, the
biological evaluation of the fermentation and on farm studies including comparative field
trials were carried out between 2006 and 2008. The future of the biogas plant at Yttereneby
has not yet been decided. To cover the costs for managing the biogas plant it would be
necessary to increase production and the price of the biogas in order to cover production
5
costs. This would be possible if the application to the Swedish Board of Agriculture to use
slaughter wastes from the local wild meat slaughterhouse close to the farm is approved and
the subsides for investments to produce electric power from the gas produced in the biogas
plant are granted.
Material and methods
Technical description of Skilleby – Yttereneby biogas plant
The first reactor is continuously filled with solid manure from a stanchion barn. The organic
matter contains 17.7 to 19.6 % total solids. After discharge the digestion residue is separated
into a liquid and a solid fraction. The liquid fraction is further digested in a methane reactor
and the effluent is used as liquid fertiliser. A complete technical description of the biogas
plant has been published (Schäfer, Lehto and Teye, 2006).
6
Figure 2. The Material flow chart of the biogas plant at Yttereneby, Järna, Sweden (
Schäfer, Lehto and Teye, 2006)
Figure 3. Material flow diagram with manure, feeding and mixing marked.
(Schäfer, Lehto and Teye, 2006)
7
Figure 4. Pictures illustrating manure from the cow, feeding and mixing
Feeding and mixing 1 (Figure 3 and 4)
A hydraulic powered scraper shifts manure into feeder channel (1 in figure 2). The manure of 65
livestock units kept in a dairy stanchion is a mixture of faeces, straw and oat husks. A part of the
output of the hydrolysis is conveyed back to the feeder channel and inoculated into the fresh manure.
The urine is separated in the stall via a perforated scraper floor.
Figure 4. Pictures illustrating manure from the cow, feeding and mixing
Hydrolysis reactor (figure 5)
The manure is pressed to the top of the 30o inclined hydrolysis reactor with a 53 m
3 capacity. The
bottom of the hydrolysis reactor on both sides of the feeder pipe is provided with hot water channels.
The 400 mm wide feeder pipe is made of PVC. The substrate is discharged through a bottomless
drawer in the lower part of the reactor. The drawer is guided within a regular channel and powered
by a hydraulic cylinder.
.
8
Figure 5. Outside and inside of the hydrolysis reactor
Separation in liquid and solid fractions (Figure 6)
From the transport screw the major part of the substrate partly drops into a down crossing extruder
screw where it is separated into liquid and solid fractions. The liquid fraction is collected in a buffer
container of 2 m3 capacity (8 in figure 2) and from there pumped in methane reactor (10 in figure 2).
The solid fraction from the extruder screw is stored on the dung yard for composting. Liquid from
the buffer container returns into the feeder pipe of the hydrolysis reactor to improve the flow ability.
Figure 6. Separation into liquid and solid fractions.
Methane generation (figures 7 and 8)
The methane reactor is 4 m high with a total capacity of 17,6 m3 and filled with elements offering a
large surface area for methane bacteria settlements. After a reaction time of 15 to 16 days at 380C
the effluent in the methane reactor is pumped into the slurry store (11 in figure 2). The gas generated
in both reactors is collected and stored in a sack in a container. A compressor generates 170 mbar
pressure to supply the burners of the process and estate boiler with biogas for heating purposes.
The first biogas production started in 15th
of November 2003 and continued until the animals were
let out to pasture on the 8th
of May 2004. The production, is shown in Figure 9. A frozen gas pipe
blazed the gas yield of the hydrolysis reactor impeding correct measurement of the gas yield in
9
April. The potential cumulative gas yield capacity was therefore assumed to be higher than this first
test year and this was later confirmed.
In contrast to the design calculations, the methane reactor produced less gas than the hydrolysis
reactor. The methane reactor generated in average the first period 34 vol % and in the second period
11 vol % of the methane. This indicates that the process management can be improved so that the
load rate of the second reactor is increased (Schäfer, Lehto and Teye 2006).
Figure 7. Material flow diagram the methane gas generation, methane gas compressor store, and
effluent store are marked.
Figure 8. Pictures showing the inside of the biogas reactor, elements for the bacteria, store sack and
the slurry store.
10
Figure 9. Observed biogas yield, mean day temperature, total observed cumulative methane yield
and yield separated into the production from the methane reactor and from the hydrolysis reactor
(Schäfer, Lehto and Teye 2006.
The farm
Geographic localisation and climatic conditions
The Skilleby-Ytterenby farm has until recently been two farms, Skilleby and Yttereneby but
nowadaysis running as one unit. The field experiment wasfirst started on Skilleby in 1991.
The biogas plant was constructed in 2002 and received manure from the cow barn which is
shared by both farms. The farm is situated 50 km south of Stockholm, on a clay soil in
eastern Sörmland (Figure 10) with a northern latitude 59o30´ , at 30-40 metres above sea
level, with an annual average precipitation of 590 mm, a yearly average temperature 6,2oC
and 6-8 snow free months (Figure 2). The topsoil is generally frozen 3-4 months in the year
(December – March). The weather conditions are presented in more detail for the
experimental period in Supplement 1. The Skilleby experimental farm has 42 ha arable land
which lie on each side of a small water way which after some kilometres south east of the
farm feeds into the Stafbofjärden in the Baltic Sea. Since 2002 Yttereneby and Skillebyfarms
have been managed as one working unit with 137 ha with the same five years crop rotation
on each and the manure distributed on both until 2010.
Soil conditions The soils are composed mainly of clay loam with a humus content between 2,8 and 4,2 %, a
large proportion of silt predisposes them to crust formation. The soil under topsoil depth is
stratified, with glacial clay at the bottom. The natural history for this soil formation is shown
in Figure 11 where the top soil with the secondary sorting of the soil texture fractions (post
glacial clay, loam and silt) are seen. The glacial clay is close to the topsoil in elevated areas.
In the more low-lying areas the clay content is lower and the soils dry out more quickly in the
spring. This geological background where most of younger fossil sediments were eroded
11
during the last ice age, and the sediment clay is based mainlyon primary rocks, explains why
the soil is high in potassium and low in phosphorus.
Three soil samples were taken from each experimental plot from the top soil (o – 20 cm),
from 30 – 60 cm depth and 60 – 90 cm depth at the start of the long term field experiment
1991. These samples were analysed for their chemical and biological properties including Ctot,
Ntot, pH, P-Al, K-AL, Ca-Al, Mg.AL. These analyses were repeated after each five year crop
rotation period and are of special interest for the evaluation of the biogas manure effects on
soil on HV1 (2006), HV2 (2007), HV 5 (2008), HV 3 (2009) and HV 4 (2010). The P-AL
values in top soil are mainly between 2 – 3 and the K-AL values between 10 – 15 mg in 100 g
soil and pH values between 5,5 -6,0 according the figures presented from HV1 and HV2 in
Supplement 2.
The Biodynamic Research Institute
A B
Figure 10. Localisation of the Skilleby long term trial in East Central Sweden, at latitude 59
o
North and longitude 18 o East, 30 – 40 m above sea level.
12
The Biodynamic Research Institute
Map with simplified high coast-
line (HK), Area above the HK
and under the HK.
In Sweden most arable land is found
where there are sedimentary soil types
below the high coast- line after last ice
time 10 000 years ago..
Natural history
Figure 11. The soils are postglacial sedimentary clay and loam with low humus content in the
lower parts mixed with some mud clay
The Biodynamic Research Institute
Granstedt, A., L-Baeckström, G.( 2000): Studies of
the preceding crop effect of ley in ecological
agriculture. American Journal of Alternative
Agriculture, vol. 15, no. 2, pages 68–78. Washington
University.
Figure 12. The focus of the Skilleby long term trial has been to study how soil fertility and
food quality is effected by manure managements regimes and soil treatments. Between 1991
and 1996 a special study comparing the effects on different durations of ley and the effects of
the preceding crop (Granstedt and Baeckström, 2000).
13
Crops, fodder production, animal husbandry, manure and plant nutrient recycling
The distribution of crops and animal husbandry is exemplified for 1997 in Figure 13. The
animal husbandry consist of milk and meat production adapted to the farm'sown fodder
production on 84 % of the total arable area (Granstedt, 2000). the remaining 16 % of the area
is used for production of food crops. The nitrogen input is based on the biological nitrogen
fixation mainly in the first and second year clover grass crops. The proceeding crops' effect
and long term crop rotation effect of clover grass on Skilleby farm was studied during 1991 to
1995 and published in Granstedt and L-Baeckström (2000). The plant nutrients in the
harvested field crops are mainly recycled through thesolid and liquid manure. The total
animal density is 0, 7 (Figure 13 says 0,6 AU/ha on the farm and also that some feed is
imported – clarify) animal unit per ha producing, on average, 250 tonnes of stable manure and
180 tonnes of liquid manure each year. The plant nutrient recycling is presented in Figure 22
(Granstedt et al 2008).
7/8/2011 AG
The prototype farm
Yttereneby –
Skilleby in Järna)
•The animal density is
adjusted to the farm’s
feed production
capacity. In this case
fodder crops on 84 %
and crops for sale on
16 % of the farm area
and with a animal
density of 0,6 AU/ha
(= average for Sweden
and European food
consumption)
Yttereneby and Skilleby 2003
Import---> Recycling Export
Feed Herd: Milk
Seed 47 cows Meat products
39 heifers
10 calves
29 sheep
0,6 AU / ha
450 m3 urine + 600 m
3 manure
+dung/urine pasture
Biogas
Arable land ha Crop rotation
Crop rotation 106 Year 1 Spring cerals + insowing
Pasture 29 2 Ley I
Vegetable - 3 Ley II
root croops 2 4 Ley III
Total 137 5 Winter cerals
Natural pasture 25
0,5%
Veget.
Root crops
1,5%
Bred grain
15%
Ley (grass
land)
47%
Pasture
21%
Feed grain
15
%
Ow
n f
eed
>84
% o
f th
e a
rea {
Bread
grain
Example of Ecological Recycling Agriculture / ERA
14
Figure 13. Fodder food crops and animal production and recycling of solid and liquid manure
(urine) on Skilleby - Yttereneby farm.
.
Crop rotation
When it started in 1967 this biodynamic farm had a seven year crop rotation with two and
sometimes three years of clover grass leys followed by bread grain, oats, green fodder and
bread grain with oats or barley sown in. The nutrient management on Skilleby with special
focus on nitrogen is well documented in a doctor's thesis by Granstedt (1990 and 1992).
From 1991, when the long-term field experiment was initiated, a new five year crop rotation
was established and followed until today:
1) oats with under sowing of clover grass
2) clover grass ley I
3) clover grass ley II (support of liquid manure)
4) clover grass ley III (only one cut before cultivation, application of farm yard
manure and sowing of winter wheat.)
5) winter wheat (with additional support of liquid manure some years).
This crop rotation was designed to improve the humus content and soil fertility.
The effects of applications of non-composted and composted manure were studied, with and
without biodynamic preparation treatments, at three levels of application (12.5, 25 and 50 tons
per ha 1991-1995 and 0, 25 and 50 tons per ha 1996-2008). This resulted in 12 treatments all
together and with 2 – 4 replications of each treatment. The trial was established on each of
the five fields in the crop rotation on Skilleby farm. From 2003 – 2010 manure from the
biogas plant was used as stable manure and special studies to compare the manure from the
biogas plant and manure direct from Nibble farm with no biogas treatment but both
composted and non-composted were carried out between 2006 – 2010. The results of nutrient
content analysis in the manure for the years 2006 and 2007 area presented in Table 1 and
Table 2.
15
Design of field trial
The Biodynamic Research Institute
Rotation Skilleby experimental
farm
1. Summer crop + ins
2. Ley I
3. Ley II
4. Ley III
5. W. wheat
Farm own manure (0.6 au/ha)
On farm long term experiment from
1991
- non-composted and composted
manure
- with and without biodynamic
preparation (split plot design)
- three levels: 12.5 (0), 25 (normal)
and 50 tons per ha)
- 2 – 4 replicates on the five rotation
fields Figure 14. The field trials are located on representative spots in each field starting with winter
wheat in the autumn 1991 on field number one. The following year winter wheat was sown on
field number 2 and so on until 1995 when the trial plots were established on the last field,
number 5.
The Biodynamic Research Institute
Experimental plan from 1991
Without BD preparation-
BD preparation each plot each yearSubplots +
50 tonK3
25 tonK2
Composted manure 12.5 ton ( 0 from 1995)K1
50 tonF3
25 ton F2
Not composted manure 12.5 ton ( 0 from 1995) F1
Treatments winter wheat
Main plot
Skilleby long-term trial started in 1991 and still continuing
Figure 15. Field trial implementation and the experiment design.
16
Manure
Table 1. Nutrient content analysis of fresh, stored (not composted) and composted manure
2006.
Table 2. Nutrient content analysis of fresh, stored (not composted) and composted manure
Figure 40. The relation between non-composted (FM) and composted (CM) manure and the
yields of winter wheat 1993 - 2020
Influence of biogas fermentation on yields
From 2003 manure from the biogas plant (BGFYM) was used and studied through
comparison studies with Nibble manure (NFYM) both non-composted (F) and composted (C)
from 2006 to 2010 (Figure 41 and 42). There was no significant difference in yield on plots
treated with biogas and Nibble manure. In HV4 and 5 only the normal manure application
(30 kg per ha) of Nibble and biogas manure were compared. In 2006, the first year of this
comparison study, only non-composted manure was used in the field HV1. The results
showed that both biogas and Nibble composted manure gave higher yields than non-
composted manure. The biogas plant produces two fractions of manure, one solid and one
liquid fraction. Mass balance calculations show that about the same amount of solid manure is
produced from the biogas plant as composted biogas manure from the compost heap. The
effect on yield of the additional liquid manure from biogas plant (BLM) was studied in 2010
(Figure 43). The addition of 20m3 BLM per ha to the F2 treatment (30 t per ha of non-20 m3
BLM to the C2 treatment (30 t per ha of composted manure) gave a significantly higher yield
of 760 kg ha-1
. (16 %). The average nitrogen yield of winter wheat was 73 and 81,5 kg N ha-1
respectively and gave 13 and 10 kg N ha-1
in higher yield respectively (+ 18 and 12 %).
39
Winter Weat 2006-2010
0
1 000
2 000
3 000
4 000
5 000
6 000
Year
Yie
ld k
g /
ha
F NFYM 2 887 2 938 2 681
F BGFYM 2 930 3 077 2 618
C NFYM 2 845 3 027 3 081 4 509
C BGFYM 2 689 2 737 2 909 4 949
HV1 HV2 HV5 HV3 HV4
2006 2007 2008 2009 2010
Figure 41. Yield of winter wheat after treatments with Nibble farm yard manure (NFYM) and
biogas farm yard manure (BGFYM) both non- composted manure (F) and composted manure
(C) during the five years 2006 – 2010 on the five years crop rotation on the fields HV1 – HV5
on Skilleby experimental farm.
W Wheat HV4 2010
0
1 000
2 000
3 000
4 000
5 000
6 000
yie
ld k
g/h
a
BGM 4 203 4 723
plus BLM 4 675 5 483
F2 C2
Figure 42. Average annual yield of winter
wheat after treatments with normal farm
yard manure (NFYM) and biogas farm
yard manure (BGFYM) used as non-
composted manure (F) and composted
manure (C) during the five years 2006 –
2010 on the five years crop rotation on
the fields HV1 – HV5 on Skilleby
experimental farm.
Figure 43. The yield of winter wheat on HV4
2010 with regular application (30 t per h
)of non-composted and composted (F2
and C2) biogas farm yard manure
(BGFYM) and additional application of
20 m3 biogas liquid manure ( BLM) per
ha.
Winter Wheat 2006-2010
0
1 000
2 000
3 000
4 000
kg / ha and
year
F NFYM 2 835
F BGFYM 2 875
C NFYM 3 366
C BGFYM 3 321
1
40
Discussion
Introduction One hundred years ago agriculture production depended on the use of local renewable energy
resources. The farmer used the wood from the forest for heating and raised horses and oxen
for draft power The farmer was also dependent on maximal recycling of nutrients and humus
building organic material from manure in combination with crop rotations with a high share
grasslands to build biomass and biological nitrogen fixation (Granstedt, 1995).
Recent economic developments in countries like Sweden have forced a specialisation in
agriculture with increasing areas of arable land under crop production without clover and
grass leys and without animal production producing farm yard manure. Animal production is
on other hand concentrated to a smaller group of specialised animal farms were high surpluses
of nutrients cause dangerous levels of emissions to the environment This highly specialised
agriculture is to a great extent dependent on external inputs of both fossil energy and
imported fertilizers fodder as well as a growing use of pesticides especially in simplified crop
rotations with low variation.
In a farming system without animals and leys a reduction of 0,24% per year of the carbon
content in the top soil has been observed On an average mineral soil this can mean a loss of
about 600 kg C or 1440 kg CO2 per ha and year (Bertilsson, 2010). At the same time the lack
of nutrient recycling has led to a decrease of trace elements in soils.
Ecological recycling agriculture documented through on farm studies in the countries around
the Baltic Sea (Granstedt et al 2008) has shown the potential of the integration of crop and
animal production (where the animal production is adapted to the farms own fodder
production capacity) to increase the recycling, reduce use of external resources and reduce
losses of nitrogen and phosphorus compounds to the environment. An additional important
step to realise sustainable agriculture based on local resources is the capacity to produce
renewable energy on the farms. Through anaerobic fermentation of manure before recycling
it is possible to produce methane gas for heating and power for agricultural machines and
transports.
One of the world's first large scale dry anaerobic-digestion on-farm biogas plant has been
built in Järna/Sweden in the context of the highly self-supporting farm organism, Skilleby-
Yttereneby by Biodynamic Research Institute in Järna. This on-farm biogas plant employs a
new process technique: Dairy cattle manure and organic residues originating from the farm
and the surrounding food processing units are digested in two different reactors.
This biogas plant has been evaluated in relation to the following goals:
1) Biogas production and energy self-sufficiency at farm level
2) Reduce negative impact to the environment
3) Effective internal recycling of plant nutrients and improved crop production
4) Improved humus content, fertility and long term production capacity of soil.
41
Biogas production and self sufficiency with energy on farm level The biogas production was evaluated during the years 2003 – 2009. During optimal
conditions it was possible to convert in percent of total carbon close to 50 % of the total
carbon content in the 2 m3
produced manure per day (Figure 43).
Figure 43. Exchange of carbon in gases of the total carbon content in manure.
The X axes shows the different stages of biogas production from the manure input to the
biogas plant on Skilleby-Ytterenby farm in Järna.
During one year total methane gases production was 18 644 m3 but with a documented
potential to produce 29 000 m3.
The production capacity of the plant is presented in figures 9,
17 and 18. Of this the biogas plant needs energy for heating the reactors to stabilise the
temperature to the optimal process temperature of 370C 37 and uses up about 9 000 m
3 during
one year. With an additional 0,5 m3d
-1 food residues from kitchens in the nearby ecological
hospital Widarkliniken and process improvements biogas production increased to more than
70 m3d
-1 and a net production capacity of 500 kWh d
-1. The average use of vehicle fuels on
ecological recycling farms was in the BERAS project calculated to 554 kWh d-1
(Granstedt,
et al 2006).
It can be concluded that based on the farms own manure it is possible to produce 50 – 100 %
of the farms requirements for the vehicle fuels and that the higher level can be realised if it
possible to add additional carbon sources such as food residues. This energy production in
combination with biological nitrogen fixation, recycled manure and animal production based
on the farms own fodder demonstrates how, with the help of modern technology, it is
possible to realise a self-sufficient sustainable agriculture production based on local and
renewable resources.
100 81 74
55
0 19 26
45
0 10 20 30 40 50 60 70 80 90
100
Fresh Low Normal High
Exchange stages
Gas % of C tot
C in CO2 and CH4
C in org. matter
42
Reduce negative impact to the environment
The comparison between the conventional manure management with winter storage on a
dung plate and composting (C NFYM) and the biogas manure system (C BGFYM) show that
total nitrogen losses can be reduced by half in the biogas system from 9 N kg-1
y-1
(39 %) to
4,5 N kg-1
y-1
(19 %). This means that more nitrogen is recycled to the soil. These
calculations confirm the findings of Schäfer et al (2008) but with the difference that the
reduction of nitrogen losses was 38 % lower in the biogas system compare to the previous
manure management system on the farm used system. Use of liquid manure can give higher
gas emissions compared to use of solid manure which can reduce the total higher nitrogen
efficiency in the biogas system.
The lower nitrogen emissions and higher nitrogen efficiency mean that emissions of NH4 N
and N2O N are reduced with about 50 %. However the effect on N2O and NO3 N emissions
from soil after the use of liquid manure fraction need further study. In the literature lower
emissions of CH4 have also been documented.
Effective internal recycling of plant nutrients and improved crop production The field experiment with additional application in May of 20 tonnes biogas liquid manure
ha-1
gave 14 % higher yield of the cash crop winter wheat (15 % higher N yield) and also a
corresponding increase of crop residues. In the total balance the nitrogen surplus was 35
instead of 36 N kg-1
y-1
thus reducing the total potential nitrogen emissions from the biogas
plant system compared to the conventional manure management system. The higher
production of crop residues with a high C/N ratio also increases nitrogen immobilisation and
in this way also contributes to increased humus content in the soil.
Humus content in soil, long term fertility and production capacity
Carbon balance in a sustainable system with clover grass ley
Based on data from this study and field experiments with clover grass leys on Skilleby
(Granstedt and L-Bäckström, 2000) it has been calculated that a three-year clover grass ley
with an annual nitrogen fixation between 100 – 200 kg N ha-1 can result in the net
assimilation of 18 tons of carbon in biomass which is then going to the soil organic matter
formation process both directly from crop residues and roots and indirectly through recycled
manure and food residues. The effect of grassland leys in different years is exemplified in
Figure 45.
43
Soil Organic Matter in topsoil as a fuction by ley
0
1
2
3
4
5
6
7
8
0 2 3 5
Number of leys in 6 years crop rotation
SO
M %
Silt loam
Silt loam
Till clay
Soil Organic Matter = SOM in top soil after three rotations in North Sweden (Persson, 1994)
Soil Organic Matter in topsoil as a fuction by ley
0
1
2
3
4
5
6
7
8
0 2 3 5
Number of leys in 6 years crop rotation
SO
M %
Silt loam
Silt loam
Till clay
Figure 45. Soil organic matter after three crop rotations with different numbers of leys in the 6
years crop rotation (Persson, 1994)
Previous experiment
In the thirty-two year long K-experiment (1958 – 1990) the treatments with organic manure
combined with the clover/grass ley gave a clear increase of organic carbon in the topsoil
compared with no use of organic manure (Reents, Pettersson & Wistinghausen, 1992). The
mineral fertilized treatments and the unfertilized treatment gave no increase of the carbon and
humus content despite the inclusion of leys in the crop rotation. The total amount of organic
carbon to a depth of 60 cm, after interpolation of the humus content in the soil layers between
them, was calculated to an annual average increase of organic carbon in the order of 800 kg
per ha in the biodynamic treatment (Granstedt and Kjellenberg, 2008). This amount is
comparable to what is reported from the renowned Rhodale long term experiment from 1981
to 2005 in Pennsylvania in USA in a more legume based farming system with farm yard
manure, Soya beans and clover/grass ley (Hepperly, Douds & Seidel, 2006) and correspond
with the DOK experiment in Switzerland where the effect of biodynamic (BD) preparation
and composted manure are also reported (Mäder et al, 2002).
In a study comparing biodynamic and conventional cultivation, the UJ-experiment (1971-
1979), it was possible to analyse the importance of leys in each system (Pettersson, 1982).
The humus concentration in the biodynamic trial B2 with ley increased from 2.72% to 3.06%
(1.58 to 1,77 % C-org) during the 8-year trial period (slightly more than 10%) while the
humus content remained at the same level in the trial with conventional cultivation A1
without leys (Figure 46).
44
Soil Organic Carbon Järna experiment
1,45
1,5
1,55
1,6
1,65
1,7
1,75
1,8
1971 1973 1976 1979
Co
rg -
%
0
-20
cm
B2
B1
A2
A1
L+FYM
L+MinF
FYM
Min
Figure 46. Trials comparing biodynamic and conventional cultivation in Järna 1971 – 1979. (
L – ley, MinF – mineral fertiliser and FYM – farmyard manure)
In these trials the importance of leys and organic fertilizer for the assimilation of organic
carbon and the building up and maintenance of the humus content in the soil and with this the