J. agric. Engng Res. (1997) 66, 239 – 250
Estimates of Volumes and Exposed Surface Areas of Stored Animal Manures
and Slurries in England & Wales
R. J. Nicholson*; A. J. Brewer†
*ADAS, Boxworth, Cambridge CB3 8NN
†ADAS, Nobel House, 17 Smith Square, London SW1P 3JR
(Receiy ed 1 February 1996; accepted in rey ised form 12 December 1996)
Estimates of animal manure (solid material) and
slurry (liquid material) stored on farms are needed by
the Ministry of Agriculture, Fisheries & Food
(MAFF) for compiling national inventories of gaseous
emissions. Data needed for this purpose include the
total volume and surface area of stored manures and
slurries from different livestock species. Existing
sources of data were reviewed but have limitations in
the context of an emissions inventory. Suppliers of
prefabricated stores were approached for numbers
and sizes of stores sold since 1970.
ADAS pollution control consultants made informed
estimates of the geographic distribution of methods of
storage in use in England & Wales for manure and
slurry from dairy cows, other cattle and pigs. This
information was combined with June 1992 census
figures to provide estimates of volumes (raw and
diluted) and exposed surface areas of stored manures
and slurries. ADAS livestock consultants were used to
interpret census data and provide estimates of the
distribution of poultry manure handling methods. A
computer spreadsheet was used to store and process
this data and is available to allow future adjustments
or sensitivity analyses. In this paper, these estimates
are reported on a national basis but they were
originally gathered separately for each of 15 areas and
appended to a report produced for MAFF. These
detailed figures are available on request.
The majority of diluted livestock slurry is stored in
earth-banked lagoons, with an estimated total volume
of 15?5 Mm3 and an estimated surface area of
7?0 Mm2. The total volume of stored solid manure is
14?9 Mm3 with an estimated surface area of 11?9 Mm2.
The estimates were compared with data from other
sources and show an acceptable level of agreement.
÷ 1997 Silsoe Research Institute
0021-8634 / 97 / 040239 1 12 $25.00 / 0 / ag960139
1. Introduction
Housed livestock and stored manures (solid) and
slurries (liquid) are thought to contribute significantly
to emissions of ammonia and methane from
agriculture.1 Because of their environmental effects,
an inventory of these gaseous emissions is needed to
guide policy makers. MAFF has recently commissioned such an inventory. MAFF is funding research
on gaseous emission rates from stored animal excreta
which is largely being undertaken by Silsoe Research
Institute and the Institute for Grassland and Environmental Research. To complement this research, data
on types and numbers of slurry and manure stores in
the UK were needed in order to complete the
proposed inventory.
Limited data on this subject were included in a
study by Manchester University2 and a survey by the
former Milk Marketing Board (MMB),3 but the figures were not comprehensive, nor were they presented in a form which was suitable for compiling the
proposed inventory. Therefore ADAS produced estimates of the types and numbers of manure and slurry
stores in use in England and Wales, with data presented in a form that would allow them to be used to
produce the proposed inventory. The results of the
ADAS work4 form the subject of this paper.
The exposed surface area of stored material is likely
to be a major factor influencing the amounts of
ammonia emitted.5 Method of storage, physical form
of the material, and species from which it originates
are likely to be important in determining emission
rates. Existing information6 indicates that the y olume
of stored material, its dry matter content, and the
species from which it originates are the major factors
influencing methane emissions. For both ammonia and
239
÷ 1997 Silsoe Research Institute
240
R. J . N I C HO LSON ; A. J . B RE W E R
methane, the period of storage will influence the
amounts of gas emitted.
It was agreed that it would be desirable to have an
indication of the geographical distribution of amounts
and types of stored manures and slurries: this was
undertaken for England and Wales. It was concluded
that estimates of actual numbers and sizes of stores
were not as relevant in this context as total surface
area and volume.
2. Existing data
The following sources of data were reviewed, and
their limitations identified before formulating a strategy for compiling the required estimates.
Table 1
Storage facilities for manure and slurry on farms in Great
Britain with dairy herds (estimated numbers and percentages of farms)2
All sizes , population
estimate
Type of store
Midden with impermeable base
Midden with permeable base
Underfloor slurry tank
Slurry: steel tank
concrete tank
weeping wall store
lagoon, impervious lining
lagoon, without impervious lining
Other
Number
%
12370
2300
4560
4940
3620
1830
2830
3910
2360
34
6
12
14
10
5
8
11
6
* Stores per 100 farms
2.1. MAFF Farm and Consery ation Grant Scheme
Data have been collected by MAFF Countryside
Division on the uptake of the Farm and Conservation
Grant Scheme and its precursors, but records are only
easily accessible from 1986 at the earliest. The existing
database could be interrogated to provide information
on numbers of holdings claiming grant, amount of
expenditure, and species, in relation to improvements
to waste handling facilities. However no central records were kept of the detail of improvements, such as
store type or size. This source of information therefore, while essential in detailing which industry sectors
have taken up grant aid, is of no use in providing
information for an emission inventory.
2.2. Manchester Uniy ersity study
A study by Manchester University,2 provides data
on the uptake and effectiveness of the MAFF Farm
and Conservation Grant Scheme, and contains useful
estimates of types and numbers of manure and slurry
stores in use in 1991 based on a sample of around 900
farms. However, the data do have a number of
limitations as they make no estimate of size of stores,
do not include poultry, and are therefore difficult to
interpret in the context of a gaseous emission
inventory.
The study included an assessment of types of
storage facility on farms with dairy herds, on nondairy farms with cattle, and on farms with pigs.
Information was presented for small, medium and
large farm businesses in a survey of 900 farms in
England, Wales and Scotland. However, an estimate
for all farm sizes, based on the sample studied,
106
* Some farms have more than one type of store, e.g. provision for both slurry and solid manure.
indicated the number of different types of store on
farms with dairy herds, non-dairy farms with cattle
and farms with pigs (Tables 1, 2 and 3).
The study also provides information on the destination of dilute effluent (commonly called dirty water)
arising from contaminated run-off following rainfall
and washing water from dairy, cattle and pig farms.
This indicates that 32% of dirty water on dairy farms
Table 2
Storage facilities for manure and slurry on non-dairy farms
in Great Britain with cattle (estimated numbers and percentages of farms)2
All sizes , population
estimate
Type of store
Midden with impermeable base
Midden with permeable base
Underfloor slurry tank
Slurry: steel tank
lagoon, impervious lining
lagoon, unlined
Other
No specific store*
Number
%
8900
4000
2800
2000
800
1700
3600
27400
17
7
5
4
1
3
7
51
* For farms with housed cattle: many leave manure in
bedded yards.
Note: data presented as given in original source.
VOLUMES AND EXPOSED SURFACE AREAS OF STORED ANIMAL MANURES AND SLURRIES
Table 3
Storage facilities for manure and slurry on farms in Great
Britain with pigs (estimated numbers and percentages of
farms)2
All sizes , population
estimate
Type of store *
Midden with impermeable base
Midden with permeable base
Underfloor slurry tank
Slurry: steel tank
concrete tank
lagoon, impervious lining
lagoon, pervious lining
Other (including field heaps)
*Stores per 100 farms
%
2.5 . MAFF census data
4100
540
2930
520
1460
870
540
940
41
5
30
5
15
9
6
9
120
June census data collected annually by MAFF
Census Branch at Guildford provide very accurate
information on numbers and types of livestock on a
county basis. This information was used in conjunction
with advisers’ estimates as described in Section 3.3.
is stored with slurry and 13% is stored separately; on
pig farms 16% of dirty water is stored with slurry and
10% is stored separately. Hence dirty water must be
taken into account when calculating slurry store
capacity.
2.3. MMB sury ey
The survey carried out by MMB3 in 1993 included
questions on slurry storage methods. All milk producers in England and Wales were sent a questionnaire
which drew replies from 8212 producers (a 28%
response rate). The majority of farms in the sample
housed cows in cubicles (83%). For farms with some
form of slurry and manure storage, the different types
of store were assessed (Table 4).
2.4. Liy estock housing
Estimates produced by ADAS, for MAFF Environmental Protection Division, on types and numbers of
Table 4
Slurry and manure storage methods on dairy farms in
England & Wales3 (An unspecified number of farms had
no storage facilities)
Towers*
Earth-walled lagoons
Weeping wall stores
Concrete pads
Other
poultry houses and types and numbers of pig housing
in England and Wales provided useful background
data on the forms in which excreta are likely to be
handled. The data on poultry housing are reasonably
straightforward, while the data on pig housing are
complex and difficult to interpret.
Number
* Some farms have more than one type of store.
Store type
241
Percentage of farms %
20
30
15
19
23
* ‘‘Towers’’ are above-ground cylindrical stores.
Note: some farms have more than one type of store.
Data presented as given in original source.
3. Methodology
3.1 . Oy erall approach
While attempts were made to collect data on
numbers and types of prefabricated stores, it was
apparent that this would not take account of large
numbers of structures built in -situ . ADAS consultants
in the field were not able to give a direct estimate of
store numbers, or volumes and surface areas of stored
material. However, using their experience they could
reliably assign values to the percentages of different
types of system installed in their particular geographic
area, and relate these values to class of livestock.
Therefore, it was decided that an indirect approach
would be adopted. MAFF census figures for numbers
of livestock are known to be accurate. ‘‘Text-book’’
values7,8 of excreta output for a particular livestock
species give realistic estimates and are extensively
used for calculating storage capacity needed on a
particular site. It was concluded that the best accuracy, within the limitations of an indirect approach,
could be achieved by calculating total volumes of
undiluted excreta from livestock numbers and excreta
output, and then subsequently estimating the proportion stored by different methods.
Therefore, effort was targeted on collecting information in the broad sub-divisions of species, for the
form in which excreta are handled (solid or liquid),
and type of store and storage period (Table 5, the
categories in this table apply to more than one species
and the table is not to be read across line by line).
Manure and slurry stored within buildings was not
included in this study.
In respect of storage capacity (Table 5) it was
arbitrarily decided to ignore any storage capacity of
less than two weeks, because it was unlikely to be
significant in contributing to overall emissions. An
attempt was made, in the case of dairy cows, to make
242
R. J . N I C HO LSON ; A. J . B RE W E R
Table 5
Categories used for data collection and presentation
Species / Numbers
Dairy cows
Other cattle
Pigs
Slurry storage
Above-ground circular
Weeping wall
Lagoons and compounds
(below-ground)
Manure storage
Concrete pad
Field heap
Storage capacity
Months
Quantitatiy e data
Volume stored
Exposed surface area
Poultry
a separate estimate of quantities of dilute effluent
(dirty water) stored for more than two weeks. As
estimates drew heavily on the knowledge of local
ADAS pollution control consultants, any data on
geographical distribution were based on the fifteen
ADAS Consultancy Centres which existed in 1993 / 4.
3.2. Manufacturers ’ data
Manufacturers and suppliers of prefabricated slurry
stores, in particular circular above-ground structures
and weeping-wall structures, were presumed to have
records of numbers of stores sold. A decision was
made to approach them for this information but it was
accepted that any data collected by this route could
have limitations if replies were not received from all
companies. A large number of stores currently in use
(e.g. earth-banked structures and manure stores) are
constructed locally and would not be covered by this
approach.
A total of 21 manufacturers or suppliers of prefabricated slurry stores were sent questionnaires to obtain
information on the likely population of above-ground
circular stores and weeping-wall stores in England and
Wales. They were asked to estimate store numbers
and typical store size, by livestock species (pigs and
cattle) and by area (ADAS Business Centre) installed
since 1970. For those who could not provide this level
of detail, an opportunity was given to record information for ‘‘Southern Counties’’, ‘‘Northern Counties’’
and Wales or on a total (England and Wales) basis.
3.3. ADAS estimates
ADAS pollution control consultants have good
local knowledge of types of store in use, largely
through pollution control advisory visits.
Questionnaires were developed to obtain informed
estimates of manure and slurry storage methods on
dairy, beef and pig farms. Each questionnaire broadly
followed the same format but allowed for differences
in slurry management between livestock species. In
addition, to improve the quality of these estimates, the
‘‘dairy cow’’ questionnaire contained questions for
herds of less than 100 cows and for herds of 100 cows
and over. Consultants from each Business Centre
were asked to reach a consensus opinion on the
proportion of manure and slurry stored for each
livestock species. Methods of storing manure and
slurry were estimated as percentages of their respective total volumes. For each storage method an
estimate was made of typical capacity (months) and
typical storage depth (m). The destination of dirty
water was assessed and allocated to ‘‘stored with
slurry’’ or ‘‘stored separately’’ or ‘‘stored for less than
two weeks’’. Methods of storing dirty water separately
(i.e. not with slurry) were assessed and a proportion
was allocated to above-ground circular stores and
lagoons.
Data from the questionnaires were processed using
a computer spreadsheet (Microsoft Excel). Data for
livestock numbers were taken from the June 1992
MAFF Census Frequency Distribution Tables. Information on volumes of excreta produced was based on
standard data,7,8 but modified to accord with the
appropriate feeding method (pigs), weight, age, and
class of livestock where necessary. Spreadsheets were
developed for each livestock species, that is, for dairy
cows, other cattle and pigs. Specialist ADAS consultants for cattle and pigs assisted with interpretation of
census data.
Estimates of manure output from two classes of
poultry (laying hens and broilers) were made separately with assistance from a specialist ADAS consultant. Spreadsheets were developed for each class.
3.3 .1 . Data inputs
For each livestock species, an appropriate set of
data was used in the calculation of manure, slurry and
dirty water volumes and exposed surface areas. Examples are given in Tables 6 and 7. Common data
used in these calculations, such as dilution factors and
storage depths, are given in Table 8. The effect of
changing any of these data could be demonstrated by
allowing the appropriate spreadsheet to re-calculate
volumes and surface areas.
A dilution factor for above-ground circular slurry
stores has been used to take account of incident
rainfall. Similarly, a dilution factor for lagoons serves
the same purpose and allows for the typical surface
VOLUMES AND EXPOSED SURFACE AREAS OF STORED ANIMAL MANURES AND SLURRIES
243
Table 6
Example input data for cattle and pigs
Dairy
Beef
Pigs
Age
Excreta output *
Age (months )
Excreta output *
m 3 d 21 animal 21
Adult
0?057 m3 d21 cow21
,6
6 – 12
12 – 24
.24
0?007
0?012
0?022
0?027
Parlour wash water
Fouled, unroofed
yard area
*18 l d21 cow21
10 m2 cow21
Wash water
Fouled, unroofed
yard area
Not applicable
1 m2 animal21
Weight / type
Excreta output *
m 3 d 1 pig 21
Breeding (dry fed)
Breeding (wet fed)
,20 kg
20 to 40 kg
Finishing (dry fed)
Finishing (wet fed,
3?5 to1)
0?0065
0?0075
0?002
0?003
0?0045
0?007
Finishing (wet fed,
5 to 1)
Finishing (swill)
Clean down water
Fouled, unroofed
yard area
0?011
0?014
*0?0005
Not applicable
* Volumes based on sources.7,8
area of a lagoon to be greater than for an aboveground circular store of similar volume.
Where manure is collected as a ‘‘solid’’ it is most
often mixed with straw bedding. The addition of straw
provides greater bulk and the volume assessment uses
the ‘‘straw addition factor’’ to take account of this.
It is impossible to estimate surface areas of stored
manure without making assumptions about typical
stack size, since exposed surface areas will consist of
stack top plan area and the area of its sloping sides.
For the purpose of this study it is assumed each stack
is rectangular with a flat top and vertical sides. A
consensus of opinion from ADAS pollution control
consultants indicated that the plan area of a typical
stack is 200 m2 with 20 m by 10 m sides (perimeter is
60 m). The combined surface area of a series of stacks
of this size, forming an estimated total volume arising
from a particular species and / or geographical area can
then be calculated as follows (all dimensions in m):
Estimated number of stacks (n ) 5 Total estimated
volume of manure / 200D
Total exposed surface area 5 n 3 [200 1 60D ]
where D is the depth (or height) of stack.
Similarly, following consultation with ADAS pollution control consultants, typical values have been
assumed for solid manure depth in buildings and for
slurry depth under slats. These values allow for
checking calculations and provide consistency in
spreadsheet operation although manure and slurry
storage within buildings is not included in this study.
Considerable amounts of dirty water are produced,
particularly on dairy farms, and where this is added to
slurry it will increase the size of slurry store required.
No specific surveys have been carried out on quantities arising. The ADAS Agro-meteorological Unit
therefore provided an average October to March
rainfall for each of the 15 areas to enable appropriate
calculations to be made. Values ranged from 309 mm
(Bury St Edmunds) to 748 mm (Cardiff).
3.3 .2 . Census data
June census data for all dairy cows and according to
herd size were used in the calculations.9 Non-dairy
cattle numbers were derived from the total numbers
of cattle and calves10 less the numbers of dairy cows.9
The percentage distribution of all non-dairy cattle by
age was combined with individual county estimates to
Table 7
Example input data for poultry
Excreta output* kg d21 bird21
Specific volume of manure l kg21
Housing occupancy %
* Source.8
Laying hens
Broilers
0?115
1?0
96
0?073
1?0
88
244
R. J . N I C HO LSON ; A. J . B RE W E R
Table 8
Standard dilution factors and store dimensions
Dimension
Measurement
Dilution factor, circular slurry stores
Dilution factor, slurry lagoons
Straw addition factor (for farmyard
manure)
Solid manure depth in buildings
Solid manure store perimeter
Solid manure store area
Under-slat slurry depth
Depth of typical above-ground circular
stores
Depth of typical lagoons
1?15
1?35
1?5
0?75 m
60 m
200 m2
1m
3?5 m
2?5 m
provide the distribution of such animals for each of
the 15 areas. This has been aggregated (Table 9) into
estimates for England and for Wales.
For simplicity, census data on pigs relating to herd
size groups 1 – 9, and 10 – 19 pigs were omitted both for
the breeding herd11 and for total pigs12 as these
represented very small numbers. Data for the remaining pig breeding herd were multiplied by a factor of
1?22 to take account of boars, maiden gilts and barren
sows. Data for all other pigs 20 kg and over13 were
subtracted from data for total pigs to arrive at
numbers of pigs 20 kg and under. For pigs 20 kg and
over, 30% were calculated to be in the 20 kg to 40 kg
weight range and 70%, 40 kg and over.
Census data for all laying hens14 and all broilers15
according to flock size were used in the calculations.
3.3.3. Dairy cows , calculation
The volume of excreta produced per month was
calculated and data from the questionnaires were used
to allocate this output into slurry and solid manure.
Slurry store volumes were calculated using the
consultants’ estimates of the proportion allocated to
different store types, multiplied by the storage capaTable 9
Percentage distribution of non-dairy cattle by age
Age
Fully grown animals:
2 yrs old and over
Growing cattle:
1 yr to 2 yr old
Six months to 1 yr old
Calves under six months old
Total
England
Wales
33%
38%
30%
20%
17%
100%
28%
17%
17%
100%
city (months). A value was given for undiluted excreta
and for a dilute product (rainfall and dirty water
added). The dilute slurry volume was calculated by
applying the appropriate dilution factor to the excreta
volume and then adding any dirty water (subsequently
calculated) which was destined to be stored with
slurry. Any dirty water added in this way was assumed
to be stored for the same period and was allocated on
a pro-rata basis only to above-ground circular stores
and to lagoons. Surface areas were calculated by
dividing volume by depth.
Excreta volume was converted into an ‘‘excreta and
straw’’ manure volume by using the straw addition
factor. Exposed surface areas of manure heaps or
stacks were calculated using the formula given in
Section 3.3.1.
Dirty water production per month was calculated
from the standard figure for parlour wash water with
the addition of rainfall from unroofed fouled yard
area (10 m2 cow21). An assessment of the destination
of dirty water was made because some is stored with
slurry and some is stored separately. Volumes of dirty
water stores were calculated using a proportion allocated to different store types multiplied by the storage
capacity (months). Surface areas were calculated by
dividing volume by depth.
3.3 .4 . Non dairy cattle , calculation
Calculations were made in a similar way to those for
dairy cows once the assessment of excreta output (m3
month21) had been made. However, there was no
parlour wash water and a nominal 1 m2 animal21
fouled yard area was used to calculate an allowance
for dirty water production.
3.3 .5 . Pigs , calculation
There is large variation in slurry output from
finishing pigs depending on weight of pig and feeding
regime. It is estimated that approximately 35% of
finishing pigs (40 kg and over) are wet fed and 65%
dry fed but with variations across the country (Table
10). Pig numbers were split into 8 categories (Table 6)
and a value of excreta output (m3 month21) assigned
to each, taking into account these regional estimates
of feeding methods.
Again, calculations were made in a similar way to
those for dairy cows. However, there were some
differences. It was assumed there were no weepingwall stores. An allowance for pen cleaning water and
disinfection, and drinker leakage was based on 0?5
l pig21 day21. Dirty water run-off was calculated from
VOLUMES AND EXPOSED SURFACE AREAS OF STORED ANIMAL MANURES AND SLURRIES
4. Results
Table 10
ADAS estimates of feeding method for finishing pigs
(40 kg and over)
ADAS Business Centre
Bury St Edmunds
Wales
Guildford
Huntingdon
Oxford
Preston
Starcross
Taunton
Leeds
Lincoln
Maidstone
Newcastle
Wolverhampton
Worcester
% Dry fed
% Wet fed
85
40
70
80
80
50
30
30
80
85
70
80
60
60
15
60
30
20
20
50
70
70
20
15
30
20
40
40
245
4.1 . Manufacturers ’ data
the exposed surface areas of solid manure heaps
stored on concrete pads. No other fouled yard areas
were assumed. It was assumed there was no separate
dirty water storage on pig farms; and slurry and foul
water were stored together.
3.3.6. Poultry , calculation
The calculation of laying hen excreta output (m3
month21) assumed that its specific volume is 1 m3 t21.
The amount of excreta was calculated according to the
percentage of the bird population in each type of
housing (deep pit, cages, perchery and free range). An
estimate was made of the percentage split of manure
spread directly to land and of that destined for storage
from each housing type. It was assumed that all
excreta which is subsequently stored is in the solid
manure category and the stack volumes (field heaps)
were calculated using an assumed average period of
storage (6 months).
Calculations were made in a similar way for broilers
except that all birds were assumed to be housed on a
deep litter system.
There were twelve replies, including all known
major suppliers, but only three of these were able to
provide detailed information on a regional basis. The
remainder gave information on a national basis. The
number of stores and their size allowed typical slurry
volumes and exposed surface areas to be estimated.
This information was aggregated (Table 11).
Seven of the replies contained estimates of store
numbers and five were ‘‘actual figures’’. One supplier
of weeping-wall stores indicated that a number of
their stores were sold as ‘‘lagoon’’ types with no gaps
to allow seepage. It is likely that other suppliers of
weeping-wall stores have also included such stores. At
least two suppliers indicated their records did not go
back to 1970 and therefore their estimates are likely to
be low. Many companies were not in business in 1970
and one company contacted had gone into liquidation.
There are many other types of slurry store on farms
which are not pre-fabricated. These include reinforced
concrete structures, farm constructed weeping-wall
stores using railway sleepers / steel supports and earthbanked lagoons (lined and unlined).
4.2 . ADAS estimates
The output data from the calculations were presented as follows
(1) Estimated slurry volumes stored given as undiluted excreta (slurry) and diluted slurry.
(2) Estimated exposed surface areas of stored
diluted slurry.
(3) Estimated manure volumes stored given as
excreta and excreta plus straw / litter.
(4) Estimated exposed surface areas of stored
manure (including straw / litter).
(5) Estimated volumes and exposed surface areas of
stored dirty water where appropriate.
Table 11
Manufacturers’ data on store types for cattle and pig slurry in England and Wales,
installed since 1970
Store type
Store numbers
Slurry y olume
(m 3 )
Exposed surface
area (m 2)
Weeping-wall stores
Above-ground circular stores
Total
1669
6735
8404
951,990
6,800
6,908,790
446,511
1,530,716
1,977,277
246
R. J . N I C HO LSON ; A. J . B RE W E R
16
14
Volume stored Mm3
12
10
8
6
4
2
0
Aboveground
circular
stores
Earthbanked
lagoons
Weeping- Concrete Field heaps
walls
(manure)
pads
(manure)
Above- Earth-banked
lagoons*
ground
circular
stores*
Storage method
Fig. 1. Slurry (dilute) , manure and dirty water storage in
England & Wales: ADAS estimates of total y olumes stored.
.........
uuu layer hens; h pigs ; h non-dairy cattle;
h
broilers; h
h dairy cows. * Used for dirty water storage only
of field manure heaps (including straw bedding) was
attributed to non-dairy cattle at 6?6 Mm3, with
3?2 Mm3 from dairy herds, 1?2 Mm3 from pig herds,
0?5 Mm3 from broilers (including litter) and 0?2 Mm3
from laying hens (excreta only). Manure stored on
concrete pads accounted for 1?6 Mm3 (non-dairy
cattle), 1?0 Mm3 (dairy cattle) and 0?5 Mm3 (pigs).
Exposed surface areas were based on the estimated
volumes. Above-ground circular stores containing diluted cow slurry had surface areas of about 1?2 Mm2,
earth-banked lagoons 4?7 Mm2, and weeping-wall
stores 0?8 Mm2. For non-dairy cattle the exposed
surface area estimates were 0?07 Mm2, 1?6 Mm2 and
0?2 Mm2 respectively. For pig slurry the estimates
were 0?1 Mm2 (above-ground circular stores) and
0?7 Mm2 (earth-banked lagoons). Exposed surface
area of dirty water stores is only significant on dairy
units, accounting for 0?7 Mm2. Surface areas of field
manure heaps (including straw bedding) were 5?3 Mm2
(non-dairy cattle) , 2?5 Mm2 (dairy cattle), 1?0 Mm2
(pigs), 0?3 Mm2 (broiler, including litter) and 0?1 Mm2
(laying hens, excreta only). Manure stored on concrete pads accounted for 1?3 Mm2 (non-dairy cattle),
0?7 Mm2 (dairy cattle) and 0?5 Mm2 (pigs).
5. Discussion
5.1. Compatibility of estimates from different sources
The estimated volumes related to the maximum
amount of slurry, manure or dirty water that were
likely to be stored at any one time. They did not
include slurry and manure stored within or beneath
livestock buildings. Estimates for each of the 15 areas
were calculated separately; all data were brought
together for England and Wales and are shown in Figs
1 , 2 and 3 . Figure 3 is for undiluted excreta volumes
which are included in Figs 1 and 2 .
These estimates indicated that 4?5 Mm3 of diluted
cow slurry was stored in above-ground circular stores,
10?7 Mm3 in earth-banked lagoons and 1?7 Mm3 in
weeping-wall stores. For non-dairy cattle the storage
estimates for diluted slurry were 0?3 Mm3, 3?3 Mm3
and 0?4 Mm3 respectively. Diluted pig slurry was not
normally collected in weeping-wall stores, but an
estimated 0?4 Mm3 was stored in above-ground circular stores and 1?5 Mm3 in earth-banked lagoons. Some
dirty water arising from dairy and non-dairy cattle
enterprises was stored separately in earth-banked
lagoons or above-ground circular stores; this accounted for an estimated (dairy cattle) 1?6 Mm3 and
0?3 Mm3; and (non-dairy cattle) 0?1 Mm3 and
0?02 Mm3 respectively. The largest estimated volume
Data from different sources were obtained in
different ways, including postal survey, interview,
estimates based on a representative sample of farms
and, in this study, consultants’ informed opinion.
Some sources had different objectives compared with
this study where the intention was to provide input to
a gaseous emissions inventory. Comparisons of estimates from various sources were made in respect of
above-ground circular stores, weeping-wall stores and
earth-banked lagoons (Tables 12, 13 and 14). These
tables contain information on store numbers and
volumes which includes slurry and all dirty water.
Information from the Manchester University study
includes Scotland and contains some double counting.
The MMB Survey also includes some double counting
and, since it was a postal survey, the results may not
be from a representative sample. An unspecified
number of farms had no storage facilities which
indicates that the MMB estimate of store numbers is
likely to be too high.
The estimated volumes arising from slurry store
manufacturers’ data are based on an estimate of
typical store size by each manufacturer. Since this has
been done, in the main on a national basis, there will
VOLUMES AND EXPOSED SURFACE AREAS OF STORED ANIMAL MANURES AND SLURRIES
247
10
9
8
Surface area Mm2
7
6
5
4
3
2
1
0
Aboveground
circular
stores
Earthbanked
lagoons
Weepingwalls
Concrete
pads
(manure)
Field heaps
(manure)
Aboveground
circular
stores*
Earth-banked
lagoons*
Storage method
Fig. 2. Slurry (dilute) , manure and dirty water storage in England & Wales: ADAS estimates of exposed surface areas.
.........
uuu layer hens; h pigs ; h non-dairy cattle; h dairy cows . * Used for dirty water storage only
h
broilers; h
9
8
Volume stored Mm3
7
6
5
4
3
2
1
0
Above-ground
circular
stores
Earth-banked Weeping-walls
lagoons
Concrete
pads
(manure)
Field
heaps
(manure)
Storage method
Fig. 3. Slurry and manure storage in England & Wales:
ADAS estimates of y olumes of undiluted excreta stored.
h pigs; j non-dairy cattle; h dairy cows
be further error in deriving store volume from store
numbers.
The number of above-ground circular stores (Table
12) associated with dairy cows (MMB and Manchester
University) and total store numbers (Manchester University and manufacturers) are in reasonable agreement; the total volumes estimated (manufacturers and
ADAS) are also similar.
If it is assumed that the majority of weeping-wall
stores (Table 13) will be found on dairy farms, there is
some agreement between two sets of data (Manchester University and manufacturers). ADAS estimates
of volume are double those of the manufacturers’
estimates. This is not surprising since ADAS consultants were asked to consider not just prefabricated
stores, that is, those provided by manufacturers, but
also their estimates will include farm constructed
stores such as those made from ex railway
sleepers / steel supports. The ADAS estimate of volume stored is therefore likely to be the more reliable.
There is reasonable agreement on earth-banked
lagoon numbers (Table 14) associated with dairy cows
and the authors conclude that if a typical earth-
248
R. J . N I C HO LSON ; A. J . B RE W E R
Table 12
Number and volume of above-ground circular stores, comparison of estimates
Liy estock species
Dairy cows
Non-dairy cattle
Pigs
Total store numbers
Total volume Mm3
MMB 3†
Manchester
Uniy ersity 2*
Store manufacturers
ADAS
5865
NA
NA
NA
NA
4940
2000
1460
8400
NA
NA
NA
NA
6735
5?95
NA
NA
NA
NA
5?42
NA Not available.
* Manchester University data include Scotland.
† Based on 29,328 registered milk producers.
banked lagoon holds 1500 m3 slurry, the ADAS total
estimate of 17 M m3 equates to 11,333 stores.
5.2. Limitations of ADAS estimates
The census data used in the calculations are accurate but for non-dairy cattle and pigs estimates have
been made of age distribution, liveweight distribution
and (for pigs) feeding regime by geographical area.
Consultants estimates of types of storage were based
on a consensus of opinion from more than one person
at each ADAS Business Centre. Some Centres have a
wide variability in rainfall and topography.
Stores of less than 2 weeks capacity were not
considered relevant to this study. In three Centres,
consultants believe there are substantial numbers of
below-ground tanks which contain dirty water with
greater than 2 weeks capacity. These were excluded
from the results, since dirty water was assumed to be
stored in above-ground circular tanks or earth-banked
lagoons.
Factors and assumptions used in the calculations
were based on the best available information and
published data. At best the ADAS estimates are likely
to represent the true figure to within Ú10% for
surface area and volume and at worst within Ú20%.
However, when ADAS output data are compared
with existing figures (see Section 5.1), there is good
agreement for specific store types.
5.3 . Storage period
It should be noted that storage capacity relates to
the physical size of the facility and that storage period
is the time for which the facility is in use. Storage
period is likely to be an important factor in compiling
a gaseous emissions inventory. No specific data were
collected on the likely storage period for each store
type or livestock species. An individual slurry store
may be emptied and refilled continuously during the
year. Typically an above-ground circular store on a
dairy farm may have three months storage capacity,
but could contain slurry from October until May, and
possibly all year round. A similar store used for pig
slurry would be likely to contain some slurry throughout the year.
Table 13
Number and volume of weeping-wall stores, comparison of estimates
Liy estock species
Dairy cows
Non-dairy cattle
Total store numbers
Total volume Mm3
MMB 3†
Manchester
Uniy ersity 2*
Store manufacturers
ADAS
4899
NA
NA
NA
1830
NR
NA
NA
NA
NA
1669
0?95
NA
NA
NA
2?13
NA Not available. NR Not recorded.
* Manchester University data include Scotland.
† Based on 29,328 registered milk producers.
VOLUMES AND EXPOSED SURFACE AREAS OF STORED ANIMAL MANURES AND SLURRIES
249
Table 14
Number and volume of earth-banked lagoons, comparison of estimates
Liy estock species
Dairy cows
Non-dairy cattle
Pigs
Total store numbers
Total volume Mm3
MMB 3†
Manchester
Uniy ersity 2*
ADAS
8798
NA
NA
NA
NA
6740
2500
1410
10,650
NA
NA
NA
NA
NA
17?0
NA Not available.
* Manchester University data include Scotland.
† Based on 29,328 Registered milk producers.
Weeping-wall stores for cattle slurry usually require
a period for drying out and are often emptied in
mid-July and August, therefore the storage period is
likely to total at least nine months, although typical
storage capacity is only six months.
Earth-banked lagoons containing cattle slurry will
be continuously filled during the winter housing period, and apart from dewatering (removing liquid) on
some farms, the contents are likely to be removed
from April / May onwards. Pig slurry in earth-banked
lagoons is likely to be stored over winter and pumped
out during the Spring and Summer, but there will be a
continuous input of ‘‘new’’ slurry.
Storage periods for solid manure are extremely
variable ranging from a few weeks to months and
sometimes years. However, in the majority of situations three to nine months would be typical.
6. Conclusions
The majority of diluted livestock slurry from farms
in England and Wales is stored in earth-banked
lagoons accounting for an estimated 15?5 Mm3, with
another 1?7 Mm3 stored separately as dirty water.
Slurry and dirty water from dairy herds account for
about 70% of these products. Earth-banked slurry
lagoons have a total exposed surface area of about
7?0 Mm2.
About 5?1 Mm3 of diluted slurry is stored in aboveground circular stores, with another 0?4 Mm3 stored
separately as dirty water; slurry and dirty water from
dairy herds account for about 88% of these products.
Above-ground circular slurry stores have a total
exposed area of about 1?4 Mm2.
Weeping-wall stores are used for storing slurry from
both dairy and non-dairy cattle accounting for about
2?1 Mm3; slurry from dairy cows contributes about
80% of the total. Total exposed surface area is about
1?0 Mm2.
The total volume of solid manure from farms in
England and Wales is 14?9 Mm3 with a total exposed
surface area estimated at 11?9 Mm2. The majority is
stored in field heaps accounting for an estimated
11?6 Mm3; manure from non-dairy cattle accounts for
about 57%, manure from dairy cows about 27% and
manure from pigs about 10% of this total.
It is believed that, despite limitations, these ADAS
estimates of slurry and manure storage volumes and
exposed surface areas provide the best currently
available data for use in a gaseous emissions inventory
for England and Wales. The computer spreadsheet
developed in the course of this work will allow
information to be updated and sensitivity analyses to
be carried out.
7. Acknowledgements
Assistance has been given by many ADAS consultants whose efforts were co-ordinated at ADAS Business Centres. Interpretation of census data was carried
out by John Baines, ADAS Leeds (non-dairy cattle),
David Moorhouse, ADAS Crewe (pigs) and David
Mercer, ADAS Nottingham (poultry). Special thanks
are given to Ian Muir, ADAS Maidstone for developing the computer spreadsheet, processing data and
assisting with data output. Funding from MAFF
Environmental Protection Division which enabled this
research to be carried out is gratefully acknowledged.
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2
3
4
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