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Physical Properties of Solid and Liquid Manures and their Effects on the Performance of Spreading Machines
J. agric. Engng Res. (1996) 64, 289 – 298
Physical Properties of Solid and Liquid Manures and their Effects on the Performance of Spreading Machines Johan Malgeryd*; Christian Wetterberg† * Swedish Institute of Agricultural Engineering, PO Box 7033, S-750 07 Uppsala, Sweden † Swedish National Machinery Testing Institute, Fyrisborgsgatan 3, S-754 50 Uppsala, Sweden (Receiy ed 7 October 1994; accepted in rey ised form 14 February 1996)
During 1990 – 1993, experiments were carried out to investigate how the physical properties of solid and liquid manures (i.e. farmyard manures and slurries) affect the performance of spreading machines, e.g. the feeding-out process and the lateral manure distribution. The results show that different spreader types are influenced in different ways when the manure properties change. Dry matter content alone is not enough to completely describe the relevant physical properties of the manure. Together with bulk density (solid manure) or fluidity (liquid manure) it can, however, be used to classify solid and liquid manures used for spreader testing. The results and conclusions from the project constitute a basis for the work on a European standard for testing methods and requirements for manure and slurry spreaders. The standard proposals are, at present, being dealt with in CEN, Technical Committee 144, Working Group 3, Ad Hoc Group 3. ÷ 1996 Silsoe Research Institute
Notation icl ncls ns drets do M24
CVT
Tn F50 F40 WoptKidd
1. Introduction When testing manure and slurry spreaders, it is important that a spreader is always assessed in the same way when tested at different testing stations and at different times. For this to be possible, it is necessary to know how the physical properties of manures and slurries affect the spreading results and also to have access to equipment and methods for testing spreaders and characterizing manure which have good repeatability. During 1990 – 1993, investigations were carried out in co-operation between the Swedish National Machinery Testing Institute (NMTI) and the Swedish Instit* Presented at Ag Eng 94, Milan, Italy, 29 August – 1 September 1994. 0021-8634 / 96 / 080289 1 10 $18.00 / 0
° SKidd f stKidd f stJF SJF
clogging index number of clogged holes in section s of the clogging meter, s 5 1 . ..4 number of holes in section s of the clogging meter depth of slurry retained in section s of the clogging meter original depth of slurry in the clogging meter mean torque when measuring the comminution resistance of nonpumpable manure with the desometer coefficient of variation for the torque values (a measure of the heterogeneity of non-pumpable manure) torque value number n , n 5 1...24 fluidity as measured with the 50 mm hole fluidity as measured with the 40 mm hole optimum working width for the Kidd spreader bulk density of non-pumpable manure setting of the Kidd spreader steady flow for the Kidd spreader steady flow for the JF spreader setting of the JF spreader
ute of Agricultural Engineering (JTI), in order to provide the necessary knowledge of the factors mentioned above. The projects were part of the Certification 93 programme, a research programme concerning a system for certification of fertilizer and manure spreaders from an environmental point of view, which was initiated by the Swedish Board of Agriculture in order to reduce nutrient leaching from agriculture.
289
÷ 1996 Silsoe Research Institute
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J. MALGERYD ; C. WETTERBERG
The results and conclusions obtained within the Certification 93 programme constitute a basis for the work on a European standard for testing methods and requirements for manure and slurry spreaders. The standard proposals are, at present, being dealt with in CEN (Comite´ Europe´ en de Normalisation), Technical Committee 144, Working Group 3, Ad Hoc Group 3.
Overflow outlet
2. Physical properties of manures Rubber ball
Solid and liquid manures [i.e. farmyard manures (FYM) and slurries] are very heterogeneous containing everything from urine, faeces and straw material to bale strings, pieces of wood and stones. A survey of the literature (Malgeryd and Wetterberg1) revealed various attempts at their characterization by measuring numerous different properties. However, the study also revealed a lack of overall knowledge about which properties are important in practice and how they should be measured. Taking into account practical experiences and theoretical knowledge, JTI elaborated a proposal on this matter. For manures which can be pumped (i.e. liquid manures or slurries), four properties were considered to be important, namely, fluidity, separation tendency, risk of clogging and dry matter (d.m.) content. For manures which cannot be pumped (i.e. solid manures or FYM), five properties were considered important, namely, bulk density, stacking ability (manure consistency), comminution resistance, heterogeneity and d.m. content.
2.1. Measuring methods Since the properties of interest are different for pumpable and non-pumpable manures, specific measuring methods and equipment were developed for these two materials. The methods are briefly described below. More details are given by Malgeryd2 and Malgeryd et al .3 2.1.1. Pumpable manures Fluidity was measured with the fluidimeter method . The fluidimeter is shown in Fig. 1 . When the rubber ball is removed, the slurry flows out through the outlet aperture. The operator measures the emptying time with a stop-watch. Measurements are carried out on each sample until the time difference between the
Fig. 1. The fluidimeter dey eloped at JTI. The y olume is 15?5 l and the outlet aperture is 40 or 50 mm in diameter. The aperture can easily be changed from 50 mm to 40 mm using an additional cone
highest and lowest values of three consecutive measurements does not exceed 0?15 s. Which hole size to use may be decided from time to time with regard to the thickness of the slurry and the risk of blockage. Methods for measuring the separation tendency with different types of sedimentation columns were investigated, but no practicable method could be developed. For slurries which contain straws and lumps, the sedimentation process is affected by the diameter of the sedimentation column. If the column is too narrow, the walls restrict the movements of the particles in the slurry and thus prevent or delay natural separation. This means that plexiglass or glass columns with a diameter of 100 mm cannot be used. To overcome this problem, a sheet-metal column which is 400 mm in diameter and has a plexiglass window on one side was manufactured at JTI. It was, however, very difficult to see the different layers in this column. Trials with a light source inside the column to increase visibility were not successful. The risk of clogging was measured using a ‘‘clogging meter’’ (Fig. 2 ). The meter has a total volume of approx. 80 l and is divided into four sections. In the bottom of each section, there are holes with diameters of 15, 25, 35 and 45 mm, respectively. The total hole area, however, is the same in all four sections. When the meter is filled with slurry, the bottom is opened and the slurry flows out through the holes. When the flow has ceased, the operator notes the number of holes clogged in each section and, if all the holes in a
PHYSICAL PROPERTIES OF SOLID AND LIQUID MANURES
45·5 mm. Hole area 7 16·25 =113·75 cm2
24·7 mm. Hole area 24 4·71 =113·04 cm2 +
+
+
34·7 mm. Hole area 12 9·45 =113·4 cm2
+
15 mm. Hole area 64 1·767=113·08 cm2
291
Fig. 2 . Outline of the ‘‘clogging meter’’ dey eloped at JTI
section are clogged, the amount of slurry retained. The percentages of clogged holes in all four sections are summed with the percentages of liquid manure left in the sections where all holes are clogged according to Eqn (1). The sum is called ‘‘clogging index’’ (icl)
and can vary between 0 and 200. Measurements are made on three different samples from each batch of slurry. icl 5 25
Snn
cl1 1
1
D
ncl2 ncl3 ncl4 dret1 1 dret2 1 dret3 1 dret4 1 1 1 n2 n3 n4 d0
(1) The dry matter content is determined using the conventional oven method. Six replicates of 50 g samples of slurry are dried at 1058C until they reach constant weight (i.e. overnight). The slurry has to be well-mixed before the samples are taken.
Fig. 3. The characterization box for non-pumpable manure. The box holds 1?3 m 3 of manure and weighs 480 kg with and 300 kg without the lifting stand. The desometer plate is 250 mm in diameter and has six 100 mm long spikes underneath
2.1 .2 . Non -pumpable manures In order to measure the physical properties of manures that cannot be pumped, a characterization box (Fig. 3 ) was developed. The box holds 1?3 m3 of manure and is moved with a front-end loader on a farm tractor. It is filled with manure using the loader. Bulk density is measured by weighing the whole box. Measurements of comminution resistance are made with a desometer (shearing strength gauge) and performed eight times in each box of manure; four times when the box is half full and four times when it is completely full. The desometer plate has six 100 mm long spikes underneath, which are forced down into the manure. The plate is then turned 908 at constant speed by an electric motor. Each turn takes 2 min. The torque is measured with an electronic torque sensor mounted just above the plate and the peak value is registered. All characterization measurements
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are carried out three times on each type of manure (i.e. with three boxes of manure). This gives a total of 24 torque values from which the mean torque (M24) is calculated. Heterogeneity is calculated as the coefficient of variation of the torque values measured, (CVT), see Eqn (2)
–
24
o (Tn 2 M24)2
n 51
CVT 5 100
23
(2) M24 For measurement of stacking ability, the characterization box is elevated 1?75 m from ground level with the loader. The bottom flap of the box is opened, causing the manure to fall down onto the ground. The length, breadth and height of the heap is measured, from which the angle of repose can be calculated later. The main problem when measuring the dry matter content of non-pumpable manure is to get a representative sample. In order to obtain this, two sub-samples are taken with a pitchfork in the middle of each box of manure; one when the box is half full and one when it is completely full. The sub-samples (six altogether) are put together and thoroughly mixed with the pitchfork. From the small heap thus obtained, 15 100 g samples are taken and put into the drying oven.
3. Performance of manure spreaders Testing of manure spreaders from an environmental point of view includes measurements of parameters that affect the nutrient utilization, such as lateral and longitudinal evenness of distribution, optimum working width, ability to maintain a specific rate during the feeding-out process and the possibilities for the farmer to set the spreader at the desired rate.
3.1. Test methods The test methods should preferably be designed so as to resemble practical spreading as much as possible. The evenness of distribution should be measured at a realistic speed and calculated with methods that reflect the best possible evenness that can be achieved on the field. The testing procedure applied in this project is divided into two parts; one where the working width and the lateral distribution is measured and one where the longitudinal distribution and the spreader’s ability to maintain a specific rate is studied. In the lateral tests, 0?5 3 0?5 m wide boxes are used
to collect the manure from broadcasting spreaders (i.e. spreaders that distribute the manure all over the ground surface). Non-broadcasting spreaders, such as injectors and booms with trailing hoses, are tested using one box per outlet. The boxes are attached to a horizontal ladder which moves on rails from the stationary spreader backwards through the manure stream (Fig. 4 ). When they have passed through the area in which manure falls, the boxes are weighed by a robot scale connected to a computer. Four test runs are made at normal speed (usually 6 km / h) and one at low speed (1 km / h) with intermediate weighings. The test runs made at normal speed represent four successive snapshots of the lateral manure distribution when driving along the bout. The run made at low speed is used to improve accuracy in the calculations of the optimum working width. The coefficient of variation (CV), which is defined as the standard deviation divided by the mean value, is used to assess the evenness of distribution only for broadcasting slurry spreaders. The reason for not calculating the coefficient of variation for non-broadcasting spreading equipment is that it would not be comparable with the CV for broadcasting spreaders. To avoid misleading comparisons, the mean and maximum deviations, which basically give the same information, are used instead for this type of spreading equipment. For solid-manure spreaders, the random flow variations during the steady part of the feeding-out process are so big that the CV cannot be calculated with acceptable repeatability on only four test runs. To simulate the total manure distribution in the field after overlapping with adjacent bouts, each of the four test runs made at normal speed is overlapped with itself to the defined working width. The coefficient of variation or, for non-broadcasting spreading equipment, mean and maximum deviations are then calculated on all weights from the four test runs. With this method of calculation, longitudinal variations occuring during the steady part of the feedingout process are also taken into account when the CV is calculated. Further details about the calculation methods are given by Malgeryd et al .3 During the studies of the feeding-out process, the whole spreader is placed on load cells connected to a computer which registers the weight decrease twice a second. From the unloading curve thus obtained the steady flow (Fig. 5 ) can be calculated. The steady flow is, together with the optimum working width, used when the application rate is calculated. For slurry spreaders, it is defined as the average flow during the whole unloading time. If the same definition were to be applied to solid-manure spreaders, the calculated
PHYSICAL PROPERTIES OF SOLID AND LIQUID MANURES
293
Fig. 4. Inside y iew of the test site used when measuring the lateral distribution and optimum working width of manure spreaders. The speed of the ladder to which the collecting boxes are attached is continuously y ariable in the range 0 – 9 km / h
application rate would occur only momentarily during practical spreading and would thus not reflect the rate achieved during the steady part of the feeding-out process. Therefore, the steady flow for solid-manure spreaders is defined as the highest average flow that can be defined for a continuous period of time corresponding to 30% of the unloading time. The value of 30% was chosen from practical experiences to suit a majority of the spreaders available on the market today. The stretch within the tolerance zone describes a spreader’s ability to maintain a specific rate during the feeding-out process. It is defined as the percentage of the unloading time during which the manure flow does not deviate more than Ú10% from the steady flow.
Manure flow, kg/s
60
Experiments were carried out to investigate the relationship between the characterization parameters and the spreading characteristics obtained when testing manure spreaders. In these trials, five solidmanure spreaders were tested with 20 batches of manure, the properties of which were measured with the above-mentioned characterization methods. For slurry, four different types of spreading equipment were tested with five batches of slurry and with water. Interactions between the characterization parameters and the different spreading properties of the spreaders, and the mutual relationship between the characterization parameters, were subjected to statistical processing.
4. Results Stretch within the tolerance zone
40
4.1 . Pumpable manures
Steady flow 20
0
0
50
100
150
200
250
300
350
400
Unloading time, s
Fig. 5. Unloading cury e showing the ‘‘steady flow’’ and the ‘‘stretch within the tolerance zone’’ for a slurry spreader. The steady flow was , in this case , 33?5 kg / s and the stretch within the tolerance zone 89?5%
As shown in Fig. 6 and Table 1, there is no clear relationship between fluidity and the dry matter content for pumpable manures. Neither is there any unequivocal relationship between the risk of clogging and the d.m. content (Table 1). The first and second slurries in the table have almost the same fluidity as water although they contain 7?3 and 6?8% d.m., respectively. The third slurry, which has a d.m. content of only 4?9%, has a higher fluidity than the
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6·0
12
Fluidity, 50 mm hole, s
Dry matter content, %
10
8
6
5·5
5·0
4·5
4 4·0 6·5
2
7·0
7·5
8·0
8·5
9·0
Fluidity, 40 mm hole, s
Water 0 6·5
7·0
7·5
8·0
8·5
9·0
Fluidity, 40 mm hole, s
Fig. 7. The relationship between fluidity as measured with the 50 mm hole (F50) and with the 40 mm hole (F40). The algebraic form of the regression line is F50 5 0?67 F40 and the coefficient of correlation (R2) is 0?94
Fig. 6. The relationship between fluidity (measured with the 40 mm hole) and the d .m. content
first two and, in addition, an extremely high clogging index. These results imply that it is time to reject the accepted approach where only certain dry matter concentrations are stated as limits between different types of slurry. Since there is a linear relationship between the emptying times (fluidities) obtained with the 40 mm and the 50 mm holes (Fig. 7 ), the fluidity can be measured at discretion with either of these two hole sizes. Which aperture to use may be decided from time to time with regard to the thickness of the slurry and the risk of clogging. Experiences from characterization of 24 batches of slurry during a period of four years show that the repeatability of the fluidity measurements is very
good, provided that the slurry is well mixed. When the operator has practised a few times, it is no problem to get three successive measurements with a time difference less than 0?1 s between the highest and lowest values. The clogging and dry matter measurements also show a high repeatability. Fig. 8 presents the relationship between fluidity and the slurry flow obtained when unloading an Omas vacuum tanker. The tanker was equipped with a spreading boom with trailing hoses. Though there are just a few data points in the diagram, it can be seen that fluidity is descriptive of manure flow properties. Measurements on an Olby tanker with a displacement pump indicated that fluidity affects the steady flow for this type of spreader too, but to a much lesser extent. We do not yet know whether the clogging index
45
Description Thin cattle slurry with solitary long straws Cattle slurry without any visible lumps or straws Pig slurry with plenty of chopped straws in a liquid, watery phase * Water 4?64 s.
Fluidity * , Dry 50 mm Clogging matter hole index content , % 4?7
24
7?3
4.9
64
6?7
4?9
131
4?9
40 Steady flow, kg/s
Table 1 Results from characterization of three batches of pumpable manure
35 30 25 20 15 6·6
6·8
7
7·2 7·4 Fluidity, s
7·6
7·8
8
Fig. 8. The relationship between fluidity (measured with the 40 mm hole) and the ‘‘steady flow’’ of slurry obtained when unloading an Omas y acuum tanker
295
PHYSICAL PROPERTIES OF SOLID AND LIQUID MANURES
50 Active angle of repose, deg
Fluidity, 40 mm hole, s
11
10 9 8 7 0
40 30 20 10
1 2
4
6
8
10
12
Dry matter content, %
Fig. 9 . Manure classes for pumpable manure
properly reflects the risk of clogging in the spreading equipment. When this was going to be investigated in 1993, it turned out to be problematic to find farmers with manure causing heavy clogging problems in the neighbourhood of Uppsala. Interviews conducted by Malm4 showed that clogging problems are very rare with modern band spreading equipment. The equipment for measuring separation tendency has to be further developed. The lack of practicable measuring methods is not a problem when testing spreaders as long as all tests are conducted with non-separating slurry, which is now the case in Sweden. Nevertheless, separation sometimes causes trouble in practical spreading, especially for farmers dealing with pig and poultry manures. Liquid manures for testing can be divided into two classes, defined using fluidity and dry matter content (Fig. 9 ). At present we can, however, only set the limits for one class since we do not know enough about how different types of spreaders are affected by various types of viscous manure. The classification system is further described by NMTI5 and Malgeryd et al .3
0 10
15
20
25
30
35
40
45
Dry matter content, %
Fig. 10. The relationship between the actiy e angle of repose as measured with the characterization box and the dry matter content for non-pumpable manure
The coefficient of variation (CV) can, for slurry spreaders, be calculated with high repeatability on four test runs made at normal speed. This is illustrated in Table 2. Twelve runs were made during the steady part of the feeding-out process and the CV was calculated on different groups of four series. As shown in the table, the CV ranged only from 45?2 to 46?8%. 4.2 . Non -pumpable manures In conformity with the results for liquid manures, there is no clear relationship between the active angle of repose and the dry matter content for nonpumpable manures (Fig. 10 ). The active angle of repose is, however, in good agreement with the visual impression of manure consistency, which is illustrated in Fig. 11 . In most cases, bulk density and the active angle of repose are closely related to each other (Fig. 12 ). This means that it would normally not be necessary to measure both these parameters. The active angle of repose can
Table 2 Changes in CV for a liquid-manure spreader when calculated on different groups of four series within the ‘‘stretch within the tolerance zone’’ Series number
CV , %
1–4 2–5 3–6 4–7 5–8 6–9 7 – 10 8 – 11 9 – 12
46?4 46?8 46?3 46?6 46?6 46?0 46?0 45?8 45?2
Fig. 11. The actiy e angle of repose as measured with the characterization box for different types of manure
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50
20
30 20 10 0 300
400
500
600
700
800
900
1000
1100
Optimum working width, m
Angle of repose, deg
40
18 16 14 12 10
Bulk density, kg/m3 140 130 Sp 120 rea 110 de r s 100 ett ing 90 ,c 80 m
Fig. 12. The relationship between bulk density and the actiy e angle of repose. The manures characterized represent the types of most frequent occurence in Sweden
70
60
60
50
50 40 30 20
900 800 700 600 70 500
, sity
3
m
kg/
en
lk d
Bu
Fig. 14. The relationship between bulk density , setting of the discharge opening and optimum working width for a Kidd Tankaspread 1500. The algebraic form of the computer-generated surface is WoptKidd 5 261?86 1 0?1305° 1 0?5132SKidd 2 0?000068° 2 2 0?00219°SKidd 2 0?0157SKidd2 and the coefficient of correlation (R 2) is 0?37
Steady flow, kg/s
Steady flow, kg/s
be estimated from the bulk density, which is easier to measure. Figures 13 and 14 , respectively, show how the steady flow and the optimum working width for a Kidd Tankaspread 1500 are influenced by the bulk density of the manure and the setting of the spreader. The Kidd spreader distributes the manure laterally with a front-mounted discharge wheel. The black dots in the diagrams indicate data points. The deviations of the data points from the regression surface created by
1100 1000
40 30 20 10
10 130 120 Sp 110 rea de 100 rs ett ing 90 ,c m 80
1100 1000 900 800 700 600 70 500
3
/m , kg sity
en lk d
Bu
Fig. 13. The relationship between bulk density , setting of the discharge opening and ‘‘steady flow’’ of manure for a Kidd Tankaspread 1500. The algebraic form of the computergenerated surface is FstKidd 5 123?0 2 0?4843° 1 0?3262SKidd 1 0?000305° 2 1 0?000881°SKidd 2 0?001551SKidd2 and the coefficient of correlation (R 2) is 0?87
7 Se tti 6 ng of t
1000 900
5 he bo
800 tto 4 m co
700 3 ey or
nv
600 500 2 400
3
/m
, kg sity
en
lk d
Bu
Fig. 15. The relationship between bulk density , setting of the speed of the bottom cony eyor and ‘‘steady flow’’ of manure for a JF ST70 H. The algebraic form of the computergenerated surface is f stJF 5 64?16 2 0?1267° 2 15?90SJF 1 0?000042° 2 1 0?02346°SJF 1 1?569SJF2 and the coefficient of correlation (R 2) is 0?94
297
PHYSICAL PROPERTIES OF SOLID AND LIQUID MANURES
the computer, are marked with vertical lines. The zones with different shadings indicate height curves, i.e. different levels of steady flow and optimum working width, respectively. Figure 15 illustrates the relationship between steady flow, bulk density and setting for a JF ST70 H, which has a bottom conveyor and four vertical beaters. From Figs 13 – 15 it can be concluded that bulk density and / or the active angle of repose (i.e. manure consistency) affect important spreading parameters such as the steady flow and the optimum working width and that different spreader types are influenced in specific ways depending on their construction. The relevance of the torque and the coefficient of variation as measured with the characterization box have not yet been entirely investigated. A few trials were carried out in 1993 in order to investigate whether there is any connection between the comminution resistance of the manure and the p.t.o. power requirements per kg of manure spread. The results, which are further described by Malm,4 seem to indicate that there is, at least for some types of spreaders. This finding might be of importance in the future when spreaders with rate control systems based on torque measurements become more common. Another parameter that might be affected by the comminution resistance is the scattering of the manure. This should also be investigated further. Solid manures for testing can be divided into five classes, defined by means of the bulk density and the dry matter content (Fig. 16 ). The classification system for solid manures is further described by NMTI5 and Malgeryd et al .3 Many solid-manure spreaders show random flow variations during the steady part of the feeding-outprocess that are so big that the coefficient of variation (CV) cannot be calculated with acceptable repeatability on four test runs made at normal speed.
1100
Bulk density, kg/m3
1000
5 4
900
3
800 700
2
600 1 500 400 300 10
15
20
25
30
35
40
Dry matter content, %
Fig. 16. Manure classes for non-pumpable manure
Table 3 Changes in CV for a solid-manure spreader when calculated on different groups of four series within the ‘‘stretch within the tolerance zone’’ Series number
CV , %
1–4 2–5 3–6 4–7 5–8 6–9 7 – 10 8 – 11 9 – 12
39?6 34?3 34?5 31?5 22?1 23?5 33?3 40?5 44?8
Table 3 illustrates how the CV can vary when calculated on different groups of four series within the ‘‘stretch within the tolerance zone’’. The low repeatability implies that the coefficient of variation for the spreading does not constitute an objective basis for assessment in type approvals for solid-manure spreaders. The CV can, however, be used for broadcasting spreaders for liquid manure since the repeatability there is much higher. For non-broadcasting spreading equipment, the mean and maximum deviations, which basically give the same information, should be used instead to avoid misleading comparisons. 5. Conclusions
1. Manure properties affect the performance of manure spreaders. Different spreader types are influenced in different ways when the manure properties change. 2. The dry matter content alone is not enough to completely describe the relevant physical properties of manure. Together with bulk density (solid manure) or fluidity (liquid manure) it can, however, be used to classify solid and liquid manures used for spreader testing. Solid manures can be divided into five classes and liquid manures can be divided into two classes. 3. The bulk density of solid manure affects spreading properties such as the flow of manure and the working width. The fluidity of liquid manure affects the flow of manure. The relevance of other characterization parameters, e.g. the comminution resistance and the clogging index, need to be further investigated in the future. 45 4. The coefficient of variation for the spreading does not constitute an objective basis for assessment in type approvals for solid-manure spreaders. The CV can,
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however, be used for broadcasting spreaders for liquid manure. For non-broadcasting spreading equipment, the mean and maximum deviations should be used instead to avoid misleading comparisons.
2
3
Acknowledgement Financial support by the Swedish Board of Agriculture is gratefully acknowledged. 4
References 1
Malgeryd J; Wetterberg C Metod fo¨ r teknikva¨ rdering: Utrustning fo¨ r stallgo¨ dselspridning. Karakta¨ risering av stallgo¨ dsel. Provningsmetoder fo¨ r spridare (Evaluation method: Manure spreading equipment. Manure characterization. Equipment and methods for testing manure
5
spreaders). JTI-rapport 132, Swedish Institute of Agricultural Engineering, Uppsala, 1991. (Summary in English) Malgeryd J Manure Characterization. International Agrophysics 1994, 8 (1): 93 – 101 Malgeryd J; Wetterberg C; Rodhe L Stallgo¨ dselns fysikaliska egenskaper -ma¨ tmetoder-betydelse vid provning av go¨ dselspridare (Physical properties of manuremeasuring methods-influence when testing manure spreaders). JTI-rapport 166, Swedish Institute of Agricultural Engineering, Uppsala, 1993. (Summary in English) Malm P Utva¨ rdering av karakta¨ riseringsmetoder fo¨ r stallgo¨ dsel (Validation of methods for characterizing manure). JTI-rapport 173, Swedish Institute of Agricultural Engineering, Uppsala, 1994. (Summary in English) NMTI Technique and Methods for the Type-Testing of Fertilizer- and Manure Spreaders. Final report from the Certification 93 programme. Swedish National Machinery Testing Institute, Uppsala, 1994
Physical Properties of Solid and Liquid Manures and their Effects on the Performance of Spreading Machines Johan Malgeryd*; Christian Wetterberg† * Swedish Institute of Agricultural Engineering, PO Box 7033, S-750 07 Uppsala, Sweden † Swedish National Machinery Testing Institute, Fyrisborgsgatan 3, S-754 50 Uppsala, Sweden (Receiy ed 7 October 1994; accepted in rey ised form 14 February 1996)
During 1990 – 1993, experiments were carried out to investigate how the physical properties of solid and liquid manures (i.e. farmyard manures and slurries) affect the performance of spreading machines, e.g. the feeding-out process and the lateral manure distribution. The results show that different spreader types are influenced in different ways when the manure properties change. Dry matter content alone is not enough to completely describe the relevant physical properties of the manure. Together with bulk density (solid manure) or fluidity (liquid manure) it can, however, be used to classify solid and liquid manures used for spreader testing. The results and conclusions from the project constitute a basis for the work on a European standard for testing methods and requirements for manure and slurry spreaders. The standard proposals are, at present, being dealt with in CEN, Technical Committee 144, Working Group 3, Ad Hoc Group 3. ÷ 1996 Silsoe Research Institute
Notation icl ncls ns drets do M24
CVT
Tn F50 F40 WoptKidd
1. Introduction When testing manure and slurry spreaders, it is important that a spreader is always assessed in the same way when tested at different testing stations and at different times. For this to be possible, it is necessary to know how the physical properties of manures and slurries affect the spreading results and also to have access to equipment and methods for testing spreaders and characterizing manure which have good repeatability. During 1990 – 1993, investigations were carried out in co-operation between the Swedish National Machinery Testing Institute (NMTI) and the Swedish Instit* Presented at Ag Eng 94, Milan, Italy, 29 August – 1 September 1994. 0021-8634 / 96 / 080289 1 10 $18.00 / 0
° SKidd f stKidd f stJF SJF
clogging index number of clogged holes in section s of the clogging meter, s 5 1 . ..4 number of holes in section s of the clogging meter depth of slurry retained in section s of the clogging meter original depth of slurry in the clogging meter mean torque when measuring the comminution resistance of nonpumpable manure with the desometer coefficient of variation for the torque values (a measure of the heterogeneity of non-pumpable manure) torque value number n , n 5 1...24 fluidity as measured with the 50 mm hole fluidity as measured with the 40 mm hole optimum working width for the Kidd spreader bulk density of non-pumpable manure setting of the Kidd spreader steady flow for the Kidd spreader steady flow for the JF spreader setting of the JF spreader
ute of Agricultural Engineering (JTI), in order to provide the necessary knowledge of the factors mentioned above. The projects were part of the Certification 93 programme, a research programme concerning a system for certification of fertilizer and manure spreaders from an environmental point of view, which was initiated by the Swedish Board of Agriculture in order to reduce nutrient leaching from agriculture.
289
÷ 1996 Silsoe Research Institute
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J. MALGERYD ; C. WETTERBERG
The results and conclusions obtained within the Certification 93 programme constitute a basis for the work on a European standard for testing methods and requirements for manure and slurry spreaders. The standard proposals are, at present, being dealt with in CEN (Comite´ Europe´ en de Normalisation), Technical Committee 144, Working Group 3, Ad Hoc Group 3.
Overflow outlet
2. Physical properties of manures Rubber ball
Solid and liquid manures [i.e. farmyard manures (FYM) and slurries] are very heterogeneous containing everything from urine, faeces and straw material to bale strings, pieces of wood and stones. A survey of the literature (Malgeryd and Wetterberg1) revealed various attempts at their characterization by measuring numerous different properties. However, the study also revealed a lack of overall knowledge about which properties are important in practice and how they should be measured. Taking into account practical experiences and theoretical knowledge, JTI elaborated a proposal on this matter. For manures which can be pumped (i.e. liquid manures or slurries), four properties were considered to be important, namely, fluidity, separation tendency, risk of clogging and dry matter (d.m.) content. For manures which cannot be pumped (i.e. solid manures or FYM), five properties were considered important, namely, bulk density, stacking ability (manure consistency), comminution resistance, heterogeneity and d.m. content.
2.1. Measuring methods Since the properties of interest are different for pumpable and non-pumpable manures, specific measuring methods and equipment were developed for these two materials. The methods are briefly described below. More details are given by Malgeryd2 and Malgeryd et al .3 2.1.1. Pumpable manures Fluidity was measured with the fluidimeter method . The fluidimeter is shown in Fig. 1 . When the rubber ball is removed, the slurry flows out through the outlet aperture. The operator measures the emptying time with a stop-watch. Measurements are carried out on each sample until the time difference between the
Fig. 1. The fluidimeter dey eloped at JTI. The y olume is 15?5 l and the outlet aperture is 40 or 50 mm in diameter. The aperture can easily be changed from 50 mm to 40 mm using an additional cone
highest and lowest values of three consecutive measurements does not exceed 0?15 s. Which hole size to use may be decided from time to time with regard to the thickness of the slurry and the risk of blockage. Methods for measuring the separation tendency with different types of sedimentation columns were investigated, but no practicable method could be developed. For slurries which contain straws and lumps, the sedimentation process is affected by the diameter of the sedimentation column. If the column is too narrow, the walls restrict the movements of the particles in the slurry and thus prevent or delay natural separation. This means that plexiglass or glass columns with a diameter of 100 mm cannot be used. To overcome this problem, a sheet-metal column which is 400 mm in diameter and has a plexiglass window on one side was manufactured at JTI. It was, however, very difficult to see the different layers in this column. Trials with a light source inside the column to increase visibility were not successful. The risk of clogging was measured using a ‘‘clogging meter’’ (Fig. 2 ). The meter has a total volume of approx. 80 l and is divided into four sections. In the bottom of each section, there are holes with diameters of 15, 25, 35 and 45 mm, respectively. The total hole area, however, is the same in all four sections. When the meter is filled with slurry, the bottom is opened and the slurry flows out through the holes. When the flow has ceased, the operator notes the number of holes clogged in each section and, if all the holes in a
PHYSICAL PROPERTIES OF SOLID AND LIQUID MANURES
45·5 mm. Hole area 7 16·25 =113·75 cm2
24·7 mm. Hole area 24 4·71 =113·04 cm2 +
+
+
34·7 mm. Hole area 12 9·45 =113·4 cm2
+
15 mm. Hole area 64 1·767=113·08 cm2
291
Fig. 2 . Outline of the ‘‘clogging meter’’ dey eloped at JTI
section are clogged, the amount of slurry retained. The percentages of clogged holes in all four sections are summed with the percentages of liquid manure left in the sections where all holes are clogged according to Eqn (1). The sum is called ‘‘clogging index’’ (icl)
and can vary between 0 and 200. Measurements are made on three different samples from each batch of slurry. icl 5 25
Snn
cl1 1
1
D
ncl2 ncl3 ncl4 dret1 1 dret2 1 dret3 1 dret4 1 1 1 n2 n3 n4 d0
(1) The dry matter content is determined using the conventional oven method. Six replicates of 50 g samples of slurry are dried at 1058C until they reach constant weight (i.e. overnight). The slurry has to be well-mixed before the samples are taken.
Fig. 3. The characterization box for non-pumpable manure. The box holds 1?3 m 3 of manure and weighs 480 kg with and 300 kg without the lifting stand. The desometer plate is 250 mm in diameter and has six 100 mm long spikes underneath
2.1 .2 . Non -pumpable manures In order to measure the physical properties of manures that cannot be pumped, a characterization box (Fig. 3 ) was developed. The box holds 1?3 m3 of manure and is moved with a front-end loader on a farm tractor. It is filled with manure using the loader. Bulk density is measured by weighing the whole box. Measurements of comminution resistance are made with a desometer (shearing strength gauge) and performed eight times in each box of manure; four times when the box is half full and four times when it is completely full. The desometer plate has six 100 mm long spikes underneath, which are forced down into the manure. The plate is then turned 908 at constant speed by an electric motor. Each turn takes 2 min. The torque is measured with an electronic torque sensor mounted just above the plate and the peak value is registered. All characterization measurements
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J. MALGERYD ; C. WETTERBERG
are carried out three times on each type of manure (i.e. with three boxes of manure). This gives a total of 24 torque values from which the mean torque (M24) is calculated. Heterogeneity is calculated as the coefficient of variation of the torque values measured, (CVT), see Eqn (2)
–
24
o (Tn 2 M24)2
n 51
CVT 5 100
23
(2) M24 For measurement of stacking ability, the characterization box is elevated 1?75 m from ground level with the loader. The bottom flap of the box is opened, causing the manure to fall down onto the ground. The length, breadth and height of the heap is measured, from which the angle of repose can be calculated later. The main problem when measuring the dry matter content of non-pumpable manure is to get a representative sample. In order to obtain this, two sub-samples are taken with a pitchfork in the middle of each box of manure; one when the box is half full and one when it is completely full. The sub-samples (six altogether) are put together and thoroughly mixed with the pitchfork. From the small heap thus obtained, 15 100 g samples are taken and put into the drying oven.
3. Performance of manure spreaders Testing of manure spreaders from an environmental point of view includes measurements of parameters that affect the nutrient utilization, such as lateral and longitudinal evenness of distribution, optimum working width, ability to maintain a specific rate during the feeding-out process and the possibilities for the farmer to set the spreader at the desired rate.
3.1. Test methods The test methods should preferably be designed so as to resemble practical spreading as much as possible. The evenness of distribution should be measured at a realistic speed and calculated with methods that reflect the best possible evenness that can be achieved on the field. The testing procedure applied in this project is divided into two parts; one where the working width and the lateral distribution is measured and one where the longitudinal distribution and the spreader’s ability to maintain a specific rate is studied. In the lateral tests, 0?5 3 0?5 m wide boxes are used
to collect the manure from broadcasting spreaders (i.e. spreaders that distribute the manure all over the ground surface). Non-broadcasting spreaders, such as injectors and booms with trailing hoses, are tested using one box per outlet. The boxes are attached to a horizontal ladder which moves on rails from the stationary spreader backwards through the manure stream (Fig. 4 ). When they have passed through the area in which manure falls, the boxes are weighed by a robot scale connected to a computer. Four test runs are made at normal speed (usually 6 km / h) and one at low speed (1 km / h) with intermediate weighings. The test runs made at normal speed represent four successive snapshots of the lateral manure distribution when driving along the bout. The run made at low speed is used to improve accuracy in the calculations of the optimum working width. The coefficient of variation (CV), which is defined as the standard deviation divided by the mean value, is used to assess the evenness of distribution only for broadcasting slurry spreaders. The reason for not calculating the coefficient of variation for non-broadcasting spreading equipment is that it would not be comparable with the CV for broadcasting spreaders. To avoid misleading comparisons, the mean and maximum deviations, which basically give the same information, are used instead for this type of spreading equipment. For solid-manure spreaders, the random flow variations during the steady part of the feeding-out process are so big that the CV cannot be calculated with acceptable repeatability on only four test runs. To simulate the total manure distribution in the field after overlapping with adjacent bouts, each of the four test runs made at normal speed is overlapped with itself to the defined working width. The coefficient of variation or, for non-broadcasting spreading equipment, mean and maximum deviations are then calculated on all weights from the four test runs. With this method of calculation, longitudinal variations occuring during the steady part of the feedingout process are also taken into account when the CV is calculated. Further details about the calculation methods are given by Malgeryd et al .3 During the studies of the feeding-out process, the whole spreader is placed on load cells connected to a computer which registers the weight decrease twice a second. From the unloading curve thus obtained the steady flow (Fig. 5 ) can be calculated. The steady flow is, together with the optimum working width, used when the application rate is calculated. For slurry spreaders, it is defined as the average flow during the whole unloading time. If the same definition were to be applied to solid-manure spreaders, the calculated
PHYSICAL PROPERTIES OF SOLID AND LIQUID MANURES
293
Fig. 4. Inside y iew of the test site used when measuring the lateral distribution and optimum working width of manure spreaders. The speed of the ladder to which the collecting boxes are attached is continuously y ariable in the range 0 – 9 km / h
application rate would occur only momentarily during practical spreading and would thus not reflect the rate achieved during the steady part of the feeding-out process. Therefore, the steady flow for solid-manure spreaders is defined as the highest average flow that can be defined for a continuous period of time corresponding to 30% of the unloading time. The value of 30% was chosen from practical experiences to suit a majority of the spreaders available on the market today. The stretch within the tolerance zone describes a spreader’s ability to maintain a specific rate during the feeding-out process. It is defined as the percentage of the unloading time during which the manure flow does not deviate more than Ú10% from the steady flow.
Manure flow, kg/s
60
Experiments were carried out to investigate the relationship between the characterization parameters and the spreading characteristics obtained when testing manure spreaders. In these trials, five solidmanure spreaders were tested with 20 batches of manure, the properties of which were measured with the above-mentioned characterization methods. For slurry, four different types of spreading equipment were tested with five batches of slurry and with water. Interactions between the characterization parameters and the different spreading properties of the spreaders, and the mutual relationship between the characterization parameters, were subjected to statistical processing.
4. Results Stretch within the tolerance zone
40
4.1 . Pumpable manures
Steady flow 20
0
0
50
100
150
200
250
300
350
400
Unloading time, s
Fig. 5. Unloading cury e showing the ‘‘steady flow’’ and the ‘‘stretch within the tolerance zone’’ for a slurry spreader. The steady flow was , in this case , 33?5 kg / s and the stretch within the tolerance zone 89?5%
As shown in Fig. 6 and Table 1, there is no clear relationship between fluidity and the dry matter content for pumpable manures. Neither is there any unequivocal relationship between the risk of clogging and the d.m. content (Table 1). The first and second slurries in the table have almost the same fluidity as water although they contain 7?3 and 6?8% d.m., respectively. The third slurry, which has a d.m. content of only 4?9%, has a higher fluidity than the
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6·0
12
Fluidity, 50 mm hole, s
Dry matter content, %
10
8
6
5·5
5·0
4·5
4 4·0 6·5
2
7·0
7·5
8·0
8·5
9·0
Fluidity, 40 mm hole, s
Water 0 6·5
7·0
7·5
8·0
8·5
9·0
Fluidity, 40 mm hole, s
Fig. 7. The relationship between fluidity as measured with the 50 mm hole (F50) and with the 40 mm hole (F40). The algebraic form of the regression line is F50 5 0?67 F40 and the coefficient of correlation (R2) is 0?94
Fig. 6. The relationship between fluidity (measured with the 40 mm hole) and the d .m. content
first two and, in addition, an extremely high clogging index. These results imply that it is time to reject the accepted approach where only certain dry matter concentrations are stated as limits between different types of slurry. Since there is a linear relationship between the emptying times (fluidities) obtained with the 40 mm and the 50 mm holes (Fig. 7 ), the fluidity can be measured at discretion with either of these two hole sizes. Which aperture to use may be decided from time to time with regard to the thickness of the slurry and the risk of clogging. Experiences from characterization of 24 batches of slurry during a period of four years show that the repeatability of the fluidity measurements is very
good, provided that the slurry is well mixed. When the operator has practised a few times, it is no problem to get three successive measurements with a time difference less than 0?1 s between the highest and lowest values. The clogging and dry matter measurements also show a high repeatability. Fig. 8 presents the relationship between fluidity and the slurry flow obtained when unloading an Omas vacuum tanker. The tanker was equipped with a spreading boom with trailing hoses. Though there are just a few data points in the diagram, it can be seen that fluidity is descriptive of manure flow properties. Measurements on an Olby tanker with a displacement pump indicated that fluidity affects the steady flow for this type of spreader too, but to a much lesser extent. We do not yet know whether the clogging index
45
Description Thin cattle slurry with solitary long straws Cattle slurry without any visible lumps or straws Pig slurry with plenty of chopped straws in a liquid, watery phase * Water 4?64 s.
Fluidity * , Dry 50 mm Clogging matter hole index content , % 4?7
24
7?3
4.9
64
6?7
4?9
131
4?9
40 Steady flow, kg/s
Table 1 Results from characterization of three batches of pumpable manure
35 30 25 20 15 6·6
6·8
7
7·2 7·4 Fluidity, s
7·6
7·8
8
Fig. 8. The relationship between fluidity (measured with the 40 mm hole) and the ‘‘steady flow’’ of slurry obtained when unloading an Omas y acuum tanker
295
PHYSICAL PROPERTIES OF SOLID AND LIQUID MANURES
50 Active angle of repose, deg
Fluidity, 40 mm hole, s
11
10 9 8 7 0
40 30 20 10
1 2
4
6
8
10
12
Dry matter content, %
Fig. 9 . Manure classes for pumpable manure
properly reflects the risk of clogging in the spreading equipment. When this was going to be investigated in 1993, it turned out to be problematic to find farmers with manure causing heavy clogging problems in the neighbourhood of Uppsala. Interviews conducted by Malm4 showed that clogging problems are very rare with modern band spreading equipment. The equipment for measuring separation tendency has to be further developed. The lack of practicable measuring methods is not a problem when testing spreaders as long as all tests are conducted with non-separating slurry, which is now the case in Sweden. Nevertheless, separation sometimes causes trouble in practical spreading, especially for farmers dealing with pig and poultry manures. Liquid manures for testing can be divided into two classes, defined using fluidity and dry matter content (Fig. 9 ). At present we can, however, only set the limits for one class since we do not know enough about how different types of spreaders are affected by various types of viscous manure. The classification system is further described by NMTI5 and Malgeryd et al .3
0 10
15
20
25
30
35
40
45
Dry matter content, %
Fig. 10. The relationship between the actiy e angle of repose as measured with the characterization box and the dry matter content for non-pumpable manure
The coefficient of variation (CV) can, for slurry spreaders, be calculated with high repeatability on four test runs made at normal speed. This is illustrated in Table 2. Twelve runs were made during the steady part of the feeding-out process and the CV was calculated on different groups of four series. As shown in the table, the CV ranged only from 45?2 to 46?8%. 4.2 . Non -pumpable manures In conformity with the results for liquid manures, there is no clear relationship between the active angle of repose and the dry matter content for nonpumpable manures (Fig. 10 ). The active angle of repose is, however, in good agreement with the visual impression of manure consistency, which is illustrated in Fig. 11 . In most cases, bulk density and the active angle of repose are closely related to each other (Fig. 12 ). This means that it would normally not be necessary to measure both these parameters. The active angle of repose can
Table 2 Changes in CV for a liquid-manure spreader when calculated on different groups of four series within the ‘‘stretch within the tolerance zone’’ Series number
CV , %
1–4 2–5 3–6 4–7 5–8 6–9 7 – 10 8 – 11 9 – 12
46?4 46?8 46?3 46?6 46?6 46?0 46?0 45?8 45?2
Fig. 11. The actiy e angle of repose as measured with the characterization box for different types of manure
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J. MALGERYD ; C. WETTERBERG
50
20
30 20 10 0 300
400
500
600
700
800
900
1000
1100
Optimum working width, m
Angle of repose, deg
40
18 16 14 12 10
Bulk density, kg/m3 140 130 Sp 120 rea 110 de r s 100 ett ing 90 ,c 80 m
Fig. 12. The relationship between bulk density and the actiy e angle of repose. The manures characterized represent the types of most frequent occurence in Sweden
70
60
60
50
50 40 30 20
900 800 700 600 70 500
, sity
3
m
kg/
en
lk d
Bu
Fig. 14. The relationship between bulk density , setting of the discharge opening and optimum working width for a Kidd Tankaspread 1500. The algebraic form of the computer-generated surface is WoptKidd 5 261?86 1 0?1305° 1 0?5132SKidd 2 0?000068° 2 2 0?00219°SKidd 2 0?0157SKidd2 and the coefficient of correlation (R 2) is 0?37
Steady flow, kg/s
Steady flow, kg/s
be estimated from the bulk density, which is easier to measure. Figures 13 and 14 , respectively, show how the steady flow and the optimum working width for a Kidd Tankaspread 1500 are influenced by the bulk density of the manure and the setting of the spreader. The Kidd spreader distributes the manure laterally with a front-mounted discharge wheel. The black dots in the diagrams indicate data points. The deviations of the data points from the regression surface created by
1100 1000
40 30 20 10
10 130 120 Sp 110 rea de 100 rs ett ing 90 ,c m 80
1100 1000 900 800 700 600 70 500
3
/m , kg sity
en lk d
Bu
Fig. 13. The relationship between bulk density , setting of the discharge opening and ‘‘steady flow’’ of manure for a Kidd Tankaspread 1500. The algebraic form of the computergenerated surface is FstKidd 5 123?0 2 0?4843° 1 0?3262SKidd 1 0?000305° 2 1 0?000881°SKidd 2 0?001551SKidd2 and the coefficient of correlation (R 2) is 0?87
7 Se tti 6 ng of t
1000 900
5 he bo
800 tto 4 m co
700 3 ey or
nv
600 500 2 400
3
/m
, kg sity
en
lk d
Bu
Fig. 15. The relationship between bulk density , setting of the speed of the bottom cony eyor and ‘‘steady flow’’ of manure for a JF ST70 H. The algebraic form of the computergenerated surface is f stJF 5 64?16 2 0?1267° 2 15?90SJF 1 0?000042° 2 1 0?02346°SJF 1 1?569SJF2 and the coefficient of correlation (R 2) is 0?94
297
PHYSICAL PROPERTIES OF SOLID AND LIQUID MANURES
the computer, are marked with vertical lines. The zones with different shadings indicate height curves, i.e. different levels of steady flow and optimum working width, respectively. Figure 15 illustrates the relationship between steady flow, bulk density and setting for a JF ST70 H, which has a bottom conveyor and four vertical beaters. From Figs 13 – 15 it can be concluded that bulk density and / or the active angle of repose (i.e. manure consistency) affect important spreading parameters such as the steady flow and the optimum working width and that different spreader types are influenced in specific ways depending on their construction. The relevance of the torque and the coefficient of variation as measured with the characterization box have not yet been entirely investigated. A few trials were carried out in 1993 in order to investigate whether there is any connection between the comminution resistance of the manure and the p.t.o. power requirements per kg of manure spread. The results, which are further described by Malm,4 seem to indicate that there is, at least for some types of spreaders. This finding might be of importance in the future when spreaders with rate control systems based on torque measurements become more common. Another parameter that might be affected by the comminution resistance is the scattering of the manure. This should also be investigated further. Solid manures for testing can be divided into five classes, defined by means of the bulk density and the dry matter content (Fig. 16 ). The classification system for solid manures is further described by NMTI5 and Malgeryd et al .3 Many solid-manure spreaders show random flow variations during the steady part of the feeding-outprocess that are so big that the coefficient of variation (CV) cannot be calculated with acceptable repeatability on four test runs made at normal speed.
1100
Bulk density, kg/m3
1000
5 4
900
3
800 700
2
600 1 500 400 300 10
15
20
25
30
35
40
Dry matter content, %
Fig. 16. Manure classes for non-pumpable manure
Table 3 Changes in CV for a solid-manure spreader when calculated on different groups of four series within the ‘‘stretch within the tolerance zone’’ Series number
CV , %
1–4 2–5 3–6 4–7 5–8 6–9 7 – 10 8 – 11 9 – 12
39?6 34?3 34?5 31?5 22?1 23?5 33?3 40?5 44?8
Table 3 illustrates how the CV can vary when calculated on different groups of four series within the ‘‘stretch within the tolerance zone’’. The low repeatability implies that the coefficient of variation for the spreading does not constitute an objective basis for assessment in type approvals for solid-manure spreaders. The CV can, however, be used for broadcasting spreaders for liquid manure since the repeatability there is much higher. For non-broadcasting spreading equipment, the mean and maximum deviations, which basically give the same information, should be used instead to avoid misleading comparisons. 5. Conclusions
1. Manure properties affect the performance of manure spreaders. Different spreader types are influenced in different ways when the manure properties change. 2. The dry matter content alone is not enough to completely describe the relevant physical properties of manure. Together with bulk density (solid manure) or fluidity (liquid manure) it can, however, be used to classify solid and liquid manures used for spreader testing. Solid manures can be divided into five classes and liquid manures can be divided into two classes. 3. The bulk density of solid manure affects spreading properties such as the flow of manure and the working width. The fluidity of liquid manure affects the flow of manure. The relevance of other characterization parameters, e.g. the comminution resistance and the clogging index, need to be further investigated in the future. 45 4. The coefficient of variation for the spreading does not constitute an objective basis for assessment in type approvals for solid-manure spreaders. The CV can,
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however, be used for broadcasting spreaders for liquid manure. For non-broadcasting spreading equipment, the mean and maximum deviations should be used instead to avoid misleading comparisons.
2
3
Acknowledgement Financial support by the Swedish Board of Agriculture is gratefully acknowledged. 4
References 1
Malgeryd J; Wetterberg C Metod fo¨ r teknikva¨ rdering: Utrustning fo¨ r stallgo¨ dselspridning. Karakta¨ risering av stallgo¨ dsel. Provningsmetoder fo¨ r spridare (Evaluation method: Manure spreading equipment. Manure characterization. Equipment and methods for testing manure
5
spreaders). JTI-rapport 132, Swedish Institute of Agricultural Engineering, Uppsala, 1991. (Summary in English) Malgeryd J Manure Characterization. International Agrophysics 1994, 8 (1): 93 – 101 Malgeryd J; Wetterberg C; Rodhe L Stallgo¨ dselns fysikaliska egenskaper -ma¨ tmetoder-betydelse vid provning av go¨ dselspridare (Physical properties of manuremeasuring methods-influence when testing manure spreaders). JTI-rapport 166, Swedish Institute of Agricultural Engineering, Uppsala, 1993. (Summary in English) Malm P Utva¨ rdering av karakta¨ riseringsmetoder fo¨ r stallgo¨ dsel (Validation of methods for characterizing manure). JTI-rapport 173, Swedish Institute of Agricultural Engineering, Uppsala, 1994. (Summary in English) NMTI Technique and Methods for the Type-Testing of Fertilizer- and Manure Spreaders. Final report from the Certification 93 programme. Swedish National Machinery Testing Institute, Uppsala, 1994