Urea blocks. I. Methodology of block making and different formulae tested in Syria
M Hadjipanayiotou*, L Verhaeghe**, M Allen***, Abd El-Rahman Kronfoleh, M Al-Wadi, M Amin, T Naigm, H El-Said and Abdul Kader Al-Haress
Animal Production Research Division, Deir El-Hajjar, Ministry of Agricultural and Agrarian Reform, Damascus, Syria
(Present address: *Agricultural Research Institute, Nicosia, Cyprus; **FAO, Animal Production and Health Division, Via delle Terme di Caracalla, 00100 Rome, Italy; ***University of Auckland, New Zealand).
Three tests were carried out from May to October 1991 to make urea- blocks using a variety of agricultural by-products and binders. Solvent-extracted olive cake (20 to 35%) with and without screened poultry litter was used in Test 1. The effect of binder was established in the second part of this test. In Test 2, molasses was added to the formulation using seven different proportions (0, 5, 10, 15, 20, 30 and 40%). The effect of the type of binder (cement, slaked lime) each at three different levels (0, 4 and 8%), was studied in a factorial arrangement of treatments for blocks containing a reduced level of molasses (Test 3). Gypsum [CaSO4. 1/2 H2O] was found to be a good binder in Test 1; however, in part 2 of Test 1, it produced blocks of less hardness and compactness than when slaked lime [Ca(OH)2] was used. Ten percent cement in a formula without any molasses or poultry litter gave good blocks, whereas when poultry litter was present, the blocks were of medium hardness and compactness. Increasing the level of cement was found to produce good blocks even at the presence of poultry litter.
In the formulae without molasses larger quantities of binder and water were required (Test 2). The same test showed that blocks can be made with or without molasses and that even 5% molasses was sufficient for making good blocks with low levels (6%) of slaked lime. In Test 3, the addition of as little as 4% slaked lime gave very good blocks when molasses (20%) was present. In general, formulae containing cement were found to be less hard than those with lime. The density of blocks was found to decrease with decreasing molasses content and also with increasing levels of bulky materials. It is concluded that blocks can be made with and without molasses; slaked lime is a better binder than gypsum and selection between slaked lime and cement should depend on availability and price. The order of introduction of the ingredients seems to be less important than was previously thought.
KEY WORDS: Blocks, urea, poultry litter, lime, cement, molasses
Low quality roughages are sometimes the only ruminant feed in the Syrian Arab Republic (SAR) for a considerable part of the year. Voluntary intake of such feed resources is known to be low (Fick et al 1973; Hadjipanayiotou et al 1975; Capper et al 1989). Animals on such diets experience weight losses and sometimes are unable to survive until the next rainy season (Sansoucy 1986). Molasses has been used as a palatable carrier for other nutrients when supplementing low quality roughage diets and also as a gelling agent in block manufacturing (Sansoucy 1986; Aarts et al 1990).
Liquid molasses-urea supplements have been widely used in Australia and in Southern Africa (Preston and Leng 1984). However, handling and transporting large quanitites of liquid molasses to distant areas for distribution to farmers poses some serious problems (Kunju 1986). As a result, molasses-urea blocks (MUB) have been utilised as a means to reach extensive livestock systems or small farmers (Sansoucy 1986).
Although MUB feeding has given some very positive results in many parts of the world, their wider use could not be applied in many countries because molasses was not available. Therefore, urea-block (UB) manufacturing with reduced quantities of molasses has been attempted (Hassoun 1989).
The present paper reports on UB manufacturing using a variety of agricultural by-products, type and level of binders and different levels of molasses.
Materials and methods
Three tests were carried out over the period May to October 1991. Thirty UB formulae were tested. The composition of each formula is given in Tables 1, 2, 3 and 4.
The purpose of Test 1 was to examine the effect of the use of solvent-extracted olive cake (SEOC)(a mixture of kernels and pulp) and screened poultry litter (PL). These two agricultural by- products were not much investigated in prior work on blocks. The test consisted of two parts: level of by-product inclusion (Table 1) and level and type of binder. Three types of binders: slaked lime, gypsum and cement, were studied (Table 2).
Starting from the FAO-standard formula (Aarts et al 1990) including 40% of molasses an attempt was made in Test 2 to produce blocks with less molasses (30, 20, 15, 10, 5 or 0% ). The composition of all formulae is shown in Table 3.
Taking into account the relative scarcity of molasses in the SAR at the time of doing the experiments, a reduced level of molasses (20%) was used to study the effect of amount and type of binder on the quality of urea-blocks (Test 3). In a factorial arrangement of the treatments, two binders (slaked lime and cement) at three levels (0, 4 and 8%), were tested. The composition of the formulae is shown in Table 4. The mix without any binder was excluded.
|Table 1. Formulation (%) and characteristics of Urea Blocks with solvent extracted olive cake (SEOC) and other agricultural by- products (Test 1, part 1).|
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|Table 2. Formulation (%) and characteristics of Urea Blocks with SEOC and other agricultural by-products (Test 1, part 2).|
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* In this and subsequent tables, M/G means that C or H is between medium and good.
|Table 3. Composition (%) and characteristics of urea blocks with and without molasses (Test 2).|
|(l/100 kg mix)||20||14||15||15||15||15||40||40||40||40|
* DPM: Dried Poultry Manure
|Table 4. Formulation (%) and characteristics of Urea Blocks using different types and levels of binders (Test 3).|
+ Means that C or H are very good within the test.
Preparation of ingredients
Molasses, SEOC, dried poultry manure and wheat bran were used as purchased. Urea and salt were dissolved prior to mixing in order to avoid lumps of these ingredients. The binders used were finely ground; the quicklime (CaO) used was no longer active [Ca(OH)2, slaked lime]. Poultry litter (a mixture of wood shavings, feed, feathers and excreta), was screened using a 20 mm metal grid to remove unwanted materials (nails, wood etc) and was stacked (1.5 m heap) under a shed for at least 6 weeks to eliminate pathogens (Ruffin 1977).
Mixing of ingredients was done by hand in a 200 litre drum cut to a height of 25 cm. Approximately 10 kg of ingredients were mixed per batch. The mixing procedure was as outlined by Aarts et al (1990). The urea was dissolved in water followed by salt. The binders were dissolved in another bucket and after being mixed together, they were poured in to the drum which already contained the molasses. After they were well mixed to ensure a homogenous mixture, the other ingredients were added as follows: dried poultry manure/poultry litter, olive cake and finally the wheat bran. Each new ingredient was added only after a homogenous mixing of the other ingredients was attained.
A number of UB formulae (5, 10, 12, 14, 17, 18, 19, 20, 21 and 22) were also made using a concrete mixer. The concrete mixer used was locally made with a high length-to-diameter ratio (3:1) drum. The revolutions of the mixer were reduced to 28 rpm by changing the gearing on the sprocket drive from the electric motor. The ingredients were added as follows: water, urea, salt, molasses, poultry manure and finally wheat bran.
The well mixed material was placed in plastic containers (20 x 11 cm) and/or in rectangular (20 x 17 cm) or round ( 20 cm) metal moulds. The surface of plastic containers (moulds) was covered with plastic sheet (0.05 mm) to facilitate demoulding and avoid cleaning of the surfaces. The material placed in plastic moulds was pressed by hand (formulae with 20% molasses) and/or using a simple hand operated press consisting of a square/round plate (0.6 cm thickness) mounted on a T-type handle (63 x 30 cm). The material placed in metal moulds, without any plastic sheet on the surfaces, was pressed manually using the same press.
Steel plate (1.25 mm thickness) moulds were made to form 16 blocks at one pouring of the mixer as described by Allen (1992). Four wooden moulding-boards (100 x 20 x 2 cm) were fitted in the base of the plate-moulds. The moulding board was effective in making a "mini-pallet" to transport the blocks, immediately after demoulding, to storage shelves for curing and drying.
Blocks formed in metal moulds were removed immediately from the moulds and those made in small plastic moulds were removed after 16 to 24 hours. The plastic liner was used many times. All blocks were dried in the open air under shelter.
Assessment of blocks
Hardness (H) and compactness (C) of blocks were tested four days after drying (Hassoun 1989). The test was made by three persons independently by assessing hardness on the scale: soft (S), medium (M) or good (G), and compactness as null (N), medium (M) or good (G). Hardness was determined by pressing with the thumb in the middle of the block and compactness by trying to break the block by hand.
Results and discussion
The chemical composition and the density of the ingredients is given in Table 5; the composition of the finished block was considered to be a function of that of the individual ingredients.
|Table 5. Chemical composition (g/kg) and density (g/litre) of the ingredients.|
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In the first part of Test 1, gypsum was shown to be a good binder for blocks including SEOC with and without poultry litter, resulting in blocks of satisfactory C and H (Table 1). This is in line with earlier studies (Hadjipanayiotou et al 1991) where gypsum alone (formula: 10% urea, 10% salt, 20% gypsum and 65% wheat bran) gave good blocks especially after 10-20 days of drying. Contrary results were obtained in part 2 of the test, where gypsum gave blocks of less H and C than when slaked lime was used (Table 2, formula 7 vs 8, 9 vs 10 and 11 vs 12).
Ten percent cement in the blocks without poultry litter gave satisfactory results (formula 2, Table 1) whereas, with poultry litter, the block was of medium H and C. Increasing the level of cement (Table 1, formula 5) to 15% gave good blocks even in the presence of litter. It seems therefore, that the combination of the basic ingredients may play a significant role in the level of binder(s).
In accordance with our previous study (Hadjipanayiotou et al 1991) it was clearly demonstrated in Test 2 that blocks can be made without any molasses; the amount of binder used, however, was relatively higher especially when poultry excreta was incorporated in the mix. The present study showed that more than 10% binder is required to make good blocks without molasses (Table 3, formulae 19-22).
Even with low levels of molasses, the amount of binder required can be reduced significantly (Table 3). Ten percent slaked lime gave unsatisfactory blocks without molasses (formula 20) but with 5% molasses even 6% slaked lime gave good blocks (formula 18).
It was previously asserted that if CaO is used as a binder, the latter should be active (Aarts et al 1990). In the present study (Test 2 and 3), in line with our previous work (Hadjipanayiotou et al 1991), slaked lime (Ca(OH)2) was found to be an effective binder. Furthermore, in formulae with 20% molasses, even 4% slaked lime gave blocks of good H and C (formula 23, Table 4). Blocks with cement were less hard than those with slaked lime (formulae 19 vs 20 and 23 vs 25). This is in accordance with Aarts et al (1990) who recorded that lime gives better results, concerning setting time (hardening quicker) and hardness of the block.
Hardening of blocks increased with advancing storage period; long storage of at least some formulae resulted in extremely hard blocks that could not be utilized by sheep and goats. It is concluded that it is important for some formulae at least, to be manufactured shortly prior to their use especially in the dry summer period. Blocks intended for use in very dry areas may be stored in large polyethelene bags when they have reached the desired degree of hardness. Some limited work indicated that the presence of 30% (or more) of molasses reduced block hardness brought about by storage in a dry climate.
The density of blocks was found to decrease with decreasing molasses content and also with increasing the content of bulky materials. The density (kg/m3) of blocks made is shown in Tables 1, 2, 3 and 4. Pressing was found to have a significant role on the density of blocks. Thus at high levels of molasses (40%), less pressing could be applied; this being the main reason why formula 22 was more dense than formula 21. Although, with the manual press technique we were unable to apply standard pressing to all blocks, in general, the density of the finished block was found to be closely related to the density of the ingredients used.
Aarts et al (1990) reported that when using a concrete mixer, the bran must be introduced in successive small quantities at a time in order to get a homogenous mix. In our most recent tests however, introduction of bran in large portions (formula: 8% urea, 5% salt, 6% slaked lime, 20% molasses, 31% dried poultry manure and 30% wheat bran) resulted in a homogenous mix quite free of balls and lumps. The homogeneity of the mix and the presence or absence of balls was related to the speed of the mixer, the amount of water present and the quantity of the mix as a proportion of the volume of the concrete-mixer used. For the formula listed above, up to 75 kg mix along with 19 to 20 l of water should be added to a drum of 300 l capacity. Care should be taken to ensure that the mixer is not overloaded otherwise balls of mix cannot be broken by the mixer. The mixer should be used at a speed of about 25 rpm which is lower than that customarily used for concrete. Indeed, reducing the mixer speed from 38 to 28 rpm by changing the gearing on the sprocket drive from the electric motor resulted in a significant reduction in the number of balls formed, less sticking of the molasses on the walls of the drum and consequently better mixing.
It was found that the amount of water used should be increased with decreasing molasses level in the mix; with mixtures without any molasses, up to 50 litre of water per 100 kg mix were required.
The maximum quantity of mix which could be processed was found to be closely related to the density of the individual ingredients; in a 300 litre capacity drum it was found that a maximum of 75 kg of ingredients could be mixed when the molasses content was less than 20% of the mix.
Hassoun (1989) reported that the use of dried olive cake presented some difficulties and recommended that it should be moistened before use, and recommended use of fresh olive cake. Similarly, Sansoucy (1986) has stated that for cement hardening, the ingredients should be mixed beforehand with water. However, in the present trials, there was no need to wet either the dried poultry manure or olive cake, and the use of dried olive cake did not present any problems.
Aarts et al (1990) reported that the order of introduction of the ingredients plays an important role for obtaining a homogenous mix. Their recommended order being the following: molasses, urea, salt, binder, wheat bran. In our studies, introducing the ingredients in the order: water, urea, salt, binder, molasses, poultry excreta, olive cake and bran showed that the order of mixing is not as critical as had been previously proposed. Once a formula has proved to produce good blocks, mixing procedure can be altered in order to find the easiest and quickest way to produce the blocks.
It is concluded that it is possible to make blocks with and without molasses. The use of molasses, even small quantities, reduces the level of binders that is needed to get blocks of an acceptable quality.
Slaked lime is a better binder than gypsum. Although in this study, slaked lime was slightly better as a binder compared to cement, the choice between both should depend on relative availability and price.
Blocks can be made using a variety of agricultural by-products and animal wastes; the choice of ingredients should be made according to their availability, nutritional value, ease of handling and their overall effect on the quality of the block.
Though it was not the purpose of this study, it was concluded that the mixing procedure was not that critical as was previously thought.
The authors are grateful to the FAO and UNDP offices in Damascus for continuous support and encouragement and to his Excellency the Minister of Agriculture and Agrarian Reform and his staff for making available all necessary facilities for the implementation of this work. This work was carried out in conjunction with the Greater and Improved Use of Agricultural Residues for Animal Feeding Project, a joint undertaking between the government of Syria and the UNDP and FAO.
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(Received 1 August 1993)