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Experience with straw treatment
Field testing and demonstration of straw treatment
Annex 1. The energy efficiency of the two-stage, feed-fuel processing of straw in indian villages
Annex 2. Method of calculating the value presented in table 2 for the efficiency of naoh energy usage
Annex 3. Recommendations to farmers on the treatment of straw
Annex 4. Calculated efficiency of milk production by straw-fed village buffaloes
College of Agriculture, G.B. Pant University of Agriculture and Technology, Pantnagar, India
Straw is a major by-product of crop production in the world. It is potentially useful as a source of energy, though it also contains worthwhile amounts of plant nutrients. Being bulky, it must, for the most part, be processed on the farm where it is produced. Ploughing it under or composting it are efficient wads of recycling plant nutrients, but these methods waste all of the energy the straw contains. In India virtually all straw is put through a two-stage process that both taps some of its energy and recycles plant nutrients. This process consists of feeding the straw to livestock and then using the dung as fuel. Usually, the dung is dried and burned directly, but this is undesirable because nitrogen is lost. A significant improvement is the introduction of the biogas plant to produce fuel gas from the dung; nitrogen is recovered from the slurry after fermentation (1 - 3). The efficiency of this two-stage, feed-fuel system ranges from 9 to 14 per cent (Annex 1).
Aside from purely energy considerations, the Indian system of processing straw on the farm has much to commend it. The relative simplicity of using an animal to convert straw energy to draught power is perhaps foremost. The same applies to milk production, a process in which straw provides the energy for the bioconversion of low-quality, inedible plant proteins (miscellaneous vegetation, grain-and oilseed-milling offals) into high-quality milk protein; the gain is not simply in proportion to the energy converted. Finally, it may be noted that straw cannot be used as a fuel in villages unless it is first passed through an animal; even present-day biogas plants cannot handle straw directly.
The efficiency of the livestock feed step can be increased by treating the straw before it is fed. The data presented in this paper indicate that the live weight gain in growing animals can be increased substantially if the straw is treated. The overall energy recovery from straw might not increase as a result of straw treatment because the more complete digestion of the treated straw by the animal would leave relatively less dung for use as fuel. Milk is, however, a more valuable form of energy than fuel.
The purpose of this paper is to review the Indian experience with various methods of straw treatment. It will include a discussion of the improvements obtained in animal productivity, the economics of such treatment, as well as the larger considerations of its energy cost and environmental impact. A special point made in this paper is that straw treatment techniques, like any new farming practice, will have to be evaluated on small private farms; satisfactory testing in an experiment station is not possible. A procedure for farm testing is outlined.
Straw, like all mature plant tissue, is relatively indigestible by the micro-organisms that inhabit the digestive tract of ruminants, This is because straw cell walls are heavily lignified or silicified. The objective of straw treatment is to increase digestibility by disrupting the cell wall. A number of methods have been developed, all of which have been described in detail by Jackson (4). These methods may be classified as chemical, physical, and biological. The chemical methods all involve the use of alkali solutions and are the most widely tested methods at present. Among the physical treatments, only pressure cooking alters the cell wall; simple grinding does not increase digestibility. A promising method of biological treatment is the growing of lignin-digesting fungi on straw. In the Indian village context, the feeding of alkali-treated straw will usually require the simultaneous feeding of additional nitrogen, as it will be the limiting nutrient in straw for both ruminant digestion and growth and production of the animal. As feed nitrogen is extremely scarce, the use of a urea supplement is an essential adjunct to straw treatment.
Sen et al. (5) experimented with the Beckmann method of straw treatment using wheat and paddy during the Second World War. In this method, straw is soaked for about 20 hours in 10 to 201 of a 1.5 per cent NaOH solution per kg straw, and subsequently washed with large volumes (up to 50 I/kg) of clean water to remove residual alkali. The results of the Sen et al. experiments (5) were similar to those from experiments conducted in Europe at the same time (6); the digestibility of the straw was increased by an average of 25 percentage units - from 40 - 50 per cent to 65 - 75 per cent. In spite of its effectiveness, this method of straw treatment did not become widespread in Europe, mainly because costs were too high. Some 8 kg NaOH are needed per 100 kg straw and the yield of treated straw is only 75 per cent.
In India, cost was not a factor (see Table 1, for example), but even so it never came into widespread use. Many state departments of animal husbandry began straw treatment by the Beckmann method on their livestock breeding farms, but it was not continued for long, and it was never really introduced into villages. There are several reasons for this. The units set up on livestock farms were ail small-scale, manual treatment installations that were too small for herds of 100 or more animals. The Beckmann straw treatment method gained ground in Norway only in the 1950s after a mechanized installation was designed (7), a development which did not occur in India. In any case, even if it had, the treatment of straw on a handful of government farms would not have much significance for the bulk of Indian livestock, which is owned by small farmers.
The reason the Beckmann method was never adopted by small farmers in India is primarily that new practices have to be demonstrated on the farm to convince farmers of their usefulness, and in the 1940s and early 1950s there were no organizations that could do this. The very concept of on-farm demonstrations of animal husbandry practices, though introduced two decades ago (8), did not receive any attention until very recently (4). A purely technical problem would probably severely limit the spread of the Beckmann method of treatment - it requires huge amounts of water. In many villages water is scarce.
In the early 1950s, Kehar (8) demonstrated the value of Beckmann-treated straw for animals maintained in villages by their owners (Table 1). The heifers with which he did his experiment were fed only very limited amounts of supplemental feeds, and even these supplements were given irregularly. The heifers suffered all the vicissitudes of a poor village environment. The simple treatment of the straw in their diet nearly doubled the rate of weight gain.
TABLE 1. Comparative Costs of Feeding Growing Heifers Untreated and Treated Paddy Straw (Beckmann Method) in Rural India
|Straw consumption (kg/day, dry straw basis)||3.00||3.00|
|Feed cost (Rs/head/day)||0.36||0.56|
|Liveweight gain (kg/day)||0.10||0.18|
|Days to gain 100 kg||1,000||555|
|Feed cost/kg gain (Rs)||3.60||3.11|
Source: Kehar (8).
Much more could probably have been achieved if a supplement of urea had been fed along with the treated straw, and if the straw had been fed ad libitum. These results are noteworthy for two reasons. First, they indicate that straw treatment can be profitable under village conditions. Second, it was the first, and probably still the only, example of what has now come to be considered an important technique for testing new animal husbandry practices. The need for on-farm testing of straw treatment techniques is emphasized later.
In the late 1960s, a simple spray method of alkali treatment was developed. Some of this work was done in India (9, 10). This was an improvement over the Beckmann method in that less alkali is used (only about 4 kg/100 kg of straw), no washing is necessary, and recovery is 100 per cent. On the other hand, digestibility increases by only about 10 units on average. Greater increases in digestibility are theoretically possible with higher levels of alkali (up to 8 kg/100 kg of straw), but animals cannot tolerate such large amounts of sodium. Improved rates of weight gain in growing calves of 0.1 - 0.15 kg/head/day have been found by treating straw by this method (see, for example, data in Table 2) (11). The economics are also favourable, as the table shows.
TABLE 2. The Performance of Calves on Untreated and Treated (Spray Method) Straw Diets
|Straw consumption (kg/day)||4.5||6.0|
|Groundnut cake consumption (kg/day)||0.8||1.0|
|Feed cost (Rs/head/day)||0.95||1.39|
|Liveweight gain (kg/day)||0.25||0.42|
|Days to gain 100 kg||400||238|
|Feed cost/kg gain (Rs)||3.80||3.31|
|NaOH energy input (MJ) additional energy stored as body-weight gain (MJ)||12.1**|
total energy stored (MJ)
|NaOH energy input (MJ)total protein energy stored (MJ)||5.0***|
Source: Singh et al. (1 1).
* Straw was treated with 3.3 kg NaOH/100 kg straw.
** For the method of calculating this value, see Annex 2.
*** Protein energy content of the gains made by the calves is assumed to be half the total energy stored.
On the basis of this limited information, a set of recommendations for farmers has been prepared (Annex 3). A few progressive farmers here and there are treating their straw with this method. Demonstrations of straw treatment (alkali and urea) have also been done on animals in one dairy development project, and some experience has been gained. On the whole, however, there is a need for further testing under village conditions. A proposal for doing this has recently been made and is described in a later section. The exercise presented in Annex 4 indicates the type of evaluation of straw treatment that should be made, and the information that needs to be generated.
Two newer methods, more effective than the spray treatment, are potentially applicable under Indian village conditions, and experimentation has already begun on these. One is the modified Beckmann, also known as the Torgrimsby method. Straw is soaked as in the original Beckmann method, but washed in a fixed amount of water, which is then recycled. Straw is effectively treated as in the original method, but residual sodium is less completely removed. Recovery is 100 percent. Two digestibility trials to date have yielded increased digestibility values of 15 and 18 units. Further work is in progress in India (D.V. Rangnekar, personal communication, 1978) as well as in Europe (F. Sundstol, personal communication, 1978).
The second method is spray treatment and stacking. If the amount of NaOH solution applied to the straw is kept low (not more than 10 - 151/100 kg of straw), and the straw is stacked (minimum size of stack 3 tons), the heat generated in the chemical reaction between the alkali and the straw causes a temperature rise in the stack. This temperature rise increases the efficiency of treatment (units increase in digestibility/kg of NaOH used). To apply such small amounts of solution uniformly, specially designed treater-mixers must be used. Such treater-mixers have been designed for use in factories and for on-farm use in Europe. Capacity is 2 - 6 tons/hour.
A small machine, operated by a 5 hp electric motor and giving an output of 0.3 tons/day, has been developed in India (12). Farmers always stack their straw after threshing; it is envisaged that they could put it through this machine at the time of stacking. Many farmers already have an electric motor on their pump or wheat thresher that could be used on a straw treater. Manufacturing cost without the motor is about Rs 3,000. Evaluation of straw treated in this way is in progress.
Supplementation of Straw with Nitrogen and Minerals
It has been conclusively demonstrated that treated straw will not be digested to its full potential digestibility if the nitrogen content of the diet is below 1.2 per cent (E.R. Orskov, personal communication, 1977) (13). This corresponds to rates of supplementation of 1.5 per cent for urea or 10 - 15 per cent for oilcake. These levels of supplementation must be ensured if straw is to be treated. From the point of view of the ability of the animal to utilize the energy available from treated straw, these levels of supplementation must be considered a bare minimum. Under average village conditions, animals, particularly growing animals, do not receive even this level of 1.2 per cent nitrogen in the diet from the meagre supplements of grass/forage and milling offals they are fed. Thus, a urea supplement is an essential adjunct to straw treatment. Further experimental work on this subject is proposed in a later section.
In many parts of India, animals suffer from deficiency diseases such as rickets and anaemia. Some progress has been made in mapping these areas. General purpose mineral mixtures are now widely available, although still not as widely used as they might be. Obviously, where a mineral is the first limiting factor for productivity, increasing energy intake by straw treatment will be futile.
Among crop scientists it is now widely recognized that the on-farm testing of new varieties and production techniques can lead to greater success in developing usable new technology and also save time. On-farm tests also have a potential demonstration value. Experience with on-farm testing of maize in Pakistan has been described by Palmer (14). The need for onfarm testing of new animal husbandry techniques is even more essential, because it is impossible to simulate village conditions in which livestock are reared on an experiment station. At the same time, it is as essential to demonstrate new techniques on a farmer's animals as it is to demonstrate new cropping practices on his fields. For these reasons, I have suggested a field testing and demonstration project for straw treatment (4).
In this project, the preferred method of straw treatment on a suitable scale (i.e., individual farm or village co-operative society) would be used to treat straw fed to village animals. The treatment and supplementation of straw will be super-imposed on the feeding and general management regime normally followed by each farmer. A standard experimental design will be used. The "herd" or statistical population from which the experimental animals will be selected will comprise all the heifers in the age group of six to nine months in a cluster of four to six villages. These animals will be divided into groups of three on the basis of age and similarity of management conditions.
Each one of these three animals will be randomly allotted to one of three dietary treatments. The results can then be analyzed statistically in the manner appropriate to a randomized block design. Because management practices will be a long-term one, about 60 animals should probably be taken at the outset in order to obtain statistically significant results. The heifers will continue on the experiment from the age of 6 months until they complete their first lactation.
For each village, or for each two villages, one man will be employed to guide farmers in the feeding of the selected animals according to the experimental plan. He will weigh feeds offered and refused on one day per month, measure the animal to estimate weight, weigh milk produced by animals when they come into lactation, and record the dates of first oestrus, service, and calving. Caustic soda, urea, minerals, and any other supplement to be used will be supplied free of cost to the participating farmers.
The three experimental diets will be:
|Existing farmer feeding practices.||Existing farmer feeding practices, except that urea is sprayed on straw and a mineral supplement is fed.||Existing farmer feeding practices, except that straw is alkali treated, urea is Sprayed on straw, and a mineral supplement is fed|
If the protein supply from grass or cultivated legume forage in some seasons is adequate, the use of urea would be discontinued at such times.
The project has been proposed as a co-operative one among institutions in several countries where straw is traditionally fed to livestock. As far as possible, these institutions would be those which have successful livestock development programmes based upon co-operative societies so that a regular supply of materials (caustic soda, urea, mineral mixture) can be guaranteed and, after the project is over, the farmer can pay for these conveniently (e.g., by adjusting their costs against income from milk sales).
While experimental data are limited, we may nevertheless attempt to evaluate straw treatment in a wider context. Indeed, it is essential that we make the attempt at this stage when we are contemplating a rapid expansion in our research and extension programmes on straw treatment.
A major concern in India should be the high support-energy cost of alkali treatment. Support-energy is obtained by burning fossil fuels, from falling water, and nuclear fission as opposed to the energy of the sun that is trapped on the farm. In the systems of farming that have come into existence in Europe and North America during the era of cheap fossil fuels, support-energy costs have been found to be very high and are, in the present changed circumstances, a cause for concern. Krummel and Dritschilo (15) have calculated the support-energy cost of producing one MJ animal protein in the United States. These figures are 6 MJ for milk and 32 MJ for beef. The corresponding support-energy costs for feed alone are 4 and 20 MJ, respectively. The values for beef include, however, the maintenance of cow herds as well as the rearing of animals for slaughter. In India, support-energy costs for animal protein production are near zero, as by-products are fed and few chemicals or machines are used. The introduction of alkali treatment would, at one stroke, raise support-energy costs to as much as 5 MJ/MJ animal protein (Table 2, Annex 4).
If all 200 million tons of straw produced in India every year were to be treated, some 10 million tons of NaOH would have to be manufactured at an energy cost of 510 x 109 MJ. This is three times the amount of energy currently expended in manufacturing nitrogenous fertilizers in one year (1,774,000 tons N x 84,000 MJ/ton). Not only is the support-energy of this magnitude not available, it can also be argued that even if it were, it would best be used to manufacture more nitrogen fertilizer, which would provide more additional feed energy than the NaOH would, and at the same time solve many other problems. One example will serve to indicate the strength of this argument.
One kg of urea applied to crops in India, under favourable conditions, can return 10 kg of grain, or 100 kg of green forage. In the example given in Annex 4, a buffalo cow would consume 883 kg of NaOH in her lifetime. This is equivalent to 1,272 kg of urea which, if applied to crops, would produce enough additional grain to feed the buffalo 3 kg per day for life, much more - probably three times more - than would be needed to produce the increment of milk resulting from the treatment of straw. If this urea were applied to non-leguminous forage crops, the additional yield would be enough to feed the buffalo 30 kg of forage per day, again much more than would be needed to produce the increment of milk produced by straw treatment.
Aside from energy considerations, NaOH treatment may prove unacceptable in the long run because of the sodium pollution it would cause. Newer methods of NaOH treatment avoid river pollution at the treatment stage, but each 100 kg of treated straw fed contains 3 - 5 kg of sodium that will find its way into soil and rivers. In the humid countries of Northern Europe this may not be a cause for concern, but in an arid country like India, with vast areas already afflicted with soil salinity, it could be. In the German Democratic Republic, KOH is being used extensively in place of NaOH (A. Hennig, personal communication, 1978), but soils in that country must be fertilized with potassium; Indian soils need not be. Indian soils also do not need calcium, which makes Ca (OH)2 less attractive than it might otherwise be. In any case, these alkalis are also expensive to manufacture in terms of support-energy.
What, then, are the alternatives? There are several possibilities, and each of them is discussed briefly in the following paragraphs. Unfortunately, considerable research and development effort would be needed to develop these alternatives to alkali treatment. By drawing attention to these alternatives now, however, the necessary effort may be stimulated more quickly.
The biological fungal treatment of straws needs no support-energy, but the fungi derive some of the energy they need from carbohydrates in the straw that the ruminant could use itself. Thus, overall energy efficiency (milk energy output/straw energy input) might not be improved. However, there are inadequate data (4). More information should be obtained quickly in order to evaluate this method of treatment critically. There would be no pollution with this method.
Ammonia treatment offers the advantage that it can help meet the protein needs of the animal consuming the straw, and later on the same nitrogen in dung and urine can help to meet the nitrogen needs of crops. It does not cause pollution. However, the methods developed thus far for farm use employ NH3 gas and would, therefore, be difficult or impossible to use in Indian villages.
One interesting possibility is that suggested by Oji and Mowat (16). They sprayed straw with a urea solution and packed it in a silo so as to exclude air. The urea was broken down to NH3, thus subjecting the straw to an alkaline treatment and, at the same time, increasing its nitrogen content. This method deserves further testing. A disadvantage is the capital cost of constructing silos; only the more affluent farmers in India could afford to do so.
A final alternative is the breeding of varieties of cereal crops that have highly digestible straw. The extent to which this is possible is not known at present. The genetic variability that may exist would have to be ascertained. Next, the compatibility of highly digestible straw with high grain yields would also have to be determined. Some varietal differences do exist (17). Growing cereal varieties that produce straw of high intrinsic digestibility could be combined with urea treatment in a silo.
Indian experience with alkali treatment of straw is reviewed. Earlier experiments with the Beckmann treatment of wheat and paddy straws confirmed European work with respect to the effectiveness of the method. It was also found to be profitable to treat straw under village conditions, but because suitable extension machinery and concepts were lacking, it was not popularized. Scarcity of water was another limiting factor. There have been recent experiments with newer methods, but it must be determined whether they will be economical under village conditions. A method of on-farm testing and demonstration is suggested to accomplish this, and at the same time popularize straw treatment.
An analysis of the energy cost of straw treatment with alkali under Indian conditions suggests that it may be unacceptably high. Alkali treatment also poses a distinct pillution problem in India. The rapid development of alternative methods is therefore urged. The use of wood rotting fungi or ammonia (straw treated in silos with urea) is suggested, as well as an effort to breed cereal varieties with highly digestible straw.
Table 3 shows the calculation of energy efficiency for different methods of using dung as fuel. The following factors are taken into consideration.
|Traditional open fire-place||Closed fireplace with chimney||Biogas production|
|Energy content (MJ) of:|
|Resulting animal products and services||4.6||4.6||4.6|
|Gas produced from dung||15.4|
|Useful energy obtained from dung (MJ)||5.5||11.0||9.2|
|Deduction for energy equivalent of nitrogen lost (MJ)||- 1.5||- 1.5|
|Total useful energy recovered from straw||8||14.1||13.8|
|Efficiency of processing (%)||8.6||14.1||13.8|
1. 6.9 kg straw containing 90 per cent dry matter and having a rate of combustion of 16 MJ/kg dry matter contains 100 MJ combustible energy. This amount of straw is approximately the daily consumption by an adult bovine.
2. The efficiency of animal production on a typical straw diet is calculated (see Annex 4) to be 4.6 per cent. This value is for the diet as a whole, the value of the straw component is probably slightly less.
3. 18.3 kg of dung containing 20 per cent dry matter and having a rate of combustion of 15 MJ/kg dry matter (the digestibility of straw energy averages 45 per cent) = 55 MJ.
4. 18.3 kg wet dung x 37 I biogas/kg wet dung x 0.61 CH4/l biogas x 0.038 MJ/l CH4 = 15.4 MJ.
5. The efficiency of burning dung in an open fireplace is estimated to be 10 per cent, in a close fireplace with chimney, 20 per cent, and in a gas burner, 60 per cent (2).
6. Assuming that 50 per cent of the nitrogen contained in straw is recovered in dung, the manufacturing energy value of this nitrogen is:
7. Total useful energy = energy contained in animal products and services + useful heat energy - deduction for energy equivalent of nitrogen lost.
8. Efficiency of processing = (total useful energy obtained x 100) / (energy content of original straw)
The MJ of NaOH energy input per MJ additional energy stored as body-weight gain was calculated as follows.
1,000 kg untreated straw provided for
1,000 kg treated straw provided for
In 222 days a calf fed untreated straw also consumed
222 x 0.8 = 178 kg oilcake
In 167 days a calf fed treated straw also consumed
167 x 1.0 = 167 kg oilcake
In 222 days a calf fed untreated straw gained
222 x 0.25 = 55.5 kg
In 167 days a calf fed treated straw gained
167 x 0.42 = 70.0 kg
Therefore, the treatment of straw increased weight gain by 70.0 - 55.5 = 14.5 kg/1,000 kg straw. (This figure is conservative, because a calf fed treated straw consumed slightly less oilcake/1,000 kg straw than the one fed untreated straw.) The energy value of this bodyweight gain is taken as 9.6 MJ/kg (calves about 1-year-old gaining at a rate of 0.40 kg/day), or 139.2 MJ for 14.5 kg. The manufacturing energy cost of NaOH is estimated to be 51 MJ/kg;
1,000 kg straw x 3.3 kg NaOH/100 kg x 51 = 1,683.
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