Chapter 2 The uneven process of appropriation by industry of basic mushroom inputs: mushroom compost (part I)
Introduction After covering mushroom spawn in the previous chapter, this chapter will introduce the reader to composting, its principles and general historical development in Europe. This input in mushroom growing did not become a commodity until the mid 1963 in Europe with the establishment in the Netherlands of a composting centre by the Co-operative Dutch Mushroom Growers' Association. In Northern Ireland, there were a few commercial compost centres at the end of the 1960s. They also provided compost to some small growers in Monaghan, in the Republic. We have to wait until 1979 to see the first custom compost centre in the South, in Gorey, Co.Wexford.
For most of the history of the cultivation of mushrooms in Europe, from the mid seventeenth century to the mid twentieth century, mushroom workers, and growers in small farms, prepared compost on-farm more or less with the only help of manual tools. Tractors with front-end loaders and homemade turners were introduced only well into the 1900s, and only in large farms. This primary form of mechanisation in composting, which must be placed in the context of the general mechanisation of European agriculture from the second half of the nineteenth century onwards, was of some help to those who could afford it.
This chapter is just a general introduction to composting up to the eve of development of bulk pasteurisation in tunnels in the 1970s. In the next section, I will continue with the latest development in composting, with a particular focus on the relationship between compost producers and growers in Ireland, drawing also on comparisons with Britain and making use of specific case studies.
Since this work has a social dimension, the reader is not going to find a technical description of composting. My chief aim is to understand the process of concentration (business expansion) and centralisation (mergers) in compost making, particularly the technological developments that have lead to mechanisation, and to bigger and fewer composting centres. In the following chapters, I will merge technical developments with market forces for a more holistic approximation to the tendencies of concentration and centralisation in spawn making, composting, mushrooms farming, and marketing.
The period between the 1950s and 1980s represented the moment of greatest expansion in the mushroom industry in Europe, particularly in the Netherlands, Britain and Ireland, the countries to which I chiefly refer in this work. The main technical and commercial development in composting also took place at that time. The current mushroom industry is grounded on the developments of that period. In this first section, I draw from texts produced in the Netherlands and Britain around the 1970s and 1980s. Since the Dutch mushroom Industry is the most technologically advanced of Europe, it constitutes a good example to draw from. It constitutes also a good introduction before going into a characterisation of the Irish industry because of the average small scale of growing operations of the mushroom industries in both countries. In recent times Irish growers have even adopted the Dutch shelf growing system. In both countries, composting and growing are separated business operations, although in Holland growers have a cooperative structure for the production of compost that Irish growers have not been able to achieve.
Subsequent chapters will deal with the evolution of different growing systems, issues about commercialisation and quality, and the labour question. The focus will be on Ireland, but I will keep drawing comparisons from mainly the Netherlands and Britain, and sometimes from the USA. The work that I am publishing in The Mushroom People is a preparatory work for a doctoral dissertation in anthropology (National University of Ireland) and has not been revised by any of my academic supervisors or any expert within the mushroom industry. Any suggestion or comment from the readers will be appreciated and acknowledged (francisco.arqueros@nuim.ie). Work towards this dissertation has been possible thanks to a three-year Government of Ireland Scholarship 2004-2007.
Early preparation of mushroom compost As we have already seen in the previous chapter, French growers started to cultivate mushrooms in Europe sometime during the first half of the seventeenth century. In 1650, N. de Bonnefons described the cultivation of mushrooms in Le Jardinier Francais; John Evelyn put it in an English translation later, in 1659, French Gardener (Atkins 1983: 168).
The first cultivation method consisted in inoculating horse manure compost, rich in straw, with mycelium from previous crops. Horse manure was the chief raw material, which mycelium would later colonise and in which mushrooms would later germinate. But horse manure had to undergo first a period of fermentation, or composting, before it was suitable for inoculation with mycelium.
In 1779, John Abercrombie provided us with the first description of composting in English (Mushroom Journal, March 1979, p. 82):
To prepare for making the beds, provide a sufficiency of the only proper material, horse stable dung; no other answers the purpose; such as has lain sometime in collected heaps or dung-lays in the stable yards, etc., consisting of the moist warm strawy litter, and dunging of the horses together, cleared out from the stalls, the whole having been rendered wet in the sables by the urine of the animals - but as [its] heat generally proves too violent at first for the growth of vegetables, and more particularly that of the Mushroom Spawn, the dung should, for the most part, be previously prepared before worked up into a bed, by forking it up mixedly in a heap, to remain a week or two, in order to reduce it to a more moderate temperature; and if turned over once or twice, the rank burning steam will sooner and more effectually evaporate, and thereby reduce its fierce fermentation to a moderate state and being thus prepared to an equally meliorated state generally discovering a somewhat blackish putrefying commencement internally, proceed to make the bed in proper time, accordingly, while the dung remains fully in this particular state of perfection for that purpose.
Early composting: the marl pits in Limburg, Holland, first half of the twentieth century (van Griensven)
This early description contained the basic features of all subsequent composting until Lambert (already mentioned in the previous chapter in relation to his work on mushroom spawn in the US in the first two decades of the twentieth century) explained in 1934 that composting consisted in two different phases (I and II) and that phase II should be carried out indoors under controlled conditions.
Based on Vedder's account of old composting (1978: 181), it is possible to reconstruct how "advanced" composting was performed in Europe and North America before Lambert's breakthrough. It developed into a schedule consisting in manually wetting horse manure and stacking it loosely in a pile, where it fermented between 5 and 7 days. After the first week, a compost worker had to pull the pile apart. He had to wet it, shake it, mix it, and stack it again. The most important thing was to turn the outer parts to the interior of the pile. That was the only way to keep the compost fermenting uniformly because composting is an aerobic process. The compost makers had to repeat this action of airing the compost, called "turning", at least once a week, until the compost cooled down and the grower, or the manager in large farms, decided whether the compost was ready for spawning.
Following Abercrombie's account (Atkins 1983: 168) we also know how the business of growing mushrooms went on after composting. Growers used to make the mushrooms beds outdoors, and some under a cover in a barn or a shed until the French, again, made another breakthrough. Towards the end of the eighteenth century, they realised that mushrooms could grow without light. So, as early as 1810 they started to grow mushrooms in caves around Paris and the Loire Valley (van Griensven 1988: 13). The compost beds were then made on the cave floor "in the shape of small hills similar to asparagus beds" (Vedder 1978: 20). Then they spawned the beds with mushroom mycelium and covered them with a thin layer of marl. Yields of 50 to 70 kg per tonne of compost were considered good (Vedder 1978: 184). One of these enterprises in caves was producing a daily average of 1,500 kg of mushrooms as early as 1867. The mushroom beds on the ground of that cave had a total length of 30 km (van Griensven 1988: 13).
Back to old method of composting, the whole process lasted around four weeks according to Vedder (1978: 20, 181) and six weeks according Gerrits (1988: 30). It was based in the accumulated experience of farmers rather than on the scientific knowledge of lab technicians: "Exactly what changes were taking place in the manure was not known at that time, but from experience the growers arrived at the best working method" (Vedder 1978: 20). In this way, for example, growers discovered that by adding gypsum during composting, compost turned less greasy and improved yields. This state of things was going to change in the twentieth century.
Stacking piles in a compost yard in England, 1970s (Vedder)
In Chapter 1, we have seen that lab research on mushroom spawn brought about the commercial development of the first pure-culture mushroom strains at the turn of the twentieth century. By 1907, Louis F. Lambert was marketing at least seven different pure strains of mushrooms (Agaricus bisporus) to growers around the US from his lab of St. Paul, Minnesota. It took longer for researchers to engage with mushroom compost. In 1934, Lambert discovered that the piles of compost, during composting, had four different temperatures zones because of an uneven supply of oxygen. The two outer layers were, for example, either too cool or too dry. The next layer met the best conditions for composting at 50-55C (Vedder 1978: 184). That is, Lambert discovered that the part of the compost fermented at those temperatures obtained the best yields. In a way, his discovery was not fundamentally different from those that farmers had made before. In the 1980s, Gerrits still claimed that researchers did not understand fully the process of composting in all its details (1988: 31). The difference was that Lambert was a professional researcher with a scientific background and state funding.
The consequences of his discovery were, however, far reaching because it led to a new method of composting. In order to get all the layers of compost to ferment at the ideal temperature of 50-55C, Lambert, after the initial heating in the pile (phase I), transferred the compost to a special room for "pasteurisation" or "peak-heating" under controlled conditions (phase II) (Vedder 1978: 184-5). The final quality of the compost and yields improved in this way. Therefore, Lambert is responsible for introducing the modern distinction between the two stages of composting, Phase I and Phase II. Phase I, or free heating, is performed outdoors and has not really changed since the time of Abercrombie, apart from the progressive mechanisation of the process. Phase II, also called pasteurisation or controlled peak heating, was performed indoors, in special pasteurisation tunnels or rooms.
Horse manure compost versus straw compost Horse manure rich in straw and urea, gypsum, and water have been the classical raw materials to prepare compost. But fresh straw, chicken manure (even pig manure has been used), vegetal waste and various supplements - added to improve the productivity of compost - have expanded the list of the compost recipe over time. It is a common thing to speak nowadays of two kinds of compost: horse manure compost (mainly horse manure) and synthetic compost (mainly fresh straw and chicken litter). Horse manure compost, nowadays, can have fresh straw and chicken manure; and horse manure can be added to so-called synthetic or artificial compost, which is really neither one nor the other. The Dutch, actually, also call it straw compost. At present straw compost is widely used in Ireland.
The idea of finding an alternative to horse manure compost started to take shape at the turn of twentieth century. As cars and tractors started to substitute horses in the countryside and in the city, the fear that horse manure was going to become scarce seized mushroom growers in the developed world. According to F.C. Atkins (1979: 91) artificial compost was developed in England in 1923 and first used to grow mushrooms in the USA, in 1927. It looks, however, that growers didn't start using artificial compost widely until after the end of WWII. It is only normal that the substitution of horse manure by compost started first and at a higher scale in the US as the motorisation of this country took place earlier and at a higher speed than in Europe. It also looks that US growers couldn't get enough manure from racetracks, hunting and polo clubs (Machuca 2004: 82-84).
In England and in Holland, however, horse manure was still highly popular in the 1970s and 1980s because racing horses and horses from riding schools could supply enough manure to the mushroom industry in both countries. The following table shows the amounts of different raw materials used for the total production of compost in Holland in 1985 (608,000 tonnes). The difference between the weight of the raw materials and the final weight of the compost is due to a different moister content (Gerrits 1988: 42):
We can see that the Dutch added a significant proportion of chicken manure. But the proportion between the different components could vary if, for example, horse manure became too scarce. Vedder (1978: 202) said that the compost centre of the Co-operative Dutch Mushroom Growers' Association (CNC) could mix up to 40 per cent of straw compost with horse manure and predicted that this percentage could increase in the future. The reason was because the supply of horse manure tended to be unsteady. Racing horses spent more time outdoors during the summer month and fed more on green fodder and less on straw. This factor alone provoked a shortage of horse manure during the summer months because of its lesser quality for mushroom growing (Vedder 1978: 167).
In the Republic of Ireland out of 30 growers only 2 were using synthetic compost at the end of the 1960s, and some were using a mixture of pig and fowl manure (Department of Agriculture and Fisheries, 1969: 14). Synthetic compost only started to replace horse compost during the 1980s. It is not clear which compost was of better quality, and opinions diverged. As I am not an expert, I won't take sides in technical matters. I would be rather inclined to think that opting for synthetic compost was mainly based on economic reasons. In Italy, Agrifung, a major custom compost maker, used mainly horse manure up until the mid 1970s, and then shifted to synthetic compost. Gerard Derks (1984: 63), one of Agrifung founders, said that synthetic compost was better for growers because it could be produced in a more homogenous way, but also added that the higher price and its scarcity was the main reason why they had to switch to synthetic compost.
The most positive thing about the use of horse manure, according to Vedder (1978: 167), however, had nothing to do with the quality of the compost, but with its eco-friendly recycling of agricultural waste:
Add to that an additional requirement of chicken manure and it becomes evident that mushroom growing is beneficial to the cleanliness of the environment, and is a factor in solving many of the problems arising from the organic manure produced by agriculture.
Vedder, however, seemed to forget that while mushroom growing takes waste from other agricultural industries, it produces a huge amount of waste - spent mushroom composts, most of which cannot be recycled.
Phase I The main components of straw compost are chicken manure, wheat straw[1], gypsum and water. The process does not differ much of that of making horse manure compost. Phase I for straw compost, however, takes longer, demands more skill and is more costly independently of the cost of the raw materials because the straw has to be softened, while the straw present in horse manure arrives already softened from the stables.
The pre-treatment of fresh straw also demands more labour and more skills than the sole fermentation of horse manure. Straw compost is more bulky and the straw must be cut and shred very finely to increase its capacity to absorb water. Therefore synthetic compost must be prepared on a larger scale to be as cost efficient as horse manure compost (Vedder 1978: 204).
The same considerations would apply to making horse manure compost if fresh straw is added to the horse manure. In that case, the straw has to undergo first a pre-treatment as well. But it would apply to a lesser extent since less fresh straw is used for compost based on horse manure to which straw must be added.
In order to be cost efficient, the composting centre of the Co-operative Dutch Mushroom Growers' Association (CNC) developed a straw processing machine for loosening up round bales of straw at a speed of 150 bales per hour in the 1980s. A fore-loader then pushed the straw into a liquid manure bath. Thus completed with the pre-treatment of the straw, another fore-loader took the straw to a trailer provided with a moving bottom chain that later emptied the straw into the manure (van As and van Dullemen 1988: 309-311). The whole process was fully mechanised and performed outdoors.
Compost turner (van As and van Dullemen)
Mechanisation of phase I did not end here. The piles of compost had to be stacked, turned and stacked again once every few days. This happened in the part of the composting yard covered with a simple roof to protect the piles against sunlight, dehydration, rain, snow and strong wind (Vedder 1978: 187). The CNC had in the 1980s a turning machine (the compost turner) with a capacity to turn and stack compost at 200 tonnes per hour. This machine could travel at a speed of 2 metres per minute through the pile. A remarkable machine considering that only a decade earlier Vedder had described two "modern" compost turners with turning capacities of 60 and 100 tonnes per hour. At the end of phase I, a fore-loader took the compost into loading machine with a capacity of 275 tonnes per hour to transfer the compost to the lorries, ready to go into the pasteurisation tunnel for phase II (van As and van Dullemen (1988: 315).
Gerrits gave a time frame of 24 days to complete the process just described (1988: 49). The pre-treatment of the straw would last 10 days. Tractors then mixed the pre-treated straw with horse manure and the mixture was wetted using fully automated mechanical devices. After seven days 100 kg of chicken manure and 25 kg of gypsum were added per tonne of manure; and the mixture was stacked. Seven days later the compost was ready for Phase II. During the last week the stack was turned only twice.
MacCanna (1984: 42) gave a schedule of 19 days for straw or synthetic compost and 13 days for horse manure compost. The difference lay in the schedule before the pile was stacked, which he reduced to 12 days in the case of straw compost and 5 days in the case of horse manure compost. The composting turning schedule was the same for straw and horse manure compost, i.e. 7 days. Vedder (1978: 197-205) gave an overall schedule of 23 days for straw compost and 13 days for horse manure compost.
Phase II After phase I, there was no difference in the way to carry on composting in relation to the origin, whether fresh straw or horse manure compost. The ways to carry on composting (phase II), however, differed because they were linked to the development of different mushroom growing systems. The old way to make compost, before Lambert, did not differentiate between phases I and II. It was a common practice that the whole process took place in the compost yard until the grower considered that the pile was ready for spawning. Then the beds were made in the growing area.
His discovery, however, was also based on the experience of US growers, who started to practice a period of final fermentation, "sweating out", in the mushroom beds around 1915 (Atkins 1979: 91). Vedder (1978:185) pointed out that the intention wasn't to carry on composting under controlled conditions (phase II) but to get rid of insects and mites, which were "sweated out" and came out to the surface, where they could be killed with insecticides. They also discovered that the quality of the compost improved in this way. If they were not carrying phase II out purposefully, at least they were doing it by happy accident.
The development of different systems for phase II, on the other hand, cannot be separated from the scientific developments in the field of composting and the role of state in the allocation of resources for research and economic development in agriculture. Without a doubt, Lambert's discovery of two distinct phases in composting constituted a landmark, a before and after in the world development of the mushroom industry. But it was also the product of a chain of previous, practices, research and developments in the industry.
In any case, once the community of growers acquired awareness through contacts with other growers or the advice of early mushroom consultants, and it became clear that yields increased in quality and quantity when composting continued in a special room (controlled peak-heating), different ways to perform phase II developed. The first practical consequence of changes in the way to carry on composting was the elevation of the level of skill and investment that growers needed to get it right; according to level of technical development of their time, that is.
Modern English tray farm, early 1980s (Rucklidge)
After an initial heating in the pile, composting had to continue in a special room, where the biological process could go on under controlled temperature and humidity. The objective of phase II was to finalise the biological process of conversions in the compost, in order to achieve a suitable base for the growth of mycelium and to kill all harmful organisms (Vedder 1978: 214, 219). Gerrits (1988: 30), more precisely, stated that the function of composting was to select nutrients that are suitable for the growth of the mushrooms, but less suitable for the growth of competitive organisms. Vedder, on the other hand, particularly emphasised the biological nature of the process of peak-heating, or controlled composting which phase II represents. He also attributed to technology the role of creating, and controlling, the conditions to allow the compost to undergo, in the best possible way, that biological process (214, 219): The results of a growing cycle are largely determined by whether correct or incorrect procedures are used during peak-heating. The process of peak-heating is not difficult: it depends mainly on the technical equipment available, and on very intensive control.
It is important that temperature, quantities of air used for ventilation and all other observations made, be recorded correctly so that deviations or mistakes can be recognized later Peak-heating is a biological process which promotes conversions in the compost through the activity of various types of thermophilic micro-organisms. The construction and the technical installations of a peak-heating room are important since the process can be influenced greatly by temperature control, humidity of the air, renewal of the air and distribution of the air in the room. The better the technical equipment, the better peak-heating can be controlled.
Modern English tray farm, early 1980s (Rucklidge)
There are two considerations to make here. The first, worth mentioning although not strictly relevant at this stage, is that composting, like farming, is a biological process. It admits mechanisation and high capital investment, but compost is not manufactured as a car is, nor as the tools and machinery that mushroom growers must acquire are. Yet, composting is not a biological process because straw and manure are organic matter (although they must be), but because of the thermophilic micro-organisms acting on it. Nature could be accelerated, by means of the micro-organisms, but it must, nevertheless, take its course.
Compost is also the soil of mushroom farming, but unlike the soil in tilling, for example, it can be bought, used and discharged in each different crop. A modern mushroom farm in Ireland, for example, doesn't depend on the fertility of the soil on which it stands. Actually, mushroom houses are built on concrete. These features will be fundamental to characterise mushroom farming within agriculture later on.
Tray handling line (MacCanna)
The second consideration is relevant for carrying out composting for commercial purposes, as a commodity to sell to the market or as an on-farm input in commercial mushroom growing: good composting for commercial purposes "depends mainly on the technical equipment available - [and] the construction and the technical installations of a peak-heating room." Based on this criterion, we can now trace the development of different methods to perform phase II.
The first method consisted in taking the compost to the growing room and to peak heat it there (the one-zone system) in wooden trays or shelves. It lasted between 5 and 7 days (Vedder 1978: 224). According to MacCanna (1984: 43), this system was the most common until the 1950s. The compost was consequently spawned and cased in the same trays. A later development, after the 1950s, consisted in the introduction of peak heating rooms (the two-zone system). MacCanna (1984: 43) mentions that, "economic pressures in the industry and a greater awareness of the requirement of compost at the different stages brought about the use of specialised rooms for the different functions." Small ridges covered with marl in Limburg, Holland, at the turn of the twentieth century (van Griensven)
Compost could achieve better quality and yields because the better insulation (to use supplementary heating as little as possible and thus save energy) and the better technical equipment of specialised peak heat room rendered more homogeneous compost. Since the time taken by each crop in the growing rooms was shortened, the number of crops could be increased. On the other hand, the trays in a peak heating room were less spaced than in a growing room, so the filling capacity was also higher. But it then became necessary to have a high fan capacity to guarantee sufficient air circulation in order to maintain a homogenous temperature and humidity throughout the room (MacCanna 1984: 45). Heating equipment was initially installed to help the compost to achieve the ideal temperature for pasteurisation (around 60 degrees for up to three hours) by pumping steam or dry heat if the compost was too wet (MacCanna 1984: 47, 51). Air filters increased the protection against pests and diseases (1984:48).
In the 1970s and 1980s, technological developments allowed the introduction of automatic controls, including computer control of Phase II, for an adequate control of air and compost temperature, humidity and ventilation. MacCanna (1984: 49), however, said that because of the strict atmospheric conditions to carry out phase II, it was also advisable to keep an independent monitoring manual system. Nowadays, modern mushrooms farms are equipped with environmental computer controls and, as we will see, they save labour time. But their efficiency is related to the size of the farm.
The more important capital investment in the two-zone-system, however, consisted in the mechanisation of filling and emptying the peak heating rooms. In large farms, growers also introduced mechanised filling lines to fill trays. The machinery compressed up to 150 kg of compost per m2, and forklifts took the trays to the peak heating room, where they were stacked 10 to 15 high, with only about 10 cm between them (MacCanna 1984: 50). This labour saving device became a normal practice in large farms in Britain (see picture). Yet, as it was costly, only large farms could afford it. In Holland, where small farms were the norm, the one zone system survived until the 1970s in farms. These growers bought phase I compost and then filled their growing rooms.
All these technical improvements, however, must have put at a severe disadvantage the one-zone way of carrying out phase II in tray farms throughout the 1950s and 1960s, and with it the smaller farms, which could not probably justify the capital investment needed to build special peak-heating rooms in order to get similar compost and maintain their competitiveness. That was particularly the case because at that time there was not a market for compost. Later we will see that small mushroom farms became a possibility in Ireland only in the 1980s when a market for compost was created. In fact until the late 1970s, there were just a handful of large tray farms making their own compost. Just over ten dominated the Irish mushroom industry. Something similar happened in Holland, although nearly 20 years earlier than in Ireland, when the creation of a cooperative to make compost in 1963 allowed the expansion of a Dutch industry based on small growers. Up to 1964, most Dutch growers prepared their own compost and that also lead to great variability in compost quality (Gerrits 1988: 42). The creation of a market for compost in Ireland and in Holland actually reversed in these countries the long-term tendency in commercial agriculture, including mushroom growing, towards bigger farms. But as we will see later, this counter-tendency was going to be short-lived.
The next breakthrough in Phase II was the commercial development of bulk pasteurisation in the 1970s in Italy and the Netherlands. Pasteurisation of compost in bulk, in specially designed tunnels, opened the way for the creation of a market for compost and the expansion of mushroom industries based on small growers in countries such as the Netherlands and Ireland. It was particularly in Ireland where the introduction of bulk pasteurisation completely changed the face of the mushroom industry. I will deal with bulk pasteurisation and spawn-run in bulk (phase III) in the next chapter.
References Atkins, Fred C. (1979) 'Landmarks in Cultural practices', The Mushroom Journal, no. 75. pp. 89-91
Atkins, Fred C. (1983) 'The History of Mushroom Growing in Great Britain', The Mushroom Journal, no. 125. pp. 169-171. Department of Agriculture and Fisheries (1969) Report of the Survey Team Established by the Minister for Agriculture and Fisheries on the Mushroom Industry, Dublin: The Stationary Office
Derks, Gerard (1984) 'Ten Years On"
Gerrits (1988) 'Nutrition and Compost' in van Griensven (ed.) The Cultivation of Mushrooms, Darlingtong Mushroom Laboratories Ltd. and Somycel S.A
MacCanna (1984) Commercial Mushroom Production, Dublin: An Foras Taluntais
Machuca, Milton Ricardo (2004) Catholic Here and There: Mexican Migration and the Roman Catholic Church in Southern Chester County, Pennsylvania, Ph.D. dissertation (unpublished), Pennsylvania State University.
Rucklidge, R. A. (1980) 'Modern Tray Plants', The Mushroom Journal, 85, pp. 29-34
van As and van Dullemen (1988) 'Mechanization and Equipment' in van Griensven (ed.) The Cultivation of Mushrooms, Darlingtong Mushroom Laboratories Ltd. and Somycel S.A
van Griensven (1988) 'History and Development' in L.J.L.D van Griensven (ed.) The Cultivation of Mushrooms, Darlingtong Mushroom Laboratories Ltd. and Somycel S.A
Vedder, P.J.C. (1978) Modern Mushroom Growing,
Educaboek - Culemborg, Netherland; Stanley Thornes - Cheltenham, England
Footnote [1] If wheat straw is not available, then rye, barley, or oat straw can substitute it. In Asia and Africa rice straw is cheaper and easier to obtain (Vedder 1978: 202).
