Mushroom production in Poland has exceeded 175 00 tons per year. Producing such a big amount requires huge quantities of both compost and casing soil. The latter has to be supplied all year round over a country as big as Poland. Poland has sufficient deposits of various sorts of peat to fulfil the demand for casing soil even if the pace of mushroom production increases. There’s one big problem though.

Although mushrooms have been grown in Poland since the 1960s, casing production industry dates back only to the 1990s. This time can be divided into three periods.

The first period started with the beginning of large-scale mushroom production and lasted up to the mid 1990s. During this period only frozen, dried and milled peat from high peat bogs was used. Each mushroom farm produced its own casing soil by mixing peat with lime and water and by pasteurizing it with steam.

The second period started at the beginning of the 1990s and is currently approaching its end. During this period the main material for casing soil production was peat from low peat bogs (fens), excavated locally in the areas neighbouring on mushroom farms. Initially casing was prepared individually in each mushroom farm. Fresh low peat was mixed with lime straight on the trailer. Next, it was milled and spread over the compost by hand and was not steam-sterilized beforehand. This manner of preparing casing soil was connected with an extremely dynamic growth of mushroom production for food processing industry in the 1990s and with the introduction of phase II compost in blocks.

Increasing demand for casing contributed to the appearance of the first industrial facility for casing soil production in 1992. The facility supplied the local market with casing soil in bulk, obtained by mixing low peat with spent sugar beet lime and formalin disinfected. In order to reach beyond the local market, casing started to be distributed in bags.

Fresh low peat is still an important casing ingredient, used in mushroom production for food processing industry. However, it is gradually losing its significance for two reasons. First, mushroom production for food processing industry is decreasing. Second, legal regulations put restrictions on excavating peat outside licensed sites. This type of casing soil is therefore bound to disappear completely.

The third period comprises the last five years and is marked by increasing use of ready-made casing soil and by dynamic growth of casing production industry. Polish facilities offer various types of casing, ranging from light to heavy, with different amounts of high and fresh low peat, mixed with sugar beet lime and not pressure sterilized. Phase III compost is more and more widely used, which entails an increase in the production of heavy casing, which is similar to Dutch casing and consists of high peat and sugar beet lime.

Types of casing

Currently there are five casing production facilities in Poland, two of them fulfilling 70 percent of demand on this market. Only one of them uses high peat imported from the ex-Soviet Union countries.

Three types of casing are produced in these facilities:

- Light – produced solely from the surface layers of low peat with up to 10 percent of sugar beet lime. This type is used to grow mushrooms for food processing industry. Thanks to light casing, mushrooms can be watered practically during all phases of growth;

- Medium – obtained mainly from all layers of low peat, with up to 20 percent of sugar beet lime. In order to improve water holding capacity of the casing, a small amount of high peat is added. This type of casing appeared when more mushrooms started to be produced for export and for the fresh market, with the use of phase II compost in blocks. This casing is mainly sold in plastic bags containing material sufficient for covering 0,5 or 1 square meter of compost.

- Heavy - this type of casing consists mainly of fresh high peat, with the addition of a small amount of low peat, mixed with 20 percent of sugar beet lime. This casing is usually supplied in plastic bags of the same capacity as bags for medium casing. It is also available in big bags and in bulk for mushroom growers spreading compost mechanically. Heavy casing is in growing demand thanks to its high water holding capacity, required for export mushrooms which are not watered while cultivating. This casing is watered only throughout the period following casing and between flushes.

Casing producers use fresh low peat and place mushroom production facilities near peat excavation sites, in this way managing to maintain low prices for their products. The prices equal the price of 1 kilo to 1,5 kilo of export mushroom. When casing is prepared by the mushroom grower with the use of low peat excavated locally, its price equals that of 0,5 kilo of class A mushroom for food processing industry. Transportation cost and type of packaging are also significant factors influencing the price of casing. As a result, the prices in Poland vary considerably and should be expected to increase. However, as the price of compost remains relatively high, it will continue to dominate the overall cost of mushroom growing.

Lack of uniformity

Hoe does such a system of casing production and supply influence the technology used for mushroom growing?

The basic problem stemming from this system is lack of uniformity of casing, obtained not only from different producers, but also from one producer only. Casing may differ in respect of peat and type of sugar beet lime (dry or wet), which entails difference in structure, water holding capacity and humidity. Differences are the least significant when comparing pH, although it has to be occasionally increased when there is the threat of green mould.

For mushroom growers the most important is varying humidity of casing, which may occur for the following reasons:

- The seasons; casing tends to be too dry in summer and too wet (and sometimes frozen) in winter, which hinders its spreading and giving it a proper structure;

- Placing of bags during transportation; the bags from the bottom are drier than those from the top, because the water is squeezed out from the lower layers of the shipment. The way the bags are placed also influences casing structure.

- Storage period at both the producer and supplier; the longer the casing is stored, the greater difference in humidity.

Necessary measures

The above problems did not matter greatly in the past, when Poland was mainly a producer of small mushrooms for food processing industry. Currently, however, mushrooms produced for the fresh market require that casing should be monitored for density and compression. As a result, mushroom growers need to take extra measures, such as the following:

- Monitoring the moisture level in each bag and supplying water whenever necessary;

- Preparing uniform casing for each tray/shelf, for example by mixing loose casing soil on a trail or in a pile;

- Drying the casing after it has been spread on a tray and levelling it by hand or mechanically so that the depth is uniform over the surface of the compost;

- Giving the casing a proper structure, while and after distributing it on a tray, by means of devices constructed specifically for this purpose;

- Maintaining a supply during winter, when the temperature drops far below zero.

Neglecting these measures may bring about an irregular growth of rhizomorphs and primordia. In extreme cases, pinning pattern may reflect differing casing characteristics from various bags. As a result, it could be difficult to establish the moment of shock and cause differences in crop density. Lack of casing uniformity can be burdensome, particularly because the majority of casing is spread by hand, often directly from the bags.

The near future

How is this sector of the Polish mushroom industry going to develop?

A significant increase in production should not be expected, as mushroom growing for food processing industry is decreasing. For the same reason the demand for heavy casing supplied in bulk or in big bags will grow. Its price will gradually rise, for the possibilities to open new casing production facilities are limited and the fee for the license to excavate peat is also on the increase.

The most important challenge is the standardization of casing. This factor will be decisive in determining the demand for casing from different facilities.