Sod peat is machine- cut and air-dried in blocks (sods). Its structure remains fully intact. After a drying period of one year with repeated restacking, the water content has dropped to approximately 50 to 60 weight per cent, allowing the peat to be processed.
Milled peat is harvested by removing a layer just a few centimetres thick from the peat body and turning it several times. Once a certain degree of dryness has been reached, the peat is collected and gathered into ridges. Milled peat has a higher percentage of fine material. Milled peat can only be extracted in good weather. The peat will dry to a water content of 50 to 60 weight per cent in a single day.
Drying is a key factor in white peat extraction. The degree of dryness determines the peat’s water capacity. If the degree of dryness is high, the peat has a lower water capacity and good drainage. If the degree of dryness is low, peat with the same degree of decomposition will have a higher water capacity. In contrast, in the case of frozen black peat, the key factor determining the peat’s water capacity is the degree of freezing.
Black peat (frozen):
Black peat is extracted using a scraper excavator and deposited on the field in a thin layer in the autumn. It must freeze hard in the winter to allow the ice to force open the peat colloids. The freezing process results in a good water capacity of at least 400 g of water per 100 g of organic mass. Once dried to a water content of approximately 65 weight per cent, the black peat can be harvested and processed in early summer.
In some cases, the peat can self-heat while being stored in heaps before processing. Self-heating will change the peat’s properties and cause the peat to produce a typical heating smell that is reminiscent of lovage. Self-heated peat may not be used in substrate production. For this reason, the soil operations constantly monitor the temperatures in the storage heaps.
Peat extraction and conservation of nature:
Environmental organisations have repeatedly criticised peat extraction in recent years, and they still do. However, nature conservation legislation is now in place in Germany to regulate peat extraction. New extraction sites may only be exploited after permission has been obtained from the local government’s nature conservation authority. These new sites comprise land that was drained around the turn of the 20th century or after World War II and has been dedicated to agricultural use since.
Intact bogs are protected by German nature conservation legislation and will not be authorised for peat extraction. These laws require a layer of at least 50 cm of natural peat to remain after peat has been extracted so that the land can be re-watered. Over the past few years, exhaustive research has been carried out on peat substitute products to reduce the consumption of peat. The valuable peat should be used as intelligently as possible.