Chapter Cropping in peat moss and other organic media

Peat is lightweight and provides good water-holding capacity, drainage, aeration, and biological and chemical stability. Furthermore, peat is an abundant resource in Canada and therefore is readily available. It has been used alone or in combination with other materials such as vermiculite, perlite, turface, polystyrene beads, and other materials, in a variety of mixtures with diverse physical characteristics. In addition to a high water-holding capacity, peat moss has a high cation-exchange capacity and maintains an adequate structure during cropping. Horticultural-grade vermiculite releases some potassium and magnesium during the crop season, which could be more problematic than beneficial because of reduced control over the availability of those nutrients. However, vermiculite has a high cation-exchange capacity, which increases the buffering capacity of the mix and thus reduces the risk of overfertilization. On the other hand, perlite, turface, and Styrofoam beads are completely inert and do not affect the nutrient availability in the mix other than by improving the degree of aeration; these materials are now preferred because they do not break down as quickly as vermiculite and they allow for more exact nutrition of the crop. Recent research has indicated that the porosity of peat plus perlite declines readily over time but the porosity of peat plus polysterene does not. Although polysterene effectively increases the air content of the substrate, a great deal of that air-in the polysterene beads themselves-is not useful to the plants. Sand also behaves almost as an inert material and has been used extensively in the past, but like any soil it is not recommended unless sterilized. In contrast, perlite, vermiculite, turface, and Styrofoam beads are sterile on delivery because of the high temperatures used during their manufacture.

In addition to peat, sawdust is also an important organic medium for tomato cropping, especially in Canada. However, this system is described only in general terms, in a later section, because it has already been treated in detail in other publications.

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