The effect of moisture content on fraction recovery and the development of a rapid field test for moisture determination of sod peat (sod moss and bin sods)

Peat fractions can be produced either by milling peat in the bog, or producing sod peat and breaking these sods into the desired fractions. Two types of sods exist: bin sods, and sod moss. Bin sods are produced by extrusion of peat, from more decomposed peat (H6-H7), and sod moss are sods cut directly from the bog, where less decomposed peat is used (H5-H6). Both sods are dried on the bog before being used the horticultural industry. The fractions produced from sods are more uniform compared to those from milled peat and they are reported to be more mechanically stable than fractions from milled peat However, experience has shown that considerable variation in fraction recovery can exist during the production of fractions from sods. In some cases, clean fractions are produced with very little fine particles, and in other cases, high volumes of fine particles are produced. There is some evidence to show that moisture content has a considerable bearing on the fraction recovery from sods. However, there is little or no information available other than anecdotal, on the effect of moisture content on the amount of fines generation during sod breakdown when forming fractions. In this study, the effect of moisture content of fractions from both sod moss and bin sods on fines generation were studied, under laboratory conditions. Moisture content was measured on the screened fractions. Sods were dried to various moisture levels (sod moss 30-80% and bin sods from 25 to 85% moisture content from two bogs). Resultant peat fractions from sod moss and bin sods (10-20 mm) were placed into a container with golf balls, and agitated in a cement mixer to simulate mechanical breakdown conditions. The fines generated were then determined by particle size determination using standard methods. There was a very strong correlation between fines generation and fraction moisture content in sods (r2=0.82 for sod moss and r2=0.80 for bin sods). An upper limit for moisture content of sod moss (54% v/v) and bin sods (62%) was then determined using the Cate-Nelson technique, that is the moisture content at which, when exceeded, high volumes of fines is generated. Subsequently, an accurate field test was developed for moisture determination. This cheap, quick and robust method ensures that only sods of the correct moisture content are used for fraction generation.