This section is from the book "Commercial Gardening Vol1", by John Weathers (the Editor). Also available from Amazon: Commercial Gardening, A Practical & Scientific Treatise For Market Gardeners.
Rape cake is largely used by some agriculturists not only as a manure but also as a wireworm catcher. Rape cake contains a certain amount of oil, but of late years this has been almost entirely extracted, and the cake is made up into the form of meal. As a manure it is chiefly valuable for its nitrogen, 1 ton containing about 100 lb. There are also smaller quantities of phosphates, potash, and lime present, thus making rape cake and rape dust a complete if not very rich manure. It is useful as a topdressing at the rate of 1/2 ton to the acre; or it may be dug or hoed in.