Rodale Press, publisher of Organic Gardening magazine is located in Pennsylvania where steel mills abound.  Having more experience with slag, Rodale advises the user to be alert to the fact that some contain little in the way of useful nutrients and/or may contain excessive amounts of sulfur.  Large quantities of sulfur can acidify soil.  Read the analysis on the label.  Agriculturally useful slag has an average composition of 40 percent calcium and 5 percent magnesium.  It must also be very finely ground to be effective.  See also:  Lime and Rock dust.

Beet wastes, like bagasse, are a residue of extracting sugar.  They have commercial value as livestock feed and are sold as dry pulp in feed stores located near regions where sugar beets are grown.  Their C/N is in the vicinity of 20:1 and they may contain high levels of potassium, reaching as much as 4 percent.

Brewery wastes. Both spent hops (dried flowers and leaves) and malt (sprouted barley and often other grains) are potent nutrient sources with low C/N ratios.  Spent malt is especially potent because brewers extract all the starches and convert them to sugar, but consider the proteins as waste because proteins in the brew make it cloudy and opaque.  Hops may be easier to get.  Malt has uses as animal feed and may be contracted for by some local feedlot or farmer.  These materials will be wet, heavy and frutily odoriferous (though not unpleasantly so) and you will want to incorporate them into your compost pile immediately.

Buckwheat hulls. Buckwheat is a grain grown in the northeastern United States and Canada.  Adapted to poor, droughty soils, the crop is often grown as a green manure.  The seeds are enclosed in a thin-walled, brown to black fibrous hulls that are removed at a groat mill.  Buckwheat hulls are light, springy, and airy.  They’ll help fluff up a compost heap.  Buckwheat hulls are popular as a mulch because they adsorb moisture easily, look attractive, and stay in place.  Their C/N is high.  Oat and rice hulls are similar products.

Canola meal. See:  Cottonseed meal.

Castor pomace is pulp left after castor oil has been squeezed from castor bean seeds.  Like other oil seed residues it is very high in nitrogen, rich in other plant nutrients, particularly phosphorus, Castor pomace may be available in the deep South; it makes a fine substitute for animal manure.

Citrus wastes may be available to gardeners living near industrial processors of orange, lemon, and grapefruit.  In those regions, dried citrus pulp may also be available in feed stores.  Dried orange skins contain about 3 percent phosphorus and 27 percent potassium.  Lemons are a little higher in phosphorus but lower in potassium.  Fruit culls would have a similar nutrient ratio on a dry weight basis, but they are largely water.  Large quantities of culls could be useful to hydrate stubbornly dry materials like straw or sawdust.