You can safely compost any plant material, if and only if, you do it correctly and let it aerobically compost long enough. Don't worry about any poisonous or potential toxins in any "greens" or "browns" materials. I compost all kinds of toxin plants, weedy and seedy plants, and high protein meats, and other forms of plant and animal wastes when I can get it! Aerobic composting is nature's way to neutralize and sterile biodegradable materials. I would suggest composting this stuff in small portions per week, in a large compost pile consisting of conservative greens and browns (i.e. grass clippings, leaves, straw, food scraps, etc.). Keep the pile moisturized and aerated often. NOTE: Keep in mind that composting is about moderation and balance! Also you can experiment by adding sugary substances like dry molasses, old soft drinks, etc., in the pile in order to increase microbial growth in the pile. This will both speed up decomposition and increase internal heating. The extra heat from the microbial growth will also help break down mild toxins and pathogens. Normally you can safely compost conservative greens and browns in 1-2 months in an active hot compost pile, or 6-12 months in a passive cold or static compost pile. If you have concerns about the timing of your compost pile decomposition, go an extra 1-3 months if necessary. It won't hurt anything. Actually it is a smart thing to do! Hope this helps. Happy Gardening!

I think, ultimately you're asking about the relative bio-availability of a given substance relational to it's primary consumer. Or, in other words, how easily digestible is a given substance... I don't know if a definitive list has ever been produced because of the hard to quantify variables would be very difficult to control. That being said, I don't really know beyond to say generally that the real key is surface area. A piece of watermelon rind, whole, takes infinitely longer to decompose than another piece that was run through a food processor.

Back in World Wide Web infancy, a company called Primal Seeds published the following list called "The NPK of Stuff." It's no longer on the webs, but here is the list. This will help y'all adjust your compost piles. Alfalfa hay 2.45 0.5 2.1 Apple fruit 0.05 0.02 0.1 Apple leaves 1 0.15 0.35 Apple pomace 0.2 0.02 0.15 Apple skin (ash) 0.0 3.08 11.74 Banana skin (ash) 0.0 3.25 41.76 Banana stalk (ash) 0.0 2.34 49.4 Barley (grain) 1.75 0.75 0.5 Bat guano 6 9 0.0 Bean and pod 0.25 0.08 0.3 Beet waste 0.4 0.4 3 Beet waste (root) 0.25 0.1 0.5 Blood meal 15 1.3 0.7 Bone meal 4 21 0.2 Bone (ground and burned) 0.0 34.7 0.0 Brewer's grains (wet) 0.9 0.5 0.05 Brigham tea (ash) 0.0 0.0 5.94 Cantaloupe rind (ash) 0.0 9.77 12.21 Castor bean pomace 5.5 2.25 1.13 Cattail reed & water lilly 2.02 0.81 3.43 Cattail seed 0.98 0.39 1.71 Chicken manure 1.63 1.54 0.85 Coal ash (anthracite) 0.0 0.125 0.125 Coal ash (bituminous) 0.0 0.45 0.45 Cocoa shell dust 1.04 1.49 2.71 Coffee grounds 2.08 0.32 0.28 Coffee grounds (dried) 1.99 0.36 0.67 Corn (grain) 1.65 0.65 0.4 Corn (green forage) 0.3 0.13 0.33 Corncob (ground, charred) 0.0 0.0 2.01 Corncob (ash) 0.0 0.0 50 Cotton seed 3.15 1.25 1.15 Cottonseed meal 7 2.5 1.5 Cottonseed-hull (ash) 0.0 8.7 23.93 Cotton waste 1.32 0.45 0.36 Cow manure (fresh) 0.29 0.17 0.1 Cowpea, green forage 0.45 0.12 0.45 Cowpes, seed 3.1 1 1.2 Crab (common) 1.95 3.6 0.2 Crab (king, dried and ground) 10 0.25 0.06 Crab (king, fresh) 2.3 0.0 0.0 Crabgrass 0.66 0.19 0.71 Cucumber skin (ash) 0.0 11.28 27.2 Dog manure (fresh) 1.97 9.95 0.3 Duck manure (fresh) 1.12 1.44 0.49 Egg 2.25 0.4 0.15 Eggshell (burned) 0.0 0.43 0.29 Eggshell 1.19 0.38 0.14 Feather 15.3 0.0 0.0 Felt hat factory waste 3.8 0.0 0.98 Field bean (seed) 4 1.2 1.3 Field bean (shell) 1.7 0.3 1.3 Fish scrap (red snapper) 7.76 13 0.38 Fish scrap (fresh) 6.5 3.75 0.0 Greasewood (ash) 0.0 0.0 12.61 Gluten feed 4.5 0.0 0.0 Greensand 0.0 1.5 5 Grape leaves 0.45 0.1 0.35 Grapes (fruit) 0.15 0.07 0.3 Grapefruit skin (ash) 0.0 3.58 30.6 Hair 14 0.0 0.0 Hare and rabbit waste 7 2.4 0.6 Hoof meal and horn dust 12.5 1.75 0.0 Horse manure (fresh) 0.44 0.17 0.35 Incinerator ash 0.24 5.15 2.33 Jellyfish (dried) 4.6 0.0 0.0 Leather (acidulated) 7.5 0.0 0.0 Leather (ground) 11 0.0 0.0 Leather (ash) 0.0 2.16 0.35 Lemon cull 0.15 0.06 0.26 Lemon skin 0.0 6.3 31 Lobster (refuse) 4.5 3.5 0.0 Lobster (shell) 4.6 3.52 0.0 Milk 0.5 0.3 0.18 Mud (fresh water) 1.37 0.26 0.22 Mud (harbour) 0.99 0.77 0.05 Mussel 0.9 0.12 0.13 Mussel mud (dried) 0.72 0.35 0.0 Molasses residue (brewing) 0.7 0.0 5.32 Moss 0.6 0.1 0.55 Oak leaf 0.8 0.35 0.15 Oats grain 2 0.8 0.6 Olive pomace 1.15 0.78 1.26 Olive refuse 1.22 0.18 0.32 Orange cull 0.2 0.13 0.21 Orange skin (ash) 0.0 2.9 27 Oyster shell 0.36 10.38 0.09 Paint processing waste 0.02 39.5 0.0 Pea pod (ash) 0.0 1.79 9 Peach leaf 0.9 0.15 0.6 Peanut (seed & kernel) 3.6 0.7 4.5 Peanut shell 0.8 0.15 0.5 Peanut shell (ash) 0.0 1.23 6.45 Pigeon manure (fresh) 4.19 2.24 1.41 Pig manue (fresh) 0.6 0.41 0.13 Pigweed (rough) 0.6 0.16 0.0 Pine needle 0.46 0.12 0.03 Potato (tuber) 0.35 0.15 0.5 Potato (leaf and stalk) 0.6 0.15 0.45 Potato skin (ash) 0.0 5.18 27.5 Poudrette 1.46 3.68 0.48 Powderworks waste 2.5 0.0 17 Prune refuse 0.18 0.7 0.31 Pumpkin (fresh) 0.16 0.07 0.26 Pumpkin seed 0.87 0.5 0.45 Rabbit brush (ash) 0.0 0.0 13.04 Ragweed 0.76 0.26 0.0 Redtop hay 1.2 0.35 1 Rhubarb stem 0.1 0.04 0.35 Rockweed 1.9 0.25 3.68 Rose (flower) 0.3 0.1 0.4 Salt-marsh hay 1.1 0.25 0.75 Salt mud 0.4 0.0 0.0 Sardine scrap 7.97 7.11 0.0 Seawood 1.68 0.75 4.93 Sheep manure (fresh) 0.55 0.31 0.15 Shoddy and felt 8 0.0 0.0 Shrimp head (dried) 7.82 4.2 0.0 Shrimp waste 2.87 9.95 0.0 Silt waste 9.5 0.0 0.0 Silk mill waste 8.37 1.14 0.12 Silk worm cocoon 9.42 1.82 1.08 Sludge 2 1.9 0.3 Sludge (activated) 5 3.25 0.6 Sludge from sewer beds 0.74 0.33 0.24 Soot from chimney fllue 5.25 1.05 0.35 Starfish 1.8 0.2 0.25 Sunflower seed 2.25 1.25 0.79 Sugar (raw, residue) 1.14 8.33 0.0 Sweet potato skins (ash) 0.0 3.29 13.89 Sweet potato 0.25 0.1 0.5 Tanbark (ash) 0.0 0.34 3.8 Tanbark ash (spent) 0.0 1.75 2 Tankage 6 5 0.0 Tea grounds 4.15 0.62 0.4 Tea leaves (ash) 0.0 1.6 0.44 Timothy hay 1.25 0.55 1 Tobacco leaves 4 0.5 6 Tobacco stalk 3.7 0.65 4.5 Tobacco stem 2.5 0.9 7 Tomato fruit 0.2 0.07 0.35 Tomato leaves 0.35 0.1 0.4 Tomato stalk 0.35 0.1 0.5 Wheat, bran 2.65 2.9 1.6 Wheat grain 2 0.85 0.5 Wheat straw 0.5 0.15 0.6 White clover (green) 0.5 0.2 0.3 White sage (ash) 0.0 0.0 13.77 Wood ash (leached) 0.0 1.25 2 Wood ash (unleached) 0.0 1.5 7 Wool waste 5.5 3 2

The difference is, I believe, and in very non-scientific terms, that autumn leaves are dead before they fall and nutrients have been recouped by the tree whereas dried grass was still alive when cut and nutrients are preserved by the drying process. If the grass was already dead before cutting, then it would be carbon rich i.e. brown.