Wheat straw is about 40% cellulose, 40% hemi-cellulose, and 15% lignin. The cellulose and some of the hemi-cellulose it what is digestible by cattle but the lignin is what keeps it all together. Hay has less lignin, usually less than 10%, while wood has more, usually over 25%. So wheat straw is somewhere in between hay and wood in structure content. Straw also has 11 lbs of nitrogen, 3 lbs of phosphorus, 15 lbs of potassium, and 2 lbs of sulfur per ton and the average wheat harvest leaves 2.5 tons of straw per acre. Nearly half of wheat straw is carbon. It’s a far cry from alfalfa but burning in the field will take half of the nitrogen and sulfur and leave the soil bare, risking erosion of soil with the phosphorus and potassium ash with it.