All living plants will die, become dry plant material and eventually become soil organic matter. Dry plant material is about half carbon (C), which was derived originally from the carbon dioxide (CO2) of the air. In the live plants the carbon dioxide is combined with hydrogen (H), oxygen (O), nitrogen (N), and smaller amounts of 12 other elements that are essential to plant life. There are many thousand of different combinations of these elements in live plants. The names given to some of the most abundant ones are plant sugars, proteins, cellulose, hemicellulose and lignin. During the decomposition of dead plants, much of the carbon is "burnt" to become carbon dioxide once again, and so returns to the atmosphere for re-use by other living plants. Much of the hydrogen is "burrnt" to water, and so returns for re-use by other living plalnts. Of the carbon taken by the microorganisms at each "bite", about 20-40% goes to make more microorganisms. A few percent is converted to humus. The rest is given off as carbon dioxide. Nature does not waste anything. Then the whole cycle starts all over again. - Millet