Soil organic matter decay

Aluminium in soils is closely connected to soil acidity and is also discussed in the chapters on acid soils and ion-water reactions. The acidity of acid soils is due to the reactions of water with exchangeable Al3+ on the surface of soil particles. The strong Al-water reaction repels H+ from the water molecules iuto the soil solution. This can create soil acidities as low as pH 4.5. Stronger acidity means other H+-yielding reactions—organic acids from soil organic matter decay, sulfur and sulfide oxidation, phosphate fertilizers, ammonia oxidation, acid rain, and Fe- and Mn-water reactions—are active. 

Several processes act to increase soil acidity. As organic matter decays, it forms many organic carboxylic acids. Peat moss, for example, is entirely organic and has quite low pH, around 4. Acid rain, the result of... 

Soil Biomass Soil Organic Matter Soluble Organic P Decaying Plant Residues... 

Soil organic matter is a product of the decay of plants and animals. It usually includes a large number of things in various stages of decomposition. Most plant and animal materials break down rapidly at first, then more slowly as the easily decomposed parts disappear. All of these plant and animal residues are collectively referred to as organic matter. The fraction of organic matter in a relatively advanced state of decay, now decaying only slowly, may be referred to as humus. 

When organic matter decays, say, in the soil of cattle yards and stables, ammonia and ammonium compounds are produced by the action of certain bacteria. If the soil be fairly dry, but not too dry, a white scum appears on the exposed surface. The scum is made up of small crystals of potassium nitrate and, after a time, if the soil be extracted with water and strained, the liquid, on evaporation, furnishes yellowish-brown crystals of crude nitre. The crude nitre can be purified by resolution and crystallization. The white efflorescence sometimes seen on the walls of stables, etc., is sometimes, though not always, due to the formation of nitrates in this way. 

Melillo, J. M., Aber, J. D., Linkins, A. E., Ricca, A.,Fry, B., and Nadelhoffer, K. J. (1989). Carbon and nitrogen dynamics along the decay continuum plant litter to soil organic matter. Plant Soil 115,189-198. 

Van Bergen P. F., Nott C. J., Bull 1. D., Poulton P. R., and Evershed R. P. (1998) Organic geochemical studies of soils from the Rothamsted Classical Experiments IV. Preliminary results from a study of the effect of soil pH on organic matter decay. Org. Geochem. 29(5-7), 1779-1795. 

The chemical composition of atmospheric depositions reflects the types and rates of biogeochemical reactions in the troposphere. These chemical compositions change seriously after interactions with humid acids of the soil layer, higherplant metabolites, and soil microbes. Carbon dioxide, the end product of any organic matter decay, is readily soluble in water to yield carbonic acid, the dissociation of which... 

Solutes, electrolytes, and nonelectrolytes in the soil solution are the immediate sources of the elements required by plants for growth. This supply can be continuously renewed by the many mechanisms of ion-soil interaction that remove and add ions in the soil solution (1) mineral weathering, (2) organic matter decay, (3) rain, (4) irrigation waters containing salts, (5) fertilization, and (6) release of ions retained by the colloid or clay fraction of soils. 

Soils retain K+ more strongly than Na+, because the hydrated K ion is smaller than the hydrated Na ion. In addition, K fits well between the sheets of several soil clay minerals, while Na does not, so K is retained strongly in soils containing these clay minerals. The K concentration in soil solutions is low but is replenished by K diffusion from between the sheets of these clay minerals, from the slower weathering of K-containing feldspar minerals, and from the decay of soil organic matter. 

The rates of soil phosphate reactions also may differ from the rates of phosphate uptake by plants and of phosphate release by organic matter decay. This phosphate turnover would further upset soil phosphate equilibria. If a steady state (concentration is constant with time) existed between the soil and dissolved phosphate ions, it might be described by a reaction such as... 

Soil organic matter has over the centuries been considered by many as an elixir of life - in this case of plant life. Ever since the dawn of history, some eight thousand or more years ago, man has appreciated the fact that dark soils, commonly found chiefly in the river valleys and broad level plains, are usually (but not always) productive soils. He also realized at a very early date that color and productivity are commonly associated with organic matter derived chiefly from decaying plant materials. 

Soil organic matter is not known to play any appreciable role in either the spread or control of air-borne virus diseases. This is an obvious statement since these viruses are obligate parasites on green plants and the vectors are insects. There is more likelihood that soil organic matter plays a role, even if a minor one, in soil-borne virus diseases since the vectors are nematodes, fungi and probably other forms of life that feed in part on decaying crop residues. 

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