Humus soils structure

Sjoberg, G., Knicker, H., Nilsson, S. I., and Berggren, D. (2004). Impact of long-term N fertilization on the structural composition of spruce litter and mor humus. Soil Biol. Biochem. 36, 609-618. 

Humus degradation Internal Direct Indirect Disturbance of soil structure and associated disaggregation Degradation of recalcitrant organic compounds aided by obligate or facultative symbionts... 

Although humus constitutes, generally, only a small part of the soil (below 10%), it exerts a profound influence on the physical, chemical, and biological properties of the soil. Attempts have been made to attribute particular influences to specific compounds in humus. The observation of the ameliorative effect of polysaccharides on soil structure has greatly stimulated research on the nature of soil carbohydrates. 

Humus affects soil structure and thus soil tilth, aeration, and moisture retention. The deterioration of structure that accompanies intensive tillage is usually less severe in soils adequately supplied with humus. When humus is lost, soils tend to become hard, compact, and cloddy. 

Ca is needed in greater quantities for the soil itself than as nutrient for plants. In particular, the soil structure and biological activity are a function of the Ca-content. Humus, as a mixture of organic acids, is transformed by lime to Ca humate, which is insoluble. Also in the case of clay, Ca is bound to a higher content than the other basic ions. Only in add soils is Ca exchanged by Al. 

Soil crumbs owe their stability in part to the presence of naturally occurring polymeric materials (humus), which bind to the soil. The first synthetic polymers to improve soil structure and enhance crop growth were introduced in 1951. The results of incorporating polymers into soil were spectacular, but the dose rates required made their use uneconomical. 

The first stage consists of the breakup of the soil structure under the mechanical action of water drops and the removal of the cementing bases, humus, and colloidal particles. 

Long-term grasslands provide plenty of organic matter for humus formation. If the soil is not acidic or waterlogged, the soil fauna and flora create humus and the subsequent useful development of a porous crumb and granular structure. Porosity encourages root growth and the uptake of soil nutrients. 

Many researchers have attempted to unravel the mystery of the structure of humus. One approach has been to isolate fractions by extracting humus using various extraction procedures. These procedures result in the isolation of three or more fractions humic acid, fulvic acid, and humin. Humic material is isolated from soil by treating it with alkali. The insoluble material remaining after this treatment is called humin. The alkali solution is acidified to a pH of 1.0 and the precipitate is called humic acid, while the soluble... 

These results suggest that pure aromatic polyesters may function like the long-lived components in humus and may provide useful properties as a soil additive. Grass sod growing studies using municipal-waste-derived compost in combination with chopped plastic fibers demonstrated improved growing rate and root structure development to accelerate sod production. 

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