02128nam a2200229 a 450000100080000000500110000800800410001910000290006024500610008926000460015030000100019649000230020650000360022952015430026565000090180865000200181765000110183765000090184865300110185765300110186865300190187916214841996-01-24       1977    bl uuuu  m   00u1 u    #d1 aLINHARES, L. F. de T. L.  aMicrobial synthesis in relation to soil humus formation.  aRiverside: University of Californiac1977  a114p.  aTese de Doutorado.  aOrientada por: James P. Martin.  aSoil organic matter consists of plant, animal and microbial residues, fresh and at all stages of decomposition, and the relatively resistant, dark brown to black humus. Although constituting only about 1 to 10% of most agricultural soils, this organic fraction has been, since the dawn of history, a key to soil fertility and productivity. About two centuries have been devoted to studies of the nature, origin and properties of humus, but progress has been slow. This has not been due to failure in making use of advanced technology, but to the inherent complexity of humic polymers. Humus constitutes about 85% or more of soil organic matter. It is a natural product of the soil environment and is formed during the biological decomposition of organic residues. Generally about 15 to 30% of the original residue carbon remains in the soil after one year. A small part is in the more resistant cell structures of the soil organisms, but the major portion is present in new humus. Humus, however, does not usually accumulate in the soil under natural conditions, as the annual additions are balanced by the losses. This process confers to humus a state of dynamic equilibrium which maintains a constant amount of organic matter in a particular soil under a given set of environmental conditions. Based on differences in solubility in alkali and acid, humus can be separated into three main fractions: humic acids, fulvic acids and humins. The humins are not soluble in dilute alkali (0.1 to 0.5 N NaOH), the humic acids are soluble in ...  asoil  aAdubo Orgânico  aHúmus  aSolo  aFungis  aFungos  aOrganic manure