Soil organic matter decomposition rate

Happen J. D. and Chanton J. P. (1993) Carbon remineralization in a North Florida swamp forest effects of water level on the pathways and rates of soil organic matter decomposition. Global Biogeochem. Cycles 7, 475 -490. 

In wetland soils, organic matter decomposition is frequently limited by electron acceptor availability, rather than carbon availability as in upland ecosystems. The concentration and type of electron acceptors available in soils determine the types of microbial communities involved and the rate of decomposition process. Much of the detrital matter produced in wetlands is deposited on the soil surface. It is unlikely that there is enough oxygen in this matrix to decompose this material. Therefore, the decomposition of detrital matter is also dependent on the activity of anaerobic microorganisms using alternate electron acceptors. Similarly, the rate of organic matter decomposition in soils is dependent on the availability of electron acceptors (see for discussion in Chapters 3 and 4). 

An increase in the supply of fertilizer N can, in turn, result in an increase or decrease in below-ground C production, depending on the experimental conditions and plant species used. At high N rates, the decomposition of native. soil organic matter seemed lowered (conserving effect), as reflected by the decrease in the rate of respiration of unlabeled soil-C, both in crop (90) and forest soils (108,109). 

Soil minerals play a stabilizing role in organic matter. The Al and Fe that complex and stabilize organic matter against microbial decomposition are released from soil minerals during soil formation. The supply rates apparently control the content of soil organic matter to a great extent. This is demonstrated by the relationship between pyrophosphate-extractable C and pyrophosphate-extractable Al plus Fe (Wada 1995). 

Chen QQ, Sun YM, Shen CD, Peng SL, Yi WX, Li ZA, Jiang MT (2002b) Organic matter turnover rates and CO2 flux from organic matter decomposition of mountain soil profiles in the subtropical area, south China. Catena 49 217-229... 

Evidently rates of decomposition are greater than expected for simple anaerobic decomposition. Figure 3.10 shows comparable rates of organic matter decomposition in soils that were kept continuously flooded or well-drained under otherwise similar, tropical conditions for 3-4years (Neue and Scharpenseel, 1987). Clearly,... 

Gunapala, N., Venette, R.C., Feris, H. and Scow, K.M. 1998. Effects of soil management history on the rate of organic matter decomposition. Soil Biology and Biochemistry 30 1917-1927. 

Production of roots on top of the mineral soil has been explained as a consequence of the low nutrient availability in Amazon forests (Herrera et al. 1978, Cuevas and Medina 1983, Medina and Cuevas 1989). Vertical root distribution results from differential nutrient availability in the soil profile (Berish 1982, Berish and Ewel 1988). Shallow rooted systems may be a result of litter and soil organic matter production and decomposition rates in systems where nutrient input from litter exceeds that of nutrient release by soil weathering, as is the case of Ca, Mg, and P in terra firme forests (Medina and Cuevas 1989). In the Middle Caqueta region of Colombia, for example, Ca and Mg concentrations in the L and F layers are between 15 and 20 times higher than in the mineral soil (Duivenvoorden and Lips 1995). 

The soil organic matter of cleared tropical forest contributes substantially to atmosphere CO2 About 25% of organic carbon is lost from forest soils within 12 months of clearance (Miller et d., 1982). When it is considered that a typical forest soil contains over 100 ha of organic matter in the first 30 cm and about the same amount from the 30-100 cm horizon (Klinge, 1976) then it is clear that the potential production of CO2 is very high. Ewell et d. (1981) studied slash and bum technique at a Cost Rican wet forest site. They found that after burning, the forest soil evolved CO2 at such a rate that after 154 days decomposition and respiration as much C would be released into the atmosphere as was released by the burn. 

Since the phenoxyalkanoic acid herbicides are degraded in the soil by biological processes, factors that affect microbial activity will directly affect their breakdown. Soil pH, soil type, soil organic matter, herbicide formulation, and herbicide concentration can all influence the rate of microbial decomposition ( 4, 5). Greater effects are experienced with moisture and temperature, since these factors have a profound influence on microbial activity and thus on herbicide breakdown (4 5). It has been concluded ( 5), that soil temperature above 10°C and moistures above the wilting point are necessary for biological degradation of phenoxyalkanoic acids. 

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