Soil organic carbon input

Figure 2.1. Diagram of factors controlling the main inputs and outputs of soil carbon, superimposed over a global map of soil organic carbon stocks. DOC, POC, and DIC stand for dissolved organic C, particulate organic C, and dissolved inorganic C, respectively. The background soil organic carbon (SOC) map (Miller Projection 1 100,000,000). See color insert. Reprinted from Davidson, E. A., and Janssens, I. A. (2006). Temperature sensitivity of soil carbon decomposition and feedbacks to climate change. Nature 440,165-173, with permission from Macmillan.

Long-term cultivation and cropping of native grassland soils in North America without phosphorus inputs has been shown to result in a marked decrease in soil organic carbon and phosphorus. For example, Tiessen and Stewart (1983) found that similar decreases in organic carbon and organic... 

Input rates of organic C into the soil system are hard to quantify, particularly for natural ecosystems and to a lesser extent for agricultural ecosystems. Whereas quantity and quality of carbon inputs via litter fall and plant residues after harvest might be directly measurable, inputs via roots and rhizodeposition are more difficult to assess. 

The quantification of gross root production, rhizodeposition, microbial assimilation, and the production of organic materials in soil has made increasing progress ever since stable ( C) and radioactive ( C) carbon isotopes have been used (see Chap. 12). Measurements of soil organic matter dynamics without these isotopes are difficult due to the large amount present as compared to the smaller rates of input. 

Several authors have applied in situ pulse labeling of plants (grasses and crops) with C-CO2 under field conditions with the objective of quantifying the gross annual fluxes of carbon (net assimilation, shoot and root turnover, and decomposition) in production grasslands and so assess the net input of carbon (total input minus root respiration minus microbial respiration on the basis of rhizodeposition and soil organic matter) and carbon fixation in soil under ambient climatic conditions in the field. 

Important, poorly-constrained variables in this carbon balance include temporal and spatial variations in precipitation and RO DIC, carbonate dust, and pedogenic carbonate and soil C02. In addition, ocean and lake response to river carbon input is not well known. Although marine and freshwater aquatic organisms can be fertilized by increases in N, P, Si, Fe, Zn and C02 (Cassar et al. 2004 Zondervan 2007), it is not clear how much of the... 

Kuzyakov Y, Cheng W (2001) Photosynthesis controls of rhizosphere respiration and organic matter decomposition. Soil Biol Biochem 33 1915-1925 Kuzyakov Y, Domanski G (2000) Carbon inputs by plants into the soil. Rev J Plant Nutr Soil Sci 163 421—431... 

Compared to baseline levels, soil organic C and N increased by 22% in the organic treatment and <1 % in the conventional treatment (Clarke et al. 1998). Carbon inputs to the organic treatment (poultry and green manures) were 6.2 times greater than to the conventional system (Cunapala and Scow 1998). 

Jenkinson, D. S., and Coleman, K. (1994). Calculating the annual input of organic matter to soil from measurements of total organic carbon and radiocarbon. Eur. J. Soil Sci. 45, 167-174. 

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