Rhizodeposition measurement

Rhizodeposition is measured as 0 recovered from soil adhering to the roots or soil not adhering to the roots. Soil moisture content was constant in all treatments. 

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. 

Rather than measuring rhizodeposition in nutrient. solutions chemically, another approach has been to expose shoots to COi for a short period of time and to follow the spread of the through the plant, into the roots, and then into the nutrient solution. Kinetics of carbon flow and quantification of rhizodeposition can then be obtained (e.g.. Ref. 24). Advantages and limitations of this approach are discussed more fully in Sec. II.C. 

Rhizodeposition in nutrient solution culture is relatively easy to measure and readily altered. It may not reflect what happens in vivo due to the absence of a solid substratum for root growth. Simply including glass beads in nutrient solution can significantly increase rhizodeposition in maize (16), and such an effect must be considered when estimating rhizodeposition in relation to the natural environment. Consequently, a range of systems using various solid supports have been developed. Rhizodeposition in soil is considered in Sect. II.C. 

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