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aValues are expressed on an ash-free, dry-weight basis.

bIncrement is grams of total root (structural plus labile) between that sampling time and the last sampling time. c14C = (DPM sample) (60s/min) [Ci(3.7 x 1010 DPS)] (0.22442g/Ci).

dR = 14C/12C; Ri = 14C/12C for that sampling time; and R2 = 14C/12C for the last sampling time.

eRC = R2 corrected for the amount of 14C incorporated into structural material between that sampling time and the last sampling time. fC = % cell wall at time 1 or 2; B1 = biomass (structural plus labile) at time 1. i(Dilution-harvest)/harvest x 100. Modified from Milchunas et al., 1985.

aggregates might be left intact, if they do not contain any roots [Steen, 1991].) What effect is caused by higher water contents in soil volumes without living roots? Advantages of the technique include being able to get a clear, more accurate measure of production of roots over discrete time intervals. Also, it is possible to obtain information on decomposition of dead roots by placing fine-mesh (<0.1 mm) cloth bags into the soil cylinders and determining the loss rates of dead roots simultaneously with measurement of new root ingrowth over time (Titlyanova, 1987). However, see papers by Reid and Goss (1982) and Cheng and Coleman (1990) for comments about live root and organic matter interactions. Some of these concerns will be addressed further in a discussion of decomposition processes in soils later in this chapter.

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