Piñeiro check details et al. (2006) contend that this phenomenon argues against using whole-soil C:N ratios. This begs the question, however, as to how finely we must divide up our soil organic matter pools to avoid such problems both in terms of age and depth, and the practicalities of doing so on a routine basis. Studies where N inputs to N saturated systems have been reduced have shown that N once retained

in forest ecosystems is not easily released by leaching. Reduced N inputs were applied experimentally in NITREX studies in Europe, where roofs were constructed over N-saturated forests and clean rain was sprinkled underneath (Bredemeier et al., 1998 and Quist et al., 1999), and another where high rates of N fixation and nitrate leaching in red alder (Alnus rubra) were truncated by clearcutting ( Van Miegroet et al., 1992a and Van Miegroet et al., 1992b). In the

NITREX studies, reduced N inputs in N-saturated sites Screening Library in Germany and the Netherlands resulted in rapid decreases in nitrate leaching ( Bredemeier et al., 1998). Increased N inputs to N-limited sites in Norway, Sweden, Denmark, and Wales caused varying responses in nitrate leaching, with very small increases inthe sites that had low initial nitrate leaching rates (Norway, Sweden, and Denmark), but large increases in the site which had high initial nitrate leaching rate (Wales). Similarly, in the case of the red alder harvesting study, nitrate leaching rates declined precipitously after clearcutting, apparently a result of greatly reduced inputs via fixation (vegetation regrowth

was too low to attribute the observed decline to post-harvest uptake). Most of the excess N stored in the red alder soil (judging by comparing it to N stores in an adjacent Douglas-fir ecosystem) remained in it ( Van Miegroet et al., 1992a and Van Miegroet et al., 1992b). Other authors have also found reduced nitrate leaching after harvesting, but for different reasons. Parfitt et al. (2002) also found reduced nitrate leaching after clearcutting mafosfamide in an N-rich Pinus radiata plantation, which they attributed to post-harvest uptake by weeds and microbial biomass. Ranger et al. (2007) found reduced nitrate leaching after clearcutting in zero tension lysimeter solutions and only weak increases in nitrate leaching with tension lysimeters. They attributed these responses to reduced N mineralization and nitrification (which is found to be quite high in these ecosystems) and reduced N inputs via dry deposition in the absence of scavenging by the forest canopy. Finally, some studies of clearcutting forests previously fertilized at high rates have shown that these systems do not display particularly high rates of nitrate leaching ( Ring, 1995 and Johannisson et al., 1999). Collectively, the studies cited above suggest that N once retained in forest ecosystems – even those systems formerly “saturated” with N – it is not readily released back into soil solution.