Agriculture Reference
In-Depth Information
(a)
0
20
40
60
80
100
% Water-filled pore space
(b)
0
−4
−2
2
Stdev of treatment level WFPS (natural log transformed)
Figure 3.3
An illustration of how variance in biogeochemical controls (e.g., water-filled pore space)
influences aggregation bias in the case of a complex nonlinear function. (a) A complex nonlinear
function describing how the percentage of soil pore space filled with water (i.e., %WFPS) affects
soil microbial activity (Linn and Doran, 1984; Stehfest et al., 2007). (b) The aggregation bias of nitri-
fication rate estimates introduced when aggregating %WFPS data across treatment replicates (for
monthly sampling from 1989 to 2001) before applying the %WFPS-microbial activity function (a)
versus obtaining the unbiased estimate by deriving the mean nitrification rate for each treatment-
sampling date after evaluating each replicate-sampling date separately. (Data for this comparison
are from the KBS-LTER.)
within a growth season) may show quite different patterns. For growing seasons with
higher-than-average soil moisture contents (i.e., a greater proportion of soil moisture mea-
surements near field capacity), there will be a greater probability of significant aggregation
bias because soils will more often be in the nonlinear soil moisture range (i.e., near the
optimal soil moisture). In contrast, seasons with drier soils will have less aggregation bias
Search WWH ::
Custom Search