Agriculture Reference
In-Depth Information
Its chemical constituents include soil organic matter, pH, base saturation, cation
exchange, and nutrient pools. Biologically, soil fertility is related to food web com-
plexity, pest and pathogen suppression, and the delivery of mineralizable nutrients.
Most of these components are interrelated, which frustrates attempts at a compre-
hensive definition of soil fertility or soil quality. At heart, however, soil fertility is
the capacity of a soil to meet plant growth needs; all else equal, more fertile soils
support higher rates of primary production.
Building soil fertility is closely tied to building soil organic matter: A century
of work at Rothamsted and other long-term agricultural research sites (Rasmussen
et al. 1998) has shown positive associations with most—if not all—of the indica-
tors noted above. At the KBS LTER site, relative to the Conventional system, soil
organic matter increased in the No-till, Reduced Input, and Biologically Based sys-
tems (Syswerda et al. 2011). A major reason for soil carbon gain in these systems
is slower decomposition rates as a result of organic matter protection within soil
aggregates, particularly within larger size classes. Grandy and Robertson (2007)
found greater soil carbon accumulation in KBS LTER ecosystems with higher rates
of large (2-8 mm) aggregate formation. The formation of large aggregates and car-
bon accumulation were greatest in the successional and mature forest systems, and
lowest in the Conventional system; the Biologically Based, No-till, and perennial
systems were intermediate. Aggregates in smaller size classes (<0.05-0.25 mm)
expressed the opposite trend.
That the No-till system accumulated carbon and primarily in larger, more vul-
nerable aggregates is no surprise (West and Post 2002, Six et al. 2004); however,
carbon and large aggregate accumulation in the heavily tilled Reduced Input and
0.3
R
0.2
0.1
No-till
Conventional
0.0
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Year 2012
Figure 2.6
. Seasonal variation in soil moisture in Conventional and No-till systems during
the 2012 soybean growing season. The 6-week drought began after a June 3 rainfall (R on
figure). Error bars denote the standard error (n = 6). Redrawn from Robertson et al. (2014).
