Agriculture Reference
In-Depth Information
in this landscape. Development of better indicators of microbial functions
in organic systems may help farmers evaluate and discover management
options that continue to improve the nutrient cycling capacity of the soil.
13.4.1 PATTERNS AND DETERMINANTS OF SOIL POTENTIAL
ENZYME ACTIVITY
In this landscape, the majority of the variation in potential enzyme activi-
ties could be explained by soil characteristics related to nutrient availabili-
ty and microbial biomass, which are well-known to be strongly influenced
by management on relatively short times scales, as well as soil properties
well-known to be influenced by both management and soil type at longer
time scales (e.g. soil C and N). Soil variables determined by soil type (e.g.
texture) did not contribute to explaining variation in enzyme activities,
which may be partly a result of the similar soil types and relatively nar-
row range of soil textures sampled. MBC was positively correlated with
increases in the potential activity of most enzymes, as reflected in the first
axis of the RDA, and strongly related to the geometric mean of enzyme ac-
tivity, an indicator of overall microbial metabolic capacity (García-Ruiz et
al., 2008). Most fields showed fairly similar values along this axis, except
for fields at opposite ends of the SOM gradient. At the low extreme are
fields 1 and 2 with soil C below 10 g kg
−1
and much lower MBC and en-
zyme activities than other fields. Below a certain level of MBC, microbial
functioning may be reduced. At the high extreme is field 13, with high soil
C, MBC, and potential enzyme activities, especially for those involved
in nutrient release. The other fields, with mid-range values for soil C and
MBC, suggest that a diverse set of soil conditions and nutrient manage-
ment strategies result in similar overall soil metabolic capacity, albeit with
differences in the activity of certain enzymes related to C vs. nutrient cy-
cling processes. Interestingly, this may also be reflected in tomato yields.
Nine of the 13 fields had similar yields (104.0 ± 3.6 tons ha
−1
, mean ± SE)
that were above the Yolo County average in 2011 (86 tons ha
−1
), which
included both conventional and organic Roma-type tomatoes (Bowles et
al. ms. in preparation).
