Figure 2.2. Partially decomposed fresh residues removed from soil. Fragments of stems, roots, and fungal hyphae are all readily used by soil organisms.

1
(No Transcript)
2
Figure 2.2. Partially decomposed fresh residues
removed from soil. Fragments of stems, roots, and
fungal hyphae are all readily used by soil
organisms.
3
Increased biological activity ( diversity)
Add organic matter
Reduced soilborne diseases, parasitic nematodes
Decomposition
Aggregation increased
Pore structure improved
Nutrients released
Humus and other growth-promoting substances
Harmful substances detoxified
Improved tilth and water storage
Figure 2.3. Adding organic matter results in many
changes. Modified from Oshins and Drinkwater
(1999). Designer Note odd font of item lower
right should be like the others
4
Figure 2.4. The cycle of plant nutrients.
5
Ca
Ca
Ca
Mg
-
-
-
-
-
-
Ca
-
-
-
-
-
-
K
-
Mg
-
Ca
-
K
-
a) cations held on humus
b) cations held on clay particle
c) cations held by organic chelate
Figure 2.5. Cations held on negatively charged
organic matter and clay.
6
infiltration
runoff
a) aggregated soil
b) soil crusts after aggregates break down
Figure 2.6. Changes in soil surface and
water-flow pattern when crusts develop.
7
Figure 2.7. Corn grown in nutrient solution with
(right) and without (left) humic acids. Photo by
R. Bartlett. In this experiment by Rich Bartlett
adding humic acids to a nutrient solution
increased the growth of tomatoes and corn as well
as the amount and branching of roots.
8
root respiration and soil organic matter
decomposition
respiration in stems and leaves
Figure 2.8. The role of soil organic matter in
the carbon cycle. Losses of carbon from the field
are indicated by a dark border around the words
describing the process.
9
nitrogen gas (N2) (78 of atmosphere)
NH4 NO3-
crop harvest
legumes
free-living bacteria
nitrogen in soil organic matter
ammonium NH4
nitrate NO3-
Figure 2.9. The role of organic matter in the
nitrogen cycle. Losses of nitrogen from the field
are indicated by the dark border around the words
describing the process.