Download Figure 18.1

Figure 18.1. Influence of soil organic matter and its management on nutrient availability.
Growth promoting substances
A
B
residue
C
During the decomposition process growth
promoting substances are produced (A),
soil structure is improved and water
holding capacity is increased (B) nutrients
are mineralized (during C, D, and E), CEC
is produced (C, D, and E).
D
Better soil structure and improved water
holding capacity
Active organic matter
(particulate, light fraction)
E
Passive organic matter
(humus, organo-mineral complexesaaa0
Indirect Effects on nutrient availability
1) Growth promoting substances
Direct effects on nutrient availability
1)Nutrients released during residue decomposition
Relatively high amounts of mineralization of available
nutrients is produced by a combination of rapid decomposition
plus previously accumulated POM or a high amount of added
residues. Rapid decomposition is stimulated by intensive
tillage, good soil drainage, coarse texture, and alternating wet
and dry conditions.
2) CEC produced during decomposition process.
Substances produced by bacteria promote better root growth
and healthier roots and leads to more soil volume explored
and more surface area for nutrient interception and for mass
flow of nutrients to roots.
2) Better soil structure and improved water holding
capacity
Better soil structure may enhance root development and
exploration (see above). Good soil structure and plentiful
humus content contributes to higher amounts of plantavailable water following rains or irrigation. This results in
better plant growth and health and more nutrient movement to
roots.