46
transfer and transformation of SOC are affected by soil temperature, oxygen, and
soil moisture (Walcott et al. 2009; Post and Kwon 2000; FAO 2001). Higher temperatures coupled with adequate water supply result in faster decomposition of soil
organic matter (SOM), less storage of C in the slow and passive pools, and greater
loss of C through respiration. This provides the rationale behind the occurrence of
thick surface accumulation of light fraction organic C in boreal and tundra ecosystems where temperatures are low. Since rainfall stimulates plant growth, soils in the
humid regions contain more SOC than soils in the dry regions. Microbial activity is
also enhanced in wet soils under aerobic conditions, which causes more breakdown
of organic matter than in dry soils. However, in continually saturated soils, decomposition rates are reduced and highly organic soils, such as peats, develop.
Lastly, management practices and microbial activities also influence the amount,
decomposability, and placement of organic matter inputs in SOC pools. For instance,
cultivation impacts on SOC by causing soil disturbance leading to the release of C
into the atmosphere. However, this depends on the initial SOC content, the intensity
of cultivation, and the level and type of plant residue inputs. For example, conservation tillage loses less C, and adding plant residues with higher C:N and lower
N:lignin ratios reduces decomposition rates and increases SOC. Similarly, earthworms, ants, and termites increase the amount of stable organic C in some soils and
enhance the decomposition of plant residues. Overall, altering land management
practices can create a system where SOC levels either become unstable or stable in
the long term.
2.3 Functions of SOC
Ecosystem functions and services delivered by SOC are manifold and integral to
securing food and fiber production. The main functions of SOC, which have found
their lucid expression in the work of Lal (2004), Bationo et al. (2007), and FAO
(2001), are as follows:
(a) Maintaining soil quality for agricultural and environmental purposes (e.g., sustaining agronomic productivity, C sequestration, and creating climate-smart
soils and agro-ecosystems).
(b) Improving the dynamics and bio-availability of main plant nutrient elements
(e.g., N, P, and K) and enhancing cation-exchange capacity.
(c) Supporting biological activity in the soil (i.e., the amount, diversity, and activity
of soil biota).
(d) Determining the physical, chemical, and biological soil properties. For instance,
aggregation and stability of the soil structure increases with SOM content. This
in turn improves the infiltration capacity, plant available water capacity, resistance of soils against erosion, and soil tilth.
(e) Enhancing efficiency in fertilizer and water use due to reduction in losses by
drainage, evaporation, and volatilization.
K. Were et al.
transfer and transformation of SOC are affected by soil temperature, oxygen, and
soil moisture (Walcott et al. 2009; Post and Kwon 2000; FAO 2001). Higher temperatures coupled with adequate water supply result in faster decomposition of soil
organic matter (SOM), less storage of C in the slow and passive pools, and greater
loss of C through respiration. This provides the rationale behind the occurrence of
thick surface accumulation of light fraction organic C in boreal and tundra ecosystems where temperatures are low. Since rainfall stimulates plant growth, soils in the
humid regions contain more SOC than soils in the dry regions. Microbial activity is
also enhanced in wet soils under aerobic conditions, which causes more breakdown
of organic matter than in dry soils. However, in continually saturated soils, decomposition rates are reduced and highly organic soils, such as peats, develop.
Lastly, management practices and microbial activities also influence the amount,
decomposability, and placement of organic matter inputs in SOC pools. For instance,
cultivation impacts on SOC by causing soil disturbance leading to the release of C
into the atmosphere. However, this depends on the initial SOC content, the intensity
of cultivation, and the level and type of plant residue inputs. For example, conservation tillage loses less C, and adding plant residues with higher C:N and lower
N:lignin ratios reduces decomposition rates and increases SOC. Similarly, earthworms, ants, and termites increase the amount of stable organic C in some soils and
enhance the decomposition of plant residues. Overall, altering land management
practices can create a system where SOC levels either become unstable or stable in
the long term.
2.3 Functions of SOC
Ecosystem functions and services delivered by SOC are manifold and integral to
securing food and fiber production. The main functions of SOC, which have found
their lucid expression in the work of Lal (2004), Bationo et al. (2007), and FAO
(2001), are as follows:
(a) Maintaining soil quality for agricultural and environmental purposes (e.g., sustaining agronomic productivity, C sequestration, and creating climate-smart
soils and agro-ecosystems).
(b) Improving the dynamics and bio-availability of main plant nutrient elements
(e.g., N, P, and K) and enhancing cation-exchange capacity.
(c) Supporting biological activity in the soil (i.e., the amount, diversity, and activity
of soil biota).
(d) Determining the physical, chemical, and biological soil properties. For instance,
aggregation and stability of the soil structure increases with SOM content. This
in turn improves the infiltration capacity, plant available water capacity, resistance of soils against erosion, and soil tilth.
(e) Enhancing efficiency in fertilizer and water use due to reduction in losses by
drainage, evaporation, and volatilization.
K. Were et al.