Agriculture Reference
In-Depth Information
Atmospheric C
3.5 Mg C ha
-1
net primary productivity
2 Mg C ha
-1
respired by soil
1 Mg C ha
-1
removed at harvest
Grain C
Residue C
2.5 Mg C ha
-1
added
to soil
0.1 Mg C ha
-1
eroded?
Soil C: 60 Mg C ha
-1
+ 0.4 Mg C ha
-1
fIguRe 16.4
Schematics of annual carbon flows and soil carbon stocks in an agroecosys-
tem. Most of the carbon captured by plants from the atmosphere via net primary production
(photosynthesis-respiration) is respired back to the atmosphere by microbes, removed from the
ecosystem as harvestable products, or transferred to other places via erosion. Soils gain (seques-
ter) carbon due to a positive balance between inputs and outputs of carbon. Conversely, soils
may lose (emit) carbon when the balance is negative. Some other terms of the carbon balance
(gains of carbon via soil deposition, leaching of dissolved carbon) are not represented here.
Soil carbon sequestration is a unique mitigation option because of the many ancil-
lary benefits and environmental services associated with its practice (see Chapter 18).
Carbon accumulation in soil has a direct effect on ecosystem quality and function.
Carbon is the main constituent of soil organic matter, which in turn is a universally
accepted reference for quantifying soil fertility, productivity, and resistance to ero-
sion (Carter, 2002). For example, sequestration of 1 Mg ha
−1
of atmospheric carbon
in soil leads to the retention of about 100 kg ha
−1
of nitrogen as well as significant
amounts of phosphorus, sulfur, and other essential plant nutrients in soil organic
matter. Sequestration of 1 Mg ha
−1
of atmospheric carbon in soil can increase crop
productivity in the range of 20-70 kg ha
−1
for wheat, 10-50 kg ha
−1
for rice, and
30-300 kg ha
−1
for maize (Lal, 2005). Thus, soil carbon sequestration can contribute
not only to climate change mitigation but also to global food security, especially in
developing countries.
