Sustainable Land Management for Mitigating Climate Change

D. Potential of SOC Sequestration in Salt-Affected Soils

93. There are approximately 930 Mha of salt-affected soils in arid and semi-arid regions of the world. Adoption of reclaimative measures on these soils can lead to increases in above- and below-ground biomass production and to improvements in SOC concentration and pool. The rate of SCS can be as high as 0.5-2 t C/ha/yr. Even if the rate of biomass production, in arid environments with low availability of water and nutrients, is low at 0.5-1 t C/ha/yr, total ecosystem C pool can be enhanced at 1-3 t C/ha/yr. It is estimated that 100 Mha of reclaimed soils can be used for crop production, of which 56 Mha are irrigated and 44 Mha are rainfed. In addition, 280 Mha can be used for perennial land uses. Thus, the potential of C sequestration in 380 Mha of reclaimed salt affected soils is 0.4-1.0 Gt C/yr (Table 28). If economic and realizable potential is 66% of the technical potential, reclamation of salt-affected soils can offset anthropogenic emissions at the rate of 0.25 to 0.66 Gt C/yr for about 50 years.

Table 28. Technical potential of reclaiming salt-affected soils on SOC sequestration (Lal, 2009d).
Land Use	Area (Mha)	C Sequestration Rate (t/ha/yr)		Technical Potential (Mt C/yr)
		Soil	Biomass
1. Cropland	100
a. Irrigated	56	1.0-2.0	-	56-112
b. Rainfed	44	0.5-1.0	-	22-44
2. Perennial Land use	280	0.5-1.0	0.5-2.0	280-840
Total				358-996

E. Growing Halophytes as Biofuel Feedstocks

94. Strongly and extremely salinized soils may need to be taken out of agricultural and pastoral land uses and planted with specific trees, shrubs or grass species that could be used as biofuel feedstocks. Such biomass can also be used as direct fuel for power generation through co-combustion. In addition to salt-affected soils, some water reserves are saline (brackish) with high salt content ranging from 5000 to 40,000 ppm. While common crops cannot tolerate such high salt concentrations, some halophytes can adapt to such conditions. Karlberg and de Vries (2004) collected data on several crops regarding their tolerance to irrigation with saline water. They reported that most cereals (wheat, corn, rice, barley, sorghum, rye grass, and small grains) can be grown in soils with a salinity level of 20-16 dS/m. In contrast, legumes and other crops (e.g., alfalfa, tomato, cotton, oat, choke, beet) can be grown at salinity levels of 2-8 dS/m. A major opportunity in biotechnology lies in designing new germplasm that is tolerant to high salt concentrations in the root zone, and has high NPP in such environments. Examples of some useful halophytes as shown in Table 29 indicate vast potential of producing high-grade fodder, forage, oil, and food. Experiments reported by Glenn et al. (1993) show that halophytes irrigated with seawater can produce biomass yield of 17 to 35 t/ha/yr with a net C sequestration rate of 4-8 t C/ha/yr (Table 29).

Table 29. Mean annual biomass yield and carbon sequestration rate of seawater irrigated halophytes at Puerto Penasco, Sonora, Mexico (Adapted from Glenn et al., 1993).
Species	Biomass Yield (tC/ha/yr)	C Sequestration Rate (tC/ha/yr)
1. Batis maritime	34.0	8.2
2. Atriplex linearis	24.3	6.7
3. Salicornia bigelovii
Year one	22.4	5.6
Year two	17.7	4.3
4. Suaeda esteroa	17.2	4.3
5. Sesuvium partulacastrum	16.7	4.2