Marginal land resources

According to Chambers 20th Century Dictionary (Kirk Patrick, 1983), the marginal lands is defined as “less fertile land which will be brought under cultivation only if economic conditions justify it”. The term “marginal land” has been used quite loosely without a concrete definition. The difficulty in formulating a clear definition stems from the fact that “productivity” varies according to the type of land use. As an instance, a land that is “marginal” for crop production may be well suited for grazing. “Fragile” land may be sensitive to degradation under cultivation but may be sustainably used for forestry. In many dry land countries the extent and characteristics of these lands have not been systematically assessed, nor has their sustainability for biofuels or food crop production evaluated.

Marginal lands include areas with limited rainfall, extreme temperatures, low quality soil, steep terrain, shallow (depth<50 cm), imperfectly drained, poor fertility, coarse textured, stony, heavy cracking clays, salt affected, waterlogged, barren rocky soils, or other problems for agriculture are generally considered marginal lands. It means that the same lands do not have sufficient capacity for example for food production, unless significant management efforts are made to improve the land quality. So, the land could be marginal for one use (agriculture) and maybe vital for another use (grazing)…

Marginal areas are “marginal” for many reasons. In some cases, technologies can be developed that move lands from marginal productivity to higher productivity. The most obvious example is irrigation of deserts where this is economically feasible and desirable… (cited from Sustainable food production in marginal lands – Case of GDLA member countries. Shabbir A Shahid, Abdullah Al Shankiti (2013); read more... )

Marginal lands - farming land that is of poor quality and does not produce much profit: With rising prices for crops, marginal land is coming under pressure to be put back into cultivation.
Marginal lands have received wide attention for their potential to improve food security and support bioenergy production. However, environmental issues, ecosystem services, and sustainability have been widely raised over the use of marginal land. Knowledge of the extent, location, and quality of marginal lands as well as their assessment and management are limited and diverse.
(read more in web-link FAO.org marginal lands)

Salt is defined as a water-soluble compound resulting from the combination of an acid and a metal. Generally, we associate the terms saline, salt, and salinity with sodium chloride (NaCl), otherwise known as common table salt. However, salinity of irrigation water generally is a combination of numerous salts. The cations and anions most frequently found in irrigation water are: sodium (Na+), calcium (Ca2+), magnesium (Mg2+), chloride (Cl-), sulfate (SO42-), and bicarbonate (HCO3-). These salts are most often thought of by their common names (Table 1).

Table 1. Some salts commonly contributing to the salinity.

Salt accumulates and concentrates in soil when water evaporates from the soil surface, when plants use water, when leaching is not adequate to leach salts beyond the root zone, and/or when precipitation does not wash salts off the land surface. As water evaporates from a soil surface, or is used by plants, the water that is used or taken up by plants is essentially distilled or purified, leaving salts behind. In essence, water that is considered saline contains excessive amounts of soluble salts which can adversely affect the growth of plants.

Saline lands occupy vast territories, accounting, according to some estimates, for about 6-7 percent of the land surface (Flowers and Yeo, 1995). This is over 950 million hectares (FAO, 2008). In Uzbekistan about half of the irrigated lands (over 2 mln. ha) is salinized. (Ministry of Agriculture and Water Resources of Uzbekistan, 2009;National report about the condition of the environment, 2013). According to data of World Bank experts, about 20 000 ha of lands annually become not suitable for farming as a result of salinization and waterlogging (World Bank, 2003).
Salinization of lands takes place as a result of natural processes, often speeded up by human factors, for instance, by excessive irrigation in areas where groundwater table is high. A large quantity of such salts as carbonates, chlorides and sulphates, which are harmful for plants, may accumulate in the soil. Salinization worsens physicochemical qualities of the soil, reduces efficiency of fertilizers and suppresses growth and development of plants. High osmotic pressure of water and salt solution in the root zone affects the capability of the plant to absorb water. The presence of salt in the soil higher 0.25 percent of dissolved solids damages physiological function of many cultivated plants, and as a result, yield and quality of agricultural products decline.
Natural factors of formation of saline soils are the accumulation of salts in groundwater and its gradual rise to surface layers of the soil, weathering, flooding of land with saline water and etc. Human activity may considerably accelerate these processes. Natural process of salinization, which is speeded up by humans, is called resalinization. The main reason of resalinization of farming lands is improper irrigation, which speeds up the process of rise of salts together with groundwater to surface and arable layers of the soil. In irrigated farming four stages of the manifestation of resalinization are distinguished: leopard-spotted, spotted, large-spotted and continuous. All these forms of salinization are characteristic of irrigated soils of Central Asia.
Depending on the level of salinity soils are divided into the following types:
•    soils with weak salinity level (0.25-0.4 percent of salts of soil mass),
•    soils with moderate salinity level (0.4-0.7 percent),
•    soils with high salinity level (0.7-1 percent),
•    salt marches (1-3 percent),
•    alkaline soils (their particularity is predominance of sodium),
•    solod soils (their particularity is presence of amorphous silicic acid dissolvable in a 5- percent solution of caustic potash).
Salt marches is characterized by the fact that a large quantity of all salts in the soil are on the surface (up to 25 percent). These salts suppress the growth of almost all plants. Cultivated plants do not grow on salt marches; however they can be used as pastures.
Alkaline soils mostly appear on light-brown soils. The presence of a large amount of sodium at alluvial horizon is harmful for plants, since exchangeable sodium degrades physicochemical qualities of the soil. Alkaline soils appear in various conditions; therefore they are divided into alkaline meadow soils, alkaline meadow-steppe soils and alkaline steppe soils.
Solodsoilsare widespread in steppes, forest steppes and semideserts. They appear in the conditions of high humidity. These saline soils like salt marches are not fit for growing cultivated plants as a result of unfavourable water regime. However, solod soils can be used as pastures and hayfields.
For most plants, salinization of the environment (soil and water) is one of the major abiotic stresses. As a result of such impact growth and development (see table 2) is suppressed, and crop yield drops significantly, which leads to economic losses. Annual damage caused as a result of soil salinization is about 12 bn US dollars (Qadir et al., 2008).

Table 2. Impact of salinization of soil on the development of plants
(Abrolatal. 1988)

Salinization of groundwater has a big impact on the soil productivity. Soil salinity level may increase at the expense of the migration of salts from deep aquifers. On the whole in Uzbekistan, the area of irrigated lands in areas where there is groundwater with salinity level above 3.0 g/l is approximately 947,1 thous. ha (22 percent) (table 3).

Table 3. The area of irrigated lands in areas where there is groundwater (data from the Ministry of Agriculture and Water Resources RUz, 2009)