|Bio-Intensive Approach to Small-Scale Household Food Production (IIRR, 1993, 180 p.)|
Saline soils are soils that have been harmed by excessive amounts of soluble salts - mainly sodium, calcium, magnesium, chloride and sulfate, as well as potassium, bicarbonate, carbonate, nitrate and boron. The abnormally high salt concentration of saline soils reduces the rate at which plants absorb water, consequently growth is retarded. Aside from growth retardation of plants, certain salt constituents, like boron, are specifically toxic to some crops.
What Causes Soil Salinity?
1. Lack of water. Salt-affected soils are common in arid or semiarid regions because there is less rainfall available to leach and transport the salts and because the high evaporation and plant transpiration rates in arid climates tend to further concentrate the salts in soils and surface waters.
2. Poor drainage. When water table rises to within 1.5 or 2 m of the surface, groundwater containing dissolved salt moves upward into the root zone and to the soil surface. Groundwater then causes the soil to become saline.
3. Excessive irrigation. Irrigation waters may contain large amount of salt. Considerable quantities of soluble salts may be added to irrigated soils in a short time.
How to Tell if your Soil is Affected by Salinity
The salinity status of soils is appraised by measuring electrical conductivity of the solution extracted from saturated soil paste. The yields of very salt-sensitive crops may be restricted at readings as low as 2, moderately salt-tolerant crops grow satisfactorily below readings of 8; only salt-tolerant crops grow satisfactorily when readings range between 8 and 16.
Management Practices for the Control of Salinity
1. Select crops or crop cultivars that can grow successfully under saline conditions. Among the highly tolerant vegetables are beets, kale, asparagus, spinach and tomato.
2. Use land preparation and tillage methods that aid in the control of salinity. Careful leveling of land makes possible a more uniform application of water and better salinity control.
3. Modify watering practices and bed shape to alter the of salts to accumulate near the seed. Pre-emergence watering in special furrows placed close to the seed often is done to reduce the soluble salt concentration around the seeds and thus permit germination. After the seedlings are established, the special furrows may be abandoned and new furrows made between the rows.
4. Use special planting procedures that minimize salt accumulation around the seed. The tendency of salts to accumulate near the seed during irrigation is greatest in single-row, flattopped beds. With double-row beds, most of the salt is carried into the center of the bed, leaving the shoulders relatively free of salt and satisfactory for planting.
For peppers chile, ladyfinger, sweet potatoes, cowpeas and sweet corn
5. Water properly, so as to maintain a relatively high soil moisture level and, at the same time, allow for periodic leaching of the soil and reduce salinity problems. The method and frequency of watering and the amount of water applied are of prime importance in the control of salinity. The amount of water applied should be sufficient to supply the crop and satisfy the leaching requirement but not enough to overload the system.
6. "Pond" water over the entire soil surface to make leaching efficient. Soils can be leached by applying water to the surface and allowing it to pass downward through the root zone.
7. Apply special treatments, such as, adding organic matters and growing sod crops to improve soil structure. Low permeability of the soil causes poor drainage by impeding the downward movement of water. The impedance may be the result of an unfavorable increase in groundwater level, which then causes the soil to become saline.
Bower, C. A. and M. Fireman. 1957. Saline and Alkali Sails. In Yearbook of Agriculture by USDA, Washington, D. C.