Agriculture
Soil salinization is a process in which water-soluble salts build up in the root zones of plants, blocking the movement of water and nutrients into plant tissues.
Soil salinization rarely occurs naturally. It becomes an environmental problem when it occurs as a result of human activity, denuding once vegetated areas of all plant life.
Rainwater is virtually free of dissolved solids, but surface waters and underground waters (groundwater) contain significant quantities of dissolved solids, ultimately produced by the weathering of rocks.
Evaporation of water at the land surface results in an increase in dissolved solids that may adversely affect the ability of plant roots to absorb water and nutrients.
Arid Climates
In arid regions, evaporation of soil water potentially exceeds rainfall. Shallow wetting of the soil followed by surface evaporation lifts the available dissolved solids to near the surface of the soil.
The near-surface soil therefore becomes richer in soluble salts. In natural arid areas, soluble salts in the subsurface are limited in quantity because rock weathering is an extremely slow process. Degrees of soil salinization detrimental to plants are uncommon.
Irrigating arid climate soils with surface or groundwater provides a constant new supply of soluble salt. As the irrigation water evaporates and moves through plants to the atmosphere, the dissolved solid content of the soil water increases. Eventually, the increase in soil salt will inhibit or stop plant growth.
It is therefore necessary to apply much more water to the fields than required for plant growth to flush salts away from the plant root zone. If the excess water drains easily to the ground water zone, the groundwater becomes enriched in dissolved solids, which may be detrimental.
If the groundwater table is near the surface, or if there are impermeable soil zones close to the surface, over irrigation will not alleviate the problem of soil salinization.
This condition requires the installation of subsurface drains that carry the excess soil water and salts to a surface outlet. The problem with this method is that disposing of the salty drain water is difficult. If the drain water is released into surface streams, it degrades the quality of the stream water, adversely affecting downstream users.
If the water is discharged into evaporation ponds, it has the potential to seep into the groundwater zone or produce a dangerously contaminated body of surface water, as occurred at the Kesterson Wildlife Refuge in California, where concentrations of the trace element selenium rose to levels that interfered with the reproduction of resident birds.
- Modern Agriculture Problems
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- Halophytes
HalophytesHalophytes are salt-resistant or salt-tolerant plants that thrive and complete their life cycles in soils or waters containing high salt concentrations. Despite high salt content in the tissues of halophytes, they can be grown and harvested...
- Hydrologic Cycle
Hydrologic Cycle The hydrologic cycle is a continuous system through which water circulates through vegetation, in the atmosphere, in the ground, on land, and in surface water such as rivers and oceans. The sun and the force of gravity provide the energy...
- Irrigation
IrrigationIrrigation techniques supply additional water to arid and semiarid horticulture or farming regions where few, if any, crops could otherwise be grown. Approximately 350 million acres (142 million hectares) of land worldwide are irrigated. In...
- Hydroponic Fertilizer Solutions
Plants typically grow with their roots in soil and their stems and leaves in the air. They get some of the elements they require from the air (for example, most of the carbon and much of the oxygen used by the plant comes from the carbon dioxide taken...
Agriculture
Soil Salinization
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| Soil Salinization |
Soil salinization rarely occurs naturally. It becomes an environmental problem when it occurs as a result of human activity, denuding once vegetated areas of all plant life.
Rainwater is virtually free of dissolved solids, but surface waters and underground waters (groundwater) contain significant quantities of dissolved solids, ultimately produced by the weathering of rocks.
Evaporation of water at the land surface results in an increase in dissolved solids that may adversely affect the ability of plant roots to absorb water and nutrients.
Arid Climates
In arid regions, evaporation of soil water potentially exceeds rainfall. Shallow wetting of the soil followed by surface evaporation lifts the available dissolved solids to near the surface of the soil.
The near-surface soil therefore becomes richer in soluble salts. In natural arid areas, soluble salts in the subsurface are limited in quantity because rock weathering is an extremely slow process. Degrees of soil salinization detrimental to plants are uncommon.
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Irrigating arid climate soils with surface or groundwater provides a constant new supply of soluble salt. As the irrigation water evaporates and moves through plants to the atmosphere, the dissolved solid content of the soil water increases. Eventually, the increase in soil salt will inhibit or stop plant growth.
It is therefore necessary to apply much more water to the fields than required for plant growth to flush salts away from the plant root zone. If the excess water drains easily to the ground water zone, the groundwater becomes enriched in dissolved solids, which may be detrimental.
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This condition requires the installation of subsurface drains that carry the excess soil water and salts to a surface outlet. The problem with this method is that disposing of the salty drain water is difficult. If the drain water is released into surface streams, it degrades the quality of the stream water, adversely affecting downstream users.
If the water is discharged into evaporation ponds, it has the potential to seep into the groundwater zone or produce a dangerously contaminated body of surface water, as occurred at the Kesterson Wildlife Refuge in California, where concentrations of the trace element selenium rose to levels that interfered with the reproduction of resident birds.
- Modern Agriculture Problems
Modern Agriculture Many current problems in agriculture are not new. Erosion and pollution, for example, have been around as long as agriculture. However, agriculture has changed drastically within its ten-thousand-year history, especially since the dawn...
- Halophytes
HalophytesHalophytes are salt-resistant or salt-tolerant plants that thrive and complete their life cycles in soils or waters containing high salt concentrations. Despite high salt content in the tissues of halophytes, they can be grown and harvested...
- Hydrologic Cycle
Hydrologic Cycle The hydrologic cycle is a continuous system through which water circulates through vegetation, in the atmosphere, in the ground, on land, and in surface water such as rivers and oceans. The sun and the force of gravity provide the energy...
- Irrigation
IrrigationIrrigation techniques supply additional water to arid and semiarid horticulture or farming regions where few, if any, crops could otherwise be grown. Approximately 350 million acres (142 million hectares) of land worldwide are irrigated. In...
- Hydroponic Fertilizer Solutions
Plants typically grow with their roots in soil and their stems and leaves in the air. They get some of the elements they require from the air (for example, most of the carbon and much of the oxygen used by the plant comes from the carbon dioxide taken...