Salinity and Drainage

Cost-Share Programs

Irrigation Guide

USBR Water Manage-
ment Plan

Water Management Handbook

Water Quality Data

SALINITY AND DRAINAGE

INTRODUCTION

Without sufficient drainage , a salt balance cannot be maintained. Yields will decline, you will have to grow less salt-sensitive (usually less profitable crops), and in the long run, land will go out of production.

The basic problem is that all irrigation waters contain salts. Applying water to the soil adds both salts and water. But the crops will extract mostly pure water, leaving the salts behind.

Salts in agriculture can be both good and bad. Many fertilizers are salts. However, excessive salts in the soil is one of the most serious problems facing irrigated agriculture in the San Joaquin Valley.

There are many different types of salts such as sulfates, chlorides, and bicarbonates of sodium, calcium, magnesium, and potassium. Sometimes the problem is just the high level of salts in the soil and/or water (although in some areas a common problem is too little salts in the water), sometimes it is a problem of imbalance between the types of salts.

Excessive or imbalanced salts in soil and water cause four types of problems for agriculture . . .

General yield decline - This is the result of excessive total salts in the soil. The yield decline varies with the crop and management. Some crops are more salt-tolerant than others. And, there are certain techniques that can be used to minimize salt damage.
Poor soil structure and reduced water infiltration - This is a result of an imbalance of salt types. The extent of the problem depends on the imbalance, the amount of salts in the water, and also the clay content and type of clay in the soil.
Specific crop toxicities (direct action to stunt or kill the plant) - Boron is the most recognized toxic salt by Growers, especially in almonds.
Miscellaneous problems with quality (taste or appearance).

With some very poor quality water, damage to components (corrosion, encrustation) of the irrigation system becomes important. The problem of salts can be very obvious or very subtle. Most Growers will recognize a salt problem if they see white crusts in a field or have problems with getting water into the soil. However there could be significant crop yield reductions for years without realizing the problem.

Please follow this link for an additional source of information on this topic in the NRCS National Engineering Handbook, part 652.

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Sources and Measurement of Salinity

There are three main sources of salts in agricultural soils, irrigation water, fertilizer, and naturally occurring salts in the soil that may be dissolved under irrigation. (Most of the time, the amount of salts dissolving from the soil is balanced by those salts precipitating out of solution.)

The water supply for Westlands includes both Grower-owned deep wells and Project contract water from the San Luis Aqueduct. Most of the deep well water in the District is of very poor quality. And, although the Project water is relatively good, it still adds about 500 pounds of salt to the soil for every acre-foot (AF) applied.

One measure of the level of salts in soil or water is in terms of a concentration, typically parts of salt per million parts of water. You may see salt levels described as "200 parts per million total dissolved solids" or, "200 ppm TDS" (about the level of salts in Aqueduct water). An AF of water weighs about 2,700,000 pounds. And at 200 ppm TDS, there are 200 pounds of salt per million pounds of water. Thus, every AF of this water contains about 540 pounds of salt. And if you apply three foot of water per acre per year, then you are putting 1620 pounds of salt on that acre.

A more common measure of salts in the soil and water for agriculture scientists is electrical conductivity. This is a measure of how much electric current will flow through water at a specific voltage. The more salts in water, the more current will flow through that water. You will see water described as having an "electrical conductivity of 1.5 dS/m", or simply ECw = 1.5 dS/m (dS/m stands for deci-Siemens of electrical conductivity per meter of water).

An approximate conversion between concentration and electrical conductivity is that 640 ppm TDS (parts per million total dissolved solids) = 1 dS/m. A comparison of some water qualities is seen below . . .

Aqueduct - 200-320 ppm TDS or .3 to .5 dS/m Friant-Kern Canal - 50 ppm TDS

Rainwater - Near Zero

Average deep well in the District, Sub-Corcoran
East of Aqueduct - <1,300 ppm TDS
Westplains - Varies < 2,600 ppm TDS

Sea-water - 35,000 ppm TDS

Colorado River - 1000+ ppm TDS at the Mexican border

You may see the symbol "EC" followed by one of several letters. If you see "ECw" then it is usually describing the electrical conductivity of the irrigation water. If "ECe" it is usually the electrical conductivity of the saturated soil moisture extract. (Here, the laboratory has made a paste by saturating a soil sample with pure water, then drawn off the excess water and measured the electrical conductivity.) "ECd" is usually used when measuring drainage water.

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Last updated September 2000


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Cost-Share Programs Irrigation Guide USBR Water Manage- ment Plan Water Management Handbook Water Quality Data	SALINITY AND DRAINAGE Next Page
	INTRODUCTION Without sufficient drainage , a salt balance cannot be maintained. Yields will decline, you will have to grow less salt-sensitive (usually less profitable crops), and in the long run, land will go out of production. The basic problem is that all irrigation waters contain salts. Applying water to the soil adds both salts and water. But the crops will extract mostly pure water, leaving the salts behind. Salts in agriculture can be both good and bad. Many fertilizers are salts. However, excessive salts in the soil is one of the most serious problems facing irrigated agriculture in the San Joaquin Valley. There are many different types of salts such as sulfates, chlorides, and bicarbonates of sodium, calcium, magnesium, and potassium. Sometimes the problem is just the high level of salts in the soil and/or water (although in some areas a common problem is too little salts in the water), sometimes it is a problem of imbalance between the types of salts. Excessive or imbalanced salts in soil and water cause four types of problems for agriculture . . . General yield decline - This is the result of excessive total salts in the soil. The yield decline varies with the crop and management. Some crops are more salt-tolerant than others. And, there are certain techniques that can be used to minimize salt damage. Poor soil structure and reduced water infiltration - This is a result of an imbalance of salt types. The extent of the problem depends on the imbalance, the amount of salts in the water, and also the clay content and type of clay in the soil. Specific crop toxicities (direct action to stunt or kill the plant) - Boron is the most recognized toxic salt by Growers, especially in almonds. Miscellaneous problems with quality (taste or appearance). With some very poor quality water, damage to components (corrosion, encrustation) of the irrigation system becomes important. The problem of salts can be very obvious or very subtle. Most Growers will recognize a salt problem if they see white crusts in a field or have problems with getting water into the soil. However there could be significant crop yield reductions for years without realizing the problem. Please follow this link for an additional source of information on this topic in the NRCS National Engineering Handbook, part 652. Top of Page	Sources and Measurement of Salinity There are three main sources of salts in agricultural soils, irrigation water, fertilizer, and naturally occurring salts in the soil that may be dissolved under irrigation. (Most of the time, the amount of salts dissolving from the soil is balanced by those salts precipitating out of solution.) The water supply for Westlands includes both Grower-owned deep wells and Project contract water from the San Luis Aqueduct. Most of the deep well water in the District is of very poor quality. And, although the Project water is relatively good, it still adds about 500 pounds of salt to the soil for every acre-foot (AF) applied. One measure of the level of salts in soil or water is in terms of a concentration, typically parts of salt per million parts of water. You may see salt levels described as "200 parts per million total dissolved solids" or, "200 ppm TDS" (about the level of salts in Aqueduct water). An AF of water weighs about 2,700,000 pounds. And at 200 ppm TDS, there are 200 pounds of salt per million pounds of water. Thus, every AF of this water contains about 540 pounds of salt. And if you apply three foot of water per acre per year, then you are putting 1620 pounds of salt on that acre. A more common measure of salts in the soil and water for agriculture scientists is electrical conductivity. This is a measure of how much electric current will flow through water at a specific voltage. The more salts in water, the more current will flow through that water. You will see water described as having an "electrical conductivity of 1.5 dS/m", or simply ECw = 1.5 dS/m (dS/m stands for deci-Siemens of electrical conductivity per meter of water). An approximate conversion between concentration and electrical conductivity is that 640 ppm TDS (parts per million total dissolved solids) = 1 dS/m. A comparison of some water qualities is seen below . . . Aqueduct - 200-320 ppm TDS or .3 to .5 dS/m Friant-Kern Canal - 50 ppm TDS Rainwater - Near Zero Average deep well in the District, Sub-Corcoran East of Aqueduct - <1,300 ppm TDS Westplains - Varies < 2,600 ppm TDS Sea-water - 35,000 ppm TDS Colorado River - 1000+ ppm TDS at the Mexican border You may see the symbol "EC" followed by one of several letters. If you see "ECw" then it is usually describing the electrical conductivity of the irrigation water. If "ECe" it is usually the electrical conductivity of the saturated soil moisture extract. (Here, the laboratory has made a paste by saturating a soil sample with pure water, then drawn off the excess water and measured the electrical conductivity.) "ECd" is usually used when measuring drainage water. Next Page Top of Page
	Last updated September 2000