Natural Resources Conservation Service

NATURAL RESOURCES CONSERVATION SERVICE CONSERVATION PRACTICE SPECIFICATION

610 - TOXIC SALT REDUCTION

I. SCOPE III. PONDING METHOD

The work shall consist of providing water and Level land as needed for uniform ponding and surface amendments to leach the salt concentration in the soil. control and perform deep tillage.

II. GENERAL Construct dikes or borders on a contour to obtain uniform ponding. Dikes may be constructed by any The estimated quantity of water required for the initial convenient method. leaching job, and to assure sufficient supply may be determined as a general rule - for each foot of soil to be Temporary water control structures are generally leached: required to control depth of water in ponds. These structures may be wooden, metal, or concrete. Plastic a. 6 inches of irrigation water is required to leach out lined spillways may be used in lieu of the above 50 percent of the salt structures. b. 12 inches of irrigation water is required to leach Alternate wetting and drying may be more efficient out 80 percent of the salt, and than continuous wetting on some soils. c. 24 inches of irrigation water is required to leach IV. SPRINKLER METHOD out 90 percent of the salt. Sprinkling ordinarily provides better water control than For sodic soils, add such soil amendments as gypsum, ponding, giving adequate salt reduction with less water sulfur, lime sulfur solution, sulfuric acid, iron sulfate, and allows for more uniform leaching especially when aluminum sulfate, or limestone at a rate based on deep tillage is performed. laboratory analysis. Refer to Table 6, page 49, of USDA, Agricultural Handbook 60, for amounts of Design sprinkler system in the same manner as gypsum land sulfur required to replace indicated sprinkler system for irrigation. amounts of exchangeable sodium. The coefficient of uniformity (CU) should be 80 or High sodium soils may require 4 to 5 tons/acre of greater. The more uniform the water is applied the gypsum, or 4 tons/acre of lime if the soil pH is low. better the leaching will be. Incorporate low soluble amendment into the topsoil before leaching is started. Some amendments can be The application rates should be less than field intake dissolved and applied in irrigation water during the rates in order to avoid ponding. Where intake rate is a leaching period. problem, intermittent sprinkling may be desirable, especially on finer textured soils. If necessary, provide subsurface drainage so that water will move downward and out of the soil profile. More water shall be applied than evaporates. Evaporation rates are greater in the daytime. Therefore, Take periodic soil and water tests to determine the it may be advantageous to use sprinklers at night, level or salinity. The required level in reached when especially on fine textured soils where the application the electrical conductivity of a saturation extract or soil rate may be almost the same as evaporation rates. paste is at the level required for satisfactory plant growth of the desired crop. V. MAINTENANCE

Sufficient water must be infiltrated during the irrigation season to avoid new concentration of salts in the root zone.

NRCS, CA July, 2000 610-2

Avoid tillage when soil is wet and any other tillage that compacts the soil. Ripping, subsoiling and plowing when dry leaving the field rough will be helpful in getting water into the soil, but should not be used as a substitute for proper leveling, contour bordering, or other practices needed for irrigation water management.

Maintain soil tilth and productivity by using good management practices that include conservation cropping system, drainage improvement, proper water use, subsoiling, crop residue use, cover cropping, green manure and mulching. These are important practices that will help keep a soil free from salt.

Subsequent to the leaching operation, the soil may be quite sterile and devoid of organic matter and needed nutrients. A good practice is to plant a green manure crop as the first or even second crop and plow in to build up organic content and improve the tilth of the soil. Animal manure and/or commercial fertilizer are usually needed to replace nitrogen that is usually lost with the leachate.

In the event the leaching process was not complete, for some reason stopped short of completeness, consideration should be given to planting a salt tolerant crop, as a cash crop, for the first season following leaching. This will provide for further natural leaching, during the growing of the cash crop and will provide the operation with some income during this period.

VI. OTHER REQUIREMENTS

The owner, operator, contractor, and other persons shall conduct all work and operations in accordance with proper safety codes for the type of equipment and operations being performed with due regard to the safety of all persons and their property.

NRCS, CA July 1996