This table shows the degree and kind of soil limitations that affect irrigation systems. The ratings are both verbal and numerical. Rating class terms indicate the extent to which the soils are limited by all of the soil features that affect these uses. "Not limited" indicates that the soil has features that are very favorable for the specified use. Good performance and very low maintenance can be expected. "Somewhat limited" indicates that the soil has features that are moderately favorable for the specified use. The limitations can be overcome or minimized by special planning, design, or installation. Fair performance and moderate maintenance can be expected. "Very limited" indicates that the soil has one or more features that are unfavorable for the specified use. The limitations generally cannot be overcome without major soil reclamation, special design, or expensive installation procedures. Poor performance and high maintenance can be expected.

     Numerical ratings in the table indicate the severity of individual limitations. The ratings are shown as decimal fractions ranging from 0.01 to 1.00. They indicate gradations between the point at which a soil feature has the greatest negative impact on the use (1.00) and the point at which the soil feature is not a limitation (0.00).

      Irrigation systems are used to provide supplemental water to crops, orchards, vineyards, and vegetables in area where natural precipitation will not support desired production of crops being grown.

     “Irrigation, surface (graded)” evaluates a soil for graded flood or furrow irrigation systems. The ratings are for soils in their natural condition and do not consider present land use. 

     Graded surface irrigation systems include graded border and graded furrow irrigation systems.  Graded border irrigation systems allow irrigation water to flow across the soil surface while being confined by borders.  Graded furrow irrigation systems are systems that allow irrigation water to flow down furrow valleys while the crop being irrigated is planted on the furrow ridge.  Generally, graded border systems are suitable for small grains while graded furrow systems are suitable for row crops.

     The soil properties and qualities important in the design and management of graded surface irrigation systems are depth, available water holding capacity, sodium adsorption ratio, surface rocks, permeability, salinity, slope, wetness, and flooding. Features that affect system performance and plant growth are salinity, sodium adsorption ratio, wetness, calcium carbonate content, and available water holding capacity.

      “Irrigation, surface (level)” evaluates a soil for basin, paddy, level furrow, or level border irrigation systems.  The ratings are for soils in their natural condition and do not consider present land use.

     Level surface irrigation systems are irrigation systems that use flood irrigation techniques to spread irrigation water at a specified depth across the application area.  Basin, paddy, and borders generally use external ridges or borders to confine the irrigation application while level furrow systems use furrow valleys and end blocks or border ridges to confine the irrigation application during irrigation.  With furrow irrigation the crop is usually planted on the furrow ridge.  Generally, basin, paddy and level border irrigation systems are suitable for rice, small grain, pasture, and forage production.  Level furrow systems are generally suited for row crops. 

     The soil properties and qualities important in the design and management of level surface irrigation systems are depth, available water holding capacity, sodium adsorption ratio, permeability, salinity, slope, and flooding.  The soil properties and qualities that influence installation are depth, flooding, and ponding.  The features that affect performance of the system and plant growth are salinity, sodium adsorption ratio, and available water holding capacity.

     Information in this table is intended for land use planning, for evaluating land use alternatives, and for planning site investigations prior to design and construction. The information, however, has limitations. For example, estimates and other data generally apply only to that part of the soil between the surface and a depth of 5 to 7 feet. Because of the map scale, small areas of different soils may be included within the mapped areas of a specific soil.

     The information is not site specific and does not eliminate the need for onsite investigation of the soils or for testing and analysis by personnel experienced in the design and construction of engineering works.

     Government ordinances and regulations that restrict certain land uses or impose specific design criteria were not considered in preparing the information in this table. Local ordinances and regulations should be considered in planning, in site selection, and in design.  The irrigation interpretations are not designed or intended to be used in a regulatory manner.