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San Joaquin County, California 93 is about 14 inches, the average annual air temperature reduced by properly managing all crop residue and by is about 60 degrees F, and the average frost-free period minimizing tillage. Levees should be checked is about 270 days. periodically, and a proper maintenance program should Typically, the upper 22 inches of the surface layer is be developed. gray and dark gray mucky clay loam. The lower 2 This map unit is in capability units Illw-5 (MLRA-16), inches is brown and very dark gray silty clay. The irrigated, and IVw-5 (MLRA-16), nonirrigated. It is in subsoil is very dark gray and grayish brown, mottled vegetative soil group E. mucky clay loam about 21 inches thick. The underlying material to a depth of 60 inches is olive gray, mottled 205—Peltier mucky clay loam, organic substratum, clay. In some areas the surface layer is silty clay loam partially drained, 0 to 2 percent slopes. This very or silty clay. deep, poorly drained, nearly level soil is on flood plains Included in this unit are small areas of Kingile soils in and deltas. It formed in hydrophytic plant remains the slightly lower landscape positions. Also included, in derived from reeds and tules and in alluvium derived landscape positions similar to those of the dominant from mixed rock sources. Mottles in the profile indicate Peltier soil, are small areas of Ryde and Valdez soils a poorly drained soil; however, drainage has been and small areas of Peltier soils that have an organic improved by levees and reclamation projects. Elevation substratum below a depth of 40 inches. Included areas is 15 feet below sea level to 5 feet above. The average make up about 15 percent of the total acreage. annual precipitation is about 14 inches, the average Permeability is slow in the Peltier soil. Available annual air temperature is about 60 degrees F, and the water capacity is very high. The shrink-swell potential is average frost-free period is about 270 days. high. The effective rooting depth of the crops commonly Typically, the upper 22 inches of the surface layer is grown in the county is limited by an apparent water gray mucky clay loam. The lower 2 inches is brown and table that is regulated at a depth of 3 to 4 feet by very dark gray silty clay. The subsoil is black and very pumping. This soil is subject to subsidence. Runoff is dark gray, mottled mucky clay loam about 20 inches very slow, and the hazard of water erosion is slight. The thick. The substratum to a depth of 60 inches is dark rate of water intake in irrigated areas is 1.0 inch per brown mucky peat. In some areas the surface layer is hour. The hazard of soil blowing is moderate. The soil is silty clay loam or silty clay. subject to rare flooding, which occurs during years of Included in this unit are small areas of Egbert and abnormally high precipitation. Ryde soils in landscape positions similar to those of the Most areas are used for irrigated crops. This unit Peltier soil and Rindge soils in the slightly lower may provide wetland functions and values. These landscape positions. Also included are small areas of should be considered in plans for enhancement of moderately fine textured soils that have an organic wildlife habitat or land use conversion. substratum below a depth of 24 inches. Included areas This unit is suited to irrigated row and field crops. make up about 15 percent of the total acreage. The main limitations are subsidence, the high water Permeability is slow in the upper part of the Peltier table, and the slow permeability. General management soil and rapid in the organic substratum, which is at a considerations include the hazard of soil blowing. depth of 40 to 60 inches. Available water capacity is Because this soil is subject to differential subsidence, very high. The shrink-swell potential is high. The frequent leveling of the fields is needed to improve the effective rooting depth of the crops commonly grown in efficiency of irrigation. Areas adjacent to levees are the county is limited by an apparent water table that is subject to lateral seepage in wet years when the water regulated at a depth of 3 to 4 feet by pumping. This soil level is high. Careful applications of irrigation water are is subject to subsidence. Runoff is very slow, and the needed to prevent the buildup of a high water table. hazard of water erosion is slight. The rate of water — Large ditches and small spud ditches provide intake in irrigated areas is 1.0 inch per hour. The subirrigation and improve drainage. Because of the hazard of soil blowing is moderate. The soil is subject restricted permeability, water applications should be to rare flooding, which occurs during years of regulated so that the water does not stand on the abnormally high precipitation. surface and damage the crops. Subirrigation, furrow, Most areas are used for irrigated crops. This unit border, and sprinkler systems are suitable. Where a may provide wetland functions and values. These subirrigation system is used, the water table is raised to should be considered in plans for enhancement of a depth of 1 foot at planting time and then is slowly wildlife habitat or land use conversion. lowered during the growing season until it is at a depth This unit is suited to irrigated row and field crops. Of about 5 feet at harvest time. When the wind velocity The main limitations are subsidence, the high water _ is high in spring, the hazard of soil blowing can be table, and the slow permeability. General management