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TDA,TOA_ Kimball loam, hardpan substratum, 0 to 2 percent slopes. This deep to hardpan, well drained soil• on nearly level low terraces. It formed in alluvium from mixed rock sources. A few areas are dissected by intermittent sloughs that have been filled because of land-leveling. The vegetation in areas not cultivated is mainly annual grasses and (orbs. Elevation is 20 to 100 feet. The average annual precipitation is about 15 inches, the average annual air temperature is about 60 degrees F, and the average frost-free period is about 270 days. Typically, the surface layer is grayish brown loam about 14 inches thick. The upper 17 inches of the subsoil is pale brown or dark brown loam. The lower 18 inches is variegated brown and dark brown clay loam and clay. A variegated brown, dark brown and light brown strongly cemented to indurated hardpan is at a depth of 49 inches. Depth to hardpan ranges from 40 to 60 inches. In some areas the surface layer is fine sandy loam and sandy loam. Included in this unit are small areas of Bruel la, Tokay and Veritas soils on slightly higher positions. Also included are small areas of San Joaquin soils on similar positions, and Alamo and Madera soils on slightly lower positions. Included areas make up about 15 percent of the total acreage. Permeability of this Kimball soil is very slow. Available water capacity is moderate. Shrink-swell potential is high. Effective rooting depth is 40 to 60 inches. Runoff is slow and the hazard of water erosion is slight. The water intake family for irrigation is 1.0. Depth to the water table is more than 6 feet, but water may be perched for brief periods above the hardpan after heavy rains or irrigations. Most areas of this unit are used for irrigated cropland, orchards and vineyards. A few areas are used for homesite development and rangeland. This unit is suited to irrigated row, field, orchard and vineyard crops. The main limitations are very slow permeability in the lower subsoil and depth to hardpan. Because of the very slow permeability of the subsoil of this soil , the application of water should be regulated so that water does not stand on the surface and damage the crops. Irrigation water needs to be applied carefully to prevent the buildup of a high water table. The hardpan reduces the yield of deep rooted plants. Where feasible, deep ripping of this restrictive layer helps to overcome this limitation. A tillage pan forms easily if this soil is tilled when wet. Chiseling or subsoiling breaks up the tillage pan. Furrow, border, corrugation and sprinkler irrigation systems are suited to this soil. Returning crop residue to the soil or regularly adding other organic matter improves fertility, reduces crusting and increases the water intake rate. If this unit is used for homes ite development, the main limitations are depth to the very slowly permeable claypan and hardpan and high shrink-swell potential of the clayey subsoil. If the soil is used for septic tank absorption fields, the limitation of very slow permeability can be overcome by increasing the size of the absorption field. Use of sandy backfill for the trench and long absorption lines helps to compensate for the very slow permeability. The suitability of the soil for septic tank absorption fields can be improved by ripping the hardpan to increase permeability. Excavation for building sites is limited by the hardpan. If buildings are constructed on the soil, properly designing foundations and footings and diverting runoff away from buildings help to prevent structural damage because of shrinking and swelling. Where this unit is used for livestock grazing, general management considerations include saturated soil conditions in concave areas following rainy periods. The characteristic plant community on this unit is mainly soft chess, wild oat, ripgut brome and filaree. Grazing should be delayed until the soil is fir■ enough to withstand trampling by livestock and the more desirable forage plants have had an opportunity to set seed. The map unit is in capability units IIIs-3 (MLRA-17), irrigated and IVs-3 (MLRA-17), nonirrigated. This map unit is vegetative soil group D. SAN JOAQUIN COUNTY SOIL SURVEY PRELIMINARY DRAFT 7/90 SUBJECT TO CHANGE