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114 Soil Survey annual cropping, the best suited cropping system is one a depth of 12 to 20 inches and are in landscape that includes small grain and summer fallow. positions similar to those of the San Joaquin soil. Maintaining crop residue on or near the surface helps to Included areas make up about 15 percent of the total prevent excessive runoff and helps to maintain tilth and acreage. the organic matter content. Permeability is very slow in the San Joaquin soil. If this unit is used for homesite development, the Available water capacity is very low. The shrink-swell main limitations are depth to the very slowly permeable potential is high. The effective rooting depth is limited claypan and hardpan, the high shrink-swell potential, by the hardpan at a depth of 20 to 40 inches. Roots are _ and low strength in the claypan. On sites for septic tank restricted to cracks and the faces of peds in the absorption fields, the very slow permeability can be claypan, which is at a depth of 10 to 20 inches. Water overcome by increasing the size of the absorption field, is briefly perched above the claypan and hardpan after backfilling the trench with sandy material, and installing periods of heavy rainfall or irrigation. Runoff is slow or long absorption lines. Ripping the hardpan improves medium, and the hazard of water erosion is slight or permeability and thus also improves the suitability of the moderate. The rate of water intake in irrigated areas is soil for septic tank absorption fields. Excavation for 1.5 inches per hour. r. buildings is limited by the hardpan. Properly designing Most areas are used for livestock grazing. A few foundations and footings and diverting runoff away from areas are used for irrigated vineyards, irrigated pasture, buildings help to prevent the structural damage caused or dryland grain crops. This unit may provide wetland by shrinking and swelling. Properly designing buildings functions and values. These should be considered in and roads can offset the limited ability of the soil to plans for enhancement of wildlife habitat or land use support a load. conversion. This map unit is in capability unit IVs-3 (MLRA-17), Where this unit is used for livestock grazing, general irrigated and nonirrigated. It is in vegetative soil group management considerations include saturated soil D. conditions in concave areas following rainy periods and the hazard of erosion. The characteristic plant 237—San Joaquin sandy loam, 2 to 5 percent community is mainly soft chess, ripgut brome, foxtail slopes. This moderately well drained, undulating soil is fescue, and filaree. Grazing should be delayed until the on dissected terraces. It is moderately deep to a soil is firm enough to withstand trampling by livestock hardpan. It formed in alluvium derived from granitic rock and the more desirable forage plants have had an sources. The native vegetation is mainly annual opportunity to set seed. Grazing should be controlled sc grasses, (orbs, and scattered California white oak. that desirable vegetation, such as soft chess, is Slopes occur as a complex of plane and convex side maintained and enough vegetation is left standing to slopes and concave drainageways. Elevation is 20 to protect the soil from erosion. 150 feet. The average annual precipitation is about 16 This unit is suited to irrigated vineyard crops. The inches, the average annual air temperature is about 61 main limitations are depth to the very slowly permeable degrees F, and the average frost-free period is about claypan and hardpan and the very low available water 275 days. capacity. General management considerations include Typically, the surface layer is brown sandy loam the hazard of erosion. Because of the restricted about 10 inches thick. The upper part of the subsoil is a permeability, water applications should be regulated so claypan of brown clay about 10 inches thick. The lower that the water does not stand on the surface and part to a depth of 60 inches is a brown and light brown, damage the crops. The hardpan limits the suitability for indurated hardpan. In some areas the surface layer is deep-rooted crops. Where feasible, deep ripping of this fine sandy loam. restrictive layer can help to overcome this limitation. A Included in this unit are small areas of Bruella and tillage pan forms easily if the soil is tilled when wet. Rocklin soils on the slightly higher terraces, Jahant soils Chiseling or subsoiling breaks up the pan. Because the in landscape positions similar to those of the San soil is droughty, applications of irrigation water should Joaquin soil, Madera soils in the slightly lower positions, be light and frequent. Sprinkler and drip irrigation and San Joaquin soils that have slopes of 0 to 2 or 8 to systems are suitable. They permit an even, controlled 15 percent. The areas where slopes are 0 to 2 percent application of water, help to prevent excessive runoff, are on toe slopes, and the areas where slopes are 8 to and minimize the risk of erosion. All tillage should be c 15 percent are on narrow embankments. Also included the contour or across the slope. If the soil is plowed in are small areas of Redding soils that have slopes of 2 fall, runoff and erosion can be controlled by applying to 8 percent and are on the slightly higher terraces and fertilizer and seeding a cover crop. Returning crop moderately coarse textured soils that have a hardpan at residue to the soil or regularly adding other organic