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Growth and yield responses of developing almond trees ( Prunus amygdalus, Ruby cultivar) to a range of trickle irrigation amounts were determined in 1985 through 1987 (the fifth through seventh year after planting) at the University of California's West Side Field Station in the semi-arid San Joaquin Valley. The treatments consisted of six levels of irrigation, ranging from 50 through 175% of the estimated crop evapotranspiration (ET), applied to a clean-cultivated orchard using a line source trickle irrigation system with 6 emitters per tree. ET was estimated as grass reference evapotranspiration (ET) times a crop coefficient with adjustments based upon shaded area of trees and period during the growing season. Differential irrigation experiments prior to 1984 on the trees used in this study significantly influenced the initial trunk cross-section area and canopy size in the 50% ET treatment and 125% ET treatment. In these cases, treatment effects must be identified as relative effects rather than absolute. The soil of the experimental field was a Panoche clay loam (nonacid, thermic, Typic Torriorthents). The mean increase in trunk cross-sectional area for the 3-year period was a positive linear function ( r = 0.98) of total amounts of applied water. With increases in water application above the 50% ET treatment, nut retention with respect to flower and fertile nut counts after flowering, was increased approximately 10%. In 1985 and 1987, the nut meat yields and mean kernel weights increased significantly with increasing water application from 50% to 150% ET. Particularly in the higher water application treatments, crop consumptive use was difficult to quantify due to uncertainty in estimates of deep percolation and soil water uptake. Maintenance of leaf water potentials higher than −2.3 MPa during early nut development (March through May) and greater than −2.5 MPa the remainder of the irrigation season (through August) were positively correlated with sustained higher vegetative growth rates and higher nut yields. [ABSTRACT FROM AUTHOR]

Trickle irrigation of perennial crops results in local wetting near trees and vines. Methods to measure soil-water content or storage within the root zone generally require intensive instrumentation to characterize spatial patterns of soil water adequately. The goals of this research were to determine if spatial patterns of soil-water storage under trickle irrigation are temporally presistent which may make it feasible to use less intense sampling to characterize total storage. Soil-water storage from the 0 to 1.5 m soil depth was measured at 23 sites on one side of trickle-irrigated almond trees using a neutron probe over three years in the San Joaquin Valley of California. Measurements were made on two trees in each of five different irrigation treatments. The persistence of spatial patterns with time was evaluated using Spearman rank correlation and relative differences from mean values. Spatial patterns were different for each tree and irrigation treatment but remained fairly persistent with time during a season. In many cases, temporal changes in soil-water storage were adequately estimated from a single location. Single sampling locations identified during one year gave estimates of mean storage during the following year with some increase in error. However, use of the same sampling locations for more than two years increased the error in storage estimates. Soil-water content or storage in trickle-irrigated orchards may be monitored by intense sampling during the early part of the irrigation season in order to identify locations giving mean soil-water storage. Only these locations may then be sampled to monitor changes in soil water. [ABSTRACT FROM AUTHOR]

BSTRACT From 1971-1980, studies were conducted at Fresno, California, to identify and quantify, where possible, the soil and water chemistry, subsurface geologic, hydrologic, biologic, and operational factors that determine the long term (10-year) effectiveness of basin type artificial ground water recharge through alluvial soils. This paper updates previous findings and refers to publications that describe the geology beneath the basins and regional geology that determine the transmission and storage properties for local ground water management and chemical quality enhancement. High quality irrigation water from the Kings River was used for recharge. Construction and land costs for the present expanded facility 83 ha (205.2 ac) using three parcels of land were $1,457,100. The nine-year annual mean costs for only canal water, maintenance, and operation were $110.42/ha·m ($13.62/ac·ft) based on an average recharge rate of 1338 ha·m/yr (10,848 ac·ft/yr) at 86 percent facility efficiency. The measured end of season recharge rate averaged 14.97 ± 0.24 cm/day. The 10-year mean actual recharge rate based on actual water delivered, total ponded area, and total days of recharge was 12.1 cm/day. [ABSTRACT FROM AUTHOR]