No abstract

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 %0 of the estimated crop evapotranspiration (ETc), applied to a clean-cultivated orchard using a line source trickle irrigation system with 6 emitters per tree. ETc was estimated as grass reference evapotranspiration (ET0) 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% ETo treatment and 125 % ETr 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 2 = 0.98) of total amounts of applied water. With increases in water application above the 50% ETc 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 -2.3MPa 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.

Alfalfa (Medicago sativa L.) seed production differs from hay production and requires detailed research to determine appropriate water management strategies. Effects of surface‐applied irrigation amount, frequency, and prereproductive soil water content on reproductive development, seed yield, and harvest index were studied for 3 yr in the field. In 1987, 1988, and 1989, six supplemental irrigation treatments representing combinations of two irrigation frequencies (daily and after 75 mm of accumulated evapotranspiration [ETc]) and three rates of water replacement (40, 70, and 100% ETc) were used. These six treatments received 200 mm of water prior to foliage clipback in April. In 1988 and 1989, an additional 100 mm of water was applied prior to clipback to an additional three treatments that were irrigated after 75 mm of ETc and that had water replaced at either 40, 70, or 100% ETc. Seed yield response to amount of applied water differed between the establishment and two subsequent production years. for plants receiving 200 mm of water prior to clipback, increasing amounts of applied water decreased seed yield in the establishment year, but optimized yield at 70% ETc in the two subsequent years of production. Frequency of water replacement generally did not affect seed yield when 200 mm of water were applied to the soil prior to clipback. Replacement amount did not affect seed yield when 300 mm of water was applied prior to clipback. Increasing water replacement amounts increased number of floral buds plus racemes but decreased seed pod number through the growing season. Total season‐end aboveground phytomass was a positive function of water application amount and was not affected by frequency of application or amount of water applied prior to clipback. Water management can affect alfalfa seed crop response and yield.

A field experiment was conducted using a linear-move irrigation machine to test the interactive effects of irrigation uniformity, a representative length of nonuniformity and water quality on crop yield and growth responses. Christiansen's uniformity coefficient values of 60, 80, and 90% were achieved with a sinusoidal pattern of applied water superimposed on the 60 and 80% uniformity treatments. Two wavelengths 2.4 m (S) and 4.9 m (L), were used. Water qualities used were: 0.3 dS m -1 and 3 to 5 dS m -1. Results showed that both the magnitude and the scale of the nonuniformity affect the water use efficiency. Sugar yields were not affected by water quality. Yields on a row basis were significantly correlated to applied water in the 60% uniformity, long scale length (60-L) treatment.

The influence of irrigation frequency and the severity and rate of development of soil water deficits on the vegetative growth and water status of carrots (Daucus carota L. var. sativa DC.) grown for seed were investigated in a fine sandy loam soil. Beginning with the period of rapid development of primary umbels, various irrigation frequencies [daily vs. intervals corresponding to 30 mm of accumulated crop evapotranspiration (ETc)] were investigated at irrigation rates ranging from 40% to 120% of estimated ETC. The magnitude and rate of development of soil water deficits markedly influenced carrot responses to developing water deficits. Stomata] conductance and leaf water potential (LWP) measurements exhibited some potential for use in irrigation scheduling and were the most sensitive and consistent indicators of plant water status. Under low-frequency continuous-deficit irrigation, a combination of moderate reductions in stomatal conductance and major reductions in peak leaf area and late-season maintenance of viable leaf area occurred. These responses were effective water-conserving mechanisms, allowing growth at a reduced rate and continued development of viable seed. In contrast, rapid development of soil water deficits resulted in nearly complete stomatal closure, cessation of growth, and rapid reductions in leaf area.