No abstract

The reproductive growth and water productivity (WP b ) of Thompson Seedless grapevines were measured as a function of applied water amounts at various fractions of measured grapevine ET c for a total of eight irrigation treatments. Shoots were harvested numerous times during the growing season to calculate water productivity. Berry weight was maximized at the 0.6-0.8 applied water treatments across years. As applied water amounts increased soluble solids decreased. Berry weight measured at veraison and harvest was a linear function of the mean midday leaf water potential measured between anthesis and veraison and anthesis and harvest, respectively. As applied water amounts increased up to the 0.6-0.8 irrigation treatments there was a signiWcant linear increase in yield. Yields at greater applied water amounts either leveled oV or decreased. The reduction in yield on either side of the yearly maximum was due to fewer numbers of clusters per vine. Maximum yield occurred at an ET c ranging from 550 to 700 mm. Yield per unit applied water and WP b increased as applied water decreased. The results from this study demonstrated that Thompson Seedless grapevines can be deWcit irrigated, increasing water use eYciency while maximizing yields.

Despite being an ancient crop there is limited knowledge on the water and nitrogen (N) requirements of pomegranate. We conducted research at the University of California, Kearney Agricultural Research and Extension Center (KARE) to determine the water and N requirements of a developing pomegranate orchard. Pomegranate trees (Punica granatum L. var. Wonderful) were planted in 2010. The irrigation treatments were surface drip irrigation (DI) and subsurface drip irrigation (SDI) with three N sub-treatments (N application rates of 50, 100, and 150 % of current practice) and 5 replications in split-plot design. A weighing lysimeter located in the experimental field was used to automatically irrigate the orchard after 1.0 mm of measured crop water use. The trees received uniform application of fertilizers and water during the first two years of growth to insure uniform stand establishment prior to beginning the experiment. The pH of the irrigation water was maintained at 6.5+/-0.5 by injection of N as urea sulfuric acid (US-10; 10% N). Differential N treatments were started in 2012 and continued through the end of the project. Phosphorus (PO 4-P) was continuously injected during irrigation and potassium (K 2 T) was injected weekly. We report the results of the study from 2013 to 2015. From 2013 to 2015 the applied N ranged from 62 to 332 kg/ha and the total yields ranged from 33,144 to 57,769 kg/ha. There were no statistical differences in yield within any year related to total applied N. The yearly applied irrigation water increased as the plant size increased. The total water requirement is approximately 952 mm and the maximum daily water use was 10.5 mm. The DI irrigation application went from 645 mm to 932 mm and the SDI application increased from 584 mm to

No abstract

Vegetative growth and water relations of Thompson Seedless grapevines in response to applied water amounts at various fractions of measured grapevine ET c were quantified. Treatments ranged from no applied water up to 1.4 times the water used by vines growing in a weighing lysimeter. All treatments were irrigated at the same frequency as the vines in the lysimeter (whenever they used 2 mm of water), albeit at their respective fraction. Soil water content and midday leaf water potential (W l ) were measured routinely in four of the irrigation treatments across years. The amount of water depleted in the soil profile ranged from 190 mm for the 0.2 treatment in 1993 to no water depletion for the 1.4 treatment in 1992. The irrigation treatments significantly affected midday W l , total shoot length, leaf area per vine, pruning weights and trunk diameter; as applied water decreased so did vegetative growth. Pruning weights were a linear function of the seasonal, mean midday W l across growing seasons. The application of water amounts in excess of evapotranspiration negatively affected vegetative growth some of the years. A companion paper will demonstrate that over-irrigation can negatively affect reproductive growth of this grape cultivar due to excess vegetative growth.

No abstract

A water‐nutrient management method was designed to prevent plant‐water and nutrient stresses while maximizing the available soil water storage to accommodate rainfall. This method minimized the need for the soil as a storage reservoir for water and nutrients by frequently irrigating a portion of the root zone with small amounts of water and nutrients. The optimal range of soil matric potential, based on soil oxygen diffusion rate, soil strength, water desorption characteristics, and unsaturated hydraulic conductivity was used to determine high‐frequency irrigation criteria for sweet corn (Zea mays L.). Trickle‐irrigated plots yielded 12 and 14% more corn than did the furrow‐ and sprinkler‐irrigated plots. When fertilizers were broadcast and banded, soil NO3‐N profiles measured near the end of the growing season showed that, compared to furrow and sprinkler irrigation, trickle irrigation reduced NO3‐N losses from the root zone.Optimal ear yield was produced with high‐frequency trickle irrigation when the soil matric potential at the 15‐cm soil depth was controlled at about −0.2 bar and plants were fertilized with 168 kg/ha each of N and K. Ear yield for this treatment was 66% higher than that for nonirrigated corn fertilized at the same rate. Soil NO3‐N did not accumulate in the profile with depth and time in plots fertilized at the 168‐kg/ha rate, but did accumulate in plots fertilized with 336 kg/ha. Generally, plots trickle‐irrigated with fertilizer solution had a higher soil NO3‐N content on the row than 50 cm from the row.The results of this research indicate that water use efficiency, N‐use efficiency, and N leaching can be controlled in sandy soils when N and K are applied with high‐frequency trickle irrigation systems and N and K rates are adjusted to maintain an optimal N‐level in corn plants.

No abstract