Annual Report of Cooperative Regional Project, W-128, for California (UCD, Ken Shackel, Larry Schwankl, Dave Hills).
January 1, 1999 to December 31, 1999.
Progress of Work and Principal Accomplishments.
Objective 1: To evaluate and refine microirrigation management strategies to promote natural resource protection and optimal crop production.
Plant-based measurements of midday stem water potential were used to both the effectiveness of both micro- and other types of irrigation systems in tree crops (almonds, prunes and walnuts). In almonds we found that deficit irrigation during the hull split period caused improved hull split, nut drying and harvestability, although it also caused some defoliation, so that application of this method must be tested over a number of years to determine it’s sustainability. In prunes a substantial savings in applied water was achieved in a sprinkler irrigated orchard (40%), and in a flood irrigated orchard only 3 irrigations were required over a 5 month period, compared to the normal schedule of 10 irrigations. A study on alternate bearing in pistachio showed that ‘off’ year carbon gain may have little effect on ‘on’ year yield, and was used to suggest that deficit irrigation during the entire ‘off’ year may be a viable commercial practice, saving both water and other agronomic inputs.
Objective 2: To improve, modify, and evaluate microirrigation system design and components for natural resource protection and optimal production
Daily drip irrigation was compared to a 3-day cycle of microsprinkler irrigation, both using the same quantity of water, in almonds. Midday stem water potential showed that stress can develop after 4 or more days, indicating that a close control of irrigation may be necessary to prevent unintended stress in these systems, and that the larger wetted volume of microsprinklers may have an advantage in this respect. In all cases, irrigation at less than ETc increased stress and irrigation at more than ETc reduced stress. A prototype hand-pump pressure chamber for irrigation scheduling was developed and commercialized (see http://pmsinstrument.com/pump-up.htm). This tool should become an important component of irrigation system management, particularly for the application of deficit irrigation strategies. A mathematical model developed in 1998 to simulate the effects of emitter clogging in microirrigation subunits was further refined and validated with field data. Results from this study suggest the following conclusions: 1) Clogging effects in a subunit can be simulated for different clogging rates and locations. 2) Simulation results can be tabulated as a pressure database to be used by the system manager as an indication of the system clogging condition. 3) Early detection of clogging can be achieved by simulating the effects of clogging and monitoring the subunit pressure head values. 4) Monitoring the pressure head at both the pump and the manifold can eliminate the effects of water level changes on the subunit hydraulics.
Objective 3: To assess and develop decision criteria for adoption of microirrigation technologies
Objective 4: To promote appropriate microirrigation technologies through formal and informal educational activities.
Presentations were made to industry groups in almonds, prunes, walnuts and pears about the value of plant-based measurements for optimal management of irrigation water.
Usefulness of findings.
Objective 1: By using reliable plant-based measurements, site-specific irrigation decisions can be made to achieve a substantial savings in water, in addition to probable savings in labor and reductions in adverse environmental impacts.
Objective 2: A commercially available hand-pump pressure chamber will be more likely to be used by growers to obtain site-specific information on the performance of their irrigation system and the effectiveness of their irrigation strategy.
Work Planned
Objective 1: Demonstration projects in almond and prune will be continued to evaluate the long term effects of deficit irrigation on tree productivity and to establish the overall economic impact of this practice.
Objective 4: Presentations will be made to industry groups informing them of the benefits of site-specific management of deficit irrigation, and a web site will be developed describing the operation of the pressure chamber.
Publications
Shackel, K.A., S. Gurusinghe, D. Kester, W. Micke. 1998. Water stress responses of Almond [Prunus Dulcis (Mill.) Webb.] trees under field conditions. Acta Hort. 470: 309-316.
Stevenson, M.T., Shackel, K.A. 1998. Alternate Bearing in Pistachio as a Masting Phenomenon: Construction Cost of Reproduction versus Vegetative Growth and Storage. J. Amer. Soc. Hort. Sci. 123:1069-1075.
Shackel, K., B. Lampinen, S. Southwick, D. Goldhamer, W. Olson, S. Sibbett, W. Keueger, J. Yeager. (In Press). Deficit irrigation in prunes: Maintaining productivity with less water. HortSci.
Schwankl, L. 1999. Microsprinklers wet larger soil volume; boost almond yield, tree growth. California Agriculture, 53:(2) 39-43.
Talozi, S. A. and Hills, D. J. 1999. Microirrigation Computer Simulation: Pressure Sensitivity to Hydraulic Change. ASAE Paper 992213. St. Joseph, MI: ASAE.