Irrigation project addreses variability in nut yields
ByKathyCoatney Irrigation research on almonds and walnuts aims to develop strategies that
Monitoring the soil-plant-atmosphere systemprovides researchers with a better understandingofwhentotrigger irrigation andhow long an irrigation set should run. Onebigfactor is infiltration,Kisekkasaid. “Forexample, the layeredsoilsdon’t take inwater as fast as the light soils,”hesaid. “If you give them the same amount of water, thenyouseeflooding.Sothebeautyof zone irrigationmanagement is it allows you the flexibility tomanage the zonesdifferently.” Yieldwill be the gold standard to deter- mine success of theproject, he said. In the absence of a yield map, Kisekka is using aerial imagery fromCeres Inc. andcanopy light interception to develop a proxy for spatial variability in yield. The images fromCeres are converted to a fractional canopy cover related to light in- terception, measured in the orchard at so- lar noon. In turn, light interception relates to yield potential, based on research done byUCCE specialist Bruce Lampinen.With this information, Kisekka said, researchers calculateanapproximationofhowyieldwill vary inagivenblock. Kisekka is also testingmicro-tensiome- ters thathavereverse-osmosismembranes tomeasure stemwater potential. Growers have been using a pressure chamber or pressure bomb to measure SWP, but he described that as a very labor-intensive process, requiring someone to go into the field around solar noon. “We are putting thesemicro-tensiome- ters in the tree trunks tomeasure basical- ly the same thing as the pressure bomb,” Kisekka said. The information can be accessed on a computer, tablet or smartphone. “This technology is still newandunder- going testingandimprovement aswe learn more about its performance in different crops,” he said. Kisekka has also installed high quality research grid instrumentation known as eddy covariance flux towers to take atmo- spheric data. “With these flux towers, for example, we measureCO2assimilationandevapotrans- piration, sowecanseewhenthestomataof the tree open and take inCO2, and it gives offwatermolecules. Thesemeasurements of CO2 and evapotranspiration can allow
Aerial imagery shows fractional canopy cover in a nut orchard, which helps University of California spe- cialists determine yield potential in different parts of the orchard.
give farmers the flexibility in irriga- tion scheduling to minimizevariable growth and yield in their orchards. Isaya Kisekka, associateprofessor
in the Department of Land, Air andWater Resources at the University of California, Davis, began the research in2018 at Esteve Ranch in the Central Valley. The owner, in collaboration with Allan Fulton, UCCE emeritus farmadvisor, began retrofitting it to zone irrigationmanagementmore than adecadeearlier. Withalmondandwalnutacreageincreas- ing during the last decade, orchards have expanded ontomarginal soils that tend to bemore variable in terms of soil properties, Kisekka said, bringing issueswith soil infil- trationandspatial variability inwater-hold- ingcapacity,soil fertility,slopeandotherfac- tors that canresult innonuniformorchards. “Orchards canbenonuniformformany reasons, but one of them is water, which could be a function of either the soil vari- ability or irrigation systems,” he said. Kisekka is working to develop irriga- tion strategies that allowgrowers to better matchdifferences insoils, inorder tomin-
imize spatial variability in yield. “If youdo that, thenyou improve yields, you improve water-use efficiency, nutri- ent-use efficiency, energy-use efficiency as well as improving the efficiencies of your human resources on the farm and, ultimately, profitability,” he said. In his research, Kisekka employs a con- cept called zone irrigationmanagement, or ZIM, which differs from variable-rate irrigation. ZIMhas a simpler look, he said, and it is more adaptable for existing or- chard irrigation systems. “Instead of trying tomake a system that followsall theirregularpatternsof soils, you justmakeagridwitha reasonablenumber ofzones thatagrowercanmanage,”hesaid. “It’s lessexpensive thaninvesting ina total-
ly newvariable-rate system.” The ZIM approach also grants farmers the flexibility tomanage the differences in soil infiltration or soil water-holding ca- pacity, he said. “Therewill still be some soil variabilities withinagivenzone, butnot asbadasman- aging theentireblockasone,”Kisekkasaid. The grower where the research site is located hired a consultant to develop the zones, using a technique called electro- magnetic induction—also called EM38— and also used a Veris sensor in mapping soil variability, Kisekka said. “What these techniques simply do is measurewhat is calledapparent electrical connectivity of the soil that tells you how different the soils are,” he said. “They tell you something about the soil variability, andthenyoucangoandground-truththat using a soil pit or taking soil samples.” The research site has three dominant soil types: heavy, light and transitional or layered soil. “Basedon these soilmaps, they decided the irrigation zones by simply doing some plumbing to connect zones that fall under similarsoil,”Kisekkasaid. “That iswhat they did to develop the original zone irrigation management plan, but tocontinuemanag- ingthetrees, that’swheretechnologiessuch asimagery,stemwaterpotentialsensorsand soilmoisturesensorscomein, tohelpgrow- ers refine irrigation scheduling decisions and to identify areas on the ranch where irrigationsystemsmightbemalfunctioning.” Kisekka is working with companies that provide information on measuring tree water status and monitoring soil.
See VARIABILITY, Page 23
IRRIGATION SOLUTIONS • PIVOTS
PUMPS • PIPE • PARTS & SERVICE
Helping You Be Water Smart for Over 60 Years Bakersfield, CA • Imperial, CA • Salinas, CA • San Joaquin, CA Stockton, CA • Woodland, CA • Chandler, AZ • Yuma, AZ
LESS DOLLARS, MORE SENSE.
Rain for Rent is a proud authorized Reinke Dealer
rainforrent.com/AG
14 Ag Alert October 7, 2020
Powered by FlippingBook