1a.Objectives (from AD-416):
Overall objective is to optimize water-nitrogen interactions to improve fertilizer use effieiency (FUE) of young and maturing pomegranate.
Specific objectives include:
a. Determine the real time seasonal nitrogen requirements (N) of DI and SDI irrigated maturing pomegranate that improve FUE without yield reduction.
b. Determine the effectiveness of three nitrogen injection rates with DI and SDI on maintaining adequate N levels in maturing pomegranates.
c. Determine the effect of real time seasonal nitrogen injections (N) with DI and SDI irrigated maturing pomegranate on N leaching losses.
d. Develop fertigation management tools that will allow growing to achieve objective "a" and present these results to interested parties.
e. Determine if concentrations of macronutrients (P,K,Ca, Mg) and micronutrients (Zn, Cu, Mn,Fe B and Se) and eventually healthy bioactive compounds in soil, peel, and fruit are influenced by precise irrigation/fertigation management with DI and SDI.
1b.Approach (from AD-416):
Field and laboratory studies will be conducted. The field study will be conducted on a 3.5 acre field site on the Kearney Agricultural Center that contains a weighing lysimeter. The experimental design is a randomized complete block design with 2 irrigation types and 3 levels of N application with 5 replications. The irrigation systems are surface drip irrigation (DI) and subsurface drip irrigation (SDI) and the 3 nitrogen treatments are 70% of adequate, 100% of adequate and 130% of adequate determined using biweekly petiole analysis. The system will be controlled using the weighing lysimeter. Proportional injection of fertilizers will be used to meet the N objectives. Tree and fruit responses will be determined with canopy measurements, pruned plant biomass and bimonthly plant tissue analysis. In the third year flowers, fruit yields, and quality will be measured and statistically analysed.
This project supports objective 2 of the parent project. In this reporting period the CO-PI oversaw the field operation of the project. The drip tubing used in the initial installation of the subsurface drip irrigation system (SDI) was malfunctioning, and the CO-PI supervised the installation of the replacement system. During this reporting period the installation of the data acquisition system needed to control the irrigation and injection of fertilizer was completed. The CO-PI calibrated the fertilizer injection system and monitored the operation of the weighing lysimeter. The irrigation, evapotranspiration and applied fertilizer data were summarized and a report was prepared for the California Department of Food and Agriculture. The evapotranspiration for the 2 year old trees was estimated to be 250 mm and the crop coefficient ranged from 0.13 to 0.25. The light interception under the trees was used to characterize plant size. There was greater light interception under the subsurface drip irrigated trees than under the surface drip irrigated trees. The trees were uniformly fertilized during the first 2 years of the study.