Location: Water Management ResearchTitle: Determining pomegranate water and nitrogen requirements with drip irrigation Author
Submitted to: Agricultural Water Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/5/2017
Publication Date: 6/3/2017
Citation: Ayars, J.E., Phene, C.J., Phene, R.C., Gao, S., Wang, D., Day, K.R., Makus, D.J. 2017. Determining pomegranate water and nitrogen requirements with drip irrigation. Agricultural Water Management. 187:11-23. doi: 10.1016/j.agwat.2017.03.007. Interpretive Summary: Pomegranate was identified as a crop with extensive health benefits resulting in an increased interest in production with approximately 12,145 ha growing in California. Even though pomegranate has been cultivated for thousands of years, very little is known about its basic agronomic and fertilizer requirements. We conducted an experiment in the San Joaquin Valley of California to determine the water and nitrogen requirements of a multi-trunk pomegranate bush irrigated with high frequency surface and subsurface drip irrigation. We used a large weighing lysimeter to determine the water requirements and three levels of applied nitrogen to characterize the nitrogen requirements. We determined that the water requirement of a mature pomegranate bush was in the range of 853 to 932 mm depending on which irrigation system was used. The subsurface drip irrigated trees required less water than the surface irrigated trees, and these irrigation treatments did not result in reduced yield or quality. Applied nitrogen in excess of 112 kg/ha did not result in increased fruit yield in either irrigation system, and yield did not differ between the two irrigation systems. High frequency irrigation enabled close control of root zone water content that minimized deep percolation losses and transport of nitrate to groundwater. Weed pressure was lower with subsurface drip irrigation compared to surface drip. Use of high frequency subsurface drip irrigation will result in reduced water application and fewer field operations.
Technical Abstract: 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 nitrogen 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 nitrogen (N) sub-treatments (N application rates of 50, 100, and 150% of adequate) with 5 replications. A weighing lysimeter located in the experimental field was used to automatically irrigate the orchard after a loss of 1.0 mm. Phosphorus (PO4-P) was continuously injected during all irrigation and potassium (K2T) was injected weekly. 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). 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. Differential N treatments were started in 2012 and continued throughout the remainder of the project. The trees were harvested for yield and quality for the first time in 2012. We report the results of the study from 2013 to 2015. From 2013 to 2015 the applied nitrogen 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 nitrogen. 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 went from 645 mm to 932 mm and the SDI increased from 584 mm to 843 mm from 2013 to 2015. A fifth order polynomial was fitted to the crop coefficient using the 2015 data. The use of SDI resulted in lower weed pressure than in the DI irrigated plots in all three years. High frequency irrigation resulted in nitrate being managed within the soil profile to a depth of 1.5 m by minimizing deep percolation losses to the groundwater. While the yields were higher in the SDI than the DI system they were not statistically different. Although there were some differences in N content in tree leaves and fruit peels, there were no N differences in fruit arils among N rates. The nitrogen requirement is in the range of 62 to 112 kg/ha for a mature pomegranate orchard.