1a.Objectives (from AD-416):
Determine real time seasonal nitrogen requirements to improve FUE of mature pomegranates using drip and subsurface drip irrigation. Determine required level of nitrogen to maintain N levels in mature pomegrantes. Determine effect of N fertilization on macronutrient concentrations.
1b.Approach (from AD-416):
The project will use a complete randomized design of 2 irrigation treatments and 3 fertilization treatments with 5 replications. The water requirement will be determined by weighing lysimeter and the fertiliztion will be determined by tissue sampling. This is a field project on 2 acres.
This project supports research under objective 2 of the in-house project, Developing sustainable water management strategies. Nutrition and irrigation are critical components of sustainable management. This research quantifies the nitrogen requirements for pomegranate. Pomegranate is an emerging minor crop in California because of potential nutritional values. However, very little is known about the water and fertilizer requirements under the fully irrigated conditions found in California agriculture. It is thought to be both drought and salt tolerant which means that there is the potential for a wide range of responses when fully irrigated and provided with correct nitrogen nutrition. Funding from the California Department of Food and Agriculture (CDFA) was used to establish an experiment on 3.3 acres to determine the effect of irrigation system type and fertilization on pomegranate yield and quality. The site is located on the University of California, Kearney Agricultural Research and Extension Center in Parlier, California. The site contains a large weighing lysimeter that is being used to characterize the crop water use and control the irrigation system. The experimental design was a randomized complete block with 5 replications. There are 2 irrigation treatments (surface and subsurface drip irrigation) and 3 fertilization treatments (50%, 100% and 150% of required nitrogen). The subsurface drip irrigation system had the lateral installed approximately 60 cm below the soil surface with a drip line 90 cm on each side of the crop row. The surface drip system had the laterals installed on the surface and 90 cm from the crop row. The irrigation was initiated when 1 mm of crop water use was measured by the lysimeter located in the experimental field. The first 2 years were used to establish the trees and complete the installation of equipment and system operation. Complete data collection was begun in the third year and these data are included in this report. The cumulative applied water was 456 and 441 mm for the surface and subsurface drip irrigation, respectively. This is equivalent to approximately 53.5 and 51.7 L/tree/day for the surface and subsurface drip, respectively. The differences in applied water were the result of adding additional water to the surface to account for evaporation losses. Studies in India found the range of water use from developing to maturity to be in the range of 33 to 66 L/tree/day which compares favorably to our data. The fruit were harvested twice with the first harvest being classified as prime and going to the fresh fruit market and the second harvest being used for the juice market. The prime fruit yield average ranged from 11 to 13 metric tonnes per ha and the juice yield ranged from 9 to 11 metric tonnes per ha. There were no statistical differences in the total yield based on applied fertilizer. These values were comparable to reported fresh market yields. The CDFA support was through the Fertilizer Research and Education Program (FREP) and one objective of the program is to promote wise use of fertilizers, which is a major objective of this research. Soil sampling to a depth of 120 cm was used to characterize the distribution of nitrate in the soil under each of the irrigation and nitrogen treatments. The use of high frequency irrigation demonstrated that nitrate could be kept in the root zone. The soil water and nitrate profiles demonstrated that no leaching occurred during the irrigation season. This project will be repeated for 2 additional years to provide better estimates of the crop nitrogen requirements as well as the water requirement. These data are particularly valuable because of the potential for ground water pollution through deep percolation of nitrate as a result of poor irrigation practices. Plant sampling demonstrated that adequate N levels were found in leaf tissue for each of the nitrogen levels. Pomegranate is widely consumed throughout the world and is an emerging crop in California. This research will result in improved water and fertility management of an important crop.