UC Davis researchers have partnered with local UCCE Farm Advisors and industry to evaluate and update the amount of nitrogen (N) removed from orchards with the harvest of ‘Manzanillo’ table olives. Growers can utilize this information in the development of N management plans specific to individual orchards with the overall goal of improving N use efficiency, reducing N losses, and preserving groundwater quality. 

The ratio of N applied to N removed is a key metric in the Central Valley Irrigated Lands Regulatory Program (CV-ILRP). Growers report applied N and yield to agricultural water quality coalitions. The coalitions then convert yield to quantities of N removed using crop-specific coefficients and then report estimates of N removed from orchard systems to the Central Valley Regional Water Quality Control Board. The objective of this project is to develop reliable N removal coefficients for crops grown in the Central Valley, including table olive. The project is supported by a grant from the California Department of Food and Agriculture – Fertilizer Research and Education Program (CDFA- FREP). Reports containing N removal coefficients for the crops completed so far can be found at: http://geisseler.ucdavis.edu/Project_N_Removal.html

In Tulare County, thirty-two samples of ‘Manzanillo’ table olives were collected from the local fruit receiving station from 2021-2023. Samples were then sent to UC Davis for analysis of total N in the Nutrient Management Lab. Nitrogen removal rates in olive fruit ranged from 5.62-8.08 lbs N/ton of fresh fruit, with an average N removal rate of 7.1 lbs N/ton of ‘Manzanillo’ fruit. Chico State also hosts an online tool for estimating the rate of N removal from orchards comprised of dominant oil varieties including ‘Koreniki’, ‘Arbosana’, ‘Arbequina’. 

Incorporating foliar nutrient analyses will allow growers to monitor the tree’s nutrient status and make corrections to the fertilizer program if needed. Leaf analyses are a valuable tool to detect nutrient deficiencies but are less valuable as indicators of excess nutrient availability. Olive fruit is only an important N sink during the initial phase of growth, right after flowering. Foliar N content in July/August should range from approximately 1.3%-1.7% to maintain adequate plant health.