Avoid early or late applications (before bloom or after harvest) as trees aren’t taking up nitrogen during those times.
(March 13, 2020) – Last week, in the first of two-part series, we explained the vital role nitrogen plays in tree health and in the creation and maintenance of a sustainable almond orchard.
Today, we are going to demonstrate how to efficiently manage nitrogen, taking the information from last week and putting it into action.
Before we begin, don’t forget that the Almond Board of California’s (ABC) California Almond Sustainability Program (CASP) includes a Nitrogen Budgeting Calculator that allows growers to input data specific to their orchard and receive a total nitrogen fertilizer recommendation, along with recommended application amounts that are calculated by the stage of crop growth. The calculator, along with ABC’s Nitrogen Budgeting Tool, provides growers with the proper paperwork they need to submit nitrogen budgets to their local Irrigated Lands Regulatory Program coalition.
Nitrogen Management: Back to Basics
Before making any decisions around application, growers should determine their orchard’s nitrogen needs based on expected yields (using the CASP Nitrogen Budgeting Calculator). Then, growers can make a preseason fertilizer plan based on expected yield as well as nitrogen, irrigation and other inputs. In the plan, growers should base their fertilization rate on realistic, orchard-specific yield, accounting for all nitrogen inputs and adjusting, as necessary, in response to spring nutrient and yield estimates.
Once expected yield is determined and a plan is in place, growers should apply nitrogen according to specific points within the almond lifecycle, timing application to match demand as much as possible.
In mid-April, growers should conduct a leaf analysis following full leaf expansion to determine their trees’ nitrogen levels. Trees need nitrogen most between 70% leaf out (typically about mid-March) through kernel fill and hullsplit (usually in July). In fact, 80% of nitrogen uptake occurs during that time frame. While applications before bloom or after harvest are less effective, if trees are healthy, growers can apply up to 20% of nitrogen at hullsplit and then immediately post-harvest.
During the April time period, growers should avoid applying nitrogen before major storms or major irrigation events. Strong rain will likely flush some or all of the nitrogen below the root zone before the tree can use it, wasting grower time and money in addition to implications for tree health.
“Especially in sandy soils, if you know it’s going to rain the next day, that is not the best time to apply. You want to try to avoid leaching; you want the nitrogen to go into the tree instead of wasting your money and losing it,” said Sebastian Saa, ABC’s senior manager of Agricultural Research.
Saa also encourages growers to pay close attention to their irrigation systems (pumps, lines, sprinklers or micro-drip valves) and distribution uniformity to make sure water – and nitrogen – is being applied evenly across the orchard. When fertigating, nitrogen should be added near the end of the irrigation set (in the second half of the irrigation cycle). This keeps the nitrogen near the top of the root zone, where most of the active roots are. Growers should also base their fertilization rate on realistic, orchard specific yield, accounting for all nitrogen inputs and adjusting, as necessary, in response to spring nutrient and yield estimates.
UC Davis plant nutritionist Patrick Brown, speaking at The Almond Conference 2019 in December, said that understanding the differences in productivity in zones within an orchard (cultivars) also will influence how nitrogen should be applied.
“Precision fertigation is essential for efficiency,” he told growers.
In May, growers are encouraged to review their leaf analysis results and updated yield estimate. From there, it’s wise to adjust fertilization for the remainder of the season, and at harvest growers should review their yields and adjust post-harvest fertilization, as needed.
It’s important that growers remember every year, every orchard will have different levels of nitrogen demand. This ABC article, “Applying Nitrogen in Spring: Guidelines for Grower Success,” provides more detailed information on optimal application timing.
Research supports earlier leaf analysis
As mentioned in part one of this series, when it comes to nitrogen applications, growers should keep the four R’s in mind: applying nitrogen at the “right rate,” at the “right time,” in the “right location” and using the “right source.” But there is another crucial step – “right monitoring” – that plays a key role in efficient nitrogen management.
Monitoring frequently involves leaf tissue sampling, which provides insight into how nitrogen is being absorbed and used by the tree. Research done at UC Davis and funded by ABC suggests that analyzing leaves earlier in the growing cycle allows maximum time to adjust nitrogen levels.
Experts recommend that sampling take place in April – roughly 43 days after full bloom. The results from this earlier sampling, Saa explained, will allow growers time to evaluate their trees’ nitrogen status and also provide critical data of what applications may be required in the current year to meet yield targets. (For step-by-step instructions on how to gather leaf samples, check out the ABC article, “Early Leaf Tissue Sampling Reveals Actionalble Insights.”)
“There’s still value in conducting a July sample; however, adding an April sample allows you to be proactive and adjust your fertilization plan accordingly,” Saa said. “Following up with more sampling in the summer would allow growers to evaluate the impacts of the changes in application made in spring, thus informing plans for future seasons.”
For more information on proper nitrogen management and nutrient management, in general, growers are invited to check out the slides presented at The Almond Conference 2019 during the session titled “Research Update: Nutrient Management.” Growers with more specific questions on their orchards’ nitrogen needs are encouraged to contact Saa at ssaa@almondboard.com.
