Nitrogen Use within Young Orchards

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April 9, 2022

Postharvest Nitrogen Management 2018

Many operations often apply nitrogen postharvest. Application rates vary from orchard to orchard, but typically I hear applications between 30 and 50 lbs/acre. This nitrogen is used to rebuild the nitrogen reserves within the tree and help with a variety of tree processes. Being applied late in the season, however, it is susceptible to leaching from over-irrigation and early rains. While it is critical to make sure there is nitrogen available for the tree, postharvest nitrogen budgets should be evaluated to determine if they are too high or not needed. Work at UC Davis has indicated that 15-20% of the nitrogen demand occurs from harvest through the post-harvest period. This suggests that somewhere between 20-30 lbs of nitrogen is utilized during this period, which could be sourced from residual nitrate in the soil or post-harvest applications. A further breakdown of the uptake curve shows that less than 8% of the annual need occurs after September, suggesting the importance of timeliness in application (Figure 1). Applications can begin when the abscission layer begins to form on the later harvesting varieties, but consider lowering rates to reduce the risk of hullrot flare ups (e.g. apply 10-15 lbs/acre instead of 25-30 lbs/acre). Applications of nitrogen in the post-harvest tend to be relatively inefficient due to several factors, including tree defoliation, leaching by early rains or long irrigations, shorter days and lower water use. This suggests that more nitrogen may be needed to achieve a 20-30 lb uptake, but studies in Kern County failed to see a response from applications greater than 50 lbs/acre of nitrogen applied after Nonpareil harvest (mid-August). Rates should not exceed this amount and applications made in September and October should be significantly reduced. Mid-July leaf nitrogen and residual soil nitrate should be taken into consideration when determining the amount.

September 13, 2018

Almond Postharvest Management: Nitrogen Considerations

Written by David Doll (UCCE Merced) and Franz Niederholzer (UCCE Yuba-Sutter-Colusa) Applications of nitrogen in the postharvest period have been promoted as a good farming practice.* Trees utilize nitrogen at this time to rebuild nitrogen stores and provide nutrients for bud development. Research from the Kern County nitrogen trials found that trees can absorb approximately 15% of annual nitrogen demand in the 8 weeks after harvest (30-45 lbs/acre, excluding application inefficiencies). This work was done in a highly productive orchard (3000+ lbs/acre) and applications were applied as multiple fertigation events through the entire year. Fertilizer nitrogen applications should be made as soon as possible after harvest to allow the trees the most time to absorb fertilizer nitrogen before the leaves drop, when root nutrient uptake essentially stops. Whole almond tree nitrogen need after harvest is much less than in the spring (no shoot growth or crop), therefore fall fertilizer nitrogen needs are relatively minor compared with leaf out to hull split.  Fall nitrogen fertilization need is further reduced by remobilization of leaf nitrogen into woody tissue storage as trees prepare to drop their leaves in November (if they are not burned off with zinc sulfate.) Interestingly, recent research suggests that late postharvest fertilization (October) can be skipped if mid-July leaf nitrogen levels are adequate (over 2.5% nitrogen). This work by Franz Niederholzer conducted at the Nickels Soil Lab in Colusa County has found no negative impact on yields when skipping postharvest nitrogen applications within orchards over the past two years. In this trial, trees had mid-July leaf nitrogen values of 2.55% or greater. Trees receive 0 or 30 lbs/acre of postharvest nitrogen in mid October. Trees didn’t receive late zinc sulfate foliar spray and maintained leaves up to or through Thanksgiving. Over the past two years, there were no differences

September 19, 2017

Young Tree Nitrogen Fertilization

In attempts to incorporate varying media within the website, here is my first go at using Google Hangouts to LiveCast a presentation. The recorded presentation below provides nitrogen fertilization considerations for  newly planted and developing orchards. Total length is around 15 minutes. A quick overview of the presentation: Nitrogen is nitrogen. Several studies within CA have indicated that there is no benefit in using different types of nitrogen for fertilizing young almond trees. Some fertilizers, however, may influence soil pH as well as be more prone to leaching; Studies within Merced and Colusa COunty have indicated that newly planted trees will maximally grow with actual nitrogen applications between 3-4 ounces. This has to be adjusted for tree density and application efficiency; Developing trees have developing rootzones which leads to inefficient applications. If fertigating, the best irrigation system would deliver nitrogen directly to the rootzone of the tree (e.g. single line drip with punched emitters). If not possible, controlled release fertilizer has been shown to grow as well as conventional fertilizer and have a lower labor cost (one application and done for the season). The 120 day controlled release blend in this trial was supplied by Agrium Technologies; Do not apply more than one ounce of actual nitrogen per application per year of growth. This helps reduce lanky growth and nitrate uptake toxicity; Take into account residual soil nitrogen and nitrogen within the irrigation water if using a well. In some cases, these may provide sufficient nitrogen; Finally, don’t start too early. Give the trees time to grow and draw down some of the moisture within the rootzone. Around 6″ of growth should be visible prior to the first fertilization. Here is a link for a pdf copy of the presentation.

March 29, 2015

Almond Nitrogen Uptake: Seasonal Perspective

There has been a lot of workshops and seminars discussing nitrogen management in almond. The data and conclusions discussed from these trials has been thought provoking, and has provided information to help better manage almond orchard nitrogen.  One particular slide has caught my attention – and provides the basis of nitrogen timings for almond orchards.

March 7, 2014

A quick review of UC ESP sampling for accurate almond orchard nitrogen fertilization.

This is the first year that the UC Early Season Protocol (UC ESP) model for predicting July almond leaf nitrogen (N) levels from April leaf samples, has been available for public use.  This model was developed by UC Davis researchers led by Dr. Patrick Brown.  Based on calls to several reputable ag labs and questions from PCAs, there seems to be some uncertainty about availability and use of the new model.  Where is the model?  How does is it used?  Who should use it to develop the July leaf N prediction and what should be done with the results?  Does an analytical lab run it for growers and PCA/CCAs?  If the lab doesn’t do it, should/can the grower or their PCA/CCA to do it, and, if so, where is the model?  This blog post is intended to answer these questions and help interested almond industry members use the UC ESP model.

April 20, 2013

Nitrogen Management in Mature Almonds, Part II

In a recent post, I talked about the 4 R’s – Right Rate, Right Timing, Right Place, and Right Material.  How do all these R’s fit together to help produce a profitable, sustainable almond crop?  I’ll use an example familiar to me: the Nickels Soil Lab in Arbuckle in the southern Sacramento Valley. 

March 26, 2013

Nitrogen Management in Mature Almonds, Part 1

Nitrogen is the most important mineral nutrient in almond production.  It is absorbed as nitrate or ammonium by active roots.  Mature almond trees use 80% of their total annual N requirement between March (full leaf out) and mid-May – June (kernel fill).    If the N isn’t available in this key application window, yield can be lost. To maximize yield (income) while minimizing N losses from the root zone ($ losses) that hurt growers wallets and may harm the environment attention to the four R’s – Right Rate, Right Time, Right Place, and Right Material — is needed in all orchard fertility programs.  Different nutrients are needed at different times and amounts by almond trees.  Spring is a key time for almond orchard nutrient management and the key time for nitrogen inputs.

March 14, 2013

Post Harvest Nitrogen: How Much?

Generally, we recommend 20-25% of the season’s nitrogen budget to be applied in the post harvest period. This is based upon having a Mid-July leaf nitrogen value within the range of 2.2-2.5%.  This nitrogen is used for the post-harvest growth processes, which includes both vegetative and fruit bud development and some vegetative growth. When making this application, the sooner, the better, as it will help reduce tree stress.  Studies have shown that ‘Nonpareil’s’ fruit bud differentiates about 7-14 days after harvest, while other varieties, such as ‘Carmel’, the majority of fruit buds differentiate prior to ‘Carmel’ harvest. This timing will be delayed in cool, mild years. Tree stressed imposed during this period will reduce fruit bud set, and the buds will remain vegetative (leaf buds). In the cases of above recommended mid-July leaf nitrogen levels, nitrogen should still be applied, but the amount should be reduced. For example, if leaf nitrogen values are around 2.8%, apply 15-20% of the total seasonal nitrogen budget. If over 3%, reduce that application further to 10-15% of the total nitrogen budget. Nitrogen should be applied with caution in the post-harvest period as early rains may leach nitrate in sandier soils. Late fall (Late September, early October) nitrogen applications should also be reduced; the trees ability to pick up nitrogen is decreased due to lower levels of transpiration.

September 6, 2012