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Forget June 1^st, fertigate almonds all season

We prayed for rain, and apparently, we really asked for it!

No almond growing region in California has escaped the unrelenting downpours and lower than average spring temperatures this season. Growing Degree Days for the state are currently at a 12 year low for the period from January to present (Bountiful Ag). And without even getting into the details of rainfall accumulation, we all recognize that fields are saturated. And even though we are past 70% leaf-out, it’s difficult in some cases to justify turning on our irrigation to run nutrition to our trees. This makes for a very condensed application window based on outdated management strategies.

June 1^st has been a historical target for finishing nitrogen applications in almonds for a couple of reasons.

The first reason the industry has adopted a June 1^st cutoff for nitrogen applications is to minimize the chance for excessive N at harvest so that we can shake cleanly and minimize potential trunk damage if trees are shaken when bark is still green. Excessive irrigation plays a key role here as well.

The second reason pertains to hull-rot infections. Hull rot can manifest from various fungal pathogen infections. Currently, the most common are Monolinia, Rhizopus, Aspergillus niger, and Phomopsis. Spores from these pathogens are ubiquitous in our production systems and will infect nuts at various stages of hull-split. Two conditions that have proven to increase infection rates are excessive irrigation and excessive nitrogen content at hull-split.

It is necessary to point out the commonality between these cultural management objectives is mitigating excessive nitrogen and/or irrigation.

Now let’s consider the management practices that perpetuated this June 1st cutoff goal.

Historically, many growers have managed nitrogen applications by splitting the season’s total nitrogen target over 3-4 mostly equal applications in the spring/early summer and post-harvest. We lovingly refer to this strategy as the “slug” approach. For these growers, with a target N rate of 200 lb/ac, they would typically apply about 50+ lbs of N per ac, 4 times per year; a wildly inefficient strategy. Let’s put this in the context of human nutrition… They say the average adult requires 2000 calories per day. So on a monthly basis, imagine this adult that requires a total of 60,000 calories decides to consume those calories in four meals spaced out every 7.5 days. As you might imagine, a painful food coma will follow one 15,000 calorie meal, and after a day or two this individual will likely be starving for several days before their next meal. Literally, feast and famine.

Now aside from the obvious value of ease of application and decision making, why have we managed our orchards in this way? Let’s look back at the old 20-30-30-20 rule for nitrogen management. This older rule stated that 20% of your nitrogen budget needs to be applied in March, 30% applied in April, 30% applied in May, and the last 20% applied post-harvest. Though the accuracy based on the information at the time is not disputed, the problem with this rule is that it unintentionally gave growers the recipe and schedule for a slug-based approach and did not highlight the fact that trees do not only require nutrition at discrete times, but more continuously through the season. This oversupply, followed by undersupply has negative consequences for tree physiology, environmental losses, crop productivity and grower profitability.

Ultimately, because we were putting on larger applications of nitrogen fewer times per year, in order to reduce the total nitrogen content at hull-split, we began to cut off these applications by June 1^st.

Consider this 20-30-30-20 approach as it pertains to hull-rot specifically. When we oversupply any element, nitrogen, in this case, we create nutritional imbalances. When we are making large applications of nitrogen early in the season when cells are dividing and growing into various functional components, if we oversupply N relative to elements like calcium and boron, then we are creating weak cell walls and membranes.

These weakened cell walls and membranes predispose those hull cells to fungal infection upon splitting. Therefore, it doesn’t matter when you cut off your nitrogen applications, if you create this imbalance the damage has already been done early in the season and is irreversible.

So what can be done to mitigate this issue of feast and famine feeding?

The answer is continuous fertigation.

The MyAlmonds program at the Incubator Farm has taken on the challenge of attempting to match our nitrogen applications to the defined demand curves for the past 3 years. There is one caveat to our strategy that is our first application of nitrogen has been ammonium sulfate at 25% of the total N budget. This is to support our trees with a much need source of sulfur, to mildly acidify the soil that is slightly basic in nature, and to have a non-leaching source of N that becomes plant available as the soil warms and microbes become active (which tends to coincide with root activity). We then initiate weekly fertigation applications from early nut sizing through till harvest. It is important to note that we are predominantly utilizing nitrate-N during these fertigation events to make sure that when we are supplying only what the tree needs for that week, that it is delivered in a form that is fully plant-available. We call this strategy On-Demand Feeding.

The core elements of this strategy are continuous fertigation from 70% leaf-out till harvest (or later), breaking down seasonal demand into weekly demand based on demand curves, and supplying nutrients in plant available forms. It is equally important to schedule our applications to be delivered at the right time during the irrigation set, relative to soil texture for each site. As we have stressed for many years now, this is essentially a practical implementation of the 4R’s of Nutrient Stewardship! When you adopt continuous fertigation and move from 3-4 applications per year to 15-20, that you have 5x the opportunities to fine tune your rates relative to demand by calibrating applications by tissue sampling along the way.

So how has this strategy performed?

As you can see, from the 3-year averages above, we have produced double digit improvements in yield, net grower ROI, and actually reduced hull rot infections by over 30% even though we are fertigating more than 2 months later than the historical June 1st cutoff. This On-Demand Feeding strategy has increased production while simultaneously reducing total nitrogen waste (nitrogen not recovered in yield) and the volume of water required to produce a pound of almonds.

Yara’s Incubator Farm in Modesto is committed to validating best management practices in commercial almond production systems. The results from the last 3 years show that On-Demand Feeding results in less input waste, greater productivity, and improved profitability. So ditch the historical constraints of slug-based feeding and limiting your application window, and begin aligning management practices based on crop demand for better results.

Please reach out to our team to learn more about On-Demand Feeding, continuous fertigation, or trials being conducted at the Incubator Farm.