Know when it’s time to boost nitrogen for almond crops

For almond growers, 2022 is shaping up to be another interesting year. As I write this a few weeks before bloom, January appears to be mostly dry, Shasta Lake storage is half the January average, the market is closed, and fertilizer costs are up from there. one year old. No one can know for sure what the season will bring, but getting the most out of more expensive fertilizers is an overall goal worth considering.

Will it pay? I think there’s a good chance that’s the case. For example, with UN32 currently hovering around $1.15/lbs N, increasing nitrogen fertilizer efficiency (pounds of nitrogen removed from the orchard in the crop per acre/lbs of nitrogen applied per acre) goes from 70% to 80% at a savings of $35/acre. (minus UN32 required) for an orchard producing 2,500 lbs of seed/acre with no impact on tree status or nitrogen yield. In addition, ensuring that the orchard’s nitrogen nutrition is more adequate than excessive could save hundreds of dollars by reducing the incidence of hull rot.

This is the March edition, so what would an efficient and effective N program look like at this time of year?

At the beginning of March, it is the beginning of the nitrogen supply season in the almond orchards. The 30-day supply of N that trees store over winter in woody tissue (roots, trunk, and branches) and remobilize to grow new tissue from flowering is depleted. External sources of N, mainly ammonium and nitrate in the soil of the root zone, become the main sources of N; the building blocks for continued nut and sprout growth.

SMALL BUT CRITICAL NEED

Nitrogen requirements of the orchard from March to mid-April are much lower than those from late April to early June, but are essential for the development of healthy current and future almond crops. Indeed, 80% of the almond trees of a tree grow on spurs. A tree’s spur dies at a rate of 5-25% per year, so vegetative growth (new extension shoots and short spur on the previous year’s shoots) is needed to provide a “harvest” spur replacements for future production.

Spurs sprout in the spring, usually stopping the growth of the extension in April or early May. Adequate N availability in March feeds both the current year’s crop and the shoots/sprouts where future crops will grow. Click here to learn more about the vegetative growth of the almond tree.

How much N is needed to meet the N demands of the orchard in March? Current recommendations can be found in the free publication, Nitrogen Best Management Practices (BMP), available from the Almond Board of California. The crop’s total N requirement is still the same as it has been for the past decade – 68 lbs N/1000 grains of harvest. Therefore, a 2500 kernel/lb crop will contain 170 lbs of N, and this amount of N will leave the orchard at harvest.

The research-based recommendation is that 20% of an orchard’s total annual N budget be available at the root surface between 70% of leaves (so applications should start just before) and when nuts are full. cut. This time is roughly mid-March to mid-April or late April. Estimated crop yield and nitrogen fertilizer inputs in March-April should be based on estimated crop yield from orchard history and flowering conditions. In the new Nitrogen BMP publication, 30-40 lbs N/acre/yr is recommended to support vegetative growth of trees at the sixth leaf or later. How much of that should go to applications from March to April? It’s up to growers and CCAs to decide how much, but I’m guessing it’s at least N10 lbs/acre followed by that rate or higher in April.

What is the source of March-April nitrogen inputs in almond orchards? Typically this is N fertilizer. Soils are typically cool in March/April compared to May or summer, so there is relatively less N available through mineralization of soil organic matter. Groundwater used for irrigation may contain nitric nitrogen; however, little irrigation water is usually applied early in the season (March-April), so the N added in this way can generally be much lower than that added later in the season. This leaves the N fertilizer.

The most effective N fertilizer program provides several small amounts of N compared to a single application in March. There has been widespread adoption of this strategy in California. At a statewide meeting in the fall of 2020, more than 30% of the grower or CCA audience reported applying low rates of fertilizer with each irrigation. These little “shots” of N add up to a very effective “spoon” fertilizer program, especially if N is injected into the second half of the irrigation set so that the fertilizer stays in the zone. upper root where the greatest number of active roots are found.

LEAF SAMPLING TIME

Finally, to ground-check the March-April N program described above, take a leaf sample early in the season. This sampling protocol and schedule was developed at UC Davis to accurately predict orchard leaf nitrogen levels in summer from a mid-April sample. Since the July leaf sample is too late to modify a fertilizer schedule for the current season, the April sample results, predicting summer leaf levels, should be useful in adjusting a fertilizer program to maintain proper leaf levels – not too much or too little. If the prediction is for high summer N levels, subsequent N fertilizer rates should be reduced, while the reverse is true if the foliar N prediction is for lower than desired summer foliar N levels. . For more details on spring leaf sampling as well as general N rates and schedules for the rest of the year, click here to view the Almond BMP publication.

Good luck to all producers for this new year. Hopefully the information in this column will be helpful in starting to chart a course through the upcoming season.



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