Using Mid-Summer Leaf Samples to Guide Fertility Programs, Part 1

By this time, mid-July leaf tissue sample results should be available. These tissue results are critical for any nutrient management plan. They should be taken annually to determine if the nutrient program is adequate for the orchard, and the values should be used to tune the orchard´s nutrient program. Research has shown that once an orchard reaches sufficiency of a specific nutrient, increasing it further will not improve yields. This has been demonstrated several times, both within nitrogen and potassium. Second-guessing and adding more fertilizer beyond sufficient levels to address existing yield problems will not improve the situation. This fact is relatively unpopular as it is easier to add more fertilizer than it is to fix the problems that limit orchard production, or assure oneself during a period of second guessing.  More on that can be found here (slide 17) and here (slide 20), and this article will focus on nitrogen The typical nitrogen program often budgets for 20% of the nitrogen to be applied during the post-harvest period. Mid-summer leaf samples should be used to determine if the post-harvest fertility plan should be changed. Within nitrogen, leaf tissue samples that exceed 2.5% can reduce or even eliminate the need for postharvest nitrogen applications. This is based on: Many orchards with leaf levels above 2.5% often have high residual nitrogen within the soil that will meet post-harvest needs, The reduced transpiration rates of the postharvest period reduce uptake of nitrogen, There is significant canopy loss from the harvest process, reducing nitrogen uptake, Nitrogen remobilization back into perennial tissues is happening earlier than previously thought – probably sometime between hull-split and harvest (or maybe even earlier!). Additionally, a long-term study in Arbuckle found that postharvest nitrogen applications did not improve yields in a reasonably high producing almond orchard. Nitrogen levels within

August 1, 2022

Re-evaluating operational costs for a difficult year

2022 will be a difficult year. Increased input costs, including water, fuel, and fertilizer, and decrease crop pricing will impact the operational expenses and crop revenues significantly. Many operations will struggle to maintain cash flows through the year. Operational costs should be closely evaluated to determine if savings are possible. Some expenses may be reduced on a short-term basis until pricing improves. Others may be eliminated from the current and future budgets due to more efficient management. A list of things to consider in helping reduce costs for the coming year include: Balance nitrogen rates. Typically, nitrogen budgets utilize a nitrogen use efficiency factor of 70%. By integrating more frequent, smaller applications of nitrogen, it is possible to assume a much higher utilization ratio – maybe closer to 85-90%. This could reduce nitrogen needs by 15-30 lbs/acre without impacting tree performance. Mid-summer leaf samples can provide feedback to this process (target range 2.2-2.5%). Test groundwater and accounting for nitrogen content. Groundwater in many parts of the San Joaquin Valley contains nitrate-nitrogen. If groundwater is used to irrigate orchard and it contains nitrate, make sure to account for the nitrogen and reduce the nitrogen budget. Balance potassium applications with any compost usage. The amounts of potassium and phosphorus within compost contribute to the nutrient budget of the orchard. Testing compost and accounting for moisture percentage should provide an estimate of the nutrients applied. This can reduce the need for fertilizers containing potassium and phosphorus (as well as many micronutrients). Review annual soil samples to determine if certain nutrients are not needed to be applied. It is common to see very high phosphorus amounts within CA soil samples and additional P may not be needed. Additionally, many loamy to clay containing soils contain potassium reserves. If the amount of potassium is high

April 25, 2022

Managing low hull boron: late season corrective measures before next year’s bloom.

Recently, boron hull analysis was provided by an almond farmer. The analysis consisted of two samples from his ~300 acre (~125 ha) third-year farm. The results were 62 and 84 ppm from the cultivars Nonpareil and Monterey, respectively. Both values were under our targeted hull analysis of 95-105 ppm, with the Nonpareil sample also being deficient (<80 ppm). This orchard has followed a boron program since the beginning of its development. Initial soil samples had indicated very low boron (<0.2 ppm, undetectable), high soil pH (7.7-8.2), and a clay loam texture across the operation. Prior to planting, soil sulfur was applied to lower the pH, as well as diammonium phosphate and potassium sulfate. After establishment, boron in the form of disodium octoborate tetrahydrate (20.5% boron, tradename: Solubor®) was applied at 5 lbs/acre (~5.5 kg/ha) twice a year (spring and fall) through the drip system. A foliar application of sodium tetraborate was also made at 1.8 lbs/acre (2 kg/ha) in the fall after the second year of growth and pink bud. As a result, soil boron levels have improved slightly, with some detectable boron within the wetting pattern. Boron deficiency can greatly impact almond yields. Boron improves pollen tube germination and growth, helping to increase the number of flowers fertilized during pollination. Being deficient in boron can lead to very low nut set and yield, and a willowy- look to the trees. More on this can be found in previous articles (here and here are a few). Given that the most recent hull samples indicate deficiency or borderline deficiency in boron, a new plan has been developed. This plan will utilize additional foliar sprays and soil boron applications and will be applied through dormancy and into the next year. The grower has already applied 5 lbs/acre (5.5 kg/ha) and 2 lbs/acre

December 5, 2021

Major Nutrient Fertilizers: Thoughts to Reduce Operational Costs without Impacting Productivity

Increasing input prices are being observed across the farming sector. Fertilizer prices have increased due to demand, government regulations, weather, trade issues, and energy prices. Prices are some of the highest in a decade, with nitrogen and phosphate fertilizer prices nearly double what they were in 2020. Within almonds, maintaining the proper fertilizer status within the tree is important to maintain yields. Research projects have determined how much of each major nutrient is needed for the tree to maximally produce. These studies first occurred in the early 1990’s and were re-done between 2008-2013. In summary, the projects concluded that for every 1000 lbs of almond kernels harvested, 68 lbs of nitrogen, 92 lbs of K2O, and ~12 lbs of P2O5 are removed from the orchard. These nutrients need to be re-applied to maintain yields. Leaf tissue, soil samples and other in-season assays and monitoring can be used to determine if optimal levels have been achieved. If optimal levels are present, input levels should only match crop demand, while if excess amounts are present, applications can be reduced. These adjustments will help reduce waste, run-off, and leaching.   More on this here and here. Nitrogen (N) usage and uptake occurs when there are leaves on the tree. As such, N applications should only occur in-season. When applying N, more than 68 lbs/1000 kernel pounds of production is applied – typically around 85 lbs/1000 kernel pounds of production. This inefficiency of about 20-30% considers the N lost to NOx conversion, run-off, and leaching. Fortunately, I have observed many orchards much more efficient than this. These orchards have been able to reduce N amounts applied based on the observation of high N within leaf samples.  They have found that maintaining N levels at 2.5% in mid-July allow for the maintenance of high yields (>3000

October 30, 2021

Phosphorus and Almonds

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March 17, 2021

2020 Bloom Considerations

As the 2020 almond bloom/crop year begins, there are several considerations to keep in mind. These points may be useful to help understand observations from the field as well as provide an understanding of any direction received. Nut set. Flower set percentages will vary from year-to-year. For mature trees, about 20-30% of the flowers will set while younger trees will be slightly higher. Even though this is low, crop loads are still high due to the number of flowers that are in each tree. A mature tree will have an estimated 35,000-50,000 flowers, depending on tree size. For more information on this, please see this article: https://thealmonddoctor.com/2016/03/07/almond-set-and-nut-drop/ which discusses the results of a tagging study which followed the development of almonds through the season. External factors greatly influence the set percentages. Crop load from the previous year impacts the amount of energy available for flower formation and bloom. High yields from the year before will reduce the number of flowers that will set nuts. Poor weather conditions can reduce bee flight hours, kill flowers in freezing temperatures, or promote disease. The period of weather risk extends into the fertilization period, which continues for several weeks. Keep in mind that the crop is susceptible to frost and diseases as long as there is a risk of frost and rainfall.   Several factors can be mediated by good farming practices. These include the presence and strength of pollinators (usually honeybees), post-harvest practices, and nutrient deficiencies. Honeybees are required for varieties needing cross pollination (most CA orchards – 2.0-2.5 hives/acre) and recommended for self-compatible varieties (0.5-1.0 hive/acre, although the exact number is unclear). Stronger hives (8+ filled frames) are essentially an insurance policy for poor weather conditions. Hive numbers and placements should take into account the weather. Post-harvest treatment of the trees is

February 9, 2020

Phytophthora: An Update

As previously written (2009 article and 2015 article), Phytophthora is a plant pathogen of almond trees. This fungal-like water mold is common throughout the various almond growing regions of the world, with 6* or more known species causing disease. When conditions are conducive for infection, the pathogen directly invades plant tissues at the crown or roots, leading to loss of nutrient and water uptake, causing tree decline and eventual death. The rate of infection and tree loss depends on the inoculum present, the choice of rootstock, environmental conditions, and cultural practices that may favor disease. Phytophthora inoculum can be endemic to the orchard area or introduced through a variety of ways. Low levels of Phytophthora probably exist in most soils, but typically are not at the levels or location to cause infection unless there are prolonged conditions favoring disease.  Generally, introduction of inoculum into the area of close proximity to the plant is most likely responsible for infections and tree death. This includes the crown or base of the tree where the pathogen infects the plant just below the surface of the soil. These types of infections are most common and can lead to rapid tree loss.  Root infections, which occur when soils are saturated with water, lead to a gradual decline. Finally, aerial Phytophthora happens when spores are deposited on limbs or in crotches of the trees through dust or flooding, followed by wet conditions (e.g. rain). Surface water is believed to be the major contributor of Phytophthora inoculum in perennial nut orchards. Surveys have found several species of pathogenic Phytophthora in high elevation, upstream waterways of the major rivers in California. Due to the ability of the pathogen to survive in water, this pathogen is probably found in all surface water used to irrigate trees worldwide.  This inoculum

September 29, 2019

Fertilizing First Year Almond Trees: Major Nutrients

Determining fertilizer needs for newly planted orchards is challenging. This is due to the desire to grow the trees as rapid as possible while considering the risk of uptake burn and irrigation system inefficiencies. To determine the optimal fertilizer plan, the amount and type of nitrogen and other nutrients need to be considered. Nitrogen: Rate studies conducted in California have found that tree growth seems to peak with 3-4 ounces of nitrogen application per tree. This is based on three different studies – one located near Arbuckle, CA and the other two in Merced County. Within the most recent studies in Merced County, applications were made every three weeks from April through July for a total of six applications. A total of 0, 1, 2, 4, and 6 ounces of actual nitrogen was applied during this period to replicated plots using a NPK blended fertilizer. The source of nitrogen did not create a difference in trunk caliper in the multiple studies within Merced County. Very simply stated, “nitrogen is nitrogen.” There are benefits, however, to the various nutrients that are within fertilizers. If soil levels of phosphorous or potassium are low, utilizing an NPK blend would provide an addition of these major nutrients. The same could be said about calcium-containing fertilizers. If these nutrients are at sufficient levels for plant growth, however, there is minimal benefit from adding additional amounts. Potassium and Phosphorous: Within California conditions, phosphorous (P) and potassium (K) do not appear to be the limiting factor with most soils. The two trial locations within Merced County were located on sandy soil and found no increase in growth from the inclusion of P and K within the fertilizer programs. This does not mean that these major nutrients are not important, rather that many soils contain adequate levels of

April 25, 2019

Alkaline treatments have been shown to reduce hull rot

Recent research has found that alkalizing treatments applied at hull split are able to reduce the severity of hull rot caused by Rhizopus stolonifer. Over the past two years, work by Dr. Jim Adaskaveg and colleagues out of UC Riverside has repeatedly shown that several products reduce hull rot incidence. These products included dipotassium phosphate (applied as the product diKaP) applied at 48 ozs/acre, calcium hydroxide applied at 320 ozs/acre, and Cinetis applied at 24 fl. ozs/acre. A single application of each of these products made at 5% hullsplit was shown to be as effective as several fungicide combinations and reduced hull rot strikes by over 75% in comparison to the untreated control. Multiple applications, with one made at early suture split (traditional first navel orangeworm (NOW) timings), did not seem to reduce strikes further. The cause of the reduction in strikes is unknown. It doesnt appear to have a fungicidal effect on the fungus as often the fungus is present within the hulls. The current thought is that these products neutralize the fumaric acid that is produced by this fungus (this is the acid responsible for limb death).  It could also be due to an increase in tolerance to the toxin from the foliar product. Work is ongoing. With these products, timing is key. Apply around 5-10% hull-split. Since these products may be tank mixed with NOW products as well as other fungicides, confirm compatibility by running a jar test. If struggling in managing hull rot, consider trying these products on a selected blocks to see if they provide any reduction in observed damage. Just remember to leave an area untreated in order to determine treatment effectiveness.  Finally, keep in mind that the use of these type of products for hull-rot enters the “grey world” of registration.  Follow appropriate

June 22, 2018