#SoilMatters

Almond bloom: A very important stage in the life of the crop; one filled with anticipation and trepidation. At this stage, growers work to get pollen (from the Anther; male part) in contact with the Stigma (female part) by various means.

The Science: Almond bloom is beautiful sight to see, but don’t think it is just for our enjoyment. Almond trees’ primary objective is to propagate the species into the next generation. Blossoms are the “lure” plants use to attract pollinators. At the same time, plants’ physiological activities run at a feverish pace with time, temperature and weather all contending against the plants pollination efforts. The process, while orderly, behaves a lot like a Rube Goldberg device, due to the many intricate, interdependent activities involved. For example: When a pollen grain connects with the stigma, it is considered “pollinated” and starts the Pollination process. Next begins the “fertilization” process: The pollen tube elongates (while the sperm travels along it simultaneously) down the length of the Style to the ovary where it attaches to the ovule allowing the sperm a chance to fertilize the egg and form a Zygote. This process requires a large amount of energy from within each pollen grain. Every pollen grain contains both sperm and tube cells and the health and viability of the pollen is directly related to the nutrition available to the plant. There are many factors which can affect the almond bloom period. These are called “stressors”. Stressors are a problem, because plants must manage them, in addition to normal activities, at each stage of development. Some examples are Environmental (Temperature, precipitation, etc.), Cultural (Nutrition, irrigation, etc.) Biological (fungal, pest pressure, etc.). Without a plan, these can all significantly ill affect your crop’s yield potential.

Practical application: At the start of the bloom stage, there is an internal plant “tug-of-war” between a large volume of plant “dormancy” hormones and the introduction of “reproductive/bloom” hormones. As the tree awakens, it is thirsty (dehydrated) and hungry (energy deficit) from the dormancy period. Think of it like a grizzly bear awakening from hibernation; the bear’s top priorities are water and food, because much of its reserves were depleted while sleeping. Almond trees are no different. As a grower, you can take an active role in these needs. This is where a fertility plan can benefit you by increasing not only your orchard’s health, but yield and profitability. Let’s take a look at each of the stages of bloom and where your nutrient focus should be and why.

Green bud: Flower buds are swollen and green plant tissue is exposed, but no blossoms are yet visible. This is due to hair-root activity which has already been underway for 2 to 3 weeks. Roots are actively foraging for food and water supplies in preparation for the upcoming bloom event. Start fertigation plans now, with nitrogen and “plant-ready” orthophosphate for strong root support. Application rates should be based on soil texture, to avoid over-applying for the soil’s capacity and plants’ needs. Why orthophosphate? When soil temperatures are under 63-65°F (top 6” of soil), phosphate (P2O5) is still soil-bound (especially in calcareous soil types) and not yet available for feeder roots’ use. “Plant-ready” orthophosphate (H2PO4- or HPO42-) is not temperature dependent and therefore immediately usable by the roots, in cold soils. After dormancy, the root system and crop set are limited to the amount of stored nutrient energy available. This critical development stage is much like the start of a race and stumbling is not an option. Why take the chance of running short on nutrient supply? It is a Good Management Practice (GMP) and a major benefit to fortify roots and restock the root-system with phosphate, for the high energy demands that bloom puts onto the entire plant system.

Pink bud: Without a bud, you can have no bloom. Without bloom, you can have no almonds. Plant energy is vital for a good bloom. At this point, buds have been swelling up, growing rapidly. Nutrient application focus should now shift from fertigation to foliar feeding. While there is not yet a leaf in the field, there are on average, 75,000 to 150,000 blossoms per tree and each is rapidly drawing on stored plant energy reserves, which cannot be supplied via the root system, in cold soil temperatures. Applying “plant-ready” foliar nutrients directly to these plant parts, requires low per acre rates and provides nutrients/energy to supplement the demands of the pollination process. Foliar applications supplement the developing crop while soil temperatures warm and then begin soil-nutrient release for root uptake.

Full bloom: This is one of the most effective times to directly increase crop yield potential. When blossom pollination happens it triggers the fertilization stage. This is a time of massive energy demand. When fertilization occurs, almond kernel cell division starts. Under normal conditions, this takes 23 to 27 days to complete. However, it is directly affected by temperature and nutrient availability; warmer than normal temperatures accelerate (shorten) the cell division “window” and cooler than normal temperatures extend this process. Applying “bio-available” nutrients delivers energy and food, at this critical stage of crop development. In simple terms, more cells per kernel equals more weight per kernel at harvest. Remember, this is also a period when the plant is susceptible to infection through the blossoms and steps should be taken to avoid disease flare ups. Applying foliar orthophosphate helps plants build their own defenses for better health and disease resistance.

Petal fall: At this point, almond kernel cell division continues to occur at a very rapid rate. Soil temperatures are still cold (<63-65°F) and foliar feeding is an efficient way to supplement plant and crop nutritional needs. Time is of the essence here as the plant will soon begin to shift the growth emphasis from crop-set into canopy-development. Feeding focus should now be on the developing nutlets and canopy. Crop retention is vital to profitability and photosynthesis from a healthy canopy plays a major part from now and until harvest time. Almond trees instinctively know how much crop they can support based upon current stored energy reserves. Remember, a plants primary objective is to perpetuate the species into the next generation and trees will not set more crop than can be matured. When trees run short of energy during bloom, they will begin to self-regulate at Petal-fall stage, by aborting nutlets. This is a time to be very aware of the orchards growth response and be ready to make rapid GMP fertility decisions, as needed. The crop won’t wait for you, so be readiness is crucial!

40-45 days Post-Full bloom: Soil temperatures are normally still below 65°F, so you won’t yet be benefitting much from soil-fixed nutrient release. Foliar applications will still be very useful and should focus on boosting canopy health and vigor. Photosynthetic production and efficiency are crucial to get the plant feeding itself as early as possible. If you notice a weakly growing canopy, just after Petal-fall, it can be an early indicator of a heavy crop set (See everything you are looking at!). The tree could be sending extra nutrition to developing nutlets due to positive fertilization activity. Tissue sampling should happen once mature leaves are visible. Use the tissue results as a treatment guide for making fertility decisions. Don’t guess at what your orchard or crop needs. At this stage, fertility applications are building internal solids (oils) for more kernel weight. Total Soluble Solids (oils) are heavier than water and will not evaporate when you dry down the orchard before shaking. This stage lasts (April 15—June 15) approximately 60 days. Fertility plans should include fertigation and foliar feeding with emphasis on nitrogen, potassium, calcium and traces as needed.