Fall is an important foundational stage
The Postharvest window is foundational for preparing for winter dormancy and early spring development demands. Fortifying plants with the needed mineral nutrients for the dormant period requires a good volume of energy and nutrients for plant development activities. These reserves are built up in the previous growing season and then stored in bio-available forms within the plant. But, before you call it a year, realize that a significant amount of reserves can be produced and stored up in the fall while plants are still photosynthesizing and soil temperatures are above 45°F. Which means there are things that can (and should) be done annually to improve plants’ preparedness for winter and spring needs.
When we begin to see plant canopies changing color and the green starts to fade away, it is a reminder that this is a key time to take advantage of Nature’s cycle as we move towards the end of the growing season. Canopies change color in the fall when the pigments present in the leaves change proportions; these pigments include chlorophyll, carotenoids and anthocyanins. During the growing season these three pigment compounds are in proportions that give leaves a green color.
In the fall, much of the chlorophyll is translocated back into the plant and carotenoids and anthocyanin compounds are more prevalent. This gives leaves their yellow, yellow-orange or red-orange colors, based upon which of these secondary metabolite compounds are most prevalent. Nature is, if nothing else, efficient. In the fall, this includes the decomposition and redistribution of many of the leaf-stored mineral nutrients. Some of these are in mobile forms, some are immobile and others are in compounds which can be disassembled through the synthesis of specialized enzymes.
At the same time, the plant internally shifts to a phloem-dominant flow directed back into the plant and fortifies buds, spurs and shoots for a more productive growth response in the spring starting with early development (i.e. pollination, pollen tube growth, fertilization, canopy growth, etc.). This shift in internal flow can work for you or against you. This is why it’s a good idea to apply plant-ready and bio-available forms of nutrients to plants and why care should be taken in the fall with systemic herbicide applications prior to leaf senescence.
What does this equate to in plant nutrient values? There are some logical conclusions which can be drawn based on fall plant tissue nutrient levels and canopy leaf weight per acre. For example, researchers have calculated there are 12,000 pounds of leaves per acre, in an average producing almond orchard. When that canopy weight is multiplied times the plant tissue nutrient percentage values for nitrogen, phosphorus, potassium, calcium, magnesium and sulfur we get a good indication of how many pounds of each of these nutrients are present and “potentially” available per acre, with the right treatments for recycling and future growing needs.
Take for example, the fall plant tissue values from a mature almond block in the central San Joaquin Valley.
These nutrients are already contained within the plant canopy and are therefore ‘bio-available’ and readily plant absorbable. Taking advantage of the phloem-dominant flow with a microbially fermented micronutrient enzyme formulation increases the plant’s ability to translocate its canopy stored nutrients back into the plant. Otherwise, it’s impossible to know when those nutrients will be re-mineralized and recycled if defoliation is stimulated with a zinc sulfate foliar application. Leaves will senesce and fall to the soil surface, but it’s anyone’s guess as to how efficiently the decomposition process will occur for soil absorption and rootzone assimilation. And this is assuming leaves stay on the soil surface under each of the trees and aren’t swept or blown away during the fall or winter.
The same calculations can be made with an apple and cherry tree, but they are physically smaller trees than mature almond trees and this should be taken into consideration. For these calculations, let’s consider there are half as many leaves per acre as almond trees. At 6,000 pounds of leaves per acre we can still make these calculations against fall plant tissue analysis values. Based on those conditions, mature apples and cherries would have the following nutrient values. The top row for each crop is the actual plant tissue nutrient percentage and the following row is the calculated pounds of nutrient per acre stored in the canopy.
Based on the current national average major fertilizer prices (as of 9/2023), from DTN Retail Fertilizer Trends, nitrogen is at $0.62/pound for urea and $0.65/pound for UAN32 ($2.275/gallon), $3.54/gallon for 10-34-0 and $508/ton for potash (0-0-60). Apples need 1 ton/acre gypsum (CaSO4) and cherries need 3.1 tons/acre for calcium replacement (this will also cover the sulfur replacement). Gypsum price/ton is between $85-90 delivered, but not applied. The nutrient values in pounds are what is stored in the plant canopy and with the right fertility applications can be recycled and reused in the coming season. These plant stored nutrients can help to offset some of the plant nutrient needs and expenses, especially in the early season.
As you can see, in the chart below, if these nutrients are not being recycled effectively with your nutrient management plan, it adds up to a significant additional fertilizer input cost that could be avoided with a fall treatment.
We recommend having this discussion with your crop advisor and, if necessary, get a second opinion regarding your fall treatments. There are affordable and effective “bio-available” formulations available in California and Washington State which stimulate and improve canopy nutrient translocation for plant reuse.
At this point, it’s important to mention that we’ve given a good amount of attention to the “big-six” nutrients and haven’t discussed micronutrients in terms of needs or costs. They are critical, but in calcareous soils (which are prevalent in the western states), micronutrients are more likely to be soil-fixed and unavailable than available for plant use. This is due to the amount of available calcium in the soil solution, which binds up many micronutrients and the lack of adequate rainfall to stimulate extra carbonic acid production.
It is vital to have adequate amounts of boron, zinc, manganese, copper and iron as they are the raw materials plants need in order to maintain productive growth and development. They are all needed but not figured into the aforementioned canopy-nutrient calculations. They are, however, present in the canopy and potentially available for release and translocation within the plant for reuse.
There are many crops which are in down market cycles, but I think you can see that regardless of the crop you grow or the condition of the market, your soil needs to be tended properly. These fertilizer “replacement costs” may not be exactly the same pricing you can get at your supplier, but they are close enough to make the point about the importance of stewardship, both in the plant, soil and your checkbook. Our goal, at SoilMatters: Marc Suderman Consulting, LLC, is to shed light on the fact that there are many areas in the growing system where nutrient inefficiencies can be improved and, in the process, worked to your advantage. New agricultural technology benefits us in more ways than just automated farm equipment and drone mapping. Being concerned about your nutrient stewardship or looking for ways to innovate your nutrient management planning, requires an innovative mindset. A mindset that will benefit you, the grower, as you navigate the current market landscape into a profitable future.
The technology is here and available for a more innovative treatment alternative. To learn more about the options available to you, or for a second opinion on your fall fertility plans, give us a call. We are here to help.
Here’s to your crops’ success!
