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Phosphorus is a necessary tool for plant growth and energy. With every essential plant nutrient comes the risk of a yield- and profit-limiting nutrient deficiency. When additional phosphorus is needed, questions begin to form around when and how to apply. With many benefits to applying phosphorus fertilizer in the fall, the “when” part of the equation can be more easily determined. There are a number of advantages and benefits to applying fall phosphorus that will help increase its availability for crops planted in the spring.
Crops can suffer seriously from phosphorus shortages during the growing season. A lack of available P can lead to a drastic fall in yield. The high reactivity of phosphorus is one reason for this. Metals in the soil can complex with P and it is attracted to soil particles. Therefore, even if it exists in the soil, your phosphorus may be unavailable to plants. This happens because P(-) has a negative charge and other elements in the soil have a positive charge and this ionic bonding can severely limit the crop’s access to the nutrient.
Plants require phosphorus from their soil, but they can only recover a small amount of it due to the inactivity of the soil. A number of factors affect phosphorus diffusion in the soil. Under wet conditions, as moisture levels increase, diffusion will also increase. Soil bulk density, along with soil buffering capacity will make maintaining nutrient concentration difficult. It is important to consider the temperature of the soil since this will increase its concentration.
In order to manage phosphorus levels effectively, soil pH should range between 6.0 and 7.0. This will have a direct impact on phosphorus availability. Phosphorus is rendered unavailable to plants once soil pH drops below 6.0, due to more iron and aluminum binding chemically to Phosphorus.
Even in soils with an ideal pH, only a small fraction of Phosphorus is soluble and is available for plant uptake, despite the fact that there is often plenty of Phosphorus in the soil. Phosphorus must be kept at critical levels. Due to the removal of nutrients via grain and stalks at harvest, soil testing in the fall after harvest provides you with crucial information about your fields’ nutritional status.
When time is of the essence, getting into the field for phosphorus applications can stretch the grower’s most valuable resource, time. Little differences in yield have been shown when phosphorus was applied in the fall, or in the spring. This flexibility can have an advantage to growers to take a bit of the spring workload off, while still having P availability and ready to go in the spring.
All crops tends to be highly responsive to phosphorus. In general, phosphorus is the second most limiting nutrient in crop production after nitrogen, and in some areas, phosphorus is more limiting than nitrogen. When a limitation of phosphorus is seen in soil and tissue reports early in-season, this can lead to limited yield potential. Generally, when crops are in need of phosphorus, it is 5-6 weeks after emergence. It’s a critical component to a well-rounded fertilizer program, making P levels in the fall extremely important when it first germinates.
During a full season, it can be expected to lose approximately 85% of applied phosphorus, making applications a requirement for most seasonal crops.
To stay ahead of phosphorus loss, applications of Ferticell® Pro Phos™ or Active™ can be tremendous tools before or during fall tillage and will allow for the efficacious use of the nutrient in the key root zone. Incorporate Pro Phos™ into the soil with tillage to reduce the risk of runoff. Even in no-till fields, fall application gives a wider window for Pro Phos to slowly move beneath the soil surface before spring planting.
My concern with Autumn (Fall) applied P, as you suggest, is P Retention (Fixation).
All trials show that within 21 days of application, 90% of applied P is fixed and unavailable. The best way to ensure there is available P is to have a good soil Ca %.
In NZ, Japan, China and Australia where I have consulted, best results have always been with the application of P at seeding. Interested in your comment
With processing including our phytohormone process, the release and continued release of P can avoid some of the conditions that literally “tie-up” and never to be found again.
One of the best additions to anions to prevent the loss is adding organic acids as we find in rhizosphere activity. Citric acid is one of the acids produced by healthy roots for this same action.
Adding Protein N that is derived from Amino acids will increase the uptake success and may promote a longer availability for P. The additional gain is a plant-based Carbon that is found in a light fraction category and immediately available to support nutrient cycling.
Side dressing at very low rates has been successful for us in mild alkaline soil conditions