Balanced fertigation strategies in the fall, while leaves on permanent crops are still actively photosynthesizing, can support optimal carbohydrate production to ensure maximum crop performance. Carbohydrates are the product of photosynthesis. For most of the crop year, plants are at a carbohydrate deficit as the fruit acts as a significant sink. The period between crop maturity and leaf senescence is the only window all season to store carbohydrates that improve plant health and productivity. Soluble carbohydrates interfere with ice crystal formation, protect cells and membranes, and reduce mechanical injury related to freezing. Potassium is required for the transport of carbohydrates for use by the plant.
Approximately 90% of nitrogen uptake by crops is in the nitrate form. Nitrate nitrogen fertilizer is readily available to crops from soil solution. Nitrate uptake enhances the uptake of cations like Ca, Mg, and K.
Potassium is present in large quantities in the plant. It regulates the water balance within the cells and controls water loss through transpiration. The transport of K+ into guard cells helps to maintain optimal stomata function. Proper guard-cell function allows the plant to cool itself when necessary, pull nutrients through the transpiration stream to where they are required, and conduct photosynthesis. Healthy, vigorous trees and vines will resume photosynthesis sooner and at a more active rate following harvest. Balancing potassium with other available cations in the soils is critical to overall nutrient use efficiency.
Beyond defending the plant from heat stress and supporting healthy root development, calcium supplementation has been documented to reduce cellular ion leakage; a direct result of frost damage. This increases woody plants’ ability to withstand below freezing temperatures by increasing extracellular Ca2+ levels. This ultimately limits ice crystal formation which can compromise cell structure and lead to tissue death.
While many soils show sufficient amounts of calcium, less than 0.05% of that calcium is soluble and available to plants. A calcium nitrate solution works well when applying via fertigation.