Studies corroborate it. When it comes to trees and vines, post-harvest fertigation is fundamental to ensure next season's crop success.
Why post-harvest?
Fertigating at this stage is good for the roots. Studies show that after the fruits have been collected, roots become the sink for carbohydrates to fuel their growth and access to readily available essential macro and micronutrients -such as nitrate and potassium- that can boost their development.
Nutrient storage is another reason. After heavy fruit and nut load, the tree's nutrient reserves are significantly reduced. Post-harvest fertigation will assure that the tree can reload nutrient reserves to be well prepared to support next season's early development.
Tree crops grown in cooler climates with low temperatures during dormancy stage in winter, will face low soil temperature in early springtime, therefore limited root activity, even if ambient temperature is mild. In these conditions, tree crops and grape vines mainly rely on stored nutrients in the stem and roots.
In the case of many fruit tree and nut crops, post-harvest fertigation could also reduce the "on-off' years incidence, where one year of heavy fruit load is followed by a year of low fruit yield.
This phenomenon may be related to depleted nutrient stocks in the tree after heavy fruit load and nutrient export with harvested fruits from the orchard, rendering the tree crops unable to support a consecutive year of abundant fruit yield.
At the early bloom and fruit initiation stage, the tree fully depends on nutrient reserves, stored in the tree itself. The most important nutrients that are needed to top-up at this period are nitrogen (N) and potassium (K). Up to 30% of the total annual application of N & K nutrient should be applied at this period. lt is important to select readily available nutrient sources, such as potassium nitrate, which will provide immediately available N in the form of nitrate, while tree crops need to be replenished with K, as significant amounts of K are exported with the harvested fruits from the orchard.
In the case of almonds, nitrogen can be applied any time after hullsplit up until a few weeks postharvest. In earlier harvested varieties and 'Nonpareil', nitrogen can be applied shortly after harvest with the first post-harvest irrigation. With later varieties, such as 'Monterey' or 'Fritz,' the application can be made post-hullsplit prior to harvest.
Post-harvest potassium applications may be a reasonable strategy if you are on a soil that is able to hold the potassium. In sandy soils, potassium can be leached out of the root zone, which may create a situation of deficiency in the following year.
In the case of grapes, the period after harvest before leaf fall is one of the best times of the season for the uptake of nitrogen and potassium which the vine needs along with carbohydrates to provide for the period of rapid shoot growth in the spring after bud break. Replacing minerals is important as they are transported off-site in the crop and not recycled back into the soil like leaves or canes.
Studies show that post-harvest fertigation is key on root development
There are two main stages of root growth. In a rhizotron study in Chile in 1993 with two table grape varieties (Flame Seedless, Moscatel) it was shown that the first (and larger) peak root growth stage takes place from bud break to petal (fall/fruit initiation. The second (and smaller) peak root growth stage takes place after fruit harvest until leaf fall (post-harvest). Root development is linked to the competition for carbohydrates between roots and developing fruits. Developing fruits are stronger sinks for carbohydrates produced in the leaf than roots. Therefore, root growth and development are suppressed during fruit development growth stages. Once the fruits have been harvested, roots become the stronger sink for carbohydrates to fuel their growth. Access to readily available essential macro- and micronutrients, applied with fertigation during post-harvest, is equally essential to support root development. The recommended dose rate of nutrients in fertigation is to be decided for by plant-soil-water diagnostics.
References:
"Balanced soil fertility management in wine grape vineyards.'" Stan Grant. Practica/ Winery May/June 2002.
"Best Management Practíces for Nitrogen Fertilízatíon of Grapevines." Bill Peacock, Pete Christensen, and Donna Hirschfelt. University of California Cooperativa Extension.
'Grapevine nutrition and fertilization in the San Joaquín Va/ley'" -Pete Christensen, Amand Kasimatis, and Fred Jensen. UC ANR pub. 4087 - Foothill Vineyard News, /ssue 9, October 2013.
'"Post-harvest Vineyard Management: Growers Guide for Riverina
