UGA Extension Viticulture Blog

A note about post-harvest fertilization

I have been asked about the need to apply fertilizer after harvest.

Studies have shown that root mass increases considerably after harvest, and continues on this trend for about five to six weeks before levelling off at leaf fall.  During the post-harvest / pre-leaf drop period, roots can take up nitrogen, phosphorous, potassium, magnesium, and calcium.  However, just because roots grow, are able to take up nutrients, and you can apply fertilizer does not mean you should apply fertilizer…

I would advise the following:

You may NOT need to apply post-harvest fertilizer if:

Your canopy looked healthy throughout the season and did not show any late-season visual foliar mineral nutrient deficiency symptoms.

Your plant tissue nutrient reports (from bloom and/or veraison) showed that nutrients that were within recommended ranges, or at least did not show deficiencies.

Your latest soil report showed pH in the 6.0-6.5 range and nutrients were within sufficient ranges.

You may need to apply fertilizer if:

Your canopy looked generally weak and chlorotic, or otherwise tended to show visual foliar mineral nutrient deficiency symptoms later in the season.

Your plant tissue nutrient reports (from bloom and/or veraison) showed that nutrients were deficient.

Your latest soil report showed pH below 5.5 and/or nutrient deficiencies.

 

Some considerations about late-season nutrient applications in vineyards:

One consideration for late-season soil mineral nutrient uptake is the relative health of the grapevine canopy.  If the canopy is all-but-gone due to disease infestation, then transpiration (movement of water from the roots, through the plant, out of the stomates – the small pores on leaves used to exchange water for carbon dioxide) will likely be diminished.  Consequently, the uptake of dissolved mineral nutrients from the soil may also be diminished.

Ample soil moisture will aid in soil mineral nutrient uptake.  As such, if you are going to apply fertilizer, it is sound to apply fertilizer when the soil is moist, or will become moist (i.e. over the next couple days due to tropical storm rains, or when rain is next forecasted for a couple of days in the near future).

Some may be concerned with how the late-season application of nitrogen and other mineral nutrients will affect vine “hardening off” (i.e. the ability of the vine to effectively acclimate to colder temperatures and become dormant without increasing the risk of cold damage to buds or tissues).  While I share this concern, as it follows logic, I am ignorant to any work that has been done to show that post-harvest fertilizer application reduces the vine’s ability to acclimate to cold temperatures.  Thus, I am not certain my concern is justified.

 

Please contact your local county extension agent if you have questions about the need to apply fertilizer in the post-harvest period.  Please work with your county extension agent on developing a vineyard nutrient management plan if you have not already done so.

 

For further reading on post-harvest vineyard management considerations, and seasonal grapevine root growth and soil mineral nutrient and nitrogen uptake, please read the following links:

201103_Post-harvest-vineyard-management-growers-guide-for-riverina-vineyards

UC Davis best nitrogen management in vineyards