We are well into harvest now and the end is in sight. The trees have done it tough this season with hot dry conditions—they will be looking to replenish their reserves in preparation for next season.
Applying post harvest fertiliser is arguably one of the most important and valuable times for tree nutrition.
After harvest, orchardists have an opportunity to address any issues in the trees nutrient status before next season.
Post harvest fertiliser is especially important for early varieties such as Gala that have a short growing season.
Post harvest is also a key time to apply fertiliser to trees that may not have received nitrogen inputs during the season. This may have been due to excessive vigour, or for issues relating to fruit colour (for example Pink Lady™ and Fuji).
Applying fertiliser post harvest also has the least impact on tree vigour.
Research has shown that autumn applications of nitrogen give the best response for blossom quality, fruit set and early leaf expansion.
Post harvest fertiliser applications can have a significant beneficial impact on next seasons crop, especially for trees that have been doing it tough due to environmental conditions or other factors such as heavy crop loads.
Once the fruit is harvested it’s like ‘flicking a switch’ for the tree which changes from fruit production, to replenishing nutrients and carbohydrates in preparation for next seasons crop.
A new flush of root growth occurs to aid the uptake of water and nutrients.
What to consider
Things to consider when deciding on post harvest fertiliser applications include: fertiliser rates, type of fertiliser, crop load, soil type and, amount of nutrients consumed by trees and incorporated into tree growth.
In general it is good practice to apply both foliar and ground fertiliser to meet the post harvest needs of fruit trees.
When deciding on post harvest fertiliser applications, consider fertiliser rates, type of fertiliser, crop load, soil type, and the nutrients consumed by trees and incorporated into tree growth.
Key nutrients
The key nutrients important for post harvest applications include boron (for flowering and fruit set), zinc (for flowering and fruit set), magnesium (for photosynthesis), calcium (for fruit firmness, bitter pit, storage), and nitrogen (for yield and fruit size).
Trees low in nitrogen have an increased risk of biennial bearing. Both zinc and boron help play direct and indirect roles in the movement of calcium within trees.
Fertiliser program
Below is a typical fertiliser program that incorporates the key nutrients apple trees require post harvest:
- Calcium nitrate—ground applied or fertigated
- Bud-Wiser—foliar application
- Lo-Biuret Urea—foliar application
Soil amendments & testing
The autumn/winter period is also a time when soil amendments can be made with gypsum or lime.
Soil testing can be carried out in established tree blocks or in preparation for new blocks.
Regular testing (about every three years) helps identify any nutritional deficiencies and underlying trends.
Early detection of these trends allows management to plan the necessary course of action, before any major nutritional problems arise—ensuring the soil’s status remains in check with the trees requirements.
For more information, see Tree Fruit March 2013
