John Kempf explains how nutrient timing during fruit development controls firmness and storage life. Calcium applied during the 10-14 day cell-division window after pollination (up to 45 days in apples) builds firmer fruit by increasing cell number. Potassium, boron, and manganese timing also matter; mistimed nutrients can cancel out calcium's benefits.
Questions this video answers
About 10 to 14 days.
Up to 45 days (depends on weather, environment, and plant status).
Typically 45 to 60 days after application.
Likely in January or February.
Chapters
We know we can have tremendous impact on fruit quality by managing nutrition at different stages of the fruit development period. But what is not so well understood is how we can greatly improve storability, shelf life, fruit firmness. We can make fruit that is very firm, that has low susceptibility to cracking, to splitting and to damage and storage based on how we manage different nutrients at different stages of fruit development. So the requirements for calcium and potassium and boron and manganese, in particular those four elements, the requirements for those elements are not equally distributed throughout the entire fruit development period. We require higher levels of some nutrients at specific stages and lower levels of other nutrients at specific stages. And this is where crop nutrition often really gets on, gets off on the wrong rails, is because we apply a lot of nutrients up front and, and the release curve of those nutrients doesn't match with the crop demand curve. Immediately after pollination, we have this blossom, a fertilized blossom. We have this developing embryo with going through a very rapid cell division stage. We start with two cells, then we go to 4, 8, 16, 32. You have this geometric progression in the number of cells for a very tight window of time. Most crops, the cell division window is about 10 to 14 days. Some crops, such as apples, it's as long as 45 days. And it depends on weather and environmental conditions and plant nutritional status and a number of different variables. The highest quality, firmest fruit is fruit that has a very large number of very tightly, dense, tight, densely packed small cells. That is what gives you firm fruit. If you have soft fruit, you end up with fruit that has fewer cells, that are larger, filled with water and sugar and nutrients, etc. A soft fruit with larger cells is much more susceptible to bruising and to all types of different damage. So you want, in that 10 to 14 day window, you want to produce as many tiny cells as possible or as many cells as possible. Cell size then becomes constrained as a result of the number of cells and the amount of nutrition that is available. So what happens in that 10 to 14 day window? The nutrient that limits the number of cells formed is calcium. So peak demand for a plant in terms of quantity of calcium. The grams of calcium required doesn't peak at this cell division stage in the two week window after pollination, but peak profitability, peak economic reward for calcium supply does occur at this stage. So during this 10 to 14 day cell division window is the period where we need to make sure that this developing embryo has a surplus level of calcium. And then later on, obviously, we need additional calcium supplies throughout the remainder of the fruit development period. But it is this window that determines the greatest economic crop response from calcium fertilization. So if you look at. Imagine me drawing a sketch here. If you look at a plant's annual growth cycle, and let's just say this blossoming pollination window happens here. What happens if you apply a calcium soil amendment and you're looking at calcium supply here on the vertical axis, you want any amendment that you apply to have a release curve. Where the release curve comes up looks like this. And we see a common practice is putting on calcium soil amendments where the release curve does not match up with the peak economic crop response curve, the peak demand curve. So what frequently happens is, let's say on a perennial tree fruit crop, such as stone fruit or apples or something like that, we'll put on full applications of gypsum or calcium amendments. And what happens then is this release curve. The peak of the release curve will occur depending on environmental factors and particle size and product availability. Lots of variables. But a release curve typically will peak 45 to 60 days after application. Well, if you put a product on in November, that means your peak is likely to be in January or February, which is months before you need it. So many growers are actually doing the right thing, but at the wrong time. Timing calcium application so that we have a peak release curve right at the moment of the cell division window is one of the easiest ways to get a significant economic crop response from calcium supply. Now, this is all confounded with potassium management and manganese and boron management. You can destroy whatever gains you might achieve by properly putting on a calcium application from a timing perspective, with improperly timing potassium applications. And that's one of the next things I want to talk about.
