When we talk about post-harvest, it may cover an extended period, which for some varieties can even extend from November to March or beyond. However, in this case, post-harvest refers to the point when nutrients are stable in the plant and does not necessarily coincide with the stage when the fruit is harvested. But immediately, a new question arises: when are the nutrients stable in the plant? Physiologically, this corresponds to a crucial period, which is the transition of the flow of reserves or the flow within the plant that occurs during the change from spring to summer, marking the beginning of shortening photoperiod, an important signal of pre-dormancy in deciduous leaf plants. In other words, it can be theoretically established that after December 21st, the nutrients are already stable in the plant, and if a foliar analysis is conducted, it is possible to recognize this state through the numerical values provided by the analysis for each nutrient.
So, what would happen if the foliar analysis is conducted before the mentioned period?
“The result of the foliar analysis only reflects the moment when the material for the analysis was collected. However, it does not indicate whether the numbers obtained from this analysis are correct within certain ranges. Therefore, it is like a snapshot or an X-ray of that moment. If this nutritional foliar analysis is conducted from December 20th or 25th onwards, it is possible to trust that the range provided by the laboratory is already established in the plant,” stated Carlos Tapia, Founder and Technical Director of Avium.
Now, how is this foliar analysis conducted? There are many methodologies to learn how to perform it, but the most important aspect from a statistical perspective is that the foliar sample accurately represents the orchard or block from which it is taken.
“A composite sample must be taken, consisting of many randomly selected plants, ensuring that it represents the variety or block. There has been much discussion about which leaf sample should be taken, and in general, laboratories work well with 100 to 150 leaves per sample, considering that many of them keep a duplicate sample. It is important to collect both the leaf blade and the petiole, as the petiole can also provide important nutritional information,” explained Carlos Tapia, specialist advisor in cherry production.
Which leaf should be collected? The leaf from the middle third of the annual sprout is recommended, although Carlos Tapia disagrees with this.
“Personally, I don’t entirely agree with sampling that leaf because it is a new leaf that could generally provide inaccurate information about certain nutrients, mainly those that can travel through water, such as potassium and calcium. Potassium will always be more present in new leaves or in leaves of the annual shoot because it is involved in water transport and has significant osmotic power. Therefore, it might provide misleading information. Personally, I believe that the leaf that would best represent the nutritional status from a foliar perspective is the leaf from the two-year-old wood. In other words, it is the leaf immediately following the annual sprout. We have the annual sprout, which is the terminal bud, and the leaf in the wood right after that sprout should generally represent the nutritional status through the foliar analysis,” cautioned the specialist.
What can be observed in a foliar analysis? Carlos Tapia explains in detail what aspects to pay attention to when interpreting the results.
“Personally, I would focus on certain important nutrients, with some characteristics specific to rootstocks. Number one is nitrogen, which I believe is important. Although it is an important indicator in the foliar analysis, it is essential to observe the plant and understand its nitrogen condition or the nitrogen range indicated by the analysis. It often happens that we perform a foliar analysis, and it shows nitrogen levels around 1 percent, which is low according to the standard. However, when we observe the tree, we see that the annual growth exceeds 60, 70, or even 80 centimeters. Therefore, the nitrogen levels, although important in the analysis, may not necessarily reflect what we observe in reality.”
Tapia emphasizes the relevance of considering different rootstocks, taking into account their vigor, as the reference values vary.
“For vigorous rootstocks, potassium status is crucial, and we should aim for ranges between 2 and 2.5 percent. However, in vigorous rootstocks, this range is usually lower, and it is an important indicator that we are deficient in potassium in vigorously growing orchards. In the case of magnesium, which is vital for rootstocks such as Mahaleb, Pontaleb, and the more practical evolution of the last decade, the entire MaxMa series, including well-known rootstocks like MaxMa 14 or MaxMa 60, magnesium status is crucial. It should be around 0.5 parts per million, but in general, it is challenging to reach that level,” explained Carlos Tapia.
In the case of the entire Gisela series or the acid rootstocks, which are acidic cherry lines or direct descendants of acidic cherries, or often acid cherry selections, zinc status is very important.
“It should ideally be above 40 parts per million, but in practice, we are seeing that in general, this type of less vigorous rootstock or rootstocks from less vigorous series falls below these 40 parts per million. It is important to establish these differences. Nowadays, we are talking about rootstocks that we believe represent a significant advance, and we are deviating from talking about the species itself,” detailed the Founder of Avium.
Which analysis should be requested? A comprehensive foliar nutritional analysis is essential, and in some cases, it is important to include boron. It is worth noting that in the laboratories available in Chile today, where these types of analyses can be performed (a total of 6 or 7 laboratories), simply requesting a complete foliar nutritional analysis will provide all these ranges, that is, a comprehensive analysis.
It is not necessarily necessary to consider the ranges provided by some of these laboratories, which, although well supported by previous research, are believed to be more specific to Chile, including, as previously mentioned, the different rootstocks.
Foliar analysis are fundamental for making decisions regarding the nutritional program, especially for the recovery of nutrients in orchards during the post-harvest period.