Potential nutrient depleted soil -- concerns for nutrient addition treatment

[christophe-rd]

Hi all!

I would like to address concerns that I thought about last week.

I repotted trees using the soil from 2023 Phaenoflex soil mixture (medium for perennials consisting of 50% peat, 25% crushed pumice and 25% crushed bark (www.westcreekfarm.com).

1. I am worried that the soil might be depleted of nutrients even though @FrederikBaumgarten added a slow-release fertilizer last year. My questions are:

• Should I fertilize the plants using a slow/fast-release fertilizer?
• Should we first analyze the nutrient content of the soil?

2. The other concern I had was regarding the nutrient addition treatments. We want to give the trees a nutrient boost in the fall. Therefore, we should maintain a meaningful difference between the controls and the nutrient addition treatments. @FrederikBaumgarten, do you have something in mind regarding this?

[FrederikBaumgarten]

Here are my thoughts on this:

1. yes, the soil is nutrient poor which is perfect as almost all natural ecosystems are nutrient limited. As long as they don't show dramatic symptoms (like yellow leaves) I think we are fine.
2. this is good to discuss! I think we need a nutrient boost that is only available during a autumn to check if species are able to profit from that. I had an interesting conversation with Günther Hoch from Uni Basel. He thinks that nutrient uptake is only possible if there are still some leaves attached. This is because transpiration causes a basic flow that allows to the transport of nutrients away from the root tips. Otherwise diffusion would be the only way to get rid of accumulated nutrients. This would be a good hypothesis: evergreen species and indeterminate deciduous species would profit more from this nutrient boost compared to determinate deciduous species. I think we need to give also a nutrient boost to the control so that every plant receives the same amount of nutrients just the timing is different. I could imagine to give the nutrient boost somewhen in October (nutrient treatments) and all the other treatments receive their dose in winter (e.g. January). Exactly 2 month after the nutrient injection we wash the nutrients out of the soil by watering the pots excessively. Curious what others think...

[lizzieinvancouver]

• Should I fertilize the plants using a slow/fast-release fertilizer?
• Should we first analyze the nutrient content of the soil?

@christophe-rd Great to be thinking about this. I think you should try a cheap soil test kit (they type they sell to gardeners) and see how depleted soils are based on that ... I agree we want to try to prep the plants to need nutrients in the fall, but not at the expense of the rest of the experiment... If we massively deplete nutrients in the plants, the experiment will be hard to interpret so we need to make sure the plants have enough nutrients this summer. If we see any evidence of yellowing leaves we need to have a plan in place of what to do immediately.

I think we need to give also a nutrient boost to the control so that every plant receives the same amount of nutrients just the timing is different. I could imagine to give the nutrient boost somewhen in October (nutrient treatments) and all the other treatments receive their dose in winter (e.g. January). Exactly 2 month after the nutrient injection we wash the nutrients out of the soil by watering the pots excessively. Curious what others think...

@FrederikBaumgarten I like the idea of the different timings, but I think the plan is currently to give nutrients earlier than October ... I thought soon after budset was the goal? Also, I do not understand why we would wash out the nutrients.

[lizzieinvancouver]

@FrederikBaumgarten meant that we add nutrient boost to ALL pots but at different times and wash ALL pots also. This now makes more sense to me.

If you see any plants getting yellow, then add a general slow-release fertilizer ASAP. Check with Dan for what he recommends and err on the side of too little versus too much (be sure not to add too much nutrients now, better to have them starve a little than have too much nutrients). @FrederikBaumgarten thinks he did just one boost (1-2 cap-full of a soda bottle) last time.

[christophe-rd]

Thanks @lizzieinvancouver and @FrederikBaumgarten !

I will get a few soil test kits and test the soil from different replicates.

I agree with you @lizzieinvancouver. We don't want to deplete the plants of nutrients at the expense of the experiment. Do you think that if we wait until the plants show nutrient-stress symptoms, it would be too late to act? Won't this add another factor to take into consideration in the analysis?

I was talking with Rob Guy last week, and he said that if the plants show nutrient-stress symptoms, then we should add a fast-release fertilizer (liquid form). I thought if the leaves ever turn yellow, then we could use this instead. I'll ask Dan's opinion on this.

[christophe-rd]

@FrederikBaumgarten meant that we add nutrient boost to ALL pots but at different times and wash ALL pots also. This now makes more sense to me.

If you see any plants getting yellow, then add a general slow-release fertilizer ASAP. Check with Dan for what he recommends and err on the side of too little versus too much (be sure not to add too much nutrients now, better to have them starve a little than have too much nutrients). @FrederikBaumgarten thinks he did just one boost (1-2 cap-full of a soda bottle) last time.

I like the idead of washing out the nutrients. This seems to answer a concern I had on how to differentiate nutrient absorption in the fall vs the spring. However, I am not sure I understand this idea of different timings. To clarify, is this what you were thinking @FrederikBaumgarten ?

September Nutrient addition to Nutrient boost treatment

November Nutrient wash-off of Nutrient boost treatment

January Nutrient addition to controls

March Nutrient wash-off of controls

Please let me know if this is what you meant.

One thing to keep in mind is that we will need to repot all the trees during winter, so it might facilitate nutrient wash-off.

[lizzieinvancouver]

We don't want to deplete the plants of nutrients at the expense of the experiment. Do you think that if we wait until the plants show nutrient-stress symptoms, it would be too late to act? Won't this add another factor to take into consideration in the analysis?

I don't think it will be too late, but it would be better if we did not have plants that are clearly nutrient limited ... but if we want to make sure they are not overloaded in nutrients then I am not sure how to balance these competing desires. Maybe Ron Guy has an opinion! His advice is generally good.

I was talking with Rob Guy last week, and he said that if the plants show nutrient-stress symptoms, then we should add a fast-release fertilizer (liquid form). I thought if the leaves ever turn yellow, then we could use this instead. I'll ask Dan's opinion on this.

Rob Guy usually has very good advice ... I would go with his unless Dan has a convincing argument against Rob's advice.

[FrederikBaumgarten]

@lizzieinvancouver @christophe-rd: To make my suggestion clear: ![Uploading Fertilization_plan.jpg…]()

[FrederikBaumgarten]

Fertilization_plan.pdf

[christophe-rd]

Hi @FrederikBaumgarten @lizzieinvancouver ! Sorry for the slow reply and thanks Fredi for the figure. It was very helpful and gave me lots to think about.

I talked with Rob this morning to get his opinion on all of this. Below are my questions and his answers: 1. How can we make sure that the nutrient wash-off is effective? First, Rob told me that experiments he did in the 90s showed that plants do absorb nutrients in the fall and store them in their tissue (the exact location depends on the species). He found this by tissue analysis. He also told me that even if we wash off the soil, there will still be leftovers. He strongly advised that we test this before we perform this technique and he gave me a reference in Victoria where soil analysis can be done. The other option is to get rid of much of the soil, but the roots will suffer damage. 2. How can we know if the trees are nutrient-depleted? There are 2 options:

• Analyse the soil. It might not be necessary, because of the low nutrient content of the soil mix. Also, getting a representative sample will be hard and very time-consuming.
• Analyse leaf tissue. He mentioned that trees could be nutrient-stressed without showing any symptoms. Their response could be simply a reduction of growth -- as it is in natural conditions. Therefore, analyzing leaf tissue would be the most accurate measurement of nutrient availability. @lizzieinvancouver @FrederikBaumgarten, let me know what you think, but I don't think neither should be performed. Which brings me to my following question:

3. What would be the best way to release nutrients? We applied slow-release fertilizer last year in the form of small spheres. One thing that remained a mystery for me: how do spheres on the soil surface can be released in the soil effectively if the water is not being poured on the surface (we use drip irrigation where water is released below the surface. Rob told me there could be some diffusion if the soil surface remains moist. However, I think arguing how much nutrients is actually being released in the soil will be hard. Therefore, here is what we thought would be a good plan: Apply a precise amount of liquid fertilizer individually to all the trees (perhaps once a month). Just enough to mimic natural conditions. In my opinion, this will be the most precise way to argue how much nutrient was available for the trees prior the nutrient boost treatment. What do you think?

[lizzieinvancouver]

@christophe-rd Thanks for working on this and thanks to Rob!

Apply a precise amount of liquid fertilizer individually to all the trees (perhaps once a month). Just enough to mimic natural conditions. In my opinion, this will be the most precise way to argue how much nutrient was available for the trees prior the nutrient boost treatment. What do you think?

This sounds reasonable to me -- do you know how much would 'mimic natural conditions'?

@FrederikBaumgarten Do you have opinion on this?

[FrederikBaumgarten]

@christophe-rd @lizzieinvancouver : Yes I have an opinion on this:

1. All natural plants and whole ecosystems are strongly nutrient limited but this has nothing to do with stress. In contrast often these very conditions allow many species to exist in the first place (because they evolved strategies to deal with these limitations). As long as nutrient deficiency only leads to lower productivity we are a long way from stress. Stress in ecology only occurs when fitness is negatively affected and/or critical tissue damage occurs. I suggest to read the Grubb review from Körner: https://doi.org/10.1080/17550874.2018.1540021

2. Liquid fertilizer will never mimic natural conditions (unless you apply it in extremely low concentration over a long period). It will introduce spikes of high nutrient availability, which is not suitable for our autumn treatments because...

3. we want to test if trees can absorb nutrients in autumn, particularly in warmer autumns. I am worried that if plants have absorbed sufficient nutrients before (through liquid fertilizer in spring/summer) they don't profit from additional nutrients in autumn. I think we increase our effect size if trees are close to nutrient starvation and then give them a boost in autumn. Remember we are not even sure if they are able to take up nutrients in the fall. So we should reach for the highest potential to capture it and not 'dilute' our effect size because we are too worried that plants are nutrient limited.

4. I wouldn't worry to much about documentation of nutrient status. I think you can write something like: "Saplings were grown in nutrient poor soil (xxx) for two consecutive seasons with xxxg of slow release fertilizer (xxx) added at the start of the respective growing season."

5. Measuring nutrient availability: Remember that nutrient concentration in the soil are rarely available. So you could measure high nutrient status in soil with very poor availability and starving plants and thriving plants on soils barely measuring any nutrients. Hence not the absolute amount of nutrients in the soil plays a role but rather the so called 'nutrient addition rate' which is mainly defined by bacterial activity. Ingestaad (1982) (https://doi.org/10.1111/1365-3040.ep11611714) could show that plants can reach their highest growth rates under nutrient concentrations close to the detection limit, as long as the concentration is kept constant, always replacing the molecules taken up by the plant.

[lizzieinvancouver]

@christophe-rd It seems we have some conflicting opinions here! I am prone to think that plants can be nutrient stressed without visible signs and I remain worried that we may nutrient starve all the plants in an effort to get maximum effect size for one treatment (of many treatments) so we have a lot to balance here.

Before we decide, @christophe-rd Did you ask Rob if he published any of the work he mentioned? It would be good to see "the experiments [Rob] did in the 90s showed that plants do absorb nutrients in the fall and store them in their tissue (the exact location depends on the species). He found this by tissue analysis."

[christophe-rd]

Thanks @lizzieinvancouver and @FrederikBaumgarten!

1. Very interesting paper! My perspective on stress has changed and this will definitely go in my slip box! However, I am not fully convinced that our plants won’t be stressed because:
   1. How can we know for sure that they are not stressed by a lack of nutrients?
   2. Our plants are in pots. Correct me if I am wrong, but in natural conditions, trees can always find nutrient sources somehow which might not be the case for trees grown in pots.
2. I agree that liquid fertilizer won’t mimic natural conditions, but I believe it could be the better option between the two because:
   1. If we apply slow-release fertilizer:
      1. The actual diffusion rate from the spheres might remain a mystery
      2. I strongly suspect that we will have a difference in nutrient availability between blocks (B3 is not under shelter—>rain—> increased nutrient release from the spheres compared to plants under shelter.
      3. When we wash off the plants in the winter, the spheres will remain in the soil and will keep releasing nutrients (plants could therefore use these nutrients in the early spring).
3. According to Rob, trees can absorb nutrients in autumn and even in the winter. Sorry @lizzieinvancouver, I should have mentioned that he never got to publish this data… He suggested 3 articles from Vic Timmer, but I can’t find any proof that trees absorb nutrients in the fall (difference with a spring carry-over effect). In case you want to take a look, here are the 3 articles Rob suggested:
   • Timmer, V.R. 1997. Exponential nutrient loading: a new fertilization technique to improve seedling performance on competitive sites. New Forests 13:279-299
   • Salifu, K.F., & V.R. Timmer. 2003. Optimizing nitrogen loading of Picea mariana seedlings during nursery culture. Can J For Res 33:1287-1294
   • Timmer, V.R., & Y. Teng. 2004. Preplant fertilization of containerized Picea mariana seedlings: calibration and bioassay growth response. Can J For Res 34:2089-2098 You both have far more experience and knowledge than I do and @FrederikBaumgarten if you are confident that adding liquid nutrients will dilute our effect size, then I trust you on this. I am just not convinced that slow-release fertilizer won’t lead to the same result…
4. Ok for documentation on nutrient status.
5. Ok, thanks for this. If I understand your point, then measuring the nutrient availability before and after “wash-off” would be useless?

[christophe-rd]

Hi @lizzieinvancouver @FrederikBaumgarten After talking with Lizzie last Thursday, we decided to go ahead with a very low nutrient addition to the trees. I thought a lot about this and I think this was the best solution because many trees were showing nutrient-stress symptoms (e.g. Quma had chlorosis probably because of Fe deficiency). Therefore, they needed nutrients as soon as possible. @FrederikBaumgarten I gave a lot of consideration to your concern on a nutrient availability spike and did my best to avoid this.

Therefore, I asked Dan on which fertilizer I should add. He suggested the all purpose fertilizer that they use in the glasshouse. He said the current concentration should be good for seedling, but since our trees are saplings, I diluted it by half. I read many papers to figure out what would be the a very low nutrient addition and I couldn't find anything very conclusive. I wanted to fertilize the trees before my vacations so I added 125mL of diluted fertilizer to all trees on Friday. That comes to : EC: 1.58 NO3-N: 14.5mg P: 3.01 mg NH4-N: 0.81 mg K: 18.46 mg Fe: 11 mg You can see here the fertilizer analysis and here the spreadsheet to calculate how much of each element was added to each pot.

I also stopped irigation for 48 hours to avoid as much leaching as possible (the soil was still moist when I turned it back on). I will search the literature further to figure out what would be the best concentration to add and at what frequency.

Please let me know any thoughts/criticisms/questions you have!

[lizzieinvancouver]

@christophe-rd Thanks for all your thoughts and work on this! I think it is good you gave the plants some nutrients now as they appear stressed. I think the next challenge will be to plan ahead on when we might add more so we do not wait again until chlorosis.