Try to use a mixture of pine seedlings natural soil with peat in the ratio of 1:1, with the addition of one cubic meter of the mixture of 2 liters of perlite.

as to such a mixture can be added to the complex fertilizer (2 kg per 1 cubic meter of the mixture)

if you use the upland peat, then you need to add about another 4 kg of dolomite or lime for deoxidation.

successful experiments!

John Glaser EPA Cincinnatt

I would use intact soil selected from and appropriate area where the drought effect is antitipateed. If you go and reduce the soil structure through sieving and other procedures The effects that you observed in the study my be artifacts of soil manipulation.

I am not sure, what means "most natural soil conditions possible" to you.

So, if you want to evaluate the drougt effect in natural soil under conditions as natural as possible, its best to avoid any intervention, like sieving or adding perlite - just use the soil as it was collected - as said John before.

If you experiment just considers natural soil (maybe from the origin area of your plants), but texture etc. is not relevant - you could either mix with perlite (as mentioned by Maryia) or sand (2 soil - 1 cleaned sand).

Additionally, if you just want to observe plant resistence without influence of soil microorganism, autoclave the soil several times before use.

You have a very clear purpose of the research that most natural condition possible even the two-year old trees will be maintained. That means you should not mix or add anything for disturbing it. However, if you would like to find any effects with addition you may use some treatments with the addition, for examples.

For addition treatments, you cannot mix but you can cover on the surface with crop residues or other materials you mentioned as above.

In my experience, studying actual evapotranspiration in large pots on tomato, in same soil conditions of the tomato in greenhouse cropping system, I used the same soil trying to respect not only the soil type but also the composition (the soil had a lot of stones) and stratification and applying same fertilizers and water restoration of the crop.

Initially must very well known native the soil composition. conifers not have deep roots, and therefore it is necessary to know whether the source area there species of moss on the ground near trees that maintain a certain humidity. If so, you will need to take account of them in the experiment.

If they are kept in greenhouse conditions, it is necessary to take into account the humidity that is created here and can influence.

Then you can add perlite, but gradually, with small quantities initially and always checking soil acidity.

Keep the soil conditions as close to what you find naturally in the field. Don't add anything else to it, unless it is part of your experiment. By removing the soil from an undisturbed site, you have already altered the natural state, unless you are collecting large core samples of undisturbed soils. if you share greenhouse space with other experiments, then you may have to sterilize the soil to avoid introducing diseases or insects that may infect adjacent plantings. If you can't sterilize the soil, then you may have to isolate the experiment in a separate location in the greenhouse.

The growing media one uses in in drought study needs to be dictated by the trial objective. If the objective is to define the performance (i.e. growth and/or physiological response) in relation to soil conditions, then keeping the soil as close to the original site conditions is desirable. However, if the plan is to look at a specific plant-based response to some other factors (e.g. genetic variation of ponderosa pine to drought), then a soil mix that is uniform across all treatments and plants within each treatment is desirable. For example:

• In a trial looking at short-term physiological response to drought across western redcedar populations we used 1:1 mix of peat:sand to get a steady and even dry-down pattern. This mix was used because plant growth was not being studied; just the physiological response to drought. (Grossnickle, S.C. and J.H. Russell. 2010. Physiological variation among western redcedar (Thuja plicata Donn ex D. Don) populations in response to short-term drought. Ann. of For. Sci. 67:506-517)

• In a trial looking at long-term physiological response across western redcedar populations we used Sunshine Mix #3 (Sun Gro Horticulture) to get a very slow and even dry-down pattern but also ensuring that seedlings had a ready access to soil nutrients. This mix was used because plant growth and their physiological response in response to drought were being studied. (Fan, S., Grossnickle, S.C., and Russell, J.H. 2008. Morphological and physiological variation in western redcedar (Thuja plicata Donn. Ex D. Don) populations under contrasting soil water conditions. Trees, 22:671-683)

There is another factor I don't know if you have considered: one of the factors associated with that soil you intend to keep unaltered is soil volume. 2 years old pines do not need much volume, so you may be inclined to use small pots, and if the experiment is not lasting for long, root growth may no be limited, but water dynamics will, and a lot: water accessible to the tree will be just that retained in the pot, which can be not much in a natural soil. You will have difficulties in keeping a stably decreasing water content in the soil that reproduces water loss from a natural soil, as lateral of upward water movement from outside the soil volumen directly explored by the tree will not happen, so you will see your pots loosing water much faster, especially in a greenhouse, with higher temperatures. You might consider to impose a rate of water loss (you can decide it from what you can measure in the original soil location, or from similar locations in the literature) by daily adding small water quantities to replace water lost in excess from the rate you decided: you will still not be able to reproduce a steady pattern of water loss, but will oscillate around it. I would also even consider calculating, expecially when drought is advanced, applyinfg water several time a day, trying to reduce these oscillations, as it is not the same having a constant soil matric potential of, let's say, -80kPa along the day (as may happen in a natural site), that beginning just after watering at about -60, then falling in a couple of ours to -100 and staying there for the rest of the day till a new rewatering next day.

So, as Steve Grossnickle wrote, the objective of your experiment rules: if you really intend to reproduce what happens "in situ" (that's what suggests to me the use of undisturbed natural soil), you should also pay attention to soil volume, not only composition.

You can take a look to a very gross approximation to what I described in the following paper, in the part of the covered nursery study: Peña-Rojas eta l. 2005 Functional Plant Biology02/2013; 32:117-130

Hi.

If you want to test the effect of natural soil you mustn´t add peat. You must use only the soil without any other material. In that way you avoid external interferences. However, if the option is to use any other material don´t use peat because this material interferes with soil structure, porosity, permeability and pH. The best alternative is to use perlite in proportion of 1:1 or 2:1 (soil:perlite) or even sand 2:1 (soil:sand). But in my opinion you must use only the intact soil.

Hi, its better not to amend the original soil, structure or composition; however, you may add some osmotica or PEG to simulate drought; though its mostly done with liquid medium, otherwise manage water at various levels of field capacity (%).

1-You have to measure the soil osmotic potential and serve it as control experiment. 2-Add appropriate amounts of PEG to the soil and get the favorite level of drought stress.

If its a disturbed sample Sieve to < 2 mm and then recreate by packing the bulk density in the field. Sample for texture and initial nutrient content. Also get the water retention curve for soil hydraulic data.

Ifs is in disturbed soil in a lysimeter even better.