If rain is not uniform you might have several stations with replicates and discard the wet ones under circumstance. For small plots rain shelters can be a partial solution if the soil drainage at parcels border  is adequate.

Rainshelters could overcome the problem. However, rain sensors should be installed on the shelter so that shelter can pull out on the experimental plots. 

Rain shelters are the best solution.

Good luck.

Dear Furzani Paee

A simple way for application of water stress is arranging irrigation intervals based on evaporation from class A pan. In this way raining will increase the pan water and also the duration of intervals, For example, if you consider irrigation after 150 mm evaporation as one of your treatments, you should wait for this amount of evaporation even if raining occurs.

Warm regards

Kazem Ghassemi-Golezani

I think  , the bigger issue is , how to evaluate the response of drought stress , considering the fact that untimely rains would neutralise the magnitude of plant response to acquired  quantum of drought stress. Or alternatively , when a plant  on the way to reach critical drought stress and rain comes , will surely take away the stimulus of drought stress form the plant..?

In field experiments where rainfall incidences are occurred you have to study supplementary irrigation for instance you use Split within Randomized Complete Block.... for instance you irrigate your plants whenever 25, 50, 75 and wilting depletion of soil moisture. Then you measure the applied water 

Or you have to use slide movable greenhouse to avoid rainfall, as required during raining only 

Interesting question whose answer is not so simple. We need to consider amount of rains that you received in such experiments, but how far it will be successful it depends on the objective of  your study.

High, neutral  and large rain shelters are the solution to avoid rain and in the same time reduce the modification of the climate. High and horizontal to reduce temperature modification. Neutral (polyethylene) to reduce the modification of light quality. Large to avoid the influence of the rain failing on the side; this can be complemented by side ditches or a side drainage

Hello Furzani,

You need to consider the aims of the work.  If it is to get general  information relating, say, yield to water supply (rainfall or soil water deficit), then replicated field trials in different years with measurements of rainfall, perhaps with irrigation, and soil water content, would provide a lot of information.  If you want to do more detailed physiological studies, for example to know how water deficits affect a particular grow stage, then mobile rain shelters are the best way.  I speak from experience of trying to do such studies without control of rain (not successful in the UK climate!), and then working with mobile rain shelters.  Look at   Day W 1978 A drought experiment using mobile shelters: the effect of drought on ...

https://www.cambridge.org/...mobile-shelters...barley.../327F6E839C2EBCDFC9B30...

1.      

and publications are available under Lawlor DW  drought and barley  on Research Gate.

Mobile shelters are best as fixed shelters produce large effects on plants because of the changed light and other conditions. But they are costly and do require expertise to get the best from them.

Regards

David

Hi,

 it mainly depends on the expeimental design and the purpose of your experiment, carried out in the open field. For example: do you want to analyze the water stress compared to a particular gegraphical zone? A specific soil potential level? Particular  seasonal drought? Are there any control-reference? Etc., Etc.

If the rain is uniformely distributed on the experimental field and it is, however, in the seasonal average of the area  tested, I do not think that raining is a problem. However, if you provide the controls, according to the climatic characteristics of the site, sheltered areas from the rain should be provided.

If, however, the idea is to test a condition of plant natural response to drought and the rain does not create stagnant water or particular levels of  humidity, the cover might be not necessary. at last, everything depends on the experimental planr and the work  purpose, as said earlier.

Good luck!

Best regards,

Daniela.

Now that you understand that without a rainout shelter you actually have no control over the experiment, check "rainout shelters" information at Plantstress.com/Methods.

Hi,

1. If it is to evaluate the physiological response of plant to certain level of drought; the solution is to use slide movable rain shelters preferably automatic along with rain sensors, if not then manual.

2. If it is to check yield under deficit water supply (some level of drought) then either monitor water inflow (irrigation plus rainfall) and outflow (evapotranspiration) or soil available water.

Feel free to ask more details if you must.

Hello,

I agree with  Daniella about the need to carefully decide what the aims of the work are, as I tried to indicate before, but am sorry to disagree with her when she who seems to suggest that a study will be alright if the rainfall is uniform.  Rain - even a small amount - during a drying period can have large effects on crops depending on the duration and severity of the dry period , and the crop's growth stage.  And it is not possible to get uniform soil water potential ( Please see earlier discussions on Research Gate.  The science is advanced enough to know what the general effects will be, and previous studies provide a `model' to help design new, critical studies rather than starting from scratch. Read the literature - it is large and complicated but would be a necessity for a good study.

Regards

In the areas where rain occurred often and without checking the soil it is almost impossible to get results. I did my experiments in Denmark and field experiments was not possible, at least in area where we wanted to do it. Without using of tensiometars and just shelters is not good idea. Based on my experience I would always first check type of soil and then start with experiment. Based on the purpose of the experiment, you always can use greenhouse and chamber based experiments if you need some specific results for short period, For long term experiments, you need to record data for soil - plant.  

Dear Natasa Cerekovic 

You have used tensiometer to which soil depth and water depletion, Since, tentiometer can not measure -0.75 bar 

I understand that costs are often a problem, especially in open field experiments which simulate while "controlling" or monitoring, the real conditions. All depends on, as I said, on the purpose of the work and what is the question you want to answer. Then, you look for a compromise between the scientific aspects and feasibility. On the other hand, although not expert in soil and potential but of physiology and biochemistry of the plant I worked on the topic with more expert collegues and I am quite in agreement with David W. Lawlor (especially in an experiment of full field involving large areas, with different type of soil and profiles) that in absolute terms the rain, even if not very abundant, can never be completely uniform. Therefore, you need to verify, depending on the soil type and its profile, as the rain during the experiment affects the soil and climate and the experimental plan. Then you can decide what to do, but to place a rainout shelter system of control is essential. Perhaps these considerations may seem obvious, but in practice, I hope useful. The extensive literature of studies on drought stress can help.

again best regards,

Daniela.

To undertake researches related to drought stress responses at field condition is the right way and more reliable to recommend for similar  soil types and climatic conditions than doing it in the greenhouse. However, it is really difficult to come up with outcomes as designed since it is at field condition, uncontrolled. In my experience even automatic rain out shelter is not enough because crops tolerant to drought can even possitivel respond to the increased relative humidity in the atmosphere. Sorghum with stay green relaxed its leaf area that was grown undr drought condition when the main rain season was approaching in semi-arid region in Ethiopia, Melkassa research center. Therefore, with all climatic measurements and adjustments done the result with descriptions can be recommended to similar areas.

The point by Yemane  about atmospheric humidity is true : it does affect the response of plants to soil water potential/content. However, that does not mean that rain shelters are not valuable - in fact they are essential to really understand such effects.

 See: W. Day, D. W. Lawlor, A. T. Day (1987) Irrigation Science, Volume 8, Issue 2, pp 115–130.

The effect of drought on barley yield and water use in two contrasting years.

DOI: 10.1007/BF00259476

Summary

Results are presented for an experiment in 1979 in which mobile shelters were used to exclude rainfall; responses are compared with those in a hotter and drier year, 1976. The continuous drought treatment achieved a larger maximum deficit in 1979 than in 1976. The relationship between rate of water use as a fraction of the potential evaporation rate and soil water deficit was similar in the two years. Yield reductions due to drought were smaller in 1979, as expected from the smaller evaporation rates and therefore smaller potential soil water deficits. Dry matter production was related to water use, but the relationship differed between years. The difference can be related to the saturation vapour pressure deficit. Components of yield were affected differently in the two years; drought after anthesis decreased yield in 1979 by decreasing grain numbers not grain size.

Dear,

In this case you can assure that in the period of the experiment it will not rain! Mstly of people work on this during the dry period of the year. You can put irrigation in the beginning (or start experiment in the end of the rainy season) and then, continue applying water just as you chose for the experiment.

Best,

Maria Crisitna

Thank you everyone for your answers and helpful insights. I will consider all suggestions and will let you know the outcome of this project. All the best to you all!

those answers are valuable to our work.