You need additional measurements to establish that the water stress treatment "worked".  Water content of soil is a useful starting point, especially if you have a moisture release curve for your soil (or can estimate water release characteristics from soil texture).  You also need to establish that water stress was experienced by the plants.  One way to do this is by measuring leaf water potential and/or RWC of leaves.

Rain out shelter can be tried for imposing water stress in any crop.

You need additional measurements to establish that the water stress treatment "worked".  Water content of soil is a useful starting point, especially if you have a moisture release curve for your soil (or can estimate water release characteristics from soil texture).  You also need to establish that water stress was experienced by the plants.  One way to do this is by measuring leaf water potential and/or RWC of leaves.

Another method for applying water stress is to the evaluate maximum water holding capacity of your soil. Then you have to measure evapotransiration in your field, for every 7 days for example. You also know water requirements for corn. From these data you can estimate how you have to apply in every irrigation to retain maximum water content (100%). Water stress will be estimated as a percentagethe maximum eg. 70% and 45% which can be applied by lowering the dose of the irrigation. Therefore you will irrigate at the same intervals with different doses for each treatment.    

Field capacity is related to soil moisture. Field capacity can be considered relatively high soil water content. Therefore, I don't see big difference between them with respect to moisture content. you can apply various methods of water requirement of plants such as 100% ET, 75% ET,  etc. you can also apply soil water depletion.

Thank you all for your useful answer

Much appreciated 

Working with water stress in soils is a bit difficult because it actually has to involve lots of measurements including soil moisture. You have to make sure you are starting your experiment with all plants having the same water content in soil. 

If you plan to study drought stress, you can also mimic it by using a substance tat creates stress in medium. if You are able to grow soil in hydroponical system, you can then treat them with PEG, Sorbitol or mannitol. These all create osmotic stress.

we use liquid hydroponics system for rice experiments, I am not sure if you can optimize something close to this with Maize plants. This, if you don't want to go through all these measurements. Good luck.

If you do not have any equipment to measure water content in the soil you can monitor water content in root area by taking soil sample and calculate by weighing the samples and then dry them  to a constant level. then you could arrange your water stress treatment based on field capacity. also you need to calculate the water requirement of maize by weather data and equations that you can find in the articles.

your treatments my be 100% ETc, 75% ETc and 50% ETc when water content of soil reach to about 40% FC. you must apply water by contours to determined level. 

I fully agree with Dr C. Warren. The VPD can play a major role in confounding this water deficit and the way the plants experience the drought . Therefore 'a dry-down method' is usually adopted. This involves gravimetric monitoring of the soil water loss.

Hello,

The question of how to experimentally subject crops to drought seems to occur with great frequency.  Here it is to examine expression of particular genes as plants lose water, caused by stopping irrigation. I assume that the studies will be in a time/place without rain - otherwise (as already said) your study will be extremely difficult to do and the results will have little meaning.   As pointed out already, it is of great importance for such studies to know what the state of water is in the plant/organ, as the measurement of soil water (as soil water content or soil water potential) will not tell you what is essential information about the state of water where the gene expression occurs.  So some measure of water in the  plant is needed - relative water content (RWC) tells a great deal about the cell water status  and should be combined with water potential of the organ (pressure chamber or psychrometer measurement).  

 .I have a number of papers on Research Gate looking at these problems

e.g. D. W. Lawlora, W. Daya, A. E. Johnstona, B. J. Legga and K. J. Parkinson

Growth of spring barley under drought: Crop development, photosynthesis, dry-matter accumulation and nutrient content  The Journal of Agricultural Science 96(01):167 - 186 · January 1981

which gives references to other related papers from the study.  The way in which drought studies can be set up is shown clearly in the earlier papers

The paper

Lawlor DW Genetic engineering to improve plant performance under drought: physiological evaluation of achievements, limitations, and possibilities

J. Exp. Bot. (2012) doi: 10.1093/jxb/ers326 First published online: November 16, 2012

gives a detailed analysis of the problem of relating plant responses to drought to metabolism and gene expression (by implication). 

I suggest that you think carefully about such experiments and read the literature - there is a large, old literature which addressed the problem concerning you a long time ago - and things have not changed just because genes are now involved.

Best of luck

David Lawlor

You are right Dr.David. RWC  can be a better indicator than soil moisture content.Other remote sensing indicators like spectral reflectance and canopy temperature can also be tried.

Field capacity is one of the best method to measure soil water content when you don't have any devices to measure water content in the soil and apply each desired level of stress, then you can measure RWC of plants as an indicator of water stress.  

Hello Mohammed,

For your case, if you don't want to make any measurements, you can apply different trials ( once a week..... and  every two weeks ) of water application to your experiments, and use remote sensing method for collecting your data so that you will be able to determine drought tolerance of the plant. 

The original point to this discussion was "i want to study drought tolerance (at gene level-LOS5/ABA3 in corn)"   The method to be adopted was "... to apply drought stress as irrigation intervals (one week for irrigated plants and two week for droughted plants), "

The earlier points made by me and others was that it is essential to measure the water status of the plants to correlate with gene-expression changes. Otherwise what will the measurements show?  Suggestions that application of irrigation at different intervals will be sufficient and that remote sensing will be sufficient indicator of water status of the plants is not adequate, in my view. Also, soil water is not an adequate measure.   There is a long history to analysis of the problem that Mohammed is interested in, and it has been shown that there is no short cut to detailed measurements.

I agree with the previous comments. It's important to know the level of stress at soil/substrate level together with the same in plant.

I suggest the use of gravimetrical method for soil and wáter content (RWC) and in plant combinate with P-V analysis.

Once again, thank you all for your answering my Qs. Based on your useful answers we did the experiment (growth traits, yield traits, EC% and RWC beside Gene expression and Genetic diversity for the inbred lines that used in the exp) and we have got the results analysed will published soon after write the paper. 

Regards