I think you better tell us more information, at least let's know what your purpose is .... 

Your sampling design will depend on the purpose of the research and the specific objectives you need to achieve. 

I need to take plant and surficial soil samples from industrial area around a certain factory.

If you can show us the imaging map from the Google Earth, people may give you some suggestion. Thanks.

Yes, having more information would be better however, here is an answer:  Determine if the area has a slope, take samples from the down slope area with a few up-slope for comparison.  This is to evaluate weather contaminated materials are moving in overland flow (rain run off).  Also, look at the windrows (which way the wind is blowing) so that you can sample down wind to evaluation if contamination is related to wind transport.  Of course, take a few up wind for comparison.  The above only evaluates if materials are moving at the surface, not depth.  Taking a core or shovel samples will help with vertical movement.

If you are working with urban dust over streets and leafs the best option is a systematic sampling approach mixed with a stratified sampling. The systematic sampling is for represent particle distribution with geo-statistical techniques on a basic way. The stratified sampling depends of the factors that you recognize affect the distribution of the particles as well (e.g. main roads/lonely trails, the kind of land-use, etc.).

Once you find the main factors you'll make spatial-strati according to these factors. Then, inside each strata you'll make systematic sampling in order to characterize them well.

I attach you two articles which work through this approach. I hope you find more answers and new questions in them.

Article Concentration of toxic elements in topsoils of the metropoli...

Article Reconnaissance environmental magnetic study of urban soils, ...

What is your goal?  When I plan a sampling for research I look at drainage's, slope (land slope), elevation, direction of slope, what is the potential contaminate as they do not all more in the same manor, and your overall goal.  When looking at surface sediment movement it is important to understand sediment transport and, particle size within the moving sediment.  Also, groundwater, vadose zone are important to understand their part in the overall scheme of the environment.  

Dear Luis,

Thank you for the papers. I know the idea of systematic sampling approach mixed with a stratified sampling. However, how can I apply them in sampling plan? and on which basis?

Regards

Dear Sims,

My goal is very simple to collect samples of air dust and plant species. The nature of area is that polluted with industrial factories. There is no difference in slope or elevation.

What do you think?

Ok, for characterizing the pollutant distributions you have to do one map for each of the particles that you are interested on. In order to achieve this you should do: sampling design, sample-collecting, lab analysis, map-interpolation and data-validation.

In the fist step, the sampling design, you have several options according to your main and particular objectives:

1) If your target is to know the lead distribution surrounding this industrial area you should make a spatial grid. Inside each block you'd take a sample. In addition, you'd have to sample the main roads or the road this industrial zone use the more; maybe with samples each kilometer over this road. Moreover, you'll need white targets, so it's important to sample places and roads that you expect have the minimal content of this element.

2) If your target is to know the pollutant distribution on a whole city your sampling area has to be a little bit bigger than the city area, in order to obtain white-targets. Inside the city you make strati according to the road-usage (i.e. main roads, secondary roads, tertiary roads), to the land use (i.e. households, industrial zones, conservation/natural zones, agricultural zones) and basin location (i.e. upper, medium or lower part). Inside each strata you'll make a systematic sampling, as an example, every kilometer on the roads and with grids of the same sampling-size inside the land uses or basin location (this last one only if the city size is bigger enough).

One tip: the sampling grid is better for the interpolation if you include surrounding areas outside your study area.

Another tip: The more species you know which fix pollutants on its leafs the better for your samples-collecting (e.g. genera like Ficus, Cupressus, etc).

But, if you want to know the specific way to take each sample of dust or leafs, I recommend you to contact directly the authors of the papers. They can help you in a more specific way.

Dear Luis, 

I want to know how I can plan sampling through systematic or random way.

Dear Alaa,

I wrote you two messages before this one. I see you have reviewed the second one, but I don't know if you looked the first one. If you do so you can see two examples of sampling according to two objectives. Maybe this can help you.

In the same way than our colleagues have written you, is difficult to advise you if we don't know exactly what do you want to work on. I could figure out what do you like to do, but that idea is on the message with the examples.

Dear Luis,

Thank you for your clarification.

I would like to study soils in a defined geographic region in India. I plan to collect soil samples from different locations and analyse fertility parameters: pH, CEC, electric conductivity, 12 plant available nutrients, water holding capacity... Further classify soils with respect to fertility status. 

1)  I can take 100 samples or 1000 samples.. However excess number of samples has implications of cost and time.. Less number of samples would lead to insufficient classification. How do I find appropriate number of sampling points required for such classification.

My activity so far: Generally when I visit any village and interact with farmers regarding soil types in their village, they identify 4 - 6 different soils around their village (the nomenclature is more or less similar as followed in other villages). Likewise I visited 7 villages across 5 subdistricts and collected samples from each of these soil types that villagers identified to be distinct in their village. Now I have soil analysis results for around 24 samples and I need to know, 1) if the number of samples are sufficient to represent the region (which statistical analysis ll help me?) 2) If I have to designate some identity to soil type which is found to be peculair , how should I go about it? Because, there ll be some difference in soil analysis values of sample drawn from soil with identical local name.