That's a very interesting question. We need to develop a leaf sampling techniques which is largely dependent upon spatial variability in soil fertility...

Another alternative could be to divide such a large plantation area into few smaller blocks based on crop stand so the samples drawn from comparatively homogeneous field and eventually represent the true soil fertility and plant nutrition vis-a-vis crop stand..

Yes, you can divide the area into grids (as you can), and sample/survey on the nodes of each grid.

As Anoop Kumar Srivastava and Huseyin Onen mentioned above.

My first response was suggested toscale the variation in crop stand in terms of canopy volume across spatial variability in soil properties. Grid-based sampling is no doubt worth considering , but our major limitation is to first work out the optimum grid size then canopy size and optimum soil fertility levels...The biggest challenge again lies how to use spatial variability maps in decision making to identify different production cinstraints...

My first response was suggested toscale the variation in crop stand in terms of canopy volume across spatial variability in soil properties. Grid-based sampling is no doubt worth considering , but our major limitation is to first work out the optimum grid size then canopy size and optimum soil fertility levels...The biggest challenge again lies how to use spatial variability maps in decision making to identify different production constraints...

Thank you for all your responses, they are very useful!. I will try to work out with more detail the grid size according to Prof. Kumar and Prof. Onen and follow the recomendation of Ayodele Otaiku for data analysis.

I will be grateful if you suggest a paper with a related study.

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Here you are!

Best

You can combine the suggestions of Anoop, Huseyin and Ayodele for good sampling techniques.

STRATIFIED RANDOM SAMPLING SHALL BE BEST AS IT WILL TAKE INTO CONSIDERATION ALL FACTORS.

Please find enclosed an interesting PDF highlighting grid-based sampling , hope you like it...

Kindly see..

http://al-labs-plains.com/best-sampling-procedures/2527428

Please see..

https://www.ars.usda.gov/ARSUserFiles/np212/Chapter%202.%20GRACEnet%20Plant%20Sampling%20Protocols.pdf

Also to be seen...

https://books.google.co.in/books?id=PVN7_XRhpdUC&pg=PA532&lpg=PA532&dq=best+sampling+technique+for+plants+in+large+agricultural+crops&source=bl&ots=Hr4c6gutr9&sig=XuCmprPBTibZLa8OAUBODEhdJXA&hl=en&sa=X&ved=0ahUKEwjAuJfWv__YAhVLwI8KHXrnDlw4ChDoAQg0MAM#v=onepage&q=best%20sampling%20technique%20for%20plants%20in%20large%20agricultural%20crops&f=false

The area may be divided in the form of grids/blocks and sampling to be done on random basis using random numbers.

I think random sampling, cluster sampling and zigzag would be the best.

Any sampling procedure , you adopt , must address spatial variability in soil properties , so that sampling represent the true soil fertility in appraisal on plant nutrition...

Please have a look at enclosed interesting PDF...

Juvenal -

In Cochran, W.G(1977), Sampling Techniques, 3rd ed., John Wiley & Sons, under cluster sampling, sections 9.5 and 9.6, pages 243-246, he discusses optimal cluster size, if you are interested.

Cheers - Jim

systematic sampling with the arrangement of multiple quadrants is the best way to take the samples from large area.

Random sampling by using random numbers is the best solution

random sampling is suitable, see these articles: Article Correlation of banana productivity levels and soil morpholog...

Article Relationship Between Soil Properties and Banana Productivity...