I am not aware of SAMPLEPOINT (is it a software?). The short answer to you question is: To determine the "population of a weed" you will need (a) to define the target (agro-eco) region wherefor you need to determine the population, (b) To define the sampling unit that will be sampled (eg plant, quadrat, ...), (3) total number of sampling units (ie sample size) that will be sampled, and (4) A sampling design eg simple random sampling, stratified random sampling, .... You can consult a local statistician to learn more about. 

Thanks for your reply. Yes. SAMPLEPOINT is a software which reduces field days. Google it. 

Thanks Jitendra. Shall you forward the full citation of Mishra 1965. Please...

Population of a weed is typically determined by counting the number of individuals within a quadrant.  The size of the quadrant is determined by the size, density of the weed, and ability to accurately count.  The number of quadrats or samples can be determined statistically with some presampling and use of an "N" formula.  Yout may want to count by stageof growth i.e. rosette. bolted, flowering, etc. to give a clear picture of the weed population.

Please read the attached manuscript, where we explained how weed population counted in an area!

Sampling weed species largely depends on several factors; including cropping pattern, size of plot or area covered, etc. The most common technique is using ''quadrant'. This can be temporary or permanent (fixed) or movable quadrant. Dimension may vary depending on some of the factors mentioned above. I usually use 0.25m2' or 1m2 for sampling weeds in experimental plots. All weed species within the quadrant are collected, counted and identified according to species type.  I also usually make two or three throws of quadrant per plot. Total count per specie type and for all three throws are added together to give relative abundance of each specie per treatment. In addition, I also usually determine % weed  cover, ease of control and level of aggression per weed specie type. I hope this information can be helpful.

SMKanteh,

Njala University

Dear kamala the quadrat size is not fixed for any vegetation to be studied. For more accuracy, you can determine the number and size of the quadrat for a particular community may it be herbs, shrubs or trees by species area curve. 

Quadrat size is different with plant diversity, in bushes 1*1m2

Now no need of me answering this as answers have been presented 3 years ago

Dear kamala

You can download the following manuscripts, if you are interested in Biostatistics, it is free:

https://www.cell.com/heliyon/fulltext/S2405-8440(18)38688-2

https://www.cell.com/heliyon/fulltext/S2405-8440(19)35821-9

https://www.researchsquare.com/article/rs-30792/v1

However, to calculate IVI it gives the importance value of a species to other predominant ones in an area, and usually it is preferable to include ANOSIM and SIMPER test, if groups were identified. But if you want to indicate an indicator species or the preference of species and its fidelity to a certain area, you will be interested to read the last manuscript.

I recommend the answer for Dr. Walter H Fick , either.

The size of the quadrant typically depends on the weed density. A 0.1m2 is enough for weed populations >200 plants per square meter. This would equate to counts above 20 plants per quadrant. Increase the quadrant size up to 1m2 for lower weed densities enabling counts between five and 50 plants per quadrant.

If the weed is in distinct patches across the paddock:

**Carry out plant counts within the patches only.

**Do at least five counts within each of at least four patches, giving 20 counts for the paddock. The more counts carried out, the more accurate the assessment.