SoilMate · Field reference

Cotton plant tissue sampling guidelines

Sampling timing, field selection, plant part selection and sample handling, adapted from the guidelines by Chris Dowling, Back Paddock Company.

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Recommended timing

Suggested cotton tissue sampling schedule

The original guide recommends at least one leaf sample and three petiole samples over the season. Day degrees are cumulative and are supplied here as in the document.

Sample	Growth stage	Day degrees	Purpose
Leaf (youngest mature blade)	Late vegetative to early squaring	400–650	Check nutrient adequacy before rapid uptake.
Petiole	Early flowering	750–800	N and K baseline.
Petiole	During increasing uptake	900–950	N and K baseline at the start of rapid uptake.
Petiole	First maximum-size boll	1000–1050	N and K; main-season top-up decision.
Petiole	Later season	1250–1450	N management if growing fewer than 25 nodes.
Leaf (youngest mature blade)	First open boll	1450–1700	Check crop nutrition under peak nutrient demand.
Petiole	Cut-out	1800–1950	Consider N vigour at defoliation / soil N before growing on.

Why consistency matters

Plant nutrient concentration reflects water, light, heat and soil nutrient availability. Repeated measurements from consistent locations, tissue positions and conditions provide more useful trends than isolated samples.

Choose representative field locations

Use reference points that are easy to relocate, ideally near existing soil moisture and soil chemistry observations.
Avoid atypical sites such as head ditches, tail drains or leaking channels unless they are the subject of the assessment.
Yield maps, vigour maps, EM38 and other field layers can support reference point selection.
Collect samples in a consistent pattern within approximately a 10-metre radius of a reference point.

Example satellite and vigour imagery of a cotton field used to locate sampling points

Which part of the plant?

Leaf blade

Collect the youngest mature blade on the main stem, commonly at the third to fifth leaf below the terminal, without its petiole. Full nutrient analysis generally requires at least 200 g of wet leaf blade material.

Petiole

Petiole analysis is most useful for tracking nitrogen and potassium over time, particularly across flowering and boll filling. Laboratories require at least 20 g of wet petioles. Remove petioles from the leaf blade immediately after picking.

Standardise sampling conditions

Sample when growth is not being restricted by other factors where practical.
Keep irrigation cycle position, moisture availability, time of day and light conditions consistent.
Reschedule sampling where conditions fall outside the defined sampling protocol.

Handling and transport

Use paper sample bags; barcoded bags may be available through service providers or support.
Keep samples cool in transit to minimise sap bleeding.
Record days after emergence for leaves and day degrees since sowing for petioles.
If not using a local SoilMate service provider, arrange express courier to the laboratory.

Seasonal plant nitrogen and water uptake graph plotted against cumulative day degrees

These guidelines are adapted from the supplied 2023 document. Sampling advice, services and laboratory requirements should be verified for current-season use before publication.

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