Small grains and grasses
When to sample – Any time before the head emerges.
What part of plant – Select tissue from the upper third of the plant.
How to sample – Collect tissue from 50 to 60 randomly selected plants. If the stand is a mixture of grasses, sort leaves by species and submit a separate sample for each kind of grass in the stand.
Sorghums
When to sample
The ideal time is when the head is fully emerged but before pollination. Samples may be taken at an earlier stage if problems develop.
What part of plant
The second leaf from the top of the plant is sampled after heading but before pollination. If it is necessary to sample earlier, take the first leaf below the whorl.
How to sample
Take one leaf per plant from 15 to 25 randomly selected plants.
Source:
https://extension.missouri.edu/publications/g9131