Corn... before tasseling
Collect the first fully developed leaves from the top of 15 to 20 plants. (If the plant is less than 12 inches tall, collect all of the above ground portion.

Corn... from tasseling to silking
Collect the leaves below and opposite from the ear of 15 to 20 plants.

Sorghum
Collect the second leaf from the top of 20 to 30 plants before or at heading.

Alfalfa
Collect top 6 inches or upper third of the plant at tenth bloom stage or before.

Soybeans
Collect recently mature trifoliate leaves from the top of 20 to 30 plants prior to or during flowering. (In the seedling stage, collect all of the above-ground portion.)

Cotton
Collect recently mature leaves from the main stem on 40 to 50 plants selected at random at full bloom.

Pecans, Figs, Olives, Peaches, Nectarines
Collect the mid-shoot leaflets/leaves at mid season.

Small Grains
Collect the four uppermost leaf blades from the top of 25 to 40 plants. (In the seedling stage, collect all of the above-ground portion.) Sample should equal two cups.

Pistachios, Walnuts, Citrus Collect terminal leaflets/leavesat mid to late season.

Apples, Pears, Almonds, Apricots, Cherries, Prunes, Plums
Collect the leaves from non-fruiting, non-expanding, spurs at mid season.

Grapes
Collect the leaves opposite basal cluster at bloom.