Field crops plant testing

Procedure for sampling selected field crops.

Crop	Time to sample	Plant part to sample
Corn	Some time between emergence and silking/pollination. Do not sample after silks have dried.	Seedling stage: All above-ground portion (20 to 30 plants) Prior to tasseling: The entire leaf fully developed below the whorl (15 to 25 plants) Tasseling and shooting to silking: The entire leaf at the ear node (15 to 25 plants)
Corn stalk nitrate-N	Samples should be collected at one to three weeks after 80% of the kernels reach black layer stage (physiological maturity) and not after harvest.	Six-inch stalk samples should be cut at 6 to 8 inches above the soil surface, at black layer stage, no leaves included. Preferable to sample at least a minimum of 10 stalks from the area of interest.
Soybean	The ideal time is when the first bloom appears. However, if problems appear prior to bloom, a sample can be taken. Do not sample after the first pods begin to fill.	Seedling stage: All the above-ground portion (20 to 30 plants) Prior to or during flowering: Two or three fully developed trifoliate leaves at the top of the plant (20 to 30 plants)
Small grain	Any time before head emerges.	Seedling stage: All the above-ground portion (50 to 60 plants) Prior to heading: Select tissue from upper one-third of plant (50 to 60 plants)
Alfalfa and clovers	Just prior to bloom (1/10 bloom) or at harvest stage.	Take top 6 inches of plant or top 1/3 of plant (40 to 50 plants)
Sorghum	Ideal time is when head is fully emerged but before pollination. Samples may be taken at earlier stage if problem develops.	Fully expanded and mature leaves (15 to 25 plants)
Cotton	Before bolls start to set.	The most recently matured leaves (30 to 40 plants)