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When Should I Test My Corn or Sorghum Plants?

By Charles Walters

There are three critical stages in corn (grain or sorghum) plants you should test around. The final stage deserves a close visual examination.

Less than 12 inches height: At 25 days, analyze the entire plant for N plus minerals (P, K, Ca, Mg, Na, Zn, Fe, Mn, Cu). Pull 15 plants with roots and wash off all dirt before wilting. Air-dry and place in a paper bag (not plastic) for shipment to the lab. Take plants from a repre­sentative area of the field, one plant for every fifth row in a diagonal pattern across the field, starting 50-feet inside the field and away from the edges. Do not mix problem areas. Sample problem areas sepa­rately. At this critical period, before plants form embryo in the ear, essential nutrients can be adjusted to affect yield potential. Apply a balanced formula foliar fortified with deficient nutrients and adjuvants, as in growth aids, humic acid, microbes, energy (molasses), etc. Help overcome weather stress with plant growth hormones & enzymes. Only minimal rates are needed when sprayed directly on plants. Note: by the 5-6 leaf, embryo in the ear is forming and a balanced nutrition adds rows of grains.

corn stages
Corn stages are important to know as you plan your testing.

At Boot: This stage occurs when less than 15% of tassels or heads are peaking out. Pull 12 leaves from the most recently mature leaf — when the full dew-lap (sheath) is showing. Cut at the dew-lap and take the entire leaf including the base of the midrib. Mature leaves will have most of the sheath showing. Take samples from the same area and pattern of the field as the first samples. At this point moisture and all nutrients are entering a maximum usage period. Apply deficient nutrients in water or as foliar spray (especially zinc for N use efficiency and proper plant growth). Hormones can be added to stimulate root and grain growth.

At Pollination: When corn silks are turning dark. The major need at this time is nitrate or urea nitrogen for grain filling. Pull 12 ear leaves for sampling. Use the same pattern and area as previous samples. Take full leaves. N, foliar or water applied at this stage has increased yields by 15 to 20 bu. per acre when needed. Only soil nitrate or urea (applied soil and foliar) works this late. Testing evaluates how well this crop has been fed and aids as a tool for adjustment for next year’s fertility program.

At Maturity: At this stage, do a crop scene investigation (visual autopsy).

Source: Ask the Plant