Much like we all experience an awkward stage of growth during our formative years, corn plants can also between growth stages V5-V7. This can occur as the plant transitions from seed root system to its nodal root system which carries the plant through its remaining growth stages. Additionally, height differences and varying degrees of greenness across the field can be due to spotty adverse environmental conditions throughout the field. The more severe these conditions, the more prolonged this transition can be. Often, a full field investigation is warranted to determine if corrective action needs to be taken or to uncover improvements we might take in coming years.
Different degrees of greenness typically associated with nitrogen deficiency can be due to many different crop nutrients. The stuff that gives plants it greenness, chlorophyll, requires not only nitrogen but also sulfur, copper, iron, and manganese for maximum production. It’s for this reason best to first determine the reason for the difference in color intensities before taking any corrective action. Nutrient deficiencies can be both true (soil actually deficient) or positional (plant roots cannot reach nutrients) in nature. The nature of the problem can be determined via further investigation of the soil environment throughout the field in both good and bad areas of growth. Begin with plant tissue analyses, coupled with soil tests to provide a good snapshot of the plant’s nutritional status and soil nutrient supply. Collect tissue and soil samples from a series of both affected plants, and nearby normal plants to provide a comparison (off green vs. green) and to confirm true versus positional nutrient deficiencies.
Reasons for positional nutrient deficiencies lie below the slow surface. Dig roots to uncover the presence or evidence of past activity from soil born insects and pathogens. Look for root abnormalities due to compaction or shallowly planted seed. Examine soil conditions for signs and reasoning of excessively wet or dry, in all cases comparing affected versus unaffected areas and plants across the field.
Height differences of two or more V-stage spread many times are solely due to uneven emergence that can be cause by uneven planting depth, differences in soil moisture and/or soil temperature during germination. Residue blanketing of the soil surface alone can result in soil temperature differences of 10°F alone that results in uneven emergence. These growth stage differences of two or more leaf collars, especially which occur between V5 and V7, can create varying degrees of color across due to differences in the transitional timeframe between permanent nodal root system versus a seed root system.
After thorough field investigation it should be easier to determine what you are dealing with, whether and to chart a course action.
Mike Gill serves the FS System as GROWMARK’s crop nutrient technical manager. He can be reached at mgill@growmark.com.