When corn plants emerge, it's not uncommon for seedlings to have a purplish tint or some uneven early growth. These observations often worry some corn growers. However, when the purple color disappears—usually after the six-leaf stage—so do growers’ concerns. The ultimate goals of corn production are harvestability and yield, and current evidence shows purple seedling color does not relate to either.
Concern about purple seedling color is understandable. If there is something wrong, growers want to know the cause of the problem. What causes corn to turn purple? Is it bad? Will it affect crop development or yield? What can or should be done about it?
This article discusses factors that can influence purpling in corn seedlings and explore another seedling condition; uneven early growth. It is important to remember that while both these conditions occur during the seedling stage in corn growth, they are not correlated.
Phosphorus deficiency symptoms can be manifested as an accumulation of purple pigments in leaves. Phosphorus level as determined by soil tests and an examination of the fertility programs used, may determine whether phosphorus is likely deficient. If sufficient levels of phosphorus are already present, adding extra phosphorus will not turn purple seedlings green.
Some of the same stress factors that can limit phosphorus availability can also cause uneven early growth. Both green and purple corn plants can exhibit uneven seedling development. There is little hard evidence to explain why uneven seedling growth occurs in the spring because so many environmental factors may be present. Cool-temperature stress is a factor, and this may interact with variable soil conditions, seed placement, compaction, fertilizer placement, and amounts of crop residue.
Each seedling has a unique environment for growth and, as a result, some unevenness in plant development will occur. Growers should only be concerned when uneven growth is abnormally great. Perhaps a management strategy is needed to minimize some of the stresses to which the seedlings are being subjected.
The most critical assessment of seedling stress is stand establishment. If stands are reduced, yield potential may be limited. If adequate stands are achieved, then most research data show seedling growth has little influence on final yields. However, modern agriculture is pushing seedlings into a more stressful environment. Factors increasing stress on seedlings include:
Cold Soils: Early planting increases the likelihood of cold temperatures during emergence and early seedling growth. Minimum tillage leaves more residues on the soil surface, thus insulating the soil and delaying its warming.
Tillage: Shifts in tillage systems have resulted in less uniform seedbeds. Greater variation exists in aeration, seed coverage, and perhaps planting depth.
Compaction: Compacted zones can influence soil moisture for germination and limit root growth and nutrient uptake.
Fertilizer Placement: Current tillage trends result in less uniform fertilizer distribution in the root zone. Often times much of the fertilizer is localized on or near the soil surface.
Pesticide Application: Misapplication of chemicals including over-application, non-uniform application, and improper incorporation, is a costly error that can also affect crop growth and performance. Take time to calibrate chemical applications to comply with label recommendations.
The stresses that cannot be controlled, such as weather conditions, are likely the most critical. Whether too hot or cold, too wet or dry, the weather will rarely be ideal for plant growth.