Potassium deficiency problems showing up in corn
The nutrient uptake process
Once the nutrients are delivered to the root surface, nutrient uptake can occur. Three factors determine the amount of nutrients that will move into the root:
- The concentration of nutrients at the root surface.
- The amount of root surface area (number of roots); and
- The amount of nutrient inside the plant, and the feedback that provides to the uptake process.
If the amount of water moving to the roots is limited, nutrient uptake is limited through the limitation of the delivery of nutrients to the root surface that creates. If the root system or root growth is limited -- by compaction or soil density and limited pore space (as in no-till) -- uptake is limited since each unit of roots has a finite maximum uptake rate. If the concentration of the nutrient in the soil is limited, either because you didn’t apply enough fertilizer or you put it on and it was lost, nutrient uptake is limited.
When nutrients dissolved in the soil water reach the surface of the root, the root selects the ions it needs and moves them across the cell membranes. The ions it doesn’t need remain at the root surface and accumulate. This process is highly selective and requires energy. In some special cases such as might occur with young wheat shortly after green-up, during a prolonged period of cool cloudy days which would limit photosynthesis, nutrient uptake could be limited by a lack of available energy.
How growth stage of the corn impacts nutrient uptake
One additional important issue impacting nutrient uptake is the growth stage of the corn, especially early in the season. When corn seed germinates, the radicle or seed root grows down and begins to expand and take up water along with a limited amount of nutrients. This seminal root system supports the corn seedling for the first 20-30 days, but it doesn’t grow deep, nor does it become very dense. Its job is primarily to take up water and anchor the plant until the permanent nodal root system develops.
About the 4-leaf stage, the nodal or crown root system will begin to develop, and the seminal roots will reach their maximum size. Around V-6 the nodal root system will begin to take over and the seminal system will begin to die. Between V-4 and V-6 or V-7, it’s not unusual to see plants exhibit pale green color, purple color, striping, and so forth as nutrients can be limiting. This is not because of a real deficiency of nutrients in the soil per se, but rather it is because of a limit in the amount of active roots available to take nutrients up as this root system transition occurs.
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