April's Ag Advice by April Borders Cool air and soil slow corn plant and root development in the spring. When root growth is restricted, corn plants often turn purple. Early season purpling varies with variety, but most often it is a symptom of phosphorus (P) deficiency. The deficiency is described as induced because it may occur on soils that test high for phosphorus. It occurs because phosphorus moves slowly in the soil. If roots do not grow enough to reach soil phosphorus reserves, the plant begins to starve for that nutrient.
In most cases, phosphorus deficiencies are temporary, and symptoms disappear as soon as soil temperatures rise to a point where root growth is stimulated and the plants can reach more phosphorus. Additional factors that limit root growth can also induce phosphorus deficiencies. Some common causes include soil compaction, herbicide injury, and insect or nematode damage to the root system.
Starter fertilizer may be used to overcome slow root growth and the potential for reduced nutrient uptake. Starter and "pop-up" fertilizers involve at-planting placement of a small amount of nutrients near the seed (for starter fertilizer) or in the seed furrow (for pop-up types) so seedling roots can rapidly reach the nutrient source. These fertilizers are not intended to supply all nutrients needed by the crop. Their primary purpose is to provide an accessible nutrient source for root and plant growth when adverse conditions occur soon after planting.
The benefits of placing a portion of the crop's fertilizer needs in a concentrated band near or with the seed at planting have long been recognized. Phosphorus, potassium, nitrogen and other nutrients placed as starter or pop-up at planting often result in early season response that translates to yield increases and greater profit in the production of corn and other crops.
Another important factor in considering the potential of starter fertilizer is residue level and degree of tillage. High levels of crop residue increase the potential of a profitable response to starter due to prolonged cool, wet spring soil conditions. Also, with reduced tillage, stratification of immobile nutrients such as phosphorus and potassium is increased, resulting in a greater potential for response to subsurface banding, especially for potassium.
When starter is applied in a 2×2 (2 inches to the side and 2 inches below the seed) placement, the chance of injury and stand reduction from salt damage is negligible. However, where fertilizer is applied as a pop-up in-furrow with the seed, care should be taken to avoid seedling injury, stand reduction, and yield loss. The amount of fertilizer that can be used depends on fertilizer source, crop, row width, and soil moisture.
South Dakota State University's recommendation for corn in 30-inch rows is that nitrogen plus K2O application in contact with the seed should be limited to 10 pounds per acre. Nitrogen as urea, UAN and ammonium thiosulfate (12-0-0-26) should not be in contact with the seed. Reduce seed placed fertilizer rate by 50 percent when soil conditions are dry or sandy.
The use of starter fertilizer is an effective management practice that is based on sound agronomic principles. However, in most cases it should not be used as the sole fertilizer program. The best approach to starter is to view it as a catalyst for a crop that will have adequate and balanced available nutrients in the soil rooting volume as the season progresses.
For more information on starter fertilizers or any other questions that you have, please contact the Clay County Extension Service at 677-7111.