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Nutrient inputs are critical for optimal corn production, even when corn prices are low. Soil testing is important to take advantage of residual nutrients in the soil. Timing nutrient applications to provide nutrients closer to crop needs helps increase use efficiency and reduce losses. Nutrient placement of phosphorus (P), potassium (K), and other nutrients in bands near the seed can increase efficient nutrient use.
Fertilizer needs should be determined after evaluating the current fertility level of the soil and the nutrient needs of the crop to be grown and should be based on realistic yield expectations. Fertility planning should start with a good estimate of previous crop nutrient removal because replacing nutrients used by the previous crop is critical for maintaining nutrient balance and soil nutrient sufficiency (Table 1). The crop nutrient removal calculator (http://ipni.info/calculator) can be used to estimate crop nutrient removal of nitrogen (N), phosphorus (expressed as P2O5), potassium (expressed as K2O), and sulfur (S) for many field crops.
Figure 1. Kochia seedlings.
Nitrogen (N) applications should be applied according to crop need. Split applications can reduce the likelihood of N loss from leaching and denitritification during wet spring weather. Corn extracts only 15% of required N prior to rapid vegetative growth. N should be applied prior to rapid vegetative growth (V5 to V8 growth stages). A corn plant will need the most N at the V10 growth stage, which occurs about 40 days after plant emergence.
Figure 2. Waterhemp seedlings.
Phosphorus (P) can be applied either in the fall prior to tillage or in the spring. P is nearly immobile in the soil, so incorporation is recommended within the corn root zone.
Potassium is essential for the plant to move energy from the leaves for grain fill. If K is limited, silk emergence may be delayed, and ears with unfilled tips may result. Low K levels can result in yellow leaf margins on lower, older leaves. Because K may be recycled back into the soil through crop residue, K deficiencies can occur when crop residue is removed from the field. K requirements will be higher in production environments with heavy crop removal, such as silage production. Soybean seed production requires more K and will deplete the soil at a faster rate than other crops.
Figure 3. Common ragweed seedling.
Although the uptake of nutrients such as sulfur, zinc, and manganese make up less than one percent of fertilizer applied in corn, they are critical for corn development and it is important to identify and manage deficiency symptoms.1
1 Mallarino, A.P., Oltmaus, R.R., Prater, J.R., Villavicencio, C.X., and Thompson, L.B. 2011. Nutrient uptake by corn and soybean, removal, and recycling with crop residue. Iowa State University. 2011 Integrated Crop Management Conference: 103-113. http://www.agronext.iastate.edu. Web sources verified 10/10/16. 161011153444