Michigan State University Extension
Soils & Soil Management - Fertilizer - 06039717
07/10/97
Tri-state Fertilizer Recommendations for Corn, Soybeans, Wheat and Alfalfa Extension Bulletin E-2567 (New), July 1995
M.L. Vitosh, Michigan State University; J.W. Johnson, The Ohio State University; D.B. Mengel, Purdue University; Co-editors
Most soil test report forms do not provide information on how farmers should apply their fertilizer To be used efficiently, P and K fertilizers should be applied properly and at the appropriate time. Because the choices of application depend greatly on the fertilizer material used and the equipment available, it is up to the farmer to see that the fertilizer is properly applied. When plants are small, soil test levels low, soil surface residues high and soil temperatures cold, starter fertilizers become very important for optimum plant growth. For well established crops such as forage legumes, topdressing is the normal recommended practice.
Starter Fertilizers
In many instances, applying some or all of the fertilizer needed with the planting unit improves fertilizer efficiency. If starter fertilizer is used, apply 20 to 40 lb. of N. P2O5 and/or K2O per acre in a band 2 inches to the side and 2 inches below the seed. The total amount of salts (N + K2O) should not exceed 100 lb. per acre for corn or 70 lb. per acre for 30-inch-row soybeans.
The amount of P2O5 added in the band is non-limiting except that most P fertilizers are combined with N such as diammonium phosphate (DAP), monoammonium phosphate (MAP) and ammonium polyphosphate (APP). When these fertilizers are used as a starter, do not band more than 40 lb. N per acre on corn and 20 lb. N per acre on 30-inch-row soybeans. Nitrogen and P are the most important major nutrients for early plant growth, particularly in no-till production systems. On high P testing soils (greater than 30 ppm P), N is the most important nutrient for corn and should not be omitted from the starter in high residue no-till systems unless at least 40 to 60 lb. N per acre has been broadcast applied prior to emergence. It is not necessary to include K in the starter fertilizer unless the soil test K levels are very low (less than 75 ppm K).
For drilled soybeans, wheat and forage legumes, it is unlikely that any P can be banded beside and below the seed at planting time because most new drills do not have fertilizer attachments. In this situation, all nutrients should be broadcast before planting. Only on extremely low P testing soils (less than 10 ppm P) will this create any significant P deficiency problems.
Fertilizer with the Seed
The general practice of applying fertilizer in contact with seed is not recommended. Band placement to the side and below the seed is usually superior to any other placement. Some farmers, however, have grain drills or planters that place fertilizer in contact with the seed. In this case, caution should be used to prevent seed or seedling injury from fertilizer salts. For corn, do not place more than 5 lb. N + K2O per acre in contact with the seed on low CEC soils (CEC less than 7) and no more than 8 lb. N + K2O per acre when the CEC is greater than 8. Soybean seed is very sensitive to salt injury; consequently, all fertilizer for drilled soybeans should be broadcast before planting. For small grain seedings, do not drill more than 100 lb. of plant nutrients (N + P2O5 + K2O) per acre in contact with the seed. Do not apply more than 40 lb. N per acre as urea in contact with small grain seed. Young germinating seeds and seedlings are very sensitive to salt injury. Dry weather will accentuate the injury.
When seeding forage legumes, do not place more than 100 lb. P2O5 and 50 lb. K2O per acre in contact with the seed. If the fertilizer is placed 1 to 1 « inches below the seed, the seeding time fertilizer may include all of the P and up to 150 lb. K2O per acre. Broadcast and incorporate any additional fertilizer requirements before seeding. For established legumes, all fertilizer requirements should be topdressed in the fall before plants go dormant (approximately October 1) or after the first cutting in the spring.
