Five items to Check off your Fall Fertility Checklist

Base Prerequisite: Soil Sampling Take complete soil samples on a minimum of 2.5 to 5-acre grids to make accurate determinations of nutrient needs throughout your operation. This will also be imperative to adjust soil pH as proper liming can increase the following nutrients by over 40%. 

1. Phosphorus
   1. Important for early root development and plant growth as well as late-season grain-fill as 80% of P is in the grain
   2. 75 bu/A Soybeans remove 43.5 lbs P₂O₅/A (95 lbs 18-46-0)
   3. 250 bu/A corn removes 87.5 lbs P₂O₅/A ((190 lbs 18-46-0)
   4. If fertilizing for 2 cropping systems of these yields and maintaining soil tests, then the requirement is 285 lbs DAP/A

2. Potassium
   1. Aids in plant structural strength (reduced lodging) and increase water and nitrogen efficiency
   2. 75 bu/A Soybeans remove 87.5 lbs K₂O/A (146 lbs 0-0-60)
   3. 250 bu/A corn removes 62.5 lbs K₂O/A ((104 lbs 0-0-60)
   4. If fertilizing for 2 cropping systems of these yields and maintaining soil tests, then the requirement is 250 lbs 0-0-60/A

3. Sulfur (Elemental)
   With less sulfur coming from the atmosphere and increasing crop yields, the sulfur requirement can exceed 25 lbs S/A. Sulfur aids nitrogen in forming proteins and is taken up by plants in the sulfate form; however, sulfate sulfur is mobile in the soil and not well suited for fall applications. Elemental sulfur slowly breaks down to sulfate but requires warmer temperatures for breakdown from microbes. This makes elemental sulfur suitable for fall fertilizer applications and a source of late-season sulfur availability so it is available when the plant needs it. At United we use Mega-S 90% Sulfur Bentonite sulfur which is 60% available for next year’s crop if applied in the fall. Typical elemental sulfur releases slower than that.

4. Nitrogen
   Ammonium forms of nitrogen such as anhydrous ammonia or manure can be applied in fall but the goal should be to keep the nitrogen as ammonium so it does not leach. Applications, when soil temperatures are below 50°F and using a nitrification inhibitor such as Instinct, can help keep nitrogen in the non-mobile form until next spring.

5. Micronutrients
   When was the last time you tested for micronutrients in the soil or in the plant? While micronutrients are needed in small quantities, statewide tests have found that several micronutrients have been below optimal thresholds and may be limiting yield. In particular, 76% of corn tissue samples were low in Mn and 63% of samples were low in Zinc. Immobile nutrients like zinc, manganese and copper can be applied in the fall to start to build soil test levels to feed the crop and in-season monitoring with tissue samples can help determine if supplemental micronutrients are needed.

Jim Kemink

Vice President - Agronomy Sales