Sub-surface nutrient placement options

By John Fulton and Trey Colley

Sub-surface placement of nutrients is a best management practice (BMP) in an effort to reduce off-site transport of P and N. There is variety of placement techniques and equipment which becomes important information as farmers decide a solution or suite of solutions to adopt. Frequently, it is unclear which types of implements are best suited to meet the nutrient management goals for a farm operation. Equipment capable of sub-surface placement can vary in horsepower requirements, placement options, and the level of surface disturbance. The “right” implement will vary from farm-to-farm based on the differing management strategies.

An Ohio State University Fact Sheet (Opportunities for Sub-surface Nutrient Placement in Ohio) has been developed to help review and understand specification of different implements for sub-surface placement of fertilizers. This publication can be accessed at https://ohioline.osu.edu/factsheet/fabe-56401. To help identify which implement(s) is best suited for your farm, the Ohio State Precision Ag Team compiled a list of sub-surface placement benefits and categorized available equipment options. The benefits of sub-surface placement of fertilizers can include:

• makes fertilizers readily available for crop uptake,
• potentially reduces pre-plant field passes to a single operation, conserving fuel and reducing compaction,
• strip-till, sub-surface placement equipment allows for optimal seedbed preparation, improving planter performance, and
• can reduce off-site transport of fertilizer in overland runoff.

It is important to understand these implements do not accomplish the same thing during field operations, but there remains a number of implements available on the market to place fertilizer below the soil surface. Implement options can vary greatly in both function and suitability-of-use. For a decision aiding tool, categorized currently available sub-surface placement implement options into one of the four categories:

1. “Deep rip and placement implements apply a fertilizer band (generally 3- to 8 inches) of liquid, dry, or anhydrous, prior to the growing season and usually involve some type of tillage or seedbed modification. Generally able to operate 3 to 6 miles per hour in a minimal till to strip-till environment, producing more soil disturbance than “zone mixing” or “injection” implements.
2. “Zone mixing” type implements mix fertilizer and soil in a tilled zone generally around 8 inches wide and 6 inches deep. They typically use a multiple coulter setup to induce a thorough mixing action on the soil while blending liquid, or dry fertilizer or manure. Generally these implements are able to operate in the 7 to 12 miles per hour range in a strip-till or similar environment, while producing more soil disturbance than “injection” type implements.
3. “Injection” Type implements apply a shallow, narrow band of fertilizer (generally 3 inches to 5 inches), of liquid, dry, or anhydrous fertilizer. Typically, these implements utilize a single coulter or similar opener to inject the fertilizer product into a thin opening of the soil. These implements normally operate in the 7 to 12 miles per hour range in a no-till or minimal till environment, while producing the least amount of soil disturbance compared to other implements.
4. Broadcast then incorporate applications are typically conducted by a dual spinner-disc spreader, followed by incorporation through disc, field cultivator, or similar tillage tool. Incorporation can be done any time after the broadcast application, but preferably within 3 to 5 days.

Sub-surface placement tools offer many advantages through optimizing nutrient placement and seedbed preparation, but often are more time-consuming than traditional (over-the-top) fertilizer spreading. Try to incorporate as many of the benefits as possible into your operation by selecting a tool that maximizes the value for that pass over the field.

Find additional information related to fertilizer application at the Ohio State University Digital Ag website under Precision Crop Management: https://digitalag.osu.edu/precision-ag/research-focuses/precision-crop-management.

Dr. John Fulton, Associate Professor, can be reached at fulton.20@osu.edu. This column is provided by the OSU Department of Food, Agricultural and Biological Engineering, OSU Extension, Ohio Agricultural Research and Development Center, and the College of Food, Agricultural, and Environmental Sciences.