Applying Manure to Tiled Fields

Ms. Amanda Meddles, Extension Program Coordinator for Environmental Management, The Ohio State University

Most producers are aware of the rich nutrient found in manure and the value that manure provides to growing crops. Fewer are aware of the potential for the nutrients to exit fields through tile lines, contaminating surface waters. Manure also moves through cracks, worm holes, dead root channels, etc. This can be avoided by matching the water holding capacity of the soil and the manure application rate to avoid saturating the soil. However, dry cracked soil can be as much of a problem as saturation. The goal of this article is to express the importance of keeping manure nutrients in the root zone where crops can use them. The following article is an excerpt from the OSU Extension Fact Sheet Guidelines for Applying Liquid Animal Manure to Cropland with Subsurface and Surface Drains by James J. Hoorman, Jonathan N. Rausch and Larry C. Brown. It provides excellent tips to avoid nutrient loss through subsurface drainage. The entire fact sheet can be found at under OSU Extension Fact Sheets.

The fact that liquid animal manure nutrients can be safely land recycled in some instances, but are discharged in subsurface drainage water under different circumstances, suggests a complex system that needs to be managed. Soil texture, available water holding capacity, tillage history, as well as the type and quantity of manure applied, application method, and timeliness of rainfall after application may all play a role in determining the fate of the manure. Suggested guidelines to minimize the downward movement of liquid manure are:

a. Identify subsurface drain outlets, and control or regulate discharge prior to application, or have on-site means of stopping the discharge from subsurface drains. Subsurface drainage outlets should be monitored before,
during, and after application for potential liquid manure discharge.

b. Liquid manure should not to be applied on soils that are prone to flooding, as defined by the National Cooperative Soil Survey (or in the Flooding Frequency Soil List posted in Section II eFOTG), during the period when flooding is expected. Manure can be applied if incorporated immediately or injected below the soil surface during periods when flooding is not expected.

c. Avoid applying manure when rainfall is predicted, eminent, or directly after a rainfall event. After a significant rainfall event, the site should be allowed to drain to below field capacity, so that the soil has the capacity to absorb additional water or liquid animal manure.

d. Repair broken drains and blowholes prior to applica­tion, and follow recommended/required minimum setback requirements (setback distances vary from state to state) for surface inlets. See fact sheet on Liquid Manure Application Rates for Subsurface and Surface Drained Cropland.

e. Liquid manure should not be applied to subsurface drained cropland if the drains are flowing. Generally, flowing subsurface drains indicate soil moisture levels that are near or exceeding the soil water holding capacity.

f.   Application rates should be closely tied to nutrient requirements and available holding capacity of the soil. The method of application can influence application rates.

g. Liquid manure should be applied in a manner that will not result in ponding, or runoff to adjacent property, drainage ditches, or surface water regardless of crop nutrient need and should be uniformly applied at a known rate.

h. Fields with a history of downward movement of manure and/or bare/crusted soils may require some tillage to improve infiltration and absorption of the applied liquid. Prior to manure application, use shallow tillage to disrupt the continuity of worm holes, macropores and root channels (preferential pathways) to reduce the risk of manure reaching drain lines, or till the surface of the soil 3 to 5 inches deep to a condition that will enhance absorption of the volume of liquid manure being applied.

i.   Clay soils with a high shrink swell capacity tend to have larger deeper cracks during dry conditions. These soils may require tillage to disrupt the cracks and macropores, and a lower initial application rate applied to the soil to help close the cracks.

j.   Shallow injection is recommended for liquid manure. Till the soil at least 3 inches below the depth of injection prior to application, and/or control outflow from all drain outlets prior, during, and after manure application.

k. For perennial crops (hay or pasture) or continuous no-till fields where tillage is not recommended, all subsurface drain outlets from the application area should be monitored, and if manure laden flow should occur, all effluent should be captured. Crops with deep tap root systems (alfalfa) tend to have more problems than hay crops with fibrous roots (grass) because liquid animal manures may flow along the tap roots to subsurface drains and outlet to surface water.

These criteria may be waived if the producer can verify there is no prior history of manure discharge via subsurface drains, or if a system is in place to capture the discharge. However, if there is a discharge, the producer is liable for damages and is subject to being classified as a Concentrated Animal Feeding Operation (CAFO).