Spreading Manure Now Can Lead to ‘Incidental Transfer’ to Streams

When manure is applied at this time of the year, most of the soil pores are continuously filled with water, infiltration capacity is low, and the threat of runoff high.
Spreading Manure Now Can Lead to ‘Incidental Transfer’ to Streams - Articles
Spreading Manure Now Can Lead to ‘Incidental Transfer’ to Streams

Soil is a wonderful medium that filters, decontaminates, and processes almost anything you put in or on it. Billions of bacteria, fungi, protozoa, arthropods, earthworms, moles, mice, groundhogs and more work together in a giant foodweb that helps accomplish this.

Just imagine what would happen if the leaves in the forest did not decompose for one year -a tremendous carpet would accumulate, the trees would start suffering from nutrient deficiencies, and birds would run out of food. A gamut of pore spaces ranging from submicroscopic to half an inch or larger create the habitat for the different soil organisms. The pores of different dimensions allow water to infiltrate, percolate, and be held so the different life forms have water as well as oxygen.

At this time of the year most pores are filled with water and sometimes the soil is still frozen. Low temperatures lead to low evaporation (the loss of water from the soil surface) and transpiration (the loss of water through living vegetation). Because most pores are continuously filled with water infiltration capacity is low, and the threat of runoff high.

Unfortunately, manure piles are growing and pits are filling up! Farmers are anxious to get the manure spread before the busy planting season starts. This confluence of events may mean that the soil will not have a chance to soak up the nutrients and carbon from the manure. Instead, the manure completely by-passes the soil and nutrients and dissolved organic carbon from surface applied manure runs unprocessed into streams or sinkholes. Researchers call this type of runoff 'incidental transfer'. It only occurs at certain times of the year when the soil is not able to take in water and there is a ready source of nutrients, dissolved organics, or even pesticides at the soil surface. Although the farmer has done everything to improve soil health this type of runoff can still be problematic. The best solution is to wait until the soil has dried out until infiltration capacity has improved.

Further, we recommend that manure be applied only to living and growing vegetation, such as a cover crop. The cover crop helps to dry out the soil, provides natural barriers to runoff and the roots improve soil aggregation and porosity, boosting infiltration. Besides, the cover crop is part of the soil food web and will take up nutrients from the manure. It is also wise not to spread manure immediately before a heavy precipitation event is expected. Incorporating manure using tillage would remove the manure from the soil surface and mix it with soil. However, when the soil is as wet as it is now the soil is wholly unsuited to tillage so this is a bad proposition. Tillage is also not consistent with continuous no-tillage that helps to improve soil health. Injecting manure would combine the benefits of no-tillage and bring the manure into contact with soil organisms so it can be processed. However, manure injection should not take place at high soil moisture conditions, either. Therefore, patience is your best companion until soil conditions are fit for manure application.

Authors

no-tillage cover crops soil compaction soil health soil erosion soil conservation nitrogen fixation

More by Sjoerd Willem Duiker, Ph.D., CCA