Manure Timing Plays Key Role in Reducing Phosphorus Loss

By Andi Anderson

Manure is a valuable source of nutrients for crops, but the timing of application plays a major role in how well those nutrients stay in the field.

Research shows that applying manure during winter greatly increases the risk of phosphorus loss, which can harm nearby water bodies.

Studies conducted over several years found that manure applied in December and January resulted in much higher phosphorus losses than manure applied in October and November.

Winter applications lost several times more phosphorus per acre, both in total and dissolved forms. These losses came directly from recently applied manure, showing that timing alone can strongly affect nutrient movement.

The higher risk during winter is caused by several factors. Tile drainage systems are more active in winter as precipitation increases after dry fall months. 

Water moves quickly through tiles, bypassing dormant vegetation and carrying phosphorus into drains. Freeze and thaw cycles also play a role.

Manure applied on unfrozen ground can freeze under snow, then wash away during snowmelt or rain events. These conditions create strong water flow that moves phosphorus off fields.

Winter applications also tend to use higher manure rates than fall applications. Even when application rates are only moderately higher, phosphorus loss increases sharply because water movement is the main driver of nutrient loss during winter.

Applying manure soon after harvest in early fall is a safer option. Dry soils allow phosphorus to bond with soil particles, reducing the chance of leaching. Using incorporation or injection methods further improves results.

If injection is not available, lightly incorporating manure after surface application helps mix nutrients into the soil and limits runoff.

Controlled drainage systems offer another effective solution. By slowing tile flow after manure application, these systems reduce phosphorus movement during major drainage events.

Planning ahead is also critical. Adequate manure storage allows farmers to apply nutrients when field conditions are favorable rather than during high-risk winter periods. Storage systems should be inspected regularly, as winter weather can affect their stability.

Farmers are encouraged to follow established manure management guidelines. Key practices include avoiding spreading on frozen or snow-covered ground, maintaining buffers near water, using conservation practices, and evaluating fields with risk assessment tools.

Together, these steps help protect water quality while making the best use of valuable manure nutrients.