What’s the P Index?

The P Index is the Phosphorus Index, a risk assessment tool to quantify the potential for phosphorus runoff from a field. The P Index helps to target critical source areas of potential P loss for greater management attention. It includes source and transport factors. Source factors address how much P is available (for example, soil test P level and P fertilizer and manure application amounts). Transport factors evaluate the potential for runoff to occur (for example, soil erosion, distance and connectivity to water, soil slope, and soil texture). The P Index allows for relative comparisons of P runoff risk. When the P Index is high, recommendations are made either to apply manure on a P basis or not to apply manure at all. When the P Index is low, manure can be applied on a N basis. Also, if the P Index is high, the factors that are responsible for the higher risk of P loss are identified, and this information provides guidance for management practices to reduce the risk. For example, if the P Index is high because of high soil erosion, a recommendation to implement soil conservation best management practices (BMPs) may lower the risk and allow safe manure application.

For additional information:

To find your state’s P Index, do a web search for “phosphorus index” plus your state name.

Author: Jessica Davis, Colorado State University

How do you calibrate a manure spreader?

Calibrating a manure spreader is critical to ensure that the appropriate rate of manure nutrients is being applied to a field. For some livestock operations, this practice may be a required practice as part of their permit. Calibration will differ depending on the equipment and type of manure being applied.

If you know the capacity of the spreader, you need to determine the width of each pass and the distance it takes to empty the spreader to determine the rate of application. A measuring wheel is a useful tool and can often be borrowed from a local Cooperative Extension or Natural Resources Conservation Service (NRCS) office. After you have determined both of those measurements, use the charts in the publication linked below to determine application rate.

If the capacity of the manure spreader is unknown and solid manure is being spread, you can use a process that involves setting out plastic sheets or tarps of known size and driving the manure spreader over them and weighing the amount of manure that is collected on the sheets. A 22-square-foot tarp is a convenient size because the net weight of the manure on the sheet will be equal to the application rate in tons per acre. A step-by-step guide on making these calculations for other size tarps is available in the publication linked below.

For more, including specifics on calibrating solid, liquid, and irrigation manure equipment, visit Calibrating Manure Application Equipment.

Author: Jill Heemstra, University of Nebraska Extension Educator