With the storm season in full swing, intensive rainfall events increase the likelihood of water quality impairments through sediment transport and P intake into surface waters. Several BMPs for phosphorus management are available and can be implemented relatively easily by landowners. While it is difficult to measure the effect of a single BMP, it has been shown that the combination of several BMPs together will have an overall positive effect on water quality.
BMPs addressing P mitigation are essentially split into source and transport BMPs, or a combination of both. In general, P input and outputs should ideally be balanced at the farm or watershed scale. While a precise balance may be difficult to calculate, measures can be taken to reduce the risk of excessive P loss. First, testing pasture soils for fertility levels goes a long way of keeping P in- and output in check. Over-application of P is avoided by applying recommended fertilizer amounts. This also means that fertilizer and manure spreaders should be calibrated and in good working order to ensure even distribution of the applied material. For some farmers the application of poultry litter is an option and a good opportunity to increase soil organic matter besides providing plant nutrients. The application of litter should be timed carefully however, as heavy rainfall can lead to runoff and transport of P away from pastures.
Because P is attached to soil particles that can be transported away, so-called transport BMPs are aimed at retaining P on site before it enters water ways. One of the first things to consider is, therefore, minimizing soil erosion. Proper grazing management is a very effective way of avoiding excessive erosion as rainfall can infiltrate on pastures with sufficient grass cover where runoff is usually filtered before it reaches streams or creeks.
Cover crops can be used on bottom land with the purpose of reducing erosive potential and filtering runoff. Filter strips are another option for retaining excess nutrients. These strips can be situated alongside riparian zones and infrequently grazed when conditions permit. Grassed waterways, also called vegetated swales, are very common in the Midwest where they help reduce runoff and filter nutrients in crop fields such as corn or soybean. In a pasture situation, these swales can easily be established alongside intermittent streams. There appears to be interest among landowners to work with native plant species such as switchgrass, big bluestem, indiangrass, or gamagrass that are adapted to a variety of conditions and are well suited for establishment in grassed waterways. In pasture situations, vegetated swales need to be strategically placed to avoid a large reduction of grazable land, although these areas can be grazed infrequently. Such waterways need to be fenced off, but this is easily accomplished with polywire. Grassed waterways can also be linked to riparian zones to increase their efficacy.
It should be kept in mind that a combination of several well-executed BMPs is the most efficient way of maintaining or improving water quality. BMPs do not have to be implemented at once, but a long-term plan is useful for establishing several over time. As it has been mentioned before, good grazing and animal management help protect water quality. A more intensive management approach will require planning on how to section pastures, where to locate watering sources, which forages may need to be established, and what grazing method will maximize forage utilization, all of which improve pasture management.
There is a lot of good material available from the UA Division of Agriculture, NRCS, and USDA on grazing management and BMPs for the livestock industry including cost share options. Contact your local county extension office for advice and help in implementing P mitigation measures that suit your situation.