TWIN FALLS, Idaho — Dairies will see a phase-in of a new nutrient management standard if the Idaho Legislature approves phosphorus indexing in their nutrient management plans.
The new standard, which went through the Idaho State Department of Agriculture rulemaking process this summer, is aimed at better preventing phosphorus losses though runoff or leaching.
It would also give dairies more flexibility in nutrient management by determining risks and appropriate phosphorus application in individual fields, as opposed to the existing total farm threshold standard.
Best management practices to minimize the loss of phosphorus to the environment are a key component of the standard, said Rick Naerebout, CEO of Idaho Dairymen’s Association, during the association’s district meeting on Tuesday.
The existing standard came into play in 1999 and needed updating. IDA set out to develop a new standard for Idaho that would both protect the environment and give dairymen more flexibility to manage their operations, he said.
After looking into existing standards in surrounding states and other major dairy-producing states, IDA Consulting Services staff and scientists with the USDA Agricultural Research Service at Kimberly, Idaho, agreed on phosphorous indexing, he said.
Indexing looks at the source of phosphorus in the landscape and how it’s being managed and transported to assess the risk of loss from that landscape, said April Leytem, ARS research soil scientist.
It provides an overall rating for potential phosphorus loss from a site, with a relative ranking that allows dairy producers to focus management on high-risk sites, she said.
It includes practices that can be used to mitigate risks, such as the use of cover crops, conservation tillage, drip irrigation, perennial crops, residue management, absorbent polyacrylamide, dikes, berms and sediment basins.
It provides credits for those best management practices in the equation, she said.
Fields are assessed on an individual basis to target management strategies for risk, said Stephanie Kulesza, nutrient and water management specialist with IDA Consulting Services, a division of IDA.
The indexing involves a matrix of factors that score sources of phosphorous and transport of phosphorus to the environment, as well as management practices that can lessen the risk, she said.
The source factors include soil phosphorus levels and application rate, method and timing. The transport factors include soil erodibility, surface runoff, leaching potential and distance to surface water.
The overall score runs from low risk to very high risk, which dictates the amount of phosphorus that can be applied on individual fields.
“It really gives you options of how you manage the field,” she said.
It will take a little extra time writing a nutrient management plan the first time but will only require small annual checkups after that. Nutrient management plans will be more in depth, thorough and defensible, she said.
Indexing is used in eight of the top 10 dairy-producing states, and the Idaho standard was developed specifically for Idaho conditions. IDA, ARS and nutrient management planners were able to field test the indexing while it was being developed, she said.
The new standard is expected to pass the Legislature and go into effect July 1 with a five-year phase-in period.