4Rs Right for Nutrient Management
by Jason Johnson, February 2011
USDA's Natural Resources Conservation Service (NRCS) is encouraging Iowa agricultural producers to adopt the 4R nutrient stewardship concept to help define the right source, rate, time, and place for plant nutrient application.
John Myers, state resource conservationist with NRCS in Iowa, says the 4R concept considers productivity, profitability, cropping system durability, and a healthy environment. "The approach is simple and universally applicable," says Myers. "Apply the correct nutrient in the amount needed, time and place to meet crop demand."
The 4Rs will change and improve with new gains in knowledge and technology development, says Iowa NRCS Nutrient Management Specialist Eric Hurley. "The 4Rs provide flexibility to nutrient management," he says, "depending on soils, climate, crops, cropping history, management style, and farm size."
Breaking Down the 4Rs
The right source means matching the right fertilizer product with soil properties and crop needs. Hurley says it's important to balance applications of nitrogen, phosphorus, potassium, and other nutrients according to crop needs and available soil nutrients. "Take care to address all nutrient needs in your fertilizer plan," he says. "Nitrogen is wasted if inadequate P or K is stunting your crop."
Hurley also recommends taking time to review the forms and formulations that best fit your management and the needs of your crops.
The right rate means matching application rates with crop requirements. Hurley says soil testing, crop history, in-season testing, and crop nutrient budgets will impact application rates. "Time and money can be saved by applying only the nutrients needed to optimize your production," he says.
Iowa NRCS State Agronomist Barb Stewart says to test soil for P, K and micronutrient availability. "Use the Iowa State University N-Rate Calculator's MRTN (Maximum Return to N) rate to determine your nitrogen needs," she says.
The right time means synchronizing nutrient availability with crop demand. Hurley recommends applying N fertilizer in the spring, and encourages producers to look at split applications of nitrogen.
Controlled release fertilizers and urease and nitrification inhibitors are designed to manipulate the timing of nutrient availability. "As research demonstrates the effectiveness of these products, they may become important tools in improving fertilizer efficiency," says Hurley.
The right place means placing and keeping nutrients where the crop can get to them and where nutrient use efficiency will be maximized. Crops, cropping systems, and soil properties will dictate the most appropriate method of placement. "Injection or incorporation is usually preferred to keep nutrients in place and to increase their use efficiency," says Hurley, "though this soil disturbance needs to be balanced with your soil erosion control goals."
Stewart says cropping systems such as strip-till place the nutrients close to the developing plant to insure its availability. "Less fertilizer is lost to the environment this way compared to broadcasting fertilizer across the field," she says.
According to Myers, deciding the best application, method of placement or best nutrient source must be site-specific. "Research supports the 4Rs, but stakeholders such as farmers, fertilizer companies, natural resource specialists, and crop advisers must help decide what is the right or best nutrient management practice," he says.
The 4R system will be officially endorsed by USDA-NRCS in the new 590 Nutrient Management Standard. "The 4R concept is gaining acceptance, but continued education and dialog between all stakeholders is needed to keep it moving forward," says Myers.
To formulate a nutrient management plan for your farm, visit your local NRCS field office. More information about nutrient management is available on the Iowa NRCS website at www.ia.nrcs.usda.gov.
Eric Hurley, Nutrient Management Specialist