Research Reviews Yield Goal and MRTN Nitrogen Methods
Research recently conducted by the South Dakota State University Extension, underscores what every farmer knows, selecting the correct nitrogen fertilizer rate is an important step for successful oat production.
Nitrogen supports strong crop growth, but applying too little can lower yields, while applying too much can reduce profits and harm soil and water quality.
The study compared two common nitrogen recommendation systems used in crop production. These include the yield goal method and the maximum return to nitrogen, also called the MRTN method.
The yield goal method estimates nitrogen needs based on expected yield, soil test nitrogen levels, and legume credits. This approach is easy to use but depends heavily on accurate yield estimates made early in the season.
The MRTN method uses data from many nitrogen rate trials to calculate the fertilizer rate that provides the best economic return. It considers both fertilizer cost and grain prices. However, this method does not automatically adjust for nitrogen already present in the soil unless soil test values are included.
Researchers conducted 28 nitrogen rate trials on oat fields across central and eastern South Dakota between 2017 and 2022. These locations included different soil types, tillage systems, and crop rotations. Nitrogen fertilizer rates ranged from 0 to 150 pounds per acre. Soil samples were collected before planting, and grain yields were measured at harvest.
The results showed that oat yields ranged from 65 to 162 bushels per acre. The average economically optimal nitrogen rate was 27 pounds per acre. When using the yield goal approach, nitrogen recommendations were generally close to the true optimal rate, with only a small average underapplication.
The MRTN method, when used alone, often suggested higher nitrogen rates than needed. However, accuracy improved when soil tested nitrogen from the top 2 feet of soil was subtracted. When full soil nitrogen was included, the MRTN method closely matched the optimal fertilizer rate.
“We think it’s some pretty significant news, and we’re excited about getting it in front of our Cattlemen’s Education Day audience,” the research team noted. “What we’re always working toward is trying to find solutions for the citizens of South Dakota, things that solve real problems and help cattle producers.”
Overall, the study showed that both nitrogen recommendation methods can be reliable when soil test nitrogen is included. This helps oat producers make better fertilizer decisions, improve economic returns, and protect natural resources.
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