IPNI's Expert Advice on the 4Rs of Crop Nutrition

When it comes to the 4Rs of crop nutrition (right source, right rate, right time, right place), many farmers focus most of their attention on right rate. The 4Rs should be thought of as a system that intertwines and works together to create a well-managed crop nutrition program. Four International Plant Nutrition Institute (IPNI) experts offer helpful insights to better achieve each R.

  1. Right Source

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    According to Dr. Cliff Snyder, there are several important implications to consider when attempting to select the right nutrient source for both profitability and environmental responsibility. Also important is looking beyond your own historic practices, asking the right questions of the right people, and gathering knowledge from various sources to make informed decisions when selecting the right nutrient source.

    "Increasingly, I encourage growers to be sure to not just be stuck where they are, but try to explore something new each year," Snyder says. "But to do it in a replicated manner and work with their crop advisor and ag retailer to evaluate what works best in their own farming systems with their management skills. That's where the advice of the local ag retailer and the local certified crop advisor are, in my opinion, irreplaceable for growers. Growers have just got to work with those professional advisors. And also work with their neighbors. We need to continue to learn from one another."

  2. Right Rate

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    Profitability significantly drives application rate decisions. If the rate is too high, growers could lose on the cost side. If the rate is too low, growers could lose on the yield side. Growers can significantly miss profit goals if the rate is off. However, Dr. Paul E. Fixen states that when it comes to meeting multiple goals, not just financial goals, but in making nutrient management and fertilizer decisions, thinking needs to go beyond these basic short-term numbers and even beyond the immediate economic impact.

    "What we see out of research that focuses on reaching multiple goals while following the 4Rs is that if we control the balance between what is applied and what is needed by a specific crop, we can get a long way toward minimizing nutrient losses and optimizing efficiency of water use, as well as other nutrients, and really make the whole system more efficient," Fixen says. "We aim to have just enough nutrients in the system. That's how you accomplish multiple objectives, is to get it just right. This means there is little room for error in the other R's."

    Fixen also suggests, all four Rs need to be factors in planning, or the whole process falls apart. If one R is wrong, it is likely they are all wrong.

  3. Right Time

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    According to Dr. T. Scott Murrell, the R that coordinates them all is right time, because the right time is the best way to synchronize the application of nutrients for the time that the crop needs them.

    Decisions about nutrient timing are dependent on nutrient availability in the soil and many other management factors, according to Murrell, farmers have a greater opportunity than ever before to understand the optimum fertilizer timing for their crops. One way this can be done is by participating in on-farm research.

    "It's easier than ever before to participate in on-farm research, thanks to farmer networks that provide support and precision agriculture tools, which have reduced the time and labor required to put out trials and collect data," Murrell says. "If farmers want to know if nutrient timing can be improved under their specific set of conditions, I highly recommend they put out a trial and find out for themselves."

  4. Right Place

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    When trying to achieve the right nutrient placement, Dr. Tom Bruulsema has five key considersations for better placement on your operation. 

    “Even though you may not expect that much of an agronomic benefit from better phosphorus placement, for instance, paying attention to it and ensuring you have the right equipment to get the job done at the right time – there's a lot of ROI in that,” Bruulsema says. “A sound strategy starts with paying close attention to your soil tests and the variability within your field; and there's opportunity to make money by saving on inputs where the input is less needed and by gaining yield where the nutrient is needed more.”

    One of the key principles of the 4Rs approach to nutrient stewardship is that they each have to be integrated. Placement can't be considered in isolation from right time, right rate and right source. And not one of the four can even can be considered without looking at the entire cropping system.

    “The fact that our goal is not only economic, but environmental and social as well, requires addressing all those systems comprehensively,” says Bruulsema. “I think there's huge opportunity for progress and, in turn, communicating that progress to the public when this approach is applied.”

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