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Windrower at work in a 4R nutrient stewardship trial field in P.E.I. during the 2014 harvest season. all Photos: Steve Watts, Genesis Crop Systems.

4R Nutrient Stewardship

Making potato production more sustainable.

4R nutrient stewardship represents an innovative approach to nutrient best management practices. Proponents of applying this concept to potato production believe that the principles of this approach provide a sound framework for growers to achieve cropping system goals, such as increased production, increased farmer profitability, enhanced environmental protection and improved sustainability.

In essence, 4R nutrient stewardship implies that growers put the following best management practices in place in terms of the nutrient management of their potato crops:

  • Apply the right source of fertilizers best used by the crop and its soil
  • Apply the right rate of fertilizer to match nutrient supply with crop requirements
  • Apply fertilizer at the right rime so nutrients will be available when crop demand is high
  • Apply or maintain fertilizer in the right place where the crop can access the nutrients most effectively

4R nutrient stewardship in Canada is being spearheaded by the Canadian Fertilizer Institute. According to, the CFI’s website dedicated to the 4R nutrient management method, following this approach optimizes the efficiency of fertilizer use by matching nutrient supply with crop requirements and minimizing nutrient losses from fields.

Prince Edward Island was the first province to sign on to the 4R nutrient stewardship program. Fertilizing potato crops under 4R nutrient stewardship principals was introduced to Island growers in 2013 through a series of field-scale demonstration trials conducted by agronomist Steve Watts of Genesis Crop Systems under contract to CFI.

The three-year contract was to last until the end of the 2015 cropping season, but at a press conference in early April, CFI Acting President Clyde Graham announced that funding for the program was being extended for another three years.

“The initial funding was for $150,000 over the three years until 2015, and we are committed to renew the project and provide another $150,000 worth of funding over the coming three years,” Graham said. “We are very much encouraged by the results of the trial program thus far, and we are excited about its continuation.”

Watts conducted several demonstration trials on potato farms for the program in 2013 and 2014. The purpose of the demonstration trials was to compare various 4R best management practices with fertilization practices currently popular among P.E.I. potato growers. A total of 13 farms were involved in the trial last year.

“Introducing subtle changes to the way a crop is fertilized can produce crops with at least as much economic value as the current level of management while lessening the potential environmental impact,” says Watts.

In his view, the best result of the work so far is that all participating growers have faith in a positive outcome and truly believe there are better ways to feed their crops. “Island growers are not hesitant to continue to try to identify and evaluate ways to adopt and practice new cropping methods that deliver beneficial results,” Watts says.

Different Strategies

Watts implemented a number of different strategies at the 4R nutrient stewardship demonstration sites, including the following:

  • Splitting nitrogen (N) applications into two or three separate applications, including a reduced level of N in the planter mix as compared to areas treated with GSP fertilizer. A number of sites also featured reductions in total N application by 10 to 20 per cent under the grower standard practice (GSP).
  • Reducing application of phosphorus pentoxide (P205). The reason for this was that most soils in the potato growing areas of P.E.I. already have high levels of P205 and likely do not need as much phosphorus applied as the amounts currently favoured by many Island growers.
  • Split applying potash (K2O) with a pre-plant broadcast/incorporated application of muriate of potash (MOP) and a banded application at planting with a combination of KMag fertilizer and sulfate of potash. The GSP K2O program traditionally used by Island growers involves almost exclusive use of MOP, which increases the salt concentration around the tuber zone and may reduce tuber specific gravity when banded at planting.
  • Because magnesium, boron and zinc can be quite low in many Island fields, these micronutrients were added to fertilization programs where soil tests indicated potential benefits to crops.
  • All growers were asked to avoid application of any foliar fertilizer products on the 4R sections of the field unless advised to do otherwise by Genesis Crop Systems.

The official report on the 2014 trial results concludes that 4R nutrient stewardship practices trended towards equal or better performance than conventional crop fertility practices. The report further states that 4R nutrient stewardship management on the participating potato farms resulted in lower soil nitrate levels (which reduces the potential for nitrate movement to the environment) at eight out of 10 locations.

The field trials that Watts has evaluated to date have also helped increase grower awareness of the 4R approach. Island potato grower and P.E.I. Potato Board Chairman Alex Docherty says the board is a strong supporter of the 4R program.

“The board views the 4R program as a perfect fit for P.E.I. potato farmers who are committed to economic and environmental sustainability. There is no doubt that an improved marketable yield with less impact on the environment is a win-win situation for everyone, farmers and the public alike,” he says.

Reflecting on the trial results during the past two seasons, Docherty says it’s clear the 4R approach can have a big impact on marketable yield, while at the same time reducing the level of nutrients that could be lost to ground and surface water.

“Minimizing the impact of farming on the environment is a priority in Prince Edward Island as concerns remain about nutrient losses to ground and surface water. We are indeed very encouraged by the results of the 4R program that have been shared so far,” he says.

“We are also very happy that CFI has extended the trial program for an additional three years here on the Island. We believe that the benefits for Island growers will be huge.”

Potatoes being planted under the 4R nutrient stewardship model at Birch Farms Ltd., one of the P.E.I. producers involved in demonstration trials of the 4R method.

Good Fit with Precision Ag

One of the trials with the 4R nutrient stewardship program was conducted on a field belonging to Island Holdings. Farm manager Jared Wright says that the 4R principles and its practice are a perfect fit for modern technologies that enable growers to move successfully towards the application of precision farming techniques.

“We can definitely see the benefits of the 4R approach in terms of nutrient application in our operation,” he says. “For example, we might have a field where in the past nutrients were ‘blanket-applied’. When we follow the 4R approach we may ultimately use the exact same amount of fertilizer as in the past, but apply it in a more targeted way, where some areas of the field receive less, some more, and some none.

“This ensures that we treat the field and consequently the crop in a much more site-specific and precise manner. We can see the positive results of this approach when harvest time rolls around, no question about that,” he says.

According to Watts, the 4R nutrient stewardship programs evaluated to date should be considered as “works in progress.” The main objective, he says, is to “continue to identify and demonstrate new and modern methods of fertilizing the potato crop that will meet the goals of the producer, but also the environment, and society in general.”

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