Fertigation Facts for your Potato Farm Spud Smart Winter 2011

Fertigation: Facts for Your Farm


Mike Wind seeds 800 acres of potatoes on his 35-year-old farm located 10 miles east of Taber, Alta. Wind began using fertigation technology in his operation in 1997. “I did it because I was finding it difficult to determine how much fertilizer to apply each day,” Wind says. “With fertigation, I have a much better chance of getting it right.”

Susan Ainsworth, farm production advisor with Manitoba Agriculture, Food and Rural Initiatives, says more potato growers in the area of Carberry, Man., are turning to fertigation. “The benefits show up in both quality and yield,” she says. “Fertigation gives growers the ability to better utilize their nitrogen fertilizer by spoon-feeding the plants at the appropriate growth stage. It also allows growers the flexibility to adjust rates within the season to better adapt to growing conditions and plant requirements,” says Ainsworth.

Fertigation is the use of irrigation systems for the fertilization as well as watering of crops, thus ensuring a steady supply of nutrients for the plants as they grow. While the process can be used to feed potassium, sulphur and other nutrients to the plants, nitrogen is the primary nutrient fertigation is intended to supply plants because nitrogen is most susceptible to leaching down in the soil profile.

Fertigation Challenges

Ross McKenzie, agronomy research scientist for Alberta Agriculture and Rural Development, says that a growing number of Alberta producers are using the practice, and most potato growers in southern Alberta are set up for using fertigation. The standard practice for most growers, he notes, is to apply a portion of their nitrogen fertilizer prior to and/or during planting, with additional nitrogen applied by fertigation as required during the growing season.

McKenzie and his colleagues have reviewed a small number of case studies involving the use of fertigation. He says the results have been mixed, depending on farm management.

“There is not a benefit every year,” says McKenzie. “It depends on rainfall patterns. This past year, there was a lot of rain. Most potato producers grow their potatoes on sandier soil concomitant with a greater potential for leaching nitrogen when conditions are wetter. The challenge with fertigation in a wet year is you may need to apply nitrogen through the irrigation system to meet crop nitrogen needs but the soils are at their capacity to hold water and may not need to be irrigated.”

Another challenge is on very hot days producers can lose 20–30 per cent of their nitrogen by volatilization to the air because urea accounts for about 50 per cent of the nitrogen in liquid fertilizer, and urea is highly susceptible to gaseous loss when applied in hot or windy conditions, thus reducing the potential benefits derived from using fertigation, McKenzie adds.

Environmental Benefits

But growers may experience environmental benefits when using fertigation, says Ainsworth. “In coarser- or sandier-textured soils,” she says, “you can avoid the potential of groundwater contamination through leaching by reducing the amount of nitrogen applied in a single application.”

“Fertigation has a real environmental benefit on coarse-textured soils,” she says. “Those soils have lower nutrient-holding capacity and higher potential for leaching.” According to Ainsworth, one drawback to fertigation is farmers can negatively impact yield and quality if they apply the wrong rate at the wrong time. “If you give your plants too much nitrogen late in the season, for example, it can lower specific gravity,” she says.

Monitoring is Essential

Farmers must keep an eye on their plants above and below the ground, and use all of the tools available to them: petiole sampling, periodic in-season soil sampling, and consideration of growth stage and weather conditions to help determine when, and if, they should apply additional nitrogen, says Ainsworth.

McKenzie notes that many Alberta potato producers conduct weekly petiole tests to measure nitrate levels in their fields. If the nitrate level is marginal or in the lower range of adequate, producers need to add more nitrogen through fertigation, he says, but it takes about two weeks for three-quarters of the nitrogen in the liquid fertilizer to be transformed by microorganisms in the soil into the nitrate-nitrogen form for plant uptake. Growers using fertigation need to understand and account for this time lag for nitrogen fertilizer to convert to a plant-available form when using fertigation.

“It’s better to stay ahead of the game and apply fertilizer before the potato nitrate levels drop below the adequate petiole level,” McKenzie says. “You should be testing for nitrates weekly so that there will be no time lag.”

Wind says he takes weekly petiole samples of his plants to help determine how much more fertilizer he has to apply. Petiole testing should begin 40–45 days after planting, continuing until 90 days after planting to monitor crop nitrogen status. Wind notes it is not wise to be completely dependent upon fertigation. For example, if there is a lot of rain, growers can’t fertigate and the potatoes may be short of nitrogen. Also, if you aren’t set up for irrigation—or can’t irrigate for some reason—then you lose the ability to apply fertilizer.

In rolling landscapes, McKenzie also points out growers must be careful that surface run-off of irrigation water into low spots does not occur during fertigation or the growers will not achieve uniform application of fertilizer. One of the downsides of using liquid nitrogen fertilizer, McKenzie notes, is the cost is higher than other nitrogen sources—but it is the only nitrogen form that can be used for fertigation.

Further studies on the benefits and use of fertigation are in the works. Agriculture and Agri-Food Canada is presently conducting research on the efficacy of fertigation. In Manitoba, those studies have just begun says Ramona Mohr, a researcher with AAFC. “We are comparing fertigation with other practices to see how efficient these practices are in applying nitrogen, and how much nitrogen is taken up.” No data is available from these studies yet, she says.

In order to be effective, proper testing, careful monitoring and an understanding of exactly what fertigation can do, and when, is essential for growers employing the practice to reap its benefits. “Fertigation can be a useful practice as long as you are aware of, and manage for, its limitations,” McKenzie says. “You have to use excellent management to do it right.”

Myron Love