Potatoes in Canada

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Tweaking fertility

Adjusting fertility programs by the tiniest increment could net a yield increase. All that might be required is better understanding the soil’s needs or choosing nutrient materials that will work more effectively in particular soil profiles. Three top potato experts share their tips for tweaking fertility that are valid for any potato operation. While most of the recommendations are not new, they may be getting overlooked or they may need to be combined with others in order to get better results.

June 10, 2013
By Rosalie Tennison


Dr. Bernie Zebarth, a research scientist with Agriculture and Agri-Food Canada (AAFC), is an advocate of the 4R approach to fertility. “You need to use the right source, the right rate, apply at the right time and in the right place,” he explains. “Growers generally use the right source, but in areas where there is a problem with leaching, those growers may want to consider switching to a controlled release fertilizer, like ESN, for their nitrogen source. Using the right rate is the most critical, but also the toughest. In Western Canada, nitrate remains in the soil, so a residual soil nitrogen test can be used. But, in Eastern Canada, rainfall washes the residual nitrogen away and there isn’t a nitrogen test yet.” He says a new nitrogen test for this circumstance is being developed to measure how much nitrogen is released from the soil organic matter but, until it is available, growers have to rely on petiole nitrate testing to manage their crop. He adds that potato growers tend to put on the rate that will be good in any year, but, he hopes, the new nitrogen test can identify when growers can cut back without hurting the crop.

As for putting fertilizer on at the right time, Zebarth says split applications are only useful if there is a problem with leaching, so timing application correctly will depend on weather and planting. For placement, when the choice is between broadcasting or banding, he believes banding is more efficient because the nutrients are placed at the roots. However, in Western Canada, where nutrients do not move as much in the soil, both methods are acceptable.

“I think there should be a fifth ‘R’,” he adds, “and that is the ‘right cropping system.’ The four Rs are about fertility, but growers also need to maintain soil, rotate crops to minimize disease and insect pressure, and maintain soil organic matter.”

Ontario potato specialist Dr. Eugenia Banks agrees with Zebarth’s idea about adding another R to the list, but she sees that fifth R as part of maintaining good fertility in a well-rounded production plan. “In order to ensure any fertility program is successful there are nine areas that are important,” she says. Her list includes crop rotation and cover crops, soil tests, petiole analysis, adequate irrigation, drainage improvement, organic matter level above three per cent, reduced compaction, keeping pH within the 6 to 7.5 range, and doing soil preparation for tillage operations when the soil is not wet.

“Crop rotation maintains soil fertility,” Banks explains. “It will also reduce soil erosion, insect pressure, and soil-borne diseases.” She recommends including rye in a rotation with potatoes because it does not need high pH and is competitive with weeds, which, in turn, compete for nutrition. She adds that rye is one of the best crops to prevent nitrate leaching in the fall and it will withstand low winter temperatures.

For any crop in any region, soil tests are always recommended. Banks says soil tests provide the best information for predicting how the crop will respond to applied fertilizer. The tests will indicate if minor nutrients are needed and the recommendations could be different for each one depending on whether soils are sandy or heavier. More than any other tip, Banks believes growers should always start with a soil test and then tweak the fertility program to the desired results in combination with all the other requirements for successful crop production.

“Nitrogen is usually the nutrient that is most limiting in potato production systems,” comments Dr. Carl Rosen, a nutrient management specialist for horticultural crops at the University of Minnesota in St. Paul. “Potash and potassium can be accurately identified with a soil test and they don’t move in the soil like nitrogen. The mobility of nitrogen in soil and the lack of a reliable nitrogen soil test make managing this nutrient more of a challenge, especially in regions with high rainfall. As noted above, soil nitrogen tests can be useful in dry climates to help adjust nitrogen fertilizer recommendations. Make sure you have a soil test calibrated to local conditions and keep an eye on pH levels.” He suggests putting lime on in a rotation year, if scab is a problem.

Rosen is an advocate of a petiole analysis as well because it is a good guide for nutrition within the plant. “Petiole analysis is just another tool to help guide in-season nitrogen applications and assess the nutritional status of the crop. It is important to interpret the results carefully along with other indicators, such as plant vigour, tuber bulking conditions and canopy colour,” he cautions. “We are currently looking at chlorophyll meters as well as other reflectance measurements to assist with identifying stress and determining the need for supplemental nitrogen applications.”

Getting nutrition right isn’t just about the amount of each product applied, according to Zebarth. “Good agronomy, such as planting at the right time, planting into good soil, and using good seed, can have an effect on the success of a fertility program. You could have two fields side by side and one has not been managed well and the other has been well maintained and they both have the same nitrogen program and the result will be like night and day!”

Whether the approach is the four – or five – Rs or Banks’ top nine tips for ensuring success with a fertility program, there is more to getting success from a program than just applying according to the soil test. In order to get the best result, extra steps may need to be taken in the management of the crop to ensure the fertility program has the opportunity to be effective. Until researchers perfect tests that can provide more definitive recommendations regarding nitrogen, in particular, managing all aspects of crop production is the number one tip for getting top results from a fertility program. The rest is up to the weather.

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