AgronomyBest Practices: Irrigation and Fertility Management

Best Practices: Irrigation and Fertility Management


[deck]Four growers from four potato-growing regions of Canada discuss their irrigation and fertility management practices.[/deck]


Homer VanderZaag grows about 900 acres of potatoes, primarily chipstock for Frito-Lay, near Alliston, Ont.
Rob Van Roessel, chairman of the Potato Growers of Alberta, farms 390 acres of Russett Burbanks in Bow Island, Alta.
Jason Kehler grows Russett Burbanks and Innovators on 450 acres at his farm near Carman, Man.
Gary Linkletter is chairman of the Prince Edward Island Potato Board and farms 1500 acres of potatoes near Summerside, P.E.I.

Spud Smart: What methods do you use to determine how much soil water is available to your plants? Do you rely mostly on feel and appearance, or instruments?

JK: Generally we just use the feel and appearance method. We haven’t used instruments too much. I have used water marks in the past. If it’s dry, usually we just dig down about four or five inches in the hill, and if you can make a ball with your hand and bounce it five times, you’re at about 65 per cent water content; if you can’t bounce the ball five times before it falls apart, it’s too dry.

RVR: We’ve tried instruments but haven’t had great luck with them—we were having reading problems. Right now I work with an agronomist who comes out every week to do a soil moisture reading on the potato fields, and we measure in the 0-24 inch range, and what’s gone below that root zone. That information gets put on a graph. Each field has a gauge under the pivot, so you see how much the pivot supplied. And I balance that with what I see, grab a handful of dirt from each part of the field and see if it backs up what the consultant says.

HV: I never have used instruments. I primarily use physical hand testing as well as kind of a loose evapo-transpiration concept. I keep in mind just how much photosynthesis and weather we’ve been having and how hard the plants are pulling, so I’m factoring that into my decision, along with the soil holding capacity of a particular field, the forecast, and the disease risk for potato blights.

GL: Mostly we use feel and appearance, based on knowing when the last rain came and the time of year and so on.

Spud Smart: What type of irrigation system do you currently use on your farm?

RVR: Centre pivot irrigation.

JK: [We use] centre pivots, and then we have duns (reels), but those have gone by the wayside. They’re basically for if we need to grow potatoes on a smaller field with trees or something where we don’t have access to the pivot.

GL: Reels—we have two reels and so basically every eight to 12 hours you go out and pull out the spigot. It tends to be a strain on people to operate it, and it’s very expensive, so we don’t use it any more than we should. The other thing that can happen is that you put a lot of water down and have the fields in a really good condition, then you get a rainfall event and the field gets flooded out. It makes it difficult to engineer solutions.

HV: We use a centre pivot and irrigate all of our acreage, so we can change our application rate by segments of the field. About 50 percent of my fields are tile drained, which has been absolutely worth the cost.

Spud Smart: What do you base your decisions on with respect to irrigation scheduling?

HV: Forecast, disease pressure, water holding capacity, crop stage, irrigation capacity. If it takes four days to put water on a farm you have to know that the last acre won’t get watered until four days from the decision.

GL: We are very unscientific. We just watch the fields and the forecast—if it starts to get dry, with no rain in sight, especially early in the season we will make the decision to irrigate. It takes a couple of days to get the pipe laid and everything set up, so before it makes a complete circuit it’s 11 or 12 days altogether.

RVR: Readings, temperature and humidity and the forecast, the whole series of variables. We have a pretty good idea of what the plant will use; we balance that with what the soil is like, what the weather is like.

JK: It was pretty simple this summer—it didn’t rain and didn’t forecast rain! Normally we pay attention to the forecast pretty closely and adjust our irrigation accordingly. If it’s looking like soil moisture is down but there might be rain in the forecast, we give [the plants] four tenths of an inch instead of eight tenths, or something like that. Last fall we put in some drain tile. If we are irrigating but have a freak storm, the drain tiles take some of the risk factor out of it. It’s pretty expensive, but it’s worth it! This year we had a terribly wet spring—we wouldn’t have been able to get our potatoes in the ground had we not had [the tile].

Spud Smart: Do you focus on micronutrients in your fertility regime?

RVR: No, we do a test for that but we don’t have a chronic shortage of any micronutrients. The biggest variables for yield are nitrogen and moisture.

HV: We do use a micronutrient package, and it’s based on a combination of lab work and historical soil tests as well as advice from agronomists. You’re always in limbo because you know there’s something to it and there are crop responses, but trying to quantify the crop responses is the challenge.

JK: We use a small regime of it. We don’t focus on it but we have a blend that we put on [the crop] in spring.

GL: We try to soil test every field every year, and we’ve got a good lab here on the Island. I have a book with every soil sample we’ve done for 20 years, and we always see we’re low on zinc and boron, so we put zinc in the fertilizer and boron in the foliar. We engineer a lot of stuff around micronutrients. Sometimes you see yield results, and sometimes you don’t.

Spud Smart: What about fertigation?

RVR: Yes, that’s a standard practice. It’s been effective. It’s not as good as physically putting down some dry nitrogen fertilizer exactly where you want it, but when the crop is filled in that’s your only option to get fertilizer to the plant.

GL: If you have a centre pivot system, which is a lower pressure system which makes more even passes, that’s more conducive to fertigation. We’re using reels, so we haven’t gotten into it too much yet. As well, unpredictable rains make it difficult to know if you will be using the reels, and you can’t risk being unable to apply fertigation, so we put all the fertilizer on at planting.

JK: I wanted to get into this year, but with inclement weather I didn’t feel it was justified. But we’re going to go into that this coming year.

HV: We do fertigate, almost all of our acres. It’s been successful—we feel we’re getting higher efficiencies per unit of fertilizer, better yields and better quality. It’s worth the investment.

Spud Smart: Do you use precision agriculture, GPS or GIS technology to help determine your irrigation and fertility needs?

GL: We’ve gone all to GPS planting. It facilitates a lot of other technologies. An example is when we subsoil a field, we can place the tooth right on the centre of the future drill—so rather than breaking up the hard pan randomly we do it right under where the potato plants will be, which will hopefully help water movement to and from the plant. On GIS, we haven’t been convinced of the payback of the technology at this point. Here in Summerside it tends to be flat, so we don’t have to plan around our hillsides, which reduces the GIS benefits for us.

RVR: We’ve done a little bit. The rows are made with GIS technology. This fall we just started variable rate irrigation. There’s a program where we can break the circle into 180 two-degree wedges. Over the winter we’ll figure out how to fit the info we have into these wedges to see what will and won’t work. During the next growing season we’ll be trying to implement it. A year from now I’ll have a lot more to say on this subject!

JK: We’re using variable rate fertilizer application technology. I’d have to say the results are quite positive. We grow processing potatoes and were tending to have issues with quality, in terms of colour and gravity. We were blanketing with fertilizer, and in some areas it would be not enough, and some it would be too much. This has given us a more even product to work with. We’ve also done a Veris map on one of our pivots—it makes an infrared map of your field, and you base your fertility program on that.

HV: We use GPS only a limited fashion. All of our farms are GPS grid soil tested, and we use variable rate technology for PH adjustments and for potash applications, but that’s the extent of it. We’ve had good success with what we’ve done, but the first benefit has been the largest, so now our return on investment is actually diminishing somewhat. I’m looking into variable rate irrigation technology on a per-acre basis, so there’s an opportunity there I want to explore.

Spud Smart: What advice would you offer other growers on successful irrigation and fertility management?

HV: In a nutshell, you have to do your homework. [Conditions change] daily, not weekly. Crop monitoring needs to be intensive. There’s a host of different possibilities in terms of fertigation, so it’s both art and science to find the right program that’s cost-effective, fits the end goal of improving the customers’ product and adds return to your bottom line.

RVR: Know your fields as well as possible, and monitor them. Every field is different.

JK: Watch the weather. Obviously every farm is different—but where we farm we have mostly enough natural precipitation that we have to be careful with irrigation. Don’t get carried away with irrigation.

GL: Different areas have different rainfalls, so really you have to see what’s paying for you.

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