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What Fertilizer Form Is Best?

In his Editor’s Blog of January 6, 2010, Jay Whetter posted the following few excerpts from a workshop on liquid fertilizer held in Westlock, Alta., on November 24, 2009. These points came from a first draft of my article “A pitch for liquid fertilizer” in this issue:

With dry fertilizer it is difficult to get all the nutrients to every seed. Prills of phosphorus in particular are spaced fairly far apart, simply because there isn’t as much P in a blend. You just won’t get P prills to every seed. With liquid fertilizer you get every nutrient to every seed all the time because every drop of the blend has every nutrient in the same strength.

Only in liquid fertilizer can you get all three forms of nitrogen: nitrate nitrogen, ammonium nitrogen and urea. The three different forms release their nutrients at different times, so that the plant has some N available from the first moment on until maturity.

With liquid fertilizer it is possible to put more nutrition closer to the seed than with dry.

With liquid, one-pass farmers can seed far more acres at a time before having to fill again.

Liquid fertilizer is easy to store and handle. There aren’t any safety concerns as with anhydrous ammonia. You just need to have a few tanks to keep a supply handy in spring.

WHAT DO THE EXPERTS SAY?

I passed those thoughts on to Jeff Schoenau, senior research scientist in the Department of Soil Science at the University of Saskatchewan, and Rigas Karamanos, agronomy manager with Viterra, who in turn discussed it with other colleagues. Here are some of their thoughts:

“I would not expect miracles from liquid fertilizer formulations,” says Schoenau. “In fact, I would expect little difference in performance of the same fertilizer compound like urea, whether it is dissolved in water or in granular form if it is placed in the soil at the same time and same place.”

“In my opinion the greatest advantage of liquid over dry fertilizer comes in its convenience and versatility of use. You can dribble band UAN (28-0-0) on the surface, squirt 28-0-0 fertilizer away from the seed row and achieve separation in a relatively simple fashion,” Schoenau says.

Karamanos says, “Yes liquid fertilizer is more expensive and yes it is more convenient to use, but it is not more efficient than dry fertilizer.”

Liquid fertilizer can deliver phosphate to every seed if used in large amounts. A full rate liquid fertilizer blend of 90-25-0-25 (potash is usually best placed dry) would normally be applied at a rate of 28-32 imperial gallons per acre. At this rate, there would be a continuous dribble of liquid. As each drop of the liquid blend contains all the nutrients, there would be P to most every seed.

Schoenau says, “The plant needs P early on in the growth cycle, especially when soils are cold and root growth is restricted. Therefore early access by roots is important. At low rates of P, there may be an advantage of having a ribbon of liquid versus widely spaced granules in ensuring that all plants in the seed-row have some early access.” He adds, “The extent to which this would translate into consistent yield responses is difficult to predict.”

Karamanos has some reservations. “If we were to accept that liquid provides a continuous stream, then I am not convinced this is a good thing as P moves by diffusion, so a very high concentration in a prill may be better, plus it may reduce the potential for rapid precipitation by soil minerals. In the end, a doubtful advantage either way,” he says.

In fact, if liquid P is applied on its own, the drops are farther apart than P granules would be. This principle was illustrated by demonstrations set up last summer by Manitoba Agriculture at their Crop Diagnostic School in Carman, Man. For a presentation on this topic, go to www.umanitoba.ca/afs/agronomists_conf/2008/,click on Proceedings Current at the left, then look for John Lee’s name under the heading, “P fertilizer management panel.” Click on his name to get his short presentation, which shows that on canola, with seven inch spacing, applying 20 pounds of actual P in liquid form (5 gal/ acre of 10-34-0) places droplets 2.8 inches apart. Dry fertilizer prills (38 lbs of MAP fertilizer) at the same actual rate were 1.9 inches apart.

Some farmers wanting to use a one-pass system (all the fertilizer with the seed) might benefit from using liquid fertilizer, Schoenau says. “If you have single shoot (seed-row fertilizer placement capability only) as on many older seeders, one can set up a liquid system and use the squirt concept to squirt the fertilizer N away from the seed row and achieve separation of N fertilizer from seed-row and go to higher rates of N without worry of crop injury.

“If you have lots of acres to cover in a hurry, dribble banding of liquid pre-plant or post emergent can also be effective especially in moist region where rainfall will move the fertilizer from the surface into the root zone.”

While he agrees that the nutrient distribution with liquid is better and nutrients are more available, Christian Doelger, assistant manager of Viterra at Dencross, Man., asks, “How can you cover more acres with liquid 28-0-0 if granulate is 46-0-0 and NH3 is 82-0-0?”

“In general, the liquid tanks tend to be 1,200 to 1,500 gallons, so filling is every 30 to 50 acres,” says Lyle Cowell, manager of agronomic services with Viterra in Tisdale, Sask. “Overall, the bulk of liquid requires more handling….simple math.”

There are also some safety concerns with liquid fertilizer. “Storing liquid fertilizer has to adhere to regulatory requirements to avoid contaminating the environment. If there is an ammonia spill, it can be cleaned and off we go. If there is a liquid N spill, then things are not as simple,” says Karamanos.

He also raises the touchy question of carbon footprint: “I agree that 28 gallons would provide an almost continuous flow, but I am wondering of the carbon footprint this farmer leaves behind by hauling all this water.”

For most farmers it comes down to one thing: cost per bushel. “Economics will depend on the differences in cost per pound of actual N contained in the different N fertilizer products and forumulations as well as differences in product performance under field conditions (N use efficiency), and application/ equipment/time availability considerations,” Schoenau says.

“Farmers who choose to use liquid or dry or NH3 fertilizer are never wrong on their choice,” Cowell says. “It is just a personal choice based on their farm location, fertilizer price and equipment on their farm.

“Once the fertilizer is in the ground, it is essentially equally used by the crop, and no one should suggest that one form of fertilizer is better. This could lead to farmers assuming they can reduce rates, and then compromise potential yields.”

Marianne Stamm is a freelance farm writer from Jarvie, Alta. Email her at [email protected]

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