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What mixture goes where? Starter fertilizer

While no-tillers are trumpeting starter fertilizer to enhance early plant growth in cool, wet conditions, with the potential for added yield later, Steve Curley of The Consulting Company warns that starter is no panacea. Improper placement, timing and formulation can ruin starter potential for many users, says the Apple Valley, MN, consultant.

He points out that one reason no-tillers seem to benefit more from starter is because a no-till corn root establishes more mass in the top 3 in. of soil, whereas on chiseled ground the root mass is distributed through the top 6 in. No-till may keep the soil cooler and wetter a few weeks longer than conventional tillage, which, he says, can result in a longer phosphorous-induced nutrient tie-up.

"No-till gives a higher degree of response to starter across the board and even higher if we get the phosphate in-furrow with the seed," Curley says. "The cooler, wetter soil conditions last longer and immobilize the nutrients longer, especially phosphate, zinc and nitrogen."

Because starter, especially phosphorous uptake which is aided by zinc, establishes the young plant's early girth, proper placement of available phosphate on the growth point of the seedling at the three- to five-leaf stage in ideal temperatures is crucial, he adds.

Curley's argument is two-fold: First, common 2-x2-in. placement of starter is off the mark; and second, growers may need to reassess starter formulations.Maximize nutrient absorption."The plant gets direct absorption (of nu trients) as soon as its seed begins to metabolize and break down and starts shooting root development. That's the optimum place to put starter because the growing point is the maximum point for absorption of water and nutrients in the emergence through five-leaf stage," Curley says. "When there is an optimum level of phosphate in the plant tissue at the three- to five-leaf stage, the genetic potential for girth and the length of the first 15 kernels on the embryonic ear are optimized. It's a function of phosphorous, with zinc facilitating the phosphorous uptake."

But Ohio State University soil fertility specialist Jay Johnson expresses reservations about in-furrow applications. "Phosphorous goes on with other nutrients, mainly with a 10-34-0 formula in the furrow, and I'm concerned about the uniformity of stand. You're more likely to get more damage to your plant population in the furrow unless you keep your rates extremely low. A 2x2 placement eliminates that as a factor in crop production. The root system in the early stage grows much faster than the top growth, by the time the plant emerges, the root is 2 in. long and is reaching over and picking up the starter fertilizer."

At that early stage of development, all focus should be on minimizing plant injury that may result through the improper use of products. Ultimately, that responsibility lies with the formulation of your starter.

Phosphorous needs to remain soluble for plant uptake, which requires only a slightly acid pH. The problem is that urea N can overwhelm the job that phosphate is trying to do early on and there's a chance that urea N can inhibit the phosphoric acid (and therefore the work of the phosphate molecules) by liberating free ammonia in the soil when applied in a band too close to the seed. Curley's point is that prolonged free ammonia, situated right on top of the seed, can suck up all the available moisture, decrease the solubility of P, and desiccate the seed.

Under cool, wet conditions, this may not necessarily be much of a problem. However, under dryer conditions, prolonged free ammonia can burn the plant's root system and incur a loss of anywhere from 5,000 to 10,000 ppa. An ideal in-furrow starter would buffer against free ammonia, somewhat increase P, and provide lower K so that urea N does not overwhelm the girth-giving and early plant growth that P offers, and excess K does not inhibit the nutritional values that N offers later on.

The solution, Curley says, is to apply the correct N, P and K formulation in the right place. To facilitate uptake, phosphorous needs to be close to the growth point of the seedling at the plant's three- to five-leaf stage. "Because phosphate does not move from where it is placed in the soil, 2x2 is generally too far away," he says. "Soil will not solubilize phosphorous and allow it to be absorbed into the root until we hit about 70 degrees."

But Johnson says he's never seen such a problem with 2x2 placement. "At that stage, the plant is taking up very little of anything," Johnson says. "It's too small. It is taking up some nutrients but not in large quantities. The rapid uptake period for nutrients happens 25 to 30 days after emergence through tasseling."

Formulations. With 2x2 placement, Curley says, phosphorous is not getting into the plant in high enough amounts soon enough. And unless they've put zinc in their phosphate fertilizer, a lot of 2x2 phosphate starters create a zinc deficiency," he says.

Tests on high-phosphate soils in northern climes at the University of Guelph in Canada determined that a starter phosphorous is beneficial because the cool soil temperatures do not allow the residual fractions of phosphorous already in the soil to become soluble early in the season. In those conditions the Guelph studies compared a popular 9-18-9 formulation with common polyphosphate 10-34-0 and 8-19-3 formulas and found that the 8-19-3 worked best to get phosphate into the plant at the three- to five-leaf stage when placedin furrow.

"The 9-18-9 has way too much potash right on the seed," Curley explains. "If you overload the plant with too much soluble potassium early, what you'll do with the 9-18-9 is block N uptake later. That limits your ear size. The key on starter is to not cause seedling injury or create yield decrease due to reaction of products or your formulation. That's how 8-19-3 came about, as a specialty grade, in-furrow starter formulation that's specifically designed for seedling safety and N, P and K response."

Johnson explains that any starter formulation is based on the nutrient needs for a particular soil and climate. He says 10-34-0 is popular because of its cost. "It can be made cheaper than any other liquid formulation of phosphorous; it's easy to handle and store and blends well with a lot of liquid fertilizers."

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