Corn Phosphate Fertility

Phosphate and Corn Development
Yield potential is compromised and delays in maturity and quality can occur without adequate phosphate nutrition throughout the growing season. Phosphate uptake begins even before the plant emerges from the soil and young seedlings require high phosphate fertility, but have difficulty obtaining it because of a small root system and the slow release of phosphate from cool soils.

Early in the season, corn does not have access to broadcast and starter fertilizer because the roots are just beginning to explore the soil rooting zone. Because phosphate fertilizer cannot be seed-placed, corn is often deficient in optimum phosphate fertility, especially early in the season in cold soils. Throughout the rest of the growing season, phosphate availability may also be limited in low pH soils, or high pH calcareous soils.

Phosphate Optimizes Corn Yields
Phosphate is a key nutrient in the drive for higher corn yields. A 180 bushel per acre corn crop takes up in excess of 102 pounds of P2O5 per acre. Research across much of the corn belt shows that adequate phosphate fertility allows corn to reach its full genetic potential. For example, research in Ohio and Illinois on low phosphate soils showed that yields continued to increase even with the highest fertilizer rate tested.

Corn Establishment
Corn yields are increased with seed-placed phosphate. Field trials show that an application of 9 - 13 pounds of P₂0₅ per acre directly with corn seed will give greater yield increases than 18 pounds P₂0₅ in a side band. At phosphorus soil tests of 13 to 45 ppm, seed-placed phosphate showed more profitable response than a side-band application1. Maximum safe rates of seed-placed phosphate must be observed to protect against fertilizer burn and reduced corn emergence.

Phosphate Fertility in Corn on Corn Rotations
A continuous corn growing system requires higher phosphate fertilizer applications to maintain needed soil phosphate levels compared to a common corn-soybean rotation. Part of the reason is that corn removes more phosphate per acre in the grain (60 lbs P2O5, 150 bu/ac yield) than soybeans (40 lbs P2O5, 50 bu/ac yield). Therefore, a continuous corn system has a higher phosphate nutrient requirement. Also, soybean roots have a distinctly different root system compared to corn, thus a corn-soybean rotation results in much more thorough exploration and use of relatively immobile soil nutrients, like phosphorous.

Phosphate fertility can be a challenge in a continuous corn system for two interrelated factors. Corn roots excrete calcium as part of its normal growth process. The excreted calcium may accumulate around root channels. This calcium has a tendency to bind with phosphate in the soil forming insoluable calcium phosphate. The result is a calcium “shield” forming around root channels.

The other factor affecting phosphate uptake in a continuous corn system is that corn roots will often follow the path of least resistance – i.e. an existing root channel in the undisturbed soil zone. The calcium “shield” can act as a chemical barrier and precipitate (bind) phosphate as it diffuses toward the root surface. Thereby keeping much needed phosphorous nutrient from the root.

It is reasonable to expect that in a continuous corn system the percentage of roots that will follow an old root channel will be higher than a corn-soybean rotation. The end result is a potential phosphate fertility challenge.

Safe rates of seed-placed fertilizer with corn

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