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High Plains N, P & K Basics

Tuesday, February 1, 2011
filed under: Fertility

The information below is excerpted from the “Nutrient Management” section of the High Plains Sunflower Production Handbook. The lead author of this section was Merle Vigil, soil scientist and research leader with the USDA-ARS Central Great Plains Research Station near Akron, Colo.

The entire High Plains Sunflower Production Handbook can be accessed on the National Sunflower Association’s website — Go to “Growers” and then click on “Production Resource Books.” The nutrient section provides tables and formulas pertaining to nitrogen, phosphorus and potassium recommendations, as well as more details on these nutrients importance and utilization in sunflower production.


Nitrogen (N) is the nutrient of greatest accumulation in the above-ground portion of the sunflower crop. Nitrogen recommendations vary with yield expectations associated with soil, climate, soil moisture, cropping sequence, and

residual nitrogen in the soil.

The results of a seven-year study conducted at the USDA-ARS Central Great Plains Research Station, Akron, Colo., indicated that sunflower requires 6 to 7 lbs of nitrogen for every 100 lbs of production. This has led to an increase from a previous recommendation of 50 lbs of nitrogen for every 1,000 lbs of

potential grain production, to 65 lbs of nitrogen for every 1,000 lbs of expected yield.

If fertilizer is placed in contact with the seed, the starter material should contain no more than 10 lbs of actual nitrogen plus potash per acre. The nitrogen and potash can cause germination damage because of their high salt index when placed with the seed. Much higher amounts can be applied in a 2x2 band or broadcast without seedling damage.

Nitrogen application for sunflower can be made preplant, sidedress or a combination of these methods with equal results. Applications should be timed so nitrogen is available for rapid plant growth and development.

Since sunflower is efficient in recovery of residual N, a soil test for available nitrogen is strongly encouraged. Profile nitrogen samples should be taken to a depth of at least two feet. On deep, well-drained soils, sampling may be justified to four feet.


Phosphorus (P) application should be based on a soil test. Consistent sunflower response to phosphorus fertilization has generally occurred on soils testing very low or low in available phosphorus where yield potential is not restricted by lack of moisture or other environmental factors. With medium-testing soils, yield responses have been erratic and normally quite small. Phosphorus applications are recommended with medium and low soil tests for potential yield response and to maintain the soil in a highly productive condition.

Phosphorus should be applied preplant-broadcast, preplant-knifed, or banded at seeding. Starter applications are most efficient, particularly when small amounts are applied on soils low in available phosphorus. Phosphorus can be placed in direct contact with the seed or to the side or below the seed with no restrictions in economical rates. If placed in contact with the seed, the starter material should contain no more than 10 lbs of actual nitrogen plus potash per acre.


Like phosphorus, a soil test is the best guide to potassium (K) need. Potassium removal is much greater with silage than with grain production. Potassium deficiencies are not likely unless soil test levels are low, which normally occurs in sandy soils.

Potassium should be applied preplant-broadcast or as a starter. Remember, sunflower is sensitive to fertilizer salts (nitrogen and potassium). When applying starter applications with the seed, limit application to no more than 10 lbs actual nitrogen plus potash per acre. Preferred fertilizer placement is 2x2.
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