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  AGRONOMIC NEWS ITEMS
From Agronomists of the
Potash & Phosphate Institute
655 Engineering Drive, Suite 110
Norcross, Georgia 30092-2837
Phone (770) 447-0335

Spring 1996, No. 1

ROLE OF POTASSIUM IN CROP ESTABLISHMENT

Planting high quality seed in a well prepared seedbed with enough moisture to assure a rapid, uniform stand is the first step in achieving acceptable yields. Seedbed fertility is also important, especially for immobile nutrients such as potassium.

Potassium plays many key roles in plants. It activates enzymes, maintains cell turgor, enhances photosynthesis, reduces respiration, helps transport sugars and starch, aids in nitrogen uptake and is essential for protein synthesis. In addition to plant metabolism, potassium improves crop quality because it extends the grain-filling period, increases kernel weight, strengthens stems, increases disease resistance and helps the plant better withstand stress.

Potassium is critical to get the crop off to a good start and good finish. Deficient plants have poorly developed root systems, grow slowly, lodge easily, produce smaller seeds and have lower yields. They also use water inefficiently, are less winter hardy and are more susceptible to disease.

Phosphorus is well known to promote early root formation and growth, but potassium may have an even greater effect on root development. Cereal plants have two root systems ¾ seminal roots which develop from the seed at planting and nodal roots which develop at the crown level later in plant development. Potassium deficiency affects both of these root systems.

An Australian study, where wheat was grown with and without nitrogen, phosphorus and potassium, has shown root growth is most severely affected by potassium. Lower root numbers were evident in the potassium-deficient plants within four days after seeding. Three weeks later, the plants grown without potassium had half the seminal roots of the plants grown without nitrogen or phosphorus. And, 30 days after seeding, the potassium deficient plants had not initiated any nodal roots, although the nitrogen and phosphorus deficient plants had.

Potassium shortage influenced root length in the same way. Length of seminal roots for plants grown without potassium 16 days after seeding was only 15 percent of plants supplied with normal potassium. This compares to 70 percent for phosphorus and 98 percent for nitrogen.

Because potassium plays such an important role in early root development, and because it moves very little in the soil ¾ starter fertilizers should be an important part of your nutrient management plans.

Remember, plants need as much potassium as nitrogen...some plants need even more.

-TLR-
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