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

Winter 1996, No. 5


Potassium has been directly linked to plant disease resistance by numerous researchers on a wide variety of crops and diseases...but what about phosphorus? Does phosphorus have a part to play in disease suppression?

Phosphorus is present in every living plant cell and has a direct role in plant growth. Plants need it for photosynthesis, respiration, energy storage and transfer, cell division and enlargement, and several other processes. Phosphorus promotes early root growth and development, hastens crop maturity, increases winter hardiness and improves crop quality. And yes, it helps suppress plant disease, especially root diseases in wheat and barley.

Common root rot, take-all and other root diseases are an unseen problem --- but they cost cereal crop growers millions of dollars every year in lost yield. These diseases are difficult to control. Cultivars vary in their tolerance to these diseases. Seed treatment and shallow seeding reduce the risk of infection and crop rotation can limit the pathogen populations. Maintenance of good soil fertility is also helpful.

Research has shown phosphorus fertilization to be effective in reducing losses from take-all in wheat and common root rot in barley. One recent Saskatchewan study found seed-placed phosphate reduced the frequency of the take-all pathogen in wheat roots by about 50 percent and root rot severity in barley by 10 percent. Another Alberta study showed seed-placed phosphorus reduced the average yield loss of nine cultivars of barley infected with root rot from 40 to 30 percent.

Phosphate fertilizers are most effective in reducing root rot problems when nitrogen is not limiting crop growth. The best disease control is obtained with the application of both nitrogen and phosphorus. Balanced and adequate soil fertility supports healthy plant growth.

How phosphorus reduces disease severity is not known...but it does stimulate root development. And, a healthy, vigorous root system will better compensate for infections by root pathogens.

Phosphorus deficiency is common in the cereal growing areas of the Northern Great Plains. About 60 to 90 percent of soils from the Canadian prairies and the bordering states test medium or less in plant available phosphorus, and require fertilization. Suppression of root disease is one more reason for a good phosphorus fertility program.

Root diseases...out of sight but not out of mind. Pay careful attention to phosphorus fertilization and your crop will have a competitive edge, both above and below ground.

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