How To Identify Phosphorus Deficiencies
Many soils in North America are testing below the critical level for phosphorus. As levels continue to decline it’s important to supply adequate phosphorus to meet crops’ demand throughout the growing season. If nutrient removal rates continue to outpace nutrient application your crop may experience phosphorus deficiency. From soil test levels to visual cues, here’s how to determine phosphorus deficiencies in your fields.
Plant Symptoms
Visual diagnosis for phosphorus deficiency is difficult to detect. In mild cases plants may experience stunted growth. In severe cases symptoms may include purpling or browning beginning on the lower leaves. Symptoms appear first on leaf tips and progress towards the base of the plant.1 Young plants are more likely to exhibit symptoms because their rapid growth makes greater demands on the phosphorus supply that is available and young root systems have only explored a small volume of soil.1
Visit IPNI for a guide to visual symptoms in crops including canola, corn, soybeans and wheat.
Proper Diagnosis
Yearly soil tests are the most effective method for identifying nutrient deficiencies because they can also tell you how much of that nutrient your soil is lacking. Testing after harvest is recommended to capture the nutrients your harvested crop removed from the soil and how much will need to be added back through fertilizer applications. Your soil test will also reveal your soil pH, which affects plant availability of phosphorus. In general, phosphorus is more plant-available in a pH range of 6.0-7.5.2 Work with your local lab to determine the best soil testing method for your soil and field history.
Another option to diagnose phosphorus deficiency is a tissue test. If you suspect a phosphorus deficiency in-season, use a tissue test to confirm it. It should be noted that if the tissue test confirms phosphorus deficiency, the deficiency is difficult to correct in-season. You may choose to top dress, but phosphorus does not move down into the soil readily and much of that phosphate will remain in the soil for future crops.3 Prevention by soil testing and proper pre-plant applications is the best strategy.
Unsure about nutrient deficiencies or fertilizer needs for your crop? Talk to your agronomist or a local Smart Nutrition rep. Adding Smart Nutrition™ MAP+MST® to your fertilizer program can help you meet your sulfur and phosphorus application needs.
Sources:
1 – https://www.alberta.ca/phosphorus-management-in-crops.aspx
3 – https://www.canolacouncil.org/canola-watch/2012/03/09/station-4-diagnosing-nutrient-deficiency/
