Common Nutrient Deficiencies in Plants: How to Diagnose and Correct
Early summer is the time of year when homeowners discover what their soils lack. Newly planted plants take a few weeks to grow and establish. Once they are comfortably entrenched in the soil, and have established good root systems (or have at least had time to establish a good root system), if they are lacking a particular nutrient, they will begin to show signs of stress. Depending upon the nutrient that is lacking, different symptoms will appear.
The amount of available nutrients can be different than nutrient availability. Several factors affect whether plants can take up the nutrients. Nutrient elements bind with parts of the soil. Factors such as the amount of organic matter in the soil, the soil pH, soil moisture content, soil temperature and other weather. Some nutrients are more accessible to plants when the pH is high, others when it is low. When you recognize that your plant is suffering from a nutrient deficiency, first you need to identify the problem, and then check to see if there are cultural issues that could be causing the problem.
Macronutrients—Functions and Symptoms of Deficiency
Primary plant nutrients are Nitrogen, Phosphorous and Potassium. These are the nutrients commonly found in most synthetic fertilizers. The ratio of each ingredient relative to the other is shown in a number such as 2-1-2 or 30-30-30. Nitrogen is listed first, then Phosphorous and then Potassium. This is called the NPK number. For the examples listed, the first one with an analysis of 2-1-2 contains twice as much Nitrogen and Potassium as Phosphorous. The second analysis shows that there is an equal ratio of active ingredients for each nutrient.
Nitrogen is involved in formation of proteins and plant growth. This nutrient is highly mobile—in soil and in the plant. Symptoms of nitrogen deficiency show first in old leaves, because nitrogen moves from the older leaves to the newer leaves as the plant tries to keep growing. The picture of the rose shows yellowing caused by a nitrogen deficiency.
Nitrogen can be delivered to plants in a quick release and slow-release form. Over-fertilizing can cause plants to grow too quickly and not “mature” or produce fruits or flowers.
Phosphorous is involved with nucleic acid activity, which is part of reproduction—flower and fruit set. The leaves of plants with phosphorous deficiencies turn purple, with the symptoms showing up in the oldest leaves first. Without enough phosphorous, a plant will not produce fruit.
Over fertilizing with quick release phosphorous can cause major water pollution problems.
Potassium is important for water movement in the plant. Plants with potassium deficiencies have leaves that appear to be burned at the edges. A potassium nutrient deficiency will also show up in older leaves first.
Sulfur, magnesium and calcium are secondary nutrients, also important to plant growth.
Calcium is important in building cell walls within plants. Plants growing in sandy soils, or acidic (low pH) soils have a greater chance of calcium deficiency problems. Calcium can be leached (or lost) from the soil quickly in the case of heavy irrigation or heavy rains. Several other factors beyond soil type and pH affect the availability of calcium. The ration of magnesium, manganese and potassium affects calcium availability. Different plant species show calcium deficiencies differently. Tomatoes and peppers with blossom end rot (pictured) most likely suffer from a lack of calcium.
Sometimes, calcium deficiencies can be corrected by raising the pH of the soil so that the calcium present is more accessible to plants.
Plants use sulfur for manufacturing proteins. Most soils are not sulfur-deficient, though more have become so, as organic matter is washed away, and farmers fertilize with highly concentrated fertilizers that do not contain sulfur.
Sulfur deficiencies show as yellowing, or chlorosis between the veins of the plant.
Micronutrients are incredibly important to plant functions, though the general public does not know much about their function, since most commercial, synthetic fertilizers do not contain micronutrients. The importance of micronutrients for plant growth was first discovered in the 1920s by soil scientists. Micronutrient deficiencies vary greatly by geographical location, and depend entirely upon the soil type and pH. Micronutrients essential for plant health, and problems that cause spare availability are:
Not available in: cool, wet soil with high pH
||Not available in: poorly drained soil with low pH
||Not available in: overly organic soils
||Not available in: soils with neutral or high pH
||Not available in: sandy soils, soils with little organic matter
||Not available in: acidic soils (low pH)
Micronutrients, while necessary in small amounts, are highly important to plant growth. Boron is essential for cell wall formation. Copper aids in prevention of wilting. Iron is important for enzyme function and energy transfer. Manganese is important to photosynthesis. Molybdenum is very important for legumes that grow in symbiosis with nitrogen fixing bacteria. Zinc is not mobile, so deficiencies show up in new leaves.
Many micronutrient deficiencies show up as chlorosis—yellowing of veins, or in-between veins. Some deficiencies stunt plant growth, and show up in new growth, which is small and weak.
Diagnosing Nutrient Deficiencies
Before adding fertilizer to your garden, you definitely need to correctly diagnose the plant problems. The easiest way for home gardeners to diagnose plant problems relating to nutrients is to look at pictures of nutrient deficiencies. For large scale commercial growers, plant material tests can help determine nutrient deficiencies. For home-gardeners, that is expensive and not necessary. If you have trouble diagnosing the plant problem, you can always go to your local cooperative extension agency. They are quite helpful with plant problem diagnosis.
Once you determine the nutrient deficiency problem, you need to make sure that you do not need to amend the soil to fix the problem. If a nutrient is immobilized in acidic soils, and you have a low soil pH, first try to amend the soil to raise the pH to make the nutrient available. If cultural controls do not help, then you need to fertilize.
Natural Fertilizer to Correct Nutrient Problems
Most conventional, synthetically produced fertilizer does not contain anything other than the macronutrients nitrogen, phosphorous and potassium. For secondary and micronutrient deficiencies, natural fertilizers are more helpful. Fertilizers made from Seaweed are a superb source of micronutrients. Many types of natural fertilizer are available that can give your garden a boost, and help your plants recover from micronutrient problems.
The Rodale Book of Composting New, Revised Addition, 1992
The Truth about Organic Gardening, Gillman 2008
Missouri Botanical Garden: Gardening Help http://www.mobot.org/gardeninghelp/plantinfo
University of Minnesota Cooperative Extension
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