Plant Nutrition - Micronutrients

More snow! No outdoor gardening in sight. You might as well read the blog...

In a recent post  we discussed plant macronutrients along with a little information about types of fertilizers. So check that post again in case you've already forgotten about it. Now,  let's review the eight micronutrients. These elements are needed in much smaller quantities than the six macros, but they are also very  important -- Otherwise, they would not be identified as  part of the "essential" fourteen.

For most  backyard agrarians discerning  nutrient deficiencies, especially those of micronutrients,  may be more art (or more likely guesswork) than exercising analytic skills because symptoms frequently are quite similar to one another. Fortunately,  micronutrient deficiencies are quite rare in garden soils. When they occur, problems are usually triggered by soil pH levels falling outside of the comfort range of vegetables. The good news is that most micronutrients are replenished by  regularly adding new compost to garden soils. 

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Boron deficiency.  Source: U Mn

Boron (B) -  Boron is transported through a plant by evapotranspiration. Because it concentrates in plant growth areas, a deficiency will show up quickly as wrinkled and deformed leaves that eventually die. Deficiencies may commonly occur in sandy soils and can also be triggered by inadequate watering in any soil. Deficiencies may be addressed by applying a solution of 3/4 ounce of Borax (barely 2 tablespoons) to 100 gallons of water. That ratio makes a concentration of 20 ppm (parts per million). Plants respond quickly, but it's very easy to reach toxicity levels. So be frugal, maybe just use a skimpy pinch of Borox in that watering can.  

 

Chlorine toxicity. Source: U Md

Chlorine (C) -  Chlorine is used in several photosynthesis processes. Chlorine usually derives from the natural weathering of soil minerals and its deficiency is very uncommon. In fact, I could find  no specific commercial source for it as just a fertilizer...  However, chlorine toxicity  poses a real risk.  Salt run off from roads, walkways and, yes, seepage and evaporation from swimming pools can quickly affect plants. Symptoms first appear as yellowing at leaf tips followed by leaf chlorosis. If this wasn't enough, (C) chlorine from industrial  air pollution can also lead to leaf chlorosis and plant death.  

Copper deficiency.
Source: haifa-group.com

Copper (Cu) - At 5 ppm  copper's presence has  one of the smallest footprints, but as a nutrient it is required for photosynthesis and other foliar (leaf) activities. In deficiency, vegetable leaves may develop a pale bluish tint, grow twisted and later show spotty chlorosis. In grains,  symptoms are different, e.g.  corn leaves may be yellowish and remain small. Toxicity also inhibits root growth and triggers iron (Fe) deficiency.

Iron deficiency.
Source: haifa-group.com

Iron (Fe) - Iron is also used in photosynthesis and some enzymic activity. It's generally readily available in soils. Deficiency can occur if soils are over-fertilized,  remain water-logged or pH levels are out of whack,  especially when on the  alkaline side (pH > 6.5).  The initial symptoms appear as tiny spots of interveinal chlorosis, i.e.  dead spots showing up within the vein lines of a leaf. Toxicity is rare but can inhibit the take up of manganese (Mn). So like many of these nutrient deficiencies, maybe the deficiency you think you see in your plants  is actually caused by something else...

Manganese deficiency.
Source: allotment-garden.org

Manganese (Mn) - Manganese usually occurs with iron (Fe) in soils and shows up in plant "mertistematic tissue" [i.e. the growth areas:  roots & shoots] as well as in photosynthesis. Deficiency can also develop from water logged conditions as manganese (Mn) is leached away.  The symptoms look a lot like iron (Fe) deficiency symptoms: interveinal chlorosis in younger leaves.  Plant tolerance for high levels of manganese varies from species to species, but will appear as dark purple or brown spots around leaf margins when it occurs. An interesting twist for us amateur plant diagnosticians to note is that too much manganese (Mn) interferes with the take up of iron (Fe)...  So guess what it might look a lot like?

Molybdenum deficiency.
Source:  hazerain.com

Molybdenum ( Mo) - Molybdenum has an exceedingly  small presence with many plants only needing  a concentration of about .20 ppm! Upon take-up molybdenum goes into the leaves where it stokes the first of two enzymic  activities involved in reducing nitrate to ammonia that in turn gets processed  into amino acids. If there is a deficiency, it shows up with the symptoms of  nitrogen (N) deficiency because some amino acids were not produced. Symptoms start with chlorosis in mature leaves, then leaf wilting and leaf death followed by death in other growing areas.  Toxicity is so extremely rare, however, that you really don't have to worry about it because plants can tolerate high levels of molybdenum. 

Nickel deficiency.
Source: eplantscience.com

Nickel (Ni) - Nickel is another nutrient commonly available  in soils, and sometimes too available  either at former industrial sites or in excessive concentrations in treated sewer sludge. Plants only need concentrations between .05 - 5.5 ppm in order to metabolize urea into ammonia. Legumes, pitted fruits and nuts are very sensitive to its deficiency in soil. Concentrations of nickel over 100 ppm  are quite toxic to plants with tomatoes being especially sensitive by exhibiting toxicity starting at only 20 ppm.  Symptoms may  appear in young leaves as dead tips  or as symptoms  similar to iron (Fe) deficiency.  Plant death can rapidly follow.

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Zinc deficiency
Source: plantphys.net

Zinc (Zn) - Just accept it that zinc is involved in a wide variety of a plant's chemical processes, too  many to name or  much less for most of us  backyard gardeners to care about. Its deficiency shows up in mature leaves as interveinal chlorosis, then scorch and finally "necrosis" (i.e. tissue death in limited other areas). Regarding toxicity, to quote the U of Maryland's Master Gardener's Handbook, "toxicity may occur in low pH soils or where  municipal sludge has been added to soils."  This is our second reference to sludge in this post, and maybe  we should start having second thoughts about those free offers for municipal compost etc. from our town offices... 


That's all for micronutrients, folks.  Thanks for persevering and remember:

"All gardeners know better than other gardeners.  - Chinese proverb

Plant Nutrition : Macronutrients 

While we wait for the snow to melt and our gardens to dry out, let's review what plants need and   what fertilizers provide.   Also, if you haven't had your garden soil recently tested and think your vegetables are not up to snuff, we'll identify some of the major "aha" nutritional deficiencies you can look for....   You'll just have to try to remember all this once the growing season starts...

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Every bear in the woods probably knows that plants use the three elements, Hydrogen, Oxygen and Carbon. Plants obtain these three  from  air and water.  But there are 14 other elements that are vital for plant nutrition. Of these, six are identified as "macronutrients" with the remaining 8 elements characterized as "micronutrients" or "trace elements."  Plants actually use other elements as well, but these 14 are needed by all plants. We'll cover micronutrients later  in  a separate post. 

Macronutrients

 Lack of Ca. Source: Cornell Extension

Calcium (Ca)  - Calcium is generally available in soils and is taken into plants through evapotranspiration (water siphoning from the roots through the leaves to the atmosphere). It is the key ingredient  in plant  cell walls. During times of drought (and/or a gardener's under watering) or high humidity, plants do not move enough water through their tissues to supply cell needs resulting  in calcium deficiency.  This is important to note because calcium may not necessarily be deficient in the soil. In either case, this deficiency dramatically manifests itself in tomatoes and peppers, for example,  as blossom end rot. An over abundance of calcium is more subtle to detect because  too much calcium can interfere with the take up of other elements whose deficiencies may exhibit markedly different symptoms.

Chlorosis.  Source: Cornell Extension

Magnesium (Mg)  - Also typically available in soils, especially in clays.  It is incorporated into chlorophyll and plant enzymes.  Its deficiency appears initially as raised areas of  light yellow in mature leaves.  Later, these areas become more pronounce and eventually turn into dead leaf areas (chlorosis). 

Nitrogen (N)   - Nitrogen is utilized by plants in several forms,  but let's skip  over the complex chemistry of the Nitrogen Cycle and just say  that  plants  absorb  these  compounds  incorporating  much of it into   their leaves and the enzymes essential for photosynthesis.  A deficiency will first appear as a paling of mature leaves, then evolve to  yellowing before ending in chlorosis (dead leaves).  Although  nitrogen is essential for plant growth, too much will also cause chlorosis in leaves.  

[n.b. Fertilizers meant for house plants  are typically loaded with nitrogen; and if you use them on vegetables, you will get lots of vegetative growth and less fruit.]

Excess Phosphorus.  Source: U Maryland Extension

Phosphorus (P)   - Phosphorus is used in cell membranes and serves as the primary carrier of energy throughout plant cells.  It is incorporated into DNA and RNA as well as  regulating enzyme activity. It generally occurs naturally in soils, but its availability to plants depends upon soil pH.  A deficiency shows up as dark green or  purplish tints in tomato leaves. Eventually, flowers and fruit do not develop.

 

Potassium deficiency.  Source: Yara.us 

Potassium (K)   - Plants need potassium almost as much as they   need nitrogen, and   potassium also abets nitrogen take up. It maintains various metabolic activities by regulating water within the plant. Potassium deficiency may first appear as yellowing of older leaves before they turn brown. (This may also be called leaf scorch or leaf burn, but other conditions such as exposure to salts, insecticides or too much fertilizer might also cause it.)   The taste and appearance of fruit can also be affected.  

Sulfur deficiency.  Source: haifa-group.com

Sulfur (S)  - Sulfur is utilized in amino acids, proteins, vitamins  and other compounds, e.g. sulfur gives onions and mustard their distinct flavors.  Although sulfur also occurs naturally in some soils, its concentration is relatively low compared with other nutrients and  tends to be  especially low  in sandy soils. Much of the sulphur that is found in soils derives  from the decomposition of  organic materials, e.g. compost.  [This is another  good reason for you to start composting.] A very small amount of  sulphur can also  come from the atmosphere.  Its deficiency appears as yellowing of younger leaves and woody looking stems.

Nutrients and Fertilizers

From what I have observed of neighbors and friends who  try  container gardening, nutrient deficiencies  can show up  relatively quickly because the gardeners do not replenish  the soils from year to year, fail to fertilize during the growing season and/or do not maintain adequate moisture levels. For gardeners, like me, who dig up their front or backyards, deficiencies may take many growing seasons to appear because we are accessing  a greater reservoir of nutrients. Maintaining a consistent moisture level (apart from timely cultivating) is probably our major challenge!

Soils typically have all of the above macronutrients to some extent because these elements  originate from mineralogical sources. However, large percentages of these elements  frequently  are chemically bonded with other compounds in the soil  and rendered  unavailable to plants.  Over time  the usable forms of these  elements   decline as  crops are harvested, remaining plant stock  removed (i.e. diseased plants pulled up and stuffed into lawn bags), leached or washed away by rains etc. Adding compost, natural or synthetic fertilizers replenishes these otherwise lost nutrients.

When backyard gardeners talk about fertilizers, they  are mainly referring to  commercial balanced fertilizers that supply N-P-K (Nitrogen, Phosphorus and Potassium), three key nutrients of the macronutrient group. The concentration of these elements is typically cited as percentages of package weight, e.g. 5-10-5, 10-10-10. The amounts of other macronutrients may or may not be mentioned, and micronutrients hardly ever. The N-P-K combo get the spotlight because they are significant in foliar, root and fruit development; but, as hopefully discernible  from the above text, they are not the whole story.

Fresh & Mature Compost.  Source: permaculturenews.org

Commercially produced fertilizers offer the advantage that they tell you the amounts of some or all of the macronutrients you are getting as opposed to what you sprinkle on your garden from your compost pile. Nutrient specific fertilizers also are available to address  specific soil needs, e.g. sodium nitrate or superphosphate, that might have been identified from a soil test.  Commercial fertilizers derived from organic sources, e.g. those containing bone meal, fish meal,   vegetative compost, manure etc.,  will include more nutrients and also be sterile. The best summary about  the types fertilizers available, I have found, is this one from the Weekend Garden Net.   Scroll past the self-test and look are the chart.

Putting your compost on your garden and mulching does a lot to maintain nutrient levels, especially micronutrients; and if you do not observe any plant problems, keep doing it. Just be aware that our backyard compost piles typically show a N-P-K ratio of around 1-.5-1.  Although you might come to think that plants need a 7 course fertilizing banquet, in reality they make do with very little.  For example, if you want to apply a liquid fertilizer to your vegetable garden, Cornell suggests the following ratio of a dry fertilizer (15-15-15) to water: 1 1/4 ounces of dry fertilizer to 2 1/2 gallons of water. This concentration provides a nutrient drink of only a couple of hundred parts per million!   If you were going to use this concoction for seedlings, cut it down to about 1/8 of a teaspoon. [And, REMEMBER: it is always better to use less fertilizer than too much and do not put either dry or liquid fertilizers directly on plants.] To get better guidance about using fertilizers in your garden, see the Monroe County Extension's publication,  Soil Preparation and Fertilizers for the Home Flower and Vegetable Garden.

"If the grass on the other side of the fence appears greener... it must be all the fertilizer they are using." -  Kevin Rodowicz, MD