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. 

--------------------------------------------------------------------------------------------------------------------------

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.

,

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