PLANT NUTRITION 101-1

 

Plants receive their nutritional elements from three sources: AIR, WATER, and the SOIL.  Of the 17 known essential elements, three are from AIR and WATER, with the other 14 delivered via the SOIL.  45% of a plant’s needs is Carbon (C), coming from the CO2 in air.  Another 45% is Oxygen (O), and 6% is Hydrogen (H), both realized primarily in the plant’s water supply.   The carbon combines with the oxygen and hydrogen to form carbohydrates.

 

 

The other 14 nutrients (4%) are categorized as either Primary, Secondary, or Micronutrients.

 

The Primary nutrients are:       

*Nitrogen (N)

*Phosphorous (P)

*Potassium (K)

( the familiar N-P-K on fertilizer containers )

 

The Secondary nutrients are:

*Calcium (Ca)

*Magnesium (Mg)

*Sulfur (S). 

 

The Micronutrients are:

*Boron (B),

*Chlorine (Cl),

*Copper (Cu),

*Iron (Fe),

*Manganese (Mn),

*Molybdenum (Mo),

*Nickel (Ni)

*Zinc (Zn).

 

 

Some of the nutrients are immobile in the soil such that continued applications of a general purpose fertilizer can build up an excess of that nutrient (e.g. Calcium is immobile in soils and the excess can cause micronutrient deficiencies and a high pH). Other nutrients are mobile in the soil and can leach out and cause deficiency symptoms. (Nitrogen is very mobile, so the yearly addition of nitrogen should be split up into multiple feedings)

The nutrients can be either mobile or immobile in the plants as well.  A nutrient may or may not have the same mobility in the plant as in the soil.

The mobility in the soil and plant will be discussed when that element is covered.  An example of this is the movement of Nitrogen from older to younger leaves (translocation) within the plant.

 

The pH of the soil is a factor in the ability of the plant to take up nutrients.  Above a pH of 7, the availability of manganese diminishes.  Above 7.5, both iron and boron have reduced availability.  A pH below 6 reduces the uptake of phosphorous.  A slightly acid soil (pH 6.5 - 7) is ideal. 

 

 

Mobile in Soil (leaches readily in sandy soils):

        N, K , Mg,  S,  Mn

Immobile in Soil (can buildup to toxic level)

        P, Ca, Ni

Mobile in Plant (older leaves show signs first)

        N, P, K, Mg, Zn

        Ca, S, Mn, Mo (limited mobility)

Immobile in Plant (newer leaves show signs first)

        Fe, B, Cu

 

Some signs of nutrient deficiencies are:

Yellowing of leaves (Chlorosis) ­mobile nutrients show signs in older leaves, immobile nutrients show signs in newer growth

Interveinal chlorosis

Stunting of plant  lacking vigor ­slow growth

Curling (distortion) of leaves

Defoliation ­ Necrosis

Discoloration of fruit or leaves (purple & red)

Blossom end rot

Tip Necrosis (burn)

Poor root growth

Green veins on yellow leaves

 

An early indication of a deficiency is the yellowing of the leaves, but which nutrient?  By noting where the yellowing occurs you can get a good hint of what needs to be corrected.  Nitrogen is mobile in the plant which causes the yellowing to be seen in the older leaves, and the central vein green. Iron, which is immobile in the plant, shows up as yellowing of the newer leaves on a stem, with the veins remaining green.   Manganese is mobile in the soil but only partially in the plant.  This causes spotty yellowing of the leaves with the newer leaves being more pronounced.  Each of these symptoms can be accompanied by other symptoms which can help in determining what corrective action is needed.

Future articles will cover each nutrient in more detail.  For those who can¹t wait, here are some references:

 

­California Master Gardener Handbook.

    D. E. Pittenger Editor -  Univ. of Ca. ANR Pub # 3382

­Western Fertilizer Handbook, 2nd edition

Calif. Fertilizer Assoc.

    Interstate Publishers

­Biology of Plants  6th edition

    P. Raven, R. Evert, S. Eichhorn -  W.H.Freeman & Co.

­All-New Encyclopedia of Organic Gardening

    Rodale Press

­Abiotic Disorders of Landscape Plants ­ A Diagnostic Guide

    UC ANR Publication 3420