Wednesday, February 6, 2008

Nutrient deficiencies

This is part 2 of material I think I need to know for tomorrow's exam. I will not go into any detail with regards to fertilizer. I think I'm comfortable enough with my knowledge on that as it is.

Part 1-Plant growth medium
Part 3-Plant growth regulators
Part 4-Postharvest longevity of flowers
Part 5-Legal protection of cultivar propagation

Most of the information here is from a handout given in a class I took about a year ago, supplemented with information found on the internet.
Plant nutritionists usually divide essential nutrients for plants into macronutrients (required in larger amounts) and micronutrients (required in smaller amounts). Essential nutrients are those that are required for the plant to complete its life cycle. There is some discussion about this, because silicon (Si) is not considered an essential element, but contributes to resistance of plants against pathogens and abiotic stress. Rice is a prime example of a plant that takes up Si in large amounts, and which is much more resistant against fungal infection as a result. Si also has other effects on rice, including preventing lodging, improved yield, and such. Rodriguez and Datnoff (2005) also mention that Si improves tolerance to excess nutrients. In the discussion below, approximate concentration of the element is given as a percentage of dry weight, then which leaves show deficiency symptoms first, and then the symptoms themselves are listed. Macronutrients generally result in symptoms on older leaves first, while micronutrient deficiency symptoms first show up on young leaves. Ca-deficiency is an exception to this.

N (1.5-4%)-Older leaves to whole plant-Reduced plant growth, light green leaves, followed by general chlorosis
P (0.3-0.5%)-Older leaves and stems-Stunted growth, leaves becomes dark green, older leaves and stems may become red or purple
K (1.5-4%)-Older leaves-Marginal chlorosis becomes necrosis (sometimes only along the margins)
Ca (1%)-Young leaves-Leaf distortion and marginal chlorosis, may become marginal necrosis, causes increased susceptibility to certain plant pathogens
Mg (0.5%)-Older leaves-Interveinal chlorosis more pronounced at leaf margins, most at the leaf tip. Necrosis is possible, but less common than in K deficiency. Very common in the South in palms (see photo, credit: T.K. Broschat, click on photo for original context)

S (0.5%)-New leaves to whole plant-General chlorosis, more pronounced near the top of the plant

Fe (100 ppm)-Young leaves-Interveinal chlorosis with a netted appearance, can become general, small veins yellowing first, most common cause is high pH of the growth medium
Mn (100 ppm)-Young leaves-Interveinal chlorosis, less likely to become general than Fe-deficiency, may turn into necrotic margins and spotting, commonly caused by high medium pH or high Fe
B (50 ppm)-Young leaves-Thickened smaller leaves, shorter internodes. Leaves first become dark green, then develop chlorosis and necrosis, can result in tip dieback, and witches' broom symptoms
Zn (30 ppm)-Young leaves-Distortions, smaller leaves, short internodes (rosette appearance), mild interveinal chlorosis
Cu (15 ppm)-Young leaves-Distortions, interveinal chlorosis
Mo (5 ppm)-Young leaves-Distortions, marginal chlorosis or necrosis

Rodriguez, F.A., and Datnoff, L.E. (2005) The role of silicon in suppressing diseases. APSnet feature story February 2005.

No comments: