Lecture 3Plant nutrition

3.4c

Potassium deficiency

Symptoms- mottled or marginal chlorosis, whichthen develops into necrosis on tips,margins and between veins- symptoms initially on more mature(“older”) leaves- leaves may curl and crinkle- stems may be slender and weak, withabnormally short internodal regions- in K-deficient corn, nodes may haveincreased susceptibility to root-rottingfungus present in the soil- this together with stem weaknessresults in bending of stems to theground (lodging)

Soybean

Corn

Iron deficiency

Symptoms- strong chlorosis at the base of the leaves with some green netting- deficiency starts out withinterveinal chlorosis of theyoungest leaves, evolves into anoverall chlorosis, and ends as atotally bleached leaf- bleached areas often developnecrotic spots- because iron has a low mobility,iron deficiency symptoms appearfirst on the youngest leaves- iron deficiency is stronglyassociated with calcareous soilsand anaerobic conditions, and it isoften induced by an excess ofheavy metals

Analysis of plant tissues reveals mineral deficiencies

Influence of the pH on the availability of nutrientelements in organic soils

- main losses of nutrients fromagricultural systems is due to leachingthat carries dissolved ions, especiallynitrate, away with drainage water- in acid soils, leaching may bedecreased by the addition of lime –a mix of CaO, CaCO3 and Ca(OH)2 –to make the soil more alkaline,because many elements form lesssolublecompounds when the pH ishigher than 6- width of the shaded areas in the graphindicates the degree of nutrientavailability to the plant root

Treating nutritional deficiencies

• Inorganic fertilizer…– Straight fertilizer..Super phosphate,ammonium nitrate– Compound fertilizer (i.e. contain two or moremineral nutrients)• Organic fertilizer– Residues of plant and animals– Mineralization (organic compounds brokendown by microorganisms)

Foliar application of fertilizers

• Uptake is faster• Deficiency can be prevented• Not tied up in soils (Fe, Mn and Cu)• Expensive• Vineyards

The principle of cation exchange on thesurface of a soil particle

- cations are bound tothe surface of soilparticles, because thesurface is negativelycharged- addition of a cationsuch as K+ can displaceanother cationsuch as Ca2+ from itsbinding on the surfaceof the soil particle andmake it available foruptake by the root- mineral anions (NO3_, Cl_) tend to berepelled by the negative charge of thesurface and remain dissolved in soilsolution; capacity of exchange of anionsis smaller than of cation