PLANT

NUTRITION

Macro Elements in PlantsIn addition to large amount of carbon(C), hydrogen(H) and oxygen(O)needed for manufacture of carbohydrate during photosynthesis, a green plant requires small but appreciable quantities of several other chemical elements for healthy growth.

Macro Elements in PlantsFour of these macro elements are;

• nitrogen(N)• phosphorus)• potassium(K)• magnesium(M).

They are present in fertile soil and absorbed by the plant’s root.

Percentage of dry weight

N P K Mg

Barley (arpa)

1.94 0.13 4.04 0.29

Sunflower 1.47 0.08 3.47 0.73

Wheat 2.26 0.06 4.16 0.23

Table shows the results of an experiment in which three different species of plant were grown in the same soil under identical environmental conditions.When analysed, all three species were found to contain significant, thought not identical, quantities of each macro-element.

Micronutrients  are those elements essential for plant growth which are needed in only very small (micro) quantities. The micronutrients are boron (B), copper (Cu), iron (Fe), chloride (Cl), manganese (Mn), molybdenum (Mo) and zinc (Zn). Recycling organic matter such as grass clippings and tree leaves is an excellent way of providing micronutrients (as well as macronutrients) to growing plants.

• Mg structure of chlorophyll• Fe synthesis of chlorophyll, protein synthesis

(Ferredoxin and cytochromes), PQ• N structure of chlorophyll, proteins, DNA,

RNA, ATP, NAD, NADP• K synthesis of chlorophyll, growth• P DNA, RNA, ATP, NADP • Ca formation of cell membrane, cell wall• S protein synthesis• Cu Plastocyanin synthesis• Mn and Cl catalysts of photolysis

MINERALS NEEDED FOR PLANT GROWTH

PRINCIPLE OF LIMITING FACTOR (1905 –Blackman)

When a chemical process is affected by more than one factors, its rate is limited by the factor which is nearest its minimum value. (The rate of a biochemical process is limited by the factor which is nearest its minimum value.)

Element Symptoms of Deficiency

Nitrogen Overall growth reduced, leaves chlorotic (pale green or yellow), leaf bases red, roots long and thin

Phosphorus Overall growth reduced, leaf bases red,

Potassium Overall growth reduced, early death of older leaves

Magnesium Overall growth reduced, leaves chlorotic (pale green or yellow)

Phosphate: Leaves darker than normal. Loss of leaves

Magnesium: Lower leaves turn yellow from inwards. Veins remain green

CO2: White deposit. Stunted growth. Plants die back

Manganese: Yellow spots and /or elongated holes between veins

Calcium: New leaves misshapen or stunted

Iron: Young leaves are yellow-white

Potassium: Yellow tips and edges. Spots on leaves

Nitrogen: Upper leaves light green or lower leaves yellow

Note "burned" necrotic leaf edges.

Note overall growth reduced

Note Interveinal chlorosis on the youngest leaves. This symptom disappears within a day or two if leaves are sprayed with iron solution.

Note rot on the end of the fruit to which the blossom was attached.

Note reddish color of younger leaves

Note whitish leaf tips poorly unfolded. Most common on acid sandy soils.

Organic Fertilizer

• Organic fertilizer is a slow release fertilizer that feeds the roots as they need it. As the roots are fed, branch extension takes place, buds start to form and the plant blooms.

• As nitrogen leaches from the soil, organic fertilizer will release its nutrients. With organic fertilizer, roots will grow deeper, providing stronger and healthier plants.

Organic Fertilizer

• It also protects the soil from erosion. Organic fertilizer is nontoxic to the fascinating earthworms. Earthworms make the garden healthy because they keep the organic materials turned.

• Another major bonus of using organic fertilizer is that hummingbirds and bees will be attracted to your garden. Hummingbirds and bees are important to plants, because they pollinate them.

ROOTS AND MICROORGANISMS

NODULES

Colonizing bacteria that supply nitrogen to legumes -- rhizobia, reside in protective nodules formed by the plant. The bright red color of the opened nodule is an indication of healthy rhizobia inside.

Nitrogen fixing bacteria require oxygen-free conditions to fix nitrogen, so they only inhabit the cells in the central core of the nodule (the darker mass of cells in the center). Though not visible in this photo, the interiors of legume nodules are normally pink due to the presence of leg-hemoglobin. Leg-hemoglobin has a high affinity for oxygen, and it locks up oxygen, thus fostering the oxygen-free conditions needed for nitrogen fixation.

MYCORRHIZA

Many plants have fungi that grow on their root.

When a fungus grows in a symbiotic relationship with the roots of a plant, the resulting fungus root is called mycorrhizae. All mycorrhizal fungi have hairlike filaments that grow into the soil.These filaments act like a vast network of root hairs and provide the plant with water and nutrients that are absorbed from the soil.

The fungi, in turn, seem to gain nutrients that are necessary for growth and development from the plant.

Some plants with few or no root hairs at all are so dependent on the fungi living on their roots, that they cannot survive without them.

 EXPERIMENT   Researchers grew soybean plants in soil treated with fungicide to prevent the formation of mycorrhizae in the experimental group. A control group was exposed to fungi that formed mycorrhizae in the soybean plants' roots.

 RESULTS   The soybean plant on the left is typical of the experimental group. Its stunted growth is probably due to phosphorus deficiency. The taller, healthier plant on the right is typical of the control group and has mycorrhizae.  CONCLUSION   These results indicate that the presence of mycorrhizae benefits a soybean plant and support the hypothesis that mycorrhizae enhance the plant's ability to take up phosphorus and other minerals

Does having mycorrhizae benefit a plant?