Week 8 – SS2 First Term Agricultural Science Notes

 WEEK EIGHT
TOPIC: PLANT NUTRIENTS AND NUTRIENT CYCLES
CONTENT

• Classify plant nutrients
• Functions and deficiency symptoms of nutrients
• Nutrient cycles

 PLANT NUTRIENTS AND NUTRIENT CYCLES
Plant nutrients are classified into two, these includes macronutrient and micronutrient.

 MACRONUTRIENTS
These are mineral elements or nutrients required by crops in large quantities. Examples are: nitrogen, phosphorus, potassium, magnesium, calcium and sulphur.

 MICRONUTRIENT OR TRACE ELEMENTS
These are mineral elements or nutrients required by crops in small quantities. Examples are: Zinc, Copper, boron, molybdenum, Iron, Chlorine and Manganese.

 FUNCTIONS AND DEFICIENCY SYMPTOMS OF PLANT NUTRIENTS

 EVALUTION

1. Give five examples each of macro and micro nutrients.
2. State the functions and deficiency symptoms of sulphur, iron, manganese copper, zinc, boron and molybdenum.

 NITROGEN CYCLES
Nitrogen cycles refer to the circulation of certain nutrients like nitrogen, carbon and water in nature.
Nitrogen cycle is the nature’s way of regulating the amount of Nitrogen in the soil and air

 Ways by which Nitrogen is added to the soil in Nitrogen Cycle

1. Direct fixation by lightening during rainfall.
2. Incorporation into the soil by free living bacteria or non-symbolic bacteria.
3. Nitrogen fixing bacteria in the root nodules.
4. Decomposition of organic matter.
5. Application of Nitrogen fertilizer.
6. Ammonification.
7. Nitrification.

    Soil can gain Nitrogen through the following ways
   

8. Symbiotic Nitrogen Fixation
9. Electrical discharge
10. Non symbiotic Nitrogen Fixation
11. Ammonification and Nitrification
12. Application or organic manure and Nitrogen fertilizers

     Ways by which nitrogen is lost from the soil are:
    

13. By Denitrification
14. Soil erosion
15. Leaching
16. Soil PH
17. Bush burning
18. Crop removal
19. Volatilisation
20. Oxidation reaction
21. Reduction reaction

     Processes that lead to formation of Nitrate from organic matter in Nitrogen Cycle
    

    1. Putrefaction: Delay of plant and animal remains into similar nitrogenous compounds by microorganism
    2. Amminization: Products from putrefaction reactions converted to simple amino compounds and animal
    3. Ammonization: Conversion of amino compounds and amines into ammonium compounds
    4. Nitrification: Oxidation of ammonium compounds into nitrites and Nitrates

     
    CARBON CYCLE
    This involves the series of processes which contribute to the circulation of carbon in nature.

     Explanation

    1. Carbondioxide is removed from the air mainly by photosynthesis
    2. Carbon is lost in form of carbonates of calcium and magnesium through leaching and drainage.

    The atmosphere gains carbondioxide through

22. Burning of fuel like coal and wood
23. The action of volcanoes which releases carbon dioxide
24. The respiration of plants and animals
25. Death and delay and putrefaction of plants and animals
26. Diffusion of carbon dioxide from seas and other bodies of water

     IMPORTANCE OF CARBON CYCLE
    

    1. Plant use carbondioxide obtained from the air to manufacture their food during photosynthesis
    2. Provision of carbon which is the essential building block of all organic matters
    3. Organic matter which is made from carbon helps to replenish soil nutrients.

    
    
     WATER CYCLE
    This is the continuous movement of water from the atmosphere to the earth and from the earth to the atmosphere.

     The atmosphere receives water through
    

27. Evaporation from oceans and land
28. Transpiration from plants
29. Breathing and respiration by plants and animals

     Land receives water through:
    

30. Rainfall and precipitation
31. Infiltration and percolation

     FORMS IN WHICH WATER EXISTS IN THE SOIL
    

32. Hygroscopic water
33. Capillary water
34. Gravitational water

     Ways of conserving water in the soil
    

35. Stoppage or reduction of water-run-off
36. Addition of humus or organic mature
37. Removal of weeds to reduce transpiration and water loss
38. Mulching
39. Cover cropping
40. Contour ridging
41. Appropriate tillage
42. Strip cropping

     EVALUATION
    

43. Explain Nitrification.
44. List five ways the soil can gain nitrogen.

     IMPORTANCE OF WATER TO CROPS
    

45. Water provides the medium for absorption of minerals salts
46. It facilitates transfer of nutrients to other parts of plants
47. It is an essential raw material during photosynthesis
48. Facilities enzymatic activities occurring in crop plant protoplasm
49. It is a constituent of protoplasm
50. It has cooling effect on crops
51. It helps to sustain life
52. It helps in seed germination
53. It helps to maintain plant turgor or turgidity

    

     GENERAL EVALUATION
    

54. List five importance of water to crops.
55. List three form which water exist in the soil.
56. List three ways by which Nitrogen is lost from the soil.
57. What is macro nutrient? List five examples.
58. What are micronutrients? List five examples.

     READING ASIGNMENT
    Essential Agricultural Science for Senior Secondary Schools by O.A. Iwena, Chapter 18, pages 187 – 201

     WEEKEND ASSIGNMENT
    

    1. The conversion of nitrates to nitrogen gas by certain bacteria is ___ (a) oxidation (b) reduction (c) nitrification (d) de-nitrification
    2. Microbial delay of plant and animal remains into simpler nitrogenous compound is ___ (a) nitrification (b) putrefaction (c) leaching (d) burning
    3. The washing away of soil nutrient down beyond the reach of the root is called ___ (a) erosion (b) mulching (c) leading (d) fertilization
    4. The following are macro nutrients expect (a) boron (b) nitrogen (c) magnesium (d) calcium
    5. Which of these is not a micro-element? (a) copper (b) zinc (c) boron (d) potassium

     SECTION B
    

    1. (a) Differentiate between macro and micro nutrients

           (b) List three factors influencing nutrient availability in the soil
       2.     (a) State three function of Nitrogen to plants
           (b) State three importance of organic matter in Agricultural