Plant nutrients and nutrients cycle

Agricultural science S.S.S 2 First Term

Week 1                

Plant nutrients and nutrients cycle

PERFORMANCE OBJECTIVES

At the end of this chapter, students should be able to:

 

1. List plant nutrient elements under the major classes
2. Recognize deficiency symptoms of different elements in crops
3. State the factors affecting nutrient availability in the soil
4. Describe the different methods of replenishing lost nutrients
5. Illustrate the different nutrient cycles using diagrams

 

MACRO-NUTRIENTS AND MICRO-NUTRIENTS

 

Plants require nutrients or elements obtained from soil for good growth and healthy development. These elements or nutrients are classified into two main groups which are:

 

Macro-Nutrients

Macro-Nutrients are mineral elements or nutrients required by crops in large quantities. Examples of macronutrients are nitrogen, phosphorus, potassium, magnesium, calcium and Sulphur.

 

Micronutrients or Trace Elements

Micronutrients are mineral elements or nutrients required by crops in small quantities. Example of micronutrients are zinc, copper, boron, molybdenum, iron, chlorine and manganese.

 FUNCTIONS AND DEFICIENCY SYMPTOMS OF PLANT NUTRIENTS

 

The functions and deficiency symptoms of these elements or nutrients are summarized below:

 

	Elements	Functions	Deficiency symptoms
(1)	Nitrogen	Its aids plants’ growth and reproduction because it is an essential constituent of all proteins. It increases the size of grain in cereals or carbohydrate synthesis. It promotes vegetative and short system growth Excess nitrogen delays maturation and fruiting. It promotes uptake of potassium and phosphorus from the soil. It promotes chlorophyll formation or deep green colour of leaves. It is necessary for the synthesis of plant hormones/ enzymes/ auxins.	Stunted growth Yellowing of leaves (Chlorosis) Leaves tend to drop Poor formation of fruits and flowers.
(2)	Phosphorus	It aids enzyme reactions It is a constituent of the cell nucleus and essential for cell division It increases crop resistance to diseases It helps in ripening of fruits It helps in root development, seed germination, fruit formation and maturity. It aids seed germination It aids fruit formation and maturity It improves the good taste of forages and vegetables	Logging results in cereal crops Leaves turn to purple and brownish colouration from tip backwards Stunted growth Inhibition of flowering, fruits and seed formation Poor root development. Immature fruit drop
(3)	Potassium	It is an important constituent of plant tissues It aids the synthesis of carbohydrates It activates various plant enzyme reactions It promotes the development of young plants It is necessary for neutralization of organic acids in plants It is associated with stomata movement and therefore influences water relationship within plants It is a major constituent of plant tissue It helps nitrate uptake from the soil	Weak slender stems Delayed growth Premature loss of leaves Brown colour at margin of leaves
(4)	Calcium	It strengthens plant cell walls with calcium pectate It helps in the translocation and storage of carbohydrate and proteins into seeds and tubers It controls the toxicity of aluminium manganese and sodium ions. It is necessary for the normal growth of root tips. It strengthens the cell walls It helps in high flocculation i.e. good aeration, water infiltration and retention It improves the pH of the soil so that nitrogen fixation can be carried out	It causes stunting of the root system There is appearance of pale yellow colour in the leaves Weak slender plants
(5)	Magnesium	It is important in the synthesis of carbohydrate as it is a constituent of chlorophyll. It assists in the transportation of phosphate, an essential material to developing fruit seeds It enhances plant growth. It is required for normal cell division. It is necessary for the synthesis of oils in plants	Chlorosis along the leaf veins Stunted growth Premature leaf fall
(6)	Sulphur	It is a constituent of plant proteins since it occurs in some amino acids such as cysteine and methionine. It is also a constituent of plant hormones such as biotin and thiamin. It is essential for chlorophyll formation. It is also required for carbohydrate metabolism and nitrogen fixation by legumes	Yellowing of leaves Stunted growth Poor rate of photosynthesis.
(7)	Iron	It is necessary for chlorophyll It is necessary for protein synthesis contained in chloroplasts It is important in enzymes systems associated with oxidation a reduction reactions	Chlorotic condition in leaves, which becomes pale green.
(8)	Manganese	It is a constituent of responsible enzymes or protein synthesis. It is important for certain nitrogen transformation in plants and micro-organism	Young leaves shows pale greenish-yellow discolouration between veins.
(9)	Copper	It is a constituent of certain enzymes It is necessary for photosynthesis It is involved in respiration and utilization of iron	Pale green colour of leaves The tips of older leaves dry off and die Young leaves tip dieback
(10)	Zinc	It is in involved in the action of certain enzymes	Production of mottled of extremely small leaves
(11)	Boron	It is an important nutrient in protein synthesis It facilitates the development of roots It assists in the formation of fruits and seeds It encourages the division of cells in the growing regions of plants It increases yield. It facilitates nodulation in leguminous plants	It causes death of tips of  roots and shoots Failure of flower buds to develop It causes poor growth of plants It causes breaking or lodging. It decreases the rate of water absorption and translocation of sugars.
(12)	Molybdenum	It aids nitrogen fixation acids and proteins. It is an essential part of the enzymatic system involved in facilitating nitrogen change.	Promotes metabolism of nitrates into amino acids and proteins. It causes mottled leaves. It leads to curling and breakdown of leaf edges. It causes premature flower drops.

FACTORS INFLUENCING NUTRIENT AVAILABILITY IN THE SOIL.

 

The factors which influence the availability of nutrients in the soil include the following:

 

1. Soil pH: The degree of acidity or alkalinity of the solid affects the availability of nutrients, both in the soil and also to plants.

1. A low pH (high acidity) will encourage the disintegration of clay minerals like calcium, iron and aluminium, which are leached away from the soil.
2. At high pH (high alkalinity), calcium and magnesium ions accumulate in the soil and this affects the growth of plants.
3. A low pH also reduces the activities of the soil living organisms which aid the decomposition of organic matter.

 

2. Concentration of Other Nutrients.

1. The presence of a certain element(s) in high concentration may prevent the absorption or utilization of other elements.
2. The concentration of nitrogen and phosphorus in the soil results in the non-availability of potassium.
3. This condition results in retarded growth, low yield or even death of the

 

3. Leaching

1. This is the removal of nutrients from the topsoil to the inner parts of the soil beyond the reach of the roots of the plant.
2. It results in the loss of nutrients such as calcium, magnesium, potassium from the topsoil in solution.
3. It also results in the accumulation of aluminium and hydrogen ions which become acidic and toxic to plants.

 

4. Crop Removal.

1. Nutrients are removed from the soil by the crops for growth, development and production.
2. When the crops are harvested, the nutrients are contained in the plants ae never returned to the soil.
3. The rapid removal of nutrients from the soil by continuous cropping completely deprives the soil of such nutrients.

5. Oxidation and Reduction of Organic Material.

1. Some compounds such as ammonium radicals are oxidized to gaseous ammonia.
2. Nitrates are also reduced to molecular nitrogen or oxides of nitrogen by denitrifying bacteria.
3. These products (i.e. ammonium radicals and nitrates) which escape into the atmosphere in the form of gases make the soil poorer in nutrients.

 

6. Burning

1. It exposes the soil to erosion which can wash away plant nutrients in the soil.
2. It burns the organic matter content of the soil, thereby reducing the amount of nutrients in the soil.
3. It kills or reduces the number of soil organisms which aid decomposition of materials, and consequently most nutrients may not be available in the soil.

 

7. Soil Texture

1. Fine texture, such as clay and silt, ensures the availability of nutrients in the soil.
2. But coarse texture like sand prevents the availability of nutrients in the soil.
3. Coarse texture encourages the leaching of nutrients from the soil.

 

8. Erosion

Heavy rainfall causes the washing or carrying away of topsoil which is rich in plant nutrients.

Topsoil can also be blown away by winds, resulting in nutrient reduction in the soil.

 

 

9. Soil Moisture Content.

1. Soil Moisture content determines the level of nutrients in the soil.
2. High level of soil moisture can lead to toxicity of nutrients in the soil
3. High moisture content can lead to soil erosion that can wash away nutrients in the soil.
4.  
5. Very low soil moisture leads to dryness or non-availability of nutrients for plants.

 

10. Level of organic matter/ micro-organisms in the soil

1. High level of organic matter and micro-organisms lead to adequate availability of nutrients in the soil.
2. High level of organic matter ensure availability of water in the soil and vice versa.
3. High level of micro-organisms in the soil ensures good growth for crop plants.
4. High level of organic matter in the soil helps prevent soil erosion.
5. Adequate level of organic matter improves the activities of the micro-organisms in the soil.
6. Organic manure also helps to improve the structure of the soil.
7. It also reduces rapid soil temperature fluctuations.

 

METHODS OF REPLENISHING LOST NUTRIENTS.

 

Different method are used by farmers to maintain the fertility of the soil or replace lost nutrients. These methods include:

 

1. Crop rotation
2. Organic manuring
3. Bush fallowing
4. Cover cropping.
5. Liming
6. Inorganic manuring or fertilizers.

 

1. Crop Rotation

Crop rotation is defined as the planting of different ………………………. Piece of land in a definite sequence. In other words, it is a system of farming whereby different crops are grown in the same piece of land year after year in a definite manner to maintain the fertility of the soil. The cycle is planned in such a way as to restore nutrients removed from the soil. The layout of a four-year crop rotation plan is shown in this table.

 

	Plot I	Plot II	Plot III	Plot IV
Year 1	Yam	Cowpea	Cassava	Maize
Year 2	Cowpea	Cassava	Maize	Yam
Year 3	Cassava	Maize	Yam	Cowpea
Year 4	Maize	Yam	Cowpea	Cassava

                       

                                                                        Crop Rotation System

 

The land is divided into sections, usually between 3 - 6, and each year, a different crop is planted in each section. For example, the land in the table is divided into four sections and in each year, different crops like yam, cowpea, cassava, and maize are planted.

 

Crop rotation as a Method of Replenishing Soil Nutrients.

 

To maintain soil fertility, certain principles of crop rotation must be observed.

 

These are:

1. Deep-rooted crops like yam and cassava should not follow each other because they will absorb nutrients from the same level in the soil.
2. Shallow-rooted crops lie rice and maize should also not follow each other because of the same reason as above.
3. Crops which have the same diseases should not follow one another.
4. Crops which have the same pests should not follow one another.
5. Crops of the same family should not follow one another. This is to prevent the uptake of the same nutrients and also to break the life cycle of pests and diseases that might accompany such crops.
6. Crop rotation helps to control the growth of weeds which tend to remove nutrient from the soil.
7. The inclusion of a legume in crop rotation also adds nutrients to the soil.
8. Crop rotation also helps to control erosion which tends to remove nutrient from the soil.

 

Conditions necessary for the practice of Crop Rotation.

1. Where land is scarce or limited in supply
2. Where the population is high
3. The need to have different varieties of crops
4. The need to maintain soil fertility.
5. Where the soil is exhausted of nutrients.

 

2. Organic Manuring: Organic Manuring involves the application of organic manure to the soil to improve its fertility.

 

Organic Manuring as a Method of Replenishing Soil Nutrients.

Organic manuring as a way of improving soil fertility has the following advantages:

1. It promotes the activities of soil living organisms such as earthworms, termites and microbes. These organisms promotes aeration of the soil, easy percolation of water, mixing organic materials with soil form humus and fix nitrogen into the soil. All these help to promote the fertility of the soil.
2. Organic manure helps to improve the structure of the soil by building the particles of coarse texture soil together.
3. Mineralization of hummus adds nutrients to the soil
4. It reduces rapid soil temperature fluctuations. As a result of its dark colour, humus easily absorbs heat during the day and loses it slowly at night.
5. Organic manure helps to conserve moisture and prevent evaporation from the soil.
6. Organic manure (humus) has a buffering effect on the soil; that is, it balances the acid-base condition of the soil or soil ph.
7. It prevents erosion because it improves the structure of the soil and reduces the speed of the run-off.
8. Organic matter increases the water-holding capacity of the soil.
9. It increases the rate of water percolation through clay soil
10. It increases the activities of soil micro-organism.
11. It improves the aeration of the soil.

All these advantages of organic manure help to maintain or even promote the availability of nutrients in the soil.

 

Organic Manure

Definition: Organic manure refers to the decayed plant and animal products which have been carefully prepared to supply nutrient to plants or crops.

 

Types of Organs manure: There are three types of organic manure. These are (a) Green manure (b) Farm-yard manure (c) Compost manure.

 

1. Green Manure: Green manure is formed from leguminous crops and other fresh plants which are ploughed into the soil while they are still growing. The plants have to be ploughed in when they are very young, i.e. before the flowering stage so that they will decay rapidly to release the nutrients to the soil.

The crops which are suitable for green manure include legumes like mucuna, cowpea, Centrosema, calopogonium, Pueraria and grasses.

 

2. Farm-Tard Manure: Farm-yard manure is a combination of animal waste such as animal dung or faeces, urine and animal bedding which collectively undergo a series of decomposition before the manure is applied to the soil. Poultry birds, generally, produce manure of a higher nutrient quality than larger animals. Large animal like cattle feed on grasses, which are high in fibre content which cannot easily decompose. Pig, goat and sheep also produce manure which are rich in nutrients. Farm-yard manure must be allowed to complete its decomposition before it can be applied to the soil, otherwise, the heat produced during decomposition would burn the roots of crops.
3. Compost manure: Compost manure is the type of manure formed as a result of the rotting down of plants and animal remains in heaps or pits before the residue is applied to the soil.

There are two ways of preparing compost manure. These are:

1. Pit Method: This is suitable for areas where rainfall is low such as in the savanna areas.
2. Stack Method: This is suitable for areas where rainfall is high such as in the south. Both methods require the same materials and duration.

 

The Pit Method

Size of the Pit: The size of the pit will depend on the quantity of the compost needed, but a dimension of 180cm x 120cm x 60cm could be appropriate.

 

Material Required: Three pits (A, B, C) (Fig 18.1 ) are dug. Grasses and legumes – to for compost, ash or urine – to remove traces of acidity, animal dung- to introduce bacteria of decomposition, and a little water- to provide a moist environment for the agent of decomposition.

 

Procedure:  In pitA, a layer of grass and legume is put at the bottom. Then a layer of animal dung is added followed by a thin layer of ash. Water is further sprinkled on the materials to make it moist but not wet. The whole process is repeated. Layers are added in this manner until the pit is filled up. Cover each layer up and place a long stick called a tester at the side.

                                    

PREPARATION OF COMPOST MANURE

 

Check if the operation is successful, by feeling the tester. If the tester is hot, you can continue, but if cold, it means the operation is a failure and the whole process as to be repeated.

        After two weeks, the materials are turned with a shovel and packed into pit B. This turning provides air for the compost so that the bacteria continue to work on the decaying materials. Pit A is filled with fresh materials. After another two weeks, pit B is turned into C and A turned into B. This process continues until the last pit is reached. Compost prepared in this manner can be applied directly to the soil but planting cannot be done; otherwise, the roots pf the seedling may be burnt.

 

3. Bush Fallowing: Bush fallowing is the practice in which farmlands are left to lie fallow after one or two years of cultivation. The purpose of this is to allow nutrients to revert to the soil. When a piece of land is laced on continuous cropping, year after year, the nutrients are completely used up from the soil with replacement.

Fallowing as a Method of Replenishing Soil Nutrients.

1. When land is allowed to fallow, plant food has time to form in the soil as a result of humus accumulation.
2. This system helps to check some plant diseases because when farms are left to fallow for many years, disease organisms lose their hosts and die.
3. Fallowing helps to check erosion.
4. Land becomes relatively cheap to replenish with lost nutrients as farmers may not need fertilizers.
5. Fallowing helps to dislodge pest from farm plot due to the absence of hosts during fallowing.
6. Fallowing also improves soil physical properties like soil structure, texture, etc.
7. Fallowing improves the activities of soil flora and fauna.

The period of allowing the land to rest to re-grow back to bush and rebuild the used-up nutrients is called fallow period.

 

4. Cover Cropping.

Cover cropping is a process of planting certain plants mainly to cover the soil surface. By so doing, the nutrients are conserved in the soil.

 

Some commonly used crops are mucuna, utilise, Pueraria, phaseoloides, (Fig, 18.2), Centrosema, pubescent, crotalaria juncea, calopoginiummucunoides and cowpea. All these are leguminous crops.

 

 

Cover cropping as a Method of Replenishing Soil Nutrients.

 

Cover cropping has many advantages, especially in the recovering of lost nutrients to the soil.

These advantages are:

1. It reduces the erosive capacity of moving water, thus checking erosion
2. It adds organic matter to the soil when dead.
3. Leguminous cover crops increase the nitrogen level of the soil through the bacteria in the root nodules.
4. It increases the water-holding capacity of the soil. That is, it influences soil water supply.
5. It improves soil development
6. Cover cropping suppresses weeds
7. It protects the surface of the soil from the direct heat of the sun
8. It reduces leaching of the soil nutrients
9. It acts as windbreaks and cuts down wing movement.
10. It provides a suitable cover for soil organisms, eg, earthworms and millipede.

 

5. Liming

Liming refers to the process whereby calcium or magnesium-containing compound are added to the soil to reduces soil acidity.

 

Some common limin materials are:

1. Limestone          -              
2. Quicklime           -               CaO
3. Slacked lime       -               Ca
4. Basic slag          -              
5. Dolomite or calcite
6. Calcium bicarbonate
7. Gypsum
8. Wood ash
9.  

Generally, most crops perform well between pH ranges of 6-8.

 

Uses of lime in agriculture

Application of lime helps to maintain soil fertility in the following ways:

1. It helps to reduce or neutralize soil acidity.
2. Lime application helps to increase the activities of soil living organism.
3. Liming makes nutrients like calcium and phosphorus more readily available for tissue development
4. Liming also improves the soil structure.
5. It also increases the availability of phosphate and molybdenum ions.
6. Lime increases the rate of water percolation in clay soil.
7. It reduces the toxicity of dissolved copper and manganese in the soil.
8. It serves as additional sources of calcium for bone development in fish.
9. It reduces turbidity in fish ponds through flocculation property.

 

6. Application of inorganic fertilizers:

Fertilizers are chemical substances generally in the form of powder, granules, pellets or crystals which can be added to the soil to increase its fertility. The use of fertilizers is the surest way of replenishing lost nutrients from the soil and increase the productivity of crops.

Uses of fertilizers in agriculture.

1. Fertilizers help to increase the yield of crops.
2. They improve the structure of the soil.
3. They increase the activities of soil organisms.
4. They improve soil aeration.
5. The increase the fertility of the soil.
6. They increase the growth of planktons in fish ponds.

 

Types of fertilizers.

Fertilizers are grouped into two major classes based on their compositions:

1. Straight or single fertilizers:  These fertilizers contain only one element. Such element may be nitrogen, phosphorus and potassium.

1. Fertilizers which are rich in nitrogen are called Nitrogen fertilizers  and examples include:

1. Ammonium sulphate
2. Ammonium nitrate
3. Urea
4. Sodium nitrate
5. Potassium nitrate
6. Anhydrous ammonia
7. Ammonia liquor
8. Calcium ammonium nitrate
9. Diammonium phosphate.

 

2. Fertilizers which are rich in potassium are called Potassium fertilizers and example is muriate of potash………….
3. Fertilizers which are rich in phosphorus are called Phosphorus fertilizers and examples include

1. Single superphosphate
2. Triple superphosphate
3. Rock phosphate
4. Basic slag
5. Dicalcium phosphate
6. Diammonium phosphate
7. Guano (poultry/bird droppings)

 

2. Complete or Mixed or Compound fertilizers: These are fertilizers which contain two or more nutrients. A good example is N.P.K fertilizer, which contains nitrogen, phosphorus and potassium.

 

Methods of Fertilizer Application.

Different methods are used to apply fertilizers to the soil. These include:

1. Broadcasting: This is the spreading of fertilizers evenly on the ground before they are ploughed in the soil.
2. Ring method: A circular hole is made round the crop and fertilizer is placed inside the hole after which the hole is covered. The circular hole must not come too close to the plant, otherwise, fertilizer will touch the plant and burn it.
3. Row or side placement: Make a hole a few centimetres from each plant and apply a teaspoonful of fertilizer per plant in each hole, then cover it up with soil.
4. Topdressing: This refers to the second application of fertilizer several weeks after the first dose had been applied. The second is to supplement the first application.
5. Folial Spray: This is the method in which some trace elements or micronutrients are dissolved in water and sprayed on the crop directly. The leaves are capable of absorbing the nutrients directly into their body.

WAYS IN WHICH SOIL NUTRIENTS CAN BE LOST.

(1)  Crop Removal:

1. Nutrients are removed from the soil by crops for growth, development and production
2. When the crops are harvested, the nutrients contained in the plants are never returned to the soil.
3. The rapid removal of nutrients from the soil by continuous cropping completely deprive the soil of such nutrients.

 

(2)    Erosion:

1. Heavy rainfall causes the washing or carrying away of topsoil which is rich in plant nutrients.
2. Topsoil can also be blown away in winds, resulting in nutrients reduction in the soil.

 

(3) Leaching:

1. This is the removal of nutrients from the topsoil to the inner parts of the soil beyond the reach of the roots of plants.
2. It results in the loss of nutrients such as calcium, magnesium, potassium from the topsoil in solution.
3. It also results in the accumulation of aluminium and hydrogen ions which become acidic and toxic to plants.

 

(4) pH: The degree of acidity or alkalinity in the soil affects the availability of nutrients both in the soil and also plants.

1. A low pH(high acidity) will encourage the disintegration of clay minerals like calcium, iron, aluminium ions which are leached away from the soil.
2. At high pH(high alkalinity), calcium and magnesium ions accumulate in the soil which affects the growth of plants.
3. A low pH also reduces the activities of soil living organisms which aid the decomposition of organic matter.

 

(5) Excess of other Nutrients

1. The presence of a certain element(s) in high concentration may prevent the absorption or utilization of other elements.
2. The concentration of nitrogen and phosphorus in the soil results in the non-availability of potassium.
3. This condition results in retarded growth, low yield or even death of the plant.

 

7. Oxidation and Reduction of Organic Materials

1. Some compounds such as ammonium radicals are oxidized to gaseous ammonia.
2. Nitrates are also reduced to molecular nitrogen or oxides of nitrogen by denitrifying bacteria
3. Their products i.e., ammonium radicals and nitrates which escape into the atmosphere in the form of gases make the soil poorer in nutrients.

 

NUTRIENT CYCLES

 

Nutrient cycles refer to the circulation of certain nutrients like nitrogen, carbon and water in nature.

 

Nitrogen cycle

Nitrogen cycle involves the complex process by which nitrogen is naturally added and removes from the soil. It is a sequence of reaction, indicating the various means by which nitrogen is added to and removed from the atmosphere and the soil.

 

Importance of Nitrogen cycle.

Nitrogen cycle is nature’s way of regulating the amount of nitrogen in the soil and air. Nitrogen fixation process involves soil organism which add a reasonable amount of nitrogen to the soil.

 

Ways by which nitrogen is added to the soil in the Nitrogen cycle.

These are the ways by which nitrogen is added to soil in the nitrogen cycle.

1. Direct fixation by lightening during rainfall (electrical discharge).
2. Incorporation into the soil by free-living bacteria or non-symbiotic bacteria.
3. Nitrogen-fixing bacteria in the root modules.
4. Decomposition of organic matter.
5. Application of nitrogenous fertilizers.
6. Ammonification
7. Nitrification

 

 

Soil can gain nitrogen through the following.

1. Symbiotic Nitrogen fixation: Some bacteria, such as rhizobium, leguminotarium, which live root module of leguminous plants can fix atmospheric nitrogen directly into the plants. The plants supplies carbohydrates for use by the bacteria, while the bacteria supply the plant with combined nitrogen.
2. Electrical discharge: Nitrogen can also be fixed into the soil during lightening. Nitrogen in the air combines with oxygen to form Nitric Oxide which further undergoes oxidation to form nitrogen dioxide. The Nitrogen dioxide will dissolve in rainwater to form nitrous and nitric acid which later dissociates to form nitrates in the soil.
3. Non-symbiotic nitrogen fixation: Some bacteria such as azotobacter and clostridium also live freely in the soil and can fix atmospheric nitrogen into the soil either aerobically or anaerobically.
4. Ammonification and Nitrification: the process involving the ammonium compounds from dead and decaying plants and animals and their waste products like urine and faeces is called ammonification. A further reaction known as Nitrification involves the conversion of ammonium compounds first to nitrate by nitrifying bacteria Nitrosomonas. These nitrates are converted by oxidation to nitrates by another bacterium called Nitrobacter. Plants can only absorb nitrates from the soil.
5. Application of organic manure and nitrogen fertilizers: These also add or supply nitrogen to the soil.

 

Ways by nitrogen is lost from the soil.

1. By Denitrification: this process involves the conversion of nitrates to nitrogen gas by certain bacteria. The nitrogen gas escapes into the air.
2. Soil erosion
3. Leaching
4. Soil pH
5. Bush burning
6. Crop removal
7. Volatilization
8. Oxidation reaction
9. Reduction reaction.

 

Processes that lead to the formation of nitrates from Organic matter in the Nitrogen cycle.

1. Putrefaction
2. Amminization
3. Ammonification/Mineralization
4. Nitrification.

 

1. Putrefaction: Decay of plant and animal remains into simpler nitrogenous compounds by micro-organisms.
2. Amminization: products from putrefactions reaction converted to simple amino compound and amines
3. Ammonification: Conversion of amines compound and amines into ammonium (NH4+) compound
4. Nitrification: Oxidation of ammonium compound into nitrites and nitrates.

 

Carbon cycles

Carbon cycle involves the series of processes which contribute to the circulation of carbon in nature,

1. Carbon dioxide is removed from the air mainly by photosynthesis during which plants use it to manufacture their food.
2. Carbon is lost in the form of carbonates of calcium and magnesium through leaching and drainage.

The atmosphere gains carbon dioxide through:

1. 1. Burning of fuel like coal and wood.
   2. The action of volcanoes which releases carbon dioxide.
   3. The respiration by plants and animals
   4. The death, decay and putrefaction of plants and animals.
   5. Diffusion of carbon dioxide from seas and other bodies of water, acting as a reservoir of carbon dioxide.

Importance of carbon cycle.

1. Plants use carbon dioxide obtained from the air to manufacture their food during photosynthesis.
2. It provides carbon which is the major building block 0f all organic matters.
3. It helps to purify the atmosphere and also to maintain the atmospheric level of carbon dioxide.
4. Organic matter which is made from carbon helps to replenish the soil nutrient.

Water cycle

Is defined as the continuous movement of water from the atmosphere to the earth and from the earth to the atmosphere.

           

The atmosphere receives water through:

1. Evaporation from oceans and land.
2. Transpiration from plant.
3. Breathing or respiration by plants and animals.

The land receives water through:

1. Rainfall or precipitation.
2. Infiltration and percolation.

Importance of water to crops

1. Water provides the medium for absorption of mineral salt.
2. It facilitates the transfer of nutrients to other parts of the plant where they are used in various metabolic processes.
3. Water is an essential raw material in the process of photosynthesis.
4. It is used hydrolyzing food substances such as starch, proteins, fats and oil for easy transmission to other parts of plants.
5. Water facilitates enzymatic activities occurring in crop plants.

Forms in which water exist in soil.

1. Hygroscopic water
2. Capillary water
3. Gravitational water.

Ways of conserving water in the soil.

1. Stoppage or reduction of surface water runoff.
2. Addition of humus or organic manure.
3. Removal of weeds to reduce transpiration and water loss
4. Mulching
5. Cover cropping
6. Contour ridging
7. Appropriate tillage
8. Strip cropping.

Organic agriculture.

It simply means the use of ruminants and decay of plant and animal by-product to improve agricultural production.

In this regard, the use of artificial chemical like inorganic fertilizer does not constitute which is called organic agriculture.

Forms of organic agriculture.

1. Organic manure; refers to the decay plants and animal products which have been carefully prepared to supply nutrients to plants or crops.

Types:

1. 1. 1. Green manure
      2. Farmyard manure
      3. Compose manure
2. Cover cropping: is a process of planting certain plants mainly to cover soil surface conserving nutrients in the soil.
3. Mulching
4. Crop rotation.

Importance of organic agriculture.

1. It promotes the activities of soil living organisms such as earthworms.
2. It helps to improve the structure of the soil by building the particles of coarse texture soil together.
3. Mineralization of hummus adds nutrients to the soil.
4. It prevents erosion because it improves the structure of the soil and reduces the speed of the runoff.
5. It increases the activities of soil microorganisms