Soil fertility and management (…continued)

Class: JSS2

Subject: Agricultural Science

 

Objective

By the end of the lesson, student should be able to;

1.      List the advantages of fallows and cover crops and disadvantages of the fallow system.

2.      Explain the types of fertilizers and advantages/disadvantages where applicable.

3.      Cite examples of inorganic chemical fertilizers.

4.      Explain application of fertilizer.

 

 

Day One:

 

Advantages of Fallows and Cover Crops

a.       During fallow periods, plant nutrients build up in the soil as a result of the formation of organic matter.

b.      Fallowing is designed to clear the land, leaving it free of pests, diseases and weeds.

c.       Fallowing is also relatively cheap because no extra costs are incurred in applying fertilizers.

Some major disadvantages of the fallow system

a.       It encourages repeated land clearance which involves energy, time and in the process, valuable forest areas will be destroyed.

b.      During clearing and burning, loss of humus and soil fertility occurs.

c.       After clearing, the soil is left bare and this encourages soil erosion.

 

Day Two:

Fertilizers

Whenever a crop is harvested, there is considerable loss of nutrients from the soil. Nutrients may also be lost from the soil due to erosion or leaching. The best and quickest way of replacing plant nutrients lost from the soil is by adding fertilizers which may be in the form of animal and plant refuse (organic manure), or chemical manure which are also known as inorganic fertilizers.

 

Organic Manures

a.     Green manure

You have learnt that leguminous plants such as beans, mucuna and peas have swellings on their roots which are called nodules. These nodules contain tiny microorganisms on their roots which are known as nitrogen-fixing bacteria. Land which has become deficient in plant food is planted with green manure plants. Before the next crop is planted, the green manure plants are uprooted and covered with the soil. If manure is exposed, the heat of the sun may change it and reduce its value as plant food. Availability of moisture is essential for rapid decomposition of green manures. Therefore under stable rainfall conditions, green manuring can be useful for the maintenance of soil fertility.

One major disadvantage of green manuring is that this method is short-lived. Consequently, green manure crops must be grown frequently in the rotation program to maintain crop yields. It is also not practicable to maintain fertility with green manure crops alone, hence other methods are used to supplement this method of soil fertility management.

b.    Farmyard manure

Farmyard manure consists of faeces of excreta, urine and other waste products of livestock and other domesticated animals. These are known as animal droppings. Together with a bedding of grass, animal droppings are deposited in a shaded place or pit which has been specially prepared for this purpose. New layers of grasses and droppings are continually added until a heap of a mixture of droppings and grass refuse has been formed. Later the heap decomposes and rots through bacterial activity to form a rich, cheap source of manure. Farmyard manure contains all the essential plant nutrients. It can be produced cheaply and easily on the farm. It acts for a long time in the soil, improves soil structure and readily absorbs and retains moisture.

 

The disadvantages of farm yard manure are:

        i.            Preparation of farmyard manure requires plenty of labour for spreading on the farm.

      ii.            It can also encourage rapid weed growth.

 

c.      Compost

The best manure consists of rotten animal and plant refuse usually prepared in compost pits. To make compost, all refuse including crop residues from the farm and household refuse are thrown into a pit which is covered with a layer of soil and watered. When this pit is full, more pits are dug and filled in the same manner. The compost heap should be turned over three times at intervals of two –four weeks so that all the materials become well decomposed. Each heap should be kept moist to encourage rapid decay by bacteria. Compost pits should be sheltered from the heat of the sun and heavy rain. When the compost is well rotten, it is dug up and used in the farm. Composting is a valuable practice because of the nutrients it supplies to crops. Compost also promotes the activities of earthworms, termites and microbes in the soil, all of which are beneficial in maintaining the fertility of agricultural soils.

 

Day Three:

Inorganic Chemical Fertilizers

Inorganic fertilizers are chemical substances which are usually prepared in the form of liquids, powders, granules, pellets or crystals. Two kinds of fertilizers can be identified according to whether they contain either one or more of any of the three major nutrients namely, nitrogen (N), phosphorus (P); and potassium (K).

        i.            When fertilizers contain only one of the three major nutrients, they are referred to as single, simple or straight fertilizers. These fertilizers are further divided into three classes according to the major nutrient they contain. When nitrogen is the major nutrient it is called nitrogenous. When it is phosphorous, it is called phosphatic fertilizer. When potassium is the major nutrient it is called potash or potassium fertilizer.

Examples of nitrogenous fertilizers are ammonium sulphate, ammonium nitrate, urea, sodium nitrate, potassium nitrate.

Examples of phosphatic fertilizers are single superphosphate, triple superphosphate.

The major potash fertilizers are murate of potash, sulphate of potash, potassium nitrate, potassium magnesium sulphate.

The second kind of chemical fertilizers are usually referred to as compound or mixed fertilizers such as a combination of nitrogen, phosphorus and potassium, shortened to NPK. When only two of the major nutrients are mixed, we have NP or potassium PK.

 

Day Four:

Application of Fertilizers

Fertilizers are generally applied to the soil before sowing or planting and during crop development at intervals of 114-21 days. The time interval depends on the type of soil and the requirement of plant.

Two main methods are commonly recommended for the application of fertilizers.

a)      Broadcasting; and

b)      Localized placement in the row or in a circle around the plant.

Broadcasting involves mixing the fertilizer thoroughly and uniformly with the topsoil. It may be left on the soil surface or ploughed into it. Broadcasting could be done before ploughing and planting. The fertilizer should not come in contact with the plant roots because it can burn them.

For larger crops such as cocoa or oil palm and citrus, localized placement of fertilizers is usually recommended.

The use of fertilizers results in increases in the yields of crops and subsequently, more food becomes available for sale and consumption.

 

 

Liquid and solid fertilizer application (sourced online)

Day Five:

Home Work

 

1.      List three advantages and disadvantages of fallow system.

2.      Explain organic and inorganic fertilizers with examples.

3.      What do you know about fertilizer application?