Fertilizers

When ever a crop is harvested there is considerable loss from the soil. Nutrients may also be lost from the soil die to erosion or leaching. The best and quickest way of replacing plant food lost from the soil is by adding manure which maybe in the form of animal and plant refuse (organic manure) , or chemical manures which are known as inorganic fertilizers. To derive maximum benefit from manure, it should not be left on the soil. If manure is exposed, the heat of the sun may change it and reduce its value as a plant food.

Types of Organic manures

Green manuring

In one of my write up on fallows and cover crops, we learnt that leguminous plants such as beans, mucuna and peas have swellings on their root which are called nodules. These nodules contain bacteria which can make nitrogen. Land which has become deficient in plant food is planted with green manure plants. Before the next crop is to be planted, the green manure plants are uprooted ad covered with the soil. The green manure then rots and forms humus.

   Moisture availability is essential for rapid decomposition of green manures. Thus, under stable rainfall conditions green manuring can be useful in the maintenance of soil fertility. 

   A major disadvantage is that this method is short lived, consequently , green  manure crops must be frown frequently in the rotation programme to maintain crop yields. It is also not practicable to maintain fertility with green manure crops alone, hence other methods are used to supplement their effect.

Farmyard Manure

Farmyard manure consist of faeces, or excreta, urine and other waste product of domesticated animals. These are know n as animal droppings. Together with a bedding of grass, animal droppings are deposited in a shaded place 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. In the course of time, decomposition and rotting occurs through bacterial activity and eventuality a rich, cheap source of manure is formed.

   Farmyard manure contains all the  plant nutrients. It can be produced cheaply and easily on the farm. It last long in the soil , improves soil structure and readily absorbs and retains moisture. Preparation, however , requires much labour during spreading on the  farm. It can also encourage rapid growth.

Composting

The best manure consists of rotten anima and plant refuse and is usually prepared in compost pits. To make compost, all refuse including crop residues from the farm SNF 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 three times at intervals 2-4 weeks to get all the materials decomposed. Each heap should be kept moist to encourage rapid decay by bacteria. Compost pits should be sheltered from the strong heat of the sun and heavy rain. When the refuse is well rotten it is dug up and used in the farm. Composting is a worthwhile practice became of the nutrients it supplies to crops. Compost also promotes the activities of earth worms, terminates and microbes in the soil.

Inorganic chemic fertilizers

Inorganic fertilizers are chemical substances which are usually prepared in the forms 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 three major nutrients namely, nitrogen. (N) , phosphorus (P) and Potassium (K). When they contain only one of the three major nutrients, they are referred to as single, simple or straight fertilizers. 

These fertilizers are further divided into 3 classes according to the major nutrient they contain. When nitrogen is the major nutrient it is called nitrogenous. When it is phosphorus it is called phosphatic fertilizer. When potassium is the major nutrient it is called potash or potassium fertilizer.

  The second kind of 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 ha e NP or NK or PK.

Examples of nitrogenous fertilizers are :

    Ammonium sulphate, ammonium nitrate, urea, sodium nitrate, potassium nitrate.

Examples of phosphatic fertilizer are :

     Single superphosphate , triple superphosphate.

The major potash fertilizers are : 

     

     Muriate of potash (KCI), sulphate of potash, potassium nitrate, potassium magnesium sulphate.

Storage and  Handling of fertilizers

Fertilizer Application

Fertilizers are generally applied to the soil before sowing or planting and during crop development at intervals of 14-22 days. This time interval depends on the type of soil and the requirements of the plant.

   There are two main methods recommended for the application of fertilizers.

(a) Broadcasting , and 

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

Broadcasting involved mixing the fertilizer thoroughly and uniformly with the topsoil. It maybe 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 brings about an increase In the yields of crops and subsequently more food becomes available for consumption.