methods to study the mineral requirements of plants

Methods to study the mineral requirements of plants

Soils normally contain sufficient quantities of essential minerals.

However, three important elements need to be replenished in crop fields as they are depleted by repeated cultivation.

These fertiliser elements called critical elements are nitrogen, phosphorus and potassium (NPK).

The common sources of these elements used in India are: nitrate of sodium, ammonium sulphate, ammonium nitrate, ammonium chloride, urea, etc.

The NPK fetilisers comprising bags of fertilisers are labelled 17-18-19 or 15-15-15 or other combinations.

These numbers refer to the percentage by weight of nitrogen, phosphorus and water soluble potassium.

To determine the elements essential for plant growth and deficiency symptoms of an essential element, well defined nutrient medium has to be used.

Seeds are grown in highly washed pure sand in a glass or glazed procelain or plastic container and supplied with a carefully made up nutrient solution.

Arnon and Hoagland's Medium prescribed a medium containing micronutrients.

Iron was earlier supplied as ferrous sulphate, but it often precipitated out.

This problem has now been solved by dissolving the ferrous sulphate along with a chelating agent Na-EDTA (disodium salt of ethylene diaminetetra acetic acid.)

Solution Culture

It is performed in glass jars or polythene bottles.

The container is covered with black paper after pouring solution into them.

Black paper has two functions -(a) Prevention of growth of algae (b) Prevention of reaction of roots with light.

Seeds are allowed to germinate over split cork.

Cotyledons are removed after seedling formation.

The plant is properly supported with the help of split cork.

Solution is aerated at regular intervals and is changed after 2-3 days.

Hydroponics

Commercial technique of soil less culture is called Hydroponics, which was first developed by Goerick (1940).

In 1860, Julius von Sachs, a German botanist, demons rated for the first time, that plants could be grown to maturity in a defined nutrient solution in complete absence of soil.

Culture is performed in large tanks of metal or Reinforced Cement Concrete (R.C.C.) Tanks are covered with wire mesh.

Tanks are provided with aerating and circulating techniques.

Seeds are suspended in solution from the wire mesh with the help of threads.

As plant grows up additional support is provided.

Significance

(i).Useful in areas having thin, infertile and dry soils.

(ii).It can regulate the pH at optimum for a particular crop.

(iii).It controls soil borne pathogens.

(iv).It avoids problem of weeding.

(v).Out of season vegetables (like tomato, seedless cucumber, lettuce) and flowers can also be obtained.

Aeroponics

It is technique of soil-less culture in which roots of plants are suspended in mist of oxygenated nutrient solution.

Sand Culture

In this method, sand is used as a rooting medium and nutrient solution is added to it. It is better than solution cultures w.r.t. providing solid medium and natural aeration for plant. growth. However, this method has following drawbacks:

(i).The sand being highly alkaline in nature, has to be treated with acid before use.

(ii).The sand get very warm during summer and very cool during winters, hence may cause injury to the root system.

(iii).The water holding capacity of sand is very low, hence, it requires freqent watering.