To know the E.C. and pH of your field soil and irrigation water, and to control that E.C. and pH, is the cornerstone to increase in agricultural and related products productivity. Experts advise in a general way to give so many kg per hectares of this and/or that fertilizer for a crop. It pays not to follow that advise without full knowledge of the E.C. and pH before and after application of that fertilizer regimen.
Agriculture is the most important industry. Mankind depends for its survival on this industry. Whether developed or developing country, the aim is always to make agriculture in its various forms and spread more and more productive.
The availability and use of fertilizers per acre in a country is a primary parameter of development for a country. For all the increase in fertilizers taking place in the world, the trend shows that increase in consumption of fertilizers is not linear with increase in productivity.
Why this non linear relationship is happening is mainly due to imbalance of fertilizers in the soil. Research, on Soil and water for their E.C. and pH, as well as inherently available nitrogen, potassium, phosphate and other nutrients, is done for the same. Full knowledge of the E.C. and pH of field soil and irrigation water must be available before deciding on any fertigation regimen. Not considering E.C. and pH and only relying on standard fertilizer application rates causes imbalance in field soil and irrigation water.
There is importance of research and measurement of the E.C. and pH for any particular crop to be produced in a particular type of field soil and irrigation water.
We have introduced two terms here : one is E.C. and second is pH. Let us discuss the terms in a greater detail.
E.C. – ELECTRICAL CONDUCTIVITY :
Whenever a chemical fertilizer is dissolved in water, it would produce electrically charged ions – and more the concentration of fertilizer in water, more would be the number of ions introduced in the solution. The higher the number of ions, higher is the conductivity of the solution. The ions are measured in many ways and a convenient measure is parts per million (ppm) of total dissolved solids. Fertilizers available are generally having more than one chemical each of which ionizes and contributes to the E.C .of the solution. Measurement of E.C. gives us assurance that indeed the correct dosage of fertilizer is present in the Fertigation water.
E.C. meter is used to measure this conductivity of the solution. There are meter which are pure electrical conductivity meter; however, usual method is to use a TDS meter and calibrate the readings using charts to read E.C. In practice, over a period of time, with experience, farmer would know if he has added proper dosage of fertilizer to the Fertigation water. According to generally available crop data, different crops have different requirement of fertilizers and this measurement of E.C./TDS allows the farmers to check if is he adhering to the same standards.
Farmers would generally be advised to have xxx ppm of a particular fertilizer in the irrigation water. An E.C. meter would be used to ascertain that the advised level of ppm fertilizer has been reached.
According to dictionary, pH is a figure expressing the acidity or alkalinity of a solution on a logarithmic scale on which 7 is neutral. Lower values are more acidic and higher values more alkaline. The pH is equal to −log10 c, where c is the hydrogen ion concentration in moles per liter. Solutions with a pH less than 7 are acidic and solutions with a pH greater than 7 are alkaline. Pure water is neutral, at pH 7 (25°C), being neither an acid nor a alkaline.
pH is a dimension less quantity.
The United States Department of Agriculture Natural Resources Conservation Service, formerly Soil Conservation Service classifies soil pH ranges as follows:
(this part is taken from Wikipedia.org)
|Ultra acidic||< 3.5|
|Very strongly acidic||4.5–5.0|
|Very strongly alkaline||> 9.0|
Typical pH values in living cells
|Granules of chromaffin cells||5.5|
|Blood (natural pH)||7.34–7.45|
|Cerebrospinal fluid (CSF)||7.5|
Need for knowing E.C. and pH of soil and water
So that is some discussion on what is pH based mainly on information existing on Wikipedia and other sources. The farmer uses this value of pH to ascertain:
- The Fertigation solution suitability for the crop concerned, and
- The soil suitability for the crop concerned.
For example, a crop may require pH value between 6.6 to 7.4 for the soil. The farmer would then mix fertilizers to see that soil gets this pH value by what ever fertilizers he is giving to the crop. This is because different types of fertilizers have differing pH values (please refer to fertilizers and Fertigation sections). Use of acids and base materials would also be required to tune up the soil.
- Litmus Paper is the earliest method to check the acidity or alkalinity of a solution. Putting a drop of solution on the litmus paper if color turns red then it is acidic solution; if color turns blue then it is alkaline solution. If there is no color change then solution is neutral.
- A number of pH meters are available in the market to measure this quantity. At the bottom and also most used is the pen type pH meter. In line pH meters are used in drip systems so that farmers have a ready hand on maintaining and correcting the pH by controlling the Fertigation process through different types of fertilizers.
Measurement of E.C. and pH of Soil:
There are a number of soil laboratories available to the farmer and these labs would provide analysis of not only the E.C. and pH of the soil but also provide how much of essential nutrients are present in the soil. This analysis is very helpful as the Fertigation would take care of any deficiencies in the soil.
Additionally soil testing kits are also available in the market. Though these kits do not provide as wide an analysis the soil laboratories, but they do inform farmers about the major nutrients in the soil besides the E.C. and pH values. They are useful in case soil laboratories are far away or take time for analysis.
Soil E.C. and pH can be easily measured by the meters available commercially. The farmer needs to have a control reading and then make comparison for every next time test readings. The soil is taken from different locations of the field, mixed up, dried and powdered. Then either a 1:2 soil water mixture is made or 1:1 mixture is made (it is important that for next readings the same mixture ratio is kept). This soil and water mix is allowed to settle and then the water on top drained into a beaker and tested for E.C. and pH.
It is necessary to keep the hand held meters maintained properly as per the manufacturer’s instructions and to keep the calibrated from time to time.