What, Why and How

Process of Fertigation

When we wet our field through directly from well or canal water, water flows forcefully over the surface and depending on the force would cover the surface faster but penetration into the soil would be much less. With development of drip systems localized water irrigation is possible. In the drip method water falls drop by drop therefore surface covering is less and penetration into the soil and root zone is more.  This trickle irrigation then restricts development of root zone to the wet zone. And this has enabled modification to the age old methods of fertilization management.

Fertigation, as the name implies, is the process in which fertilizers are being applied with the irrigation water: Fertilization + Irrigation.  The fertilizers are  dissolved complete in irrigation water in advance, kept in stock tanks and then delivered to soil. Fertigation also implies use of drip system for delivery of irrigation water. Advantages of the fertigation method over other fertilization methods  are:

Advantages of Fertigation

  • Fertilizer application is more accurate and uniform
  • Fertilizers are applied to specific areas, where they are needed
  • Nutrient are immediately available to plants
  • Uptake of nutrients by roots is improved
  • It using lower rates of fertilizer
  • It saves labor
  • It helps to save water, because plants develop a healthier root system
  • Nutrient losses are minimized

Factor consideration for Fertigation

  • Fertilizers compatibility with each others.
  • Fertilizers solubility in water or other media.
  • Types of fertilizers to be used whether dust, solid or liquid.
  • Number of stock tanks.
  • Injection ratio or injection time.
  • The use of chelates.
  • Interaction of fertilizers with water (endothermic reactions,  reactions with elements present in water).

Interaction in Fertilizers

Some fertilizers interact to form insoluble compounds and precipitates. This causes clogging in drip lines and also obstruct nutrients. For example calcium containing fertilizers mixed with sulfates or phosphates would form insoluble compounds. Solubility of fertilizers in water also means that more than that fertilizer can not be mixed in water otherwise precipitation would occur. Generally, solubility increases with increase in temperature of water. To obviate precipitation, the exact number of stock tanks needs to be provided so that incompatible fertilizers are stored separately and injected separately in the drip lines. As an example, farmer needs to fertilize with MAP, Calcium Nitrate, Magnesium sulfate and Potassium nitrate then 3 tanks would be required: 1. Tank for MAP 2. Tank for calcium nitrate + potassium nitrate and 3. Tank for Magnesium sulfate.

Solubility of Fertilizers

Solubility of fertilizers gm/liter indicative figures only
Fertilizer / Temperature (C˚) 10 20
Potassium nitrate 170 209
Ammonium nitrate 1510 1920
Ammonium sulfate 730 750
Calcium nitrate 1130 1290
Magnesium Nitrate 690 710
MAP (Mono Ammonium Phosphate) 295 374
MKP (Mono Potassium Phosphate) 180 230
Potassium chloride 238 255
Potassium sulfate 90 111
Urea 850 1060

Fertigation Methods

There are two  fertigation approaches: the Quantitative Fertigation and the Proportional Fertigation. There is of course a simpler method by putting the fertilizer tank above ground and then fertigation takes place through drip lines with gravity. This is not considered here.

The quantitative approach is commonly used in open fields. The grower first decides how much fertilizer has to be applied per area (e.g. kg/ha, lbs/acre). This quantity of fertilizer  is then delivered through the irrigation water. A bypass fertilizer tank is a simple method for fertigation in this method. Initially the concentration of nutrient is greater and decreases as water irrigation continues.

The proportional approach is the choice of most persons. Here, a defined quantity of fertilizer stock solution is injected into each unit of water flowing  through the irrigation system., lbs/gal).

A bypass tank            and             a Ventury Injector

Nutrient Levels

Nutrient levels are determined by their concentration in the irrigation water. Most growers who use fertigation, use units of ppm (parts per million) or mmol/l.  the farmer here is concerned only with concentration of nitrogen in parts per million (ppm) without regard to area of cultivation whether in sq. feet, sq. yd or sq. m. etc. this ppm method means fertigation is applied at every or nearly every water irrigation.  The lb/Area is utilized when fertigating crops spread over the field and here the actual area is calculated. Say the farmer thinks that 100 kg/total area is required by his crop so he could do so by giving 20 kg/week for 5 weeks or 10 kg/week for 10 weeks.

TIMING of fertigation

Fertigation should start after all the drip lines are full with plain water. After fertigation is over, plain water should be run through drip lines so as to clear away all fertilizers from the drip lines. Run acid through the drip lines occasionally to clear the drip lines and drip points.

The following timings would be helpful:

  • Time taken by water from start to reach the furthest emitter say 15 minutes
  • Time from injection of fertigation say 30 minutes
  • Time taken for fertilizer to reach the last emitter say 15 minutes
  • Time taken to flush the drip lines say 15 minutes

Thus total time for fertigation cycle is 75 minutes. Now if it takes a total of 90 minutes to fully irrigate with water, then the fertigation should be after 15 minutes after the irrigation cycle.

Effect of fertigation on soil pH

Basic fertilizers like calcium nitrate, sodium nitrate would increase the pH of the soil; neutral fertilizers like potassium chloride, potassium nitrate, potassium sulfate would have no effect and acidic fertilizers like sodium nitrate, ammonium  nitrate, DAP, MAP and urea would decrease the pH of the soil.  For irrigation pH range of 6.5 to 7.5 is considered ideal.

Also see:  Method to calculate right amount of fertilisers

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