In this article we will discuss about:- 1. Meaning and Need of Fertigation 2. Forms of Fertilizers for Fertigation 3. Schedule 4. Method 5. Care 6. Advantages 7. Constraints.
Meaning and Need of Fertigation:
Fertigation implies the application of fertilizers through pressurized systems; thus forming nutrient containing irrigation water desired concentration as per the crop need. It is a controlled system to supply irrigated greenhouse vegetable crop with soluble plant nutrients at the root zone.
Fertigation facilitates optimization of nutrient supply adjusted to the specific requirements of the crops at different stages of growth and development. The right combination of water and fertilizers have key role in greenhouse vegetable production for good quality and productivity. In most of the advanced countries, the fertigation has become a standard practice of fertilizer application in greenhouses.
Need of Fertigation:
After realizing the importance of drip irrigation system, the next most essential input remains to boost the production of vegetables is fertilizer. The use of balanced fertilization at appropriate time and of proper quantity plays a vital role in enhancing the productivity of greenhouse vegetables.
At present, the farmers are using the conventional fertilizers of different grades which are not completely soluble in water and hence, it is unsuitable for fertigation. The high salt index of most conventional fertilizers often restricts their use in sensitive vegetable crops.
Existing fertilizers are generally applied manually by broadcasting, which is often labour intensive.
Furthermore, with the introduction of drip irrigation system, the traditional fertilizer application methods such as basal application and broadcasting have become rather old. The limited root zone and reduced level of mineralization in the restricted wet zones are the main reason for the reduced nutrient availability to the plants. The annual application of the fertilizer need is splitted into one to three doses.
Therefore, the major parts of the fertilizers are wasted without fulfilling the plant nutrient requirement. Moreover, these fertilizers are lost to areas beyond the active root zone and are no longer useful to the plants. It is generally recognized that out of total fertilizer application only about 50-60 per cent of the total nutrients enter the plant system and the rest is wasted either by leaching or volatilization.
Forms of Fertilizers for Fertigation:
The availability of 100 per cent water soluble solid or liquids is essential if it is to be applied through fertigation. The fertilizers which are traditionally available in the market are not completely soluble in water and also contain some non-soluble solids which make them unsuitable for application through drip irrigation system.
(a) Liquid Fertilizers:
These are solutions which contain one or more plant nutrients in liquid or suspension form. Ideally, there should be basic solution compounds containing plant food elements suited to the crop need and “tailor made” to farm requirements. At present, liquid fertilizers are not popular in India as compared to most advanced countries as the elaborate infrastructure needed for the transportation, storage, handling, distribution and application of these fertilizers is not very well developed.
(b) Water Soluble Fertilizers:
The wholly water soluble fertilizers are present in solid form which are completely soluble in water carrying two or more major as well as micro- nutrients traced as alternative to liquid and conventional fertilizers.
(c) Suitable Conditions for Fertigation:
The factors affecting the fertigation involve the irrigation system, quality of water, solubility of fertilizers and compatibility of fertilizers. The most suitable method for fertigation is drip irrigation system. The most important criteria for the suitability of an irrigation system for fertigation is accuracy of water application which largely depends upon proper designing and installation of drip system and availability of correct equipment for injecting fertilizers.
The efficient use of fertilizers requires access to information on soil fertility and understanding of nutrient balance in soil. Water is an ideal carrier of fertilizers and rain water is most suitable for irrigation. Water having a pH of 5.5 to 6.5, EC less than 0.1, low level of carbonate, bicarbonate, sodium, chlorine and free from heavy metals considered good for irrigation.
The solubility and purity of fertilizers must be considered when using solid fertilizers to prepare fertilizer solution. The grower must consider compatibility with other fertilizers and the irrigation water when combining fertilizer materials. Several factors may inhibit proper mixing of a solution because improper mixing may lead to inconsistent, incorrect nutrient concentrations and/ or irrigation system plugging.
The following basic mixing rules of compatibility may be adopted for efficient fertigation:
(i) Always fill the mixing container with 50 to 75 per cent of required water to be used in the mix.
(ii) Always add the fertilizer materials to the water in the mixing container before adding dry solid fertilizers. The additional fluid will provide some heat in case the dry fertilizers have the characteristic of making solutions cold.
(iii) Always add the dry ingredients slowly with the circulation or agitation to prevent the formation of large, insoluble or slowly soluble lumps.
(iv) Always put acid into water, not water into acid.
(v) Never mix an acid or acidified fertilizer with the chlorines, whether the chlorine is in gas form or in liquid form such as sodium hypochlorite. A toxic chlorine gas will form. Never store acids and chlorine together in the same room.
(vi) Do not attempt to mix anhydrous ammonia directly with any kind of acid. The reaction is violent and immediate.
(vii) Do not attempt to mix concentrated fertilizer solutions directly with other concentrated fertilizer solutions.
(viii) Do not mix a compound containing sulphate with another compound containing calcium. The result will be mixture of insoluble gypsum which can clog drip emitters or filters.
(ix) Always check with chemical supplier for information about insolubility and incompatibility.
(x) Since fertilizer solutions are applied in very small doses, and if injected in separate locations in the irrigation line, many incompatibility problems tend to disappear. The jar test is essential when it comes to deciding if solutions can be simultaneously injected into the irrigation system.
(xi) Do not mix phosphorus containing fertilizer with another fertilizers containing calcium without first performing the jar test.
(xii) Never use extremely hard water because it combines with phosphate, neutral polyphosphate or sulphate compounds to form insoluble substances.
Fertigation Schedule:
For deciding irrigation schedule of any crop, basically soil analysis and later on leaf analysis are necessary. This offers an opportunity to correct the nutrient status of plants regularly and thus protecting plants from nutrient deficiencies. Most important factor to work out fertiagtion schedule is specific crop needs. If plant gets balanced nutrition at all stages of growth and get the best ratio in feeding programme, it will grow fast and yield more.
It is universal truth that the requirement of micro-elements as well as trace elements varies with the growth stages of crop. For the balanced nutrition, therefore, it is essential to have knowledge regarding different growth stages of the crop and their nutritional requirement. High levels of nitrogen are required during the first 20-30 days after planting to promote vegetative growth.
Its requirement is less during the reproductive period. The requirement of phosphorous is high during 30-40 days after flowering as it promotes fruit bud formation, flower induction and fruit set. Potash requirement is very high during crop maturity stage for fruit ripening. Once it is understood then it will be helpful for selecting the water soluble fertilizer grades and their combinations to have a good quality produce.
The following points must be considered while deciding the fertigation schedule:
(i) Total nutrient requirement of crops to produce target quality yield.
(ii) Part of nutrient supplied in the form of organic matter/green manuring to the soil.
(iii) Envisaged saving in the nutrient doses through fertigation.
(iv) Relative requirement of the nutrients at different growth stages of crop and fruit.
Method of Fertigation:
There are number of techniques which can be used to add fertilizers into the irrigation system. These may be drip irrigation, micro-sprinklers, micro-jets or sprinkler irrigation. While fertigating, it should be ascertained that the optimum concentration is maintained taking into consideration the crop reaction.
The 100 per cent water soluble solids and liquid fertilizers are to be added into bucket full of water. Fertilizers and water can be mixed in water tank. This mixture is then required to be mixed for five minutes prior to its use by any of the methods mentioned above.
Fertilizers can be added into drip irrigation system by selecting appropriate equipment from a wide assortment of available pumps, valves, venturies, etc. The size and the capacity of the addition system depend upon the concentration, grade and frequency of application. Normally, less fertilizer solution and more frequent application require smaller and less costly units.
The equipments used for fertilizer application are described as under:
(a) Ventury:
The system of injection is of very low cost, grid works by creation of a practical vacuum in the system and suction of the fertilizers into the irrigation stream. The vacuum is created by diverting as percentage of water from the main line and passing it through a construction, which increases this velocity of flow, thus, creating a drop in pressure. When the pressure drops, the fertilizer solution is sucked into the ventury through a suction pipe. It is simple and inexpensive method of fertilizer application.
(b) Fertilizer Tank:
In this system a part of irrigation water is diverted from the main line to flow through a tank containing fertilizer in fluid or soluble solid forms, before returning into the main line. The pressure in the tank and main line is the same, but a slight drop in pressure is created between off-take and return pipes for the tank of a pressure-reducing valve. This causes dilution and flow of diluted fertilizers into the irrigation stream.
(c) Fertilizer Injector:
These are piston or diaphragm pumps, which are driven by the water pressure of the irrigation system, and as such injection rate is proportional to the flow of water in the system. A high degree of control over the fertilizer injection rate is possible and no serious head losses are incurred. Another advantage is that if the flow of water stops, fertilizer injection also automatically stops. This is the method of fertilizer dosing for most situations.
Special Care during Fertigation:
i. Fertilizer tank or piston pump may be used to inject water soluble fertilizer solution.
ii. For precise placement of both water and fertilizer, it is necessary to use pressure compensating drippers instead of micro-tubes.
iii. If it is not possible to apply doses daily in that case an alternate day, dose must be ensured.
iv. Necessary changes in the schedule can be made based on soil/petiole analysis results.
v. Fertigation should be done in the last half an hour of the total irrigation period and then continue drip system for another about 5-6 minutes after completion of fertigation.
vi. The concentration of the solution should never exceed more than 10 per cent.
Advantages of Fertigation:
(i) Fertilizers are completely dissolved in water leaving no precipitate. Therefore, there is absolutely no problem in fertigation clogging of drippers and emitting pipes.
(ii) Every plant irrigated received a regular flow of both water and nutrients directly in the root zone resulting in improving growth and increasing the productivity. Over two fold increases in yield is possible due to correct fertigation schedule.
(iii) Nutrients can be applied as and when required to meet specific crop nutrient demand. Also fertilizers can be applied at a predetermined time according to the critical growth stages of crops.
(iv) Since the nutrients directly reach to rhizosphere in liquid form so there is no loss of nutrients, especially through volatilization.
(v) The fact that three major and micro-nutrients are supplied in one solution to plants, it gives better root absorption and consequently higher yield and good quality.
(vi) Safer application methods eliminate the danger of burning the plant root system, as the fertilizer is greatly diluted in the irrigation water.
(vii) Since these fertilizers can be applied through drip irrigation through Ventury Fertilizer Tank or Injection Pump, the application becomes very simple than any soil application of fertilizers and thus results in saving labour, time, energy and overall application cost.
(viii) Due to frequent application in small doses, the amount of fertilizers present in the soil at any time is small which prevents losses from leaching and run off during heavy rainfall. This results in saving of nutrient requirement per unit area which, ultimately results in saving in quantity of fertilizers nearly 25 to 50 per cent of recommended level.
(ix) Wide range of compatibility of most soluble fertilizer grades facilities concurrent incorporation of fungicides, pesticides and nematicides which helps saving in labour, time, energy and the application cost.
(x) Since most soluble fertilizers are blended with chelated micro-nutrients, there is no necessity to go for additional micro-nutrient mixture or sprays which ultimately helps in reducing the additional cost on labour and mixtures.
Constraints of Fertigation:
Despite the vast advantages the fertigation is yet to be popularized in India.
The major constraints faced by farmers are as follows:
(i) Non-availability of liquid fertilizers at reasonable rates.
(ii) Lack of R & D efforts in developing fertilizers for fertigation.
(iii) Inadequate policy of government for promoting the use of fertigation technology.