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Hydroponics

Drip System in Hydroponics:

A hydroponic drip system is rather simple. A drip system works by providing a slow feed of nutrient solution to the medium. Slow draining medium, such as rock wool, coconut coir, or peat moss are recommend. For faster draining medium a faster dripping emitter must be used. It is arranged for delivering nutrient rich water equally to all the plants in the shed. Water is pressurized for optimum delivery to all plants especially at the end of the lines.

Drip systems are perhaps the most widely used type of hydroponic system in the world. Operation is simple, a timer controls a submersed pump. The timer turns the pump on and nutrient solution is dripped onto the base of each plant by a small drip line. The disadvantage of this system is that the drippers/emitters are prone to clogging. Although it is an effective method, if the clogs are avoided. Clogging occurs because some particles from nutrients build up in the emitter. Systems that use organic nutrients are more likely to have this kind of issue.

A recovery system uses nutrient solution a bit more efficiently, as excess solution is reused, this also allow for the use of a more inexpensive timer because it doesn’t require precise control of the watering cycles. The non-recovery system needs to have a more precise timer so that watering cycles can be adjusted to insure that the plants get enough nutrient solution and the runoff is reduced.

While non-recovery system requires less maintenance due to the fact that the excess nutrient solution is not recycled back into the reservoir, so the nutrient strength and pH of the reservoir will not vary. This means that you can fill the reservoir with pH adjusted nutrient solution. A recovery system can have large shifts in the pH and nutrient strength levels that require periodic checking and adjusting.

Media Carrier:

Media carrier can be of any shape and size. However plants must be provided with a suitable and sufficient space for optimum growth and development. More space per plant is no doubt beneficial but this practice reduces the number of plants per unit area. Different types of carriers can be used.

Slab

It is a plastic bag measuring 102 x 20.32 x 7.62 cm, filled with any substrate or growing material weighing 1.7 kg.

Pipe

Plastic bottles of 2.5 can be used. Inverted and cock removed bottles are used. A virus-net is wrapped around its neck, and filled in the same manner as in the pipe above and buried into the soil. Bottles selection as carrier is cost effective. Lower most 7.5 cm of the bottle are filled with zero-grade stone crush to facilities drainage. Top 7.6 cm of the bottle are fixed with rock-wool and the remaining 17.9 cm of 33 cm long bottle are filled with substrate. All the materials are sterilized before filling with growing media. All the substrates and carriers work with a varying degree of success, however indigenous coco filled slab is most cost effective.

Bottles

Plastic bottles of 2.5 can be used. Inverted and cock removed bottles are used. A virus-net is wrapped around its neck, and filled in the same manner as in the pipe above and buried into the soil. Bottles selection as carrier is cost effective. Lower most 7.5 cm of the bottle are filled with zero-grade stone crush to facilities drainage. Top 7.6 cm of the bottle are fixed with rock-wool and the remaining 17.9 cm of 33 cm long bottle are filled with substrate. All the materials are sterilized before filling with growing media. All the substrates and carriers work with a varying degree of success, however indigenous coco filled slab is most cost effective.

Nursery Raising and Planting:

It is an important step in hydroponic farming. The seed and the young seedling must be provided with good environment. The selected seed is pushed slightly into a rock-wool plug and gently placed into the tray. The seed sprouts 3-4 days after planting and during this period seed is given light spray of nutrient rich water. When the seedling grow to 2-leaf stage, the plug is shifted into rock wool box.

The seeds are generally kept for 15-20 days in the rock wool box and nutrient water is continuously spread over it. The rock wool box is shifted over to the gutter and irrigation is through drip system and they complete rest of their growth period by developing their root system. The irrigation is applied 10-12 times during winter and 16-20 times during summer season.

Harvesting:

The ripened crop is harvested manually using clippers by the workers. Later the harvested crop is sorted for various sizes and packed for marketing. Appropriate sorting and packing increases the market value of crop. For exportation of the vegetables ISO certifications are required, that a farmer may receive through a consultant.

Plant Nutrition Management:

Water Quality for Hydroponics:

Poor quality water can cause toxicity problems, diseases, pH disorders and blockage of drippers and supply lines. The important factors associated with water quality include:

  • Total dissolved salts (TDS)
  • pH and Alkalinity
  • Hardness

Total Dissolved Salts (TDS)

The majority of the total salts in natural waters consist of common ions like sodium, potassium, calcium, magnesium, carbonates, bicarbonates, chlorides and sulfates. Sodium and chloride ions consistently dominate and become toxic to plants when present above certain levels. The high total salt content (EC) in water causes wilting of leaves and stems followed by, reduced plant growth, scorching around the leaves edges leading to leaves dropping and shoots die back. These symptoms are also indicative of other problems such as water unavailability, disease, malnutrition and excessive light or heat. The level up to which a crop can tolerate salts depends on the ionic composition of water and the type of crop to be grown.

pH and Alkalinity

Carbonates and bicarbonate (CO32- & HCO3-) are alkaline and therefore uplift water pH. Generally, it is the presence of carbonates and bicarbonates which is a major cause of pH increase in nutrients solution. For this reason, it is necessary to check the pH of the nutrient solution from time to time (weekly) or whenever high alkalinity water is added. Alkalinity is removed by lowering the pH with an acid typically phosphoric or nitric. It is advised that for stable adjustment of pH of the water having high alkalinity, solution must be aerated to remove the CO2 prior to its use.

Hardness

Hardness indicates the combined concentrations of calcium and magnesium in water. The calcium level may become excessive after several additions of top-up water when hard water is used in recirculating systems. This result in the formation of a white precipitate (calcium sulfate) which may block plumbing components such as pipes and drippers. It can be minimized by maintaining the pH level below 6.0. High hardness is often associated with waters having high pH. Hardness typically originates in the groundwater from the limestone (calcium carbonate). When the limestone is attacked by the CO2 dissolved in rainwater, these deposits are slowly dissolved and produce hardness and alkalinity.

Essential Nutrients:

Seventeen plant nutrients are essential for crop growth and development. They are equally important to the plant, but are required in enormously different amounts. These differences have led to the grouping of these essential elements into three categories. Nitrogen, phosphorus and potassium are the primary macronutrients because they are most frequently required in a crop fertilization program. They are also required in large quantity by plants. The secondary macronutrients are calcium, magnesium, and sulphur. The micronutrients such as boron, chlorine, cooper, iron, manganese, molybdenum, and zinc are used in very small amounts, but they are just as important to plant growth and development. Especially, they work as activators of many plant functions.

Mineral Fertilizers for Hydroponics:

There is a very wide range of commercial fertilizers available for hydroponics and even a wider range of formulations for each crop. For the beginners, it is best to buy a premix nutrients source, but for commercial growers it is better and cost effective to buy individual fertilizers and mix them to prepare their own nutrient formulations.

However, preparation of own nutrient formulations requires a great deal of experience and training as a serious mistake in this process might result in heavy declines in crop yield or even total loss of crop. Knowledge of the forms of nutrient elements required by plants and their fertilizer sources is highly essential for the preparation of own nutrient formulations.

Preparation of Nutrient Solution:

There are two approaches to develop the feed nutrient solution for hydroponic crops. In the first approach, nutrient solution is prepared at the working strength, for instance at the EC of 2 or 2.5 dS m-1 directly by dissolving accurately calculated and weighed quantities of different soluble fertilizers in a suitable sized tank are filled with water. The EC and pH of the solution is checked and adjusted if necessary and the solution is pumped directly to plants for nutrition. This first approach suits to small scale growers.

In the second approach, concentrated fertilizer solutions (stock solutions) are prepared and pumped into the nutrient solution for dilution at the required EC and pH levels before they are circulated to system. The concentrated solutions are 100 to 200 times stronger than the normal nutrient solutions. Therefore at this strength calcium reacts with phosphate or even with sulphate and precipitates. Hence calcium, phosphorus, and sulphur all the three go out of solution and become deficient to plants. The precipitates also block nutrient supply lines and drippers.

To avoid this issue, calcium must be kept separate from the sulphates and phosphates. Hence, the concentrated solutions are split into parts, “Solution A” and “Solution B”. Stock Solution A usually contains nitrates/ chlorides of calcium and potassium and the chelated iron, while the stock Solution B contains all other fertilizers. These are then pumped separately into the water tanks or water stream for dilution to prepare a feed nutrient solution of the required EC and pH. This approach is adopted for large scale commercial farming.

For tomatoes, pepper and cucumber, the electrical conductivity (EC) of the diluted nutrient solution is kept in the range of 1.8 to 2.5 dS m-1, whereas for leafy green vegetables such as lettuce it is kept between 1.2 to 1.5 dS m-1. Electrical conductivity meter and pH meter are used for the adjustment of EC and pH at appropriate levels.

Symptoms of Nutrient Deficiencies:

Nutritional deficiency symptoms can be complicated as sometimes these results from multiple factors such as temperature, humidity, day length, diseases as well as nutrient levels. Therefore, evaluation of nutrient deficiency on the basis of visual symptoms is a complicated issue and can be dealt with care.

Nitrogen:

Nitrogen deficiency leads to chlorosis (yellowing) of older leaves, spindly plants and small fruit size, while due to the excess of nitrogen, plants become dark green with abundant foliage but little root growth or fruit production.

  • Apply 0.25% to 0.5% solution of urea as foliar spray.
  • Add calcium nitrate or potassium nitrate to the nutrient solution.

Phosphorus:

Due to its deficiency stunted growth occurs and maturity is delayed. Purplish colour appear in younger leaves. In the presence of excess of phosphorus, no any apparent symptoms occurs, however Cu and Zn deficiency symptoms may appear in presence of excess of phosphorus.

  • Add monopotassium phosphate to the nutrient solution.

Potassium:

Its absence leads to chlorosis of older leaves, scattered dead spots on leaves and uneven ripening in fruits. While high levels may lead to deficiencies of Mg, Mn, Zn, or Fe.

  • Apply 2% potassium sulphate as the foliar spray.
  • Add potassium sulphate or potassium chloride to the nutrient solution.

Sulphur:

Due to sulphur deficiency yellowing of young leaves occurs. Upper leaves become stiff and curl downward. Stem, veins, and petioles turn purple. While in the presence of excess phosphorus stunted growth, Interveinal chlorosis or leaf burning occurs.

  • i) Add any sulphate salt, preferably potassium sulphate to the nutrient solution.

Magnesium:

Its deficiency leads to interveinal chlorosis on older leaves and no visual symptoms are observed due to its toxicity.

  • Apply 10% magnesium sulphate as foliar spray.
  • Add magnesium sulphate to the nutrient solution.

Calcium:

Calcium deficiency leads to fruit blossom end rot, yellowing of young leaves margins, undersides turns purple, curling of leaves, growing tips and root tips become dead, and develops thick woody stems. No visual symptoms are observed due to its presence in excess.

  • Apply 0.75% to 1.0% calcium nitrate solution or 0.4% calcium chloride as the foliar spray.
  • Add calcium nitrate or calcium chloride to the nutrient solution.

Iron:

In the presence of excess of iron, severe interveinal chlorosis on young leaves occurs. Starting at margins, it spread to the entire leaf. Stunted growth and aborted flowers are major symptoms. Its presence in excess is usually not a problem.

  • Apply 0.2% to 0.5% iron chelate as foliar spray every 3 to 4 days.
  • Add iron chelate or ferrous sulphate to the nutrient solution.

Chlorine:

Chlorine deficiency leads to wilting of leaves and stunted root growth. Chlorotic appearance can be also observed. Its toxicity leads to burning of leaf tips and yellowing of leaves. Leaf drop and stunted growth occurs.

  • Apply 1% potassium chloride as the foliar spray.
  • Add potassium chloride to the nutrient solution.

Manganese:

Its deficiency leads to interveinal chlorosis on older leaves, fewer flowers development. Light green leaves with dead patches ringed in yellow are observed. Excess of it also leads to chlorosis and stunted growth.

  • Apply 1% solution of manganese sulphate as foliar spray.
  • Add manganese sulphate to the nutrient solution.

Boron:

Due to the boron deficiency withering occurs. Interveinal chlorosis of upper leaves and death of growing points are also observed. It can also lead to calcium deficiency. Brittle leaves can be noticed. Its toxicity leads to yellowing of leaf tips leading to browning.

  • Apply 0.1% to 0.25% borax as the foliar spray.
  • Add borax to the nutrient solution.

Zinc:

Zinc deficiency leads to internode length reduction, puckered margins on leaves, brown spots on petioles and small, long and narrow leaves. Its excess amount leads to chlorosis.

  • Apply 0.1% to 0.5% solution of zinc sulphate as foliar spray.
  • Add zinc sulphate to the nutrient solution.

Copper:

Due to the absence of copper, young leaves become dark green and starts to curl. Petioles bend downward and it ceases flower development. Its toxicity leads to stunted growth with symptoms of Fe chlorosis.

  • Apply 0.1 to 0.2% solution of copper sulphate with 0.5% hydrated lime as the foliar spray.
  • Add copper sulphate to the nutrient solution.

Molybdenum:

In the excess of molybdenum, interveinal chlorosis develops on older leaves and margins of leaves curl upwards. Due its toxicity leaves turn golden yellow.

  • Apply 0.07 to 0.1% solution of ammonium or sodium molybdate as foliar spray.
  • Add ammonium or sodium molybdate to the nutrient solution.

Insect pests and their management:

Aphids:

Aphids are soft bodied insects varying from a range of colors. These tiny insects feed in groups and aggregate on the main top shoot. Both nymph and adult suck the plant sap from tender leaves.

Control:

  • Regular monitoring of plants for their presence.
  • Yellow sticky traps can be used for their detection.
  • Use of bio control agent’s e.g. lady bird beetle, lacewing and hover fly.
  • Application of botanical insecticide are helpful to reduce the pest attack.

Whiteflies:

Adult whitefly is yellowish and covered with white powder. It feed on lower leaf part. The adult and nymph suck the cell sap. Due to this plant growth retard and the leaves turn yellowish- brown and drop. It is also vector of many diseases.

Control:

  • It can be effectively control by improving the sanitary conditions.
  • Use of biological agents are helpful to reduce the pest population.
  • Use of biological insecticide such as neem based insecticide and oil.

Mealybugs:

Adult females have oval bodies and their bodies covered with white waxy materials while males are flyer. The adult and nymph suck the cell sap due to this leaves withered and plant growth is retarded. They also secrete honeydew that causes the development of mold.

Control:

These can be managed if early precautionary procedures are adopted. Hoeing near plant roots destroys the eggs and its infestation can be reduced. Effective control can be done by improving the sanitary condition of green house. Biological control agents are helpful in reducing the pest population.

Thrips:

These are small bodied insects with typical character of fringed wings. The adult and larvae suck the cell sap by rasping and sucking mouth parts. They also rupture and damage epidermis and plat cell. In severe infestation withering and falling of leaves occurred. Leaf color turned into silvery or dirty white.

Control:

Regular monitoring of crop for their infestation must be done. By restricting the adult entry, infestation can be hindered. Biological control agents are effective against thrips.

Mites:

Mites are different from insects as they bear four pair of legs instead of three pairs in insects. They are considered as major pest in green house. They are small in size and color vary from pale to light green. Both adult and nymph suck the sap and reduces the plant vigor.

Control:

By maintaining proper sanitary conditions it can be managed. Mites entered through infested transplantation. Wild grasses and small plants near greenhouse are also source of infestation and must be removed. Sprinkle irrigation can give good control to prevent population build up. Biological control agents are also useful. Miticides are applied three times at five days interval as they have a small life cycle.

Leaf miners:

These feed in between the upper and lower surface of leaves and make tunnels. From their damage, photosynthetic area reduces and ultimately plant growth and yield reduces.

Control:

Regular observation is necessary to avoid severe infestation. Yellow sticky traps are beneficial to catch the egg laying adults. Biological control agent like Diglyphus isaea can control the larvae. Botanical insecticides give good result against them.

Fruit worm:

They are transferred as adult moths inside the greenhouses and lays eggs on the plants near fruiting parts. Larvae make hole in fruits at early stage and comes out to pupate in the soil or any bedding material used in green house. They make tunnels in fruits and destroy the whole fruit. Infested fruit remain small in size and drop early from plants.

Control:

These can be managed by restricting adults fly entry in the green house. Moths attract to light source and so unnecessary light around greenhouse must be avoided. Early detection of adults can be done by installing the pheromone traps. Adults lay eggs on lower side of leaves, by destruction of eggs manually also reduces the population. Infested fruit must be picked up and destroyed outside the green house. Neem based sprays give good control.

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