cultivation in nutrient solution also receives the names of water culture, aquaculture, or Nutriculture quimiocultura.
Ellis and Swaney (1963) define water culture that "... in its purest sense is a system that involves the growth of flowers and vegetables by dipping their roots in an aqueous solution of nutrients. "
The basic principle of growing in nutrient solution is that the roots of plants from partially or completely in a liquid medium containing all necessary nutrients.
The tub is arranged through a system of support to keep the plant upright while the roots are submerged in a tank of nutrient solution.
In another method, regarded as more acceptable from a practical standpoint, the bath contains at the top of a bed or bed of absorbent material (usually organic) supported by wire mesh. The bed main functions of serving as support to the plants, hold the solution to be used by the plant newborn, or to promote germination when provided direct seeding. Below the bed support is the nutrient solution tank which is submerged part of the plant roots anchored in the bed.
The main technical problems of cultivation in nutrient solution can be summarized in three aspects:
Nutritional characteristics: Although this culture system can be used successfully a large number of solutions nutritious, it should be noted that this is an essentially devoid of buffering capacity (buffer), and therefore requires a control, very accurate, the nutrient solution, especially with regard to the levels of pH, phosphate and iron.
In general, plants are much more susceptible to the adverse conditions of pH of the nutrient solution under cultivation in water, growing in gravel or sand. Ellis and Swaney (1963) mention that "probably a reason for this effect is that phosphates can coat the surfaces of solid media culture, exert a stabilizing action with that of acidity, so that any change that occurs in extreme the solution is not quickly reflect on the roots of the plants in contact with particles of sand or gravel. " Will then have a constant review of pH, to acquire sufficient experience to maintain the desired acidity. Because the solution is tending towards alkalinity, acidic water is typically added with sulfuric acid to restore the proper pH level.
If the level of phosphates in the nutrient solution is high, excessive rainfall occurs minor elements, mainly iron. This is true with unbalanced solutions, which tend to quickly alkalinity. However, if a proper balance between acid and alkaline ions in conjunction with a phosphate level high enough to exert a buffering action to changes in pH, the problem will not be so serious.
The iron is often difficult to maintain in a state comparable to the nutrient solution. We suggest, therefore, frequent additions (one to two per week), small doses of about one part per million (ppm) to ensure adequate supply of iron without reaching toxicity.
Physical characteristics: to promote the growth of plants under cultivation in solution is required to properly handle certain physical conditions such as:
Darkness to the nutrient solution: it is necessary to prevent the growth of green algae and other tiny aquatic plants that may compete for oxygen and nutrients. The decomposition of algae can become toxic to roots, interfering with their functions and development.
Aeration: the success achieved with this hydroponic system largely depends on adequate supply of oxygen to the roots of plants through the nutrient solution. Some published studies and practical observations indicate that excessive aeration of the solution can also be harmful to plants. Ellis and Swaney (1963) considered that the most appropriate level of oxygen in the nutrient solution is 3 to 5 ppm (at 15.5 ° C).
The oxygen supply may be natural, or forced in various ways.
The most common method of oxygenating the solution is to leave an air space between the surface of it and the bottom of the bed that supports the roots, so, so that the upper roots are surrounded by moist air while the bottoms are submerged in the solution. To increase the supply of air as they grow roots, the level of the solution is going down, to leave a maximum space of 5 cm. A larger space can damage by drying the upper roots.
is also usual to force oxygen into the solution, by passing air bubbles through it by an air pump connected to a tube with holes (1 mm in diameter and 30 cm apart), which runs along the bottom of the tank . The volume of air required depends mainly on the volume of solution, temperature and type of plant. Usually 5 to 10 bubbles per minute per hole are sufficient, or 10 to 20 bubbles per minute for 15 minutes every hour. Tub or household containers, aquarium pumps are suitable to oxygenate the solution.
Another way to aerate the solution is to take it down to air from a height sufficient to permit oxygenated (cascade effect), but the circulation of the solution should be slow to avoid damaging the roots.
Circulation of the nutrient solution: it is a commonly recommended practice because it promotes a better distribution of nutrient ions and better aeration. Presumably, the movement of the solution through the roots helps to stabilize their environment. Since then the movement should be slow enough to avoid damaging the roots.
should be noted that the movement of the solution is not sufficient to provide adequate aeration, but requires another procedure to complement it.
Warming: Some authors suggest that for temperate and cold climates should be heated, increasing between 5 and 100 above the night temperature, the nutrient solution in order to accelerate growth and development of plants. When installing circulation systems, the nutrient solution may be forced to pass through a heat source
. Stationary units may be warming through electric or steam pipes.
sudden temperature change of d (at night, typical of temperate climates, can be a serious problem for water culture and there is no added to soften its effect on the roots. Any change of the solution or water is added to the same solution should be approximately the same temperature as the solution above this. In a large facility will be very useful to have a separate tank with a heating system to preheat water or fresh solution.
Rain: Rainwater can be a serious problem because it can flood the tub or can alter the concentration of the solution. It is therefore recommended, in areas with regular rainfall to high tubs protect against rain.
Support for plants: the solution culture method without litter absorbent material, the problems of bed depth, porosity and water retention material not presented. In this case a rubber stopper or cork, or absorbent cotton padding is enough to keep the plant in place.
culture method for the solution with absorbent bedding material should be considered:
Bed depth: it is mainly determined by the type of root that provides the growing plant. Reduced root growth plants need no more than 5 cm bed depth, while ¬ after others may require up to 10 cm deep bed.
bed material porosity: Porosity the material is related to the incidence of diseases very fine aggregates stay wet longer and are more likely to become contaminated. However, the root system is an important factor to consider in choosing the material, plants like lettuce or carrots require half thinner than roses or tomatoes.
added moisture retention: materials that dry quickly are not suitable for the plants whose seeds are sown directly in the bed, because they affect germination. However, they are satisfactory for crops susceptible to crown rot. Perhaps the best substrate is a mixture of absorbent and non absorbent according to the specific needs of each crop.
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Saline soils are those that contain large amounts of dissolved salts, to the extent that a problem for the growth and development of plants. Salts commonly generate salinity, is formed by the anion: HCO3-, CO3-2, SO4-2, Cl-and cations: Ca +2, Mg +2, K +, Na +. The nitrate anion (NO3-) and ammonium cation (NH4 +) can participate in the generation of salinity, especially when applying high doses of nitrogen fertilizer or used large amounts of organic fertilizers. 
