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Nutrient Solutions for Hydroponic Systems
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2 Hydroponics A Standard Methodology for Plant Biological Researches. Ross 1994 With the exception of carbon C and oxygen O which are supplied from. the atmosphere the essential elements are obtained from the growth medium Other. elements such as sodium silicon vanadium selenium cobalt aluminum and iodine among. others are considered beneficial because some of them can stimulate the growth or can. compensate the toxic effects of other elements or may replace essential nutrients in a less. specific role Trejo T llez et al 2007 The most basic nutrient solutions consider in its. composition only nitrogen phosphorus potassium calcium magnesium and sulphur and. they are supplemented with micronutrients, The nutrient composition determines electrical conductivity and osmotic potential of the. solution Moreover there are other parameters that define a nutrient solution as discussed. below in detail, 2 1 pH of the nutrient solution, The pH is a parameter that measures the acidity or alkalinity of a solution This value. indicates the relationship between the concentration of free ions H and OH present in a. solution and ranges between 0 and 14, In soil the Troug diagram illustrates the pH effect on the availability of nutrients to plants. Fig 1 Similarly changing the pH of a nutrient solution affects its composition elemental. speciation and bioavailability The term speciation indicates the distribution of elements. among their various chemical and physical forms like free ions soluble complexes chelates. ion pairs solid and gaseous phases and different oxidation states De Rijck Schrevens. An important feature of the nutrient solutions is that they must contain the ions in solution. and in chemical forms that can be absorbed by plants so in hydroponic systems the plant. productivity is closely related with to nutrient uptake and the pH regulation Marschner. 1995 Each nutrient shows differential responses to changes in pH of the nutrient solution. as described below, In the nutrient solution NH3 only forms a complex with H For a pH range between 2 and. 7 NH3 is completely present as NH4 Fig 2 Increasing the pH above 7 the concentration of. NH4 decreases while the concentration of NH3 augments De Rijck Schrevens 1999. Tyson et al 2007 in a study to determine the nitrification rate response in a perlite trickling. biofilter root growth medium exposed to hydroponic nutrient solution varying NO3. concentrations and two pH levels 6 5 and 8 5 founded that nitri cation was signi cantly. impacted by water pH The increased ammonia oxidation rate 1 75 compared to nitrite. oxidation rate 1 3 at pH 8 5 resulted in accumulation of NO2 to levels near those harmful. to plants observed peak of 4 2 mg L 1 NO2 The potential for increased levels of un ionized. ammonia which reduced plant nutrient uptake from micronutrient precipitation are. additional problems associated with pH 8 5, Phosphorus is an element which occurs in forms that are strongly dependent on.
environment pH In the root zone this element can be found as PO43 HPO42 and H2PO4. ions the last two ions are the main forms of P taken by plants On inert substrates the. largest amount of P available in a nutrient solution is presented when its pH is slightly. acidic pH 5 In alkaline and highly acidic solutions the concentration of P decreases in a. www intechopen com, Nutrient Solutions for Hydroponic Systems 3. Fig 1 Troug diagram of nutrient availability Each nutrient is represented with a band the. thickness is proportional to the availability, www intechopen com. 4 Hydroponics A Standard Methodology for Plant Biological Researches. Fig 2 Ammoniacal speciation in function of pH, significant way Dy ko et al 2008 Namely with pH 5 100 of P is present as H2PO4 this. form converts into HPO4 2 at pH 7 3 pKa2 reaching 100 at pH 10 The pH range that. dominates the ion H2PO4 2 on HPO4 is between 5 and 6 De Rijck Schrevens 1997 The. pH dependent speciation of P is showed in Fig 3, Potassium is almost completely present as a free ion in a nutrient solution with pH values. from 2 to 9 only small amounts of K can form a soluble complex with SO4 2 or can be bound. to Cl De Rijck Schrevens 1998a Like potassium calcium and magnesium are available to. plants in a wide range of pH however the presence of other ions interferes in their availability. due to the formation of compounds with different grade of solubility As water naturally. contains HCO3 this anion turns into CO3 2 when the pH is higher than 8 3 or to H2CO3 when it. is less than 3 5 the H2CO3 is in chemical equilibrium with the carbon dioxide in the. atmosphere Thus at a pH above 8 3 Ca2 and Mg2 ions easily precipitate as carbonates Ayers. Westcot 1987 Also as mentioned above when the pH of the nutrient solution increases. the HPO42 ion predominates which precipitates with Ca2 when the product of the. concentration of these ions is greater than 2 2 expressed in mol m 3 Steiner 1984 Sulphate. also forms relatively strong complexes with Ca2 and Mg2 De Rijck Schrevens 1998b As. pH increases from 2 to 9 the amount of SO42 forming soluble complexes with Mg2 as MgSO4. and with K as KSO4 increases De Rijck Schrevens 1999. Iron copper zinc boron and manganese become unavailable at pH higher than 6 5. Timmons et al 2002 Tyson 2007 In Triticum aestivum the manganese precipitation on. root surfaces was correlated with a plant induced rise in pH of culture above 5 5 Macfie. www intechopen com, Nutrient Solutions for Hydroponic Systems 5.
Fig 3 Speciation of P depending on pH, Taylor 1989 Boron is mainly uptaken by plants as boric acid which is not dissociated until. pH is close to 7 to greater pH values boric acid accepts hydroxide ions to form anionic. species Tariq Mott 2007 Fig 4, Therefore nutrient availability for plant uptake at pH above 7 may be restricted due to. precipitation of Fe2 Mn2 PO3 4 Ca2 and Mg2 to insoluble and unavailable salts Resh. 2004 The proper pH values of nutrient solution for the development of crops lies between. 5 5 and 6 5, 2 2 Electrical conductivity of the nutrient solution. The total ionic concentration of a nutrient solution determines the growth development and. production of plants Steiner 1961 The total amount of ions of dissolved salts in the. nutrient solution exerts a force called osmotic pressure OP which is a colligative property. of the nutrient solutions and it is clearly dependent of the amount of dissolved solutes. Landowne 2006 Also the terms solute potential or osmotic potential are widely used in. nutrient solution which represent the effect of dissolved solutes on water potential solutes. reduce the free energy of water by diluting the water Taiz Zeiger 1998 Thus the terms. osmotic pressure and osmotic potential can be used interchangeably still important. considering the units that are used commonly atm bar and MPa Sandoval et al 2007. An indirect way to estimate the osmotic pressure of the nutrient solution is the electrical. conductivity EC an index of salt concentration that defines the total amount of salts in a. solution Hence EC of the nutrient solution is a good indicator of the amount of available. www intechopen com, 6 Hydroponics A Standard Methodology for Plant Biological Researches. Fig 4 Transformation of boric acid black circles and anion forms of boric acid white. circles as a function of pH Bishop et al 2004, ions to the plants in the root zone Nemali van Iersel 2004 Estimation of the osmotic.
pressure of a nutrient solution from EC can be done by using the following empirical. relations Sandoval 2007, OP atm 0 36 X EC in dS m 1 at 25 oC. OP bar 0 36 X EC in dS m 1 at 25 oC, OP MPa OP bars X 0 1. The ions associated with EC are Ca2 Mg2 K Na H NO3 SO42 Cl HCO3 OH. United States Departament of Agriculture USDA 2001 The supply of micronutriments. namely Fe Cu Zn Mn B Mo and Ni are very small in ratio to the others elements. macronutrients so it has no a significant effect on EC Sonneveld Voogt 2009. The ideal EC is specific for each crop and dependent on environmental conditions. Sonneveld Voogt 2009 however the EC values for hydroponic systems range from 1 5. to 2 5 ds m 1 Higher EC hinders nutrient uptake by increasing osmotic pressure whereas. lower EC may severely affect plant health and yield Samarakoon et al 2006 The decrease. in water uptake is strongly and linearly correlated to EC Dalton et al 1997 Table 1 shows. the classification of crops in function of salinity tolerance. As noted in Table 1 some crops can grow with high levels of EC and even a proper. management of EC of the nutrient solution can provide and effective tool to improve. www intechopen com, Nutrient Solutions for Hydroponic Systems 7. Threshold EC, Salinity group Example of crops, Sensitive 1 4 lettuce carrot strawberry onion. Moderately sensitive 3 0 broccoli cabbage tomato cucumber. radish pepper, Moderately tolerant 6 0 soybean ryegrass.
Tolerant 10 0 bermuda grass sugarbeet cotton, Table 1 Threshold EC for salinity groups and example of crops Jensen 1980 Tanji 1990. vegetable quality Gruda 2009 In particular parameters of fruit quality such as soluble. solids content titratable acidity and dry matter augmented by increasing EC level of. nutrient solution from 2 to 10 dS m 1 As a consequence deep sea water DSW is being used. for nutrient solution due to its high amount of Na Mg2 K and Ca2 Chadirin et al 2007. 2 3 Composition of the nutrient solution, As previously stated nutrient solutions usually contain six essential nutrients N P S K Ca. and Mg Thereby Steiner created the concept of ionic mutual ratio which is based on the. mutual ratio of anions NO3 H2PO4 and SO42 and the mutual ratio of cations K Ca2. Mg2 Such a relationship is not just about the total amount of each ion in the solution but in. the quantitative relationship that keep the ions together if improper relationship between. them take place plan performance can be negatively affected Steiner 1961 1968. In this way the ionic balance constraint makes it impossible to supply one ion without. introducing a counter ion A change in the concentration of one ion must be accompanied by. either a corresponding change for an ion of the opposite charge a complementary change. for other ions of the same charge or both Hewitt 1966. When a nutrient solution is applied continuously plants can uptake ions at very low. concentrations So it has been reported than a high proportion of the nutrients are not used. by plants or their uptake does not impact the production For example it was determined. that in anthurium 60 of nutrients are lost in the leachate Dufour Gu rin 2005 but in. closed systems however the loss of nutrients from the root environment is brought to a. minimum Voogt 2002 Also it has been shown that the concentration of nutrient solution. can be reduced by 50 without any adverse effect on biomass and quality in gerbera Zheng. et al 2005 and geranium Rouphael et al 2008 Accordingly Siddiqi et al 1998 reported. no adverse effect on growth fruit yield and fruit quality in tomato when reduction of. macronutrient concentrations to 50 of the control level as well as cessation of. replenishment of the feed solution for 16 days after 7 months of growth at control levels. were applied However it is expected that in particular situations too low concentrations do. not cover the minimum demand of certain nutrients, On the other hand high concentrated nutrient solutions lead to excessive nutrient uptake and. therefore toxic effects may be expected Conversely there are evidences of positive effects of. high concentrations of nutrient solution In salvia the increase of Hoagland concentration at. 200 caused that plants flowered 8 days previous to the plants at low concentrations. increasing total dry weight and leaf area Kang van Iersel 2004 Likewise high levels of K. www intechopen com, 8 Hydroponics A Standard Methodology for Plant Biological Researches. in the nutrient solution 14 2 meq L 1 vs 3 4 meq L 1 increased fruit dry matter total soluble. solids content and lycopene concentration of tomato Fanasca et al 2006. The explanation of these apparent controversial responses is the existence of optimal. concentrations of certain nutrients in a solution for a culture under special environmental. conditions as well as their relative proportions and not their absolute concentrations as. determining factors Ju rez et al 2006 In order to prevent contradictory observations. Dufour Gu rin 2005 recommend a to monitor the availability of nutrients through. changes in the ionic composition of the substrate by analysis of percolate and b to asses. plant nutrient uptake by nutrient content analysis in leaves Moreover Voogt 2002. indicates that the nutrient solution composition must reflect the uptake ratios of individual. elements by the crop and as the demand between species differs the basic composition of a. nutrient solution is specific for each crop It must also be taken into account that the uptake. differs between elements and the system used For instance in open systems with free. drainage much of the nutrient solution is lost by leachate. There are several formulations of nutrient solutions Nevertheless most of them are. empirically based Table 2 comprises some of them, Hoagland Arnon Hewitt.
Nutrient Cooper 1979 Steiner 1984, N 210 168 200 236 168. P 31 41 60 31, K 234 156 300 273, Ca 160 160 170 185 180. Hydroponic crop production has significantly increased in recent years worldwide as it allows a more efficient use of water and fertilizers as well as a better control of climate and pest factors Furthermore hydroponic production increases crop quality and productivity which results in higher competitiveness and economic incomes

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