It is estimated that in the Spanish Southeast, there is a soilless surface of ≈5500 ha (13,590.80 acres) (Urrestarazu, 2013) that consumes ≈500 to 700 L (109.98 to 153.98 gal) of water per square meter each year. Water use in soilless culture (Massa et al., 2010; Parry et al., 2005) and its efficiency in production (Patanè et al., 2011), the absorption of nutrient ions, such as nitrate and potassium (Cornillon and Fellahi, 1993; Topcu et al., 2007), and the pollution of nutrients released into the environment, especially that of nitrates (e.g., Gallardo et al., 2009; Min et al., 2012; Thompson et al., 2013; Urrestarazu et al., 2008a), are widely studied. In recent decades, many studies have been conducted to improve fertigation methods for the automation of fertigation systems in soilless cultures (e.g., Cáceres et al., 2007; Rodríguez et al., 2015; Steidle et al., 2014). Fertigation methods and their automation are based on the following: 1) the fertigation frequency (f), 2) the provision of applied volume in every new fertigation (AV), 3) the rate of water consumption by the crop, which is a function of the daily primary absorption by the plants, 4) the characteristics of the substrate used, and 5) the fertigation elements used for the supply of nutrient solutions (Urrestarazu, 2004). A large number of these fertigation methods are based on each new irrigation process being performed when 10% of the easily available water in the substrate has been exhausted plus the volume necessary to produce between 15% and 25% of the drainage (volume A, mL·m−2), which is the leaching fraction (LF) (e.g., Rodríguez et al., 2015). The LF usually varies between 0.15 and 0.25, depending on the water quality expressed by the salinity (e.g., Urrestarazu, 2004; Urrestarazu et al., 2005; Urrestarazu et al., 2008b). The amount provided in each fertigation (AV, mL·m−2) is equal to A + LF.
The number (n) of fertigation applications per unit time is f, which in turn depends on the fertigation demand that the crop requires. The time (t, in minutes) required to supply the AV amount (volume delivered per unit area, mL·m−2) will depend on the available fertigation system and is variable; it is a predetermined value in all fertigation applications. We will consider ti the time in minutes between two consecutive irrigations. The time at which the fertigation infrastructure supplies an AV volume is t, while in this study, a device was determined that transforms t to a value that is four times greater (td, in minutes).
The time td must be less than ti for the supply of fertigation to be equal in both treatments and to not overlap.
The values of EC, pH, and LF in fertigation drainage are frequently used parameters for the practical control of soilless systems (e.g., Gorbe and Calatayud, 2010; Hayward and Long, 1943; Urrestarazu et al., 2008b).
No information is available on the effect of the time of application of a fertigation volume given to a crop compared with the standard time of a fertigation based on the elements used in each fertigation installation, i.e., the emission duration to deliver the AV volume. This would not change the delivered volume but would affect the time that the roots are subject to a lower matric potential for a given time and, thus, the energy required for water absorption.
Of note, the improvement of the spatial distribution of fertigation in the cultivation unit in turn improves the production (Morales and Urrestarazu, 2013). This increase in production is due to better utilization of the substrate unit volume causing improved availability of water and nutrients (Robinson, 1994), which results in increased root growth. By occupying a greater volume, the roots can access better physicochemical conditions that are distributed unevenly, depending on the fertigation method (De Rijk and Schrevens, 1998; Sonneveld and Voogt, 1990).
The aim of the present study was to evaluate the effect of time on the application of a fertigation volume on the parameters of fertigation, water consumption, emission of pollutants, root distribution, and production of a pepper and tomato crop in a soilless culture system.
Abbreviations and concepts used:
- AV = Volume (mL) delivered in each fertigation.
- A = Volume consumed (mL·m−2) by the crop that corresponds to 10% of the readily available water consumed by the crop and must be replaced in cultivation units.
- LF = Proposed leaching fraction. Generally varies between 0.1 and 0.5.
- n = Number of fertigation applications.
- f = Frequency of fertigation applications. Number of fertigation applications per unit time.
- t = Time (in minutes) that a required applied volume (AV) lasts for a given system.
- ti = Time (in minutes) elapsed between the start of two consecutive irrigations.
- td = Time added to t (minutes) by interposing a device that reduces the flow (four times) the system issues; it is placed between the drip emitter and the cultivation unit.
- EC = Electrical conductivity of the nutrient solution.
CornillonP.FellahiA.1993Influence of root temperature on potassium nutrition of tomato plant p. 213–217. In: M.A.C. Fragoso and M.L. van Beusichem (eds.). Optimization of plant nutrition. Kluwer Academic New York
DO2000Reglamento (CE) No 790/2000 de la Comisión de 14 de abril de 2000 por el que se establecen las normas de comercialización de los tomates [Regulation (CE) No 790/2000 of the Commission of 14 Apr. 2000 through which marketing standards for tomatoes are established]. La Comisión de las Comunidades Europeas. 8 Oct. 2013. <http://www.boe.es/doue/2000/095/L00024-00029.pdf>
Fernández-GarcíaN.MartínezV.CerdaA.CarvajalM.2002Water and nutrient uptake of grafted tomato plants grown under saline conditionsJ. Plant Physiol.159899905
GallardoM.ThompsonR.B.RodríguezJ.S.RodríguezF.FernándezM.D.SánchezJ.A.MaganJ.J.2009Simulation of transpiration, drainage, N uptake, nitrate leaching, and N uptake concentration in tomato grown in open substrateAgr. Water Mgt.9617731784
ItyelE.Ben-GalA.SilberbushM.LazarovitchN.2014Increased root zone oxygen by a capillary barrier is beneficial to bell pepper irrigated with brackish water in an arid regionAgr. Water Mgt.131108114
LittleT.M.HillF.J.1978Agricultural experimentation: Design and analysis. Wiley New York
MassaD.IncrocciL.MagginiR.CarmassiG.CampiottiC.A.PardossiA.2010Strategies to decrease water drainage and nitrate emission from soilless cultures of greenhouse tomatoAgr. Water Mgt.97971980
MinJ.ZhangbH.ShiaW.2012Optimizing nitrogen input to reduce nitrate leaching loss in greenhouse vegetable productionAgr. Water Mgt.1115359
MoralesI.UrrestarazuM.2013Thermography study of moderate electrical conductivity and nutrient solution distribution system effects on grafted tomato soilless cultureHortScience4815081512
ParryM.A.J.FlexasJ.MedranoH.2005Prospects for crop production under drought: Research priorities and future directionsAnn. Appl. Biol.147211226
PatanèC.TringaliS.SortinoH.2011Effects of deficit irrigation on biomass, yield, water productivity, and fruit quality of processing tomato under semi-arid Mediterranean climate conditionsSci. Hort.129590596
PetersenR.G.1994Agricultural field experiments. Marcel Dekker New York
PulupolL.U.BehboudianH.M.FisherK.J.1996Growth, yield, and postharvest attributes of glasshouse tomatoes produced under deficit irrigationHortScience31926928
RodríguezD.RecaJ.MartinezJ.Lopez-LuqueL.UrrestarazuM.2015Development of a new control algorithm for automatic irrigation scheduling in soilless cultureAppl. Math. Info. Sci.9110
SchwarzD.RouphaelY.CollaG.VenemaJ.H.2010Grafting as a tool to improve tolerance of vegetables to abiotic stresses: Thermal stress, water stress, and organic pollutantsSci. Hort.127162171
SonneveldC.StraverN.1994Voedingsoplossingen voor groenten en bloemen geteeld in water of substraten [Nutrient solutions for vegetables and flowers grown in water or substrates]. 10th ed. Proefstation voor Tuinbouw onder Glas Naaldwijk
SonneveldC.VoogtW.1990Response of tomatoes Lycopersicon esculentum) to an unequal distribution of nutrients in the root environmentPlant Soil124251256
SteidleA.J.ZolnierS.De CarvalhoD.2014Development and evaluation of an automated system for fertigation control in soilless tomato productionComput. Electron. Agr.1031725
ThompsonR.B.GallardoM.RodríguezJ.S.SánchezJ.A.MagánJ.J.2013Effect of N uptake concentration on nitrate leaching from tomato grown in free-draining soilless culture under Mediterranean conditionsSci. Hort.150387398
TopcuS.KirdaC.DasganY.KamanH.CetinM.YaziciA.BaconM.A.2007Yield response and N-fertiliser recovery of tomato grown under deficit irrigationEur. J. Agron.266470
UrrestarazuM.2004Tratado de cultivo sin suelo [Treated soilless culture] 3rd ed. Mundi-Prensa Madrid Spain
UrrestarazuM.GuillénC.MazuelaP.C.CarrascoG.2008aWetting agent effect on physical properties of new and reused rockwool and coconut coir wasteSci. Hort.116104108
UrrestarazuM.MartínezG.A.SalasM.C.2005Almond shell waste: Possible local rockwool substitute in soilless crop cultureSci. Hort.103453460
UrrestarazuM.MazuelaP.C.2005Effect of slow-release oxygen supply by fertigation on horticultural crops under soilless cultureSci. Hort.106484490
UrrestarazuM.SalasM.C.ValeraD.GómezA.MazuelaP.C.2008bEffects of heating nutrient solution on water and mineral uptake and early yield of two cucurbits under soilless cultureJ. Plant Nutr.31527538
Van NoordwijkM.RaatsP.A.C.1980Drip and drainage systems for rockwool cultures in relation to accumulation and leaching of salts. Proceedings of the Fifth International Congress on Soilless Culture. Wageningen 1980 p. 279-287. International Society for Soilless Culture
WamserA.F.MoralesI.ÁlvaroJ.E.UrrestarazuM.2014The effect of drip flow rate with multiple manifolds on the homogeneity of the delivered volumeJ. Irr. Drain. Eng.141204014048