98 Pastos y Forrajes, Vol. 41, No. 2, April-June, 98-104, 2018 / Mineral nutrition of corn hydroponic green forage Scientific Paper Effect of mineral nutrition on the yield and bromatological characteristics of corn hydroponic green forage Freddy Soto-Bravo1 and Carolina Ramírez-Víquez2 1Estación Experimental Agrícola Fabio Baudrit Moreno, Facultad de Ciencias Agroalimentarias, Escuela de Agronomía, Universidad de Costa Rica, Apdo. postal 183-4050, Alajuela, Costa Rica 2Universidad de Costa Rica, San José E-mail: freddy.sotobravo@ucr.ac.cr Abstract The objective of this study was to determine the effect of mineral nutrition, applied through nutritional solutions, on the fresh yield (FY) and bromatological characteristics of corn hydroponic green forage (HGF). The study was conducted in a greenhouse located in the Agricultural Research Station Fabio Baudrit Moreno, Alajuela, Costa Rica. Two treatments of nutritional solution were applied: 1) with high (Nh), and 2) with low (Nl) concentration of mineral nutrients, and a control with water (Te), distributed in an unrestricted randomized design. The seed was selected; prepared through washing, disinfection, imbibition, draining and aeration; it was pregerminated in humidity chamber (3 days) on plastic trays (density of 3 kg m-2); and was transferred to the greenhouse, where it remained during 11 days until harvest. In general, no significant differences were found among the treatments, and the average values were: 15,3 kg m-2 of FY; 20,01 % of crude protein; 18,95 % of crude fiber; 1,48 % of lignin; 44,27 % of neutral detergent fiber; 0,96 % of nitrogen of the neutral detergent fiber; 22,09 % of acid detergent fiber; 0,24 % nitrogen of the acid detergent fiber; 4,5 % of ash; 7,44 % of ether extract; 88,6 % of dry matter digestibility; and 3,2 Mcal kg DM-1 of metabolizable energy. It is concluded that the application of mineral nutrients through nutritional solution did not affect the fresh yield or bromatological indicators, and the potential of utilization of the corn hydroponic green forage as feeding source in animal production was proven. Keywords: digestibility, crude protein, nutritional solution, nutritional value Introduction to climate changes; allows programmed and periodic Forage availability, in the traditional system of production throughout the year, with efficient water animal feeding based on extensive grazing in open use (Al-Karaki and Al-Hashimi, 2012), and a reduc- field, faces a series of contrasts associated with cli- tion of fertilizers, agrochemicals and labor (Candia, mate change and the world crisis of water, such as: 2014). land flooding, scarcity of arable lands, water salini- In the production of hydroponic green forage ty, increase in the cost of fertilizers and labor, long different species have been used, among them growth periods and natural phenomena (Naik et al., grasses and legumes. Some studies evaluated the 2015). quality of hydroponic green forage in corn [(Zea mayz L.) (Naik et al., 2017)], sorghum [(Sorghum An alternative in animal feeding can be bicolor L.) (Gonzales-Díaz and García-Reyes 2015)] hydroponic green forage, because it shows a series of barley [(Hordeum vulgare L.) (Quispe-Cusi et al., advantages with regards to the conventional forage 2016)], wheat [(Triticum aestivum L.) (Contreras production system in open range. The hydroponic green et al., 2015)], rice [(Oriza sativa L.) (Maldonado et forage is obtained from the germination of seeds or al., 2013)], and in mixtures of cereals and legumes grains, and can be used as nutritional supplement (Contreras et al., 2015). However, only a reduced in different animal species, because it shows and number studied the quality of hydroponic green excellent protein percentage (Contreras et al., 2015), forage in response to the application of nutritional an adequate balance in the soluble fiber/insoluble solutions; for example: in corn (Acosta et al., 2016), fiber ratio, high DM digestibility (Gómez-Burneo, wheat (Maldonado et al., 2013), barley (Quispe 2008) and good energy contribution (Bedolla- et al., 2016) and sorghum (Gonzales-Díaz and Torres et al., 2015). García-Reyes, 2015). In several of these studies, an The intensive production of hydroponic green absolute control with water without nutrients was forage in protected environments is less vulnerable used; and in some bromatological indicators simi- Pastos y Forrajes, Vol. 41, No. 2, April-June, 98-104, 2018 / Freddy Soto-Bravo 99 lar values to others in which nutritional solution in Within the structure of hydroponic green forage irrigation was applied, were obtained (Naik et al., production, the air temperature and relative humidity 2017); which generates uncertainty with regards to were monitored (Data logger HOBO U23 Pro v2) the need of using mineral nutrition in the produc- every five minutes, recording the hour averages. The tion of hydroponic green forage. maximum, minimum and average temperature and In the reviewed literature, it was found that the relative humidity were 31,5; 19,7 and 23,9 ºC, and concentration of mineral nutrients in the nutritional 97,4; 59,8 and 86,0 %, respectively. solution varied widely. For example, in the case of Plant material. Corn seed was used, based nitrogen, the ranges fluctuated between 5 mg L-1 on its availability, high production volume and (Rivera et al., 2010) and 250 mg L-1 (Vargas-Ro- low cost with regards to other imported materials dríguez, 2008); while the iron concentrations, from (Ramírez-Víquez, 2016); specifically of the local 4,3 mg L-1 (Salas-Pérez et al., 2012) to 800 mg L-1 variety Diamantes 8843, of free pollination, white (Rivera et al., 2010). This variability is due to the di- grain, with late maturity (120-135 days), fresh yield versity of factors which influence, such as climate, of 3-6 t ha-1 and a wide range of adaptation to agro- genotype, planting density and days until harvest. climatic conditions (INTA-AECI, 2005). Taking into consideration the above-stated Treatments. Two treatments of nutritional solu- facts, the objective of this study was to determine tion (table 1) were applied: 1) high nutrient concen- whether mineral nutrition, applied through nutri- tration (Nh), and 2) low nutrient concentration (Nl); tional solutions, affected the yield and bromatologi- and a control with water without nutrients (Te). cal characteristics of corn hydroponic green forage, The concentration of mineral nutrients in the and based on this basis define the need of fertilizer nutritional solution, for the treatments Nl and Nh, was application. defined based on the ranges reported in literature (Al-Karaki and Al-Hashimi, 2012; Candia, 2014), Materials and Methods and those values considered extreme were discarded. Experimental site. The study was conducted The quantity of nutrients in Te was in correspondence in the Agricultural Research Station Fabio Baudrit with the concentration present in water. Moreno, located in San José de Alajuela, Costa Rica Experimental procedure. The process of (10º 01’ N, 84º 16’ W, at 840 m.a.s.l.), with monthly hydroponic green forage production was carried out average temperature values of 22 ºC, relative humidi- according to the proposal made by Vargas-Rodríguez ty of 78% and annual average rainfall of 1 940 mm. (2008), and included seed preparation, pre-germination A multi-tunnel greenhouse, 9,75 m wide and and growth stage. In turn, seed preparation included: 50 m long, and with a height of 6 m at the center selection, cleaning, pre-washing, disinfection and of the tunnel and 4 m in the gutter, was used. The imbibition. Disinfection consisted in: immersion of the greenhouse was built with galvanized iron, cover seeds in a solution of 100 g L-1 of calcium hydroxide of trilayer transparent polyethylene (200 µm) and (8 h) washing of the lime and, finally, immersion for an anti-insect nylon mesh (43 x 28 threads inch-2) 5 min in Busamart® (TCMTB: benzothiazole) with a in the walls and the zenithal opening. The ventila- dose of 1 ml L-1. Later the TCMTB residue in the seeds tion system was passive, combined with the auto- was rinsed away; they were aerated under ambient mated functioning of zenithal windows according conditions (1 h) and were subject to an imbibition to the wind speed, which was monitored with an process, submerging them in water during a period of anemometer. 10 h. Table 1. Concentration of macro- and micronutrients in each treatment. Macro (mg L-1) Micro (mg L-1) ♦EC Treatment pH N Ca Mg K P Fe zn Cu Mn Na S (mS cm-1) Control (Te) 8,3 6,2 12,6 5,4 3,6 0,3 ND ND ND ND 9,3 0,9 0,2 Low nutrition (Nl) 6,7 94,6 94,2 22,3 145,6 18,4 0,3 0,1 0,1 ND 12,1 35 1,3 High nutrition (Nh) 6,6 227 202,7 49,5 341,4 46,1 1,2 0,5 0,5 0,7 16,3 78,8 2,5 ♦EC: electrical conductivity (mS cm-1), ND: not detectable. 100 Pastos y Forrajes, Vol. 41, No. 2, April-June, 98-104, 2018 / Mineral nutrition of corn hydroponic green forage The production process was carried out in a tion. The irrigation programming was done by fixed cultivation cycle of 14 days, which included two times through a timer, with a duration of 15 seconds stages: I: germination (3 days), and II: growth (11 and a frequency every 45 minutes, in a time interval days). Once the imbibition was concluded, passive between 6 a.m. and 6 p.m. in each treatment the runoff was carried out and the seeds were placed water inputs and outputs in the cultivation systems on plastic trays, at a density of 3 kg m-2 according were recorded, during 11 days of the cultivation cy- to the reports for corn (Acosta et al., 2016; Naik et cle (table 2). al., 2017). Afterwards, they were put to germinate Response variables. At the end of the cultiva- in dark chamber, with relative humidity higher than tion cycle the yield (kg m-2) was determined, from 85 % and temperature of 23-25 ºC. the fresh weight (FW) obtained per tray (0,165 m2). In the growth stage of the hydroponic green forage As bromatological variables, the following were the protection paper of the germinated seeds on the determined: crude protein (CP), crude fiber (CF), trays was withdrawn, and they were transferred to acid detergent lignin (lignin), neutral detergent fi- a production area located within the greenhouse. ber (NDF), nitrogen of the neutral detergent fiber Such area consisted in a structure 3 m long; 1,3 m (NNDF), acid detergent fiber (ADF), nitrogen of wide and 2 m high, with five horizontal shelves the acid detergent fiber (NADF), ash, ether extract separated by 0,40 m. The structure was vertically (EtE), dry matter digestibility (DMD) and metaboli- divided in three sections, which were randomly as- zable energy (ME). The standardized analysis signed to each of the three treatments. Each vertical methodologies of the laboratory of the Research section was composed by five shelves, and each one Center on Animal Nutrition (CINA, 2015) were contained four repetitions. used: a) Official Association of Agricultural Chemists The irrigation system was composed by: a) (AOAC) 942.05, 2) AOAC 920.39, 3) AOAC 962.69, storage tanks, b) feed pumps, c) pipelines (PVC of 4) AOAC 2001.11, and 5) AOAC 996.17. 19 mm), d) self-compensating micro-sprayers, e) The DMD (%) was estimated from the ADF pressure regulators, and f) manometers. Each shelf content, according to the equation: DMD = 88,9 - or level had four irrigation lines (PE of 16 mm), pro- (% ADF x 0,779), proposed by Di Marco (2011). The vided with two sprayers each, for a total of 20 lines ME (Mcal kg-1 DM-1) was estimated from the DMD, and 40 sprayers throughout the structure. according to the procedure described by Di Marco For the preparation of the nutritional solutions (2011), using the equation ME = 3,61 x (DMD/100). hydrosoluble fertilizers were used, such as mono- The samples were taken from the center of each potassium phosphate, potassium sulfate, magne- tray, in order to discard the edge effect. In each sium sulfate, calcium nitrate, potassium nitrate and treatment the sample by repetition corresponded a pre-mixture of micronutrients. Afterwards, they to a composite sample of all the repetitions present were stored in two tanks identified as Nh and Nl for in each of the five shelves, in order to obviate the the treatments with high and low nutrient concen- effect of the reduction of sunlight, according to the tration, respectively. descending position from the top to the lowest shelf. The nutritional solutions were applied in each Experimental design and statistical analysis. irrigation event, through fertigation by nebuliza- An unrestricted random design was used, with four Table 2. Water balance for the production of corn hydroponic green forage in the different treatments. Treatment Indicator in the production system Control Low nutrition High nutrition Inputs (L m-2) Irrigation 11,7 12,1 8,9 Lateral losses 4,1 4,1 2,6 Drainage 3,3 4 0,6 Outputs (L m-2) ETc 3,6 3,1 5,1 Total outputs 11 11,2 8,3 Balance (L m-2) 0,6 0,9 0,5 Pastos y Forrajes, Vol. 41, No. 2, April-June, 98-104, 2018 / Freddy Soto-Bravo 101 repetitions in each of the five shelves within the NADF, the treatment Te differed from Nh and Nl, production structure. Each repetition corresponded without statistical differences between the last two. to a plastic tray (0,55 m x 0,30 m = 0,165 m2) with The average of all the treatments was 0,95 % for hydroponic green forage. Between treatments, NNDF and 0,24 % for NNDF. there was a forage tray used as edge. The data of the The ash and EtE contents showed statistical response variables were subject to the verification of differences (p < 0,05) among treatments (table 4). normality and homoscedasticity, using the computer Nh showed an ash content slightly higher than that program INFOSTAT (Di Rienzo et al., 2017). of Te and Nl, without differences between the last When those assumptions were fulfilled, the data two. For the EtE, there were no significant differences were subject to variance analysis (ANOVA) and between Te and Nl, which differed from Nh. On the multiple mean comparison using LSD FISHER, other hand, there was no effect of mineral nutrition with a probability level of 0,05. on the DMD or on the ME content, with averages of 88,6 % and 3,20 Mcal kg DM-1, respectively (table 4). Results At the end of the cultivation cycle, the nutrition Discussion treatments did not affect the fresh yield of corn hy- The application of the low and high concen- droponic green forage, with values of 15,20; 15,27 trations of nutrients in nutritional solution, through and 15,37 kg m-2 for Te, Nl y Nh, respectively. There irrigation did not affect the fresh yield or the bromato- was no effect either on the CP, CF, lignin, NDF and logical quality of the corn hydroponic green forage. ADF contents. The results showed that, to obtain acceptable yields The averages of the bromatological variables and good bromatological quality of the forage, the are shown in table 3. For the variables NNDF and application of mineral nutrition was not necessary. Table 3. Bromatological variables in the corn hydroponic green forage. Variable (%) Treatment CP CF Lignin NDF NNDF ADF NADF Control (Te) 19,27 19,61 1,30 45,05 0,86 a 22,40 0,21a Low nutrition (Nl) 20,06 18,75 1,55 43,20 0,98 b 21,88 0,27b High nutrition (Nh) 20,69 18,50 1,58 44,55 1,03 b 21,98 0,25b Average 20,01 18,95 1,50 44,27 0,95 22,09 0,24 VC 6,26 4,72 13,51 3,08 4,62 4,64 7,99 P value 0,3221 0,2363 0,1531 0,1955 0,0009 0,7508 0,0028 Values with different letters in the same column indicate significant differences among treatments (p < 0,05). Table 4. Content of ash, ether extract, dry matter digestibility and metabolizable energy. Variable Treatment Ash (%) EtE (%) DMD (%) ME (Mcal kg DM-1) Control (T ae) 4,10 7,95 b 88,63 3,22 Low nutrition (Nl) 4,07 a 7,50b 88,60 3,20 High nutrition (N bh) 5,32 6,87 a 88,55 3,21 Average 4,5 7,44 88,59 3,21 VC 7,77 4,28 0,07 0,08 P value 0,0009 0,0032 0,2955 0,2437 Values with different letters in the same column indicate significant differences among treatments (p < 0,05). 102 Pastos y Forrajes, Vol. 41, No. 2, April-June, 98-104, 2018 / Mineral nutrition of corn hydroponic green forage The root system, during the early growth of The hydroponic green forage is also valued for corn seedlings, comprises the embryo roots, formed a good soluble fiber/insoluble fiber balance, which by only one primary root and a variable number of determines the digestibility of the nutrients con- seminal roots (Hochholdinger et al., 2018). These tained in it. The NDF and ADF contents in corn roots were later substituted by a permanent root hydroponic green forage were not affected by the system that emerges from the stem nodes, com- application of nutritional solution, and acceptable posed by lateral roots that substantially increase quality was maintained in the control (Te). The the absorption surface, because of the appearance above-explained facts coincide with the report by of highly differentiated roots called absorbent hairs López and Mcfield (2013) and Acosta et al. (2016), (Marzec et al., 2015). who did not find response in the NDF and ADF con- Thus, during the initial seedling growth, the in- tents in corn hydroponic green forage, when apply- cipient root system –little differentiated and lacking ing nutritional solution or water without nutrients. absorbent hairs– is not efficient in the absorption of The NDF represents the potentially digestible mineral nutrients. In studies of corn nutrition, the component of forages (Candia, 2014). In this regard, response to fertilization treatments appeared from López and Mcfield (2013) stated that those values two or three weeks (Bertsch, 2009) after planting, higher than 55 % reduce the digestibility of forage, at the end of the germination stage, emergence due to the inverse relation between the NDF content and initial growth. In addition, during such stage and the nutritional value, intake and digestibility. The the seedling can survive from the seed reserves. NDF values (43,2-45,05 %) of this study are within The seed endosperm starch and proteins are trans- formed into simple sugars and aminoacids, which the range reported by Salas-Pérez et al. (2010) and are used for the growth of the embryo, hypocotyl Acosta et al. (2016): 42,1-57,8 %, which explains and seedling (Taiz and zeiger, 2006). the high digestibility. With regards to fresh yield (FY) and the quality The ADF is the insoluble fraction of the crude of the obtained forage, in similar studies with corn fiber, and an important factor for adequate fermen- hydroponic green forage acceptable values were tation in the rumen. According to Maldonado et reported in such variables, independently from the al. (2013), the rations of dairy cattle should con- application of irrigation with water or with nutri- tain between 19 and 27 % of ADF, because lower tional solution. values can reduce the fat content in milk. In this The yields, including those of the control with study, there was no effect on ADF when applying water, were similar to the ones reported in corn nutritional solution (Nh = 21,98 %; Nl = 21,88 %) or (16,49 kg m-2) by Salas-Pérez et al. (2010) and Naik water without nutrients (Te = 22,4 %). Such values et al. (2015, 2017), who used concentrations of were similar to the ones reported by Acosta et al. nutrients and seed densities similar to the ones in (2016) when applying nutritional solution. On the treatment Nh. In turn, Rivera et al. (2010) indicated other hand, López-Aguilar et al. (2009) showed that the use of nutritional solution for the produc- that it was feasible to obtain acceptable ADF values tion of hydroponic green forage does not improve (28,5 %) in corn hydroponic green forage even with the bromatological quality of the forage, and that it the application of water alone. is feasible to use only water without nutrients. The lignin content shows a negative correlation Hydroponic green forage is valued due to its with the DMD of the forage, because low lignin values CP levels (Contreras et al., 2015). In this sense, increase its digestibility. In this study, the lignin Van Soest (1994) stated that the minimum content percentage (1,30-1,58 %) in all the treatments was of crude protein in hydroponic green forage should lower than 5 %, value from which it is considered be around 7 %. The CP contents in the forage of that there is a substantial reduction in the forage di- this study, even applying water alone, were higher gestibility, and for such reason, the DMD (88,6 %) than the ones reported in similar studies (13,5 -19,2 was high. This differs from the findings by Acosta %) by López and Mcfield (2013) and Acosta et al. et al. (2016), who reported lower DMD values in (2016). In another study, Salas-Pérez et al. (2010) corn hydroponic green forage (70,0-72,3 %), inde- proved that the application of nutrients through pendently from the application of nutritional solu- nutritional solution did not affect the CP content tions or water. (13,3 %), compared with the treatment in which wa- High values of NNDF and NADF indicate ter without nutrients was applied (12,2 %). that nitrogen appears in a non-utilizable way. The Pastos y Forrajes, Vol. 41, No. 2, April-June, 98-104, 2018 / Freddy Soto-Bravo 103 NNDF (0,95 %) and NADF (0,24 %) were similar Acknowledgements to the report by Sánchez and Soto (1998). The authors thank the Foundation for the En- The EtE represents the quantity of fat con- hancement and Promotion of Research and Tech- tained in the forage and, thus, the energy compo- nology Transference (FITTACORI), for its financial nent. In this study, the obtained range (6,87-7,95 %) contribution to this study. showed that there was no effect of the application of nutrients compared with the control. These values Bibliographic references exceed the ones reported in corn hydroponic green Acosta, N. V.; Lima, R.; Castro, A.; Avellaneda, J. H. forage (2,0-4,6 %) when the response to the appli- & Suárez, Y. G. Evaluación de diferentes siste- cation of nutritional solutions was evaluated (Acos- mas de producción de biomasa hidropónica de ta et al., 2016; Naik et al., 2017). maíz. Centro Agrícola. 43 (4):57-66, 2016. The studies about the effect of the application of Al-Karaki, G. N. & Al-Hashimi, M. Green fodder mineral nutrition are focused rather on the evaluation production and water use efficiency of some fo- of production and bromatological variables than rage crops under hydroponic conditions. ISRN on the effect on the mineral composition of forage. Agronomy. https://doi.org/10.5402/2012/924672. In this study, the average ash was 4,5 %; while in [02/09/2017], 2012. similar studies, when water without nutrients was Bedolla-Torres, Martha H.; Palacios-Espinosa, A.; Pa- applied, 3,6-6,9 % of ash was obtained (Cuesta and lacios, O. A.; Choix, F. J.; Ascencio-Valle, F de Machado, 2009; López-Aguilar et al., 2009). J.; López-Aguilar, D. R. et al. La irrigación con levaduras incrementa el contenido nutricional The DMD and ME content are important indi- del forraje verde hidropónico de maíz. Rev. Ar- cators because they show the quantity of metabolic gent. Microbiol. 47 (3):236-244, 2015. work of the organism. The average ME, based on the Bertsch, Floria. Absorción de nutrimentos por los cul- fact that there were no statistical differences among tivos. San José, Costa Rica: Asociación Costarri- treatments, was 3,2 Mcal kg-1. These results coin- cense de la Ciencia del Suelo, 2009. cide with the ones reported in corn hydroponic green Candia, Liz. Evaluación de la calidad nutritiva de fo- forage, when comparing different nutritional solu- rraje verde de cebada Hordeum vulgare hidropó- tions with a control without nutrients (López-Agui- nico, fertilizado con soluciones de guano de cuy lar et al., 2009; Acosta et al., 2016). Cavia porcellus a dos concentraciones. Salud Summarizing, high-quality forage contains tecnol. vet. 2 (1):55-62, 2014. approximately 70 % of DMD, less than 50 % of NDF CINA. Laboratorio de Bromatología de Forrajes de and more than 15 % of protein; while in low-quality la Universidad de Costa Rica. San José, Costa forage the DMD decreases to less than 50 %, the NDF Rica: Centro de Investigación en Nutrición Ani- increases to more than 65 % and protein decreases mal. http://www.cina.ucr.ac.cr/index.php/2015- to less than 8 % (Di Marco, 2011). In the control 10-28-20-54-43/laboratorio-de-bromatologia. [02/09/2017], 2015. treatment, irrigated with water without nutrients, the Contreras, J. L.; Tunque, M. & Cordero, A. G. Ren- DMD, crude protein and good balance of the fibers dimiento hidropónico de la arveja con cebada y proved that the corn hydroponic green forage has trigo en la producción de germinados. Rev. in- optimum quality, with great potential as complement vestig. vet. 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