221 Adv. Hort. Sci., 2018 32(2): 221-227 doi: 10.13128/ahs-21882 Growth analysis of lettuce under different substrate compositions J.R. Schneider 1 (*), L.A. Thiesen 2, T.D. Engroff 3, E. Holz 2, B.S. Altíssimo 2 1 Faculty of Agronomy and Veterinary Medicine, University of Passo Fundo, Passo Fundo, RS, Brazil. 2 Department of Agriculture and Environment Sciences, Federal University of Santa Maria, Frederico Westphalen, RS, Brazil. 3 Department of Plant Production, Superior School of Agriculture “Luiz de Queiroz”, University of São Paulo, São Paulo, SP, Brazil. Key words: Lactuca sativa l., leaf area, solar radiation, substrate, temperature. Abstract: The objective of this work was to evaluate lettuce growth in green- house under different types of substrates. The experiment was conducted in a greenhouse, under randomized block design, with six treatments and three replicates. The compositions of the substrates were: T1= 100% organic com- pound; T2= 75% organic compound plus 25% substrate Plantmax®; T3= 50% organic compound plus 50% substrate Plantmax®; T4= 25% organic compound plus 75% substrate Plantmax®; T5= 100% substrate Plantmax®; T6= vermiculite. The number of leaves, dry mass, leaf area index, culture growth rate, relative growth rate, net assimilation rate, specific foliar area, foliar area ratio and foliar weight ratio were evaluated. Higher growth of lettuce plants are pro- duced by mixture of organic compound and substrate Plantmax®. The isolated use of vermiculite does not give good results for the growth of lettuce plants, but is an alternative for mixing with other substrates. 1. Introduction lettuce (Lactuca sativa l.) is one of the most consumed vegetables in the world (gomes et al., 2008), due to its taste, nutritional quality and low price (teodoro et al., 2016). its adaptability to different climatic con- ditions that allows successive crops during the year, low cost of produc- tion and safe marketing, makes it a crop preferred by small producers, adding economic and social value to its cultivation (medeiros et al., 2007). lettuce is responsive to organic fertilization, varying according to the cultivar and source of nutrients used (teodoro et al., 2016). thus, the use of substrates must ensure that lettuce presents characteristics appropri- ate to plant growth, with adequate physical and chemical compositions (lima et al., 2006). it should be well structured and with good texture, adequate pH, good fertility and pathogen free (Araújo et al., 2013). the different substrates compositions have an effect on the biomass production of the plants, since they are able to comply with the species’ (*) Corresponding author: juliaschneider07@hotmail.com Citation: ScHneider j.r., tHieSen l.A. engroff t.d., Holz e., AltíSSimo b.S., 2018 - Growth analysis of lettuce under different substrate compositions. - Adv. Hort. Sci., 32(2): 221-227 Copyright: © 2018 Schneider j.r., thiesen l.A., engroff t.d., Holz e., Altíssimo b.S. this is an open access, peer reviewed article published by firenze University Press (http://www.fupress.net/index.php/ahs/) and distributed under the terms of the creative commons Attribution license, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Data Availability Statement: All relevant data are within the paper and its Supporting information files. Competing Interests: the authors declare no competing interests. received for publication 21 october 2017 Accepted for publication 23 february 2018 AHS Advances in Horticultural Science Adv. Hort. Sci., 2018 32(2): 221-227 222 requirements (Afonso et al., 2012). there is a trend toward using organic compounds because they pro- vide nutrients and contribute to good development of the root system (lima et al., 2006). A lettuce crop has high production potential with organic fertilizers (Santos et al., 2001). the organic compounds, result- ing from composting, vermicomposting or other sources, have good aeration, structure, water reten- tion capacity, ability to regulate the temperature of the substrate, and are sources of several nutrients that may be readily available (trindade et al., 2001). organic compounds are also stabilized products, rich in nutrients and derived from vegetable and animal waste (Souza and Alcântara, 2008). moreover, the use of organic substrates reduces cultivation time and consumption of chemical inputs (medeiros et al., 2015), modifying the microbial pop- ulations that improve substrate quality and plant production. these microorganisms decompose the residues, releasing nutrients and substances that stimulate plant growth (medeiros et al., 2015). growth analysis is still the most accessible and accurate way to evaluate plant growth and the con- tribution of physiological processes to plant behavior. it allows differentiating the behavior of the same cul- tivar under different cultivation conditions (benincasa, 2003). due to the influence of factors on plant produc- tion and the importance of knowing the growth and development of the plants, the objective of this work was to evaluate lettuce growth in a greenhouse under different types of substrates. 2. Materials and Methods Location of experiment, plant material and cultiva- tion the experiment was conducted in a greenhouse located on the experimental area of the federal University of Santa maria, campus of frederico Westphalen, rS, brazil, with geographic location 27° 23’ S, 53° 25’ o and altitude of 490 m. According to Köppen’s classification, the climate of the region is humid cfa-temperate with hot summer, with maxi- mum air temperatures in warmer months over 22°c (Alvares et al., 2013). the average temperature inside the greenhouse were 22±3 °c during the day and 18±3°c in the night. the lettuce seedlings, cultivar Pira Verde, were transplanted to the wooden benches on 3 days in october 2013, arranged in spacing of 20 cm between plants and 30 cm between rows. the plants were cul- tivated for 49 days until november 21, when all had reached the harvest point. A 150-micron double- sided canvas was placed on the substrate to reduce water loss through soil evaporation. before trans- plantation, small holes were opened to introduce the seedlings into the substrates. the irrigation method used was drip irrigation, allowing a distribution of the same volume of water for all plants. Water was supplied depending on environmental conditions, taking into consideration temperature, relative humidity, and other factors. Along with water, nutrients were supplied through nutrient irri- gation. the nutrients were chosen according the rec- ommendations of furlani (2009), obtaining electrical conductivity around 1.2 μS cm-2, by use of hidrogood- fert, calcinit and chelated iron, which have soluble nutrients in water. Hidrogoodfert is composed of the macronutrients nitrogen, phosphorus, potassium, magnesium, sulfur and the micronutrients boron, copper, molybdenum and zinc. calcinit is composed of calcium nitrate. the solution was replaced accord- ing to the evaporation and absorption of the plants. Experimental design and treatments the experiment was conducted on wooden benches inside the greenhouse, with a randomized block design, with six treatments and three replica- tions per treatment. each replication have had 40 plants. the compositions of the substrates were t1= 100% organic compound; t2= 75% organic com- pound plus 25% substrate Plantmax®; t3= 50% organic compound plus 50% substrate Plantmax®; t4= 25% organic compound plus 75% substrate Plantmax®; t5= 100% substrate Plantmax®; and t6= vermiculite. the organic substrates were obtained by mechanized and Automated composting Unit (UmAc), a project of the company lPc-Ambiental technology, located in the municipality of concórdia- Sc. this residue is generated by mixing pig slurry with compost shavings and storing it in retention rails. the commercial substrate Plantmax® has excel- lent physical properties and high water retention capacity. this substrate is composed mainly of pine bark and vermiculite, and presents chemical proper- ties constituted of macronutrients and micronutri- ents. Vermiculite was used for application of nutri- ents by means of irrigation, since it is a non-nutritive substrate with high water retention capacity. Schneider et al. - Lettuce under different substrate compositions 223 Evaluations and analysis the evaluations of the plants were conducted every week, when 3 plants of each treatment were sampled by the destructive method, from the trans- plant to the beginning of the stem elongation for posterior emission of the floral tassel. the evalua- tions were made by counting the number of leaves and separating the morphological parts of the plant, which was put into the drying oven at 60°c until it reached constant weight for determination of the dry mass. the analyzed variables were number of leaves (nl), dry mass (dm) and leaf area index (lAi). the number of leaves was determined by counting all the leaves of the plants, and dry mass was obtained by measuring the mass of the aerial part of the plant. leaf area (lA) was determined by the disc method, in which 10 discs were removed from the leaves, obtaining its dry mass, and estimating the leaf area of the plant through the equation: lA = disc number x nozzle number x total leaf dry mass dry mass of the discs from the leaf area, the leaf area index was calcu- lated by the following equation: lAi = lA SA where SA is the area of soil occupied by a plant. in addition, culture growth rate (cgr), relative growth rate (rgr), net assimilation rate (nAr), spe- cific foliar area (SfA), foliar area ratio (fAr) and foliar weight ratio (fWr) were calculated according to the methodology presented by barbero et al. (2013). the cgr was determined by: cgr = dm SA xΔt where Δt is the time interval of the evaluations. this variable is an indicator of productivity, since it repre- sents the increase of dry matter in a time interval, considering the area of soil occupied by the plant. the equation to obtain the rgr is: rgr = log ΔdmA Δt where log Δdm is the logarithm of the increment of dm, so rgr is an increment of productivity of dry mass in a time interval. nAr was calculated as: nAr = cgr lAi this variable indicates the rate of increase in dry matter per unit of time and per unit of leaf area. According to benincasa (2003), nAr demonstrates the photosynthetic efficiency of the leaves. fAr is the ratio between leaf area and dry mass and expresses the foliar area useful for photosynthe- sis; it is the measure of the size of the assimilating apparatus. it is obtained by: fAr = lA dm fWr relates to how much of the dry matter accu- mulated by the plant is composed by leaves, which, besides being the organ responsible for photosynthe- sis, is the organ of commercial interest. it is given by: fWr = dm leaves dm plant SfA were determined by the equation: SfA = lA dm leaves this variable indicates the accumulation of pho- toassimilates in the leaves or the translocation to the other organs, that is, differences in leaf thickening (taiz and zeiger, 2013). the data were submitted to analysis of variance and comparison of means by the tukey’s test, with a 5% probability of error. the meteorological data, like air temperature and global solar radiation, were collected at the mobile weather station installed inside the greenhouse. 3. Results and Discussion Weather conditions during the experiment, minimum and maximum average temperatures were 15-27±3°c, respectively. these values are in agreement with the values con- sidered optimal for the culture between 15-24°c (Knott, 1962) and 15-20°c (Santana et al., 2009). the global solar radiation presented variations between 653 and 1.090 kj m-2. these values are con- sidered adequate for the growth of the culture. A reduction of solar radiation at the beginning of the crop cycle can be observed, but it did not have any influence, since the plants were in establishment period and had little leaf area (fig. 1). thus, air temperature and incident solar radiation were the main environmental factors that affected lettuce growth, development and yield. Growth variables during the growth and development of the plants, Adv. Hort. Sci., 2018 32(2): 221-227 224 small burns were observed in the border of the new leaves. these were symptoms of calcium deficiency, because it is a little mobile element in the plant and then wasn’t available to the plants. However, by har- vest, the plants had recovered with no apparent symptoms. the leaves are the main component of interest of lettuce. thus, it is important that the plant produces the maximum number of leaves, dry matter and leaf area for good production. figure 2 shows that the number of lettuce leaves increased during the crop cycle for the different substrate compositions. therefore, it can be observed that the t1 treatment (100% organic compound) showed a smaller number of leaves at 28 days after transplantation. However, at 35 days after transplant, the treatment composed of 100% substrate Plantmax® (t5) was less effective than the others, with approximately 12 leaves. At the end of the cycle of the culture, the substrate with the lowest number of leaves was vermiculite, with approximately 20 leaves, but that did not differ sta- tistically from the others. this demonstrates that the combination of different substrates such as organic compost and commercial substrate present better conditions for the development of plants than when used alone. the results obtained show that the analyzed growth variables presented different behaviors in relationship to the types of substrates used in the let- tuce crop. A decline was also observed on the growth variables toward the end of the crop cycle (fig. 3), which is considered normal because they are rela- tional to growth of this culture. figure 3A shows the dry mass accumulated by the plants during the cycle. Slow initial growth due to the small size of the plants and small leaf area makes a lower nutrient absorption and a low solar radiation, causing little growth of these plants. from 21 days after transplant, an increase in the dm for all the substrates was observed, with emphasis on mixtures of substrates. the substrate composed of 50% organ- ic compound plus 50% substrate Plantmax® (t3), was outstanding for presenting higher values in most of the crop cycle, reaching maximum increment at 49 days after the transplant, with approximately 26 g. the worst results were obtained with vermiculite, reaching approximately 11 g (fig. 3A). the leaf area index presented a similar behavior to dm, with the most accentuated and perceptible increase at 21 days after transplant, when the plant presented an increase in dry matter (fig. 3b). lAi falls at certain points in the crop cycle may be related to the abscission of older leaves. lAi is important for studying crop growth, development and productivity. the leaf area will depend in addition to the number and size of the leaves of the plant and the period in which the leaves remain on the plant (monteiro et al., 2005). this demonstrates that the increase of leaf area provides greater interception and absorption of the available solar radiation, and, consequently, high- er photo assimilates production, which results in higher growth and dry matter of the plants. the best results for these variables were obtained by sub- strate mixtures. Since cgr represents the increment of dry matter per unit of soil area occupied over a given period of time, the pattern of the graph was very similar to that for dry matter. At 49 days after transplant, the substrate, composed of 50% organic compound plus 50% substrate Plantmax®, was higher than the oth- ers, differing statistically just from vermiculite (t6). At this point, t3 reached approximately 60 g m-2 day-1 (fig. 3c). According to beckmann-cavalcante et al. (2009), growth rate of the crop is mainly determined fig. 1 - Solar global radiation (kj m -2 ), maximum temperature and mini- mum temperature (°c) during the lettuce crop cycle. frederico Westphalen, rS, brazil, 2013. fig. 2 - number of leaves of lettuce growth under different substrates. frederico Westphalen, rS, brazil, 2013. Schneider et al. - Lettuce under different substrate compositions 225 by the air temperature. thus, from 21 day after transplant (dAt), cgr also increased as a function of changes in air temperature. the highest rates of rgr were observed at 14 and 21 days after transplant (fig. 3d). Substrate with 75% organic compound plus 25% substrate Plantmax® (t2) reached maximum rgr-approximately 0.25 g m-2. this may be because the plants were in a phase of high photosynthetic rate due to the elevation of lAi and high growth. this same treatment has achieved the highest rgr at 49 dAt, statistically dif- fering from the others. At 28 days after transplant, the growth rate tended to decrease. According to zuffo et al. (2016), this is mainly due to the shading between the plants and the increase in the respirato- ry rate. this shows that with shading and high respi- ration of the plants, the growth promotes a reduc- tion of the rgr of the crop. the photosynthetic efficiency of the leaves pre- sented variations along the cycle and is represented by nAr. this rate tends to be higher at the beginning of the development of the crop due to lower self- shading (gondim et al., 2008). However, in this study the nAr values increased at the end of the cycle because nAr depends on available leaf area, leaf dis- tribution, leaf angle, and translocation and assimila- tion partition (Pedó et al., 2010; Aumonde et al., 2011). Some statistical differences were observed between the treatments on 7, 14 and 42 dAt (fig. 3e). the highest rates of fAr were obtained at 7, 14 and 21 dAt (fig. 3f). After this period, the ratio steadily decreased for all treatments, corroborating the results of Pedó et al. (2013) for pepper. However, fig. 3 - dry mass (A), leaf area index (b), culture growth rate (c), relative growth rate (d), net assimilation rate (e), foliar area ratio (f), foliar weight ratio (g) Specific foliar area (H) for lettuce culture growth under different substrates. frederico Westphalen - rS, UfSm , 2013. lowercase letters differ by tukey means test at 5% error probability. Adv. Hort. Sci., 2018 32(2): 221-227 226 these authors obtained results in the higher fAr, pro- viding a greater area useful for photosynthesis, which produced higher rates of nAr. As for caron et al. (2007), the decrease indicates that at this stage, most of the photosynthesized material is accumulated in the aerial biomass of the lettuce to increase available solar radiation. this shows that the decrease may be due to self-shading and leaf fall resulting from the age of plants, or to energy demand for the develop- ment of other organs, such as flowers. Statistical dif- ferences were found only at 7, 14 and 42 dAt. foliar weight ratio remained similar between the treatments, with values ranging from 0.7 to 0.9 g g-1 during a large part of the crop cycle, with decreases at 42 and 49 dAt (fig. 3g). this may be due to the appearance of preferential metabolic sinks by the formation of the reproductive organs. t1 and t2 were superior and differed statistically to t6 at 42 dAt. Specific foliar area reached differences between the treatments at 7 and 14 dAt. At 7 dAt, the major SfA were obtained by t5, which was statistically equal to t3 and t6 treatments. At 14 dAt, the higher SfA was observed by t2, t3 and t5. At 21 dAt, the values were similar to those obtained at 7 and 14 days. in the rest of the cycle, SfA remained around 0.04 m2 g-1. After the development of the plants, there were an increase in leaf area and dry mass of the leaves, causing decreases in SfA (benincasa, 2003). table 1 shows the means of fresh mass at 42 and 49 dAt. the values show that substrates mixtures obtained the better results. Although they had not shown a significant difference from the others at 49 dAt - with the exception of vermiculite - there were differences that could bring greater profits. However, from the values observed at 42 dAt, it can be con- cluded that the treatments with mixtures of sub- strates were superior to the others. in addition, the use of mixtures such as t2 (75% organic compound plus 25% substrate Plantmax®) and t4 (25% organic compound plus 75% substrate Plantmax®) anticipate the harvest, because the fresh mass was higher at 42 dAt compared to 49 dAt. it is important to emphasize that vermiculite was used like a control treatment, since it is a inert sub- strate used in hydroponics cultivation or mixed with soil; it led to worse results for all variables evaluated and reduced the growth of plants cultivated under this substrate. 4. Conclusions Higher growth of lettuce plants are produced by mixture of organic compound and substrate Plantmax®. the isolated use of vermiculite does not give good results for the growth of lettuce plants, but is an alternative for mixing with other substrates. 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