Study area

The investigation was carried out under field conditions, on the planting date recommended for the area (october-january) of the municipality of Jiguani, eastern province of Granma, Cuba, in Unit BPC No. 1 “Ernesto Che Guevara” of the Company Cauto The Yaya, located at 176° 100’ north latitude and 506° 000’ LE (Academy of Sciences of Cuba, 1989). The average temperature and humidity during the experimentation period were 24.5°C and 77.8%, respectively according to ^{Hernández et al. (2013)}, the soil of the area is Fluvisol type, whose composition at a depth of 21-40 cm showed a pH of 7.6; an electrical conductivity of 2.45 dS m^-1, an organic matter content of 2.8% and a slope of less than 1%, with low fertility and slightly saline.

Experiment management

The Amalia tomato variety was used. Soil preparation and cultural practices were carried out in accordance with ^{Gómez et al. (2000)}. Irrigations were applied according to the water needs of tomatoes in the eastern region of Cuba. Hilling and weeding were done manually.

Experimental design

The experiment was established in a randomized complete block design with four repetitions. The treatments applied were three dilutions of Liplant^®, 1/10, 1/ 20, and 1/30 v/v and a control without application of this product (distilled water). The transplant was performed at a distance of 1.4 m between rows and 0.25 m between plants, in plots of 8 m², with a total experimental area of ​​164.45 m². The useful plot consisted in selecting the plants located in the three central furrows of each experimental unit, except for two plants at the ends of each furrow.

The Liplant^® was applied in a foliar way using a Senior model sprinkler with a conical nozzle, which was previously calibrated. The applications were made 10 and 25 days after the transplant (ddt) and 15 days after the first application.

Composition of the Liplant^®

The Liplant^® is considered a biostimulator plant and carrier of nutrients (Ca, Mg, Na, P₂O₅, K, N), free amino acids, polysaccharides, carbohydrates, inorganic elements, humified substances, beneficial microorganisms, plant hormones and soluble humus, whose composition by chemical fractions correspond to a pH of 8.7, 53.4% of C, 4.85% of H, 35.6% of O, 3.05% of N, 0.72% of S, an H/C ratio of 0.08, an O/C ratio of 0.62 , a C/N ratio of 18.4, 4.82 of humic acids and 7.17 of fulvic acids in an E4/E6 ratio of their optical coefficient.

Growth variables

For the evaluation of the growth variables, ten plants were used per treatment and repetition, randomly selected, while, for the fruit quality variables, ten fruits were randomly selected by treatment and repetition. The height of the plant (cm). It was measured 5 days after the transplant, with a flexometer from the base of the stem below the first internode to the top of the branches or crown of the plant. The stem diameter (cm). It was measured 5 days after the transplant, with a vernier or vernier caliper.

Production variables

Fresh weight of fruits (g). At 65 days after the transplant, the fruits were harvested and weighed on a precision scale (Mettler Toledo^® PR2002). The polar and equatorial diameter of fruits (mm). These variables were determined using a vernier or vernier caliper (VWR^® modelo 62379-531, S/N/ 61581129, USA). The dry weight of fruits (g). The fruits were placed in paper bags and placed in a drying oven (Shel-Lab^®, modelo FX-5, serie-1000203) at 65 ^oC, until constant weight. The weight was determined by precision balance (Mettler Toledo^® PR2002). The number of fruits per plant. The quantification of the fruits per plant was carried out, when 50% of the fruits of each plant appeared by treatment and repetition. The yield of fruits (t ha^-1). The fruits were harvested and weighed in each plot and with this the yield was estimated.

Fruit quality variables

Total soluble solids or sugar content (%). It was determined by manual refractometer (Atago^® N-1 alfa, Atago^® Co., LTD. Itabachi-ku, Tokio, Japan; °Brix 0-32%), placing two drops in the prism of the refractometer, according to the equipment instructions. The titratable acidity (expressed as percentage of citric acid). It was determined by the AOAC method (1990), homogenizing 10 g of tomato fruit pulp in a blender (Hamilton Beach^®, model 58149-MXR) with 50 mL of distilled water and once the juice or extract was obtained, it was filtered, aliquots of 10 mL were taken and 0.01 N NaOH was added until neutralization was achieved. The maturity index. It is the value that relates the total soluble solids and the titratable acidity. It was determined by dividing the values ​​of the total soluble solids and the titratable acidity.

Vitamin C (mg 100^-g). It was determined by means of an oxide-reduction volumetry, using an iodine solution as an oxidizing agent that constitutes the standard titrant (^{Ciancaglini et al., 2001}). To measure the pH of the fruit juice, a sample of 10 g of fruit pulp was taken and homogenized in a blender (Hamilton Beach^®, model 58149-MXR) adding 100 mL of distilled water; Once the juice or extract was obtained, it was filtered and the pH was measured with a portable potentiometer (Orion Stara A3215 Thermo Scientific ^®, USA). Loss of fruit weight (%). The fruit weight was obtained using an analytical balance (Mettler Toledo^®, modelo AG204). The water loss was determined with respect to the initial weight of the fruit. Firmness of fruits with peel (lb pulg^-1). It was determined by means of penetrometry, using a penetrometer or portable durometer (Mitotuyo^® Tamex Precision, Japan).

Economic valuation

To determine the economic effect of the use of the vegetable bioestimulant Liplant^®, an accounting analysis was carried out based on the yield (t ha^-1) and considering the following indicators: value of production in thousands of pesos (MP) per hectare (VP); cost of production of one hectare in MP (CP); net profit in MP (B); cost per weight for one hectare of tomato (C/P) and benefit/cost ratio in pesos (B/C), which were calculated with the following equations:

VP= R×Vm. Where: VP= value of production in MP per hectare; R= agricultural yield in tons per hectare; Vm= value of a ton of tomato.

CP= Cc+Cct. Where: CP= production cost of one hectare in MP; Cc= common cost for one hectare in MP; Cct= cost of harvest and transport of one hectare in MP.

B= VP-CP. Where: B= net profit in MP; VP= value of production in MP per hectare; CP= production cost of one hectare in MP.

C/P= CP/B. Where: C/P= cost per weight for one hectare of tomato; CP= production cost of one hectare in MP; B= net profit in thousands of pesos MP.

B/C= B/CP. Where: B/C = benefit/cost ratio in pesos; B= net profit in MP; CP= production cost of one hectare in MP.

Statistical analysis

Analysis of variance was carried out and when significant differences were found between treatments, multiple comparison tests of means were performed (Tukey HSD, p≤ 0.05). In order to comply with the assumptions of homogeneity of variance, data transformations were made when necessary. The variables expressed as a percentage were transformed using arcosine (^{Sokal and Rohl, 1989}). The analyzes were performed with Statistica^® v. 10.0 for Windows StatSoft^®, Inc. (2011).

Growth variables

Stem height and diameter showed significant differences between treatments, observing that both variables increased their values in the 1/30 dilution of Liplant^® (Table 1). ^{Napoles-Vinent et al. (2016)}, reported results with positive response of tomato variety Amalia before the action of Liplant^®, where the most effective treatment proved to be that of the dilution of the product in a concentration of 1/30 (v/v). ^{Fonseca de la Cruz et al. (2011)}, in tomato, it reports positive results with the use of arbuscular mycorrhizols by imbibition to the seeds during 12 hours and three treatments of earthworm humus (Liplant^®).

Studies using vermicompost humus as a foliar fertilizer agree that the positive effect of this product on plant growth is due to the biochemical composition of Liplant^® (^{Nardi et al., 2002}). The presence of minerals and phytohormones such as auxin, which are in greater concentration in the Liplant^®, stimulate the height of plants (^{Pierik, 1990}, ^{Mayhew, 2004}). In other species, such as tobacco, the Liplant^® also significantly increased the agricultural yield, by spraying at a dilution of 1/60 in correspondence with the greater length and width of the leaf and biomass accumulated in the leaf and stem (^{Mariña de la Huerta et al., 2012}).

Production variables

Number of fruits per plant, polar and equatorial diameter of fruits, fresh and dry weight of fruits and fruit yield, showed significant differences between the dilutions of Liplant^® and in all the mentioned variables, they increased their values in the dilution of 1/30 (Table 1).

The average fruit dry weight was higher in the 1/30 dilution, with 86.2 g, surpassing the control by 81%; similar to the rest of the production variables, fruit yield was higher in the 1/30 dilution, with 21.6 t ha^-1, surpassing 62.5% in the control (Table 1). Similar results reported ^{Napoles-Vinent et al. (2016)}, when using Liplant^® in tomato, showing a significant increase in plant height, stem diameter, number of fruits and polar and equatorial fruit diameter, as Liplant^® dilutions were increased from 1/10 to 1/30 v/v, with respect to the control. In lettuce, ^{Hernandez et al. (2013}). There are several reports of the increase in the number of fruits caused by the presence of phytohormones (^{Alfonso et al., 2010}; ^{Falcón et al., 2010}; ^{Terry et al., 2012}; ^{De la Huerta et al., 2012}).

The positive effect of Liplant^® on tomato was evident in this study, considering that this species is demanding in nutrient levels (^{Hernández and Chailloux, 2001}). ^{Torres-Rodríguez et al. (2016)}, used three dilutions of Liplant^® (1/40, 1/50, 1/60 v/v and a control treatment) in tomato plants, checking positive results 24 days after sowing.

Fruit quality variables

The variables fruit firmness, titratable acidity, total soluble solids, vitamin C, maturity index and moisture loss, showed significant differences between the treatments based on dilutions of Liplant^®, while the pH of the fruit juice showed no differences significant (Table 1) and showed average values with a minimum difference (4.35 and 4.36), which coincide with those reported by ^{Cantwell (2006)} and ^{Navarro-López et al. (2012)}. The highest values of fruit firmness, total soluble solids, vitamin C, maturity index and moisture loss, were presented in the dilution of 1/30 (v/v) and exceeded the control in 84.2, 84.11, 91.56, 64.00 and 90.34%, respectively.

The highest value of the titratable acidity was presented in the control and this decreased in the dilution of 1/30. Accord with ^{Infoagro (2017)}. Other studies report that liquid humus in dilutions of 1/30 and 1/40, in tomato variety Amalia, did not cause significant variations in the pH and acidity of the fruit (^{Arteaga et al., 2006}).

The pH of tomato fruit juice usually does not vary significantly between the different factors or sources of variation that are reported (^{Cantwell, 2006}; ^{Casierra-Posada and Aguilar-Avendaño, 2008}; ^{Navarro-López et al., 2012}; ^{Napoles-Vinent, 2016}), which coincides with the results of this research; however, for fruits that are intended for industry, a pH of 4.4 is suggested (^{Hidalgo-González et al., 1998}).

The range of the titratable acidity values of this study was from 0.36 to 0.46. It is reported that the titratable acidity in tomato differs a lot depending on the factors such as the variety, cultivation conditions, temperature or weather conditions in general. Thus, ^{Arias et al. (2000)} reports an average titratable acidity value in tomato of 0.63%, while ^{Dobricevic et al. (2007)} in his research found a range of 0.19 to 0.45%, while ^{Navarro-López et al. (2012)} reported a range of 0.27 to 0.45%. Values less than 0.25 are required for tomato industrialization (^{Hidalgo-González et al., 1998}). In relation to the content of soluble solids (°Brix), loss of humidity and vitamin C, also ^{Arteaga et al. (2006)}, reported percentage increases in tomato in these variables, when applying liquid humus in a dilution of 1/30, with values of 14-24, 22.5-37.0 and 11-26.2%, respectively. The values of total soluble solids presented by the fruits in this study (4.5-5.35%), are located in the range of those reported by ^{Navarro-López et al. (2012)}.

The accumulation of dry matter due to loss of moisture of fruits was greater in the fruits harvested in the plants to which the Liplant was applied, which increased as the concentration of the product increased (^{Yang et al., 2004}). ^{Garcés (2002)} points out that the minerals K and P present in the

Liplant^® when absorbed via foliar and found in appropriate concentrations, increase the dry matter of the fruit, by increasing the size and therefore the diameters of this. While vitamin C increased as the dose increased.

The maturity index, that is, the ratio of total soluble solids and titratable acidity is an important criterion to evaluate the quality of the tomato fruit, because the application of liquid humus, caused lower acidity (better flavor) and therefore higher nutritional quality (^{Arteaga et al., 2006}). Similar results were found in this study, other reports indicate that a value greater than or equal to 4 °Brix for fresh consumption (^{Gómez et al., 2000}; Arteaga, 2004; ^{Navarro-López et al., 2012}). Although in this study, enzymes associated with salinity stress were not determined, it is important to mention that the application of humic substances derived from vermicompost, specifically Liplant^® under conditions of abiotic stress, increases the proline content and the accumulation of biomass of the corn plants (^{Huelva et al., 2009}; ^{Reyes-Pérez et al., 2009}; ^{Reyes-Pérez et al., 2011}).

In rice grown under drought conditions, the application of humic substances in concentrations of 30 and 40 mg L^-1 increased the activity of peroxidase (^{Schiavon et al., 2010}, ^{García et al., 2012}). The application of humic substances in corn, causes an effect in the production of reactive oxygen substances and increases the activity of catalase (^{Cordeiro et al., 2011}; ^{Aydin et al., 2012}).

Economic valuation

The results of the economic analysis showed that the greatest economic benefit was obtained by applying Liplant^® at a dilution of 1/30 (v/v), which reported a benefit of $36 753.9 thousand Cuban pesos per hectare, with a higher value in the benefit/cost ratio of $3.6 Cuban pesos. The benefit was lower in the control, with $16 264 thousand Cuban pesos and a value in the benefit/cost ratio of $1.6 Cuban pesos (Table 2). In this study, it is emphasized that the introduction of Liplant^® in agriculture is economically viable.