Organic fertilization : An alternative to produce jalapeñ o pepper under greenhouse conditions

The experiment was conducted during fall-winter seasons of years 2011-2012 to determine the effects of vermicompost tea (VCT) on growth and productivity of “Hechicero” jalapeñ o pepper plants grown under organic and synthetic fertilization in greenhouse. Five different fertilization forms were applied to plants [F1 = sand + inorganic nutrient solution (control group); F2 = sand + VCT on concentration of 10%; F3 = mixture of sand + compost (ratio 1:1; v:v) + VCT on concentration of 2.5%; F4 = mixture of sand + vermicompost (ratio 1:1; v:v) + VCT on concentration of 2.5% y F5 = mixture of sand + compost + vermicompost (ratio 2:1:1; v:v:v) + VCT on concentration of 2.5%]. Treatments F4 and F5 showed an increased yield of 70 and 45% with regard to the yield obtained with F1; the F1 and F2 yields were not statistically different at the 0.05 significance level. The fruit length and the pericarp thickness were increased until 7.55 and 7.01% in F5, respectively. These results suggest that, since there were differences in yield when using the organic and inorganic nutrient source, VCT combined with mixtures of sand + compost + vermicompost may be considered a successful alternative fertilizer for organic jalapeñ o pepper production in greenhouse.


Introduction
Manure, crop residues, green manures, dairy industry sludge, herbal pharmaceutical industry waste, biosolids of agribusiness and food processing waste, once they are properly treated through the process of composting and/or vermicomposting are some of the potential sources of nutrients in organic production systems (Ramesh et al., 2005;Alidadi et al., 2007).According to Ramesh et al. (2005), organic production is an alternative for consumers who prefer food free of pesticides and synthetic fertilizers-risk-free, with high nutritional value.Additionally, organic materials are the safer sources of plant nutrient without any detrimental effect to crops and soil (Hasanuzzaman et al., 2010).
On the other hand, when mixing C or VC with inert growth media, such as sand, the physical and chemical characteristics of the latter show an important improvement, and the vegetable specimens that grow in it can avoid hypoxia.Also, it has been established that both C and VC can satisfy the nutrient demand of several crops, developed in greenhouse conditions, during the first two months post-transplantation (Márquez-Hernández et al., 2006).However, after this time the crops expressed nutrient deficiencies, especially of N (Rodrí guez-Dimas et al., 2007); this may be due to the low rate of N mineralization of both C and VC.Thus, it has been suggested that in production systems under protected conditions, nutritional stress of the culture can be avoided by adding other sources of nutrition, including the vermicompost tea (VCT).
The VCT, a water-based VC extract containing high levels of beneficial microbes and soluble nutrients (Edwards et al., 2010), has attracted the attention of growers and researchers in recent years.The most important reason to apply VCT is to supply microbial biomass, fine particulate organic matter, and soluble chemical components of VC to plant surfaces and soils in a way not possible or achievable with solid VC.However, relatively little work has been done to investigate the effect of VCT on growth and yield of vegetable crops.
We hypothesized that VCT as a fertilizer would positively affect plant growth and productivity of jalapeñ o pepper.Therefore, the specific objective of this study was to investigate the effects of VCT on growth and productivity of jalapeñ o pepper in different media under organic and synthetic fertilization.

Materials and Methods
The experiment was conducted during fallwinter seasons of years 2011-2012, in the Comarca Lagunera region (101°40' and 104° 45' W and 25º 05' and 26º 54' N), in a greenhouse at Universidad Autó noma Agraria Antonio Narro -Unidad Laguna (UAAAN-UL).The greenhouse is semicircular, with acrylic cover and protected reinforced mesh shade during the warmer seasons, gravel floor and automatic cooling system through wet wall and two extractors.It has side windows of 1.20 m high, covered and protected with acrylic roller antiaphids mesh (Mesh Plas ® ).
Treatments were distributed according to a completely randomized design; yield of jalapeñ o (Capsicum annuum L.) cv.Hechicero (Harris Moran ® ) with five forms of fertilization was assessed.
The evaluated fertilization forms were: F1 = sand + inorganic nutrient solution (control group); The population density was 4 pots•m -2 .The sand used in the substrates was previously disinfected with a solution of 5% NaOCl.
The manure-based vermicompost was provided by the vermicompost module of UAAAN-UL, and consisted of separated horse and goat solids (mixed in a 1:1 ratio by volume) with alfalfa (Medicago sativa L.), processed by earthworms (Eisenia spp.) in indoor beds (Atiyeh et al., 2000a) for a period of 90 days (Bansal and Kapoor, 2000).The compost was provided by Max Compost ® .The basic chemical properties of the substrates are summarized in Table 1.The nutrient solution used in F1 treatment (Table 2) was recommended by Castellanos-Ramos and Ojodeaagua-Arredondo (2009).The VCT at 10% of concentration was prepared using the method recommended by Edwards et al. (2010), with a variation that consisted in introduce the bag with VC in a container with 20 L of water for 5 min to wash excess salts, before being subjected to oxygenation.Whereas in a container of 60 L of capacity, 45 L of water were oxygenated with an air pump (Biopro: BP9891.Tiray ® Technology Co Ltd) for 2 h before inserting the bag with 4.5 kg of VC; oxygenation was performed continuously until completion of the process (24 h).In addition, we added 40 g of piloncillo or panela, a product similar to molasses, made from unrefined sugarcane (Saccharum officinarum L.) juice (Solis-Pacheco et al., 2006), as an energy source to promote the growth and development of microorganisms.
The VCT was constantly applied throughout the whole cycle, and to preserve its quality it remained aerated 24 h•day -1 .For treatment F2, 0.5 L of VCT at 10% of concentration was poured in each pot; for treatments F3, F4 and F5, the VCT was diluted to a 1:3 ratio using 1 L of VCT per 3 L of water to give a concentration of 2.5%, and each pot received 1 L. The pH of VCT was adjusted to a value of 5.5 with food grade citric acid (C 6 H 8 O 7 *H 2 O), applied on a concentration of 5 mM (1.2 g•L -1 ) (Capulí n- Grande et al., 2007).
To satisfy the water demand of the crop, a drip irrigation system was used in all treatments, and the amount of water applied, according to the phenological stage of the crop, ranged from 0.35 to 1.9 L•plant -1 •day -1 .It was classified as low-salinity and low sodium water (C 1 S 1 , with a sodium absorption ratio of 2.18) (Ayers and Westcot, 1994), it presented an EC of 1.05 dS•m -1 , pH 7.8; the cation concentrations were Ca 2+ = 3.51, Mg 2+ = 0.48, K + = 0.22, Na + = 2.71 mmol•L -1 , and the anion values were HCO 3 -= 3.12, Cl -= 2.3, SO 4 2-= 2.62 mmol•L -1 .During the growing period, which lasted 134 days after transplanting (dat), the temperature in the greenhouse ranged from 17.4 to 36.9°C, while the relative humidity ranged between 20 and 79%.
Plant height and total yield was recorded in each experimental unit.Fruit quality was determined in four plants of each treatment, 15 fruits per plant, considering the following variables: individual weight, pericarp thickness, number of locules in the fruit, fruit length and equatorial diameter.
To analyze the behavior of the plant height over time, we used linear regression analysis, while for yield and fruit quality an analysis of variance was performed among treatments; means were separated using Fisher´s least significant difference (LSD) test in SAS statistical software (SAS, 1999).Statistical significance was obtained at 95% confidence level (α = 0.05).

Results and Discussion
The growth dynamics of jalapeñ o plants, cv.Hechicero, are presented in Table 3, the regression line fits the data well.In our experiment, the tallest plants at the end of the crop cycle (134 dat) were in the treatment F5, with a value (1.55 m) that was statistically different from the other plants recorded in the remaining treatments (Table 3); these results suggest that VCT consistently enhanced plant growth, which agrees with the findings of previous studies (Sanwal et al., 2006;Hargreaves et al., 2008;Hargreaves et al., 2009).Also noteworthy is the fact that treatment F4 [mixture of sand + VC (ratio 1:1; v: v) + VCT at concentration of 2.5%] recorded the second highest plant (1.16 m).Pant et al. (2009) found that the use of VCT had a greater effect on plant height under VC fertilization, and had much smaller effect on plant height under Osmocote fertilization.Additionally, Keeling et al. (2003) and Siddiqui et al. (2008) observed that application of VCT and compost tea on oilseed rape plant and okra plants, increased root development, plant growth and tap root length, respectively; although we did not measure root growth and nutrient uptake, plants grown in F4 and F5 showed better plant height and nutrient uptake compared to control plants, suggesting that these two variables might be part of the mechanisms involved in plant growth stimulation.Our results might be due to the presence of the VC and the VCT, materials that provide higher quality than manure generated by traditional methods of composting (Santamarí a-Romero et al., 2001;Panikkar et al., 2004;Lopes-Pereira et al., 2005).Treatments F4 and F5 (which included VC and VCT) outperformed the control treatment (sand and nutrient solution), concurring with the results reported by Rodriguez-Ortiz et al. (2010), who concluded that VC fertilization at 1.5 to 3.0 t•ha -1 during transplanting of green onions (Allium cepa L.) favored a greater height of this species when compared with plants receiving synthetic fertilization.Arancon et al. (2007) reported that humic, fulvic and other organics acids extracted or produced by microorganisms in VCT could induce plant growth.Garcia-Martinez et al. (2002) showed that water extract of compost contained a compound with molecular structure and biological activity analogous to auxins.Leachate from well decomposed compost contains cytokinin-like substance, derived from hydrolysis of cyanogenic glucosides by the enzyme β-glucosidase produced by microbes (Arthur et al., 2001).Although phytohormones or growth regulators in VCT were not measured in the present study, they may play an important role in plant responses.
The F1 and F5 yield, fruit length, pericarp thickness and number of fruits were statistically different at the 0.05 significance level (Table 4).The heaviest fruits were obtained with treatments F1 and F5, in that order, while the lowest weight was recorded in treatment F2.On the other hand, according to the specifications of the official mark "México Calidad Suprema" for chili (SAGARPA-ASERCA, 2011), F4 and F5 treatments correspond to large fruit size.
The difference in yield obtained in the F1 and F5 treatments was due to the number of fruits per plant, not to the weight of fruits.The overall average yield obtained in our experiment was 208.74% higher than the average yield (14.76 Mg•ha -1 ) obtained by Mexican producers under irrigation and rainfed conditions (SIAP, 2011).The F4 and F5 treatments increased the yield until 70.7 and 45.42% respectively, in relation to the average obtained for the control group F1.While the F5 treatment increased the yield until 17.42% compared with the F4 treatment yield.The F2 and F3 treatments were not statistically different to the control group F1 (Table 4).The results contrast with those reported by Subler et al. (1998), who stated that the best crop development occurs when applying between 10 and 20% VC, although, Atiyeh et al. (2000aAtiyeh et al. ( , 2000b) ) indicated that using more than 20% of VC in the growth substrate decreases the yield of the plant.In our experiment, the jalapeñ o plants in T3, T4 and T5 treatments consumed 92.73, 165.65 and 194.52 kg of N to obtain the respectively yield (Inzunza-Ibarra et al., 2010).Furthermore, when making the extrapolation of percentage to kilograms of N per hectare for each one of sources of organic fertilizers (Table 1), considering a mineralization of 11% (Eghball, 2000;Adegbidi y Briggs, 2003), the N available needed in the treatments F3, F4 and F5, was 607.3, 320.0 and 463.6 kg•ha -1 , respectively.Therefore, we may assume that these three treatments showed adequate levels of N that favored the development of the jalapeñ o pepper.However, factors as leaching, a lower rate of mineralization, the volatilization and the adsorption process (Sikora and Szmidt, 2001), solely allowed reaching the yields already indicated.Regardless, it is important to note that the obtained yields reflects the high amounts of nutrients contained in C, VC and VCT, as mentioned by Edwards et al. (2010).

Conclusions
The results obtained showed that VCT, prepared from the VC (made with horse and goat manure with alfalfa straw, mixed in a 1:1 ratio by volume), caused positive effects on development indicators of jalapeñ o pepper.During this study, the organic production of jalapeñ o pepper under protected conditions and using organic fertilizers resulted in a high yield.The use of VCT, C and VC can be considered as an alternative fertilization method for organic production in greenhouses, since they contain soluble nutrients that can satisfy the nutrient demand of this plant.

Table 1 .
Chemical analysis of the materials used during the development of jalapeñ o pepper under greenhouse conditions (n = 1).

Table 2 .
Concentration of the nutrient solution used to develop greenhouse jalapeñ o pepper.

Table 3 .
Regression equations for fertilization sources regarding plant height in jalapeñ o pepper under greenhouse conditions.y= height; x = das.Values with the same letter in last column are statistically equal, LSD test P ≤0.05. *

Table 4 .
Mean values and statistical difference of the variables evaluated in jalapeñ o pepper grown with organic and synthetic fertilizer under greenhouse conditions.
*Values with the same letter within each column are statistically equal, LSD test P ≤0.05.WF = weight of fruit; FL = fruit length; ED = equatorial diameter; PT = pericarp thickness; NF = number of fruits; NL = number of locules; CV = coefficient of variation.