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Introduction
Mexico is megadiverse country considered as a center of origin and domestication of cultivations of agricultural and food importance, such as corn, bean, cotton, zucchini, prickly pear and chili pepper (Perales & Aguirre, 2008; Boege, 2008). The origin of bell pepper (Capsicum annuum L.) dates back to 7000-5000 B.C., in the state of Tamaulipas, by remains found in caves of Ocampo de la Sierra, posteriorly between 6000-4000 B.C. in Coxcatlán in Tehuacán Valley, and between 600-1521 A.D. in Silvia and Guilá Naquitz in Oaxaca (Castellón, 2014). Its importance not only lies in the fact that Mexico is the center of origin, but as well for its production capacity and contribution to worldwide production, which increased in the last decades, contributing to 7 % of worldwide production from 2010 to 2018 (FAO, 2019), ranking Mexico as the main worldwide producer (SAGARPA, 2017), with San Luis Potosi taking up the fourth place of national pepper production (SAGARPA, 2012). In the municipality of Guadalcazar, San Luis Potosi, Mexico, current issues about soil salinity and degradation, decrease in soil microbiota, less volume and quality of bell pepper harvest, due to an excessive use of agrochemicals for pepper production, caused concern and forced the productive sector to look for alternatives to recover soil quality and improve production volumes and quality.
In this context, the present research work aimed to evaluate productive and quality response of six commercial varieties of bell pepper (Capsicum annuum L.) to organic fertilization in macrotunnels in the municipality of Guadalcazar, San Luis Potosi, Mexico.
Material and Methods
Location of study site
The experiment was performed from June to November 2018 in Rancho la Terquedad, km.121 San Luis Potosí - Matehuala road, located in the municipality of Guadalcazar, San Luis Potosi, Mexico. Its coordinates were: 100º45’ West Longitude and 23º22’ North Latitude, with an elevation of 1,630 masl, the type of main climate was BSokw”(e)g, dry temperate with warm summer, rains in summer, and the driest season was winter (García, 1973), annual average temperature was 17.4 ºC, with a maximum of 45 ºC in May and a minimum of 6 ºC, annual average precipitation was of 840.6 mm, soil was loamy-type.
Vegetal material
The evaluated bell pepper genotypes were: Revolution F1 (definite habit), Mysterio F1 (definite habit), Karisma F1 (definite habit) from Harris Moran trading house (Davis, California. EU), Anaconda (indefinite habit), from Enza Zaden trading house (Beheer B.V), Green Noa 214 (indefinite habit), Monarcha 30 (indefinite habit) from Syngenta trading house (Basilea, Suiza).
Seedling production
Seedling production was performed in June 2018, in Styrofoam trays with 200 cavities, using peat moss as a substrate to make the radicular development easy, sowing depth was 10 mm, once sown, the trays were placed in a macrotunnel used in a special way for seedling production.
Soil preparation, drip irrigation tape installation and transplant beds preparation
Previous cultivation works to macrotunnels and transplant establishment consist in a step of disk plow (Massey Fergurson, MF 3026 model, of 3 disks with 18” of diameter), two steps with harrow (bissonte B456 model, of 16 disks, with disks of 12” of diameter). Furrower was performed with two furrowers, 0.30 m width and 21 m long, distance between furrows of 0.35 m. For irrigation, a drip irrigation T-tape was installed (Rivulis Eurodrip, Israel) caliber 6 thousand, with a distance between emitter of 30 cm and emitter expense of 1 lph.
Macrotunnels establishment
For experiment development, six macrotunnels were established with an oval shape with 3 m high, 7 m width and 21 m long, oriented from north to south, where the access door was located on the south side, covered with white polycarbonate with caliber of 720 gauges, with 10 furrows by macrotunnel.
Bocashi production
Bocashi was produced in January 2018, in a shed with 2.5 m high, to avoid excess of humidity and to promote anaerobic fermentation, in a surface of 36 m2 (6 m x 6 m), it was compacted and covered with a canvas, two lateral canals were done on each side to avoid humidity accumulation.
Bocashi preparation
Bocashi was produced according to the materials and procedure described by Restrepo (2009) (Table 1). Prior to preparation, the place was set up, placing a canvas with its respective posts for it to be at 3 m high, to protect compost from climatic factors: sun, wind, and rain, to avoid alterations in the fermentation process; regarding soil, it was compacted, once compacted, a black oilcloth was placed in order to avoid humidity accumulation which could originate from the soil, thus the compost being separated from the soil.
Table 1 Materials used for Bocashi preparation.
| Material | Quantity |
| Fresh cow manure | 300 kg |
| Corn stover | 200 kg |
| Rice husk | 50 kg |
| Vegetables ash | 50 kg |
| Bread yeast (Sacharomices cervicidae) | 1.0 kg |
| Sugarcane molasses | 8 L |
| Soil | 100 kg |
As a first layer, rice husk and corn stover were placed and spread out, with 10 cm width for both elements, the second layer consists in applying soil, extending it to get a layer of 10 cm width, posteriorly a layer of 10 cm width of cow manure was laid, as a fourth layer vegetables ashes (weeds) were placed; each layer was applied with its respective quantities (Table 1). Sugarcane molasses and yeast were previously diluted in 10 L of water; once diluted, 2 L of molasses and 750 mL of yeast were applied between layers; once ingredients were blended, they were turned over in order to obtain a homogenous mix, and humidity was checked by fist test until the mix got a clod shape without collapsing. When the mix was ready, bricks were placed all over the compost to avoid rain flooding or excess of humidity and it was turned over three times a week to control temperature of fermentation. Produced Bocashi had pH of 7.45 (1:2.5 ratio soil:water), electric conductivity of 4.80 ds/m; 16.50 % of organic matter, organic carbón 9.15 %, nitrogen 0.70 %, 1.307 % of P2O5-Olsen; 0.09 % of K2O; 18623 ppm of available Ca+; Mg 2254 ppm, Cu 25,80 ppm; Fe 3133 ppm; Zn 178 ppm; Mn 247 ppm; Na 2028 ppm; nitrate (NO2) 1187 μg/mL; ammonium (NH4) 136 μg/mL.
Transplant
Transplant was performed 40 days after emergence, at the time of the transplant seedlings had substrate root ball completely covered by root, 7.0 cm high, 4 mm of stem diameter and four to six true leaves. Distance between plants was of 30 cm with a single row.
Bocashi application
Bocashi application was manual, in the first vegetative stages (seedling, vegetative growth, flowering, fructification), 100 g plant-1 were applied during the growth stage (4 days after transplanting), 500 g plant-1 were posteriorly applied until the flowering stage (21 days after transplanting) and 4.5 kg plant-1 every third day for fruit mooring and fructification (40 days after transplanting) (Restrepo, 2009).
Biofertilizer
Employed biofertilizer was simple supermagro, which was prepared according to the methodology described by Restrepo (2009) (Table 2). In a 200 L plastic barrel, 100 L of water were added, posteriorly fresh cow manure, weed ashes, sugarcane molasses were consecutively added, then bread yeast (Saccharomyces cerevisiae) dissolved in warm water together with cow milk, shaking until obtaining an homogenous mix. Finally, water was added until completing 180 L of the preparation. A lid with clasp was placed on the barrel to close it hermetically, in which a nipple under pressure was placed with a plastic transparent hose close to it, a bottle of water was placed at the other end of the hose as a gas trap system or a water seal to release gas accumulated in the barrels. Fermentation time was one month.
Biofertilizer application
For biofertilizer application, a 20 L manual backpack was used with download of 630 mL per minute at 3 bars of pressure. Biofertilizer dose used at 8 days after transplanting was of 2 L diluted in 20 L of water and during flowering stage (21 days after transplanting) of 10 L diluted in 100 L of water to reach fruit mooring, the same dose was maintained during the harvest stage.
Control of pests and diseases
For pests control, leaves of bell peppers were previously monitored (upper and lower face) per experimental unit to detect their presence. Pests which were identified were: potato psyllid (Paratrioza cockerelli sulc), silverleaf whitefly (Bemisia tabaci), pepper weevil (Anthonomus eugenii). For its control, sulfocalcic broth was elaborated according to the methodology reported by Restrepo (2009) (Table 3) and it was applied with its respective doses (Table 4), by means of a 20L sprinkling backpack. Materials used were allowed by NOM-037-FITO-1995 standard for organic production.
Table 3 Materials and quantities used for sulfocalcic broth preparation.
| Material | Quantity |
| Water | 100 L |
| Sulfur | 20 kg |
| Lime | 10 kg |
Harvest
Cuts for bell pepper cultivation were performed when fruits presented harvest indexes characteristic of the cultivation, such as: color, formation of the four locules and firm and solid texture, obtained yields were estimated in tons per hectare.
Estimation of harvest quality
Twenty fruits per variety were randomly sampled for each cut and were measured for their diameter, taken in straight angle to the longitudinal axe, for their length, taken in a line parallel to the longitudinal axe from the base of the peduncle, and the percentage of bell peppers fulfilling sensorial specifications according to PC-022-2005 was determined, conditions for the use of Mexico Supreme Quality label in bell peppers (SAGARPA, 2018) according to the following criteria: a) entire and well developed, minimum length and width of 65 mm; b) fresh and healthy aspect; c) firm consistency; d) sweet flavor, with no degree of pungency nor burning aftertaste; e) well-formed and color according to the variety; f) clean: practically free of any strange visible material such as soil, excessive humidity, etc.; g) free of rotting or damage; h) free of imperfections of meteorological origin (hail, sun burn, damage by cold), mechanical, entomological (insects) or geneticphysiological origin; i) free of any strange smell and/ or flavor.
Treatment distribution, experimental design and statistical analysis
Each macrotunnel was divided into 2 sections in lengthwise as follows: 1 meter with no use at the entrance of the macrotunnel, 9 meters for the establishment of the crop (section 1), 1 meter with no use at the center of the macrotunnel as a separation between sections, 9 meters for the establishment of the crop (section 2) and 1 meter with no use at the end of the macrotunnel. In the sections of the macrotunnels, furrows were divided to have three blocks per section, alternating two furrows with crop and two furrows without crop. Varieties and treatment (organic fertilization and without fertilization) were randomly allocated to each macrotunnel and each section.
Assessed variables were yield and percentage of bell peppers fulfilling requirements for Mexico Supreme Quality label, the experimental design used was in subdivided plots (97 degrees of freedom), with 6 varieties (factor A, 5 df), 2 treatments (organic fertilization and without fertilization as factor B, 1 df), 7 periods of cut (factor C, 6 df), and 3 blocks (2 df). The analysis of variance was performed according to the procedure for General Linear Model (GLM) of SAS Statistical Analysis Software (2008), the interaction between factors block*variety (10 df), between variety *fertilizer (5 df), between block*fertilizer (2 df), between variety*cut (30 df), between fertilizer*cut (6 df), between variety *fertilizer*cut (30 df) were considered, comparison of means test was performed by means of Tukey test (SAS, 2008) with a level of significance of 0.05. No treatment with chemical fertilization was included, since the municipality is willing to switch a traditional system for an organic production.
Results and Discussion
The analysis of variance showed significant differences (p≤0.01) among varieties, type of fertilizers and interaction variety*fertilizer, with the comparison of means test, the highest yields per type of fertilizer were obtained with organic fertilization; regarding varieties, Revolution and Mysterio were the varieties with the highest yield, followed by Karisma and Monarcha , variety Green Noa and variety Anaconda were the less productive, the interaction between variety*fertilizer (Inter V*F) indicated that the yield was higher with varieties Revolution and Mysterio with organic fertilization (Table 5).
Table 5 Yield per cut and total in t ha-1, of six commercial varieties of bell pepper grown with organic fertilization and without fertilization in the municipality of Guadalcazar, S.L.P. Mexico.
| Variety | ||||||||||||
| Karismab | Revolutiona | Monarchab | Mysterioaa | Green Nc | Anacondad | |||||||
| Fertilization Cut | OFa | WFb | OFa | WFb | OFa | WFb | OFa | WFb | OFa | WFb | OFa | WFb |
| 1 | 6.1 | 2.2 | 5.7 | 1.4 | 5.6 | 1.9 | 5.5 | 2.1 | 4.9 | 1.9 | 3.6 | 1.1 |
| 2 | 2.7 | 1.4 | 3.6 | 1.5 | 3.4 | 1.5 | 3.6 | 1.9 | 3.4 | 1.1 | 3.0 | 1.2 |
| 3 | 2.3 | 1.3 | 2.9 | 1.2 | 2.3 | 1.3 | 3.0 | 1.2 | 2.5 | 1.1 | 2.4 | 1.2 |
| 4 | 2.3 | 1.3 | 2.5 | 1.2 | 2.1 | 1.3 | 2.1 | 1.2 | 2.3 | 1.0 | 2.2 | 1.1 |
| 5 | 2.1 | 1.2 | 2.4 | 1.1 | 2.1 | 1.2 | 2.1 | 1.1 | 2.2 | 1.2 | 2.1 | 1.0 |
| 6 | 2.0 | 1.2 | 1.9 | 1.1 | 2.0 | 1.1 | 2.0 | 1.1 | 2.0 | 1.3 | 1.9 | 0.5 |
| 7 | 1.7 | 0.9 | 1.5 | 0.5 | 1.3 | 0.6 | 2.0 | 0.8 | 1.8 | 0.2 | 1.8 | 0.3 |
| Total | 19.2 | 9.5 | 20.5 | 8.0 | 18.8 | 8.9 | 20.3 | 9.4 | 19.1 | 7.8 | 17.0 | 6.4 |
| Inter V*F | b | d | a | f | b | e | a | d | b | g | c | h |
| SEM | 0.8 | 0.1 | 0.8 | 0.1 | 0.8 | 0.1 | 0.7 | 0.1 | 0.6 | 0.2 | 0.3 | 0.2 |
OF: organic fertilization, WF: without fertilizer, SEM, standard error of means; a-b Means with different superscripts among columns within a row are significantly different (p≤0.05).
Regarding the percentage of bell peppers fulfilling criteria to obtain Mexico Supreme Quality label (Table 6), as well, the highest percentages were obtained with organic fertilization, compared with those that were not fertilized. Regarding varieties, Karisma obtained the highest percentage of bell peppers that fulfilled criteria, followed by Revolution, Monarcha and Mysterio, the varieties Green Noah and Anaconda were those with the lowest percentage of products with requisite characteristics (p≤0.05).
Table 6 Percentage of bell peppers classified as Mexico Supreme Quality, of the total production of six commercial varieties of bell pepper grown with organic fertilization and without fertilization in the municipality of Guadalcazar, S.L.P. Mexico.
| Variety | OFa | WFb | SEM |
| Karisma a | 92 | 35 | 1.5 |
| Revolution b | 86 | 28 | 2.5 |
| Monarcha b | 85 | 27 | 3.0 |
| Mysterio b | 88 | 33 | 2.0 |
| Green Noah c | 79 | 23 | 3.5 |
| Anaconda c | 75 | 21 | 4.0 |
OF: organic fertilization, WF: without fertilizer, SEM, standard error of means; a-b Means with different superscripts among columns or among rows are significantly different (p≤0.05).
In the review of the literature, no similar works were found in the region, maybe for its productive potential, being this work the first showing the advantages of the implementation of systems of organic production of bell peppers in the region. As expected, both the yield and the percentage of bell peppers with characteristics to be considered as Mexico Supreme Quality were higher with the application of organic fertilization. Bissala et al. (2006) mentioned that the correct way to assess the use of composts is comparing their effect on growth and production of crops to a control. In this experiment, Bocashi application was found to increase the production volume of more than 100 % in all the assessed varieties and to be over the average yield of the zone (11 t ha1), compared with the control treatment. This increase in production was similar to the results of Boudet et al. (2015), who reached increases between 95 and 100 % in the production volume of bell pepper variety California Wonder with Bocashi type organic fertilization, but higher to those reported by Jamir et al. (2017), who found that using organic fertilization mixed with chemical fertilizers in a proportion of 50-50 % resulted in an increase of 58 % in the production of bell pepper compared with chemical fertilization. The increase of the production when using organic fertilization was consistent, probably due to the contribution of nutrients, in addition to humidity retention enlarged by organic fertilizers and to improved soil biological activity, increasing fertility and thus productivity (Ormeño & Ovalle, 2007). When compared with chemical fertilizers, the capacity of organic fertilizers as a source of nutrients is low (Álvarez-Solís et al., 2010), but its effect is extended, they avoid plants burns (FAO, 2012), promote the growth of beneficial microorganisms, which control the growth of pathogenic microorganisms by effect of competition for space and energy, generate a micro-environment of biologically favorable pH (6.5 to 7.0) for radicular absorption (Agüero et al., 2014) and for its low cost, they allow reaching a long-term sustainability (FAO, 2002).
Conclusion
Organic fertilization influences fruit yield and quality, Revolution and Mysterio were the commercial varieties which had the higher productive response (20.5 and 20.3 t ha-1), and more than 85 % of produced bell peppers fulfilled criteria to obtain Mexico Supreme Quality label. Therefore, its production system with the described varieties may be a profitable and sustainable option for bell pepper production in the municipality of Guadalzacar, San Luis Potosí, México.
