Experiment Location

The experiment was conducted during 2017 in “Caprico divino” farm, in Suchiapa, Chiapas, México, located at 6° 37’ 30” N and 93° 6’ 0” W and at an altitude of 500 m. The climate is warm sub-humid with periodic rains with average annual precipitation of 956 mm.

Maize Cultivar and Microorganisms

Maize (Zea mays) cv “Tuxpeño” hybrid seeds were obtained from PROASE (Productores Asociados de Semillas, Chiapas, México). For vermicompost plus mycorrhizal arbuscular fungi (V+M) treatment, seeds were submerged in commercial mycorrhizal arbuscular fungi mixture (Tec Myc 60®) for one hour and further sun-dried. For vermicompost and chemical treatments, seeds were submerged in water also for one hour and sun-dried before soaking. Plant to plant and row to row distances were maintained at 20 and 40 cm respectively. At maturity, plants were harvested manually and grains were used for the study of proximate chemical composition and amino acid profile analysis.

Cow Manure Vermicompost and Soil Characterization

Soil was collected in the experimental field. Five random subsamples of the entire field were taken, then the subsamples were mixed to obtain a composite sample that was used to perform the analyses. Soil and vermicompost were characterized in terms of pH, organic C, organic matter, total N, and available phosphorus as reported by ^{Contreras-Ramos et al. (2004)}.

Both soil and vermicompost total N contents were used to calculate the amount of chemical and vermicompost fertilization. In the chemical treatment, fertilization was done with a mixture of N-P-K 150 kg ha^‑1 of 46-00-00, 200 kg ha^-1 of 18‑46‑00 and 100 kg ha^-1 of 00-00-60 after 15 days of plant emergence. In the vermicompost treatment, the fertilization was done after 15 days of plant emergence using 1600 kg ha^-1 of vermicompost.

Maize Grain Chemical Analysis

The crude fiber content (%) was determined by following Soxhlet extraction method (^{AOAC, 1995}) in which two grams of maize grain ground powder was extracted with petroleum ether. The maize grain ground powder was transferred to 1 L beaker and then 200 mL boiling 1.20% sulfuric acid, 1 g of freshly prepared asbestos, bumping chips and one drop of diluted antifoam were added. After that beaker was placed on the digestion apparatus with pre-adjusted hot plate and boiled for 30 min. Finally, beaker was removed and the contents were filtered and dried 2 h at 135 °C, cooled and weighed, ignited for 30 min at 600 °C in the oven, cooled and reweighed. Finally, crude fiber (CF) in maize (%) was calculated using the following equation.

For ash content two grams of the dried sample was weighed into a dry porcelain dish and then heated in a muffle furnace at 600 °C for 6 h. It was cooled in desiccators and weighed. The percentage ash content was calculated by using the following equation.

The crude protein contents in maize grain was determined by Kjeldahl method and it was calculated using the following equation.

Energetic Parameters and Amino Acid Quantification

Gross energy (GE), available energy for growth pigs (EDCE), digestible energy in female pigs (EDC), metabolizable energy for growth pigs (EMCC), gross energy for growth pigs (ENCC), net energy in female pigs (ENC) and apparent metabolizable energy (EMA) were determined with near-infrared reflectance spectroscopy (NIRS). NIRS was also used to quantify essential amino acids (^{De Oliveira-Pereira et al., 2018}).

Experimental Design and Statistical Analysis

The experiment was accomplished under a randomized complete design. Three treatments were evaluated: 1) Maize seeds inoculated with a commercial mycorrhizal arbuscular fungi mixture (Tec Myc 60^®) plus vermicompost (V+M). In this treatment, two kg of maize seeds were soaked in 1 L of Tec Myc 60^® for one hour and then they were dried in the sun before planting them. Vermicompost and chemical fertilization were additionated to soil after 15 d of plant emergence 2) vermicompost (V) and 3) chemical fertilization (CF). All treatments were carried out by triplicate. 250 plant were used for each treatment and 15 corn cob were sampled for chemical analysis, energetic parameters and amino acid quantification. All determinations were realized by duplicate.

Significant differences were determined by analysis of variance (ANOVA). Mean comparisons were made using the least significant difference (Fisher test) with a significance of 5%. The general linear model procedure was used (PROC GLM SAS Institute, 1989).

Cow Manure Vermicompost and Soil Characteristics

Soil had an organic carbon (13.2 g kg^-1), organic matter (22.8 g kg^-1), total nitrogen (1.86 g kg^-1) and available phosphorus (61.7 g kg^-1). ^{Ruíz-Valdiviezo et al. (2010)} and ^{Ruíz-Valdiviezo et al. (2013)}, found similar values in different soil types of the state of Chiapas. Also, these values indicate that these soils may be suitable for the establishment of different types of crops such as maize. A very important factor that determines the quality and fertility of the soil has been the C/N ratio. This ratio has been reported high for soils that have not been cultivated or plowed (^{Fan and Guo, 2010}). The C/N ratio had a value of 7.1, which indicates that the soil in this study has a low level of organic matter. Values between 10 and 14 correspond to a mineralization and rapid rupture of tissues, since the microbial activity is stimulated, there are enough nutrients for the microorganisms and for the vegetables (^{Gamarra et al., 2018}). The content and the decomposition of soil organic matter has been rapid due to the high content of N (^{Ostrowska and Porebska, 2015}), and possibly the nitrogen is mineralized due that with low C/N values the native microorganisms have been more efficient in the decomposition of organic matter. Phosphorus content in the studied soil was higher (6.17 g kg^-1) compared to the P content (4 g kg^‑1) in another Chiapas soil studied by ^{Abud-Archila et al. (2018)}. Likewise, the P soil content is an important factor for the best plant yield, since it has been reported directly influences the growth of the plant and the colonization of AM fungi (^{Deng et al., 2017}). On the other hand, cow manure vermicompost had an organic C content of 163 g kg^-1, a total N content of 11.4 g kg^‑1, available phosphorus was 0.35 g kg^-1, an electrical conductivity (EC) of 5.37 mS cm^-1, a CEC of 37 cmol_c kg^‑1 while the pH was 8.818. In relation to these results obtained for the physical-chemical characterization of vermicompost of cow manure, it was found that the pH and EC of the vermicompost was 8.18 and 5.37 mS cm^-1, respectively, corresponding to an organic material or substrate that has been used as organic fertilizer, as reported by ^{Méndez-Moreno et al. (2012)} and ^{Doan et al. (2013)} when they applied vermicompost with these characteristics to maize crops. The C/N ratio was 14.29 for vermicompost. It is known (^{Aalok et al., 2008}) that vermicompost with C/N ratio >12 have a mature composting and have been suitable for use as organic fertilizer, favouring the increase of the organic matter of the soil (^{Zerzghi et al., 2010}; ^{Yu et al., 2019}).

Proximate Chemical Composition of Maize Grains

Starch content in grain was 1.9% higher in V+M treatment in comparison with CF, whereas crude protein, ether extract, crude fiber, acid detergent fiber, neutral detergent fiber, total phosphorous and phytic phosphorous were not different between treatments (Table 1). In relation to crude protein content, our values were lower than ^{De-Oliveira Pereira et al. (2018)} who reported values of 9.86% and 9.28% for maize produced by conventional and organic culture. The crude fiber values varied between 2.04 and 2.14%, however values lower than 2.51% were reported by ^{De-Oliveira Pereira (2018)}. The ether extract content varied between 3.62 and 4% for all treatments, and, no significantly differences can be observed among treatments (Table 1). In our case, no significant differences were obtained for crude protein content in maize produced by conventional and organic agriculture management. These results are important because it indicates that this “Tuxpeño” hybrid of maize can be cultivated with vermicompost in substitution of the chemical fertilizers without the grains of maize being of lower nutritional quality. The results could be explained because the amount of vermicompost applied per plant was calculated by matching the nitrogen content that was applied to it with chemical fertilizer ^{(De-Oliveira Pereira et al., 2018)}.

Energetic Parameters and Amino Acid Profile

Gross energy (GE), available energy for growth pigs (EDCE), digestible energy in female pigs (EDC), metabolizable energy for growth pigs (EMCC), gross energy for growth pigs (ENCC), net energy in female pigs (ENC) and apparent metabolizable energy (EMA) were not different between treatments (Table 2). Therefore, maize can be cultivated with vermicompost in substitution of the chemical fertilizers without that the grains of maize are of lower energetic parameters quality. From the point of view of soil ecology, it is better to fertilize the soil with vermicompost than with chemical fertilizers. In addition, the results show that maize can be produced to feed pigs at various stages of growth, for the commercialization of organic meat.

Results shown that only tryptophan, aspartic acid, valine and histidine amino acids content were higher for chemical fertilization treatment that for vermicompost and V+M treatments (Table 3). However, amino acid content of corn in treatment V+M were not different with respect to plants fertilized with vermicompost (V) for the rest of amino acids of Table 3. However, it was observed than no significant differences (P ≥ 0.05) can be observed between chemical, V and V+M fertilization treatments. These results are different to reported by ^{De Oliveira-Pereira et al. (2018)} who reported that the organic management showed lower levels (P < 0.05) of methionine, threonine, arginine, isoleucine, leucine, valine, histidine and phenylalanine, compared with conventional culture of a hybrid maize. Our results are according with ^{Tejada and Benítez (2011)} who found no significant differences between the organic amendment based on vermicompost and compost in maize. These results can be explained also, because the amount of vermicompost applied per plant was calculated by matching the nitrogen content that was applied to it with chemical fertilizer. The higher content of tryptophan, aspartic acid, valine and histidine obtained with chemical fertilization could be explained by the availability of phosphorus that is more immediate when using chemical fertilizer than using compost.