Location

The experiment was established in a plot called "Seminario Mayor", located in San Luis Potosi municipality, at 22°07'11.0 "N 100°54'27.0 "W coordinates, with an altitude of 1810 masl. The predominant climate is BSk, with an average annual temperature of 16.8 °C and precipitation of 542 mm (^{García, 1973}). The soil present at the site has a sandy loam texture, with a pH of 7.26, electrical conductivity of 0.67 dS m^-1, organic matter of 0.5 %, cation exchange capacity of 1.28 cmol ⁽⁺⁾ kg^-1, and total nitrogen content of 0.65 %. Laboratory analyses were performed at the Instituto de Investigación de Zonas Desérticas of the Universidad Autónoma de San Luis Potosí.

Bokashi preparation

The bokashi was prepared by adjusting the ingredients and technique described by ^{Restrepo (2009}) (Table 1), and following the recommendations described by ^{García-Hernández et al., (2020}) for the adequate mixing and fermentation process care, using sheep, cattle, and swine manure obtained from commercial productions which were dried in the shade, the particle size was homogenized to 5 mm with a hammer mill. Samples of manure from each species were collected for proximate chemical analysis.

Manure chemical analysis

Samples collected from the manure used for bokashi preparation were dried in a forced air oven to constant weight, mixed for each species to make a composite sample, and ground in a Willi mill with a 2 mm sieve diameter, for chemical analysis. Dry matter, moisture, nitrogen, ash, organic matter, pH, and neutral detergent fiber content were determined (^{AOAC, 2016}).

Recording and temperature control of the bokashi

Daily, for 60 days the average temperatures were recorded, placing a thermometer in three random locations of the bokashi at three different depths (10, 20, and 30 cm), taking care that the first 20 days the temperature of the preparation did not exceed 60 °C, if the temperature recorded was close to this, with a shovel, manual turning was performed to decrease it (^{Restrepo, 2009}).

Physical-chemical and organic analysis of the bokashi

Once the fermentation phase was finished, each bokashi was mixed with a shovel to homogenize it, then 3 samples were collected and mixed to make a composite sample, this procedure was repeated six times to collect six composite samples of each one. The physicochemical and organic analysis was performed according to the methodology described in the ^{Mexican Official Standard NOM-021-RECNAT-2000}.

Planting of corn for silage

In June 2021, the corn variety CAFIME (Semillas Iyadilpro y Ya S.A. de C.V. Jalisco, Mexico) was planted in 15 plots of 24 m long by 12 m wide, with 3 m spacing between plots. The planting density was 23,000 plants per ha, a distance between furrows of 0.8 m and 0.4 m between plants according to the technological package proposed by ^{INIFAP (2013)}; The auxiliary irrigations were applied by sprinkling according to the water needs of the crop.

Application of bokashi and fertilizers

The experimental plots were randomly assigned a treatment (OM: bokashi made with ovine manure, BM: bokashi made with bovine manure, PM: bokashi made with pork manure, chemical fertilizer, and unfertilized), the bokashi dosage was 2 ton ha^-1, chemical fertilization was 140-60-00, using urea (46-00-00-00) and diammonium phosphate DAP (16-46-00) (^{INIFAP, 2013}), applying 50 % at pre-sowing and the rest was divided into three applications, at 15, 25 and 35 days post-emergence (^{Barrera-Violeth et al., 2017}).

Corn harvest

Harvesting was performed when more than 50 % of the plants in each experimental unit were in the milky-messy stage (^{INIFAP, 2013}).

Yield estimation

From each plot, 3 central furrows were harvested, in 30 randomly selected plants, standing, their height was measured from the ground to the end of the ear, they were cut, weighed green, subsequently, their components were divided into the stalk, leaf, and whole cob (grain) and weighed separately, the ears were considered part of the stalk, placed in paper bags and taken to drying until counterweight. These data were used to determine green yield, total dry matter, and yield by components.

Experimental design and statistical analysis

The data were analyzed in a completely randomized design, for the characterization of the bokashi fermentation, 3 treatments were used (sheep, bovine, or swine manure), 3 regions for measuring temperature, 3 depths, and 60 temperature records per treatment (n = 1620). For chemical analysis, 3 treatments were used (sheep, cattle, or swine manure) with 6 replicates per treatment (n = 18). For corn yield and by components, 5 treatments were used (bokashi made with sheep, cattle, or swine manure, chemical and unfertilized), 3 plots per treatment, 3 furrows per plot, and 30 plants per furrow (n = 1350). The analysis of variance and mean comparison test was performed using the PROC GLM procedure and Tukey's test with a significance of 0.05 for ^{the SAS OnDemand for Academics Communities program (2021)}.

Chemical analisys of manure used in bokashi processing

There was no significant statistical difference (p > 0.05) between dry matter, nitrogen, and neutral detergent fiber content among the three manure sources, however, the amount of nitrogen and ash was lower in swine manure (Table 2), this may be explained since, in recent decades, swine feed formulations are designed to cover the requirements of specific amino acids and decrease the nitrogen content in the diet (^{Millet et al., 2018}).

Bokashi characterization

The bokashi temperature, regardless of manure source, raised from 35° to 60° C in the first three weeks (mesophilic phase), from week three to week five, the average temperature remained at 60° C, and gradually decreased to 38° C (thermophilic phase) at the end of week six, and then maintained at room temperature (30 to 35° C) until day 60 (cooling and maturation phase) (Figure 1). The temperatures recorded suggest that the fermentation was correct, the first days favor the growth of mesophilic organisms, which degrade carbohydrates of the organic matter (^{Sanchez et al., 2017}), during this fermentative phase, exothermic processes cause gradually increasing the temperature, thus promoting the growth of thermophilic microorganisms, initiating the thermophilic phase, degrading by enzymatic action compounds of complex structure such as proteins and eliminates pathogenic microorganisms (^{Neklyudov et al., 2008}), as the amount of fermentable organic matter in the bokashi decreases, the temperature decreases, reducing the amount of thermophiles and increasing again the mesophilic population until the remaining fermentable carbohydrates are exhausted (^{Zeng et al., 2010}) and the cooling and maturation phase begins; in this phase, the less degradable compounds are decomposed and the precursors of humic substances emerge (^{Vélez-Sánchez-Verín et al., 2008}), resulting in a good quality bokashi.

Figure 1 Temperature changes in the bokashi prepared with different manure sources. 

OM compared to BM and PM, presented a higher number of desirable physicochemical and organic characteristics (Table 3), a lower amount of Na, and, therefore, lower electrical conductivity (p < 0.05). The optimal carbon:nitrogen ratio for a mature compost has been described since ^{1989 by Senesi}, who mentions that a C:N ratio below 20 is indicative of an advanced degree of stabilization and maturity of the organic matter, so our results indicate that the three bokashi produced reached the stage of maturity.

Corn yield

Green forage yield, dry matter, dry matter yield (Table 4), and grain proportion (Figure 2), were similar (p > 0.05) in corn to which OM and chemical fertilizer were applied, however, leaf proportion was higher (p < 0.05) in corn to which BM was applied, compared to the rest of the treatments. The dry matter content is within the recommended by ^{Filya (2004}) for the successful ensiling of corn. ^{Garcés et al. (2004}) mention that, to achieve a quality silage, the material must contain a good supply of water-soluble carbohydrates, which will be fermented by epiphytic bacteria and transformed into lactic acid, being the corn grain the main source of these, followed by the leaves and finally the stalk, so that, with the forage produced, excellent quality silage could be obtained.

Figura 2 Stem-Leaf-Grain Proportion (%) of foder corn at 112 days post-sowing fertilized with different types of fertilizer