Location, type of soil and climate of the study area

The locality where the planting took place was the common Cayal, in lands of the Produce- Campeche Foundation (19° 45’ 11.57” north latitude, 90° 09’ 52.65” west longitude). The approximate altitude is 34 m above sea level. The soil is known as Kancab type in Mayan language, is clayey and is classified as Luvisol Ferric by ^{FAO/UNESCO (1970)}. These soils are found in mechanizable soils of high potential for corn production in the state (^{Medina, 2006}). They are flat topography with a slightly undulating microrelief.

The analysis of this soil in the profile of 0-20 cm reported 3% of organic matter, 15 to 20 ppm of nitrates, Olsen phosphorus 8 to 12 ppm, high in interchangeable potassium, without problems of salinity and neutral to slightly acid pH. The climate in the locality is of type AW₁, being the intermediate variant of the warm-subhumid climates with rains in summer. It presents 85% of annual rainfall in the months of May to October, with amounts ranging from 450 to 700 mm from planting to the physiological maturity of the grain. The average temperature in the crop development cycle ranges from 21 to 28 ºC.

Treatments under study

The research was developed using 11 maize hybrids as a genetic material, from the companies Monsanto and Syngenta, as well as a commercial hybrid released by INIFAP, recommended for planting in the Entity (Table 1). These materials were evaluated in two environments, one including fertilization with the formula recommended for commercial sowings and another without fertilization. For the treatment with fertilizer formula 110-46-00 was used, with fertilization sources such as diammonium phosphate and urea (^{FAO, 2002}).

Experimental design

The distribution of the treatments (hybrids) and field repetitions was done according to Figure 1, which denotes an experimental design of random blocks with four repetitions (blocks). As can be seen in Table 1, the trial had 11 treatments and four repetitions. Of these repetitions, only three were fertilized and one of them (the II) was not fertilized. The size of the experimental plot was four rows of 6 m in length separated at 0.8 m from each other, the useful plot were the two central furrows. The arrangement of the plants within the furrows was of two plants every 35.7 cm, for a density of 70 thousand plants per hectare.

Figure 1 Aclareo of plants to leave two of them per site. 

The statistical analysis of grain yield was carried out through the experimental designs program of the Autonomous University of Nuevo León (^{Olivares, 1994}). Two analysis of variance was carried out with the randomized block design, the first of them considered four repetitions, including the unfertilized one, and the second only included the three fertilized repetitions.

Agronomic management of the crop

The sowing date was July 09. The arrangement of the plants within the furrows was of two plants every 35.7 cm, for a density of 70 thousand plants per hectare. The preparation of the soil consisted of two semi-heavy harrow passes, which were applied in the months of May and june. The sowing took place on the ninth of July, the soil being humid. There were no setbacks between the sowing and the emergence of the crop, making the seedlings visible five days after sowing, with very few failures of germination. Initially, three seeds were planted per site to ensure adequate population and in the three-leaf phase, thinning was done to leave only two plants per site, as shown in Figure 1.

The fertilizer was applied once only 20 days after sowing (Figure 2) in the aforementioned repetitions, incorporating the fertilizer to the soil with a hoe. In the second treatment, where no fertilizer was applied, it was also hoened and in this way we tried to avoid any difference in handling. The most important pest was the armyworm and its control was carried out with a single application of Cypermethrin.

Figure 2 Application of fertilization in stage V5-V6. 

The weed was manually combed with hoe in stages V5-V6, just when the fertilizer was applied and it was also combated chemically using Nicosulfuron in mixture with 2,4-D amine, at 35 days after sowing. The harvest was carried out on november 28 (Figure 3), 141 days after sowing, with the grain at a humidity between 18 and 21%. Only the plants that had complete competition in the useful plot were harvested. Although different characteristics of the plant were recorded, such as days to flowering, health, plant height and stubble production, the main variable in this study was grain yield adjusted to 14% moisture (^{INIFAP, 2017}).

Figure 3 Harvesting of the hybrid trial with and without fertilization. 

Meteorological conditions

The climate was characterized by an average temperature of 27.6 °C in the month of July, 22.4 °C in the month of October and finally 21.8 in the first tenth of the month of november, which indicates that this factor was more stressful for the plant at the beginning of development and more favorable at the end of it. The most critical stage in the development of the plant, flowering, was affected by the rainfall deficit that took place during the month of august during the drought period called ‘canicula’ (Figure 4). During the development of the plant, from the sowing to the physiological maturity of the grain, 603 mm were rained, of which 343 were between sowing and flowering and 260 mm between flowering and the physiological maturity of the grain. This volume of rainfall was close to ideal for the good development of corn (600-700 mm), but had an unequal distribution over time, which undoubtedly had a negative impact on grain yield (Paliwal et al., 2001), avoiding that these could show their true potential of yield.

Figure 4 Accumulated rainfall and average temperature during the phases of crop development. 

Statistical analysis of grain yield

Two variance analyzes were performed for the yield, one considering the four repetitions and another without considering the unfertilized repetition. In both cases, this analysis indicated the existence of highly significant differences in the treatments and in the blocks (Table 2), which indicated that there was a differential response of the hybrids in the yield, and that at least one of the repetitions recorded a performance different to the others. This gave the guideline to analyze the means of the hybrids and identify and if necessary select the best ones and also analyze the means of the repetitions to verify if in fact the repetition that was not fertilized and that by the way had the lowest performance, was statistically different from the fertilized repetitions ^{Martínez (1988)}.

The means test of the treatments (Table 3) considering only the fertilized repetitions indicated that five statistical groups were formed, the group with the best performances being the hybrids 7W69C, MH-9058, DKB-399, NK-254, which had an average yield of 5 982 kg ha^-1; while the group with the lowest performance and statistically different from the first group included the hybrids 8H08C, Murano, H-431 and impact, with an average yield of 48 60 kg ha^-1.

The test of means of the repetitions (Table 4), indicated that in effect, the non-fertilized reptile (block II) obtained the lowest yield (4 194 kg ha^-1) and was statistically different from the three fertilized, I, III and IV, which recorded average yields of 4 773, 5 645 and 5 860 kg ha^-1, respectively.

Analysis of the impact of fertilization and genetic material on performance

According to Figure 5, all hybrids showed a positive response to fertilization by increasing their yields; however, this response was differentiated, undoubtedly influenced by genetic and environmental aspects and their interaction (^{Etchevers et al., 1991}; ^{Turrent et al., 2005}). As shown in Table 5, the average response to fertilization was 1 231 kg ha^-1 and was in a range of 749 to 2 559 kg ha^-1.

Figure 5 Response of 11 maize hybrids to two fertilization environments. 

The increase in yield could be due to the fact that the fertilization impelled the development of the root and this helped the plant to cushion the effect of the drought that occurred in the vegetative phase and thus the fertilized corn produced greater biomass in general (^{Marcano et al., 1994}; ^{Dhuyvetter and Schlegel, 1994}). For its response to fertilization the best materials were 7W69C, MH-9058 with average yield of 6 172, 6 004 kg ha^-1, for the case in which it was not fertilized, the best materials were DKB-399 and 7W79C, with average yields of 5 185 and 4 748 kg ha^-1. The procedure for the discrimination and selection of these materials was by adding the mean and the standard deviation in each fertilization environment.

Financial and productivity analysis

From the average yield values reported in Table 6, it is found that with the application of fertilizer 5 426 kg ha^-1 is obtained, which is higher in 1 231 kg than the yield obtained without fertilization, of 4 195 kg ha^-1. At current prices of 2017, the cost of fertilization treatment with formula 110-46-00 was $2 900, which included the input and the cost of its application. Also, at current prices of 2017, with a value of $3.30 kg of corn, the value of 1 231 kg of corn was $4 062.3, if at this value we subtracted $2 900, which is the cost of fertilization, obtains that the application of fertilizer to corn left an average profit margin of $1 162.3 ha^-1, which is considered an incentive for the producer to fertilize corn with the recommended fertilization formula.

In the profitability aspect, according to Table 6 indicates that the cost of the technological package of unfertilized corn was $7 725 per hectare, while in the fertilized corn it was $10 625. This leads us to obtain income net of $6 618 for unfertilized corn, due to its lower yield and $7 280 per hectare, for fertilized corn, which demonstrates the profitability of fertilization (^{CIMMYT, 1988}; ^{UF/IFAS, 2014}). Translating the above to pesos per hectare, the fertilized corn registered a higher productivity (0.73), being lower (0.61) for the non-fertilized corn.

One way to maximize the income in the fertilized corn is to use the genetic material of higher productivity, such is the case of the hybrids 7W69C, MH-9058, DKB-399, NK-254, 7W79C and DK-380, which have an above-average productivity of unfertilized corn.

At the same time, it is necessary to point out that some specific trends were found among the hybrids; for example, the MH-9058 and the NK-254 respond better to the fertilized environment, while the 8H08C stood out in the unfertilized environment and is probably a hybrid with aptitude for disadvantaged or low fertility environments. Likewise, it can be observed that four of the 11 materials stood out in both fertilization environments, being these 7W69C, DKB-399, 7W79C and DK-380, so they are considered stable hybrids before the environmental variability (^{Carballo and Márquez, 1970}; ^{Orona et al., 2013}).

Finally, according to this study, the cost of fertilization formula 110-46-00 was $2 900.00 and represented 27% of the total cost of $10 625.00; however, its importance is based on the fact that, according to the conditions in which the study was carried out, its effect was estimated at 16% of the net benefit obtained. Also, from the information provided by the present study it was estimated that a crop without fertilizer like the present one would be extracting from the soil about 61 kg ha^-1 of nitrogen, 13 kg of phosphorus and 17 kg of potassium, according to estimates by authors such as ^{García (S/F)} and ^{Campitti and García (2007)} which is useful information for the calculation of fertilizer quantities that should be applied annually through fertilization to maintain the soil in its current fertility status (^{Mallarino, 2005}).