Height and number of leaves per plant

The height and the number of leaves produced in the plants of the TA increased during the whole development cycle, their values were significantly lower (p≤ 0.05) than those registered in the plants developed with fertigation and FB+fertigation, without existing differences in the height values of these last plants. The values of both characteristics generated in the evaluations were significantly adjusted to quadratic models (Table 3), with which the annual rate of accumulation of height and leaves was estimated, during the development of the plant (Table 4).

In the plants of the TA, during the first year of established an increase of 7 cm in the height was estimated, growth rate that increased year by year, registering during the sixth year 13 cm as the highest annual growth rate (Table 4). The height in the plants of the TA at the end of the cycle (77 MDP) was 129 cm, height that in the plants that received water and nutrients in the irrigation system was registered in the first third of its cycle (22 MDP). In the same way, the tendency that the TA plant showed to increase the height with advancing age, was inverted in the plants with Fertigation and FB+fertigation, during the first year (12 MDP) these plants presented the highest growth rate increasing its height 46 and 54 cm, respectively; as the development cycle progressed, its growth rate decreased, at 48 MDP the height of the plant only increased 14 cm.

The number of leaves produced in the agave plant presented a behavior similar to the height previously described. The TA plants at 41 MDP had 57 leaves and was the largest number of leaves; amount that represented only 43% of the number of leaves that were recorded on average in plants developed with fertigation and fb+fertigation, the differences between plants that received fertilizer in the irrigation system and those that developed without irrigation were significant (p≤ 0.05).

The estimated annual rate of leaf production, allows us to infer that the TA plant in the first two years produced three leaves each year, later the plant increased its production to four leaves per year; this trend in the annual rate of leaf production was invested in the agave plants developed with fertigation and FB+fertigation (Table 4). In these last plants during the first two years an annual production of leaves 10 times higher was estimated with respect to the estimated production in TA plants. As the plant cycle progressed, the number of leaves produced per year decreased (Table 4), a situation that could be associated with a 48% decrease in the volume of irrigation water and the contribution of nutrients received by these plants in the sixth year of its development.

The greater production of leaves in the first years of development of the plant and its decrease in advancing the cycle of the plant, stage in which the pineapple develops, may indicate less internal competition of the plant between both structures. These results differ from those recorded by ^{Nobel and Valenzuela (1987)}, in commercial plantings established in Tequila, Jalisco, who recorded an annual leaf production of 34 and 46 in A. tequilana plants, of three and six years, respectively.

Biomass in plant and pineapple

Biomass in the agave plant increased as the development cycle progressed, a tendency that at 41 and 77 MDP was modified negatively in TA plants, while in those developed with fertigation and FB+fertigation the biomass decreased only at the end of the cycle (77 MDP) (Table 5). In the TA plant, this decrease in biomass can be directly associated with a lack of moisture in the soil caused by the scarce rainfall registered between 54 and 77 MDP, without considering the distribution of rainfall during this period, the total rainfall represented only 44% of recorded evaporation.

In the pineapple, the biomass increased during the whole cycle, independently of the conditions in which the agave plant was developed, indicating that, faced with a stress due to lack of moisture, the plant sacrifices the accumulation of biomass in the foliage, for the benefit of pineapple development, (Table 6). And this last body, until two years after the plant was established, it accumulated 23% of the total biomass of the plant and at the end of the cycle this percentage increased to 49%, a value slightly lower than 54% of the biomass reported in pineapple plants between 6 and 7 years by ^{Nobel (1990)}.

The agave plants that received water and fertilizer in the treatments with fertigation and FB+fertigation, presented values ​​of fresh weight (PF) of the plant and pineapple equal to each other (p≤ 0.05), but much higher than those registered in both characteristics of the plants developed in the TA; the greatest difference in the production of biomass accumulated between these plants and those developed in the TA was observed at 63 MP, at this stage they exceeded on average 5.5 and 5.7 times the total biomass recorded in the plant and pineapple of the TA, respectively.

The high MS production recorded in agave plants developed with fertigation and FB+fertigation shows that the negative effects of a high temperature on the agave plant mentioned by ^{Nobel et al. (1998)} and ^{Pimienta-Barrios (2001)}, were minimized when the agave plant was developed without moisture limitations during the whole cycle, through fertigation (Table 5).

With the values of biomass recorded at 77 MP, in plants developed with the technique of fertigation and FB+fertigation and considering a commercial planting density of 3 300 plants ha^-1, a production of 491.4 and 456.1 t ha^-1 was estimated. total biomass in the plant and pineapple of 218.1 and 252.4 t ha^-1, respectively; while in the TA plants, the total biomass estimated in the plant was 97 t ha^-1, and in pineapple, a yield of 46.5 t ha^-1. This shows that the water and nutrients provided to the agave crop in an intensive production system (fertigation) allows pineapple yields higher than 100.1 t ha^-1 to be recorded as the average production value in the 2006 to 2015 period in the state of Jalisco (^{SAGARPA, 2016}).

From the total biomass recorded in the agave plant to 4 MDP, the MS represented 14% and the remaining 86% was humidity, as the age of the plant increased, the MS increased to 27% to the detriment of humidity. Five years and 5 months after the plant was established (65 MDP), the highest amount of MS was recorded in the plant, with an estimated 140.4 t of MS ha^-1 as an average value of production in plants developed with fertigation and FB+fertigation, amount significantly higher than the 25.5 t ha^-1 estimated in the TA plant (Table 5). The water and nutrients that were received through the irrigation system plants developed with fertigation and FB+fertigation originated up to 65 MDP, variable increases in the annual MS production rate (Table 7), the highest estimated annual MS production rate it was 54.4 and 49.2 t ha^-1, respectively, values that averaged 6.2 times the maximum annual accumulation of MS that occurred in the TA plant and also exceeded the production of 21.1 t ha^-1 year-1 reported by ^{Nobel and Valenzuela (1987)} in six-year-old A. tequilana plants, established in the state of Jalisco.

In the TA plants between 30 and 41 MDP and during the last evaluation between 66 and 77 MDP the annual rate of DM production in the whole plant presented negative values; while, in the pineapple, the estimated MS accumulation rate increased throughout the plant’s development cycle (Table 6).

The negative values in the annual rate of production of MS, indicate that in two continuous evaluations carried out in plants selected at random, the highest MS value was registered in plants of the first sampling. On the other hand, in the early stages of development of the plant, the annual MS production rate registered lower negative values with respect to those registered in adult plants; this situation can be associated, among other things, with a lower demand for humidity in small plants and also in that period coincided with the record of low temperatures of the cycle that, according to the studies of Novel et al. (1998); ^{Pimienta-Barrios et al. (2001)}, could be more favorable for the development of the plant. The decrease in the rate of MS accumulation in the agave plant observed at the end of the cycle (77 MDP), as mentioned above, was also associated with the reduction in the volume of water and fertilizer that they received between 54 and 77 MDP.

Sugars in the pineapple

The concentration of ºBrix and ART in the pineapple at 6 years and 7 months of development of the agave plant (77 MDP), was not modified by the fertilizer and water it received (p≤ 0.05), Table 2; in this stage, ART concentration fluctuated between 26.8 and 29%, ART values slightly lower than 30.8 and 32.7%, reported by ^{Mellado-Mojica and López (2012)}, in pineapples harvested in the state of Jalisco during the wet season and dry, respectively. According to ^{Mancilla-Margalli and López (2006)}, the environmental conditions originated that in pineapples of A. tequilana of 6 years of age harvested in Jalisco, 900 mg g^-1 of MS of soluble total carbohydrates (sucrose, fructose and glucose) were registered. While in Guanajuato, pineapples of the same age were only 550 mg g^-1 of MS.

Variations in the concentration of ART in the MS of the pineapple in the present study were recorded by the effect of the management conditions in which the plants were developed and also by the effect of the development of the plant (Figure 1); that is, at 29 MDP the mean value of ART in the pineapples of the three plants was 246.3 g kg MS, 2.6 below and 3.4 times the median concentration value of ART registered at 65 and 77 MDP, respectively; in these last two stages of cultivation in the pineapple of the plant developed in the TA the highest concentration of ART was recorded, a situation that can be associated with the metabolic flexibility of the agaves that allows them to adapt to different environmental conditions where the availability of water in these plants it is the limiting factor.

Figure 1 Accumulation of total reducing sugars (ART, kg pineapple^-1) and concentration of ART (g kg of MS) in the pineapple of agave plants developed under three conditions of fertilizer management. 

According to the above, the water and fertilizers applied through the fertigation technique to the agave plant in the warm region of southern Tamaulipas, allowed to produce greater volumes of pineapple, with a concentration of sugars similar to that determined in plants developed in the TA. However, when favoring the growth of pineapple in plants that received fertigation and FB+fertigation, the quantity of ART was increased 5.3 times with respect to the pineapple of plants developed in the TA (p≤ 0.05) (Table 4).

These differences in the values of ART in the pineapple of the plants of the TA and the pineapples of plants developed with fertigation were observed from the initial stages of development of the agave plant, (Figure 3). However, regardless of the nutritional management received by the agave plant, at 41 MDP (3 years and 5 months) the plants accumulated in the pineapple 22% of the ART, with respect to the value of ART determined in the agave pineapple. At the end of the cycle (77 MDP), the remaining 78% was accumulated in later stages.

The monosaccharides that were part of the ART of the agave pineapple (fructose and glucose) were not affected by the nutritional management that the plant received. In the initial stage at 17 MDP, the concentration of fructose and glucose in the ART showed a mean value of 28.25 g kg^-1 of pineapple MS (Table 7); that is, in the first evaluation, both monosaccharides were at the same concentration in the pineapple. Subsequently, fructose and glucose showed a tendency to differentially increase their concentration: with respect to glucose at 53 MDP, 269.7 g kg^-1 of pineapple MS was estimated, this value represented 87% of the total concentration of both monosaccharides present in the pineapple. ART and which decreased up to 12% during the last two evaluations (65 and 77 MDP).

The decrease of the glucose during the stage of greater growth of the pineapple (two last evaluations), originated increases in the concentration of fructose in the ART whose average value was 246.8 g kg^-1 of pineapple MS and represented 88% of the total of the monosaccharides evaluated. The behavior of these monosaccharides in the pineapples of A. tequilana plants was different from that previously reported by ^{Mellado-Mojica and López (2012)}, who, in pineapples of different ages collected in Amatitlán, Jal., Mexico, reported higher fructose concentrations to glucose concentration regardless of the stage of development of the pineapple.