Study area

This research was carried out from January 30 to September 18, 2020 in the GUMAIR forest nursery, municipality of Acaxochitlán, Hidalgo, at 2 400 m elevation and geographical coordinates 20° 09' 08'' N and 98° 13' 11'' W. The municipality of Acaxochitlán has mean temperature of 15.1 °C and mean annual precipitation of 915.5 mm (Comisión Nacional del Agua [CONAGUA], 2019).

Plant production

We used expanded polystyrene trays of 77 cavities of 160 cm³ capacity. The substrate consisted of a mixture of 70 % fresh pine sawdust (non-composted), 20 % composted pine bark, 5 % vermiculite and 5 % perlite; the fertilizer doses corresponding to each treatment were added to this mixture. The controlled release fertilizers used were Multicote Agri^® (8) 18-6-12 + 2CaO + 3.5MgO + 2.1Si + ME (eight months release at average substrate temperature of 21 °C) and Multicote^® (12) 19-10-13 + 2MgO + ME (12 months release at average substrate temperature of 21 °C). Seeds were purchased from the ejido Llano Grande, Chignahuapan, Puebla.

Treatments studied

The combination of fertilizer doses both in the nursery and in the field generated eight treatments, which are detailed in Table 1. All treatments were evaluated both in nursery and, subsequently, in the field, an extra dose was added to treatments T5, T6 and T7 to compare the fertilization applied only in the nursery with the option of fertilizing again in the field. Each treatment included four replicates or trays.

Materials management and production conditions

The internal walls of the tray cavities were immersed in a 7 % cupric hydroxide solution to promote chemical pruning of the lateral roots of the plants. The substrate materials were passed through a sifter with a 10 mm mesh to obtain a homogeneous mixture without coarse particles. The seeds were soaked in water for 8 h and subsequently disinfected with 5 % hydrogen peroxide for 20 min; they were also treated with Bactiva^® (Bacillus spp. and Trichoderma spp.) at a dose of 0.15 g∙L^-1.

The production area of the nursery had a shade house type structure with black mesh of 50 % coverage, with a metallic structure support, metallic tables for holding trays of 1.5 m wide by 80 cm high and a micro-sprinkler irrigation system. The shade net was kept in the production area from sowing (January) to April. Plant development in the nursery was not affected by pests, diseases or meteorological conditions.

Variables evaluated

After 7.5 months after sowing, 12 plants were randomly extracted per tray, resulting in a total of 48 individuals per treatment. Height was measured with a metal ruler from the base to the apical bud, and the diameter at the base of the stem was measured with a digital vernier (Truper®, model IP54). The plants were then cut to separate shoots and roots, placed separately in paper bags and dried in an oven for 72 h at 70 °C. The dry weight of the root and shoots was determined with a digital scale (OHAUS, model Navigator).

The data were used to establish the seedling quality indicators proposed by ^{Duryea (1985}) and ^{Landis, Dumroese, and Haase (2010}): Shoot dry weight and root dry weight ratio (SDW/RDW), sturdiness quotient (SQ), and Dickson's quality index (DQI).

Study area

This plantation was established on September 4, 2020 in a private property (2 262 m, 20° 10´ 52´´ N and 98° 13´ 30´´ W) in the municipality of Cuaunepantla, Hidalgo. The municipality has an average temperature of 15 °C and average annual precipitation of 915.5 mm (^{CONAGUA, 2019}). The plantation site is for forest use, slightly undulating with a mild slope; surrounding the site there is a forest area and a zone under forest exploitation, where P. patula and Quercus sp. predominate.

A composite mixture extracted from five areas of the site was analyzed at the Laboratorio Nacional de Investigación y Servicio Agroalimentario y Forestal of the Universidad Autónoma Chapingo. According to the NOM-021-RECNAT-2000 (^{Secretaría de Medio Ambiente y Recursos Naturales [SEMARNAT], 2002}), the soil had bulk density of 0.89 g∙cm^-3 with pH 5.02 (strongly acid), loamy texture, low cation exchange capacity (11.42 cmol∙kg^-1), high contents of organic matter (14.33 %) and inorganic nitrogen (54.59 mg∙kg^-1), and low content of phosphorus P and K (3.74 and 186 mg∙kg^-1, respectively).

Plantation management

A total of 10 plants per treatment and replication (tray) were randomly selected from the plants produced in the nursery, with 40 plants per treatment and 320 plants evaluated in the field.

The planting had a square design with a spacing of 2.5 m between plants; the planting method was traditional (common hole), using a straight spade to open holes of approximately 30 cm x 30 cm.

For the plants of treatments T5, T6 and T7, a dose of controlled release fertilizer (Multicote® 12) was added at the time of planting (Table 1). The fertilizer was applied around the tree in a radius of 10 cm at a depth of 1 cm and covered with soil using a shovel.

Variables analyzed

After the plantation was established, height and diameter at the base of the stem of each plant were measured as a reference point to estimate growth after one year.

To determine survival, a census of the trees was made at three stages of plantation. The first census was taken after four months, time in which plants had experienced the stress of planting and the cold of part of the winter; the second census was taken after nine months, after the winter and the hot season were completed before the rainy season began; and the last census was taken after 12 months, following most of the rainy season and the stage of greatest growth in the field.

Nine months after planting, the nutrient concentration (N, P and K) of the plants was evaluated. For this purpose, a sample of needles was collected from the middle part of the stems of all the trees of each treatment, according to ^{Wells and Allen (1985}), and a composite sample was formed from each treatment of the four blocks of the experimental design in the field, which was placed in properly labeled brown paper bags. Subsequently, the needles were dried in an oven at 70 °C for 72 h. Then, 100 representative needles were selected from each sample and sent to the Nutrition Laboratory of the Colegio de Postgraduados to determine N content by the micro-Kjeldahl method, and P and K by coupled plasma induction optical emission spectrometry (Varian Agilent 725-ES ICP-OES; Mulgrave, Australia), using digestions with a mixture of H₂SO₄:HClO₄ (2:1, v:v) according to ^{Alcántar and Sandoval (1999}).

Plant growth (height and diameter at the base of the stem) was evaluated 12 months after planting, when the nutrients contained in the fertilizer granules are released.

Morphological characteristics of Pinus patula

The effect of fertilizer doses on P. patula plants was significant for all variables (P ≤ 0.0001). Plants for treatments T3 (8 g∙L^-1 of eight-month release fertilizer in combination with 4 g∙L^-1 of 12-month release fertilizer) and T4 (8 g∙L^-1 of eight-month release fertilizer in combination with 6 g∙L^-1 of 12-month release fertilizer) showed the highest values in all variables. Plants in treatment T8 (4 g∙L^-1 of eight-month fertilizer and 4 g∙L^-1 of 12-month release fertilizer) had similar values to those in T3 and T4 except for height, SDW/RDW ratio and sturdiness quotient, but showed the highest average DQI value (Table 2).

The Mexican Standard NMX-AA-170-SCFI-2016 (^{Secretaría de Economía, 2016}), in its regulatory appendix C, establishes the morphological quality standards for species used for conservation and restoration purposes. In the case of P. patula, it establishes that, by the age of six to seven months, plants must be 25 to 30 cm in height and should be greater than 3.5 mm in diameter. Following these standards, treatments T3, T4 and T8 produced values higher than those indicated in the standard for height while for diameter only the plants of treatments T1 (control), T5 and T7 were below the standard; the last two treatments contained 8 g∙L^-1 of eight-month release fertilizer in nursery and different doses of 12-month release fertilizer applied in the field.

^{Prieto, García, Mejía, Huchin, and Aguilar (2009}) indicate that the value of the height/diameter ratio, known as sturdiness quotient, should be less than six, and that it is an indicator of survival and growth in dry sites and of plant resistance to desiccation by wind; therefore, values greater than six indicate that the plant has a thin stem compared to its height. According to this description, the plants of treatments T1, T5, T6 and T7 met this criterion.

Regarding the SDW/RDW ratio, la NMX-AA-170-SCFI-2016 (^{Secretaría de Economía, 2016}) indicates that the value should range between 1.5 and 2.5. Higher ratios indicate disproportion and insufficient root system to supply the shoots of the plant. In this study, the values of this ratio were higher because the trays were soaked with copper to cause chemical root pruning, coupled with the effect of fertilizer doses that caused greater increases in height.

According to studies conducted by ^{Sáenz, Villaseñor, Muñoz, Rueda, and Prieto (2010}) and ^{Rueda et al. (2014}), the DQI was classified by specific ranges from 0.2 to 0.5, where values lower than 0.2 were considered low quality, between 0.2 and 0.5 medium quality, and higher than 0.5 high quality. Results indicate that treatment T8 had the highest DQI = 0.42, thus the quality of the plant can be classified as medium.

^{Aguilera-Rodríguez et al. (2020}) mention in their research on field growth of P. patula, as an effect of root pruning and containers used in nursery, that with a dose of 8 g∙L^-1 of Osmocote® Plus fertilizer (15-9-12) of eight to nine months of controlled release, quality plants are produced in nursery.

Survival

Table 3 shows that the survival of the P. patula plantation in the three evaluations at 4, 9 and 12 months after establishment in the field, for each treatment, was higher than 72 % and the average survival in all treatments was 75 %. These values are higher than those reported by ^{Mexal, Cuevas, and Landis (2008}) in plantations established in Valle de México with the same species at 4, 10 and 26 months, obtaining 44, 33 and 27 % survival, respectively. However, the results are lower than those reported by ^{Sosa-Pérez and Rodríguez-Trejo (2003)}, who reported 93 % survival 12 months after planting P. patula on a burned area.

Survival was highest with treatment T8 (95 %), while the lowest values were found for T2 (72 %), T5 and T6 (both with 75 %); the last two treatments have the characteristic that they were additionally fertilized in the field. ^{Trubat, Cortina, and Vilagrosa (2010}) highlight that nutrient management in the nursery shows a strong potential to modify the morphology of Quercus suber L. seedlings, but the relationship between these changes and short-term seedling survival remains elusive, which can be confirmed in this research due to both environmental and plantation factors.

Nutrient content

^{Escobar-Alonso and Rodríguez-Trejo (2019}) indicate that the recommended values of foliar concentration of nutrients as physiological indicators in Pinus species are: 1.4 to 2.2 % of N, 0.2 to 0.4 % of P and 0.4 to 1.5 % of K. In another study on plant quality indicators in native pines, ^{Prieto and Sáenz (2011}) propose the following concentrations of nutrients in foliage: 1.1 to 3.5 % of N, 0.1 to 0.6 % of P and 0.5 to 2.5 % of K. According to the described scales, quality plants were produced in this study according to ^{Prieto and Sáenz (2011)}; as for the recommendations of ^{Escobar-Alonso and Rodríguez-Trejo (2019}), for N and P, quality plants were produced and in the case of P the concentrations were low. ^{Binkley and Fisher (2019}) have proposed that, generally, critical P concentrations are equivalent to 10 % of N concentrations and in this study, they are between 7 and 9 %.

According to Table 4, in all treatments, foliar N concentration increased as the nursery fertilizer rate increased, as reported by ^{Sloan and Jacobs (2013}), who analyzed controlled-release fertilizers in comparison with immediately available fertilizers and unfertilized controls in Picea glauca (Moench) Voss and Populus tremuloides Michx. They concluded that the usually higher levels of foliar N in the first year of planting were found in trees fertilized with higher rates of controlled-release fertilizers in the root zone.

In this research, treatment T4 had the highest percentage of N, followed by T8, while the plants fertilized in the field (T5, T6 and T7) showed a different behavior, being treatment T6 the one that assimilated the highest percentage of N. For P, there were no differences between the percentages contained in the plants, being in a range of 0.13 to 0.15 % in all treatments. K content in the plants also showed low variation, with treatments T1 and T7 being the ones with the highest and lowest percentages, respectively.

Plantation growth

According to the comparison made at the time of planting and after 12 months, the saplings of all treatments increased 71 cm in height on average (Figure 1) and 11.44 mm in diameter (Figure 2). Treatment T3 generated, on average, the greatest height (1.10 m) followed by T4 (1.09 m) and T8 (1.00 m); the first two treatments had the greatest height when leaving the nursery. Since the evaluation was only for one year, these values could be considered of good size if compared with those obtained by ^{Aguilera-Rodríguez et al. (2020}), who determined height growth of 1.54 and 1.47 m in P. patula, for two years in the field.

Similar results were found for diameter growth; plants in treatment T3 averaged 18.64 mm, followed by T4 and T8 with 18.32 and 17.67 mm, respectively.

Figure 1.  Average height growth of Pinus patula per treatment at field planting (light gray) and 12 months later (dark gray). The standard error of the mean is represented on the bars.  

Figure 2.  Average diameter growth of Pinus patula per treatment at field planting (light gray) and 12 months later (dark gray). The standard error of the mean is represented on the bars.