Location of the study area

The study was conducted in an orchard of avocado trees cv. Hass in productive stage (five years) located at an elevation of 2 430 m, between coordinates 17° 38' 59.79'' North latitude 99° 50' 22.17' west longitude (GPS data), in the town of Filo de Caballos, municipality of Leonardo Bravo, corresponding to the central region of the State of Guerrero, from October 2011 to November 2012.

Treatments and applications

N-P-K was used (edaphic at a concentration of 200-100-200 kg ha^-1) and Ca-Mg-B (foliar at a concentration in kg ha-¹) 30, 10 and 15 respectively and cattle manure (50 kg tree^-1) nutrient sources were: diammonium phosphate (N and P), urea (N), potassium sulfate (K), Kelik (B), fertigro^® calcium (Ca) and fertigro^® magnesium (Mg) 1 manure, 2 (manure + edaphic), 3 (manure + foliar + edaphic), 4 (manure + foliar), 5 (edaphic), 6 (edaphic + foliar), 7 (foliar) and 8 (control: without application). The edaphic and manure treatments were applied in the projection area of treetops; whereas, leaf, foliage direct manure, 50% was applied at the beginning of flowering. 50% in fruit set. The soil treatments, 33.33% for each of these phenological stages at the beginning of flowering, during fruit set and fruit growth medium were applied. The foliar treatment was applied as follows: calcium at the beginning of flowering, fruit set and fruit growth medium; magnesium and boron, during flowering and fruit growth. Treatments were arranged in a design in randomized complete block with four replications; a tree was the experimental unit, a total of 32 trees were evaluated. For data recording, four branches per tree, one for each cardinal point, with a diameter of 2-3 cm, located 1.5 m above the ground were chosen. Data were provided an analysis of variance and Tukey test and LSD, using the Statistic Analysis System (SAS) version 9.0 program.

Evaluated variables

For a year and at intervals of 15 days during a year, the following data were recorded: number of vegetative shoots (NBV) only new vegetative shoots were considered; Number of buds (NBF), only new buds; main shoot length (LBP), with a measuring tape in cm; main shoot diameter (BPD), with a vernier in mm; percentage of fruit (HR%), the amount of fruit growing was quantified and divided by the number of flowers, and multiplied by 100; harvested fruit diameter (DF), with vernier equatorial diameter of 10 fruits collected per tree; fruit weight (PF), 10 fruits per tree were collected and weighed an average obtained in a balance; number of fruits (NF), number of fruits per tree that reached physiological maturity; and leaf area (AF), a sample of 15 full leaves (leaf + petiole) was collected per tree to which its total area was obtained in cm² with the help of software ImageJ.

Analysis of variance of variables of growth and development of Hass avocado trees

Variables that showed no significant differences according to LSD (p≤ 0.05) were: number of vegetative shoots (NBV); percentage of fruit (CF%) and fruit diameter (DF) (Table 1). Other research has found similar results, as ^{Cossio et al. (2008)} who found that foliar applications of boron at a concentration of 1 g L^-1 and 0.5 g L^-1 in one two applications had no effect in the correction of boron deficiency nor increased the production, coinciding with the results obtained in this investigation; about ^{Salazar (2007)} proposed a hypothesis to explain the low fruit set, which could estarse presented a competition with vegetative growth, which develops when the flowers of the inflorescences are taking the shape fruit. ^{Espindola et al. (2008)}, meanwhile, indicated that N application increased fruit set to 50%, compared to those trees where no N was applied, coinciding with the present work.

Table 1 Probability error reported by the analysis of variance for different variables of growth and development, the effect of chemical treatments and organic nutrition of avocado trees cv. Hass. 

NBV= número de brotes vegetativos; NBF= número de brotes florales; LBP=longitud de brote principal; DBP= diámetro de brote principal; AF= área foliar; NF= número de frutos; CF%= porcentaje de frutos cuajados; PF= peso de frutos; DF= diámetro de frutos. Pruebas de Tukey (p≤ 0.05) y LSD (p≤ 0.05).

Analysis of variance (Tukey p ≤ 0.05) indicated that, the treatments showed significant differences compared with the control on the number of vegetative shoots (NBF) and number of fruits (NF). However, when the mean test LSD (p≤ 0.05) was performed in addition to the variables indicated, there were differences between treatments in the following variables: number of flower buds (NBF), length of main shoot (LBP) main shoot diameter (BPD), leaf area (AF), number of fruits (NF), fruit weight (PF) (Table 1).

Number of buds (NBF)

In means analysis using LSD (p≤0 05), treatment manure + edaphic + foliar (41 shoots/branch) was statistically better than the manure treatments + edaphic (19 buds/ branch); leaf (9 buds/branch) and the control (21 buds/ branch) (Table 2). This suggests that the combined action of these nutrients increases flowering Hass avocado trees. ^{Chaikiattiyos (1994)} indicated two associated with avocado floral initiation factors, the decrease of temperature and external fertilization, ^{Salazar et al. (2009)} found that, the development of flower buds of avocado trees cv. Hass did not altered by loading fruit on the tree is present but it does affect the number of vegetative shoots with the addition of nutrients.

Table 2 Effect of chemical and organic treatments on growth and development of avocado trees cv. Hass, in the municipality of Leonardo Bravo, Guerrero, Mexico. 

NBF= número de brotes florales; LBP= longitud de brote principal; DBP= diámetro del brote principal; AF= área foliar; NF= número de frutos; PF= peso de frutos. Prueba de medias LSD (p≤ 0.05).

Length (LBP) and diameter (BPD) of the main shoot

Regarding the length and diameter of the main bud branches, foliar treating manure +, had the highest length (16 cm), beating the treatments manure + edaphic (7 cm) and leaf (9 cm) but, did not presented significant differences with the control (12 cm) (Table 2). The correlation between LBP and DBP variables was highly significant in a negative way (Table 3) indicating that the greater the length of the vegetative shoot, the smaller the diameter.

Table 3 Correlation coefficient of the variables evaluated in avocado trees cv. Hass. 

NBV= número de brotes vegetativos; NBF= número de brotes florales; LBP=longitud de brote principal; DBP= diámetro de brote principal; AF= área foliar; NF= número de frutos; CF%= porcentaje de frutos cuajados; PF= peso de frutos; DF= diámetro de frutos. Prueba de Tukey (p≤ 0.05).

Leaf area (AF)

We found that, the edaphic + foliar treatment (75 cm²), showed higher leaf area than control (65 cm²) while other treatments had slight increases, but were not different at the same (Table 2). In this regard, it is noted that among other functions, nitrogen favours the development of avocado leaves and stems (^{Bernal and Diaz, 2006}). It has been determined that, the application of fertilizers to avocado trees, increased leaf development; therefore, improves its photosynthetic capacity (^{Maldonado, 2002}). Due to energy expenditure tree focuses on vegetative growth, provoking low productivity of fruit because at that time, indeterminate flowers are tying the fruit (^{Salazar et al., 2009}). According to this, a low productivity of fruit would be expected where the highest leaf area index was obtained; however, it was not so in this research.

Number of fruits at physiological maturity (NF)

In the analysis of means we found that, the treatment + foliar manure + edaphic (17 fruits) exceeded significantly foliar treatments edaphic + (6 fruits), leaf (1 fruit) and the control (three fruits) (Table 2), indicating that, the combined addition of fertilizers increases the number of fruit reaching physiological maturity. In this regard, indicating that nutrient application is very important to improve the quality and yield of avocado; N promotes the formation of the fruit; P involved in the formation of reproductive organs and accelerate the ripening of the fruit, and K, involved in the formation, quality and avocado fruit weight (^{Bernal and Diaz, 2006}).

Fruit weight (PF)

The analysis of means (LSD) showed that edaphic + foliar treatment (2.62 kg/10 fruits) was significantly higher than the control (1.51 kg/10 fruits). Other treatments with organic and inorganic fertilizers and foliar trend showed higher weight than the control, but did not statistically exceeded (Table 2). ^{Lovatt (2001a)} mentioned that nutrient concentration and time of application directly affect production and fruit yield. ^{Tapia (2007)} found that, the gradual increase of nutrients (N-P-K) promotes increased fruit yield, also found a maximum response as to continue increasing nutrient yields fruit decay. Indicating that, the application of N 56-168 kg ha-1, fruit size increases of 175 g to 325 g; this is reflected in the increased production by 70% (^{Lovatt, 2001b}).

This variable PF was positively significantly correlated with the percentage of fruit set (CF%) (Table 3); it means that a higher number of tied fruits, the higher the weight of fruits; yield is increased.

Conclusions

The application of organic, inorganic and foliar fertilizers had no effect on increasing the length and diameter of vegetative buds.

Flowering, leaf area and number of fruits were favoured by the application of organic fertilizers (manure), soil (N-P-K) and leaf (Ca, Mg and B); the treatment that had the best effect was (manure + edaphic + foliar).

The foliar application of manure + had the highest influence on the growth of the main shoot; whereas, the application of the soil + foliar treatment favoured greater leaf area and fruit weight.