RESEARCH WORK

Seed production of Leucaena spp. on acid soil

Hilda B. Wencomo¹, Bárbara Cepero² y J. Ramírez²

¹Estación Experimental de Pastos y Forrajes «Indio Hatuey» . Central España Republicana, CP 44280, Matanzas, Cuba

E-mail: hilda.wencomo@indio.atenas.inf.cu

²Estación Experimental de Pastos y Forrajes Cascajal, Villa Clara, Cuba

ABSTRACT

This work was conducted on a of Leucaena spp. collection that was established on acid soil in the Villa Clara province, with the objective of studying the seed production performance of this shrubby species on this soil type. Four treatments were evaluated (A, B, C and D), which were defined through the four quarters of the year, distributed according to a completely randomized design; in addition, the phenology was observed. A highly significant variation (P<0,01) in the total seed and pure seed yield, and the best result was obtained in treatment D. Besides, in this treatment the lowest weight of 1 000 seeds was observed, which represented a higher number of seeds per kilogram and a lower cost per kilogram of seed ($ 4,80). Variation was observed regarding the phenology patterns of flowering and fructification of the different studied species and accessions. The harvest of seeds from Leucaena is concluded to be more economical when it is carried out in the last quarter of the year under the conditions this trial was conducted.

Key words: Acid soil, Leucaena spp., seeds

INTRODUCTION

The collection, processing and storage of seeds from the Leucaena species, is not a complex labor; they can be dried and stored at low temperature and humidity, following the conventional methods for forestry seeds. However, in Cuba the seed production of shrubby legumes in areas dedicated to the multiplication of pasture seeds, is a little generalized practice.

For implementing silvopastoral systems in the different livestock production areas of the country, in order to utilize best the large benefits they generate, obtaining the reproductive material is important, which constitutes a need within the Cuban current livestock production, according to Simón et al. (1998).

Leucaena, especially Leucaena leucocephala, has been object of many studies and it is the most planted species in agroforestry systems, besides being one of the forage legumes with better characteristics for livestock production (Funes, 2004). There are reasons for which leucaena has been widely used, among which the following stand out: its high biomass production (even in the dry season), its acceptability by different animal species and its regrowth capacity after cutting and/or browsing (Hernández, 2000). The combination of the attributes found in this tree is likely to be unique; however, it shows some limitations, such as: its adaptation to acid soils is low, particularly when they are associated to highly exchangeable aluminum (Ruaysoongnern et al., 1989); its establishment is slow (Clavero, 1998); its productivity in the Asian and Pacific regions has been reduced (Napompeth and MacDicken, 1989) due to the attack of the psyllid insect (Heteropsylla cubana, Homoptera: Psyllidae) and its propagation is limited, very often, by low seed availability.

Due to the above-mentioned reasons, the objective of this work was to learn the performance of leucaena seed production under acid soil conditions.

MATERIALS AND METHODS

The trial was conducted at the EEPF «Cascajal», located in the central province Villa Clara, Cuba, on an Alitic soil, with pH 4,3. This soil shows organic matter contents between 2,0 and 5,0%, low base exchange capacity (< 20,0 cmol/kg) and a thick mocarrero layer in its profile (Hernández et al., 2003).

The historical annual average (23 years) of rainfall is 1 265 mm, where 75% (948,75 mm) occurs in the rainy season (May-October) and 25% (361,25 mm) in the dry season (November-April). Mean temperature varies between 22,0 and 27,8ºC, and relative humidity from 79 to 84%.

Table 1 shows the average values of maximum, minimum and mean temperature, and relative humidity, as well as total rainfall and evaporation in 24 hours. As can be observed, all the indicators reached very similar means in the four periods, except rainfall and evaporation.

One hundred and thirty seven accessions of Leucaena spp., 150 months old, were evaluated (table 2).

Design and treatments. A completely randomized design was used to determine the yield and quality of the seed produced by the Leucaena accessions, according to the four treatments, which were defined as the periods corresponding to the four quarters of the year: A) January-February-March; B) April-May-June; C) July-August-September; and D) October-November-December.

Experimental procedure. In a one-hectare area, with a population of 555 plants/ha four groups were randomly taken, which were marked to facilitate the programmed measurements and/or observations.

For the harvest moment the fact that more than 80% of the pods changed their color from green to light brown was taken as indicator. The pod harvest was manually performed and they were pre-dried under sunlight and threshed with a thin piece of wood. Seed drying was completed under shade until reaching between 8 and 10% moisture.

Afterwards, the seeds were cleaned and stored (for 6 and 18 months), under ambient conditions.

Measurements. In each treatment tree height was measured at the moment of the harvest; all the pods in optimum status to produce seeds were harvested. In 100 randomly chosen pods their length was measured, as well as the number of seeds contained in them; the size of the latter was measured and their size was observed; the total seed yield, pure seed yield and weight of 1 000 seeds were determined. The number of harvests performed was 3, 2, 2 and 2, for treatments A, B, C and D, respectively, according to pod maturation.

In order to evaluate the economic results of all the plants under study, the expenses in salaries, materials and the time used in each activity were taken into consideration; this allowed to determine the production cost of the seed kilogram according to the treatments used.

Statistical processing. An ANOVA was made according to lineal model of simple classification; the means were compared through Duncan's test (Duncan, 1955) for 1 and 5% significance, after verifying they fulfilled the normal distribution and variance homogeneity adjustment.

In addition, the Main Component Analysis (MCA) (Morrison, 1967) was used, in which those main components that showed values higher than 1 and sum or preponderance factors higher than 0,70 were taken as analysis criterion, with the purpose of transforming the abiotic factors measured (climatic variables), in a reduced set of independent factors that represent the selected variable. The practical application was carried out by means of the Varimax orthogonal method through the statistical program SPSS® version 11,5 for Microsoft® Windows® (Visuata, 1998).

RESULTS AND DISCUSSION

The plant height and seed yield of the accessions of each species had a similar performance, in the rainy as well as in the dry season, which is why they appear in the tables per species and not per accessions. Table 3 shows such indicators and the production cost.

The height varied significantly (P<0,001) and the highest values coincided with treatment D, where the plants reached the oldest age mainly in the accessions of L. leucocephala and L. diversifolia. Likewise, total seed and pure seed yield varied; for the first indicator similar results were found between treatments B and D, while in the second indicator the best value was obtained in D, which coincided with a high total seed yield, for which it can be stated that at more height better seed yields can be expected. It is valid to express that the plants of the above-mentioned accessions also stood out in these indicators.

This could have been influenced by different factors, although it is valid to emphasize that during the study the climate remained pretty stable (table 1) and was not propitious for the appearance of diseases, mainly the fungal ones, which are considered direct causes of seed damage (Lezcano, 2005), because they cause remarkable losses in seed production and quality, in addition to the decrease of germination, discoloration, weight loss and deterioration. The latter, according to Silva (1993), causes vigor reduction, non uniform emergence and yield decrease in seeds.

The results in production (mainly in the species L. leucocephala), although low as compared to the ones obtained by Matías et al. (2000), are significant, especially if it is considered that the study was conducted on acid soil, which is a limitation for the growth and development of many forage plants.

In this sense, Peña and Aira (1996), when studying the seed production of L. leucocephala in Guantánamo obtained high yields, possibly due to the exceptional climatic conditions in this region.

The production occurred in May, August and from September to December; this last month was the one with the highest production (118 accessions produced seeds, which means 81,3%). The most outstanding accessions belong to L. leucocephala: CIAT-17478 (3,4 kg); CIAT-17493 (2,5 kg); CIAT-17263 (2,3 kg) and cv. Peru (4,2 kg). This shows the superiority of this species as compared to the others. It should be stated that the accessions belonging to L. shannonii and L. lanceolata did not produce seeds during the research period. The observations made in these accessions coincide with the results from the studies conducted by Sacandé (2000) and Venter (2000), who reported that in certain environments some species do not produce fruits, as happened in L. esculenta when it was established in low hills in Hawaii. This performance could have been due to the fact that phenological patterns are manifested differently when the trees grow away from their native zones.

On the other hand, the edaphoclimatic conditions, which in certain places are not adequate for plants to show their capacity of reproduction and adaptation to the environment in which they live (Hidalgo, 2003); as well as their genetic expression in certain environments or physiological stress could have influenced it. This characteristic of producing flowers, pods and seeds on this soil type is very important, because it shows the struggle of species with the environment for survival. Its importance lies on the fact that the seed is the starting point for any farming system to be developed. For such reasons, the knowledge of the flowering and fructification period of trees, the characteristics of their seeds, as well as their processing after harvest, and the indicators and conditions for their storage, is necessary.

Regarding the calculated values for the production costs per kilogram of seed, the lowest cost was obtained in treatment D, which could have been due to the higher yield; while the highest cost belonged to treatment A, where the seed production was the lowest and besides a higher number of harvests had to be made, as a product of the little uniformity in pod maturation. The performance of the different individuals showed variation, for which neither generalized nor arbitrary criteria should be established from the evaluated indicators, but for each one individually.

The environmental factors can have significant effects on the seed production potential (Carvalho and Nakagawa, 2000). That is why the most related factors were determined, for which the MCA was used (table 4). A cumulative variance of 77,01% was detected in the first three components.

The variables that best explained the variance in the first component (41,80%) were maximum, mean and minimum temperature, which were positively related among themselves; the second component extracted a variance of 23,30%, which was explained by mean and minimum relative humidity and evaporation (negatively); while the third component was explained mainly by the maximum relative humidity.

In general, the variables were well represented for the three components, because the variance explained by the values of r for all the variables was higher than 70% (Obis, 1998), except for rainfall, which indicates that this variable was little represented by the three components and that probably a fourth factor is needed to gather information from it. The climatic factors with the highest influence on the seed production potential of leucaena were maximum temperature, maximum relative humidity and mean relative humidity; although the results of the main component analysis emphasize maximum temperature as the indicator most related to this performance.

The mean length of the pods and the number of seeds per pod are shown in table 5. In the first indicator similar results were found between treatments C and D; while in the second indicator the best value was obtained in treatment D.

There was a trend towards the increase of the values in both indicators from treatment A to D. The higher value of these yield components in treatment D, could have been one of the causes that determined the highest production in this period; this could have been also due to different factors such as plant height, genetic differences, maturation conditions, seed size or type of dormancy (Sánchez et al., 2004).

Regarding the weight of 1 000 seeds (table 6) the lowest value was found in treatment D, which determined that a higher number of seeds per kilogram occurred in this treatment. According to Gómez et al. (2002) this allows a higher number of plants per kilogram as compared to the other treatments, which can be beneficial at the moment of conducting the planting and propagation of the species.

In the conditions under which this study was conducted and according to the results, it is concluded that Leucaena seeds should be harvested in the quarter October-November-December, because it is the most feasible option from the economic and productive points of view; although taking into consideration the present need for seeds of this plant, harvest can be recommended in the quarters April-May-June and July-August-September, in which the cost did not exceed $5,00 per kilogram and the productions are also acceptable, which will allow to make a more extensive use of these accessions in other zones.