RESEARCH WORK

 

 

 

Intercropping of Canavalia ensiformis (L.) inoculated with arbuscular mycorrhizal fungi for the production of Morus alba (L.) forage

 

 

 

Gertrudis Pentón-Fernández1, Ramón Rivera-Espinosa2, Giraldo J. Martín-Martín1, Katerine Oropesa-Casanova1, Francisco Soto-Carreño2 and Juan Adriano Cabrera-Rodríguez2

1Estación Experimental de Pastos y Forrajes Indio Hatuey, Universidad de Matanzas, Ministerio de Educación Superior Central España Republicana, CP 44280, Matanzas, Cuba
2InstitutoNacional de CienciasAgrícolas, Mayabeque, Cuba
E-mail: gertrudis@ihatuey.cu

 

 

 


ABSTRACT

On a lixiviated, non-irrigated Ferralitic Red soil, the effect of intercropping Canavalia ensiformis (L.), inoculated with AMF, complemented with mineral fertilizer, on the production of mulberry forage and the nutritional status of the plants was determined. The treatments were formed by the combination of intercropping C. ensiformis (common jack bean) inoculated with AMF (with CeAMF) or not (without CeAMF), and the doses of mineral fertilizer (F0: without fertilizer; F1: 100-50-50 kg ha-1 of N, P2O5 and K2O in each season; F2: 200-100-100 kg ha-1 of N, P2O5 and K2O in each season). A randomized block design with factorial arrangement was used. The highest yields were reached with CeAMF, complemented with F1 (12,15 and 16,65 t ha-1 for years 1 and 2, respectively), without differences from F2 without C. ensiformis in three of the four evaluated seasons. In the rainy season 76 % of the total yield of the year was produced. There was a high and significant relation between the seasonal yield and the accumulated amount of rainfall with determination coefficient of 0,97. The mulberry with CeAMF, complemented with fertilizer, could maintain stable yields between cuttings in each evaluated season. The yield in the rainy season varied depending on the concentration of N in the leaves, which reached 32,6 g kg-1 DM. It is concluded that the intercropping of jack bean inoculated with AMF, complemented with treatment F1, produced a higher yield of edible biomass of mulberry and a better nutritional status of the plants in terms of N concentration in the leaves.

Key words: biomass, nutritional status, yield.


 

 

INTRODUCTION

Mulberry (Morus alba, L.) is a species that stands out for its high yields of forage aimed at feeding ruminants and monogastric animals, and for its high acceptability, digestibility, nutritional value and perennial character when cut; it can also be used as green forage and preserved as silage or meal (Martín et al., 2007).

According to the literature from Latin America, the edible dry matter yield of this plant can reach 30-40 t ha-1 per year when high rainfall with uniform distribution occur, on high-fertility soils or with adequate management of plant nutrition (Almeida and Fonseca, 2002; Dingle et al., 2005; Sanginéset al., 2006).

In Cuba this crop is in extension phase and yields are obtained without irrigation varying between 8 and 12 t ha-1 year-1 of edible dry biomass (Martín et al., 2007). Cultivar Tigreada stands out for its adaptation to scarce rainfall conditions (G. Martín, personal communication).

Mulberry is characterized by its high nutrient requirements, mainly N, and its concentration in the leaves can reach 40 g kg-1 DM (Liu et al., 2002; Martín, 2004). In order to obtain higher forage yields with adequate nitrogen concentrations, high quantities of nitrogen fertilizer are generally used, which depending on the edaphoclimatic conditions vary between 260 kg ha-1 and 400 kg ha-1of N per year (Rodríguez et al., 1994; Cifuentes and KeeWook, 1998; Benavides, 1999).

The high doses of fertilizers imply high production costs (Elizondo, 2007), for which, in order to reduce such inputs, it is important to evaluate nutrition management practices that have been effective in other crops, such as the use of green manures (CIDICCO, 2004) and of mycorrhizal inoculants (González, 2014).

Green manures, particularly those of the group of legumes, show benefits associated not only to the contribution of N via biological fixation, but also nutrient recycling, soil cover, maintenance of humidity and weed control (Ramos et al., 2001; Elfstrandet al., 2007), which constitute favorable aspects for the cultivation of mulberry.

On the other hand, in recent years the results about the positive effect of arbuscularmycorrhizal inoculants when applied to the crops have increased, because an effective mycorrhizal symbiosis is established increasing the nutrient uptake, guaranteeing high yields and causing decrease in the needs of fertilizers (Rivera et al., 2007; González, 2014). Although mulberry is a mycotrophic crop, the studies about the importance of its inoculation with AMF are scarce, and basically they are located in India (Ram Rao et al., 2007).

In Cuba and in the Central American region the experiences with mulberry managed with mycorrhizal inoculants and intercropped C. ensiformis are insufficient; for which the objective of this research was to determine the effect of this management practice, complemented with mineral fertilization, on the production of mulberry forage related to the season, and its relation to the concentration of N in the leaves.

 

MATERIALS AND METHODS

Geographic location. The trial was conducted in areas of the Pastures and Forages Research Station Indio Hatuey, located between 22º, 48' and 7" North latitude, and 81º and 2' West longitude, at 19,01 m.a.s.l.; in the Perico municipality, Matanzas province, Cuba.

Edaphoclimatic characteristics. The soil corresponds to the genetic type lixiviated Ferralitic Red, according to Hernández et al. (2015), and to the RhodicFerraliticNitisol,Lixic, Eutric type, according to FAO (2014). The topography is flat, with slope from 0,5 to 1,0 %, and the depth to the limestone is 1,50 m.

The pH values and the concentrations of exchangeable Ca and Mg (table 1) were typical of these soils, which also showed low values of exchangeable K. The concentration of available P was low and the concentration of organic matter (OM) can be considered high for the grouping of the Ferralitic soils, and indicates that it is a little degraded soil (Hernández et al., 2014).

The duration of the study was two years, and it was conducted in a plantation of mulberry cv. Tigreada with four years of establishment. The experimental area was characterized by a rainfall regime which varied more between years and seasons, compared with the mean air temperature (table 2).

 

Description of the experiments

The size of the area was 1 000 m2; the planting frame consisted in double furrows (0,50 m x 0,50 m x 1 m) and it was in correspondence with a density of 26 666 plants ha-1.

The experimental plots had a surface of 13,5 m2 and were composed by 36 plants, from which 12 were considered in the calculation area, with a homogeneous age. They were cut every 90 days at a height of 30 cm.

Design and treatments. A randomized block design with factorial arrangement and four replications was used. The treatments were:

Procedure. Jack bean was manually sown, in the months of May and November of each year, with a planting frame of 0,75 x 0,54 m and a location with regards to the mulberry furrow of 0,25 m. The seeds were previously inoculated with a Glomus cubense strain following the method established by Rivera et al. (2006), with 0,15 g of inoculant per seed in each season. The mycorrhizal inoculants consisted in spores and other propagules, and was prepared by the technology of EcoMic® (Fernándezet al., 2000) in the department of biofertilizers and plant nutrition of the National Institute of Agricultural Sciences (INCA for its initials in Spanish) Mayabeque, Cuba, with a titer of 25 spores for each gram of inoculant as minimum. Sixty days after planting jack bean was cut for green manure, the aerial biomass was fractionated into equal parts and it was placed as mulch around mulberry, in a proportion of 1,25 plants of jack bean for each plant of mulberry.

The fertilizers were manually applied, on the soil surface and on the stem base, seven days after the mulberry was cut in May and November.

The manual weeding activities were maintained throughout the experimental period; and the criterion of not applying irrigation was assumed, in correspondence with the reality of most farming exploitations.

 

Measurements

Dry matter yield of edible biomass (t ha-1 in each season). It was determined by the sum of the leaves and fresh stems dry mass yield, and it was expressed as accumulated dry mass in each season (seasonal yield).

Edible dry matter yield per cutting. It was determined by the sum of the leaves and fresh stems dry mass yield in each cutting.

Concentration of N in the leaves of mulberry (g kg-1 DM). In each season the concentration of N was determined as percentage of the dry mass of the leaves, according to the analytical method described by Panequeet al. (2010) from the humid digestion with H2SO4+ Se.

Statistical analysis.The normality of data distribution in all the variables was verified through the modified Shapiro-Wilk test, and the variance homogeneity, using Levene's test. In each cutting and season, variance analyses and mean comparison were carried out through Duncan's (1955) test. Likewise, paired sample analysis (Steel and Torrie, 1992) and later t-test were made.

Relations were established, through regression analysis, between the edible biomass yield and the accumulated rainfall in each season, and between the relative edible biomass yield (with regards to the treatment CeAMFF1) and the concentration of N in the leaves. For these analyses the criteria expressed by Guerra (1986) were taken into consideration.

The statistical pack used was Infostat 2008 (Di Rienzoet al., 2008).

 

RESULTS AND DISCUSSION

In terms of seasonal yield of edible biomass of mulberry, the interaction among the studied factors was significant (table 3). High yields were found in the rainy season in the treatments with CeAMF in the presence of the doses of fertilizers F1, without differences from F2 with and without intercropped jack bean; this showed the benefits of intercropping when the forage receives 50 % of the doses of mineral fertilizers necessary to reach its high yields.

According to the studies conducted by Shankar et al. (1999) and Martín (2004), the contribution of nutrients via fertilizers in doses lower than 300 kg N ha-1 per year do not supply the requirements of the mulberry crop. Nevertheless, under the conditions of this study, treatment F1 was effective in each season, when used as complement of CeAMF. This is explained, among other reasons, by a possible efficient functioning of AMFs. According to Siqueiraet al. (2010), in the presence of a nutrient supply below the optimum one the growth of the mycorrhizal structures is stimulated and the efficiency of absorption and extraction of mineral nutrients increase; the latter was proven by Solaimanet al. (2014).

With regards to the biomass yield in the dry season, in the first year a significant response was obtained to the higher dose of mineral fertilizer without CeAMF, and in the second year the highest value was found in the treatments with mineral fertilization.

The productive response of mulberry to the fertilizer doses corroborated the results obtained by Shankar et al. (1999) in a trial in which doses of N (300 and 400 kg ha-1 per year) and K (120, 160 and 200 kg of K2O) were used, and the highest increases in the yield and chemical composition of the leaves were reached with the highest doses.

Effect of the accumulated rainfall was observed per season on the edible dry matter yield in the most productive treatments (CeAMF, complemented with F1, and F2), with a high and significant determination coefficient (fig. 1).

The results showed the importance of rainfall for the growth of mulberry without irrigation, and the high determination coefficients suggest that this is the main variable which defines that a season is more productive than the other, and even explain the variation in the yield between the years under conditions in which the nutrient supply is not a limitation.

The edible biomass yields in each cutting in the more productive treatments (fig. 2) indicated that intercropped and AMF-inoculated C. ensiformis, complemented with the intermediate doses of fertilizers, could maintain similar yields between the cuttings of the rainy season. All seems to indicate that fertilization guaranteed sufficient nutrients to the crop at short term, which was shown in the first cut, and it also should stimulate inoculation and effective functioning of AMF in mulberry, with the subsequent benefit of yield in the second cutting.

The highest concentration of N was related to mineral fertilization (table 4), and in three of the four evaluated seasons there was also significant influence of CeAMF; this is explained, among other reasons, because the plants inoculated with AMF absorb more N from the soil (Gryndleret al., 2009).

There was only interaction among the studied factors in the rainy season of the first year. In addition, the N concentration in the leaves was in the optimum range acknowledged for the species (Benavides, 1996; Noda, 2005).

The effect of season was significant, and the concentration of N was higher in the dry season in all the treatments; this was related to the higher accumulation of N in the presence of a lower growth.

The relation between the edible biomass yield and the concentration of N in the leaves, in the rainy season, is shown in figure 3. The variations of yield depending on the concentration of N were significant, which indicates a sufficiency of nutrients in the more productive treatments, associated to CeAMF, complemented with mineral fertilization.

In the dry season the variations of the yield depending on the concentration of N were not significant, and the determination coefficients showed values of 0,38 and 0,58.

The comparison between seasons and years was made through paired sampled test (values of each treatment in both seasons) and corresponding t-test (Steel and Torrie, 1992).

It is concluded that under the conditions of this study the high degree of dependence of the intensive production of mulberry with regards to the supply of nutrients and the rainfall, without irrigation was corroborated.

The intercropping of C. ensiformis inoculated with AMF, complemented with the intermediate dose of mineral fertilizers, produced in the edible biomass of mulberry higher yield and better nutritional status of the plants, in terms of the concentration of N in the leaves.

 

 

 

Received: November 2, 2014
Accepted: December 18, 2015