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RESEARCH WORK

Effect of biological and/or mineral fertilization on mulberry (Morus alba L.) forage production (Technical note)

Katerine Oropesa, Gertrudis Pentón y G. J. Martín

Estación Experimental de Pastos y Forrajes «Indio Hatuey» Central España Republicana, CP 44280, Matanzas, Cuba
E-mail: katerine.oropesa@indio.atenas.inf.cu

ABSTRACT

A study was conducted during a year in areas of the EEPF «Indio Hatuey», in order to study the morphoagronomic response of Morus alba L. cv. Tigreada associated to Canavalia ensiformis as green manure, inoculated with mycorrhizas through the product EcoMic® (biological fertilization), and their combination or not with mineral fertilization. Treatments consisted in: control (C), mineral fertilization (MF), biological fertilization (BF) and combined mineral and biological fertilization (MF + BF) in both seasons. Mineral fertilization consisted in N and K, at a rate of 300 and 150 kg/ha/year, respectively. The intercropping of C. ensiformis as green manure inoculated with AMF, caused in the rainy season an improvement of the productive response, without affecting the utilization of forage as edible biomass (6 250 kg of leaves/ha and 18 194,4 kg of fuel biomass). To continue the studies is recommended in order to determine the optimum combination of mineral and biological fertilization that allows increasing the yield and the fresh stem:ligneous stem ratio.

Key words: Manures, Morus alba.

INTRODUCTION

At present, the worldwide situation in food production, poses the challenge of generating technological proposals which imply the promotion of sustainable livestock production models, with a considerable reduction of external inputs, in order to decrease costs and increase the economic benefits per product unit, without damaging the environment.

Mulberry (Morus alba L.) stands out as a forage shrub highly accepted among those who develop and promote livestock production agroforestry systems. This species has been traditionally used for feeding silkworms (Pelicano et al., 2007) and as protein supplement for farm animals due to the high nutritional quality of its biomass, the high palatability of its leaves (Milera et al., 2010), its production capacity per area unit, as well as its wide adaptation to different climates and soil types.

In spite of its remarkable merits, the intensive production of mulberry forage demands high input quantities. In Cuba there are not sufficient works evaluating the response of mulberry before the effect of biofertilization. Hence the need to study the agronomic behavior from the combination of mineral fertilizer and the inoculation of biofertilizer EcoMic® through C. ensiformis intercropped as green manure (biological fertilization).

MATERIALS AND METHODS

The study began on April 15^th, 2007 and lasted for one year at the EEPF «Indio Hatuey», which is located at 22º48'7'' latitude north and 81º2' longitude west, at 19,01 masl. The soil characteristic of the site is Ferralitic Red (Hernández et al., 2003), with good surface and internal drainage. In it phosphorus (ppm) was determined through Oniani's method, OM (%) according to the Walkley-Black procedure and pH by Potentiometry (Fernández, 1997), and the T value was calculated. Table 1 shows the characterization of the soil chemical composition, which shows moderate fertility, the T value is around 15, has neutral pH and the organic matter contents are moderate to low.

The experiment area was 0,1 ha and the plots had a dimension of 24 m². The plantation was a year and a half old at the beginning of the study. The meteorological characteristics of the experimental period are shown in table 2. In the dry season rainfall was scarce, with a noticeable difference as compared to the rainy season. Relative humidity showed typical values representative of the seasons for Cuban conditions.

The studied species were M. alba L. var. Tigreada as main crop and C. ensiformis as green manure and incorporation means of vesicular-arbuscular mycorrhizas (VAM) in the rhizosphere of the plantation.

The commercial product used to inoculate the mycorrhizas was EcoMic®. The AMF strain (Glomus fasciculatum) was obtained from certified mycorrhizal inoculum (Fernández et al., 2001), produced in the Department of Biofertilizers and Plant Nutrition of the National Institute of Agricultural Science (Mayabeque), and contains 250 spores/g. The inoculation through C. ensiformis was made by means of the seed covering method (Fernández, 1997).

Design and treatments. A completely randomized design with four repetitions was used. The treatments were the following:

• Control-rainy season (RS-C)

• Biological fertilization-rainy season (RS - BF)

• Mineral fertilization - rainy season (RS - MF)

• Mineral and biological fertilization - rainy season (RS - MF + BF)

• Control - dry season (DS - C)

• Biological fertilization - dry season (DS - BF)

• Mineral fertilization - dry season (DS - MF)

• Biological fertilization-rainy season (RS - BF)

• Mineral and biological fertilization - dry season (DS - MF + BF)

Procedure. Soil preparation consisted in using the disc plow twice (turning and crossing) and harrowing once, The used planting frame was 1 x 0,50 m in mulberry, according to the recommendations made by Cifuentes and Kee-Wook (1998), and 1 x 0,40 m in C. ensiformis. The rows were oriented in an East-West sense.

Cultivation and weeding activities were performed after 60 days. No irrigation was applied.

Because the assimilable phosphorus content was within an acceptable range only urea and KCl were applied as basal fertilizer, at a rate of 300 and 150 kg of N and K/year, respectively. The application dose of EcoMic® was 37 kg/ha/year. The mineral as well as the biological fertilizers were fractionally applied in June and October. C. ensiformis inoculated with EcoMic® was incorporated to the soil as green manure 60 days after planting.

Mulberry was pruned with 90-days intervals at a height of 30 cm.

For the agroproductive study 12 individuals were selected in each plot, and in all cuttings the yield and quality of edible biomass were determined. In the case of growth studies three individuals were selected and an observation was made for each season (rainy and dry). The measurements were:

• Leaf yield, fresh stem (FS) yield, edible biomass (EB) yield and total yield, expressed in kg DM/ha/season

• Fresh stem: ligneous stem (LS) ratio, expressed in FS units/LS unit

• Edible biomass: ligneous biomass ratio, expressed in EB units/LB unit

Statistical processing. A variance analysis was made through the GLM (General Lineal Models) procedure, with previous verification of normal data distribution and variance homogeneity. For the comparison among means Duncan's multiple range test was used. The program used was SPSS® Version 10.

RESULTS AND DISCUSSION

Figures 1 and 2 show that the highest production of total biomass as well as fresh stems, was obtained in the rainy season with biological fertilization, without significant differences from mineral fertilization and their combination in fresh stems.

This result coincides with the one obtained by Setua et al. (1999), who observed during eight weeks the superiority of mulberry inoculated with G. fasciculatum combined with a sixth of the conventional dose of phosphorus fertilization (180 kg P/ha/year) and corroborates the statements by Hernández et al. (2006) concerning that mulberry is able to reach high yields when intercropped with green manure.

The application of Azotobacter biofertilizer with organic matter significantly stimulated the production of total and edible biomass of mulberry, which reached values between 10 and 12 t DM/ha/year in edible biomass (70% leaves only). It was also observed that with the application of foliage from Albizia lebbeck and Gliricidia sepium as green manure, the mulberry yield increased (Sánchez and Reyes, 2003).

Riera (2002) stated that the utilization of mycorrhizas as biological alternative to the use of chemical products does not imply that no fertilization is used, but that it is more efficient and doses can be decreased.

In the fresh stem: ligneous stem ratio (table 3), the fertilization alternatives and their combination did not differ among themselves. Regarding season, no differences were shown due to the use of mineral fertilizer, although they appeared as compared to the control in the dry season.

In general, it can be inferred that biological fertilization (intercropping of C. ensiformis for green manure inoculated with mycorrhizas) conditioned in the rainy season an improvement in the vegetative response, without affecting the leaf/fresh stem ratio or the fresh stem/ligneous stem. During the dry season the results after the year of starting the study did not show a clear trend.

Biological fertilization contributed an added value to the system (table 4). The intercropping of C. ensiformis inoculated with EcoMic® and incorporated to the soil as green manure allowed a higher utilization of resources and space, and macronutrients were incorporated to the soil. This herbaceous legume has a high value for forage production in marginal regions, subject to frequent droughts, or on poor or saline soils (Martín et al., 2007). Its importance lies on the high protein content of its leaves, flowers and fruits (27-29%), and its fast growth and wide adaptation (Bunch, 1994; Cáceres et al., 1995). Díaz et al. (1997), when evaluating several legumes of high protein value, found that C. ensiformis exceeded the other species in protein content .After Mucuna spp., C. ensiformis is the most widely species as green manure and cover crop (Bunch, 1994). In this study, such species planted in a wide framework (to prevent the competition effect with the main crop) incorporated to the soil a considerable volume of organic matter and nutrients.

According to the results it is concluded that there was a significant effect on the productive response of mulberry and the seasonal behavior of the species stood out. The intercropping of C. ensiformis as green manure inoculated with AMF (biological fertilization) conditioned, in the rainy season, an improvement in the productive response, without affecting the utilization of forage as edible biomass.

To continue the studies is recommended in order to determine the optimum combination of mineral and biological fertilization, which allows increasing the yield and FS:LS ratio.