Growing Mulberry and Trichanthera gigantea in association
with Flemingia macrophylla on sloping land and using
the foliages as feeds for rabbits

Introduction
 

In Vietnam, Mulberry (Morus alba) has high biomass production and a high content of crude protein (17 to 18%) in the dry matter of the leaves. However, it is an exploitive crop when grown continuously on sloping land. It exhausts the soil fertility and increases the risk of erosion. Flemingia macrophylla is well adapted to hilly-mountain land and can improve the fertility of the soil (Dinh Van Binh et al 1998).  However, growth and milk production of goats fed were decreased when the Flemingia foliage supplied more than 15% of the dietary DM (Nguyen Thi Mui et al 2001). Trichanthera gigantea is reported to have a high biomass production and does not appear to reduce soil fertility (Nguyen Phuc Tien et al 2003)..

The purpose of the present experiments was to study the growing of Mulberry and Trichanthera in association with Flemingia in sloping land and to determine the digestibility and nitrogen balance in mature rabbits fed  these foliages as the sole feed.
 

Materials and methods

Agronomic experiment
 

The study was carried out at the Goat and Rabbit Research Centre. The mean annual air temperature is 23.5 °C, with an average of 123 hours/sunshine per month. Mean annual rainfall is 1850 mm and annual humility 84%. The experimental area was divided into 32 plots (Table 1) in a 4*2 split-plot arrangement. The main plots were the plant species (Mulberry [M], Trichanthera [T] in monoculture or associations with Flemingia [M-F], and [T-F]. The split-plots were two levels of cattle manure: 15 or 30 tonnes/ha.

The soil was prepared uniformly by ploughing and harrowing and the cattle manure applied before planting.  Trichanthera and Mulberry were planted by stem cuttings (25 cm long) with 50 cm between rows and 25 cm between cuttings in the row. For the associated species there were alternate rows at 50 cm of Flemingia and either Mulberry or Trichanthera. The Flemingia was planted with 5 cm between seeds in the row. 

The foliages were harvested when the average height of the plants was 1.5 m (first time) and at 1.2 m for subsequent harvesting. The foliage was cut at 50 cm from the soil surface.

Soil samples (0-30 cm depth) were taken from the experiment plots at the beginning and  12 months after planting. An equal amount (3 kg) was put in to clay pots (about 5 litres) for a biological test of overall soil fertility. Three seeds of maize were planted in each pot. After 5 weeks the maize plants were removed from the soil, washed to remove soil from the roots and allowed to dry for one hour in the shade. The total fresh green biomass and the roots were weighed.

Digestibility experiment with rabbits

Five male rabbits with initial weights varying from 3.5 to 3.6 kg were used in a 5*5 Latin square arrangement (Table 2) to determine apparent digestibility coefficients of each of the foliages and of the conventional diet of Guinea grass alone (GG) or with concentrates (GC). The concentrate contained 49% maize, 49% rice bran and 2% minerals. The rabbits were kept in cages that allowed the collection of faeces and urine separately. The animals were fed twice daily (07.30 and 14.00h).  They were given 7 days of rest between the experimental periods, when they were fed Guinea grass and concentrates.

The rabbits were given the experimental feeds for a 7-day preliminary adjustment period, when the foliages were offered ad libitum. In GC the concentrate was restricted to 100 g/day. From days 8 to 15, the daily amount of feed offered and refused was recorded. The total quantity of faeces was collected during days 9 to 16. Twenty percent of the faeces were put in a freezer until analysis. Urine was collected in glass bottles, to which 50 ml of 0.1N sulphuric acid was added to avoid nitrogen loss. Approximately 10% of the daily urine output was frozen and pooled for each animal. All animals were weighed for two consecutive days at the beginning and the end of each 7-day collection period, prior to being offered feed and water in the morning to minimise variation in gut fill.  

Chemical analysis

The DM and ash were analysed using standard AOAC (1990) methods. Total nitrogen of the feeds was determined by the Kjeldahl technique and crude protein calculated as N*6.25. Neutral detergent fibre (NDF) and acid detergent fibre (ADF) were determined by the methods of Van Soest et al (1991).  

Statistical analysis

The data from the experiments were analysed using the GLM option of the analysis of variance software of Minitab (1998). The treatment means which showed significant differences at the probability level of P<0.05 were compared using the Fisher pair-wise comparisons procedure.

The models used in the analysis were:

Agronomic experiment:

Y_ijk = m+ T_i + B_{j  +}  S_{k +} TS_{ik +} e_ijk  

where Y_i, is the dependent variable, m = the general mean,  T_i = the treatment effect, B_j the block effect, S_k the manure effect, TS_ik the interaction of T and S and e_iik,  = the random error effect.

Digestibility experiment:

Y_ijk = m+ P_i + A_j + T_k + e_ijk

where Y_ijk  are the dependent variables, m = the general mean, P_i = the effect of the i^th period,  A_j=the effect of the j^th animal, T_k  = the effect of the k^th treatment, and e_ijk = the random error effect.   
 

Results and discussion
 

Agronomic experiment

Biomass yields were in direct proportion to the amount of organic manure used as fertilizer (Figure 1). Planting Flemingia in association with the Mulberry and Trichanthera increased total biomass yield compared with growing the foliages in monoculture. Yields were higher for Trichanthera than for Mulberry in monoculture and in association with Flemingia.

Figure 1:  DM biomass yield of Mulberry and Trichanthera in monoculture and combined
with Flemingia in the associated plots

Effects on soil fertility

Differences in soil fertility, as measured by the maize bio-test, became evident 12 months after planting (Table 5; Figure 2), with lowest value for Mulberry in monoculture and the highest for the association of Trichanthera with Flemingia.