Comparative studies on the yield and chemical composition of Panicum maximum and Andropogon gayanus as influenced by Tephrosia candida and Leucaena leucocephala

J A Odedire and O J Babayemi*

Department of Animal Science, Obafemi Awolowo University, Ile - Ife, Nigeria
*Department of Animal Science, University of Ibadan, Ibadan, Nigeria
oadeolu@oauife.edu.ng   or   oadeolu@yahoo.com

Abstract

This experiment was set up to compare the effect of Tephrosia candida and Leucaena leucocephala on the forage improvement of Panicum maximum and Andropogon gayanus. Both the browse trees and the grasses were purposely interplanted to assess the effects of the former on the latter. Harvesting of the grasses was carried out every six weeks to determine the annual yield.  Harvested grasses were analyzed for dry matter (DM), crude protein (CP), neutral detergent fibre (NDF), acid detergent fibre (ADF), lignin, cellulose, hemicellulose and ether extract (EE).

The effects of browse trees were positive on the yield of grasses, as the grass plots without the trees were lowest in dry matter yield.  Leucaena leucocephala permitted a relatively higher biomass of Panicum maximum than those planted with Tephrosia candida. Andropogon gayanus behaved differently as Tephrosia candida favoured its forage yield than as observed for Leucaena leucocephala.  Effects of browse trees on nutrient composition of the two grasses were not obvious. Crude protein (9.4%) content of Panicum maximum was higher than that recorded (6.7%) for Andropogon gayanus. Neutral detergent fibre, acid detergent fibre and lignin were moderate for the two grasses.

The study indicated that Tephrosia candida and Leucaena leucocephala improved the yield of Panicum maximum and Andropogon gayanus when compared to the grasses without tree interplanting. Both the trees and grasses can be used strategically for the managements and production of ruminants.

Key words: Browse trees, forage improvement, grass yield, nutrient composition

Introduction

One of the major concerns of the ruminant keepers is the strategic provision of feed to meeting the nutrient requirements of the livestock. In the traditional setting, this demand by the animals is presumptuously met through the basal supply of natural pasture grass. Natural pasture grasses are wild and are characterized by low yield and poor nutrients (Babayemi and Bamikole 2006) as they grow on infertile and erosion degraded soils. Tropical grasses have ability for high yield and the nutrients are simultaneously enhanced when treated with organic/inorganic fertilizers or established with nitrogen fixing shrubs or tree legumes.

Unfertilized grasses and those grown without legume companion had been described to be less nutritive as forage for goats (Bamikole and Babayemi 2004). In Nigeria, only arable crop farmers often use manure to grow their plants while livestock owners rarely cultivate pasture using fertilizers. However, in a recent study, Bamikole et al (2004) reported high yield and better value for nutrients when using Stylosanthes hamata to promote Guinea grass. The capability to fix nitrogen into the soil and as such, enhancing the crude protein content of forage with resultant increase in yield and feed quality, make legumes an integral part of pastures (Aribisala 2003; Sanginga and Mulongoy 1992). Growing creep legumes (e.g. Stylosanthes hamata, Centrosema pubescens, Pueraria phaseoloides) with grass had been observed to be limited to research stations (Babayemi 2007) due to the reason that many of the legumes are not freely grazed and are also seasonal.

Leucaena leucocephala is a widely acceptable plant being a multipurpose tree for nitrogen fixation and browse legume in the tropics (Babayemi et al 2004; Babayemi et al 2006).  Leucaena leucocephala has tendency to close canopy and grow wild.

Tephrosia candida is a relatively new plant with potential as forage for grazing livestock (Odedire 2006; Odedire and Babayemi 2007), capable of fixing nitrogen (IBPGR 1984; Tripathi and Psychas1992) and valued for its contribution to soil fertility in India (Basu and Gupta 1988). Tephrosia candida does not close canopy and being shrub, may therefore suggest its suitability as companion crop with grass. The objective of this study was to assess the effects of Tephrosia candida and Leucaena leucocephala on the yield and nutrient composition of Panicum maximum and Andropogon gayanus.

Materials and methods 

Site and pasture establishment 

A grass – legume pasture was established at the University of Ibadan Teaching and Research farm. The location is 7º 27' N and 3º 45' E at altitude 200 – 300 m above sea level; mean temperature of 25 – 29 °C and the average annual rainfall of about 1250 mm.. Treated seeds of Tephrosia candida and Leucaena leucocephala were planted into the soil by drilling along the rows at the rate of 7.5 kg/ha having an inter–row spacing of 3 m apart. Two to three tillers of Panicum maximum and Andropogon gayanus were planted in between the legume plots at a space of 1 m apart and 0.5 m along the rows. Using a randomized complete block design (RCBD), the treatments were distributed into:

Treatment One: Tephrosia candida + Panicum maximum

Treatment two: Tephrosia candida + Andropogon gayanus

Treatment Three: Leucaena leucocephala + Panicum maximum

Treatment Four: Leucaena leucocephala + Andropogon gayanus

Treatment Five: Panicum maximum

Treatment Six: Andropogon gayanus

Soil samples were taken from the pasture plots and analyzed using the method of Black (1965), to ascertain the plot’s nutrient status. Each treatment was allocated to a plot size of 7 x 13 m² and replicated three times. The grasses were cut back to a height of 15 cm above ground level with the aid of a sickle after the second year of establishment. Thereafter, total grass harvesting was obtained every six weeks. The harvested grasses were left on the field for two hours in order to allow withering before weighing. The grass representative samples were taken and known weights were obtained for dry matter determination at 65 °C.  

Chemical composition 

Grass samples were milled using hammer mill to pass through 2 mm sieve, Crude protein, crude fibre, ether extract and ash contents of the grasses were determined according to AOAC (1990). Crude protein (CP) analysis was by the process of Kjeldahl. It was effected through the breaking down of 2 g sample (n = 2) in 25 ml concentrated tetraoxo sulphate VI acids plus selenium, using Gerhardt Kjeldahtherm (Gerdart GmbH + Co. KG Fabrik fur Laborgerate Postfach 1628 D53006 Bonn) until an opaque colour was obtained. The digested sample was rested for 12 hours, diluted with distilled water and make up to the mark in 250 ml volumetric flask. Five ml of the digest was pipette and distilled with 40% sodium hydroxide and the ionized ammonium was trapped by boric acid. The distillate was immediately titrated (n = 3) with 0.01N hydrogen chloride. In order to obtain the percentage CP, the amount of nitrogen was multiplied by a factor 6.25. Neutral detergent fibre, acid detergent fibre and lignin were determined using the method of Van Soest et al (1991) and as modified by Nahm (1992). 

Statistical analysis 

Data obtained were analyzed according to the procedure of SAS (1999) and significant means separated using the Duncan multiple range test of the same package. The experimental model was

Y_ij = µ + α_i + β_j + ε_ijk

where:

Y_ij = individual observation,

µ = general mean of the population,

α_i = treatment effect,

β_j = block effect due to legumes and

ε_ij = composite error effect. 
 

Results  

Figures 1 and 2 compare the herbage yield of the grasses harvested every six weeks, when planted as sole grasses as well as when inter– planted with Tephrosia candida and Leucaena leucocephala.

The yield of Panicum maximum was significantly (P < 0.05) higher when inter–planted with the legumes (Tephrosia candida and Leucaena leucocephala) than when it was planted as a sole grass. A similar trend was also observed for the plot of Andropogon gayanus where the least value (P < 0.05) was recorded against the  sole grass plot .Panicum maximum assumed a better (P < 0.05) forage yield than Andropogon gayanus when compared as sole grasses (Table 1).

There was no significant difference (P > 0.05) between the impacts of Tephrosia candida and Leucaena leucocephala on the grasses notwithstanding the difference in the values obtained (figure 3).

The chemical composition of the grasses is shown in Table 2.

Panicum  maximum recorded superior values (P < 0.05) in its dry matter, crude protein and ash contents over those obtained for Andropogon gayanus but the values obtained for other nutrients were similar to both grasses.
 

Discussion

The effects of the browse plants were obvious as the yields of the companion grasses were enhanced. However, the yield obtained for both grasses were lower than those reported by Oyenuga (1960), Bogdan (1977) and Omaliko (1980). Oyenuga (1960) recorded the values of 12.0, 16.1, 15.2 23.4 t DM/ha/yr for Panicum maximum harvested at 3, 6, 8 and 12 weeks respectively. Omaliko (1980) also noticed an increase in the annual DM yield of Guinea grass, from 6,800 kg/ha to 13,000 kg/ha, as cutting interval increased from 3 to 10 weeks The increase in the yield of Panicum maximum under the current study from 567 kg/ha DM when cropped solely, to 622 kg/ha DM and 644 kg/ha DM when interplanted with Tephrosia candida and Leucaena leucocephala respectively, was far from those reported earlier (Oyenuga 1960; Omaliko 1980). Similarly, the yield obtained for Andropogon gayanus, when planted as sole crop (451 kg/ha DM) as well as when interplanted with Tephrosia candida (587 kg/ha DM) and Leucaena leucocephala (539 kg/ha DM) were also lower compared to that of Oyenuga (1960) and Omaliko (1980). 

Reason for the low yields might be connected with the low soil fertility level of the grass pasture, as reflected in its organic carbon and nitrogen contents (4.33 g/kg and 0.43 g/kg respectively). Also for the experiments reported, the pasture sward was adequately supplied with nitrogen and water, which would naturally enhance good yield of any plant. This was not the case in the present study as the pasture soil was just left to fallow after several years of intensive cultivation. Another obvious factor is the shading effect of the legumes upon the grasses, which was due to the vigorous growth of Tephrosia candida in particular. The resultant effect on the grass would be a reduction in the plants’ photosynthetic capability, as considerable portion of the grass would be denied optimum performance that might otherwise lead to increased yield of the plants (Bogdan 1977). This probably suggests a wider spacing than as previously reported for Tephrosia candida (Odedire and Babayemi 2007). It had also been reported that most tropical grasses are poorly shade tolerant, and the growth advantage they have over the C₃ tropical legumes largely disappears under shade, since plant growth is a function of the size and the efficiency of its photosynthetic system (Humphreys 1987).

The higher herbage yields obtained for Panicum maximum over Andropogon gayanus could be partly explained in terms of the ability of Panicum maximum to withstand the shading effect caused by the vigorous Tephrosia candida better than Andropogon gayanus. The other possible reason can be explained by the dry matter contents (Table 2), which implies that Panicum maximum might be able to accumulate nutrients better than Andropogon gayanus and as such, able to utilize more of the atmospheric carbon dioxide by converting it into useful products during the process of photosynthesis (Bogdan 1977). The influence of the forage legumes on the yield of the grasses was reflected in the herbage yield increment. Legumes have been reported to have the ability to fix atmospheric nitrogen in symbiosis with Rhizobium bacteria lodged in their roots (Nuthal and Whiteman 1972; Bogdan 1977; Elkan 1984; Dommergues 1987; Bamikole et al 2004), which is made available to the companion plants in the process of nutrient uptake. 

The crude protein contents of both grasses were still within the acceptable range for ruminant performance  (NRC 1981), but  Andropogon gayanus fell short of the critical CP level of 7 % recommended by ARC (1980) and 8 % suggested by Norton (1994)  for ruminal function. The fibre contents (NDF, ADF, Lignin, cellulose and hemicellulose) have implication on the digestibility of plants. The neutral detergent fibre (NDF), which is a measure of the plants’ cell wall contents, is the chemical component of the feed that determines its rate of digestion. NDF is inversely related to the plants’ digestibility (McDonald et al 1995; Gillespie 1998). The higher the NDF, the lower the plant’s digestible energy. The values obtained for the grasses may imply a moderately high cell wall contents. Lignin content of a plant is the most indigestible component of the fibre fractions (Gillespie 1998) and its amount will also influence the plant’s digestibility. As such, the lower lignin content of Panicum maximum (7.0 %) in comparison to that of Andropogon gayanus (9.0 %) may likely predispose Panicum maximum to better digestibility by grazing animals than Andropogon gayanus. The Acid detergent fibre (ADF) consist mainly the lignin and cellulose.  Hemicellulose has been reported to be more digestible than cellulose (Gillespie 1998).

Ether extract is the lipid fraction, which is a major form of energy storage in the plant. The energy derivable from the plant is what the animal uses for its body maintenance and production. The ash content represents the inorganic (mineral matter) content in a feed.  Its value is mainly in the contents of phosphorus, calcium, or potassium and large amounts of silica (Bogdan 1977).The values obtained for both grasses fall within the range of 3 – 12 % reported by Gillespie (1998) and 8 – 12 % reported by Bogdan (1977). 
 

Conclusion 

• The present study established the potential of Tephrosia candida, a relatively unknown forage, as capable of competing with the widely accepted Leucaena leucocephala as forage for livestock feeding.

  
  

• Tephrosia is also capable of fixing organic nitrogen to the pasture soil, thus improving the agronomic performance of the companion Panicum maximum and Andropogon gayanus which ultimately translates to an increase in the forage yield of such companion crops.

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Received 26 September 2007; Accepted 8 December 2007; Published 1 February 2008

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