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Archivos Latinoamericanos de Produccion Animal, Vol. 13, No. 1, Enero-Abril, 2005, pp. 13-18 Effect of defoliation frequencies on the dry matter yield and nutrientcontent
of two Centrosema species. J. Faría-Mármo, D. E. Morillo2nd Z. Chirinosl La Universidad del Zulia, Departamento de Zootecnia, Postgrado en Producción Animal, Recibido Abril 15, 2004. Code Number: la05002 ABSTRACT Keys words: Centrosema, defoliation frequencies, yield, crude protein, mineral composition. RESUMEN Palabras claves: Centrosema, frecuencia de defoliación, proteína bruta, composición mineral INTRODUCTION Centrosema is a legume genus native to Central and South America, and includes
species with potential adaptation to diverse habitats such as the dry
and high-altitudes tropics, subtropics, poorly drained and/or seasonally
flooded conditions, and acid, low-fertility soils (Schultze-Kraft et
al.,1990). Studies have focused on the well-drained isohyperthermic savannas
(«Llanos» ecosystem) and tropical forest ecosystem of Colombia
and Venezuela, where several Centrosema species such as C. macrocarpum
and C. pubescens have shown considerable forage potential (Grof et al.,
1997).
Centrosema macrocarpum is a promising legume for a wide range of ecological conditions throughout the tropics. Its excellent forage yield, drought tolerance and high nutritive value are considered of particular importance (Miles and Lapointe, 1992). Centrosema pubescens is the only well-known Centrosema species that has been widely evaluated, is available commercially, and has the largest number of collected germplasm accessions. Some systematic screening has been carried out on noncommercial lines of C. pubescens. Regional reports (CIAT, 1990) show to a varying degree that these accessions have potential for acid soil sites in humid tropical environments, but not in savanna ecosystems. Several studies have been conducted in different ecological areas of Venezuela to evaluate the dry matter yield (DMY) of several accessions of Centrosema pubescens (Faría-Marmol et al.,1997a; Grof et al., 1997; Pirela-León et al., 1997). Among the highest yielding accessions, CIAT (Centro Internacional de Agricultura Tropical) No. 15160, has shown the best performance. Further research on Centrosema macrocarpum and Centrosema pubescens is needed
to assess their forage yield and nutrient concentration in the local environment.
The objective of this study was to evaluate the effect of three defoliation
frequencies on DMY, crude protein (CP) concentration and mineral composition
of Centrosema macrocarpum and Centrosema pubescens during two seasons in
a wet/ dry region of Venezuela. The experiment was conducted on a farm located in Zulia State, western region
of Venezuela (10º 32' 32'' N and 72º 12' 30'' W), with climate and vegetation corresponding to a tropical dry forest. Mean annual rainfall is 960 mm, distributed in a dry (four months) and a rainy (eight months) season. Total precipitation during the experiment (336 days) was 730 mm, distributed between one «dry» (90 mm, 156 days) and one «rainy» (640mm,
180 days) period. Soil was a sandy-loam Typic Haplustalf with pH 5.2 and
2.68% organic matter. Average soil macroelement analysis (mg/kg) was: phosphorus
(P), 8; calcium (Ca), 100; potassium (K), 60 and magnesium (Mg), 324.
Two species of Centrosema, C. macrocarpum CIAT 5713 and C. pubescens CIAT 15160 were evaluated in a split-plot experimental design containing three replications, with species as the main plots (36m2) and defoliation frequencies (4, 6, and 8 week-intervals) as the subplots (12 m2). The available forage 10 cm above the ground in the central 2 x 2-m area of each plot was cut using hand shears, weighed, and a sample (ca. 500 g) consisting of 10 grab sub-samples was taken to determine dry matter concentration at 60 oC for 48 hours, and to estimate DMY. Dry matter yield was evaluated throughout the whole year. Samples from the first, mid and last cuttings for each frequency in two replications, corresponding to rainy and dry periods, respectively, were used to determine CP concentration by the Kjeldhal (Kjeldhal N x 6.25) procedure (Horwitz,1982). Sub-samples for macro and microelement analyses were processed following the methods outlined by Fick et al. (1979), and P was analyzed by a colorimetric technique (Harris and Popat, 1954). Calcium, K, Mg, Cu, Fe and Mn concentration were determined by flame atomic absorption spectrophotometry (AAS), (Perkin-Elmer Corp, 1982). Data were subjected to ANOVA for a split plot design using the General Linear Model procedure of SAS (1992). If appropriate, means were compared using Duncan's Multiple Range Test as described by Steel and Torrie (1992). RESULTS AND DISCUSSION
Mean dry matter yields of C. macrocarpum and C. pubescens as affected by the frequency of defoliation and species are presented in Table 1. The interaction species x frequencies was not significant (P>0.05) for DMY. DMY increased (P<0.05) when the cutting interval was increased from 4 to 8 weeks. Dry matter production was higher (P<0.05) in C. Macrocarpum than in C. pubescens. These results are similar to those reported in areas with low rainfall and a long dry season (CIAT, 1990; Pérez, 1995). Dry matter yields obtained in this research were comparable to those reported in savanna ecosystems but lower than those found in the humid tropics (CIAT, 1990). DM yield declined (P<0.05) in C. macrocarpum (75.9%) and C. pubescens (85.3%) during the dry season as compared to the wet season. These results are similar to those reported by CIAT (1990), Faría-Mármol (1995) and Faría-Mármol et al. (1997a), and can be ascribed to the effect of water deficit on plant growth and development (Buxton and Fales, 1994). CP, ash and mineral concentrations for C. macrocarpum and C. pubescens are shown in Table 2. No differences (P>0.05) were detected between species for CP and concentration of most mineral. Only ash and Cu concentrations were lower (P<0.05) in C. macrocarpum than in C. pubescens. All mean and individual concentrations for the macro and trace elements evaluated in this research were below the suggested maximum tolerable levels for cattle (NRC, 1980; McDowell, 1992). Mean CP concentrations (22 and 18%) were within the range reported for Centrosema spp growing in Venezuela (Pérez, 1995; Faría-Mármol,1995; Faría-Mármol et al., 1997b) and other tropical regions (Shultze-Kraft et al., 1990; Lascano et al., 1990). These values are considerably higher than 7%, which is the minimum CP content indicated by Milford and Minson (1965) to avoid a depression in forage voluntary intake by grazing livestock. The mean ash concentration was consistently below 9.5 % in both species. Mean Ca, K and Mg concentrations, as well as all the individual values, can be regarded as adequate for ruminant livestock when compared to the mineral element requirement (MER) or critical level for deficiency (McDowell, 1992; NRC, 1989, 1996). Conversely, mean P concentrations, with relative deficiencies of 44 and 78% in Cm and Cp, respectively, are inadequate according to the same reference values. Mean Ca:P ratios (6.4:1) were within the tolerable range for ruminants (NRC, 1989, 1996). Several investigations (Wise et al., 1963; Ricketts et al., 1970) have demonstrated a significant decrease in growth and feed efficiency of cattle fed dietary Ca:P ratios over 7:1. For both Centrosema species, mean Fe and Mn concentrations as well as all the individual values of these elements, are considered adequate according to the MER suggested for ruminants (McDowell, 1992; NRC 1989, 1996). However, differences (P<0.05) between forage species were detected for Cu concentrations. Cu concentrations, which were adequate in Cp in relation to the suggested requirement for grazing ruminants, but marginal in Cm with 44% of the individual values below the critical level for deficiency. The effect of defoliation frequencies on nutrient concentrations of C. macrocarpum and C. pubescens are presented in Table 3. All nutrients evaluated in this study tended to decrease with increasing forage maturity, no differences (P>0.05) among cutting frequencies were observed for ash and most minerals. Only Ca concentrations declined (P<0.05) with increasing plant maturity. The lowest Ca concentration (1.1%) was obtained with the longest cutting interval, probably due to an increase in the proportion of the stem fraction as the forage matures since stems generally contains less Ca than leaves (Minson, 1990). A general declining trend with increasing plant maturity has been reported for Ca, P, K and microelements concentrations by some researchers (Underwood, 1981; Spears, 1994), whereas Minson (1990) pointed out that except for Cu, which usually follows the general trend, plant age has had conflicting or inconsistent effects on mineral concentrations. Seasonal means for CP, ash and mineral concentrations of two Centrosema species are given in Table 4. Mean PC values were high and similar (P>0.05) for the dry (18.78%) and rainy seasons (20.28%) in both forage species and agree with those reported by Lascano et al. (1990) and Faría-Mármol et al. (1997b). Calcium concentration of C. macrocarpum was lower (P<0.05) during the rainy season (1.55%) than the dry season (1.27%), whereas no differences (P>0.05) were detected for other macroelement concentrations in that species. Phosphorus was the only macroelement affected (P<0.05) by season in C. pubescens, with a higher value during the rainy season (0.27%) than the dry season (0.22%). Mean Fe, Cu, and Mn concentrations declined (P<0.05) during the rainy season. Except for Cu, trace mineral concentrations were regarded as adequate in both seasons and in both species. Copper concentration of C. macrocarpum was below the recommended level for ruminants during the dry season. Kabaija and Smith, 1989 reported an unexplained increase in the concentration of Mn, Fe, Zn and Cu during the dry season. Seasonal changes in microelement concentrations of forage have been reported, but there is not consistency in the direction of the changes (Minson, 1990). CONCLUSIONES
Centrosema macrocarpum produced higher DMY than C. pubescens, and DMY increased with increasing harvest interval. However, crude protein, ash and most mineral concentrations were not affected by the frequency of defoliation. Only Ca concentrations decreased with increasing plant maturity. Crude protein concentrations and most mineral nutrients were similar between forage species. From the standpoint of ruminant nutrition, P concentrations in both species and Cu concentration in C. macrocarpum were deficient. Most mineral concentrations were affected by season, but those changes may not be nutritionally significant. The importance of these deficiencies will depend on the amount and composition of other ingredients of the diet, since these species are usually grown in association with grass species. LITERATURE CITED
© 2005 ALPA. Arch. Latinoam. Prod. Anim. The following images related to this document are available:Photo images[la05002t3.jpg] [la05002t4.jpg] [la05002t1.jpg] [la05002t2.jpg] |
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