Comparison of chemical composition of Atriplex spp. grown under South African conditions with regard to site, species and plant parts

 

 

W.A. van Niekerk^{I, #}; P.J. Vermaak^I; N.F.G. Rethman^II; R.J. Coertze^I

^IDepartment of Animal & Wildlife Sciences, University of Pretoria, Pretoria 0002, South Africa
^IIDepartment of Plant Production & Soil Science, University of Pretoria, Pretoria 0002, South Africa

 

 

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ABSTRACT

The aim of this study was to evaluate the nutritional value of Atriplex spp. for small stock production. Selected plants were harvested and analysed for crude protein, in vitro digestibility and leaf to stem ratio. Significant differences in nutritional value were noted between leaves and stems as well as between sites for the three Atriplex spp. Significant seasonal effects were noted in terms of composition of leaves and stems between the two sampling seasons for A. canescens (Veld Reserve I) and A. canescens (Santa Rita) but not for A. nummularia.

Keywords: Atriplex, crude protein, in vitro digestibility

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Introduction

Considerable information on the chemical composition and nutritional characteristics of the Atriplex spp. is available in the literature (Chatterton et al., 1971; Smit & Jacobs, 1978; Davis, 1981). However, such information on Atriplex spp. grown under South Africa conditions is lacking. The objective of this study was to determine the seasonal changes in chemical composition of leaves and stems of different Atriplex spp. as well as the difference in quality between localities in semi-arid areas in South Africa.

 

Materials and Methods

Mature Atriplex species were selected for this study from three sites in South Africa during March and July 2002. The sites were Hatfield, Pretoria (Gauteng), Mier, (Northern Cape) and Lovedale (Northern Cape). Samples collected from each species consisted of small branches with stems not larger than 5 mm in diameter.

Mature leaves and twigs were collected from A. nummularia, A. canescens (Santa Rita) and A. canescens (Veld Reserve I). After collection the samples were dried at 60 °C for 48 hours, the leaves separated from the stems and then ground through a 1-mm screen using a mill. By weighing the leaves and stems, a leaf to stem ratio was calculated. Organic matter digestibility (IVOMD) was estimated by the in vitro method described by Tilley & Terry (1963) as modified by Engels & Van der Merwe (1967). Crude protein (CP) concentration was determined by Kjeldahl (AOAC, 2000). Analyses of variance with the Proc GLM model (SAS, 1994) were used to determine the significance between different species of Atriplex in different locations, seasons and plant parts. Means and standard deviations (s.d.) were calculated. Significance of difference (5%) between means was determined by Bonferroni's test (Samuels, 1989).

 

Results and Discussion

The crude protein, IVOMD and leaf to stem ratio of the three Atriplex spp. collected at three different sites are presented in Table 1. The CP concentration varied from 93.8 g/kg in A. canescens (Veld Reserve 1) to 194.6 g/kg in A. nummularia (Mier). The CP values correspond well with those reported by Senock et al. (1991) for A. canescens. The CP concentration for all the species was the highest at Mier. In most cases there was a significant difference in the CP concentration for a specific species between sites. Atriplex nummularia had the highest CP concentration at all the studied localities.

Except for A. nummularia there were no significant differences in the IVOMD values for different localities. The IVOMD values for A. nummularia were in all cases higher (P < 0.05) than the other species. Significant differences were observed for leaf to stem ratios for different species and different sites.

Except for A. nummularia, significant differences were observed between March (summer) and July (winter) with respect to the CP and IVOMD concentration of the species concerned (Table 2).

The CP concentration of A. nummularia differed significantly from the other species in both seasons. The CP concentration of A. canescens (Santa Rita) and A. canescens (Veld Reserve 1) did not differ from each other. The IVOMD of A. nummularia did not show significant differences compared to the other species with respect to seasonal trends and only the leaf to stem ratio of A. canescens (Veld Reserve1) showed significant differences in the two seasons studied. In addition, the stem to leaf ratio of the species concerned also differed significantly. The same trend was reported by Sparks (2003).

The results in Table 3 show that the CP values for the leaves were in all cases higher (P < 0.05) than the stems. The leaf and stem CP-values of A. nummularia were also higher (P < 0 05) than the other species. The leaf IVOMD of all species was higher (P < 0.05) than that of the corresponding stems. In addition the IVOMD of the leaves and stems of A. nummularia were higher than the other species studied. Peterson et al. (1987) noted the same trend for fourwing saltbush.

 

Conclusion

Significant differences between leaves and stems, seasonal growth and location of the three species studied were noted, demonstrating the importance of these factors when planning fodder budgets.

 

Acknowledgement

This research was supported in part under Grant No. TA-MOU-99-C16-091 funded by the U.S.-Israel Cooperative Development Research Program, Bureau for Economic Growth, Agriculture and Trade, U.S. Agency for International Development.

 

References

AOAC, 2000. Official methods of analysis (15th ed.). Association of Official Analytical Chemists, Inc., Washington D.C., USA.         [ Links ]

Chatterton, N.J., Goodin, J.R., Mckell, C.M., Parker R.V. & Rible J.M., 1971. Monthly variation in the chemical composition of desert-saltbush. J. Range. Manage. 24, 37-40.         [ Links ]

Davis, A.M., 1981. The oxalate, tannin, crude fibre, and crude protein composition of young plants of some Atriplex species. J. Range. Manage. 34, 329-331.         [ Links ]

Engels, E.A.N. & Van der Merwe, F.J., 1967. Application of an in vitro technique to South African forages with special references to the effect of certain factors on the results. S. Afr. J. Agric. Sci. 10, 983-995.         [ Links ]

Peterson, J.S., Necket, D.N., Potter, R.L. & Huston, J.E., 1987. Ecotypic variation in selected fourwing saltbush populations in Western Texas. J. Range Manage. 40, 361-366.         [ Links ]

Samuels, M.L., 1989. Statistics for the Life Sciences. Collier MacMillan Publishers, London.         [ Links ]

SAS, 1994. Statistical Analysis Systems user's guide (Version 6). SAS Institute Inc., Cary, North Carolina, USA.         [ Links ]

Senock, R.S., Barrow, J.R., Gibbens, R.P. & Herbel, C.H., 1991. Ecophysiology of the poloyploid shrub Atriplex canescens growing in situ in the Northern Caribean Desert. J. Arid Environ. 21, 45-57.         [ Links ]

Smit, C.J. & Jacobs, G.A., 1978. Skeikundige samestelling van vier Atriplex-spesies. Agroanimalia 10, 1-5.         [ Links ]

Sparks, C.F., 2003. Interspesies variation in nutritive value of certain drought tolerant fodder shrubs. M.Sc. (Agric.) dissertation, University of Pretoria, South Africa.         [ Links ]

 

 

# Corresponding author. E-mail: willem.vanniekerk@up.ac.za