TASSILO TIEMANN1, MICHAEL KREUZER1, CARLOS LASCANO2, HANS-DIETER HESS3
1ETH Zurich, Institute of Animal Science, Switzerland
2Centro Internacional de Agricultura Tropical (CIAT), Colombia
3Agroscope Liebefeld-Posieux, Swiss Federal Research Station for Animal Production and Dairy Products (ALP), Switzerland
Ruminants play an important role as assets and sources of high quality food and income for the rural population in developing countries. Their productivity is often limited due to low protein supply owing to the limited availability of good quality forages, particularly in regions with a prolonged dry season and soils of low fertility. As part of an extensive search for forage shrub legumes that would meet the requirements as forage plants and perform well on low-fertility soils, a series of in vitro-experiments and agronomic evaluations were conducted. Five particularly promising legume species were tested in these experiments (Calliandra calothyrsus, Cratylia argentea, Desmodium velutinum, Flemingia macrophylla, Leucaena leucocephala). The results showed that the cultivation site may have an important influence on the forage quality of legumes, particularly for species containing condensed tannins (CT). In vitro"=experiments with Calliandra calothyrsus showed differences in the tannin content and the degradability of nutrients, particularly of crude protein (CP), dependent on the cultivation site. Plants cultivated on more fertile soils had clearly lower CT contents than those on low"=fertility soils. Apparent CP degradability of diets supplemented with C. calothyrsus from more fertile soils was approximately 30% higher (p < 0.001) than CP degradability of diets containing the same species cultivated on low"=fertility soils. The agronomic evaluation revealed large variations in the adaptability of the different shrub legume species to acidic low"=fertility soils and their response to fertilisation. While Flemingia macrophylla did not show any differences in biomass production due to soil type, the other species produced two to three times more biomass on the more fertile soil. Fertiliser application affected all species in terms of biomass production and leaf proportion but the extent of the response varied widely among species. Overall, these experiments showed a high impact of planting site on forage quality and yield and indicate that strong interactions between legume species and soil fertility may occur. These finding are of particular interest for future extension work, aiming at promoting legume"=based feeding technologies.
Keywords: Legumes, protein, ruminants, tannins, tropical forages