Influence of cultivation site and fertilisation on the properties of condensed tannins and in vitro ruminal nutrient degradation of Calliandra calothyrsus, Flemingia macrophylla and Leucaena leucocephala

Samples obtained from two planting experiments with tropical shrub legumes rich in condensed tannins (CT) (Calliandra calothyrsus, Flemingia macrophylla, Leucaena leucocephala) were analysed in detail for CT concentration, composition and properties, as well as for in vitro degradability. The factors evaluated included cultivation site (fertile mollisol with pH 7.8 and bimodal rainfall vs. infertile oxisol with pH 5.0, high Al saturation and unimodal rainfall) and different levels of mineral fertilisation. In vitro ruminal degradability, CT concentration and properties were affected by cultivation site or fertiliser application or both. In Calliandra and Flemingia, the CT concentration showed a trend (P < 0.1) to be higher at the site with the infertile soil. This was consistent with the increased (P < 0.001) astringency of CT extracts found in Calliandra when plants were cultivated at this site. In Flemingia, however, astringency was reduced (P < 0.001) on the infertile soil. There were certain effects of the cultivation site on the anthocyanidin profile of CT from Calliandra and Flemingia, but these were relatively small and could not explain the differences in astringency observed between sites. Fertilisation did not affect (P > 0.05) total CT concentration in Calliandra and Flemingia but clearly increased (P < 0.01) astringency of the CT extracts. This suggests that not only CT concentration but also properties of CT may be affected by cultivation site and fertilisation. Leucaena did not grow on the infertile soil and site effects could therefore not be evaluated in this species. Fertilisation did not affect (P > 0.05) CT concentration and astringency of CT extracts of Leucaena but reduced (P < 0.05) the cyanidin proportion in CT. Cultivation site affected several variables describing fermentation dynamics. Foliage of the legumes grown on the infertile soil exhibited lower (P < 0.05) gas production rates. Dry matter degradation was lower (P < 0.001) and the proportion of dietary N remaining undegraded after in vitro incubation was higher (P < 0.001) when Calliandra was grown on the infertile compared to the fertile soil. The present results indicate that the cultivation site may affect the feeding value of CT-containing legumes. Fertilisation could not compensate the negative effects of the cultivation site on CT properties and ruminal nutrient degradation. Selecting appropriate cultivation sites (with higher soil fertility) may contribute to improve the feeding value of certain tanniniferous tropical shrub legumes.