Effects of sample post harvest treatment on aerobic decomposition and anaerobic in-vitro digestion of tropical legumes with contracting quality
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Permanent link to this item: http://hdl.handle.net/10568/43398
Legume tissue quality is a key factor for enhancement of feed resources and contribution to soil fertility in mixed crop-livestock production systems. To compare methods used by soil scientists and animal-nutritionists to assess quality of plant materials, three woody tropical legumes with contrasting qualities were used: Indigofera zollingeriana Miq. (Indigofera), Cratylia argentea Benth. (Cratylia) and Calliandra houstoniana (Mill.) Stan. var. calothyrsus (Meiss.) Barn. CIAT 20400 (Calliandra). Plant material of each legume was used either fresh, freeze-dried, frozen, oven-dried (60 °C) or air-dried in order to estimate extents and rates of aerobic degradation in litterbags on the soil during 140 days and anaerobic degradation in an in-vitro gas production experiment during 144 h. Results showed, that aerobic decomposition rates of leaf tissues were highest for Indigofera (k = 0.013 day?1), followed by Cratylia (k = 0.004 day?1) and Calliandra (k = 0.002 day?1). Gas production rates evaluated under anaerobic conditions, were highest for Indigofera (k = 0.086 h?1), intermediate for Cratylia (k = 0.062 h?1) and lowest for Calliandra (k = 0.025 h?1). Decomposition and gas production rates differed (P < 0.001) among species. Differences between post harvest treatments were not statistically significant (P > 0.05). The extent of decomposition was highest for Indigofera (82.5%, w/w), followed by Cratylia (44.6%) and Calliandra (26.4%). The extent of gas production was highest for Indigofera (218.8 ml), followed by Cratylia (170.1ml) and Calliandra (80.1 ml). Extent of decomposition and extent of gas production were significantly different (P < 0.001) among species. In contrast to the extent of decomposition, the extent of gas production was affected (P < 0.001) by sample post harvest treatments. Highest gas production was observed for the fresh and frozen treatments. The forage quality parameters that best correlated with aerobic and anaerobic degradation were lignin+bound condensed tannins, lignin+total condensed tannins/N, indigestible acid detergent fibre (IADF) and in-vitro dry matter digestibility (IVDMD). Results showed that differences in decomposition and digestibility were more related to intrinsic plant quality parameters than to changes in tissue quality induced by post harvest treatments. In addition, we found that rate of aerobic degradation of legume leaves on the soil was highly correlated (r > 0.80, P < 0.001) to IVDMD and gas production (r = 0.53, P < 0.001). These results indicate that plant measurements (IADF, IVDMD and gas production) used to assess forage quality in animal nutrition studies are more rapid and resource saving predictors for aerobic decomposition of tropical legumes than initial plant quality ratios (lignin+polyphenols/N and lignin+total condensed tannins/N) commonly used by many researchers. Furthermore, this study confirms the potential usefulness of IVDMD for screening tropical legumes for soil fertility management.
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