Deutscher Tropentag, October 9 - 11, 2002 in Kassel-Witzenhausen "Challenges to Organic Farming and Sustainable Land Use in the Tropics and Subtropics"

Comparison of Aerobic and Anaerobic Methods to Assess Quality of Tropical Multipurpose Shrub Legumes

Centro Internacional de Agricultura Tropical (CIAT), Colombia

Abstract

Legume 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 and animal-nutrition researchers to assess quality of plant materials three woody tropical legumes with contrasting quality (nil, low, high contents of condensed tannins, CT) were used: Indigofera constricta (Indigofera), Cratylia argentea (Cratylia) and Calliandra.sp (Calliandra). Plant material of each legume was either used fresh, freeze-dried, frozen, oven-dried (60°C) or air-dried in order to estimate extent and rate of aerobic degradation on the soil (litterbag, 140 days) and anaerobic degradation in vitro with rumen microorganisms (gas production, 144 hours). Results showed that decomposition rates of leaf tissues, applied to soil surface, were very fast for Indigofera (k=1.35 day^-1), followed by Cratylia (k=0.33 day^-1) and Calliandra (k=0.19 day^-1). Decomposition on the soil of Cratylia and Calliandra was not affected by treatments whereas fresh leaves of Indigofera decomposed more rapidly than oven-dried leaves. Gas production rates differed significantly among species evaluated, being faster for Indigofera (k=8.57 %/hour), intermediate for Cratylia (k=6.16 %/hour) and slowest for Calliandra (k=2.51 %/hour). Cratylia showed no differences in digestion between drying treatments, whereas Indigofera and Calliandra showed significant differences between treatments. The forage quality parameters that best correlated with extent of dry matter loss under aerobic decomposition and anaerobic digestion were Lignin + CT (-0.90 and -0.95 P<0.0001 for anaerobic and aerobic, respectively) and (-0.92 and -0.91 P<0.0001 for anaerobic and aerobic, respectively). Results showed that differences in decomposition and digestibility were more related to intrinsic plant quality parameters than to changes in quality induced by drying pre-treatment. In addition, we found that rate (0.75, P<0.0001) and extent (0.87,P<0.0001) of aerobic decomposition of legume leaves in the soil (litterbag-technique) were highly correlated to the extent of dry matter loss using the in-vitro dry matter digestibility method (IVDMD). We conclude that the aerobic and anaerobic degradation of legumes used was a function of indigestible fractions of the cell wall such as lignin alone or corrected for presence of condensed tannins.

Keywords: Condensed tannins, decomposition, gas production method, plant tissue quality, tropical woody legumes

Contact Address: Karen Tscherning, Centro Internacional de Agricultura Tropical (CIAT),  Cali, Colombia, e-mail: ciat-doctorascgiar.org