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Laboratory Validation of a Resource Quality-Based Conceptual Framework for Organic Matter Management

^a Tropical Soil Biology and Fertility Institute of CIAT, P.O. Box 30677, Nairobi, Kenya
^b World Agroforesty Centre (ICRAF), P.O. Box 30677, Nairobi, Kenya
^c Tropical Soil Biology and Fertility Institute of CIAT, A.A.6713, Cali, Colombia
^d Dep. Agricultural Sciences, Imperial College London, Wye, TN25 5AH, UK
^e The Earth Institute at Columbia Univ., P.O. Box 1000, 117 Monell Bldg., 61 Route 9W, Palisades, NY 10964-8000, USA

View larger version (21K): [in a new window]   Fig. 1. Relationship between the protein binding capacity (PBC) and the total soluble polyphenol content of the used organic resources (ORs). The regression line was calculated for data points with >80 g kg–1 of polyphenols. Data presented by Handayanto et al. (1994) and Mafongoya et al. (1998) are superimposed. *** Represents significance at the 0.1% level. Note that the dry matter/methanol ratio for extraction of the soluble polyphenols was 0.75 g dry matter/50 mL methanol for Handayanto et al. (1994) and 0.1 g dry matter/50 mL methanol for Mafongoya et al. (1998), the latter using a similar ratio as in this paper.

View larger version (43K): [in a new window]   Fig. 2. Cumulative CO2–C production for the various treatments. Figures 2a, 2b, 2c, and 2d each contain the C mineralization data from eight organic resources (ORs) and the control soil. Total CO2–C production increases from Fig. 2a to Fig. 2d, resulting in different y-axis ranges. Error bars are standard errors of the difference, calculated for each sampling time.

View larger version (43K): [in a new window]   Fig. 3. Mineral N production for the various treatments. Figure 3a presents data from organic resources that have significantly lower levels of mineral N than the control soil at Day 28; Fig. 3b and 3c present data from organic resources that had slightly lower and slightly higher, respectively, amounts of mineral N than the control soil at Day 28, and Fig. 3d presents data from the organic resources that produced a significantly higher amount of mineral N than the control soil at Day 28. Error bars are standard errors of the difference, calculated for each sampling time.

View larger version (36K): [in a new window]   Fig. 4. The percentage of added organic resource (OR)-N mineralized after 28 d. ***, *, and NS represent significance at the 0.1% and the 5% level and not significant, respectively, as calculated with the LSMEANS option of the MIXED procedure (SAS, 1992). The vertical bars delineate three groups of ORs: a first group that has values significantly <0, a second group with values not different from 0, and a third group with values significantly larger than 0. The range of N, polyphenol, and lignin contents presented for the middle group, excludes Samples 24 (cattle manure: 25 g kg–1 of N, 11 g kg–1 of polyphenols and 173 g kg–1 of lignin) and 26 (Gliricidia stems: 16 g kg–1 of N, 13 g kg–1 of polyphenols and 204 g kg–1 of lignin).

View larger version (27K): [in a new window]   Fig. 5. Relationship between C and N mineralization as assessed using the aerobic incubation technique and the in vitro dry matter digestibility (IVDMD) assay.

View larger version (16K): [in a new window]   Fig. 6. Relationship between the proportions of the total amount of added residue C mineralized after 3 d over the amount released after 28 d and the soluble C content.

View larger version (15K): [in a new window]   Fig. 7. Relationships between (a) the percentage of added N mineralized after 28 d and the N content of residues for treatments with N mineralization significantly below 0, and (b) the percentage of added N mineralized after 28 d and the lignin/N ratio of residues for treatments with N mineralization significantly greater than 0. In Fig. 7b, the Gliricida leaves (Samples 10, 11, and 29) were excluded from the regression. *** and ** represent significance at the 0.1% and the 1% level, respectively.