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Total and Labile Soil Organic Matter in Organic and Conventional Farming Systems

Dep. of NRES, Univ. of Illinois, 1102 S. Goodwin Ave., Urbana, IL 61801

View larger version (43K): [in a new window]   Fig. 1. Influence of farming systems on soil organic matter fractions in surface soils (generally 0 to 25 cm) collected from nine long-term farming systems trials located across the USA. Shown are (a) soil organic C (SOC), (b) total N (TN), (c) particulate organic matter C (POM-C), and (d) particulate organic matter (POM-N), Illinois Soil N Test-N (IL-N), and exchangeable NH4+–N concentrations of manure-based organic (MLO: eight sites), legume-based organic (LO: three sites), and conventional (CV: nine sites) farming systems. Different letters within a fraction show significant differences among farming systems at the p < 0.05 level. Statistical analyses for SOC, TN, IL-N, and POM fractions were conducted on log10 transformed data to improve normality and equality of variances. Untransformed data are presented in the figure.

View larger version (21K): [in a new window]   Fig. 2. Mean percentage of relative enrichment of soil organic C (SOC), total N (TN), particulate organic matter (POM)-C, POM-N, and Illinois Soil N Test-N (IL-N) fractions in surface soils (generally 0 to 25 cm) of organic farming systems relative to conventional farming systems at nine long-term farming systems trials in the USA. The percentage of relative enrichment calculations were made on paired sets of soil organic matter fraction concentrations (g kg–1 or mg kg–1) in conventional and organic systems within sites. Different lowercase letters indicate significant differences among fractions at the p < 0.05 level. Statistical analysis was conducted on transformed data [(enrichment + 200)–1] to improve normality and equality of variance; untransformed means are presented in the figure.