Evaluating soil management using particulate and chemically labile soil organic matter fractions

Particulate organic matter (POM), an established soil quality indicator, is too costly for routine testing by analytical labs. Chemical oxidation of labile soil organic matter is less costly and may prove to be an equally effective indicator. The objectives of this study were to test the relationship between POM and chemically labile organic matter (CLOM) and to evaluate the effects of soil management on POM and CLOM. The study was conducted within a long-term crop rotation x fertility treatment study in central Pennsylvania. Crop rotation sequences were continuous corn (Zea mays L.), corn-soybean [Glycine max (L.) Merr.], 4 yr of corn followed by 4 yr of alfalfa hay (Medicago sativa L.), and corn-oat (Avena sativa L.)-winter wheat (Triticum aestivum L.)-2 yr of red clover hay (Trifolium pratense L.). Fertilizer treatments were mineral fertilizer, N-based liquid dairy manure, and P-based liquid dairy manure. A significant linear relationship between POM-C and CLOM-C treatment means was observed (r(2) = 0.74). Both POM-C and CLOM-C concentrations were greatest for manure-based fertility treatments and for crop rotations receiving the most frequent applications of manure. Only CLOM-C, however, distinguished between the N-based and P-based manure treatments. Further development of CLOM-C as a soil quality indicator may yield a reliable, cost-effective soil quality management tool.