Understanding long-term management effects on soil properties is necessary to determine the relative sustainability of cropping systems. Soil physical, chemical, and biological properties were measured in a long-term cropping system study in the Western Corn Belt. Properties were evaluated after 16 yr in four crop sequences [continuous corn (zea mays L.) (CC), corn-soybean [Glycine max. (L.)] (C-SB), corn-oat (Avena sativa L.) + clover (80% sweet clover [Melilotus officinalis L.] and 20% red clover [Trifolium pratense L.])-grain sorghum [(Sorghum bicolor (L.) Moench)-soybean (C-OCL-SG-SB), and corn-soybean-grain sorghum-oat + clover (C-SB-SG-OCL)] each at three N fertilization rates (ZERO, LOW, and HIGH) to a soil depth of 30.5 cm on a Sharpsburg silty clay loam (fine, smectitic, mesic Typic Argiudolls). Nitrogen fertilization had a greater impact on soil properties than crop sequence, with management effects most pronounced at 0 to 7.6 cm. Increased N rate resulted in greater organic C, total N, and particulate organic matter (POM), but lower soil pH. Increased N rate also reduced microbial biomass by approximately 20% between the HIGH and ZERO N-rate treatments. The C-SB-SG-OCL sequence possessed more potentially mineralizable N (PMN) (57 vs. 46 kg ha(-1) for average of CC and C-SB) and a higher percentage of POM present as soil organic matter (17.1% for the C-SB-SG-OCL sequence vs. 13.9% for other sequences). Within the context of soil functions and cropping system performance, results from this study indicate the C-SB-SB-OCL sequence enhanced nutrient cycling efficiency, while N fertilization resulted in a trade-off between its positive effect on biological productivity and negative effect on nutrient cycling efficiency.
