Crop Sequence and Nitrogen Fertilization Effects on Soil Properties in the Western Corn Belt

corn–soybean cropping systems predominate. The effect of these cropping systems on indicators of soil quality Understanding long-term management effects on soil properties is only partially understood. Soil organic C has been is necessary to determine the relative sustainability of cropping systems. Soil physical, chemical, and biological properties were measured shown to increase in monoculture corn where N fertilin a long-term cropping system study in the Western Corn Belt. Propization is adequate and no-till is used (Studdert and erties were evaluated after 16 yr in four crop sequences [continuous Echeverria, 2000; Varvel, 1994; Havlin et al., 1990; Blevcorn (zea mays L.) (CC), corn–soybean [Glycine max. (L.)] (C–SB), ins et al., 1983). Conversely, a decline in soil organic C corn–oat (Avena sativa L.) clover (80% sweet clover [Melilotus is well documented in cropping systems that include officinalis L.] and 20% red clover [Trifolium pratense L.])–grain soybean in rotation (Studdert and Echeverria, 2000; sorghum [(Sorghum bicolor (L.) Moench)–soybean (C–OCL–SG– Varvel, 1994; Karlen et al., 1994; Havlin et al., 1990; SB), and corn–soybean-grain sorghum–oat clover (C–SB–SG– Franco-Vizcaı́no, 1996). Observations of degraded soil OCL)] each at three N fertilization rates (ZERO, LOW, and HIGH) physical conditions as reflected by decreased aggregate to a soil depth of 30.5 cm on a Sharpsburg silty clay loam (fine, stability have been reported in both monoculture corn smectitic, mesic Typic Argiudolls). Nitrogen fertilization had a greater impact on soil properties than crop sequence, with management effects and corn–soybean cropping systems (Raimbault and most pronounced at 0 to 7.6 cm. Increased N rate resulted in greater Vyn, 1991; Hussain et al., 1988; Fahad et al., 1982), leading organic C, total N, and particulate organic matter (POM), but lower to concern regarding increased erosion susceptibility in soil pH. Increased N rate also reduced microbial biomass by 20% these systems. between the HIGH and ZERO N-rate treatments. The C–SB–SG– There is a need to identify corn-based cropping sysOCL sequence possessed more potentially mineralizable N (PMN) tems that do not jeopardize the capacity of the soil (57 vs. 46 kg ha 1 for average of CC and C–SB) and a higher percentage to function over the long-term. Cropping systems with of POM present as soil organic matter (17.1% for the C–SB–SG–OCL extended rotations ( 2 yr) and multiple crops offer the sequence vs. 13.9% for other sequences). Within the context of soil potential to meet this need, but information on how functions and cropping system performance, results from this study they impact soil properties is scarce. In this study, we indicate the C–SB–SB–OCL sequence enhanced nutrient cycling efficiency, while N fertilization resulted in a trade-off between its positive sought to determine the effect of four crop sequences effect on biological productivity and negative effect on nutrient cy(monoculture corn, corn–soybean, and two 4-yr secling efficiency. quences) and their interaction with three levels of N fertilization on soil properties for a long-term cropping system experiment in the Western Corn Belt. T long-term sustainability of cropping systems is largely determined by their impact on soil quality. MATERIALS AND METHODS Because soil quality is directly related to the capacity Site Description of soil to function (Karlen et al., 1997), it envelops many aspects of cropping system performance. Measures of The research site is located on the Agronomy Farm at the performance include biological productivity, erosion reUniversity of Nebraska Agricultural Research and Development Center 6 km south of Mead, NE in Saunders County sistance, nutrient cycling efficiency, regulation of atmo(41 10 12′′ N lat., 96 25 12′′ W long.). The site is on Peoriaspheric gases, and mediation of water flows (Ericksen age loess with nearly level topography (0–3% slope). The and McSweeney, 1999; Doran and Parkin, 1996; Karlen predominant soil at the site is Sharpsburg silty clay loam with and Stott, 1994; Larson and Pierce, 1991). Off-site envian average particle-size distribution for the surface 30.5-cm ronmental problems caused by cropping systems can soil depth of 5% sand, 64% silt, and 31% clay. often be linked to a compromised soil function as a result A long-term cropping systems study comprised of seven of poor soil management. Consequently, information on crop sequences (three monoculture, two 2-yr, and two 4-yr how cropping systems influence soil quality will allow rotations) with three rates of N fertilizer was established on agriculturists to design systems that are more environthe site in 1983 (Varvel, 1994). Corn-based cropping sequences mentally sustainable (Karlen et al., 1994). included in the study were continuous corn, corn–soybean, corn–oat clover (80% sweet clover and 20% red clover)– In the Western Corn Belt, monoculture corn and grain sorghum–soybean, and corn–soybean–grain sorghum– oat clover. The oat and clover intercrop represented a single M.A. Liebig, USDA-ARS, Northern Great Plains Research Laborayear in each 4-yr sequence. Oat was harvested during the first tory, P.O. Box 459, Mandan, ND 58554; G.E. Varvel, J.W. Doran, and B.J. Wienhold, USDA-ARS, Soil and Water Conservation Research Unit, 120 Keim Hall, Dep. of Agronomy, University of Nebraska, Abbreviations: CC, continuous corn; C–OCL–SG–SB, corn–oat Lincoln, NE 68583. The USDA–ARS is an equal opportunity/affirmaclover–grain sorghum–soybean; C–SB, corn–soybean; C-SB-SG-OCL, tive action employer and all agency services are available without discorn–boybean–grain sorghum–oat clover; EC, electrical conductivcrimination.Received 28 March 2001.*Corresponding author (liebigm@ ity; HIGH, high N treatment; LOW, low N treatment; PMN, potenmandan.ars.usda.gov). tially mineralizable N; POM, particulate organic matter; ZERO, zero N treatment. Published in Soil Sci. Soc. Am. J. 66:596–601 (2002).