Management and Soil-Quality Effects on Fertilizer-Use Efficiency and Leaching

outcomes to readily measurable parameters, we should be able to better optimize management within different We tested the hypothesis that particulate organic matter (POM) regions and cropping systems. and aggregate dry mean weight diameter (DMWD) are related to This work follows up on previous findings suggesting fertilizer-use efficiency (FUE) and leaching susceptibility. Soil cores measures of POM and aggregation are particularly good (15 cm diam. by 50 cm depth) were collected from 12 farm fields representing three cropping systems: conventional (CT) and no-tillage indicators of management practices’ influence on soil (NT) management of corn (Zea mays L.)–soybean [Glycine max (L.) quality (Carter, 2002). Both indicators have been found Merr.] rotations, and CT applied to more diversified corn–soybeanto be sensitive to management practices in Illinois (Wanbased rotations (R-CT). Three of the four R-CT farms were organider and Bollero, 1999), and both are likely to be related cally managed. In a 95-d greenhouse trial, cores were seeded with to crop nutrient acquisition, N leaching, and organic corn, amended with 15N-labeled urea applied at four rates (0, 75, 150, matter dynamics. Measures of POM, which represent 225 kg N ha 1), and subjected to a stressful moisture regime. Aggrerelatively young (5–25 yr) biologically and physically gate DMWD, which serves as a rough index of pore-size distribution, active organic matter, are thought to be predictive of was greater in NT cores. Although total leached N was similar in all N mineralization potential (Boone, 1994; Yakovchenko cropping systems, increased macropore flow in NT cores led to greater et al., 1998). leaching of fertilizer N and less leaching of soil-derived N, as well as greater moisture stress and decreased plant N uptake. The R-CT cores The influence of management on SOM and SOMhad more POM and organic C in the top 30 cm of soil and higher related outcomes is complex, soil specific, and croppingcrop biomass and biomass-N content. However, FUE in R-CT cores system dependent. In the corn–soybean-based cropping was relatively low since FUE does not account for contributions of systems studied here, increases in surface-soil POM conindigenous N. For the same reason, FUE remained relatively high in tents reported for soils under NT management had come CT systems despite less labile organic matter. Both FUE and SOM at the expense of POM in subsoil, and total POM levels conservation declined with increasing N application rates. Increasing in the profile were similar in NT and CT systems labile sources of N, reflected in POM pools, through crop diversifica(Needelman et al., 1999). Aggregate DMWD, which tion can substitute for incremental increases in fertilizer N and immay be inversely related to soil physical condition in prove long-term productivity on Illinois Mollisols. the Midwest, was not found to vary consistently between NT and CT soils but was greater in cultivated than uncultivated soils (Wander and Bollero, 1999). Labile C practices alter soil properties that may SOM and associated aggregate characteristics may be influence soils’ susceptibility to degradation, its less stratified by depth in diversified cropping systems ability to conserve and supply water and nutrients, dethat are tilled. Such systems are frequently reported to toxify materials, and recover from perturbation. Ideally, be more N conserving than their conventional countera set of these properties that can be practically and parts (Poudel et al., 2001). Using Century, a simulation reliably measured will be related to outcomes of remodel of long-term soil C dynamics, Yiridoe et al. (1997) gional importance. In the Midwest, where highly profound that crop rotations have a greater effect on N ductive but poorly drained soils are typically tileleaching than tillage, and that long crop rotations had drained, N leaching is an important concern (David and less N leaching than continuous corn, due to fewer N Gentry, 2000; Randall and Goss, 2001). Jaynes et al. inputs and to the uptake of spring and fall nitrate by (2001) recently concluded that economically competiwheat. Enhanced physical protection of SOM associated tive corn production cannot be sustained on an Iowa with aggregation may also explain N conservation in field without degrading both water (by producing such soils (Besnard et al., 1996; Wander et al., 1994). NO 3 in excess of 10 mg L 1) and soil (by mining soil The relationship between dry-aggregate size, which organic matter [SOM]). That conclusion was based on is likely to be reduced in soils in diversified cropping a study of corn yield and NO3 leaching response to systems compared with those supporting monoor biculfertilizer inputs. In this region, it is vital to determine ture production, and N dynamics is probably a function whether and how the adoption of practices like NT and of soil water relations (Perfect and Kay, 1995). Interacthe diversification of cash-grain based rotations that are tions between tillage, structure, and soil moisture status reputed to improve soil quality will enhance FUE, reinfluence the quantity and dynamics of labile SOM reduce N leaching losses, and conserve SOM. By relating tained in soils (Biederbeck et al., 1994; Franzluebbers T.M. Nissen and M.M. Wander, Dep. of Natural Resources and EnviAbbreviations: CT, conventional tillage; DMWD, dry mean weight ronmental Sciences, Univ. of Illinois, 1102 S. Goodwin Ave., Urbana, diameter; FUE, fertilizer-use efficiency; FUE–15N, fertilizer-use effiIL 61801. Received 26 Aug. 2002. *Corresponding author (mwander@ ciency derived with 15N; FUE-diff, fertilizer-use efficiency derived by uiuc.edu). difference method; NT, no tillage; POM, particulate organic matter; PVC, polyvinyl chloride; R-CT, CT applied to more diversified corn– Published in Soil Sci. Soc. Am. J. 67:1524–1532 (2003).  Soil Science Society of America soybean-based rotations; SOC, soil organic C; SOM, soil organic matter; Sys-FUE, system fertilizer-use efficiency. 677 S. Segoe Rd., Madison, WI 53711 USA