Management and Soil-Quality Effects on Fertilizer

Management and Soil-Quality Effects on Fertilizer-Use Efficiency and Leaching Todd M. Nissen and Michelle M. Wander* ABSTRACT

outcomes to readily measurable parameters, we should be able to better optimize management within different regions and cropping systems. This work follows up on previous findings suggesting measures of POM and aggregation are particularly good indicators of management practices’ influence on soil quality (Carter, 2002). Both indicators have been found to be sensitive to management practices in Illinois (Wander and Bollero, 1999), and both are likely to be related to crop nutrient acquisition, N leaching, and organic matter dynamics. Measures of POM, which represent relatively young (5–25 yr) biologically and physically active organic matter, are thought to be predictive of N mineralization potential (Boone, 1994; Yakovchenko et al., 1998). The influence of management on SOM and SOMrelated outcomes is complex, soil specific, and croppingsystem dependent. In the corn–soybean-based cropping systems studied here, increases in surface-soil POM contents reported for soils under NT management had come at the expense of POM in subsoil, and total POM levels in the profile were similar in NT and CT systems (Needelman et al., 1999). Aggregate DMWD, which may be inversely related to soil physical condition in 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 SOM and associated aggregate characteristics may be less stratified by depth in diversified cropping systems that are tilled. Such systems are frequently reported to be more N conserving than their conventional counterparts (Poudel et al., 2001). Using Century, a simulation model of long-term soil C dynamics, Yiridoe et al. (1997) found that crop rotations have a greater effect on N leaching than tillage, and that long crop rotations had less N leaching than continuous corn, due to fewer N inputs and to the uptake of spring and fall nitrate by wheat. Enhanced physical protection of SOM associated with aggregation may also explain N conservation in such soils (Besnard et al., 1996; Wander et al., 1994). The relationship between dry-aggregate size, which is likely to be reduced in soils in diversified cropping systems compared with those supporting mono- or biculture production, and N dynamics is probably a function of soil water relations (Perfect and Kay, 1995). Interactions between tillage, structure, and soil moisture status influence the quantity and dynamics of labile SOM retained in soils (Biederbeck et al., 1994; Franzluebbers

We tested the hypothesis that particulate organic matter (POM) and aggregate dry mean weight diameter (DMWD) are related to fertilizer-use efficiency (FUE) and leaching susceptibility. Soil cores (15 cm diam. by 50 cm depth) were collected from 12 farm fields representing three cropping systems: conventional (CT) and no-tillage (NT) management of corn (Zea mays L.)–soybean [Glycine max (L.) Merr.] rotations, and CT applied to more diversified corn–soybeanbased rotations (R-CT). Three of the four R-CT farms were organically managed. In a 95-d greenhouse trial, cores were seeded with corn, amended with 15N-labeled urea applied at four rates (0, 75, 150, 225 kg N ha⫺1), and subjected to a stressful moisture regime. Aggregate DMWD, which serves as a rough index of pore-size distribution, was greater in NT cores. Although total leached N was similar in all cropping systems, increased macropore flow in NT cores led to greater 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 had more POM and organic C in the top 30 cm of soil and higher crop biomass and biomass-N content. However, FUE in R-CT cores was relatively low since FUE does not account for contributions of indigenous N. For the same reason, FUE remained relatively high in CT systems despite less labile organic matter. Both FUE and SOM conservation declined with increasing N application rates. Increasing labile sources of N, reflected in POM pools, through crop diversification can substitute for incremental increases in fertilizer N and improve long-term productivity on Illinois Mollisols.

C

ropping practices alter soil properties that may influence soils’ susceptibility to degradation, its ability to conserve and supply water and nutrients, detoxify materials, and recover from perturbation. Ideally, a set of these properties that can be practically and reliably measured will be related to outcomes of regional importance. In the Midwest, where highly productive but poorly drained soils are typically tiledrained, N leaching is an important concern (David and Gentry, 2000; Randall and Goss, 2001). Jaynes et al. (2001) recently concluded that economically competitive corn production cannot be sustained on an Iowa field without degrading both water (by producing NO3⫺ in excess of 10 mg L⫺1) and soil (by mining soil organic matter [SOM]). That conclusion was based on a study of corn yield and NO3 leaching response to fertilizer inputs. In this region, it is vital to determine whether and how the adoption of practices like NT and the diversification of cash-grain based rotations that are reputed to improve soil quality will enhance FUE, reduce N leaching losses, and conserve SOM. By relating

T.M. Nissen and M.M. Wander, Dep. of Natural Resources and Environmental Sciences, Univ. of Illinois, 1102 S. Goodwin Ave., Urbana, IL 61801. Received 26 Aug. 2002. *Corresponding author (mwander@ uiuc.edu).

Abbreviations: CT, conventional tillage; DMWD, dry mean weight diameter; FUE, fertilizer-use efficiency; FUE–15N, fertilizer-use efficiency derived with 15N; FUE-diff, fertilizer-use efficiency derived by difference method; NT, no tillage; POM, particulate organic matter; PVC, polyvinyl chloride; R-CT, CT applied to more diversified corn– soybean-based rotations; SOC, soil organic C; SOM, soil organic matter; Sys-FUE, system fertilizer-use efficiency.

Published in Soil Sci. Soc. Am. J. 67:1524–1532 (2003).  Soil Science Society of America 677 S. Segoe Rd., Madison, WI 53711 USA

1524

NISSEN & WANDER: MANAGEMENT AND SOIL QUALITY EFFECTS

et al., 1995). In non-irrigated soils, nutrient uptake and leaching results must be considered in context with soils’ ability to provide adequate moisture in dry periods. Bypass flow has been shown to distribute rainfall more deeply in the profile, where evaporative loss is greatly reduced (Shipitalo et al., 2000). This, combined with greater soil-surface cover, is why the use of NT practices under dry conditions can increase soil moisture compared with CT soils (Ghaffarzadeh et al., 1997; Peterson et al., 1996). However, if bypass flow goes directly to tile lines, NT systems may suffer aggravated drought effects. Use of NT practices has been shown to promote and protect the macropores and pore connectivity that facilitate infiltration (Drees et al., 1994; Roseberg and McCoy, 1992). Fleming and Butters (1995) estimated that tilling an untilled clay loam slowed solute velocity by 35%. While abating runoff losses, rapid drainage to ground water or shallow tile drainage may exacerbate leaching problems and offset gains in nutrient use efficiency (Kladivko et al., 1991; Tyler and Thomas, 1977) unless bypass flow is less concentrated in soil nitrate N than is matrix flow (Heathman et al., 1995; Shipitalo et al., 2000). The objective of this study was to evaluate the relationship between N leaching, FUE, and SOM conservation and soil properties thought to be useful predictors of those outcomes, using soil from different cropping systems subject to four N treatments. The presence of relatively elevated labile N stocks in NT and diversified cropping systems may make them vulnerable to N leaching losses if they are subject to mismanagement (Bergstro¨m, 1987; Randall et al., 1997), and high rates of N application may prime labile organic matter (Liang et al., 1998). Alternatively, a greater abundance of labile SOM may enhance soils’ capacity to provide ecological services and resist degradation under stress conditions (Herrick and Wander, 1997). Enhanced water holding capacity, for example, may diminish drought effects and improve nutrient capture. We tested the hypotheses that FUE is correlated positively with POM and negatively with DMWD, and that leaching susceptibility is correlated positively with DMWD but negatively with POM. Our study design built on a tradition of on-farm research common in soil quality work by using cores obtained from working farms to ensure that influences of management on soil properties and outcomes were robust (Wander and Drinkwater, 2000). We used 15N to follow the fate and transport of fertilizer N. By conducting our study on intact cores in the greenhouse, we eliminated climate and runoff as variables. Our imposition of a moisture regime that emulated a wet early season followed by drought and then a very wet postharvest period was intended to maximize the importance of soil-water supply and transport. The use of fiberglass wicks as passive capillary samplers allowed us to generate and collect leachate under appropriate drainage conditions (Brandi-Dohrn et al., 1996). MATERIALS AND METHODS The experimental design was a split-plot in a randomized complete block. Eight soil cores were taken from 12 different

1525

farms in central and western Illinois in May 1999. The privately managed farms were blocked by four geographical locations according to soil and climate characteristics, with farms considered random within a block. Each block contained three farms, one for each of three tillage-rotation systems: conventional tillage (moldboard and chisel plow) of a corn–soybean rotation (CT); no-tillage of a corn–soybean rotation (NT); or conventional tillage of a long rotation, in which at least one green manure or cover crop (and typically an additional cash grain) was in the rotation in addition to corn and soybean (R-CT). All farms within a block contained soils of the same association. Soils are mapped as Virden silty clay loams (Argiaquolls) or Herrick silt loams (Argiudolls) in Blocks 1 and 2, Drummer silty clay loams (Endoaquolls) in Block 3, and Muscatine silty clay loams (Hapludolls) or Sable silty clay loams (Endoaquolls) in Block 4. Three of the four R-CT systems were organically managed, relying exclusively on non-synthetic sources for inputs and using biologically and culturally based practices for weed and pest control. These cropping systems had been in place a minimum of 5 yr, and all had been in the corn phase in 1998. Intact soil cores to a 50-cm depth were collected in 55-cm long sections of 15-cm diam. polyvinyl chloride (PVC) pipe, beveled on one edge and fitted with a steel cap on the other. Pipe sections were inserted and pulled from the ground with a Giddings hydraulic probe. Four cores were pulled from each of two locations within a farm for a total of 96 cores. These locations had been sampled in the spring and fall of 1998 as part of the second phase of the Illinois Soil Quality Initiative. On the same day, soils were collected from each farm from areas adjacent to the cores. Samples were taken to a depth of 50 cm and divided into 0- to 5-, 5- to 15-, 15- to 30-, and 30to 50-cm increments. Cores were hung on racks in randomized order in a University of Illinois greenhouse. A 50-cm length of braided fiberglass was attached to the bottom of each core to allow the collection of leachate samples from unsaturated soils without applying suction. The wicks acted as hanging water columns and supplied tension comparable to an additional 50 cm soil depth (Brandi-Dohrn et al., 1996). At the soil interface, an additional 6 cm of the braid was frayed and placed in contact with soil and kept in place with rubber PVC caps. The bottom of the wick dripped into a sealed container. All cores were saturated by watering in hourly 250-mL increments until leaching just commenced, which was considered Day 0. All watering was done with a solution of 0.0001M CaCl2 and 0.0001M MgSO4. Water was slowly dripped onto the central area of the core (6 cm diameter) through pinholes on the bottom of a plastic cup set on the soil surface of each core. Water remaining in the cup because of insufficient pressure was poured onto the core manually. Except for seven problem cores, infiltration exceeded water application rate and no water ran off the surface to the edge of the cores. One day after the first watering, three seeds of sweet corn (Zea mays L.‘Eagle’) were planted in each core just beyond the perimeter of the watering area. At 3 wk, all but the best plant in each core were pulled up and left on the soil surface to decompose. Vegetative- and reproductive-growth stages were recorded five times during the growing season. All standing biomass was harvested after 88 d (10 d before the final rainfall event), dried at 65⬚C for 48 h, weighed, and ground for analysis. On Day 3, a watering regime was instituted that represented, based on the Illinois Agronomy Handbook (1998), a typical wet early growing season (2.5 cm H2O wk⫺1 for 5 wk), a dry mid-season (0.25 cm wk⫺1 for 5 wk), a wet late growing season (1.9 cm wk⫺1 for 2 wk), and a wet postharvest season

1526

SOIL SCI. SOC. AM. J., VOL. 67, SEPTEMBER–OCTOBER 2003

condensed into a single event of 10 cm (Fig. 1a). No leaching events occurred during the dry mid-season regime. On Day 6, a mixture of labeled and unlabeled urea dissolved in water was applied with an auto-pipette to the soil surface in each core receiving one of four N treatments: 0, 7.5, 15.0, and 22.5 g N cm⫺2. This method was intended to minimize volatilization and simulate a broadcast application incorporated through rainfall. Final atom% excess 15N was 1.034. Leaching volumes were measured 24 h after watering. Nitrate and 15N concentrations in leachate were determined with a rapid diffusion method followed by analysis on a mass spectrometer (Khan et al., 1997). Two days after the last leachate was collected, cores were split vertically with a circular saw. Soils were split into four depths (0–5, 5–15, 15–30, and 30–50 cm), passed through a 25-mm sieve, weighed, and airdried. Subsamples for all C and N determinations were ovendried at 105⬚C for 24 h and finely ground in a Spex disk mill (Spex Industries, Inc., Edison, NJ). Attempts to minimize

cross-contamination of isotopic samples were taken by processing samples in likely ascending order of atom% 15N concentrations. Total C, total N, and 15N in soil and plant samples were measured on a Europa Scientific Integrated 13C–15N analyzer (PDZ Europa Ltd., Crewe, UK). Aggregate DMWD was determined by placing 300 to 400 g of air-dried soil on a stack of two sieves with 4- and 1-mm openings, shaking the soil for 1 min with a Ro-tap sieve (W.S. Tylor, Inc., Mentor, OH), and calculating after Youker and McGuiness (1957). We elected to use dry-sieved rather than wet-sieved aggregates because their characteristics have been related to seedbed quality, erodibility, and solute transport in structured soils (Perfect et al., 1997). Additionally, unlike measures of wetaggregate stability, which are difficult to causally link to functionality in intact soils (Young et al., 2001), aggregate DMWD is likely to be a useful structural surrogate, providing insight into water storage and transport as well as physical protection of organic matter in intact soil. Methods for determining POMC and POM-N are found in Wander and Bollero (1999). Fertilizer-use efficiency was assessed both as the percent of applied 15 N recovered in the biomass (FUE–15N) and as the difference (FUE-Diff) in N uptake between fertilized plants and nonfertilized controls, divided by the rate of N application. We also measured total fertilizer-N capture by plant and soil (Cassman et al., 2002) as an indicator of system fertilizer-use efficiency (Sys-FUE). These methods allowed us to examine labeled and unlabeled N fractions to account for the influences of priming (Rao et al., 1991) and N pool substitution (Jenkinson et al., 1985). Total biomass is used as a measure of productivity because drought stress applied during the experiment was severe enough to inhibit grain filling in many plants. Statistical analyses were performed with the SAS Univariate, Mixed, and Correlation procedures (SAS Institute Inc., 1994). Seven of the cores ponded water on the surface and did not drain. These seven were removed from the analyses.

RESULTS AND DISCUSSION Cropping Systems

Fig. 1. Cropping-system influence on (a) cumulative amount of water leached and water applied (bars), (b) leachate N concentration, and (c) cumulative amount of 15N recovered in leachate. Cropping systems are conventional tillage, corn–soybean (CT), no-tillage, corn–soybean (NT) and conventional tillage in corn–soybeanbased systems in a minimum 3-yr rotation (R-CT). Error bars are standard error.

Leachate volume was significantly greater from NT cores than from cores collected from the two tilled treatments (Fig. 1a). However, because N concentrations in leachate were lowest from NT cores (Fig. 1b), the total amount of N leached during the study was similar in all treatments (Fig. 2a). Based on 15N recovery, approximately half of the N leached from NT cores was derived from fertilizer compared with only one quarter of the leached N from tilled cores (Fig. 2a). The greater leachate volume and quantity of fertilizer-derived N leached from NT cores suggest that bypass flow was greater in the NT than the tilled treatments. In bypass flow, rainfall and fertilizer-N still in inorganic form mix at the soil surface and move rapidly through the profile in macropores, limiting opportunity for retention or transformation within the soil matrix. Reduced matrix flow in NT soils accounts for the comparatively low losses of soil-derived N from those cores (Fig. 2a) and mitigated the potential for elevated N leaching under NT management. These results support previous findings that suggest that bypass flow in NT, combined with appropriate N management, may deliver similar quantities of N to ground water, but in reduced concentrations (Heathman et al., 1995; Kumar et al., 1999). Relatively reduced losses of soil N from NT cores

1527


Fig. 2. Contributions of fertilizer-derived N and soil-derived N to (a) total leached N from cores and (b) total N uptake in plant biomass. Within each graph, column segments labeled with the same lowercase letter, and whole columns labeled with the same uppercase letter, are not significantly different at P ⬍ 0.05. For biomass N uptake, R-CT is greater than CT at P ⬍ 0.054.

might be due in part to reduced N availability in that treatment. Differences in leachate-N concentrations of tilled and NT cores were greatest during the first wetting event, which took place before fertilizer was applied (Fig. 1b). Comparatively low N availability in NT cores is consistent with observations that N limitation in the region may be greater under NT management (Illinois Agronomy Handbook, 1998). Spring tillage likely stimulated mineralization and enhanced N availability in the CT treatments. By comparison, NT cores had relatively low crop growth without fertilization and the largest increase with N additions (Fig. 3). For NT cores, the first 7.5 g N m⫺2 added to unfertilized cores significantly increased the amount of soil-derived N taken up in the plant, which suggests that in the absence of tillage, fertilization may substantially increase mineralization rates. Also, reduced crop development-stage means in unfertilized NT cores were noted before the onset of the drought, although drought-induced stress likely contributed to their greatly reduced biomass growth. Soil water that drains directly to shallow tile drains via bypass flow does not contribute to moisture recharge and may leave NT soils more prone to drought where water losses are not offset by reduced evaporation from NT soils (Shipitalo et al., 2000). Greater moisture stress in NT cores may have also limited crop N acquisition, as bio-

Fig. 3. Influence of N application rate on (a) plant dry matter and (b) N in dry matter at plant harvest in three cropping systems. Cropping systems are conventional tillage, corn–soybean (CT), notillage, corn–soybean (NT), and conventional tillage in corn– soybean-based systems in a minimum 3-yr rotation (R-CT). The lines connect experimental data points and do not represent a function.

mass-N content was less than that in tilled treatments regardless of N application rate (Fig. 3b). Greater 15N leaching losses and moisture stress in the NT cores may explain why uptake of fertilizer-derived N (Fig. 2b) and FUE–15N (Table 1) were greater in CT than in NT cores. The POM-N and initial total soil N contents of soils (0–30 cm) were similar in NT and CT soils (Fig. 4); thus, differences in soil N supply potential alone do not explain differences in FUE–15N. Estimates of FUE-diff were higher than FUE–15N, but means did not differ among cropping systems (Table 1). These results highlight issues associated with the interpretation of estimates of FUE. Estimates of fertilizer recovery obtained with the difference method are often higher than those obtained with isotopic labels due to added Table 1. Fertilizer fate as determined though percentage recovery of labeled fertilizer (FUE–15N) and the difference between fertilized and unfertilized cores (FUE-diff). System fertilizer-use efficiency (Sys-FUE) is the sum of labeled fertilizer recovered in biomass and soil. FUE–15N Treatment

Biomass

FUE-diff Soil

Sys-FUE

Biomass

% Cropping System CT NT R-CT N Rate, g m⫺2 7.5 15.0 22.5

46.4a† 36.1b 40.6b

28.6ab 26.0b 32.5a

74.7a 62.7b 73.4a

53.8a 51.0a 50.8a

43.4a 42.3ab 37.4b

31.6a 29.6ab 26.0b

76.8a 71.9a 63.6b

63.2a 52.0ab 40.5b

† Values in the same column and section followed by the same letter are not significantly different at P ⬍ 0.05.

1528


Fig. 4. Depth distribution of (a) initial total N and (c) final POM-N in conventional tillage, corn–soybean (CT), no-tillage, corn–soybean (NT) and conventional tillage in a three crop-minimum rotation (R-CT). Plots (b) and (d) are the depth-weighted means of these fractions. Values at the same depth followed by the same letter are not significantly different from each other at P ⬍ 0.05.

N interactions (ANI) (Jenkinson et al., 1985; Rao et al., 1991). As Olk et al. (1999) indicate, increases in FUEdiff do not reveal whether they result from improved fertilizer uptake efficiencies or from declines in indigenous soil N supply. Our work shows that estimates of FUE based on either method do not provide sufficient information about indigenous soil N supply. Despite differences in net crop N uptake, similar estimates of FUE-diff were obtained because crops responded similarly to N additions. The greater FUE–15N of the CT system was achieved despite declines in SOC and POM contents in that system. In this experiment, pool substitution, in which labeled N may be disproportionately immobilized or denitrified, may contribute not only to decreased recovery in biomass with the 15N method, but also to the increased soil 15N recovery at the expense of biomass 15N recovery in R-CT cores (Table 1). Even if a comparable portion of the soil-derived N in R-CT cores is suspected to have resulted from pool substitution, contributions of soil-derived N to R-CT biomass were still higher than in the other treatments (Fig. 2). This is consistent with the findings of Harris et al. (1994) and Kramer et al. (2002), who compared 15N uptake in organic and conventionally managed soils. System FUE (Sys-FUE), which removes pool substitution as a factor to the extent that 15N replaces unlabeled N that was to be immobilized and not denitrified, was lowest in the NT and similar in the two tilled treatments (Table 1).

In our study, enhanced soil N supply potential in the R-CT treatments is suggested by relatively elevated organic matter and POM-C and POM-N contents in the surface depth (Fig. 4) and by greater biomass N uptake in 0-N treatments (Fig. 3b). Greater fertilizer retention and greater POM stocks in the R-CT treatment indicate that enhanced soil N supply is not the result of net organic matter loss. Harris et al. (1994) and Kramer et al. (2002) also found greater retention of added N in the organic production systems they studied. In our work, unlike those cited, 15N was added as urea to all systems instead of added as organic N in the diversified system. Accordingly, our results demonstrate the influence of indigenous soil N supply on N dynamics by removing the separate influence of amendment quality on N turnover. In all treatments, POM was enriched in 15N compared with the bulk soil. While accounting for ⬍3% of total N, POM in the top 30 cm contained approximately 10% of all 15N retained in the soil. This is consistent with findings of Balabane and Balesdent (1992) who found fertilizer-derived N was concentrated in fine-clay and particle-size fractions ⬎200 ␮m after one season of maize culture. They equated 15N in the coarse fraction with root N assimilation. It is also likely that microbial degradation of resident POM may act as a sink for fertilizer-derived N, at least initially, facilitating incorporation of 15N into new SOM (Vanlauwe et al., 1998). Even though the amount of 15N recovered in POM was

1529


Table 2. End-of-season C and N contents in total soil and the particulate organic matter (POM) fraction. Total soil measurements are to 50cm; POM measurements are to 30 cm. Total Soil N fert 0 7.5 15 22.5

C† g 12 419ab§ 12 727a 12 771a 12 286b

N‡

POM C/N

m⫺ 2 1 022ab 1 052a 1 058a 981b

12.15b 12.10b 12.07b 12.52a

C g 285.1a 283.6a 253.6a 272.4a

N

C/N

15.7a 14.3ab 13.8ab 12.3b

18.3c 20.1b 18.6c 22.5a

m⫺ 2

† Mean initial amount was 12853 g m⫺2, with no differences between treatments. ‡ Mean initial amount was 1059 g m⫺2, with no differences between treatments. § Values in the same column and section followed by the same letter are not significantly different at P ⬍ 0.05.

Fig. 5. Influence of N-fertilizer rate on (a) cumulative water leached and applied (bars), (b) leachate N concentration, and (c) cumulative amount of 15N recovered in leachate. Nitrogen rates are 0, 7.5, 15, and 22.5 g N m⫺2 soil. Error bars are standard error.

similar in all farming system treatments, the 2.44% of POM-N derived from fertilizer in the R-CT cores was less than the 3.97% of CT cores and 3.58% of NT cores. This result, which was due to the high POM-N contents in the R-CT treatment (Fig. 4d), indicates that enhanced conservation of fertilizer-N in the R-CT treatment was due to 15N-assimilation into non-particulate humic or microbial materials.

Nitrogen Rate Leaching volume was greatest from the non-fertilized control, where poorer plant growth may have limited water uptake (Fig. 5a). Trends in leached total N (Fig. 5b) and leached fertilizer-derived N (Fig. 5c) were consistent with fertilizer application rates. Higher N application rates resulted in higher and delayed peak concentrations of leached N (Fig. 5b). In all treatments, more than 75% of all leached fertilizer-derived N did so during the first 3 wk after application. At the end of the season, after mean N concentrations had diminished to below 4 mg L⫺1, the single application of 10 cm of

water to simulate heavy fall rains again stimulated N losses that reflected N fertilization rates. Even though the amount of 15N recovered in leachate increased with N rate, the percentage of fertilizer-N leached was consistently 2.3%. Total leaching losses of 12 kg N ha⫺1 from treatments receiving the highest N rate were only 4 kg N ha⫺1 higher than losses from 0-N treatments. Given that these differences are exceeded by an order of magnitude the differences between N uptake in the biomass (Fig. 2b), leaching outcomes provide less economic incentive for reducing fertilization rates than considerations of FUE. All measures of FUE declined with increasing fertilization rate (Table 1). Increased N losses were ostensibly to the atmosphere. The amount of N remaining in soil was lowest in the cores receiving the most N fertilizer (Table 2), and the magnitude of this difference in soil N content cannot be accounted for by biomass N uptake. The significant losses of N occurring at the highest N rate were accompanied by declines in SOC (Table 2). These losses, in addition to diminished POM-N contents and reduced recovery of 15N, suggests ‘real’ priming occurred whereby fertilizer-N stimulated mineralization of SOM (Kuzyakov et al., 2000). Conditions applied in this experiment are likely to have amplified trends that might not appear in the field where priming of native SOC and N might be compensated for by residue return. Others have noted similar within-season losses of SOC when, as was true in our study, crop growth is poor or stover is not returned to the soil (Clapp et al., 2000; Grant et al., 2001). Stimulated mineralization was expected to disproportionately affect labile organic matter such as POM-C and POM-N (Gregorich and Ellert, 1993). However, POM-C did not appear to be primed by fertilizer addition (Table 2). The magnitude of N loss from POM was quite small compared with losses from whole soil, indicating that mineral-associated SOM was primed. Particulate organic matter-C and POM-N losses from priming may have occurred but offset within the season by fertilizer-stimulated root growth. The percentage of fertilizer-N that leached was small relative to unaccounted-for losses of 23 to 34%. This supports Raun et al.’s (1998) caution that unaccountedfor N losses should not be assumed to have leached when leaching is not directly measured. Although urea fertilizers are susceptible to volatilization losses, the

1530


moist and sometimes water-saturated conditions during this experiment likely made denitrification the major path of N loss in the high N treatments (Aulakh et al., 1992). Given the loss risks associated with incremental increases of fertilizer N, and considered with the observation that POM-enriched R-CT cores had the greatest uptake of total N, it is reasonable to assume that increases in efficiency can be achieved through replacement of a portion of fertilizer-derived N with indigenous N. In-field N dynamics may differ from those observed in this column study since soils would experience cropping-system based differences in water partitioning between infiltration and runoff that would affect leaching rates (Brye et al., 2001). In field soils, the residence time of N percolating through the soil matrix would likely be longer than it was in the 50-cm cores; this should increase the chances of N recovery by expanding roots and reduce losses from leaching. No cropping system ⫻ N-rate interactions were significant in the reported results.

Soil Quality Parameters Associated with Nutrient Fate, Leaching, and SOM Conservation Soil POM-C concentration was positively correlated with total biomass N and the amount of soil-derived N in the biomass, which is consistent with the thesis that POM is positively related to soil N supply capacity (Table 3). Despite the fact that there was no correlation between POM-C and any measure of FUE, including Sys-FUE, 15N recovery in soil was positively related to POM-C. We used POM-C instead of POM-N as an index of the status of labile organic matter because its greater range and abundance in soils allows this measure to better integrate management-induced changes in organic matter. Soil POM-N contents are frequently correlated with, but do not typically provide a direct measure of, plant available N (Boone, 1994; Wander and Bidart, 2000), which is expected to be associated with microbial residues typically recovered in non-particulate fractions. Unlike POM, clay content and bulk density—parameters

often used as coefficients in predictive models—were negatively correlated with measures of FUE. Plant 15N uptake declined with increasing clay content while increased bulk density was weakly related to reduced FUE-diff. This likely reflects incorporation of fertilizerderived N into SOM affiliated with clay and/or protected by aggregates (Beare et al., 1994; Hassink, 1996). Collectively these findings support Hassink’s (1996) assertion that the protective capacity of soil has more influence on N availability than the amount of N contained in POM. Aggregate DMWD of the top 5 cm of soil was negatively correlated with biomass acquisition of total and soil-derived N; this is consistent with N uptake trends noted in the NT treatment, in which DMWD (0–5 cm) was greater than in the tilled treatments (P ⬍ 0.03). Given the interplay between physical, biological, and chemical processes that result in tradeoffs between N losses in bypass flow and matrix flow, estimating leaching risk through soil quality parameters is not likely to be straightforward. While SOC concentration was correlated with the amount of total and soil-derived N leached (Table 3), it did not adequately capture the dynamics of fertilizer movement to ground water. In this experiment, DMWD of the top 5 cm soil, which itself was correlated to clay content and bulk density, provided better correlations with leaching volume, leached total N, and leached 15N than any of the other parameters. Based on hierarchical theory of aggregation (Dexter, 1988), an increase in DMWD for soils of the same bulk density probably represents an increased percentage of macropores at the expense of water-storage mesopores, especially at higher DMWD values. This is consistent with the evidence of increased macropore flow in NT cores and suggests that DMWD may serve as a rough index of surface pore-size distribution and supports our assertion that dry-sieved aggregates may provide a more useful index of structure-dependent processes than aggregates obtained by wet-sieving. In an effort to relate aggregate stability parameters to runoff

Table 3. Pearson correlation coefficients (and P values) for soil quality and leaching parameters. All parameters are for 0 to 50 cm, except where indicated. DMWD†

BD g

Nutrient Use Biomass N FUE: 15N method FUE: Difference method Soil-derived N in Biomass System FUE Leaching outcomes Leachate, mL Leached N, mg 15 N Recovery, % Soil-derived N in leachate DMWD SOM Conservation C Loss 15 N Recovery in soil

⫺0.28 (0.009) ⫺0.10 0.02 ⫺0.26 (.024) ⫺0.05 0.63 (⬍.0001) 0.27 (0.0241) 0.59 (⬍.0001) 0.09 – ⫺0.21 (0.046) ⫺0.14

† Dry mean weight diameter to 5 cm. ‡ Percentage of clay to 15 cm. § POM-C to 30 cm.

Clay‡

cm⫺3

Total C g

⫺.004 .05 ⫺.21 (.086) ⫺.09 .10

⫺.08 ⫺.26 (.0309) .02 .02 ⫺.29 (.018)

0.17 ⫺0.05 0.29 (0.016) ⫺.27 (.012) 0.34 (.001)

0.34 (0.0012) 0.03 0.16 ⫺.09 0.30 (0.0038)

⫺.39 (.0002) .05

⫺.57 (⬍.0001) ⫺.16

POM-C§

kg⫺1

⫺.06 ⫺.09 .16 .08 ⫺.22 (.07) 0.23 (0.0326) 0.25 (0.02) 0.08 0.32 (.0025) ⫺0.01 .18 (.09) ⫺.16

0.24 (.029) ⫺.08 ⫺.06 .55 (⬍.0001) .14 ⫺0.21 (0.0513) 0.15 0.02 0.23 (.039) ⫺0.10 ⫺.20 (.07) .33 (.0074)


and soil loss, Rasiah and Kay (1995) found wet aggregate stability could only be related to soil loss though its indirect influences on time to ponding. The relationship between indicators and conservation of organic matter was investigated by relating parameters to organic matter loss (SOC initial ⫺ SOC final) and to 15N retained in soil. Both POM-C and DMWD were negatively related to losses, but neither was a better predictor of SOC balance than were clay content or bulk density (Table 3). The negative relationship between POM-C and C losses likely reflects previously mentioned root offsets to losses plus the positive role of aggregate protection, while the negative relationships between DMWD, clay content, and bulk density with C losses is explained by physical protection alone. The importance of organic matter assimilation to SOM balance and its association with POM dynamics and soil N supply is further suggested by the correlation between 15 N retention in soil and POM-C content (Table 3). Cropping-system based differences in fertilizer retention in soil and POM contents may better reflect the nuanced differences in N economy than does FUE or Sys-FUE. Neither FUE nor Sys-FUE appropriately credit additions to system efficiency derived from increased indigenous N supply that result from use of diversified and, in this instance, predominately organic cropping systems.

CONCLUSION Differences in the leaching, FUE, system FUE and SOM conservation performance of the three farming systems were related to soil structure and SOM status. Dry aggregate stability appeared to reflect differences in pore-size distribution and macropore-flow potential, providing good correlations with leaching volume and leached fertilizer-N. The NT systems had greater DMWD, but increased bypass flow and leached fertilizer-N in NT did not result in elevated total N leaching because soil N was less available in NT soils during the early season when the bulk of N leaching occurred. Greater leachate losses from NT cores likely aggravated their water stress and limited their N acquisition, thereby lowering their FUE compared with CT cores. In tilled soils, greater moisture and spring-tillage-induced N availability resulted in greater crop growth in control soils and in reduced crop response to added N. In the same way that DMWD reflected differences in solute transport dynamics, measures of POM-C appeared to capture some of the short-term C and N assimilation and mineralization dynamics. Elevated levels of POM were positively correlated with soil-derived leachate-N, soil-derived plant-uptake N, and retention of 15N in the soil. Soil POM contents, along with total plant N uptake, were higher in the R-CT than in either of the 2-yr rotations. Despite this, FUE was not higher in R-CT cores because FUE does not credit additions to system efficiency derived from increased indigenous N supply. The influence of indigenous soil N supply on N dynamics was highlighted by using inorganic fertilizer and removing the separate influence of amendment quality on N

1531

turnover. Both POM and DMWD may serve useful in indices of soil quality or models of soil performance, in that each integrate to some extent the physical, chemical, and biological status of the soil but with different emphases. Fertilization rates had a strong influence on FUE and C conservation, with high rates reducing FUE, increasing N losses, and priming SOC. Results suggest improvement in N economy could likely be gained by increasing pools of POM-N through cropping system diversification to replace marginal increases in fertilizer-N. ACKNOWLEDGMENTS Appreciation is expressed to Airiazran Ahadi, L. Art Spomer, Germa´n Bollero, and Charles Boast for their assistance. Support for this research was obtained from the Illinois Department of Agriculture Council for Food and Agricultural Research: IDA CFAR 98E-47 and the Illinois Department of Agriculture Conservation 2000: IDOA SA 97-62.

REFERENCES Aulakh, M.S., J.W. Doran, and A.R. Mosier. 1992. Soil denitrification– significance, measurement, and effects of management. Adv. Soil Sci. 18:1–57. Balabane, M., and J. Balesdent. 1992. Input of fertilizer-derived labeled-N to soil organic matter during a growing season of maize in the field. Soil Biol. Biochem. 24:89–96. Beare, M.H., P.F. Hendrix, and D.C. Coleman. 1994. Water-stable aggregates and organic matter fractions in conventional-tillage and no-tillage soils. Soil Sci. Soc. Am. J. 58:777–786. Bergstro¨m, L. 1987. Nitrate leaching and drainage from annual and perennial crops in tile-drained plots and lysimeters. J. Environ. Qual. 16:11–18. Besnard, E., C. Chenu, J. Balesdent, P. Puget, and D. Arrouays. 1996. Fate of particulate organic matter in soil aggregates during cultivation. Eur. J. Soil Sci. 47:495–503. Biederbeck, V.O., H.H. Janzen, C.A. Campbell, and R.P. Zentner. 1994. Labile soil organic matter as influenced by cropping practices in an arid environment. Soil Biol. Biochem. 26:1647–1656. Boone, R.D. 1994. Light-fraction soil organic matter—Origin and contribution to net nitrogen mineralization. Soil Biol. Biochem. 26:1459–1468. Brandi-Dohrn, F.M., R.P. Dick, M. Hess, and J.S. Selker. 1996. Field evaluation of passive capillary samplers. Soil Sci. Soc. Am. J. 60:1705–1713. Brye, K.R., J.M. Norman, L.G. Bundy, and S.T. Gower. 2001. Nitrogen and carbon leaching in agroecosystems and their role in denitrification potential. J. Environ. Qual. 30:58–70. Carter, M.R. 2002. Soil quality for sustainable land management: Organic matter and aggregation interactions that maintain soil functions. Agron. J. 94:38–47. Cassman, K.G., A. Dobermann, and D.T. Walters. 2002. Agroecosystems, nitrogen-use efficiency, and nitrogen management. Ambio 31:132–140. Clapp, C.E., R.R. Allmaras, M.F. Layese, D.R. Linden, and R.H. Dowdy. 2000. Soil organic carbon and C-13 abundance as related to tillage, crop residue, and nitrogen fertilization under continuous corn management in Minnesota. Soil Tillage Res. 55:127–142. David, M.B., and L.E. Gentry. 2000. Anthropogenic inputs of nitrogen and phosphorus and riverine export for Illinois, USA. J. Environ. Qual. 29:494–508. Dexter, A.R. 1988. Advances in characterization of soil structure. Soil Tillage Res. 11:199–238. Drees, L.R., A.D. Karathanasis, L.P. Wilding, and R.L. Blevins. 1994. Micromorphological characteristics of long-term no-till and conventionally tilled soils. Soil Sci. Soc. Am. J. 58:508–517. Fleming, J.B., and G.L. Butters. 1995. Bromide transport detection in tilled and nontilled soil: Solution samplers vs. soil cores. Soil Sci. Soc. Am. J. 59:1207–1216.

1532


Franzluebbers, A.J., F.M. Hons, and D.A. Zuberer. 1995. Tillageinduced seasonal changes in soil physical properties affecting soil CO2 evolution under intensive cropping. Soil Tillage Res. 34:41–60. Ghaffarzadeh, M., F.G. Prechac, and R.M. Cruse. 1997. Tillage effect on soil water content and corn yield in a strip intercropping system. Agron. J. 89:893–899. Grant, R.F., N.G. Juma, J.A. Robertson, R.C. Izaurralde, and W.B. McGill. 2001. Long-term changes in soil carbon under different fertilizer, manure, and rotation: Testing the mathematical model ecosys with data from the Breton Plots. Soil Sci. Soc. Am. J. 65:205–214. Gregorich, E.G., and B.H. Ellert. 1993. Light fraction and macroorganic matter in mineral soils, p. 397–407. In M.R. Carter (ed.) Soil sampling and methods of analysis. Lewis Publishers, Boca Raton, FL. Harris, G.H., O.B. Hesterman, E.A. Paul, S.E. Peters, and R.R. Janke. 1994. Fate of legume and fertilizer N-15 in a long-term cropping systems experiment. Agron. J. 86:910–915. Hassink, J. 1996. Preservation of plant residues in soils differing in unsaturated protective capacity. Soil Sci. Soc. Am. J. 60:487–491. Heathman, G.C., L.R. Ahuja, D.J. Timlin, and K.E. Johnsen. 1995. Surface aggregates and macropore effects on chemical transport in soil under rainfall. Soil Sci. Soc. Am. J. 59:990–997. Herrick, J.E., and M.M. Wander. 1997. Relationships between soil organic carbon and soil quality in cropped and rangeland soils: The importance of distribution, composition and soil biological activity. p. 405–425. In R. Lal et al. (ed.) Advances in Soil Science. CRC Press, Inc., Boca Raton, FL. Illinois Agronomy Handbook. 1998. The University of Illinois, Urbana, IL. Jaynes, D.B., T.S. Colvin, D.L. Karlen, C.A. Cambardella, and D.W. Meek. 2001. Nitrate loss in subsurface drainage as affected by nitrogen fertilizer rate. J. Environ. Qual. 30:1305–1314. Jenkinson, D.S., R.H. Fox, and J.H. Rayner. 1985. Interactions between fertilizer nitrogen and soil nitrogen–the so-called ‘priming’ effect. J. Soil Sci. 36:425–444. Khan, S.A., R.L. Mulvaney, and C.S. Mulvaney. 1997. Accelerated diffusion methods for inorganic-nitrogen analysis of soil extracts and water. Soil Sci. Soc. Am. J. 61:936–942. Kladivko, E.J., G.E. Van Scoyoc, E.J. Monke, K.M. Oates, and W. Pask. 1991. Pesticide and nutrient movement into subsurface tile drains on a silt loam soil in Indiana. J. Environ. Qual. 20:264–270. Kramer, A.W., T.A. Doane, W.R. Horwath, and C. van Kessel. 2002. Short-term nitrogen-15 recovery vs. long-term total soil N gains in conventional and alternative cropping systems. Soil Biol. Biochem. 34:43–50. Kumar, A., R.S. Kanwar, P. Singh, and L.R. Ahuja. 1999. Evaluation of the root zone water quality model for predicting water and NO3-N movement in an Iowa soil. Soil Tillage Res. 50:223–236. Kuzyakov, Y., J.K. Friedel, and K.U. Stahr. 2000. Review of mechanisms and quantification of priming effects. Soil Biol. Biochem. 32:1485–1498. Liang, B.C., E.G. Gregorich, A.F. MacKenzie, M. Schnitzer, R.P. Voroney, C.M. Monreal, and R.P. Beyaert. 1998. Retention and turnover of corn residue carbon in some eastern Canadian soils. Soil Sci. Soc. Am. J. 62:1361–1366. Needelman, B.A., M.M. Wander, G.A. Bollero, C.W. Boast, G.K. Sims, and D.G. Bullock. 1999. Interaction of tillage and soil texture: Biologically active soil organic matter in Illinois. Soil Sci. Soc. Am. J. 63:1326–1334. Olk, D.C., K.G. Cassman, G. Simbahan, P.C.S. Cruz, S. Abdulrachman, R. Nagarajan, P.S. Tan, and S. Satawathananont. 1999. Interpreting fertilizer-use efficiency in relation to soil nutrient-supplying capacity, factor productivity, and agronomic efficiency. Nutr. Cycl. Agroecosyst. 53:35–41.

Perfect, E., and B.D. Kay. 1995. Brittle-fracture of fractal cubic aggregates. Soil Sci. Soc. Am. J. 59:969–974. Perfect, E., Q. Zhai, and R.L. Blevins. 1997. Soil and tillage effects on the characteristic size and shape of aggregates. Soil Sci. Soc. Am. J. 61:1459–1465. Peterson, G.A., A.J. Schlegel, D.L. Tanaka, and O.R. Jones. 1996. Precipitation use efficiency as affected by cropping and tillage systems. J. Prod. Agric. 9:180–186. Poudel, D.D., W.R. Horwath, J.P. Mitchell, and S.R. Temple. 2001. Impacts of cropping systems on soil nitrogen storage and loss. Agric. Syst. 68:253–268. Randall, G.W., D.R. Huggins, M.P. Russelle, D.J. Fuchs, W.W. Nelson, and J.L. Anderson. 1997. Nitrate losses through subsurface tile drainage in Conservation Reserve Program, alfalfa, and row crop systems. J. Environ. Qual. 26:1240–1247. Randall, G.W., and M.J. Goss. 2001. Nitrate losses to surface water through subsurface tile drainage. p. 95–122. In R.F. Follett and J.L. Hatfield (ed.) Nitrogen in the environment: Sources, problems, and managment. Elsevier Science BV, Amsterdam, The Netherlands. Rao, A.C.S., J.L. Smith, R.I. Papendick, and J.F. Parr. 1991. Influence of added nitrogen interactions in estimating recovery efficiency of labeled nitrogen. Soil Sci. Soc. Am. J. 55:1616–1621. Rasiah, V., and B.D. Kay. 1995. Runoff and soil loss as influenced by selected stability parameters and cropping and tillage practices. Geoderma 68:321–329. Raun, W.R., G.V. Johnson, S.B. Phillips, and R.L. Westerman. 1998. Effect of long-term N fertilization on soil organic C and total N in continuous wheat under conventional tillage in Oklahoma. Soil Tillage Res. 47:323–330. Roseberg, R.J., and E.L. McCoy. 1992. Tillage- and traffic-induced changes in macroporosity and macropore continuity: air permeability assessment. Soil Sci. Soc. Am. J. 56:1261–1267. SAS Institute Inc. 1994. SAS User’s Guide. Fourth ed. SAS Institute Inc., Cary, NC. Shipitalo, M.J., W.A. Dick, and W.M. Edwards. 2000. Conservation tillage and macropore factors that affect water movement and the fate of chemicals. Soil Tillage Res. 53:167–183. Tyler, D.D., and G.W. Thomas. 1977. Lysimeter measurements of nitrate and chloride losses from soil under conventional and notillage corn. J. Environ. Qual. 6:63–66. Vanlauwe, B., N. Sanginga, and R. Merckx. 1998. Soil organic matter dynamics after addition of nitrogen-15- labeled leucaena and dactyladenia residues. Soil Sci. Soc. Am. J. 62:461–466. Wander, M.M., S.J. Traina, B.R. Stinner, and S.E. Peters. 1994. Organic and conventional management effects on biologically active soil organic matter pools. Soil Sci. Soc. Am. J. 58:1130–1139. Wander, M.M., and G.A. Bollero. 1999. Soil quality assessment of tillage impacts in Illinois. Soil Sci. Soc. Am. J. 63:961–971. Wander, M.M., and M.G. Bidart. 2000. Tillage practice influences on the physical protection, bioavailability and composition of particulate organic matter. Biol. Fertil. Soils 32:360–367. Wander, M.M., and L.E. Drinkwater. 2000. Fostering soil stewardship through soil quality assessment. Appl. Soil Ecol. 15:61–73. Yakovchenko, V.P., L.J. Sikora, and P.D. Millner. 1998. Carbon and nitrogen mineralization of added particulate and macroorganic matter. Soil Biol. Biochem. 30:2139–2146. Yiridoe, E.K., R.P. Voroney, and A. Weersink. 1997. Impact of alternative farm management practices on nitrogen pollution of groundwater: Evaluation and application of CENTURY model. J. Environ. Qual. 26:1255–1263. Youker, R.E., and J.L. McGuiness. 1957. A short method of obtaining mean weight-diameter values of aggregate analysis of soil. Soil Sci. 83:291–294. Young, I.M., J.W. Crawford, and C. Rappoldt. 2001. New methods and models for characterising structural heterogeneity of soil. Soil Tillage Res. 61:33–45.