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Published in Soil Sci. Soc. Am. J. 67:1517-1523 (2003).
© 2003 Soil Science Society of America
677 S. Segoe Rd., Madison, WI 53711 USA

DIVISION S-6—SOIL & WATER MANAGEMENT & CONSERVATION

Tillage Effects on Nitrate Leaching Measured by Pan and Wick Lysimeters

Y. Zhu*,a, R. H. Foxa and J. D. Tothb

a Dep. of Crop and Soil Sciences, 116 A.S.I. Building, The Pennsylvania State Univ., University Park, PA 16802
b School of Veterinary Medicine, Univ. of Pennsylvania, New Bolton Center, 382 West Street Road, Kennett Square, PA 19348

* Corresponding author (yxz117{at}psu.edu)


   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 
No-till (NT) is a recommended best management practice for reducing erosion in agricultural production. Because of potential increases in infiltration with NT, a better understanding of tillage effects on NO-3–N leaching is required. An experiment was conducted in central Pennsylvania on a Hagerstown silt loam (fine, mixed, semiactive, mesic Typic Hapludalf) to study NO-3–N leaching under chisel-till and NT and to compare results from zero-tension pan and passive capillary fiberglass wick lysimeters from May 1995 to April 2001. Pan lysimeters collected greater leachate volumes from NT than from tilled treatments during the growing season, likely due to greater macropore flow in NT soil. When leachate collection efficiency corrected values were used, pan and wick lysimeters collected equivalent masses of NO-3–N. Flow weighted NO-3–N concentrations in leachate in both lysimeter types were also similar. Tillage had no effect on total leachate collected during the 6-yr experiment by either pan (228 mm yr-1) or wick (558 mm yr-1) lysimeters. Flow-weighted NO-3–N concentrations and NO-3–N masses in leachate were not significantly different between tilled and NT, but increased with increasing N-rate (at 0, 100, and 200 kg N ha-1, flow-weighted NO-3–N concentrations were 3.5, 8.2, and 23.9 mg L-1 and NO-3–N masses were 17, 39, and 112 kg ha-1 yr-1, respectively). The results demonstrate that under our condition NT will not result in more NO-3 leaching than chisel-tillage over a multiyear period.

Abbreviations: ANOVA, analysis of variance • CT, conventional till • LCNM, leachate collection efficiency corrected NO-3–N mass • LSD, least significant difference • NT, no-till


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 
NITRATE POLLUTION of ground and surface waters exists across the USA (Burkart and James, 1999; Nolan et al., 1998; USGS, 2001; Hallberg, 1989; Hallberg and Keeney, 1993). The main source of NO-3 has been identified as agricultural production (Keeney, 1989; Burkart and James, 1999; Schilling and Libra, 2000). Thus, modifying agricultural production practices to reduce NO-3 leaching may be the best choice to alleviate the NO-3 pollution problem.

Conservation tillage can minimize runoff and soil erosion and is recommended by government agencies and agricultural extension organizations as a component of best management practices. Conservation tillage accounted for 37% of cropland in the USA in 2000 with half of this conservation tillage acreage being in NT (Conservation Technology Information Center, 2000). However, concerns have been raised regarding the environmental soundness of conservation tillage. Some researchers think that because conservation tillage increases residue coverage on soil surface, it will increase infiltration, which may be accompanied by an increase in NO-3 leaching to the ground water. Tyler and Thomas (1977) found that leachate volume and NO-3–N and Cl- masses in leachate collected below the 106-cm soil depth were greater in NT than in conventional till (CT). A Br- tracer experiment also showed that there was greater downward movement of Br- added with a water solution in NT plots than that in CT plots (Randall and Bandel, 1987). Other researchers have also shown that NT produced more leachate and solutes than CT (Thomas et al., 1973; Kranz and Kanwar, 1995; Dick et al., 1989).

In contrast, Kanwar et al. (1985) noted that more NO-3 was leached below 1.5 m in CT than in NT using rainfall simulation on a loam soil in Iowa. Drury et al. (1993) found that tile drainage volume and NO-3–N mass were higher in CT than in NT. Similar results were reported by Angle et al. (1993), Staver et al. (1988), and Ritter et al. (1993). Other researchers found that although NT produced more percolation water, the flow-weighted NO-3–N concentrations and NO-3–N masses in percolation water from CT were higher than or equivalent to that from NT (Randall and Iragavarapu, 1995; Weed and Kanwar, 1996; Shipitalo and Edwards, 1993). Logan et al. (1994) found that flow-weighted NO-3–N concentration, NO-3–N mass losses, and percolate volume were essentially the same under the two tillage systems from tile drainage analysis.

Since research on the effects of tillage on NO-3 leaching has produced contradictory results, further experiments based on multi-year continuous observations and improved soil vadose water-sampling methods are needed. Wick lysimeters have been shown to collect approximately 100% of soil percolation water (Zhu et al., 2002), but very little information regarding NO-3 leaching under different tillage systems has been based on research with wick lysimeters. The objectives of this study were to (i) compare the differences in leachate collection by zero-tension pan and passive capillary fiberglass wick lysimeters; and (ii) to determine NO-3 leaching under chisel-till and NT treatments in a 6-yr experiment.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 
The experiment was located at the Russell E. Larson Agricultural Research Center of The Pennsylvania State University in central Pennsylvania. The field soil was a Hagerstown silt loam (fine, mixed, semiactive, mesic Typic Hapludalf) developed from limestone residuum. Selected soil chemical and physical characteristics were given in Jemison and Fox (1992).

From Spring 1988 to Spring 1991, the field was used to estimate NO-3 leaching from manured and unmanured corn (Zea mays L.) as influenced by N fertilizer rates (Jemison and Fox, 1992, 1994). From April 1991 to April 1994, it was used to study NO-3 leaching under continuous N fertilized corn and alfalfa (Medicago sativa L.) (Toth and Fox, 1998). The plots that were planted with alfalfa during the years 1991 to 1994 were the manured corn treatments from 1988 to 1990. In April 1994 the alfalfa was killed with herbicide and plowed under and the entire field was planted with corn. Beginning in 1995, the plots that had been in manured corn and alfalfa became NT, and the plots that had been in tilled continuous corn remained the same tillage treatment (chisel-plowed to a depth of 25 cm followed by disking to 10 cm before planting).

In 1997 a corn–soybean [Glycine max (L.) Merr.] rotation system was introduced into the research, starting with corn in 1997 and ending with soybean in 2000. The target plant density was 64 200 plants ha-1 with a row spacing of 76 cm for corn and 470 000 plants ha-1 with row spacing of 17 cm for soybean. Grain was harvested in October when black layer had formed in the corn kernel or when the soybeans were fully matured and dried in the field (moisture content 10–14%). All plant residue was left on the field. The experiment had two tillage treatments, five N rates on corn, and three replications. The tillage treatments were till (chisel-plowed with disking before planting) and NT. The N rates on corn were 0, 50, 100, 150, and 200 kg N ha-1 as NH4NO3. Nitrogen fertilizer was applied on the soil surface after planting and before corn germination. No N fertilizer was applied to soybean. The experiment was a partially nested design with the blocking factor nested in the tillage treatments (Neter et al., 1996). Within each tillage treatment, the experiment was a randomized complete block design. A total of 30 plots were laid out in the field.

Two lysimeter types, zero-tension pan and passive capillary fiberglass wick lysimeters, were installed in the 0, 100, and 200 kg N ha-1 treatments for the purpose of monitoring NO-3 leaching under different tillage treatments and N fertilizer application rates. Since the experiment had two tillage treatments and three replications, a total of 18 plots were instrumented with lysimeters (18 pan and 18 wick lysimeters).

Zero-tension 76 by 61 cm pan lysimeters were installed in Spring 1988. Lysimeter pits were excavated with a backhoe and plywood support structures were placed in the pits. Lysimeter installation tunnels were excavated from one side of the pits at 1.2 m below the soil surface, and polypropylene bead-filled pans were inserted in the tunnels, leaving 30 cm distance between the pit edge and the pan lysimeter. The pan lysimeters were then raised to the tunnel ceiling with turnbuckle supports. Transparent polyvinyl chloride tubes were used to carry the flow from pan outflow ports to 25-L polypropylene carboys. Detailed installation information can be found in Jemison and Fox (1992).

In April 1995, fiberglass wick lysimeters were installed at the same depth in the lysimeter pits but on the opposite side from the pan lysimeters. The wick lysimeter design was adapted from Holder et al. (1991). A 30 by 30 by 1.3 cm thick plexiglass plate with a 3.2-cm diameter center hole was attached to a pressure treated plywood support structure. The support structures had four threaded rods and turnbuckles at the four corners that allowed the lysimeter surface to be raised to contact the tunnel ceiling soil. Cleaned wick material was evenly spread on the top of the plexiglass plate and passed through the center hole of the support structure to 15-L carboys (wicks were contained in drainage hose to prevent evaporation). Tunnels for lysimeter installation were excavated 65 cm into soil on the opposite side from the pan lysimeters at 1.2-m depth below the soil surface to accommodate the lysimeters plus a 30-cm buffer of undisturbed soil between the pit edge and the lysimeters. The vertical distance from the top of the plexiglass to the bottom of the wick in the collecting jugs was 50 cm, which created up to 50 cm of water tension on the soil. The wick cleaning and installation procedure can be found in Zhu et al. (2002).

Leachate was collected after rain events that were sufficient to cause leaching to a depth of 1.2 m and on the last day of each month to provide monthly leachate data. Nitrate concentration (including nitrite [NO-2]) in leachate samples was analyzed with a Technicon autoanalyzer using a Cd reduction method (USEPA, 1979). The NO-2 concentrations were measured for several batches of leachate samples. The NO-2–N concentrations in leachate never exceeded 1% of the NO-3–N concentrations. Bergstrom (1987) also found that only minimal NO-2 existed in leachate samples. Therefore, the results from the Technicon autoanalyzer were considered as NO-3–N. The flow-weighted NO-3–N concentrations for different periods were calculated by summing up NO-3–N masses collected for the periods divided by the total leachate volume collected in the corresponding periods. For example, 6-yr growing season (May to October) flow-weighted NO-3–N concentration is the NO-3–N mass collected in leachate in six growing seasons divided by the leachate volume collected in the same periods. The leaching year was defined as from May through the next April and was given the name of the starting year.

Leachate collection efficiencies for individual lysimeters were used to correct the NO-3–N mass collected by both pan and wick lysimeters. The corrected NO-3–N mass in leachate was calculated by dividing the collected NO-3–N mass for a period by the leachate collection efficiency of individual lysimeters for the same period. Thus the corrected annual and multi-year NO-3–N masses from a lysimeter were calculated by dividing the NO-3–N masses collected annually or for a period of multi-years by the leachate collection efficiencies for the same year or the same multi-year period. The leachate collection efficiencies were estimated using a water balance method (Zhu et al., 2002). The average leachate collection efficiencies for pan and wick lysimeters were 40 and 101%, respectively. Since Radulovich and Sollins (1987) found that pan lysimeter size was a factor affecting the leachate collection efficiencies, the use of leachate collection efficiencies to correct the NO-3–N mass collected in leachate would also correct for lysimeter size effects on NO-3 leaching.

The differences in flow-weighted NO-3–N concentrations and NO-3–N masses in leachate between till and NT were analyzed using the General Linear Model in ANOVA in Minitab software (Minitab Inc., 1997). The LSD values were calculated from the error mean squares in ANOVA analysis and used to separate the differences of mean values. Year was not considered as a factor in the ANOVA analysis because of the confounding of the year factor with the crop factor due to crop rotation. Therefore, each individual year or a period of four corn years, two soybean years, and 6-yr total were analyzed separately. A paired t test was used to determine the differences between pan and wick lysimeters. A studentized deleted residual test was used to determine outliers in data sets.


   RESULTS AND DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
CONCLUSIONS
 REFERENCES
 
Anomalous High NO-3–N Concentrations in Leachate
There were seven pan lysimeters where for some samplings the leachate NO-3–N concentrations were considerably higher than would be expected for ordinary agricultural fields. These high readings occurred over various time periods and were recurrent in nature. Using a studentized deleted residual test, these high NO-3–N concentrations were detected as outliers. These pan lysimeters included those installed in one plot of the 0 N tilled treatment, two plots of the 0 N NT treatment, three plots of the 100 kg N ha-1 tilled treatment, and one plot of the 100 kg N ha-1 NT treatment. The highest observed NO-3–N concentrations in leachate from these lysimeters were 237 mg L-1 for the 0 N tilled treatment, 102 and 179 mg L-1 for the two 0 N NT treatments, 69, 140, and 414 for the three 100 kg N ha-1 tilled treatments, and 250 mg L-1 for the 100 kg N ha-1 NT treatment. The cause of the excessively high NO-3–N concentrations in leachate was probably the result of mice, ground hog, or skunk activity around the lysimeters, since we occasionally saw them in the lysimeter pits.

There were no excessively high NO-3–N concentrations in leachate found in the first 3 yr of this long-term NO-3 leaching monitoring facility (Jemison and Fox, 1994). Three of the seven lysimeters with excessively high NO-3 levels in our study also had exceptionally high NO-3–N concentrations in the second phase of the experiment (Toth and Fox, 1998). This indicates that in central Pennsylvania pan lysimeters used for long-term studies may need special measures to protect them from being affected by nuisance animals. The longer the time after installation, the more vulnerable the lysimeters are to being affected by animal activities. This view is contradictory to the traditional understanding that the longer a lysimeter is installed, the more representative the soil flow will be of native flow.

Since seven pan lysimeters had anomalously high NO-3–N concentrations, in the following discussion comparing the differences in NO-3–N concentrations and masses collected by pan and wick lysimeters, we excluded these outlier lysimeters and only compared the remaining 11 normally functioning pan lysimeters with the corresponding 11 wick lysimeters installed in the same lysimeter pits as the pan lysimeters to attain a more realistic interpretation of the data.

Nitrate-N Concentrations and Masses in Leachate: Pan vs. Wick Lysimeters
Differences in NO-3–N concentrations between pan and wick lysimeters were generally not significant at the 0.05 level (Table 1). The 11 pairs of 6-yr growing season flow-weighted NO-3–N concentrations, 6-yr nongrowing season (November to April) flow-weighted NO-3–N, and the overall 6-yr flow-weighted NO-3–N concentrations were not significantly different between pan and wick lysimeters. For the six individual years, there was no significant difference between pan and wick lysimeters in flow-weighted NO-3–N concentrations for either season or on an annual basis for 4 out of 6 yr. In the 1995 leaching year, pan lysimeters had significantly greater flow-weighted NO-3–N concentrations than that of wick lysimeters for the growing season and on an annual basis. However, the opposite was true in 1998 when wick lysimeters yielded significantly higher NO-3–N concentrations than pan lysimeters in the growing season and on an annual basis.


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  		Table 1. Mean flow-weighted NO-3–N concentrations in leachate collected by 11 pairs of pan and wick lysimeters.{dagger}

 
The leachate collection efficiency corrected NO-3–N masses (LCNM) collected by pan and wick lysimeters were also generally not significantly different (Table 2). With seven outliers excluded, the difference in total LCNM collected in the whole 6-yr experiment period was not significantly different between pan and wick lysimeters for the remaining 11-pairs of pan and wick lysimeters. For the individual 6 yr, no significant differences in LCNMs were found between pan and wick lysimeters in 4 out of 6 yr. As in the case of flow-weighted NO-3–N concentrations, pan lysimeters collected significantly more LCNM than did wick lysimeters in the 1995 leaching year, but in 1998 wick lysimeters collected more NO-3–N mass than did pan lysimeters. It should be noted that the above conclusion was based on the LCNM. If leachate collection efficiencies were not used to correct the collected NO-3–N masses in leachate, wick lysimeters collected significantly greater NO-3–N masses in leachate than pan lysimeters because wick lysimeters collected significantly more leachate on an area basis than did pan lysimeters (Zhu et al., 2002).


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  		Table 2. Mean leachate collection efficiency corrected NO-3–N masses collected by 11 pairs of pan and wick lysimeters.{dagger}

 
Based on the analysis above, at most times when corrected for leachate collection efficiency, both pan and wick lysimeters collect equivalent amounts of NO-3–N mass lost through leaching and there were essentially no consistent differences in flow-weighted NO-3–N concentrations and LCNM collected by pan and wick lysimeters. Therefore, in the following analysis, when we discuss NO-3–N concentration and mass in leachate, we will only use wick lysimeter data. By doing this we can avoid the complications of the anomalous high NO-3–N concentrations in the seven pan lysimeters discussed previously. However, we will still use the leachate volume data because leachate volumes were presumably less affected by the animal activity in the field.

Leachate Volume
Wick lysimeters collected significantly more leachate than pan lysimeters (Zhu et al., 2002). On average, pan lysimeters collected about 40% of the percolation water and wick lysimeters collected approximately 100%. For both pan and wick lysimeters, most of the leachate was collected during the nongrowing season. A paired t test for leachate volumes between growing seasons and nongrowing seasons for each lysimeter type showed that the P values were below 0.001 for all years and both lysimeter types, except for the 1998 leaching year. Excluding the 1998 leaching year, on average, wick and pan lysimeters collected 76% (standard deviation 12%) and 80% (standard deviation 16%), respectively, of the annual leachate during the nongrowing seasons. For the 1998 leaching year, the leachate collected during the non-growing season was equivalent to that during the growing season for both lysimeters. This was likely because of the dry weather from September to November 1998. The precipitation in this period was only about one-third of normal. Because of this dry period the precipitation in the following months was mainly used to replenish the profile soil water deficit and thus significantly reduced the leachate volume during the nongrowing season.

Analysis of variance showed that N rates had no significant effect on annual and 6-yr total leachate volumes (data not shown). At the 0.05 significance level, tillage had no effect on 6-yr total leachate volumes for either lysimeter type (Table 3). For the wick lysimeters, tilled treatments had greater annual leachate volumes than NT in four out of six individual years, but in only 1 yr was the difference significant. The 6-yr average annual leachate volume (6-yr total leachate volume divided by 6) was greater in till than in NT, but the difference was not significant at the 0.05 level. For the pan lysimeters, NT had greater annual leachate volumes than till in all 6 yr and the differences were significant in 4 out of 6 yr. However, the difference in 6-yr average annual leachate volumes was not significant at the 0.05 significance level.


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  		Table 3. Leachate volumes as a function of tillage and year.

 
Tillage effects on leachate volumes collected by pan and wick lysimeters were influenced by season. During the nongrowing season, wick lysimeters collected more leachate from till than from NT in all 6 yr, but the differences were significant in only 2 yr (Table 3). The 6-yr average nongrowing season leachate volumes were significantly greater in till than in NT, but no such difference was observed in the growing season. Pan lysimeters collected more leachate in NT than in till treatments in all six growing seasons. The difference was significant at the 0.05 level for the growing seasons of five individual years and the 6-yr average, but in the nongrowing season there was a significantly higher leachate volume (at the 0.05 level) in the NT only in 2 yr.

Differences in macropore flow between tillage treatments is probably the main reason why there was more leachate collected by the pan lysimeters in the NT than in the till during the growing season but not during the nongrowing season. One of the main conduits of soil moisture into pan lysimeters is through macropore flow. It has been shown that there is more macropore flow in NT soil than in tilled soil (Singh and Kanwar, 1991; Chan and Mead, 1989; Drees et al., 1994; Gantzer and Blake, 1978). During the growing season, the tillage operation before planting in the till treatment filled or smeared the soil macropores, but in NT the macropores were still open and possibly even bigger because of the soil drying. The precipitation in the relatively intense rains in summer thunderstorms could thus rapidly flow downward to the pan lysimeters in the NT soils. Edwards et al. (1992) and Shipitalo et al. (2000) observed that intense rainstorms enhance macropore flow. In the nongrowing season, soil structure would have recovered to some extent in tilled soil during the more than 6 mo since it was tilled. In addition, soil macropores would more likely be partially closed because of soil swelling (higher soil moisture content than in the growing season) or sealed by ice. Corwin et al. (1991) indicated that there was more macropore flow in summer than in winter. Therefore, differences in macropore flow between tillage treatments were not as great in the nongrowing season as in growing season. Staver et al. (1988) and Shipitalo et al. (2000) also observed that NT yielded more leachate than till during the growing season but not in the nongrowing season.

Wick lysimeters did not collect significantly more leachate in NT than in tilled plots during the growing season. This is probably because wick lysimeters collect both macropore flow and soil matrix water held at potential between 0 and 50 cm of water tension (Holder et al., 1991), so collected leachate volume by the wick lysimeters would not be as affected by macropore flow as were the pan lysimeters where there was a significant difference in volume collected between tillage treatments.

As discussed above, tillage effects on percolation water differ between the two types of leachate collection lysimeters. Since zero-tension pan lysimeters collect mainly macropore flow, use of zero-tension pan lysimeters to monitor tillage effects on percolation water will favor NT soil producing more leachate than tilled soil. This will be especially true if pan lysimeters are used shortly after tillage operations or in an intense rainfall simulation experiment. Since passive capillary wick lysimeters collect both soil macropore and matrix flows, the leaching results from wick lysimeters will better represent what is actually occurring in the field. Our wick lysimeters have been shown to collect nearly 100% of the percolation water, compared with pan lysimeters that only collect 40% of the percolation water (Zhu et al., 2002). Our lack of difference in wick lysimeter leachate volume under the two tillage treatments supports the conclusion of Shipitalo et al. (2000) that tillage has no major effect on the volume of percolation water.

Nitrate-N Concentrations and Mass Losses in Leachate
The flow-weighted NO-3–N concentrations in the till and NT treatments were compared for the periods of the whole 6-yr, 4-yr corn, 2-yr soybean, and individual 6 yr, and their correspondent growing and nongrowing seasons. Tillage treatment had no significant effect at the 0.05 probability level on average 6-yr growing season, 6-yr nongrowing season, and 6-yr total flow-weighted NO-3–N concentrations. There were also no significant differences between tillage treatments when comparing the average growing season, nongrowing season, and total flow-weighted NO-3–N concentrations for the 2-yr soybean and 4-yr corn (total NO-3–N mass collected in leachate in different seasons during a 2- or 4-yr period divided by the total leachate volume collected in the same period). For the individual 6 yr, all average annual flow-weighted NO-3–N concentrations in till and NT were also not significantly different. The only significant difference between till and NT was the average flow-weighted NO-3–N concentration in the 1996 nongrowing season, when the tilled treatment had greater flow-weighted NO-3–N concentrations than NT. The flow-weighted NO-3–N concentrations for the 4-yr corn and 2-yr soybean under different tillage treatments and N rates are shown in Table 4.


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  		Table 4. Mean flow-weighted NO3–N concentrations and annual NO-3–N mass losses in leachate for the till and no-till treatments measured with wick lysimeters.{dagger}

 
There was no significant difference in leachate collection efficiency corrected NO-3–N mass losses between till and NT in any year, for the average of 4-yr corn or 2-yr soybean or the whole 6-yr experiment. The average NO-3–N mass losses for the 4-yr corn and 2-yr soybean under different tillage treatments and N rates (Table 4) were higher than the reported 10 to 40% of applied N (Jemison and Fox, 1994; Toth and Fox, 1998; Owens et al., 2000). High NO-3–N losses obtained in this experiment were probably because of higher than normal precipitation in 1996 and 1997, which were about 20 to 25% higher than the 108-yr average.


   CONCLUSIONS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
REFERENCES
 
Pan and wick lysimeters collected equivalent amounts of NO-3–N in leachate when the collected NO-3–N masses were corrected by lysimeter leachate collection efficiencies. Average flow-weighted NO-3–N concentrations in leachate collected by both lysimeter types were also not different. However, since pan lysimeters had been used for more than 10 yr, animal activity around the lysimeters had apparently caused excessively high NO-3–N concentrations in some samples collected from seven pan lysimeters. The increasing number of affected lysimeters with time indicated that pan lysimeters might need protection to keep an experiment design intact in situations similar to ours. Tillage had no significant effect on NO-3 leaching over a multiyear period. Total leachate volumes collected by both pan and wick lysimeters during the 6-yr experiment period were not significantly different between till and NT at the 0.05 significance level. However, pan lysimeters collected significantly greater leachate volume from NT than from till in the growing season, indicating that monitoring of NO-3 leaching from different tillage treatments for short time periods and use of different soil water sampling devices might produce different results. Flow-weighted NO-3–N concentrations and NO-3–N mass losses in leachate were generally not different between till and NT. Flow-weighted NO-3–N concentrations under corn were generally <5 mg L-1 at the 0 N rate, <10 mg L-1 at the 100 kg N ha-1, and >20 mg L-1 at the 200 kg N ha-1 rates. From the results we can conclude that NT will not result in more NO-3–N leaching than chisel-tillage over a multiyear period.

Received for publication October 3, 2002.


   REFERENCES
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 





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