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Published online 11 April 2006
Published in Agron J 98:436-442 (2006)
DOI: 10.2134/agronj2005.0063
© 2006 American Society of Agronomy
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Production Papers

Tillage x Maize Hybrid Interactions

Sjoerd W. Duikera,*, James F. Haldeman, Jr.b and David H. Johnsonc

a Dep. of Crop and Soil Sciences, Pennsylvania State Univ., 116 ASI Building, University Park, PA 16802-3504
b The Monsanto Company, 269 Pine View Lane, York, PA 17403
c Pennsylvania State Univ. Southeast Agricultural Research and Extension Center, 1446 Auction Road, Manheim, PA 17545

* Corresponding author (swd10{at}psu.edu)

Received for publication March 2, 2005.

   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 
Continuous maize (Zea mays L.) yields may be depressed with no-tillage (NT) compared with conventional chisel and disking systems (CD). Shallow or deep in-row tillage (ST and DT, respectively) may help alleviate this yield reduction, whereas some hybrids may be better adapted to NT. We therefore evaluated five maize hybrids with NT, ST, DT, and CD from 2002 to 2004 on a Hagerstown silt loam (fine, mixed, semiactive, mesic Typic Hapludalf) in southeastern Pennsylvania. Residue cover, penetration resistance, bulk density, and soil temperature were measured as well as maize emergence, mid-season height, and yield. Residue cover varied in the order NT > ST and DT > CD. Bulk density and penetration resistance in NT were higher than in ST, DT, and CD to the depth of tillage. In 2002, the average soil temperature during the first month after planting varied in the order NT < ST and DT < CD, but did not vary between tillage systems in 2004. Emergence was slower in NT than the other tillage systems in 2002 only. Emergence varied between hybrids, but there was no tillage x hybrid interaction. Mid-season maize height was not lower in NT than the other tillage systems. Tillage systems did not affect yield, and there was no tillage x hybrid interaction for yield, although some hybrids yielded better than others. The study suggests continuous maize yields with NT will be similar to tilled systems on well-drained soils in the northeastern USA and that tillage system is not important for hybrid selection.

Abbreviations: CD, chisel and disk tillage • DT, deep in-row tillage • NT, no-tillage • ST, shallow in-row tillage


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 
NO-TILLAGE has many economic and environmental benefits over conventional tillage, such as lower labor and fuel needs, reduced soil erosion, reduced runoff, increased soil organic C contents, and increased soil biological activity (Filipovic et al., 2004; Dabney et al., 2004; West and Post, 2002; Souza Andrade et al., 2003); however, NT is used on only 30% of planted acres in the northeastern USA (Conservation Technology Information Center, 2004).

One reason for low NT adoption may be reduced crop yields compared with conventional tillage. Crop yield differences between conventional tillage and NT depend on climatic region, soil type, and crop rotation (Hill, 2000). Research suggests that continuous maize yields obtained with NT should at least equal those obtained with conventional tillage on well-drained soils at lower altitudes in much of the northeastern USA (Hill, 2000; Dick et al., 1997; Cox et al., 1990, 1992; Karlen et al., 1991).

Reduced NT maize yields compared with conventional tillage have been reported in eastern Canada and northern parts of the Corn Belt as well as on poorly drained soils in general (Dick et al., 1997; Vyn et al., 1994; Griffith et al., 1973, 1988). The yield reductions are usually limited to maize planted into maize or small grain cover crop residue. The reason for reduced maize yields may be a combination of reduced soil temperatures and allelopathic effects of maize or cover crop residue on the following maize crop, resulting in slow or uneven emergence and early growth (Burgess et al., 1996; Hayhoe et al., 1993; Cox et al., 1992; Griffith et al., 1988). Removal of residue from the row or in-row shallow tillage can help to increase soil warming and reduce allelopathic effects, thus alleviating the potential yield reduction in NT compared with conventional tillage (Raimbault et al., 1991). Another reason for reduced crop yields with NT compared with conventional tillage is soil compaction below the A horizon. This phenomenon is particularly common in the Coastal Plain and Tennessee Valley regions of the southeastern USA, and can be overcome with annual use of deep tillage (Raper et al., 1998, 2000; Busscher et al., 1986; Camp et al., 1984).

Maize hybrids may vary in their sensitivity to cold, wet soils or to soil compaction. In the 1980s there was much concern about the adaptability of maize hybrids bred in conventional tillage environments to the cooler and more moist soils under conservation tillage. In an evaluation of 60 commercial hybrids grown in Iowa, Newhouse and Crosbie (1986) did not observe a tillage x hybrid interaction effect on grain yield. In a later study, however, they found significant tillage x genotype interactions in progeny of one maize synthetic (Newhouse and Crosbie, 1987). Francis et al. (1986) found minimal hybrid x tillage system interactions among 19 sorghum [Sorghum bicolor (L.) Moench] hybrids tested in Nebraska. Meese et al. (1991), on the other hand, observed a significant yield reduction in continuous NT maize compared with conventional tillage with one hybrid, but not with another hybrid. Hayhoe et al. (1996) showed there are differences in the response of maize hybrids to low seedbed temperatures. Ressia et al. (2003) observed a signficant tillage x maize hybrid interaction for yield. These mixed reports suggest there may be some hybrids that are better adapted to an NT environment than others.

In this study, we evaluated crop growth and yield of five hybrids with NT, ST or DT, and CD. The soil used in this study is representative of deep limestone-derived soils intensively used for agriculture in the northeastern USA. We included maize hybrids that are or are not recommended for conservation tillage. The hypotheses we tested were that: (i) maize yield in NT would equal that in the other tillage systems on this soil, and (ii) hybrids recommended for conservation tillage would produce similar or higher yields in NT than CD, ST, or DT, whereas those not recommended for conservation tillage would produce lower yields with NT than with the other tillage systems.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 
Field Operations and Treatments
The experiment was started in 2002 on a Hagerstown silt loam at the Pennsylvania State University Southeast Research and Extension Center in Landisville, Lancaster County, Pennsylvania (40°05'43'' N, 76°24'37'' W; 126-m altitude). Average annual precipitation is ~1038 mm and average annual temperature is 11°C (Waltman et al., 1997). Monthly precipitation varies from 76 to 123 mm during the maize growing season. The experimental field has a history of conventional tillage (moldboard and chisel plowing and disking), but was not tilled in 2001. A cover crop of sorghum–sudangrass [Sorghum x drummondii (Steud.) Millsp. & Chase] was planted in July of 2001. The cover crop winterkilled when it was approximately 50 cm tall.

The experiment was a split-plot design with four randomized complete blocks. Tillage systems were main plots and maize hybrids were subplots. Subplots were 3.0 m wide by 5.3 m long. The tillage plots were maintained in their same locations every year, but the subplots for the maize hybrids were rerandomized within each tillage plot every year. The tillage treatments were as follows:

No-tillage: no soil disturbance was done except to plant the crop.
Shallow in-row tillage: A Rawson Zone-Tillage cart (Unverferth Mfg. Co., Kalida OH) was used to create shallowly tilled zones. The zone-till cart had three 41-cm-diam., 13-wave fluted coulters centered at 76 cm that tilled a 15-cm-wide by 15-cm-deep zone in which maize was planted. In 2004, the Zone-Tillage cart was unavailable and ST was done with the DT unit set to a depth of 12 cm.
Deep in-row tillage: A Case-IH Ecolo Til 2500 unit (Case-IH, Racine, WI) was run set to a depth of 40 cm. In 2002, the DT unit was equipped with minimum residue disturbance shanks with 6'' Tiger points (Case-IH, Racine WI), two offset disk-hillers, and a rolling basket behind each shank. In 2003 and 2004, the Ecolo Til 2500 was mounted with no-till shanks with 8'' no-till points and DMI Berm Tuck'rs (all manufactured by Case-IH) to maintain higher crop residue cover.
Chisel plowing and disking: The soil was tilled to a depth of 15 cm with a chisel plow mounted with twisted shanks, and one pass was made with a disk harrow and cultipacker combination tool consisting of two gangs of offset disks working the soil to approximately 10 cm. All tillage operations were done in the spring shortly before planting at near-optimal soil moisture conditions.

The hybrids planted were DKC53-34, DKC58-24, DKC60-09, DKC60-19, and DKC64-11 (Monsanto Co., St. Louis, MO). All five hybrids are Round-Up Ready/Yield Guard hybrids (resistant to glyphosate [N-(phosphonomethyl)glycine] and European maize borer [Ostrinia nubilalis (Hubner)]). Some characteristics of these hybrids from the 2004 DeKalb catalog are reproduced in Table 1. Three of the hybrids were marketed as "residue proven" (recommended for NT), whereas two of the hybrids were not. Residue-proven hybrids are selected for strong emergence, enhanced disease resistance, and high yields under high-residue conditions.


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  		Table 1. Characteristics of maize hybrids used in hybrid x tillage interaction study on a Hagerstown silt loam in southeastern Pennsylvania (from 2004 DeKalb seed catalog{dagger}).

 
Maize was planted approximately 4 cm deep on 8 May 2002, 5 May 2003, and 11 May 2004 at 76-cm row spacing. Each year, crop rows were shifted by 38 cm sideways from the previous year's rows. In 2004, the rows were again in the same location as in 2002. All plots were planted with a four-row John Deere Max Emerge planter (John Deere, Moline, IA) with 13-wave fluted coulters in front of double-disk seed slot openers equipped with Keaton seed firmers (Keaton Precision Planting, Tremont, IL), followed by rubber closing wheels. No residue cleaners were used in this trial. Stands were thinned to 64 000 plants ha–1 approximately 1 mo after planting. Starter fertilizer was injected 5 cm beside and 5 cm below the seeds with a smooth, offset disk mounted on the planter. Starter fertilizer rates were: 112 kg ha–1 7–21–7 (N–P2O5–K2O) in 2002, 112 kg ha–1 8–24–8 in 2003 and 112 kg ha–1 7–21–14 in 2004. Nitrogen fertilizer was surface applied at a rate of 180 kg ha–1 N shortly before tillage in all years (formulation was NH4NO3 in 2002, urea–NH4NO3 solution in 2003, and urea granules in 2004). No extra P or K fertilizer was needed based on Pennsylvania State University soil fertility recommendations. In-row insecticides for maize rootworm [Diabrotica barberi (Smith and Lawrence) and D. virgifera (Le Conte)] applied at planting were: in 2002 and 2004, 6.7 kg ha–1 of Force [0.2 kg ha–1 2,3,5,6-tetrafluoro-4-methylphenyl)methyl-1{alpha},3{alpha})-(Z ±)-3-(2-chloro-3,3,3-trifluoro-1-propenyl)-2,2-dimethylcyclopropanecarboxylate], and in 2003, 6.7 kg ha–1 Aztec [0.13 kg ha–1 O-[2-(1,1-dimethylethyl)-5-pyrimidinyl]-O-ethyl O-(1-methylethyl) phosphorothioate plus 0.07 kg ha–1 cyano(4-fluoro-3-phenoxyphenyl)-methyl 3-(2,2-dichloroethenyl)-2,2-dichloroethenyl)-2,2 dimethylcyclopropanecarboxylate].

Weed control was obtained with one burndown and one post-emergence application of herbicide in all years. Crop scouting indicated low weed levels in all years. In 2002, preplant weed control was obtained with Roundup Ultramax (Monsanto Co., St. Louis, MO) applied at 0.81 kg ha–1 glyphosate before planting, followed by one application of Roundup Ultramax plus HarnessXtra (Monsanto Co.; 1.30 kg ha–1 acetochlor [2-chloro-N-(ethoxymethyl)-N-(2-ethyl-6-methylphenyl)acetamide] + 1.05 kg ha–1 atrazine [6-chloro-N-ethyl-N'-(1-methylethyl)-1,3,5-triazine-2,4-diamine]) applied in early June. In 2003, preplant weed control was achieved with Roundup Weathermax (Monsanto Co.; 1.12 kg ha–1 glyphosate) plus 2,4-D (0.56 kg ha–1 [2,4-dichlorophenoxy)acetic acid]) applied shortly before planting, and Roundup Weathermax plus HarnessXtra applied in June. In 2004, weed control was obtained with Roundup Weathermax plus 2,4-D LVE (0.56 kg ha–1 a.i.) applied shortly before planting, and Roundup Weathermax plus HarnessXtra mixed with 2.24 kg ha–1 (NH4)2SO4 applied in June.

Crop and Soil Measurements and Analyses
Emergence in the two center rows of each plot was counted in the first 2 wk after planting, and expressed as a percentage of seeds planted. Maize height was determined in each subplot as the average height to the curvature of the highest leaf approximately 7 wk after planting. Maize yield (expressed at 15.5% moisture) was determined by harvesting the two middle rows of each plot with a plot combine.

All crop residue was left uniformly spread in the field. Residue cover was estimated independently by two of us using the photo comparison method of pictures taken shortly after planting in each tillage plot (Al-Kaisi and Hanna, 2002).

Bulk density was determined on 28 May 2004 to a depth of 20 cm in two different locations in the rows of tillage main plots with a moisture–density gauge (Model 3411B, Troxler Intl., Research Park, NC).

Penetration resistance was measured at least five times in the row of each tillage main plot to a depth of 42.5 cm on 17 May 2002 with a Physical Property Penetrometer (MidWest Independent Soil Samplers, Buffalo Lake, MN) and on 28 May 2004 with a Field Scout SC-900 recording penetrometer (Spectrum Technologies, Plainfield, IL). The Physical Property Penetrometer has a 60° 2-cm-diam. tip and 7-cm sleeve device to measure both penetration resistance and sleeve stress. Sleeve stress varies with soil texture; however, we assumed sleeve stress to be constant, and penetration resistance to be the sole variable. This device was calibrated as specified in the user manual using a standard penetrometer with a 30°, 12.8-mm-diam. tip. The Field Scout has a 30°, 12.8-mm-diam. tip. Rainy, overcast conditions prevailed before penetration resistance measurements. For example, in 2002, 74 mm of precipitation fell distributed over 8 d preceding measurements and, in 2004, 38 mm fell distributed over 10 d before measurements. It was therefore assumed that the soil was near field capacity in all treatments at the time of penetration resistance measurement.

Soil temperature was measured every hour by Watchdog Model 100-Temp2K dataloggers (Spectrum Technologies, Plainfield, IL). Temperature sensors were installed immediately after planting in plots planted to hybrid DKC60-19. The sensors were installed by opening a small hole in the soil, then creating a horizontal slot at 5-cm depth by gently prying the soil open with a knife. The sensors were inserted with the sensor facing downward. Care was taken not to loosen the soil around the sensor, which could have influenced temperature readings. Average daily soil temperature was calculated for the first 30 d after planting by averaging 24 hourly readings for each day. Maximum and minimum soil temperature represent the maximum and minimum temperature recorded at one of the 24 h of a particular day.

All data were analyzed with PROC GLM in SAS (SAS Institute, 2001). A split-split plot analyis for randomized complete block was used to calculate significance of the effects of years, tillage, and hybrids and their interactions on maize emergence, height, and yield, using the appropriate error terms to calculate F-factors (Gomez and Gomez, 1984). Effects of years and tillage treatments on crop residue cover were calculated as a split-plot analysis, with tillage as subplots (Gomez and Gomez, 1984). The effect of tillage on soil temperature was calculated with days after planting constituting subplots in a split-plot design as well as a randomized complete block design for each day that soil temperature was measured (Gomez and Gomez, 1984). Tillage effects on penetration resistance and bulk density were calculated separately for each depth as a randomized complete block design. Fisher's protected LSD at the 0.05 level was used to determine significant differences between means (Gomez and Gomez, 1984).


   RESULTS AND DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
CONCLUSIONS
 REFERENCES
 
Soil
Crop residue cover varied significantly among years and among tillage systems within years (Table 2); however, there was no year x tillage interaction, indicating that the relative effect of the tillage tools was the same in each year. The field had been planted to sorghum–sudangrass that frost-killed before it reached full stature in 2001, and maize yields were low in 2002. There was, therefore, little residue present in 2002 and 2003 (Table 2). Maize yields were high in 2003, explaining the highest amounts of residue cover in 2004. In all years, residue cover in NT and ST exceeded 30%, the threshold distinguishing conservation tillage from conventional tillage (Conservation Technology Information Center, 2004). The DT system left <30% residue cover in 2002, but >30% in 2003 and 2004. As explained above, a different setup of the DT unit was used after 2002 to maintain higher residue cover. In all years, <30% residue cover was measured with the CD system, which did not qualify as conservation tillage.


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  		Table 2. Effects of four tillage systems on residue cover in the first, second, and third years of study on a Hagerstown silt loam in southeastern Pennsylvania.

 
In both 2002 and 2004 (Fig. 1 ), penetration resistance never exceeded 2.0 MPa, above which root growth is considered to be completely inhibited, but it did exceed 0.7 MPa, above which root growth has been shown to be reduced (Taylor et al., 1966). Penetration resistance measured in the spring of 2002 was significantly higher in the surface 15 cm of NT than in the other tillage systems. The penetration resistance profile of ST was almost identical to that of CD to the measured depth. Reduced penetration resistance below 15 cm was measured with DT compared with the other tillage systems. In the spring of 2004, penetration resistance profiles of all tillage systems were similar to 2002 profiles with the exception of DT. In 2003 and 2004, the different DT tillage tool used caused less surface soil disturbance. Surface soil penetration resistance in 2004, therefore, also tended to be slightly higher in DT than in ST and CD, although it was still lower than in NT. Higher penetration resistance in NT than the other tillage systems is often observed (Raper et al., 1998; Busscher and Sojka, 1987; Busscher et al., 1986; Dickey et al., 1983). There are some studies that report no higher penetration resistance in NT than with tillage, but this is probably because soil reconsolidated between the tillage event and the time of penetration resistance measurement in tillage plots (Lal and Fausey, 1993; Cox et al., 1992).


Figure 1
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  		Fig. 1. Effects of four tillage systems on penetration resistance measured shortly after planting on a Hagerstown silt loam in southeastern Pennsylvania in 2002 and 2004.

 
Bulk density in the 0- to 10-cm depth was highest (1.40 Mg m–3) in NT, intermediate (1.31 Mg m–3) in DT, and lowest (1.26 Mg m–3) in ST and CD systems (data not shown). At 10- to 20-cm depth, bulk densities in NT, ST, and CD were the same (1.55 Mg m–3), whereas it was significantly lower (1.49 Mg m–3) in the DT treatment. Higher bulk density with NT than with tillage is not always recorded (Lal and Fausey, 1993; Follett and Peterson, 1988; Hill and Cruse, 1985). In most of these cases, bulk density was measured a substantial time (6 mo–1 yr) after the tillage event. Franzluebbers et al. (1995) have shown that bulk density in tilled soil increases after the tillage event until it equals that in NT. The rate of reconsolidation may depend on soil properties such as soil texture and structural stability, rainfall, and post-tillage traffic intensity.

Average soil temperature at the 5-cm depth in the 30 d after planting was significantly affected by tillage system only in 2002 (P = 0.01); therefore, only data for 2002 are presented (Fig. 2 ). The average soil temperature in the first week after planting did not differ significantly between tillage systems (with the exception of the first day), probably due to cloudy conditions. After the first week, however, soil temperature in CD was usually higher than that in NT, whereas soil temperature in ST and DT was between these two extremes. The average daily soil temperature in the first month after planting was highest in CD (21.1°C), intermediate in DT and ST (both 20.7°C), and lowest in NT (20.2°C). Although these differences are not great, soil temperature in CD was significantly higher than that in DT and ST (with the same soil temperature), which had significantly higher soil temperature than NT. A decreased average surface soil temperature in NT compared with conventional tillage has been observed by other researchers as well (Moroizumi and Horino, 2002; Hayhoe et al., 1996; Fausey and Lal, 1989).


Figure 2
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  		Fig. 2. Effects of four tillage systems on average daily soil temperature at the 5-cm depth during the first 30 d after maize planting on a Hagerstown silt loam in southeastern Pennsylvania in 2002. Significance of soil temperature differences on one date are indicated by letters placed in the same order above that date's soil temperature measurements. If letters are the same, there is no significant difference (LSD at the 0.05 level).

 
Tillage affected maximum soil temperature significantly at the P = 0.07 level (data not shown). Differences in maximum temperature due to tillage system were greater than differences in mean temperature. The average maximum daily soil temperature in the month after planting was 28.5°C in CD, 27.8°C in ST, 26.8°C in DT, and 25.8°C in NT. These values were all significantly different from each other (LSD at the 0.05 level). Minimum temperature was not affected by tillage system. The differences in temperature due to tillage are usually greatest in the early afternoon, when the sun is at its zenith (Fausey and Lal, 1989; Unger, 1988). Some researchers observed higher minimum soil temperatures under NT than conventional tillage, which can be explained by reduced heat loss of the mulch-covered soil at night (Franzluebbers et al., 1995; Fausey and Lal, 1989). Absence of a tillage effect on minimum temperature in our study may be related to the moderate cooling conditions of Pennsylvania nights. Cooling will be less if skies are overcast or air is humid (Unger, 1988).

Our results, therefore, show that soil temperature with CD are likely to be higher than with NT in the month after planting, with the greatest temperature differences in the afternoon. In a year with more frequent overcast conditions, however, soil temperature differences may be nonexistent, as was the case in 2004 in our study. In-row tillage options such as ST and DT can help to raise the soil temperature, but in our case not to the same level as CD.

Crop
Maize emergence was significantly affected by tillage system in 2002 (Table 3), but not in 2003 or 2004 (data not shown), whereas significant differences in emergence between hybrids were present in all years (Table 4). Tillage x hybrid interactions for emergence were not significant in any year, so data were pooled over hybrid or tillage in Tables 3 and 4, respectively. In NT, emergence was significantly delayed until 12 DAP (days after planting) in 2002 in comparison with the other three tillage systems (Table 3). At 15 DAP, emergence was not decreased in NT compared with CD. Emergence at 15 DAP was slightly higher with ST than with NT or CD. Emergence was affected more by hybrid than by tillage. Emergence of DKC64-11 was slowest in 2002 and 60-09 in 2003, and DKC53-34 had the fastest emergence of all hybrids. Emergence of the short-season hybrids DKC53-34 and DKC58-24 was faster than that of the long-season hybrids (Table 4). No relationship was observed between emergence and the "residue proven" logo. In other studies, no relationship was found between maturity rating and emergence (Hayhoe et al., 1996), so maturity–emergence relationships cannot be generalized. Final emergence differences among hybrids were small. In 2004, overall emergence was rapid, with small differences among hybrids. Faster emergence in 2004 was probably due to warmer temperatures after maize planting.


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  		Table 3. Crop emergence and height averaged across five maize hybrids as affected by four tillage systems on a Hagerstown silt loam in southeastern Pennsylvania.{dagger}

 

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  		Table 4. Crop emergence averaged across four tillage systems as affected by five hybrids that differ in having the residue-proven logo.{dagger}

 
There were significant tillage effects on midseason maize height in 2002 and 2004 (Table 3). No significant tillage x hybrid interactions were present for maize height in any year. Despite slower emergence in 1 yr, midseason maize height was not reduced in NT compared with the other three tillage systems (Table 3). Delayed emergence of NT maize had apparently been compensated for by faster growth afterward, similar to the results of studies in the southern Corn Belt (Hill, 2000; Griffith et al., 1988). In-row tillage did not show an advantage in increasing midseason maize growth.

Maize yields varied significantly by year (results not shown). Low precipitation in the summer of 2002 resulted in low yields (average of 4.6 Mg ha–1). Near-optimal rainfall in 2003 and 2004, however, resulted in high yields (average of 9.3 and 9.7 Mg ha–1, respectively). Maize yields were not significantly affected by tillage system in any year (data not shown), but hybrid effects were present (Table 5). No tillage x hybrid interaction effect on yield was present in any year. The absence of a tillage effect on maize yields is similar to results on well-drained soils in the southern and eastern Corn Belt and New York (Hill, 2000; Cox et al., 1992; Dick et al., 1997; Griffith et al., 1973). The three hybrids that generally yielded best in this trial were DKC53-34, DKC60-09, and DKC64-11 (Table 5). There was no correlation between emergence and yield. For example, the hybrid that emerged most slowly in 2003 (DKC60-09) had the same yield as the hybrid that emerged most quickly (DKC53-34). The lack of a tillage x hybrid interaction indicates that hybrid performance was similar in all four tillage systems. The lack of a tillage x hybrid interaction is similar to other reports in the literature (Francis et al., 1986; Newhouse and Crosbie, 1986; Carter and Barnett, 1987), but contrasts with the results of Ressia et al. (2003), Newhouse and Crosbie (1987), and Meese et al. (1991). Our study suggests that it is not important to select hybrids based on tillage system or high-residue conditions.


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  		Table 5. Grain yield averaged across four tillage systems as affected by hybrids that differ in having the residue-proven logo.

 

   CONCLUSIONS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
REFERENCES
 
This study suggests that similar continuous maize yields can be expected with NT, ST, DT, or CD on limestone-derived soils in the northeast USA. Residue cover was highest with NT, lower with ST and DT, and lower than 30% (below the threshold for conservation tillage) with CD. Higher penetration resistance and bulk density under NT than the other tillage systems did not affect maize growth and yield. Lower soil temperatures early in the season and slower emergence occurred in NT in 1 yr, but this did not affect midseason maize height or yield. Although hybrids varied in their yield potential, there was no tillage x hybrid interaction for emergence, midseason height, or yield, suggesting that the tillage system used is not important for hybrid selection.


   ACKNOWLEDGMENTS
 
Many thanks to Wayne Haas and his crew from the PSU Corn Breeding Lab for planting and harvesting this study, Hoober Inc. for performing deep tillage operations, and Unverferth Inc. for loaning us a Zone-Till cart.


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





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