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Published online 3 August 2006
Published in Agron J 98:1257-1264 (2006)
DOI: 10.2134/agronj2006.0070
© 2006 American Society of Agronomy
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Production Papers

Soil Compaction in Conservation Tillage

Crop Impacts

Dilraj Sidhua and Sjoerd W. Duikerb,*

a 2101 Raven Tower, Ct. Apt. 202, Herdon, VA 20170
b Dep. of Crop and Soil Sci., Pennsylvania State Univ., 116 ASI Bldg., University Park, PA 16802-3504

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

Received for publication March 8, 2006.

   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 
Soil compaction effects on maize (Zea mays L.) plant population, height, and yield were studied from 2002–2005 in a no-tillage/in-row tillage study on a Hublersburg silt loam soil (Typic Hapludult) in Pennsylvania. Soil was compacted annually with a three-axle truck with 10-Mg axle load mounted with road tires (700 kPa inflation pressure) or flotation tires (250 kPa). In another treatment, soil was only compacted with road tires in the first year without subsequent compaction. Remediation treatments were deep (40 cm) in-row tillage before or after compaction with road tires and shallow (10 cm in 2002–2003 and 22 cm in 2004–2005) in-row tillage after compaction. Significant yield reductions averaging 17% in 3 yr out of 4 were observed for annual compaction with road tires compared with control (no-tillage without compaction). Compaction with flotation tires reduced yield significantly in 1 yr only. Yield reductions due to compaction disappeared after 1 yr. Deep tillage after compaction increased yield (17%) in 1 yr only, whereas shallow tillage did not increase yields. Yield improvements due to deep tillage were lost if it was followed by heavy traffic. Deep tillage and no-tillage without compaction gave similar yields in the first 3 yr, but no-tillage had higher yield in 2005. In-row tillage substantially reduced residue cover. Our results suggest little need for in-row tillage to manage compaction in long-term no-tillage when axle loads are no more than 10 Mg and flotation tires are used to keep inflation pressures below 250 kPa.

Abbreviations: AFTC, annual flotation tire compaction • ARTC, annual road tire compaction • DTAC, deep tillage after compaction • DTBC, deep tillage before compaction • DTNC, deep tillage no compaction • FRTC, first-year road tire compaction • STAC, shallow tillage after compaction • WAP, weeks after planting


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 
WITH GROWING FARM SIZE in the U.S., the use of heavy machinery is also increasing to improve labor use efficiency and timeliness of field operations. Average tractor weight has increased threefold from 1950 to 2000 (Soane and Ouwerkerk, 1998). Axle loads of 10 Mg are common in many countries (Hakansson and Reeder, 1994). Single-axle grain carts in the U.S. now have axle loads of 15 to 45 Mg (Schuler et al., 2000). One of the potential threats of this increase in equipment size is soil compaction. Soil compaction is the process by which the soil grains are rearranged to decrease void space, thereby increasing bulk density (SSSA, 1997).

Subsoil compaction is a threat due to the increase in axle loads (Hakansson and Reeder, 1994). Although it usually causes smaller yield reductions than surface compaction, subsoil compaction can have much longer lasting effects on subsoil physical properties and crop productivity (Voorhees, 1983). Compaction up to 50 cm was reported when soils varying from sandy loam to clay textures were compacted with 10-Mg axle load at field capacity (Alakukku and Elonen, 1995; Hakansson, 1985; Hakansson and Reeder, 1994; Etana and Hakansson, 1994). Wheat (Triticum aestivum L.) yield reductions up to 38% on a sandy clay loam soil (Ishaq et al., 2001) and maize yield reductions up to 50% in a poorly drained silt loam soil (Gaultney et al., 1982) have been observed. Effects of deep compaction on soil physical properties and crop yields have been found to persist from 6 to 11 yr (Etana and Hakansson, 1994; Gameda et al., 1994; Alakukku and Elonen, 1995).

Surface compaction, caused by high contact pressure (Hakansson and Reeder, 1994), can be alleviated by freezing–thawing and wetting–drying cycles, biological activity, and tillage (Larson and Allmaras, 1971; Voorhees, 1983). Therefore, although the yield reduction due to surface compaction can be large, it is typically of short duration. In the absence of tillage, however, the threat of surface compaction is significant. Low ground contact pressure exerts less stress on surface soil and causes less damage to topsoil physical properties than high-contact pressure (Reeves and Cooper, 1960; Wood et al., 1991).

Soil tillage can partly alleviate compaction, but it also has negative effects. Benefits of no-tillage systems compared with conventional tillage are reduced soil erosion, increased infiltration (Lal and Van Doren, 1990), higher biological activity (Gantzer and Blake, 1978), and lower labor and equipment costs (Duiker, 2004a). Soil compaction is a concern in no-tillage because of absence of alleviation through tillage. Negative effects of compaction on plant growth (Nevens and Reheul, 2003), soil physical properties (Botta et al., 2006; Abu-Hamdeh and Al-Widyan, 1999), and maize yields (Lal, 1996) have been reported in no-tillage systems. On the other hand, long-term use of no-tillage results in increased surface organic matter contents, more stable soil structure, and increased hydraulic conductivity due to worm holes and stable biochannels (Mahboubi et al., 1993; Dick et al., 1991). Reduced compactability due to high organic C contents in the surface soil suggests lower surface-compaction threat in long-term no-tillage (Thomas et al., 1996).

Subsoiling is the process of deep tilling to a depth ranging from 30 to 90 cm (Roa-Espinosa, 1998). It has shown some success in alleviating compaction and improving yields on soils with compacted subsoil (Chen et al., 2005; Box and Langdale, 1984; Reeves et al., 1992; Abu-Hamdeh, 2003), sometimes in combination with the use of cover crops (Schwab et al., 2001). However, all soils do not respond to deep tillage (Raper et al., 2000a, 2000b). To be considered conservation tillage, deep-tillage methods need to leave at least 30% residue cover after planting, preferably leaving two-thirds of the soil surface undisturbed (CTIC, 2004). Specialized in-row tillage tools that do no soil inversion and leave residue largely undisturbed between rows have been developed for this purpose.

Soil compaction is a concern in no-tillage, especially on dairy and livestock farms where traffic intensity is high. For example, in Pennsylvania, the weight of common manure spreaders has increased from 2.5 Mg to 20 to 30 Mg in 20 yr, increasing the threat of subsoil compaction (Duiker, 2004b). Because manure spreaders commonly have multiple axles, axle load usually does not exceed 10 Mg. Because of the cost of labor and the distance to fields, it is now common to use trucks equipped with road tires to transport forages and grain and to spread manure in fields. The reason for using road tires on these trucks is that they allow higher driving speeds on the road than if farm or flotation tires are used. The threat of surface compaction increases due to high contact pressures at the tire–soil interface under road tires. The objectives of this study were therefore to investigate the effects of: (i) soil compaction with heavy axle load and high tire pressure on maize establishment, growth, and yield in a long-term no-tillage field; (ii) flotation tires as a means to avoid surface compaction in no-tillage; and (iii) shallow or deep in-row tillage to alleviate compaction. Our hypothesis was that compaction caused by 10-Mg axle load and 700-kPa inflation pressure under no-tillage conditions would reduce maize plant populations, growth, and yield more than if compaction was followed by tillage. We also hypothesized that flotation tires, which have a much lower contact pressure than road tires, would reduce surface compaction, but because of high axle load, subsoil compaction would still occur and cause yield loss. Finally, in-row shallow tillage was expected to alleviate surface compaction only, whereas in-row deep tillage was expected to alleviate both the effects of surface and subsoil compaction.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 
Experimental Site and Design
The experiment was established on a Hublersburg silt loam (clayey, illitic, mesic Typic Hapludult), a well-drained soil formed from limestone residuum with high chert and clay content in the subsoil (Braker, 1981). The experimental site is located next to the University Airport, State College, PA (40°48' N, 77°52' W; 370 m altitude). The field had been in no-tillage crop production from 1990 to 2001 except in 1998 (fall subsoiling) and 1999 (a light spring disking with a disk harrow). Treatments were laid out in field plots measuring 76 by 9.1 m in a randomized complete block design with four replications. The study was initiated with fall tillage treatments in 2001. The only crop in this experiment was maize grown every year from 2002–2005.

Precipitation and temperature deviations are shown in Table 1. In 2002, the growing season was warmer than normal and drier than normal from July to September. In 2003, rainfall was above normal whereas temperatures were close to average. In 2004, rainfall was above normal and temperatures cooler than normal. In 2005, precipitation was below normal, and temperatures were above normal. The variability in weather between years enabled comparison of treatments in a variety of weather conditions common in central Pennsylvania (Al-Adawi and Reeder, 1996).


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  		Table 1. Monthly precipitation and mean air temperature deviations from 30-yr average for State College, PA, during the growing seasons of 2002–2005.

 
The treatments used in this study are given in Table 2. The annual compaction treatments using trucks with road or flotation tires [ARTC (annual road tire compaction), AFTC (annual flotation tire compaction), DTBC (deep tillage before compaction), DTAC (deep tillage after compaction), and STAC (shallow tillage after compaction)] were performed in the spring of each year before planting. The treatment with compaction in the first year only was compacted in the spring of 2002 but not in subsequent years. Compaction was always performed when the soil moisture content was at or slightly below field capacity. The total weight used on trucks was approximately 30 Mg. The load was uniformly distributed over the three axles of the trucks, resulting in an axle load of approximately 10 Mg of both trucks (whether mounted with road tires or flotation tires). Tire inflation pressure was 700 kPa in road tires and 250 kPa in flotation tires. Multiple passes were made over the plot to compact approximately 100% of the plot surface area one time each spring.


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  		Table 2. Soil compaction and tillage treatments used in study of soil compaction in conservation tillage at State College, PA from 2002–2005.

 
Tillage operations were performed when the soil was dry enough to avoid smearing the sides of the slot created by the subsoiler or to create a cloddy seedbed. Deep in-row tillage was performed annually with an Unverferth Zone Builder (Unverferth Manufacturing Co. Inc., Kalida, OH) to a depth of approximately 40 cm. The Zone Builder had a rippled coulter to cut residues in front of each straight subsoiler shank. Points at the bottom of shanks were no wider than shanks. Behind each shank two fluted coulters were mounted to prepare a narrow seedbed (20–25 cm wide). Shallow in-row tillage was performed with a Rawson Zone-Till Cart (Unverferth Manufacturing Co. Inc., Kalida, OH) for the first 2 yr. Shallow in-row tillage involved creating narrow 10- to 12.5-cm-deep and 15- to 20-cm-wide zones with three fluted coulters. Although these coulters are usually mounted on the maize planter, we did shallow in-row tillage ahead of planting with the cart, which we had on loan from the company during the first 2 yr. In the absence of the Zone-Till Cart, we used the Zone Builder set to the shallowest depth (approx. 22 cm) to do shallow in-row tillage in 2004 and 2005. Deep in-row tillage before road tire compaction was performed to observe if deep-tillage benefits remained when followed by heavy traffic. In this treatment, compaction with road tires caused severe rutting in 2004; hence, those plots were cultivated with a field cultivator in that year to smooth the plots before planting. Because of these problems, this treatment was discontinued in 2005. In 2002 and 2003, no secondary tillage was used in DTBC.

Maize was planted without tillage except in the case of in-row tillage treatments. The row spacing was 76 cm. Field management details are shown in Table 3. Starter fertilizer was applied with the planter. Additional N fertilizer was injected between rows at planting in 2002 but sidedressed in 2003, 2004, and 2005. The low N application in 2002 was based on the N carryover benefit to maize from the soybean crop in 2001 and manure history of the field. In the in-row tillage plots, care was taken to plant maize in the zones prepared by in-row tillage equipment before planting.


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  		Table 3. Crop planting, hybrid selection, and fertilizer application details of a study on soil compaction in conservation tillage at State College, PA from 2002–2005.

 
Crop Measurements
Residue cover was measured in 2003, 2004, and 2005 with the line-transect method (Sloneker and Moldenhauer, 1977; Shelton et al., 1990). Crop residue measurements were taken shortly after maize planting in two locations per plot. In 2003, residue cover was measured only in the control, DTAC, and STAC treatments. Plant populations were counted at harvest each year by counting plants in six approximately 13-m-long sections in the middle six rows of each plot (totaling 76 m). Plant height was measured in 2004 of six representative plants of each of the middle six rows. In total, the height of 36 plants was measured in each plot from the ground level to the base of the last fully opened leaf at two stages. Plant height was determined 6 wk after planting (WAP) and immediately before harvest. Crop yield was determined by harvesting the middle six rows from each plot with a combine. Grain yield was adjusted to 15.5% moisture. All variables were statistically analyzed using PROC GLM in SAS version 8.2 (SAS 2004). Fisher's protected LSD (P ≤ 0.05) was calculated to test the significance of treatment differences.


   RESULTS AND DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
CONCLUSIONS
 REFERENCES
 
Residue Cover
In 2003, the control treatment had the highest residue cover, DTAC had less, and STAC had the lowest residue cover (Table 4). Residue cover was not measured in the other treatments in 2003. The shallow in-row tillage treatment reduced residue cover below the 30% limit, whereas deep tillage almost reduced it to that level. The shallow in-row tillage implement had three fluted coulters per row (compared with only two behind the shank on the deep-tillage tool), which may explain the greater residue reduction resulting from the use of this tool. In 2004, there was generally more crop residue left by the previous crop than in 2003 due to higher yields in 2003 than in 2002. The control had higher residue cover than all other treatments in 2004 except for the first-year road tire and AFTC treatments. Deep tillage after compaction and STAC had residue percentages slightly higher than in 2003. The coulters behind the shank on the in-row tillage tool (which was the same for deep tillage and STAC in 2004) were moved closer together in 2004 and 2005 to avoid excessive residue disturbance. Even with this narrower setting, however, residue cover was reduced to close to 30% in 2004 with both in-row tillage treatments. Despite high yields in 2004, deep and shallow in-row tillage treatments reduced the residue cover to 21 and 18%, respectively, in 2005. These results show that in-row tillage can readily and extensively reduce residue cover below desired levels. Since most environmental benefits of conservation tillage are due to residue cover, this is a concern that has to be addressed by using in-row tillage tools only when needed, and using settings to minimize residue disturbance.


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  		Table 4. Influence of tillage and compaction on residue cover in a study on soil compaction in conservation tillage at State College, PA from 2003–2005.

 
Plant Populations
Final plant stands were significantly reduced in 2002, 2004, and 2005 in the ARTC treatment compared with the control (Table 5). A major reason for reduced plant stands in the ARTC treatment was the compromised planter performance. Road tires and high axle load led to rutting in the field and a somewhat uneven soil surface. In the first year of our study, we used a 12-row planter that had lower ability to compensate for unevenness in the soil surface than the four-row planter used in subsequent years. This was probably one reason that plant populations were reduced more in 2002 than in 2003 and 2004. In 2005, however, reduction in plant population in ARTC was higher than in 2003 and 2004. The first (2002) and last (2005) years of the study had drier summers than 2003 and 2004. Dry soil conditions after compaction are therefore another plausible reason for a decrease in plant population, causing very high surface penetration resistance in compacted soil (especially when compaction was caused by road tires). The planter may have had difficulty cutting into the soil and placing the seeds at the appropriate depth. Stunted root growth may also have caused poor plant development in compacted soil, especially in the dry summers of 2002 and 2005.


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  		Table 5. Effects of soil compaction and tillage on plant populations and crop height in a study of soil compaction in conservation tillage at State College, PA from 2002–2005.

 
Plant population was significantly reduced in AFTC compared with the control in 2002 and 2005 but not in 2003 and 2004. Using flotation tires instead of road tires resulted in higher plant populations in 2 out of 4 yr. Road tires created ruts (up to 5 cm deep), whereas flotation tires did not. The greater surface unevenness after compaction with road tires resulted in poorer seeding depth control with the planter than if soil was compacted with a truck mounted with flotation tires. Poor seeding depth control in compacted soil was exacerbated by dry soil conditions at planting, which was the case in 2002 and 2005. These results suggest that the lower inflation pressure (250 vs. 700 kPa) and bigger footprint of flotation tires help reduce the negative impact of compaction on plant populations in no-tillage crop production. McBride et al. (2000) also reported deeper ruts with conventional road tires compared with high-flotation tires.

In our study, DTAC alleviated the plant stand reduction caused by annual compaction with road tires for 3 yr and partially in 2002. In contrast, DTBC did not improve plant populations compared with the ARTC treatment in 2002 and 2003. In 2004, DTBC gave higher plant population than the ARTC treatment, probably because the plots that were deep tilled before compaction had been leveled with a field cultivator in that year. In addition to that, compaction effects on plant stand were reduced in 2004 due to regular rainfall in the growing season. The DTBC treatment was discontinued in 2005. Plant populations were significantly reduced with DTBC compared with DTAC in 2003 (though not significantly in 2002 and 2004). These results indicate that in-row DTAC can significantly improve plant populations, but if heavy traffic follows deep tillage, the positive effects of this practice on plant establishment may be lost. These results are similar to findings of Murdock (1998), who reported significant increases in plant stand when compacted soil was subsoiled to a depth of 30 cm.

Shallow in-row tillage after compaction increased the plant population over ARTC in 2004 but not in the other 3 yr. The three-coulter Zone-Till system used in 2002 and 2003 was less effective in penetrating the severely compacted soil than the Zone Builder shanks set to shallow depth, used in 2004 and 2005, explaining this difference. No significant improvement in plant populations in STAC compared with ARTC in 2005 might be due to the drier soil conditions.

Deep in-row tillage without compaction and no-tillage without compaction (control) resulted in similar plant populations, suggesting that subsoiling did not improve plant population when there was no induced compaction. Differences in plant population between first-year road tire compaction (FRTC) and control were present only in 2002, indicating that compaction effects on plant establishment were only present in the year immediately following compaction in the no-tillage system. These results suggest that natural factors such as freeze–thaw, wetting and drying cycles, and high biological activity at the surface of no-tillage soil eventually help to alleviate soil compaction in the surface layer. In addition, the high organic matter content at the surface of no-tillage soil makes the soil somewhat more resistant to compaction (Thomas et al., 1996).

Crop Growth
Crop height was measured only in 2004. Maize height was affected by soil compaction both 6 WAP and at harvest (Table 5). Annual road tire compaction reduced plant height significantly by 21% at 6 WAP and 11% at harvest compared with the control, which indicates that compaction effects were most severe early in the growing season. Flotation tires helped to reduce the effect of compaction on plant growth. Plant height in the AFTC treatment was not different from that in the control treatment at either growth stage. The AFTC treatment had significantly higher plant height than ARTC at 6 WAP.

Deep in-row tillage after compaction improved plant height by 18% at 6 WAP and by 15% at harvest over ARTC. However, plant height with DTBC was not different from that in the ARTC treatment. These results show that, although compaction after deep tillage did not affect plant populations in 2004 (see above), it did affect plant growth. Deep in-row tillage can therefore help alleviate the negative effects of compaction on plant growth, but heavy traffic after deep in-row tillage can largely destroy these benefits. Our results further show that shallow in-row tillage in 2004 increased plant height at the early growth stage over ARTC but not at harvest.

In the absence of compaction, deep in-row tillage did not increase the plant height above that in control treatment. This indicates that the soil in our study was not responsive to subsoiling without compaction. Additionally, FRTC and control treatment did not show any differences in plant height in 2004, which indicates that negative effects of compaction did not persist after 2 yr.

The plant height reduction due to compaction measured in this study in a long-term no-tillage field was similar to that reported in compaction studies with tillage. This suggests that the effect of compaction on plant growth is not more severe in long-term no-tillage than in soil that is tilled after the compaction takes place. Lowery and Schuler (1991) observed 13% reduction in maize height at physiological maturity with 8-Mg axle load and 100-kPa tire inflation pressure compared with control noncompacted plots in tilled soil. Gameda et al. (1985) observed a 9% reduction in plant height in a clay soil and 4% reduction in a loam soil due to soil compaction with 10-Mg axle load and 413-kPa tire inflation pressure compared with the control in a tilled soil at harvest. Compaction effects were most pronounced early in the growing season in our study, similar to reports by Abu-Hamdeh (2003) and Gaultney et al. (1982), who also found the greatest reduction in plant height at early growth stages. It seems, therefore, that maize plants somehow compensate early plant growth reductions due to compaction with additional growth later in the season.

Crop Yield
There were significant compaction treatment, year, and treatment x year interactions. Significant yield reductions in the ARTC treatment compared with the control were observed in 2002 (27%), 2004 (11%), and 2005 (14%) (Table 6). The yield reduction in 2003 (14%) was larger than in 2004 but not significant because of higher variability. Precipitation during the growing season (Table 1) influenced the effects of compaction on maize yield. The highest yield reductions due to compaction were in the years with dry summers (2002 and 2005). The FRTC and control treatments had similar yields in 2003, 2004, and 2005, which indicates that compaction effects had largely disappeared 1 yr after compaction in this long-term no-tillage soil. Flotation tires reduced the negative effects of annual compaction. In 3 yr, yield differences between the flotation tire compaction and control treatment (16, 9, and 2% in 2002, 2003, and 2004, respectively) were not significant. However, in 2005, yield in the flotation tire compaction treatment was significantly less (9%) than in the control. It has to be noted that in the dry year 2002, the yield reduction due to compaction with flotation tires was substantial but not significant due to high variability. This study does seem to indicate, therefore, that compaction effects on yield are greatest if compaction of wet soil is followed by a dry summer in no-tillage. Deep tillage following compaction provided benefits by improving the yield by 17% over ARTC in 2003 and, though not significantly, 27% in 2002, 5% in 2004, and 7% in 2005. When compaction was applied after deep tillage (DTBC), however, yields were similar to ARTC. On noncompacted ground, deep in-row tillage did not increase yields over the no-tillage control in the first 3 yr and actually reduced yields significantly (9%) in 2005. This indicates that deep tillage had no yield benefits in the absence of compaction on this well-drained silt loam soil that had not been tilled for more than a decade. One of the reasons for a yield reduction in 2005 may have been the residue cover reduction due to in-row tillage, causing greater moisture losses, which reduced yields in this dry year. Shallow in-row tillage after compaction did not improve the yield significantly compared with annual compaction with road tires in any of the 4 yr (Table 6).


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  		Table 6. Effects of soil compaction and tillage on maize grain yield in a study of soil compaction in conservation tillage at State College, PA from 2002–2005.

 
The yield reductions measured in this study due to compaction in no-tillage are comparable to many other reports in the literature. In a long-term no-tillage field on a poorly drained clay soil, Lal (1996) observed a yield reduction (44%) in 1 yr out of 3 due to compaction with 10-Mg axle load. In another no-tillage study, Abu-Hamdeh and Al-Widyan (1999) found that compaction with 15-Mg axle load resulted in 11% yield reduction compared with 5-Mg axle load (tire inflation pressure was 400 kPa). These results suggest that yield reductions due to compaction in continuous no-tillage soil are not larger than in tilled soil for our range of axle loads and tire pressures. In studies where compaction was followed by soil tillage, Abu-Hamdeh (2003) reported a maize yield reduction of 17% due to compaction with two passes of 8-Mg axle load and 300-kPa tire inflation pressure. Similarly, Lowery and Schuler (1991) reported a yield reduction of 14 to 43% after compaction with four passes of 12.5-Mg axle load and 150- to 220-kPa inflation pressure, also followed by tillage before crop establishment. Voorhees (2000) reported a maize yield decrease of 15 to 43% in the first year after subsoil compaction with 11-Mg axle load followed by tillage in Wisconsin.

Our results also suggest that largest yield reductions due to compaction can be expected when the crop is under stress. This means that on well-drained soils, greatest yield reductions can be expected in years with dry summers (such as 2002 and 2005 in our study; compare also Hu, 2003). In soils with imperfect internal drainage, on the other hand, compaction effects may be more pronounced in wet years (Bicki and Siemens, 1991).

The effects of compaction dissipated one full year after the compaction event on this long-term no-tillage soil. The quick soil recovery may be due to the higher organic matter and biological activity in continuous no-tillage soil. Murdock (2002) reported that yields in a severely compacted no-tillage soil recovered after 2 yr compared with 5 yr in a tilled soil. In a study with tillage, compaction with 10-Mg axle load and 300-kPa tire inflation pressure affected the crop up to 5 yr, and compaction effects persisted in the soil even up to 7 to 8 yr (Hakansson, 1985). These studies suggest that compaction effects in no-tillage are shorter lasting than with tillage. Because subsoil compaction causes long-lasting yield reductions, it may be that in the firmer no-tillage soil, compaction stress is not propagated as deep as in tilled soil.

Flotation tires appear effective to avoid yield loss due to compaction in no-tillage compared with tires with high inflation pressure as shown in this study and confirmed in other reports. In one no-tillage study, Abu-Hamdeh and Al-Widyan (1999) observed 5% yield decrease due to compaction with tires inflated to low pressure (200 kPa) and 11% decrease if they were inflated to high pressure (400 kPa). Lower surface stress due to the use of tires inflated to low instead of high pressure leads to smaller decreases in air porosity and air permeability and reduced increases in bulk density (Wood et al., 1991; McBride et al., 2000; Reeves and Cooper, 1960).

Deep in-row tillage was found to be effective to alleviate most of the negative effects of soil compaction on crop growth and yield in this study. Abu-Hamdeh (2003) found that subsoiling (paraplowing to 45-cm depth) after compaction with 9- and 18-Mg axle load and 300-kPa inflation pressure improved the yield 12 to 13% in a chisel-plowed field. Al-Adawi and Reeder (1996) observed a positive response to paraplowing to a depth of 40 to 45 cm 4 yr after intentional compaction and 2 yr later when it was performed again. The benefits of deep tillage depend on weather conditions during the growing season. No yield improvement due to subsoiling after compaction was observed in 2004 in this study when precipitation was plentiful. Reeves et al. (1992) also found no effect of deep tillage (40 to 44 cm) after traffic on early-season maize dry matter production in a wet year compared with dry years.

The absence of a positive response (and in 1 yr, a negative response) to subsoiling in the absence of induced compaction suggests that not all soils benefit from subsoiling. Varsa et al. (1997) found that deep tillage up to 40-cm depth performed in the fall gave similar maize yields to no-tillage in a silt loam soil (which even exhibited compacted layers). Raper et al. (2000b) did not find an increase in cotton (Gossypium hirsutum L.) yield with deep or shallow subsoiling over no-tillage in a naturally compacted soil. On the other hand, some soils do respond favorably to subsoiling. Chaudhary et al. (1985) observed significantly greater (27 to 40%) maize yields and increased rooting depth and rooting density with subsoiling treatment (followed by conventional tillage) compared with only conventional tillage. Similarly, Al-Adawi and Reeder (1996) found about 1.8 Mg ha–1 increase in maize yield due to subsoiling (in chisel-plowed soil) without compaction. Schwab et al. (2001) observed 10% higher cotton yield with fall deep tillage plus cover crops compared with strict no-tillage.

The results of this study also suggest that heavy traffic after deep in-row tillage largely eliminates any potential benefits of tillage. Evans et al. (1996) observed that even normal wheel traffic in the spring eliminated the benefits of fall subsoiling on maize yield in both tilled and no-tilled studies. This reduces the hope that the effect of subsoiling operations will last for more than 1 yr unless controlled traffic is practiced.

Finally, the method and depth of in-row tillage is important for compaction alleviation. A lack of yield improvement with STAC in the first 2 yr of this study shows that shallow in-row tillage with fluted coulters is ineffective to alleviate compaction. On the other hand, STAC in the third year of this study (to 22 cm with Zone Builder) achieved the same yield improvement as DTAC (40 cm deep with Zone Builder). This suggests that subsoiling to 40 cm was not required in 2004 and that subsoil compaction may not have occurred in this long-term no-tillage soil. Some studies actually show a negative effect of subsoiling deeper than necessary (Raper et al., 2000a). This suggests a need to diagnose the depth of compaction and set the subsoiler depth accordingly. In 2005, however, STAC (22 cm) was not effective to improve the yield over ARTC.


   CONCLUSIONS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
REFERENCES
 
This study shows that compaction can have significant negative effects on crop establishment, growth, and yield in a long-term no-tillage soil. However, the expected yield reductions are similar to those in continuously tilled soil. Compaction effects will be greatest when a crop is under stress. In continuous no-tillage, the adverse effects of compaction on crop yield can be expected to disappear 1 yr after compaction without any tillage when compaction is not repeated. The study also shows that using flotation tires reduces the negative effect of compaction on crop growth and yield in no-tillage compared with road tires. Remediation of soil compaction using deep in-row tillage does not assure complete alleviation of compaction even if the compaction effects are significant, and the alleviation cannot be expected to last for more than 1 yr unless controlled traffic is used. The study also suggests that subsoiling cannot be recommended on these soils unless there is evidence of severe compaction. This becomes all the more necessary because all in-row tillage practices significantly reduced residue cover.

Compaction in this study was performed under worst soil conditions, close to field capacity, and on 100% of the soil surface. In practice, it is unlikely that a farmer will compact 100% of the soil surface with high surface contact pressure and axle load because (i) only part of the field is tracked and (ii) the equipment will only have a full load part of the time. So, if farmers can limit their traffic to drier soil conditions, keep axle loads below 10 Mg, and keep tire inflation pressures below 250 kPa, compaction effects on these soils on no-tillage maize yields would be minimal. Subsoiling would seldom be beneficial on these well-drained soils.


   ACKNOWLEDGMENTS
 
We thank the Penn State Farm Operations Crew whose help was indispensable in the completion of this research. Also many thanks to Jennifer Moeny, Don Rill, and Mike Poteet for help in the field as well as in the lab. The helpful suggestions of Dan Fritton, Greg Roth, and Jonathan Lynch are also greatly appreciated.


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




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B. F. Tracy and Y. Zhang
Soil Compaction, Corn Yield Response, and Soil Nutrient Pool Dynamics within an Integrated Crop-Livestock System in Illinois
Crop Sci., May 1, 2008; 48(3): 1211 - 1218.
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