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a Greenhouse & Processing Crops Research Centre, Agriculture and Agri-Food Canada, Harrow, ON, Canada N0R 1G0
b Dep. of Agronomy, Purdue Univ., West Lafayette, IN 47907-1150
* Corresponding author (druryc{at}agr.gc.ca)
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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Abbreviations: CHU, corn heat unit • CT, conventional moldboard plow tillage • FC, field capacity • NT, no tillage • PR, penetration resistance • PWP, permanent wilting point • RC, red clover • WAS, wet aggregate stability • ZT, zone tillage
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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Zone tillage has been proposed as a possible alternative tillage system that may combine the soil quality benefits of conservation tillage with the yield benefits of conventional moldboard plow tillage (e.g., Pierce et al., 1992) for cool humid climatic zones. Here, a narrow zone 10 to 20 cm wide by 10 to 30 cm deep is conventionally tilled in the crop row while the rest of the soil surface is left in an untouched no-till state. This supposedly encourages the more favorable soil temperature, moisture, aeration, density, and strength conditions associated with conventional tillage in the narrow seedbed zones, while retaining the increased erosion resistance, organic matter protection and reduced energy inputs of no tillage between the zones. Although there is much interest in the zone-till system, it has not yet been tested extensively in cool humid temperate climates, nor on the agriculturally important clay and clay loam soils of southern Ontario. In nearby Michigan, ZT on sandy loam soils did indeed improve potato (Solanum tuberosum L.) yields and soil physical conditions relative to conventional tillage in most years of a 4-yr study (Pierce and Burpee, 1995); however, corn yields were not increased by zone tillage in a similar 3-yr study, despite substantially reduced soil strength (penetration resistance) within the 0- to 30-cm depth range (Pierce et al., 1992).
Red clover underseeded in cereals can produce large quantities of plant biomass and it fixes N in the nodules, which can in turn provide the equivalent of 90 to 125 kg N ha-1 to the following crop (Bruulsema and Christie, 1987). In addition, RC can be effective in cool-temperate climates for increasing microbial biomass, improving the structure of fine-textured soils (Drury et al., 1991), and for accelerating the decomposition of surface crop residues (Drury et al., 1999). It was consequently hypothesized that including RC underseeding in a crop rotation might further improve the potential yield and soil quality benefits of zone tillage on fine-textured soils.
The objective of this study was to determine, for a clay loam soil in southern Ontario, if zone tillage and RC underseeding could achieve corn yields comparable with conventional moldboard plow tillage, but still retain most of the soil quality, environmental, and reduced energy inputs of no tillage. To accomplish this, conventional moldboard plow tillage, no tillage, and zone-tillage systems were applied to a winter wheat–corn–soybean rotation, with and without RC underseeded in the winter wheat. Evaluations were made on the basis of corn emergence, corn yield, and near-surface soil physical quality.
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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No tillage produced no disturbance of the soil except for that caused by the no-till planter. Before the establishment of this study, the conventional-till and no-till plots had been in place under a winter wheat–corn–soybean rotation since 1993. The zone-till treatment was introduced into a subset of the no-till plots in the fall of 1996. The data reported here apply only to the corn phase of the rotation from 1997-2000.
Corn was planted (76 100 seeds ha-1) in 75-cm rows for all three tillage treatments using a John Deere 6-row no-till Max Emerge planter (Deere and Company, Moline, IL) equipped with 45.72-cm (18-inch) ripple and bubble coulters to open and close the planting slot, plus residue managers to improve the seed bed. The planter was adjusted among tillage treatments to ensure that the same 4-cm planting depth was achieved for each tillage treatment. Planting was delayed in 1997 and 2000 because of wet soil conditions resulting from high spring rainfall (Table 1). The delay was long enough in 1997 to require an early-maturing 2950 corn heat unit (CHU) variety (Pioneer 3752), whereas in 1998, 1999, and 2000 a normal 3250 CHU variety (NK Max 21) was used. To encourage early plant growth, liquid fertilizer (55 L ha-1) was applied with the seed to provide 5.6 kg N ha-1, 9.8 kg P ha-1, and 9.3 kg K ha-1. Nitrogen (22 kg N ha-1), P (38 kg P ha-1), and K (37 kg K ha-1) were also applied at planting in a band 5 cm beside and 5 cm below the seed. When the corn had four visible collors (6-leaf stage), N (28% UAN) was injected (148 kg N ha-1) in a band 15 cm away from the row at a 10-cm depth.
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Measurements
Corn Emergence and Yield
Corn emergence was measured between four to twelve times per week over 2 to 3 wk until all of the viable plants emerged. Four 2-m row lengths per plot were marked with flags after planting to measure both the emergence rate and final crop stand. Plants were counted every 1 to 2 d within the marked areas until emergence was complete. Two subsamples were harvested from each plot with three rows of corn (20 m long) in each subsample on 6 Nov. 1997, 16 Nov. 1998, 29 Oct. 1999, and 15 Nov. 2000 with a Gleaner combine (Allis Chamers, Millwaukee, WI). Total corn grain yields and grain moisture content were measured and yields were normalized to 150 g kg-1 grain moisture content.
Surface Residue
Surface residue weights were measured 4 to 5 times per growing season from 1997-2000. The residue was collected from the soil surface within 20 by 76 cm metal rectangles placed perpendicular to the corn rows with two measurements made in every plot (n = 8). The residue was oven-dried at 80°C and any soil adhering to the residue was removed before a dry residue mass was determined. The sampling areas were weed-free and no living plant material was included in the residue sample.
Soil Moisture and Temperature
Volumetric soil water content measurements were made in situ in the corn row midway between plants three times per week at the 0- to 5- and 0- to 30-cm depths in four replicates of each treatment using time domain reflectometry (Topp et al., 1980; Topp, 1993). The 0- to 5-cm depth measurements were made only during germination and early growth (from planting to about the 6-leaf stage), while the 0- to 30-cm depth measurements were made for the entire growing season (from planting to the end of August). Soil temperature was measured during germination and early growth using four thermocouples inserted horizontally into the undisturbed soil profile at 5- and 10-cm depths in two replicates of each treatment. The temperature measurements were made continuously and integrated hourly using a CR-10 micrologger.
Soil Physical Quality Parameters
Estimates of in-row soil strength (cone penetration resistance) were made midway between corn plants in 1998-2000 approximately 3 wk after corn planting, using a RIMIK CP-20 cone penetrometer (Agridry Rimik, Toowoomba, Queensland, Australia) (cone basal area = 1.2 cm2, cone angle = 30°, 0–45 cm depth range, three penetrations per plot, n = 12). During the summers of 1998-2000, intact soil cores (7.6-cm diam. by 7.6-cm long) and grab samples were collected at the 5.0- to 12.6-cm depth from the corn row midway between plants (n = 8, two cores and two grab samples per plot). The 5.0- to 12.6-cm depth range was selected to reduce the near-surface artifact effects of soil cracking, but still include the near-surface effects of the tillage and red clover treatments. The cores and grab samples were used to determine dry bulk density (Culley, 1993), air-filled porosity (porosity minus volumetric water content at -100 cm pressure head), plant-available water capacity (volumetric water content at -100 cm pressure head minus volumetric water content at -15 bar pressure head, Topp et al., 1993), and saturated hydraulic conductivity (Reynolds, 1993). Soil grab samples were collected from each treatment from 1997 to 2000 at a depth of 0- to 5-cm to determine near-surface treatment effects on wet aggregate stability (Kemper and Rosenau, 1986).
Statistical Analyses
A 3 by 2 factorial randomized complete block design was used with four replicates. Treatment and interaction effects were tested for statistical significance using analysis of variance (SAS Institute, 2001). When interactions between tillage and red clover treatment were not significant, we also evaluated main effect means using a least-significant-difference test (LSD) at P = 0.05.
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RESULTS AND DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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Corn emergence in 1997 was very rapid under the conventional tillage treatments, but much slower under zone-tillage and no-tillage treatments (Fig. 1) . By Day 5, 26 to 32% of the corn plants had emerged in the conventional-tillage treatments but no plants had emerged on either the zone-tillage or no-tillage treatments. Fifty percent corn emergence was reached in the conventional-tillage treatments by Day 6, which was significantly greater than the emergence rates for both the zone-tillage and no-tillage treatments. Between 9 to 10 d were required for 50% emergence in zone-tillage and no-tillage treatments. Red clover had no significant effect on emergence rates, except for zone tillage between approximately Day 7 and Day 10, where corn emerged faster under ZT + RC relative to ZT. Final plant stands were not significantly different between tillage or RC treatments with emergence rates of 95% for the conventional-tillage treatments, 91% for the zone-tillage treatments, and 87% for the no-tillage treatments.
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The 1998 corn emergence rates were greatest under the conventional-tillage treatments, much slower under the no-tillage treatments, and intermediate under the zone-tillage treatments (Fig. 1). For example, after 8 d, the conventional-tillage treatments had a 56% emergence rate, which was significantly greater than the zone-tillage treatments (19%), which in turn was significantly greater than the no-tillage treatments (3%). There were no significant effects of RC on corn emergence at 8 d. Final plant stands were statistically similar for the conventional-tillage and zone-tillage treatments (80–86%), whereas they were both significantly greater than the no-tillage treatments (52%). Corn emergence rates were affected by RC in the zone-tillage treatments only, where corn emergence was faster under ZT than under ZT + RC especially between the 9th and 12th day after planting.
In 1998, there were significant tillage and RC effects on corn grain yields (Table 2). The corn grain yields for the CT + RC, CT, and ZT + RC treatments were similar but significantly greater than the yields for ZT, NT + RC, and NT (P = 0.1). The no tillage without RC underseeding (NT) and NT + RC treatments had by far the lowest corn grain yields (2.64 and 3.61 Mg ha-1, respectively) which were 61 to 70% lower than the two corresponding conventional-tillage treatments (8.92 and 9.26 Mg ha-1). Red clover underseeding increased yields by an average of 21% across the three tillages (4% for CT, 37% for NT, and 40% for ZT). The 1998 corn grain yields were 5 to 60% lower than those in 1997, probably because of the 28 to 55% lower rainfall in May-July relative to the corresponding 30-yr averages (Table 1). The particularly low yields for the two no-tillage treatments were probably caused at least partially by severe seed and seedling desiccation after pronounced reopening of the planting slots in those treatments.
Year 1999
The precipitation in 1999 was above the 30-yr average for April, but well below the 30-yr averages in May, June, July, and August (Table 1). In particular, the May 1 through August 31 rainfall (172.3 mm) was only about half the 30-yr average (340.8 mm). The corn plants consequently had a high emergence rate (Fig. 1) and initial growth, but then became severely drought stressed (especially during the grain filling period) which resulted in low grain yields for all treatments (Table 2).
The 1999 corn emergence rates were rapid and very similar among all six treatments (Fig. 1). Final plant stands were also high and no significant difference was found among treatments, with emergence being 88 to 91% for the two conventional-tillage treatments, 94 to 95% for the two no-tillage treatments, and 91 to 93% for the two zone-tillage treatments. We believe this occurred because 26.5 mm of rain fell during the 3 d after planting (21–23 May 1999), and because the planter slot did not reopen in the two no-tillage treatments, as it had in 1997 and 1998.
Corn grain yields in 1999 were similar for the conventional-tillage and zone-tillage treatments (4.4–4.7 Mg ha-1), but lower for the no-tillage treatments (3.7 Mg ha-1), which resulted in a significant tillage effect (Table 2). Red clover underseeded in the previous winter wheat crop did not improve corn grain yields in 1999, and no significant interactions between RC and tillage occurred. Averaged over the RC treatments, conventional tillage and zone tillage produced corn grain yields that were greater than no tillage by 21 and 25%, respectively.
Year 2000
The 2000 growing season was very wet, exceeding the monthly and cumulative 30-yr averages by substantial margins (Table 1). As a result, corn planting was delayed by wet soil conditions until June 2. Corn emergence rates were rapid, although slower for the two no-tillage treatments relative to the other treatments (Fig. 1). For example, after 8 d, conventional-tillage treatments had 58% emergence, which was significantly greater than the zone-tillage treatments (44%), and the zone-tillage treatments had significantly greater emergence than no-tillage treatments (11%). Red clover did not affect emergence in 2000. Final plant stands were nonetheless uniformly high for all treatments (
90%), and no significant tillage or RC effects were evident.
Corn grain yields were substantial and fairly uniform in 2000, ranging from a low of 8.25 Mg ha-1 for ZT to a high of 9.02 Mg ha-1 for CT + RC, with no significant tillage, RC or tillage by RC interaction effects (Table 2).
Comparison of Average Corn Yields
The treatments were compared using corn grain yields averaged over 1998, 1999, and 2000 (Table 2). The 1997 yields were excluded from the comparison because the NT treatment was missing for that year. There was a highly significant tillage effect (P 
0.001) and a significant RC effect (P 0.05) and the interaction between tillage and RC treatment was not significant (Table 2). Averaged over the RC treatments, the 3-yr average of the corn grain yields from 1998-2000 were significantly greater (P 0.001) for the conventional-tillage treatments (7.44 Mg ha-1), than the zone-tillage treatments (6.71 Mg ha-1), which was in turn significantly greater than the corn grain yields for the no-tillage treatments (5.17 Mg ha-1). Averaged over tillage treatments, including RC in the rotation resulted in significantly (P = 0.05) greater corn grain yields (6.70 Mg ha-1) than treatments without RC (6.18 Mg ha-1). Although the conventional-tillage treatments produced the greatest average yields, the ZT + RC yield was only 4% lower than CT + RC and only 1% lower than CT. The average NT + RC yield, on the other hand, was 29% lower than CT + RC and 27% lower than CT. Red clover resulted in an average yield increase of 9% across all tillages; and was especially effective for zone tillage, producing an average yield increase of 17% relative to no RC. Consequently, ZT + RC appears capable, on average, of producing corn yields, which are competitive with those from CT on a Brookston clay loam soil under a winter wheat–corn–soybean rotation.
Surface Crop Residue
As expected, crop residue on the soil surface varied substantially with tillage treatment, time of year and across years (Fig. 2) . Residue cover over the two conventional tillage treatments varied from highs of 0.1 to 1.8 Mg ha-1 in the spring to lows of <0.2 Mg ha-1 in the fall. Surface residue over the four conservational-tillage treatments, on the other hand, ranged from highs of 2.6 to 7.4 Mg ha-1 in the spring, to lows of 0.9 to 3.1 Mg ha-1 in the fall. Note that 1999 was an exception in that residue covers did not decline appreciably over the growing season for any of the treatments. This was attributed to the very dry 1999 growing season (Table 1), which undoubtedly limited biological decomposition on the soil surface. In October 1997, 1998, and 2000, ZT + RC had, respectively, 33, 49, and 31% less residue cover than ZT; and in 1998 and 2000, NT + RC had 35% less residue cover than NT (Fig. 2). Red clover has a low C/N ratio as a result of symbiotic N fixation and it also has a considerable amount of soluble C, which has been found to stimulate biological activity (McKenney et al., 1993). Hence, it is readily decomposed by soil microorganisms, which leads to an increase in soil ammonium through mineralization. In contrast wheat straw residue has a high C/N ratio and its decomposition is limited by available N. Hence the additional supply of inorganic N from RC decomposition probably contributed to the decomposition of wheat straw, which was underseeded to RC. The accelerated decomposition of wheat residues by including RC in the rotation, was observed previously by Drury et al. (1999).
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Many field crops tend to perform best when average root-zone water contents fall within a range defined at the wet end by the soil's field capacity (FC) water content and at the dry end by the soil's permanent-wilting point (PWP) water content (Kramer, 1969). The depth-averaged FC and PWP water contents for the soil were 0.36 and 0.25 m3 m-3, respectively, over the 0- to 5-cm depth, and 0.32 and 0.20 m3 m-3, respectively, over the 0- to 30-cm depth. Average water contents at 0 to 5 cm and 0 to 30 cm were within the FC and PWP limits in 1997 and 2000 (Table 3), and this is consistent with the moderate to high corn yields for those years (Table 2). In 1998 and 1999, however, the average soil water contents were at or below the PWP limits (Table 3), which is again consistent with the moderate to very low corn yields for those years (Table 2).
Soil Physical Quality
Cone Penetration Resistance
The variability and overall shapes of the cone penetration resistance profiles changed substantially between 1998, 1999, and 2000 (Fig. 3)
. This most likely occurred because cone penetrometer measurements can be very sensitive to small changes in soil bulk density, water content, texture, organic C content, and structure (e.g., Bengough et al., 2001). Among-year variability may also have been exacerbated by the fact that each year's measurements corresponded to a different (although adjacent) field. It is unlikely, however, that soil water content contributed substantially to among-treatment variability within each year (or field) because water content differences were small at the time of the penetrometer measurements, and water content did not correlate with penetration resistance (PR) (data not shown).
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In 1999, both tillage and RC effects were evident, with tillage having a far greater effect than RC (Fig. 3). Over approximately the 5- to 25-cm depth, the two no-tillage treatments produced the greatest PR values, with NT + RC producing slightly greater values than NT. From about 5 to 13 cm, the two conventional-tillage treatments produced greater PR values than the two zone-tillage treatments, while from about 20 to 30 cm the two zone-tillage treatments produced greater values than the two conventional-tillage treatments. It is also interesting to note that the small effects of RC on PR were reversed for conventional tillage relative to the other tillages within the 5- to 13-cm depth range. All six treatments reached or exceeded the PR = 2000 kPa value where root growth may be reduced by 50% because of excessive soil strength (Bennie, 1996; Bengough and Mullins, 1991). This was likely because of the very dry soil conditions both throughout the growing season (Table 3) and at the time of the penetrometer measurements (data not shown). Note that the generally high average PR values correspond to the substantially lower 1999 corn grain yields for all treatments (Table 2). The PR profiles further indicate that the average soil mechanical resistance to crop root growth in the top 20 cm of soil was lowest under the two zone-tillage treatments, greatest under the two no-tillage treatments, and intermediate under the two conventional-tillage treatments. As in the previous year, these average PR values correlate with yield in that corn grain yield was the greatest under the zone-tillage treatments (albeit by a small margin), intermediate under the conventional tillage-treatments, and lowest under the no-tillage treatments (Table 2).
In 2000, the PR values were generally much lower than in 1998 and 1999 (Fig. 3). In addition, PR increased approximately linearly with increasing depth for all treatments, ranging from near zero close to the soil surface to 1600 to 2200 kPa at 45-cm depth, with no substantial differences among treatments. These results are most likely the result of the substantially greater precipitation (Table 1) and soil profile moisture contents (Table 3) throughout the 2000 growing season, relative to the 1998 and 1999 growing seasons. The slight but sudden divergence of the CT, CT + RC, and ZT profiles at about the 18-cm depth (Fig. 3) is currently unexplained, but may be related in some way to tillage operations in the previous fall (1999), which was much wetter than average. The lack of difference in average PR over the 0- to 20-cm depth is consistent with the lack of difference among corn grain yields (Table 2).
Comparing the 1998-2000 PR results, it appears that the two zone-tillage treatments produced the lowest overall soil strengths (i.e., lowest PR values) in a low rainfall year (1999), and intermediate overall strengths in a normal rainfall year (1998). Zone tillage was also found to decrease soil strength relative to conventional tillage in loam soils cropped to potatoes (Pierce and Burpee, 1995) and corn (Pierce et al., 1992). The two no-tillage treatments tended to produce the greatest overall soil strengths in the normal and low rainfall years (1998 and 1999, respectively), while the two conventional-tillage treatments produced the lowest overall soil strengths under normal rainfall (1998) and intermediate strengths under low rainfall (1999). Under high soil moisture conditions (2000), there were no substantial differences in soil strength among any of the treatments. Given the treatment differences in PR often decrease with increasing soil moisture (Bengough et al., 2001), this result suggests that high soil moisture can override tillage effects on soil strength in Brookston clay loam. For the 3-yr period, it appears that the two zone-tillage treatments had the most favorable overall soil strength profiles, as they maintained lower soil strengths than the other treatments during a dry year (1999), reasonable strengths during a normal rainfall year (1998), and similar strengths to the other treatments during a wet year (2000). The two no-tillage treatments, on the other hand, had the least favorable soil strength profiles, as they had the greatest strengths during a normal rainfall year (1998), and excessive strengths in a low rainfall year (1999). Red clover did not have important or consistent effects on soil strength under any of the tillage treatments in any of the 3 yr (Fig. 3). As mentioned above, corn grain yield tended to be negatively correlated with average soil strength, in that lower average PR corresponded with greater yield.
Additional Soil Parameters
Bulk density ranged from a high of 1.48 Mg m-3 (CT + RC, 2000) to a low of 1.28 Mg m-3 (ZT + RC, 2000) (Table 4). Significant tillage effects occurred in all 3 yr, and significant RC and tillage by clover interaction effects occurred in 2000. The optimal bulk density for root growth in fine-textured soils is on the order of 0.8 to 1.2 Mg m-3 (e.g., Olness et al., 1998, Reynolds et al., 2002), and root growth often stops completely in clayey soils at about 1.5 Mg m—3 (Veihmeyer and Hendrickson, 1948). Consequently, corn root growth was likely to have been somewhat impeded by high soil density for all six treatments, and especially under the CT + RC treatment in 2000. The ZT + RC treatment had either the lowest, or among the lowest, bulk density in each of the 3 yr, while the two no-tillage treatments often had the greatest bulk density. This pattern is generally consistent with the soil strength (Fig. 3) and corn yield (Table 2) patterns mentioned earlier.
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Plant-available water capacity tended to be low, ranging from 0.089 m3m-3 (NT, 1998) to 0.142 m3m-3 (ZT + RC and NT, 2000), with no significant RC effects but significant tillage effects in 1998 and 1999 (Table 4). The low values occurred despite large FC water contents (0.31–0.34 m3m-3) because the PWP water contents were also large (0.18–0.23 m3m-3). It has been proposed that plant-available water capacities greater than 0.20 m3m-3 are required in fine-textured soils for optimal root growth, function, and minimum droughtiness (Cockroft and Olsson, 1997). Consequently, crops grown on all six treatments may be prone to periodic drought stress, even when the soil is still relatively moist (i.e., water contents as high as 0.23 m3m-3). No among-treatment patterns were evident.
Saturated hydraulic conductivity (Ksat) ranged from a low of 4.2 x 10-4 cm s-1 (CT + RC, 2000) to a high of 2.9 x 10-1 cm s-1 (ZT, 1999), with significant tillage effects in 1998 and 2000, but no significant RC effects (Table 4). No distinct patterns were evident, although the average Ksat in 1999 was greater than in 1998 or 2000, which corresponded with greater soil surface cracking observed in 1999 owing to very dry soil conditions (Table 3). Saturated hydraulic conductivity values in the range, 10-2 to 10-5 cm s-1, may provide an optimum between the competing needs for rapid sorption into the soil matrix of needed crop-available water, and rapid drainage of excess water that could cause water-logging and associated aeration deficits (Topp et al., 1997). All treatments exceeded this range, except for the two conventional-tillage treatments in 2000. Thus all treatments tended to be prone to near-surface droughtiness because infiltration and drainage in the near-surface soil may be too rapid to allow adequate sorption of crop-available water into the soil matrix. On the other hand, problems associated with near-surface water logging, erosion, and runoff are less likely.
Wet aggregate stability (WAS) was not consistently affected by tillage or RC (Fig. 4)
. The WAS values were of similar magnitude (
60%) among treatments and years, except for the two conventional-tillage treatments in 1997 and 2000 where WAS 30%. Generally speaking, RC increased the WAS slightly, however, this increase was not always significant, and exceptions occurred under conventional tillage in 1997 and 1998 and under no-tillage in 2000 where the RC treatment produced a slight decrease. The reasons for these exceptions are currently unknown. In three of the 4 yr the ZT + RC and NT + RC treatments had greater WAS than the two conventional-tillage treatments.
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CONCLUSIONS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
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ACKNOWLEDGMENTS |
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Received for publication January 22, 2002.
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