- Email: [email protected]
Short-term tillage effects on soil cone index and plant development in a poorly drained, heavy clay soil
Soil & Tillage Research 82 (2005) 161–171 www.elsevier.com/locate/still
Short-term tillage effects on soil cone index and plant development in a poorly drained, heavy clay soil Y. Chena,*, C. Caversb, S. Tessierc, F. Moneroa, D. Lobbd a
Department of Biosystems Engineering, University of Manitoba, Winnipeg, MB, Canada R3T 5V6 Manitoba Agriculture and Food, Soil and Crop Branch, Box 1149, Carman, MB, Canada R0G 0J0 c Manitoba Conservation, Headquarters Operations, 200 Saulteaux Crescent, Winnipeg, MB, Canada R3J 3W3 d Department of Soil Science, University of Manitoba, Winnipeg, MB, Canada R3T 5V6 b
Received 6 August 2003; received in revised form 11 June 2004; accepted 22 June 2004
Abstract Soil compaction is a big challenge in managing poorly drained clay soils. An on-farm field study was conducted over 2 years in a poorly drained, heavy clay soil, Red River Valley, Manitoba, Canada, where soil compaction, crop growth and root development were perceived as serious concerns. To address these concerns, no-tillage and sub-soiling tillage were proposed and compared with the traditional tillage system in which light-duty field cultivators were used at tillage depths ranging from 50 to 75 mm. Measurements of soil cone index indicated that a hardpan existed at approximately 175 mm soil depth in each fall as a result of wheel traffic during the growing season. It may not be necessary to break the hardpan with fall tillage operations in the studied region, as the hardpan was naturally removed over winter. Effects of tillage practices were evaluated using seeding performance and plant development. No-tillage resulted in the similar speed of emergence, plant population and crop yield, but more uniform seeding depth and more roots in the topsoil layer (0–75 mm), when compared with the conventional tillage. Subsoiling promoted much faster crop emergence, higher plant populations and crop yield as well as deeper root penetration than the conventional tillage. However, the draft force required for sub-soiling was four times that of the conventional tillage. # 2004 Elsevier B.V. All rights reserved. Keywords: Compaction; No-tillage; Sub-soiling; Root; Cone index; Crop
1. Introduction In the Canadian Prairies, producers have tendencies to till their soils at shallow depths (75–100 mm) so that * Corresponding author. Tel.: +1 204 474 6292; fax: +1 204 474 7512. E-mail address: [email protected] (Y. Chen).
they can use wide tillage equipment (10–20 m wide) for their large land base. Such a tillage practice in the Red River clay results in poor water infiltration and plant root development. No-tillage and subsoiling have emerged as solutions for solving these problems. No-tillage means less traffic, and in turn, less soil compaction, lower fuel and labour costs. Furthermore,
0167-1987/$ – see front matter # 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.still.2004.06.006
162
Y. Chen et al. / Soil & Tillage Research 82 (2005) 161–171
no-tillage has many other advantages such as controlling wind and water erosion, reducing soil moisture loss and greenhouse gas (carbon) emissions (Lindstrom and Reicosky, 1997). When compared with other tillage practices, long-term no-tillage increases soil organic matter (MNZTFA, 1998) and tends to have greater soil aggregate stability (Kladivko et al., 1986), which increases the resistance to compaction (Ball et al., 1990). However, no-tillage has not yet caught on in areas that have poorly drained heavy clay soils such as in Red River Valley. When switching to no-tillage (NT) from conventional tillage (CT) in such soil conditions, poor water infiltration and crop root development are major initial obstacles. The long-term benefit from no-tillage cannot be achieved easily, unless producers see that the system works in a short term. Sub-soiling can mechanically aerate soil at sub-soil layers, which promotes better water infiltration and absorption, and encourages crop root development (Xu and Mermoud, 2001). Increased yields have been reported when using deep tillage in a compacted soil (Camp and Sadler, 2002). However, sub-soiling requires great tractor power, especially in heavy clay soils, which limits the implement’s working width. This is a major obstacle for the adaptation of subsoiling tillage (ST) in the Red River Valley. The draft force required for sub-soiling needs to be explored for producers to select the appropriate width of implement so that the tractor power can be used to its maximum efficiency. This information can also be used for producers to make the justification between the benefit and the cost. Soil cone index (CI) is an empirical measure of soil strength and is widely used for assessment of the compacting and loosening effects of agricultural implements (Be´ dard et al., 1997; Tessier et al., 1997). Soil cone index can also be used to assess root growth and penetration. The higher is the cone index, the greater is the amount of energy that must be expended by the root to widen the soil pores. Some researchers (Gerard et al., 1982) have shown that increases in soil cone index decrease root elongation and growth. The threshold level at which soil strength hinders root elongation varies with plant species, but usually ranges between 2000 and 3000 kPa (Atwell, 1993). Letey (1995) reported a lower threshold value (1800 kPa).
The objective of this study was to investigate alternative tillage practices that could reduce soil compaction and promote crop performance in a Red River clay soil. Specifically, this study was to investigate the short-term effects of conventional tillage, no-tillage and sub-soiling tillage on soil compaction and plant development.
2. Material and methods 2.1. Site description Field trials were conducted over 2 years at a farm in Elm Creek, Manitoba, Canada. The soil type was poorly drained Red River clay (609 g kg1 clay, 365 g kg1 silt and 26 g kg1 sand, by weight) and is classified as Rego Humic Gleysol of the Osborne soil series. The normal field operations included spring seeding, post-emergence spraying, harvesting, and fall tillage. Prior to the study, the producer performed the tillage operations with a light-duty field cultivator working at fairly shallow tillage depths (50–75 mm). In the first year study, canary-seed crop was sown on barley straw, followed by canola in the second year. The row spacing was 0.20 m for both years. Crops were fertilized to soil test recommendations. The closest weather stations are the Starbuck and Carman Weather Stations that were located 26 km east and 17 km south of the experimental site, respectively. The weather data from these two stations were averaged and are listed in Table 1. The weather data indicated that experimental site experienced a dryer, colder spring, and the month of July was drier, while June and August were wetter, when compared to the 30-year averages. The air temperature during the summer generally conformed to the 30-year averages. 2.2. Equipment description The field cultivator (Fig. 1a) used featured furrower type (or hoe opener) tillage tools that were mounted on light-duty shanks with small tool spacing. The producer had used this cultivator for his conventional shallow tillage. The sub-soiling tillage was performed with a sub-soiler (Fig. 1b) having reversible straight spikes mounted on heavy-duty C-shanks with large
Y. Chen et al. / Soil & Tillage Research 82 (2005) 161–171
163
Table 1 Monthly air temperatures, precipitations and degree-days averaged from two nearby weather stations, 2002 Month
May June July August September
Precipitation
Degree days at 18 8C
Temperature
Total
30 Year normal
% of normal
Maximum
Minimum
Mean
30 Year normal
Cooling
Heating
49.4 136.6 55.3 112.2 25.8
60.6 81.2 76.3 68.2 51.3
81 168 72 165 50
30.4 34.5 33.7 31.4 31
8.2 1.3 7.4 5.4 5.3
8.4 17.7 20.6 18.1 14.0
3.35 0.75 1.15 0.05 1.6
5.1 46.8 90.4 40.0 12.0
303.1 55.6 10.8 36.8 183.7
tool spacing. A 315 kW John Deere tractor (Model 9400) was used to pull all the field equipment during field operations. More details about the field cultivator and sub-soiler are given in Table 2.
2.3. Experimental design In fall 2000, two tillage treatments: conventional tillage and no-tillage were established. In fall 2001, a new treatment, sub-soiling tillage, was added to the field plots. Treatments and equipment parameters are summarized in Table 2. Each treatment was replicated four times. The length of the plots was 90 m. The widths of the CT and ST plots were 12.2 and 3.3 m, respectively, being one pass of the respective tillage implement. The width of the NT plots was 12.2 m. Seeding was performed perpendicular to the plots with a 20 m wide hoe airseeder (John Deere 1820). 2.4. Measurements
Fig. 1. Tillage implements used; (a) side view of the field cultivator for the conventional tillage treatment (CT) in falls 2000 and 2001; (b) the rear view of the sub-soiler for the sub-soiling tillage treatment (ST) in fall 2001.
2.4.1. Soil cone index Soil CI was measured to quantify the level of soil compaction. The Rimik cone penetrometer (Model CP 20, Agridy Rimik Pty. Ltd., Toowoomba, Australia) used was comprised of an in-built data logger, an 800mm long shaft, a cone with a base area of 129 mm2 and an apex angle of 308. The penetrometer was pushed into the soil by hand at a speed of approximately 0.30 mm s1 (ASAE, 2000). Measurements of CI were made at 18 random locations over the entire field before the initiation of the field trials in 2000, and at 12 locations per plot before fall tillage in 2001 and spring seeding in 2001 and 2002. At each location, three measurements were taken to a soil depth of 400 mm at 25 mm increment. Since CI is strongly related to the water content (Materechera and Mloza-Banda, 1997), CI measurements were performed after a heavy rainfall event whenever possible, to maximize uniformity of soil moisture content through the depth profile.
164
Y. Chen et al. / Soil & Tillage Research 82 (2005) 161–171
Table 2 Description of the treatments and the equipment Treatment
NT CT ST
Description
No-tillage Conventional tillage Sub-soiling tillage
Tillage implement
Tillage tool
Type
Width (m)
Tool spacing (m)
Type
Working width (m)
Field cultivator Sub-soiler
12.2 3.3
0.2 0.6
Furrower Narrow point
0.1 0.06
2.4.2. Soil moisture content At the same day of tillage and seeding operation, 10 soil samples were taken randomly on each plot to a depth of 400 mm with 100 mm intervals. Soil samples were weighed, oven-dried at 105 8C for 24 hours, and weighed again to determine the gravimetric moisture content.
2.4.4. Tillage depth In fall 2001, immediately following the tillage operations, tillage depth was measured at 10 random locations on each plot. Loose soil was removed from the soil furrow created by the tillage tools. A board was placed across the furrow on the original soil surface. The tillage depth was measured from the furrow bottom to the board.
2.4.3. Draft force A custom-made DEOR dynamometer was used to measure the draft force of the tillage implement in fall 2001. The dynamometer was installed between the tractor and the implement (Fig. 2) and was connected to a data logger (ProDAS, Michigan Scientific Corporation, 321E Huron St., Mifford MI 48381) in the tractor cab. The force signal was recorded at 100 Hz for 40 s while the tillage implement passed the middle section of the plot. A constant tractor travel speed of 1.7 m s1 was maintained for the tillage operations.
2.4.5. Speed of emergence (SE) and plant population In spring 2002, plant counts were made in a 0.6-m long crop row at 15 random locations on each plot, 4, 7 and 10 days after the first seedling emergence, and weekly thereafter until a stable count was obtained. The speed of emergence (Tessier et al., 1991) was calculated by P ðNi =di Þ SE ¼ A
Fig. 2. The DEOR Dynamometer installed between the tractor and tillage implement hitches to measure the draft forces of the tillage implements in fall 2001.
where SE is the speed of emergence per unit area (plants d1 m2), Ni, the number of newly emerged seedlings counted per day di and A (m2) is the area calculated by the length of the row counted and the airseeder’s row spacing. The final plant count was used as the final plant population (plants m2). 2.4.6. Seeding depth (SD) It was not possible to determine the seeding depth of canola by measuring the CFL (chlorophyll-free length, from the seed remnants to the onset of green stem; Tessier et al., 1991) of the seedlings because this plant does not maintain its seed remnant below the soil surface. Therefore, canary-seed (4.5 kg ha1), having similar size, was mixed and planted with the canola seed (4.5 kg ha1). After the final plant count was completed in spring 2002, five canary-seed seedlings were uprooted from each row used for plant counting, and their CFL were measured, and considered as the effective seeding depths of the canola. After seeding
Y. Chen et al. / Soil & Tillage Research 82 (2005) 161–171
depth measurements, the canary-seed plants were destroyed using herbicide. 2.4.7. Crop yield In 2002, the canola was swathed with the producer’s 8-m swather first. Crop yields for the NT and CT plots were measured with the producer’s combine and a weigh wagon. The combine picked up a 10-m-long swath in the middle of each plot. Only one 10-m-long swath was picked up over the four ST plots. Thus, there were no replications for the measurement of the yield for the ST treatment. Grain samples were oven-dried at 60 8C for 72 hours to determine the dry matter yield. 2.4.8. Root distribution After harvest in 2002, trenches were dug across a crop row to obtain a soil cross-section with exposed crop roots (Fig. 3). The face of each trench was trimmed with shovels and trowels to get a vertical face. A 300-mm ruler was put on the soil surface as a scale reference. A digital image of the trench’s crosssection was taken. The measurements were performed at five random locations per plot. The digital images were processed with the grid method where square
165
grids (25 mm 25 mm) were overlapped on the image (Fig. 3). The major root penetration depth (d) and the lateral root spread (L) (Fig. 3) were estimated using the square grids as reference. Root distribution in the soil profile was assessed by counting the number of intersections with the vertical lines of the grids in each 25 mm vertical layer (layer divided by grid lines), which was defined as the root distribution index of that layer. 2.5. Data analysis Analysis of variance (ANOVA) was performed on the data. Means between treatments were compared with Duncan’s multiple range tests. The statistical inferences were made at a 0.1 level of significance.
3. Results and discussion 3.1. Soil moisture content and bulk density The soil dry bulk density in fall 2000 at tillage (Table 3) represented initial soil condition before the
Fig. 3. Typical image showing the soil cross-section with roots and grids overlapped on the image, used for root measurements in 2002; d = major root penetration depth and L = lateral root spread.
166
Y. Chen et al. / Soil & Tillage Research 82 (2005) 161–171
Table 3 Average gravimetric soil moisture content (%, dry basis) and dry bulk density (mg m3) at the tillage and seeding times Depth (mm)
0–100 100–200 200–300 300–400 a b c
Fall 2000 at tillage
Spring 2001 at seeding
Fall 2001 at tillage
Spring 2002 at seeding
ra
MCb
ra
MCb
ra
MCb
ra
MCc NT
CT
ST
1.27 1.46 1.53 –
32 34 35 –
0.90 1.06 1.16 1.41
47 30 34 25
0.79 1.10 1.35 1.23
31 34 20 44
0.79 1.10 1.35 1.23
39 37 32 34
36 31 34 32
29 29 29 30
Average value of soil dry bulk density over the entire plot area. Average value of soil moisture content over the entire plot area. Average value of soil moisture content for each tillage treatment.
tillage treatments were established. Those values were associated with the producer’s conventional tillage. Those initial densities were greater than those obtained in the 2001 and 2002. This implied that the introduction of the NT and ST reduced the overall soil density. Gravimetric soil moisture at the tillage times in falls 2000 and 2001 was desirable for tillage operations (Table 3). Soil moisture contents were fairly uniform along the soil profile. At spring 2001 seeding time, the soil moisture content on the topsoil layer (0–100 mm) was quite high (47%). At spring 2002 seeding time, the precipitation was below the 30 year normal (Table 1). However, the soil moisture content at the seedbed layer (0–100 mm), ranging from 29 to 39%, was adequate for seeding due to the high field capacity of the clay soil. At that time, the NT increased the soil moisture content by 8%, while the ST decreased by 11%, as compared with the CT. The higher residue cover in the no-tilled plots likely reduced soil moisture loss and the sub-soiling promoted water evaporation loss (Jolata et al., 2001; Xu and Mermoud, 2001). 3.2. Soil cone index 3.2.1. Hardpans in soil Data prior to the initiation of the tillage trials in fall 2000 showed that the CI increased continuously, reached a peak of 1088 kPa at 175 mm, and then decreased (Fig. 4a). According to the concept of the profile analysis method (Chen and Tessier, 1997), a hardpan existed at the 175 mm depth. A hardpan was also identified in fall 2001 at the same depth (175 mm; Fig. 4b). The peak CI value, 1775 kPa, was close to the
agronomical threshold of 1800 kPa (Letey, 1995). Hence, this hardpan could be a potential limiting factor for plant root development, especially if the soil is drier, as soil strength increases as the soil dries (Francis et al., 1987). 3.2.2. Cause of the hardpans CI values measured in spring 2001 (Fig. 4c) increased linearly from the 0 to 175 mm depth and slowly increased at lower depths. A similar trend was observed in the spring 2002 (Fig. 4d). The values of CI in spring were approximately 34% lower on average than those observed in the previous fall, possibly due to the effects of soil freezing-thawing cycles on soil strength. Voorhees (1983) also observed that the soil strength decreases after winter. In addition, no hardpan was detected in either spring, as indicated by the smooth CI curves along the soil depth profile (Fig. 4c,d). The expansion of water upon freezing can alleviate compacted soils through the formation of vertical and horizontal microfractures (Kay et al., 1985; Marshal and Holmes, 1988). Tillage operations can result in a hardpan at a depth immediately or other than immediately below the tilled layer in the soil profile, as grousers of tractor tires can penetrate the tilled layer and shear the soil under the tilled layer (Chen and Tessier, 1997). However, whether or not a hardpan formed as the result of the tillage operations is not a concern in the studied region, because tillage is performed in fall and a hardpan would disappear over winter. The CI results also imply that the hardpans detected each fall were the results of wheel traffics from seeding, spraying, harvesting and any other field operations during the growing season. Contrary to what
Y. Chen et al. / Soil & Tillage Research 82 (2005) 161–171
167
Fig. 4. Soil cone index (CI) versus depth under different tillage treatments; (a) fall 2000; (b) fall 2001; (c) spring 2001; (d) spring 2002.
producers think, fall tillage operations would not be necessary to break hardpans. Efforts for reducing soil compaction should be devoted to field operations during the growing season, such as minimizing wheel traffic and using wide tractor tires. It would be useful to monitor the changes in soil cone index as affected by each field operation during the growing season, so as to find out the exact time when the hardpan occurs. 3.2.3. Effects of tillage treatments As tillage effects most likely pertain to the tilled layer (Unger and Fulton, 1990), the following discussion focuses on trends within the tilled layer. CI values in spring 2001 showed that the CT had reduced soil strength in the tilled layers when compared to the NT (Fig. 4c). Wilkins et al. (2002) also reported that a short-term no-tilled soil had higher soil strengths than a tilled soil. However, the statistically significant difference in this regard was observed only at one depth (50 mm). There were no
differences in CI found between the NT and the CT in fall 2001 (Fig. 4b). In spring 2002, the ST resulted in the same level of CI as the CT and NT, although the sub-soiled plots were expected to have lower PR. This may be due to the lower soil moisture content of the sub-soiled soil (Table 3). The large shank spacing of the sub-soiler could also have been responsible for this observation because the undisturbed area was greater in the subsoiled plots than the conventionally tilled plots. Data showed that tillage effects on CI were less pronounced than weather effects in this clay soil condition. Bullock et al. (1988) have observed that the disruption of soil aggregates by freezing can be more pronounced than a single pass of most tillage implements. 3.3. Draft forces It was the intention to set the tillage depth as deep as possible to enhance root penetration. However, due to the limitation of the shank trip force, the actual
168
Y. Chen et al. / Soil & Tillage Research 82 (2005) 161–171
Fig. 5. Total draft force (Total F), draft force per tool (F/tool) and draft force per meter of the implement width (F/m) for two different tillage treatments measured in fall 2001 and predicted according to ASAE Data (ASAE Standards, 2000); bars with the same letter are not different within the same variable according to Duncan’s multiple range test at P < 0.1.
tillage depth of the CT was only 88 mm and that of the ST was 264 mm. When operated at those depths, the 12.2-m field cultivator and the 3.3-m sub-soiler had similar total draft force (Fig. 5). Furthermore, subsoiling would consume more field time and create more tractor wheel tracks in the field. Specific forces were defined as the total draft force divided by the working width of the implement or the number of tools on the implement. Due to the greater tillage depth, the ST required four times more draft force per meter of implement width than the CT (Fig. 5), although the tool spacing of the ST was much larger. As for the force per tool, the ST gave a value 12 times higher because of its three-fold greater tillage depth. This information can be used to match the implement with tractor power to ensure that the drawbar pull of the tractor is efficiently used. Note that draft force of implement changes with its operational speed. However, speed effects on draft are less pronounced than depth effects (Chen, 2002). Predictions of draft force were made with model parameters listed in Agricultural Machinery Management Data (ASAE Standard, 1999) for narrow point sub-soiler and field cultivator in a fine soil. As compared with the measurements, the predicted values for the CT are 30% lower and those for the ST were 20% lower at the travel speed and tillage depth used in the field trial (Fig. 5). Chen (2002) also found that the ASAE Agricultural Machinery Management Data underestimated draft forces of a winged tillage tool under a clay soil.
Fig. 6. Seeding depth (SD), seed scatter index (SSI), speed of emergence (SE), plant population (PP), and crop yield (CY) for three tillage treatments in 2002; bars with the same letter are not different within the same variable measured, according to Duncan’s multiple range test, at P < 0.1. Statistical analysis was not performed for the CY data due to lack of measurement replications.
3.4. Seeding performance As compared with the CT, the NT had a similar seeding depth and the ST had 6% greater seeding depth (SD; Fig. 6). The latter observation was attributable to the more loosened seedbed of the ¨ zmerzi (2002) also sub-soiled plots. Karayel and O found that loosened seedbed promoted greater seeding depth. For the same reason, the ST resulted in slightly less uniform seeding depth as indicated by its seed scatter index (SSI) that was greater than the CT (Fig. 6). As compared with the CT, the NT slightly favoured more uniform seeding depth due to its firm seedbed. 3.5. Speed of emergence, plant population and crop yield The NT had a slightly higher speed of emergence, plant population (PP) and crop yield (CY) than the CT (Fig. 6). However, the differences were not statistically significant due to the high variations of the data. Plots that had been sub-soiled in the fall showed much faster emergence and higher plant populations than the no-tilled and conventionally tilled plots. Statistical comparisons in crop yield could not be done due to the lack of measurement replications for the ST treatments. However, the value of the crop yield for the ST was higher than that for the NT and CT. The higher soil moisture content of the NT and CT (Table 3) in the dry spring did not have any advantage over the ST in terms of speed of emergence and plant population. These
Y. Chen et al. / Soil & Tillage Research 82 (2005) 161–171
169
advantages of the sub-soiling in this regard were possibly due to the better aeration and higher temperature of the ST plots in the cold spring. The higher value of the yield for the ST could be attributable to its better drainage during a wet period and better water adsorption during a dry period. 3.6. Plant root characteristics The grid method used appears to provide a rapid, quantitative and inexpensive approach for assessing plant root distribution in soil when comparing with imaging and mechanically washing methods used in the literature (Smucker et al., 1982; Harries and Campbell, 1989). However, root mass cannot be quantified using this method. Rooting system could be influence by the amount and distribution of rainfall, which was not investigated in this study. 3.6.1. Major root penetration depth and lateral root spread Major roots of canola could penetrate to as deep as 254 mm, observed in the ST plots, and roots could laterally spread as wide as 297 mm, observed in the CT plots. Most roots in the CT and NT were concentrated above the hardpan (above the 175 mm). On average, roots in the CT penetrated 170 mm deep, and those in the ST penetrated 7% deeper (Fig. 7a) due to its greater tillage depth. Deep root penetration of the ST treatment could have contributed to the higher yield of this treatment (Fig. 6). As compared with the CT, the NT did not hinder root penetration, as indicated by their similar major root penetration depths. The average value of the lateral root spread in the CT was 187 mm, while those of the NT and ST were 11% and 4% smaller, respectively. Statistical significant differences in major root penetration depth and lateral root spread were not detected due to the high variations of the data. 3.6.2. Root distribution index Root distribution indices at different soil layers are shown in Fig. 7b. The root distribution index increased below the surface and reached to its peak at the 75 mm depth for all the tillage treatments. The root index decreased below that depth, which might be due to the development pattern of canola root. Little plant roots
Fig. 7. Canola root characteristics for three tillage treatments, measured in 2002; (a) major root penetration depth, d (S.E. = 7.1 mm) and lateral root spread, L (S.E. = 10.43 mm); (b) root distribution index along soil depth profile; (c) accumulated root distribution index at three depth intervals (S.E. = 1.0, 1.4 and 1.9 mm for 0–75, 75–200 and 0–200 mm, respectively). Values followed by the same letter within the same variable measured are not statistically different according to Duncan’s multiple range test, at P < 0.1.
were found below the hardpan located at the 175 mm depth. Differences in root distribution index between treatments were significant at the 25, 50, 175 and 200 mm depths, and no significant treatment effects were detected at the remaining layers. At the 25 and 50 mm depths, the ST had smallest indices than the CT and NT, which were not statistically different. At the 175 and 200 mm, the ST had the highest index, the NT the least and the CT intermediate.
170
Y. Chen et al. / Soil & Tillage Research 82 (2005) 161–171
The accumulated root distribution index within the normal tilled layer (0–75 mm) followed the order: NT > CT > ST (Fig. 7c), which appears as the reverse trend of the tillage intensity. In the no-tilled and conventionally tilled soils, plants tried to compensate for the restricted rooting depth by increasing lateral root production, as explained by Schumacher and Smucker (1981). The accumulated root distribution index over the 75–200 mm depth followed the trend: NT = CT < ST. This could be explained by the greater tillage depth (264 mm) of the ST, which allowed for easier root penetration to a greater depth. The depth 75–200 mm was untilled layer of the CT plots, which might have been the reason why the CT had similar accumulated root indices to the NT, within this soil depth. When compared the accumulated root distribution indices over the entire soil profile (0–200 mm), there was a particular trend: NT > CT > ST which was, however, not statistically significant.
4. Conclusions In spring before planting, the soil strength was reduced significantly and the hardpan detected in the previous fall vanished. Therefore, it is unnecessary to remove hardpans by any fall tillage in the studied region. The formation of the hardpans in the clay soil may be the result of field operations such as seeding, spraying and harvesting. Reducing the number of field operations during the growing season, reducing the ground contact pressure of tractor and increasing implement width, will reduce the occurrence of hardpan. A more uniform seeding depth was observed when seeding in the firm seedbed of the no-tilled plots than the conventionally tilled plots. No-tillage showed crop emergence, population and crop yield similar to the conventional tillage. Sub-soiling resulted in a 6% greater seeding depth than the other tillage treatments. Sub-soiling dramatically improved crop emergency, plant population and crop yield in spite of its less uniform seeding depth. This was possibly due to its improved drainage, and absorption of water as well as deep root penetration. Sub-soiling required four times higher tractor drawbar pull when working at 264 mm depth than field cultivation at 88 mm depth.
Most major roots of canola in the no-tillage and conventional tillage plots penetrated to a depth above the hardpan identified at 175 mm depth, while those in the sub-soiling tillage penetrated 7% deeper. Roots for the conventional tillage spread wider when compared to those for the no-tillage and sub-soiling tillage. As compared with the conventional tillage, the no-tilled soil contained more roots, especially in the topsoil layers, demonstrated by its 21% higher root distribution index in the 0–75 mm depth, and the sub-soiled soil contained more roots in the bottom layers as indicated by its 15% higher root distribution index in the 75–200 mm depth. Considering its low cost and comparative performance, no-tillage is a feasible tillage alternative and can be practiced in a heavy clay soil. Considering the significantly higher drawbar pull requirement of a subsoiling, one may perform sub-soiling only when needed. No-tillage and sub-soiling tillage should be further studied to confirm their effects on the performance of plant development and yield in a different year, and weather effects should be also taken into account. It would be of particular interest to study if the beneficial effects of sub-soiling can be maintained in a practice such as no-tillage following sub-soiling.
Acknowledgement The authors wish to express their sincerest gratitude and appreciation to Manitoba Agricultural and Food (Covering New Ground program) for providing the financial support to this project; the producer, Carl Classen and his family, for their collaboration; Mr. Dan Caron of Manitoba Agriculture and Food for his support to the project; graduate students Jean Louis Gratton, Mofta Mohamed and Bereket Assefa for their help on fieldwork. Special thanks are given to Sophie Zhang for her editorial assistance. References ASAE Standards, 2000. EP542 Feb99. Procedures for Using and Reporting Data Obtained with the Soil Cone Penetrometer. ASAE, St. Joseph, Mich. Atwell, B.J., 1993. Response of roots mechanical impedance. Environ. Exp. Bot. 33, 27–40.
Y. Chen et al. / Soil & Tillage Research 82 (2005) 161–171 Ball, B.C., Bickerton, D.C., Robertson, E.A.G., 1990. Residue incorporation and tillage for winter barley: soil structural effects. Soil Tillage Res. 15, 309–327. Be´ dard, Y., Tessier, S., Lague¨ , C., Chen, Y., Chi, L., 1997. Soil compaction by manure spreaders equipped with standard and oversized tires and multiple axles. Trans. ASAE 40, 37–43. Bullock, M.S., Kemper, W.D., Nelson, S.D., 1988. Soil cohesion affected by freezing water content, time and tillage. Soil Sci. Soc. Am. J. 52, 770–776. Camp, C.R., Sadler, E.J., 2002. Irrigation, deep tillage, and nitrogen management for a corn-soybean rotation. Trans. ASAE 45, 601–608. Chen, Y., 2002. A liquid manure injection tool adapted to different soil conditions. Trans. ASAE 45, 1729–1736. Chen, Y., Tessier, S., 1997. Techniques to diagnose plow and disk pans. Can. Agric. Eng. 39, 143–147. Francis, G.S., Cameron, K.C., Swift, R.S., 1987. Soil physical conditions after six years of direct drilling or conventional cultivation on silt loam soil in New Zealand. J. Soil Res. 25, 517–520. Harries, G.H., Campbell, G.S., 1989. Automated quantification of roots using a simple image analysis. Agronomy J. 81, 935–938. Gerard, C.J., Sexton, X., Shaw, G., 1982. Physical factors influencing soil strength and root growth. Agronomy J. 74, 875–879. Jolata, S.K., Khera, R., Chabal, S.S., 2001. Straw management and tillage effects on soil water storage under field conditions. Soil Use Manage. 17, 282–287. ¨ zmerzi, A., 2002. Effect of tillage methods on sowing Karayel, D., O uniformity of maize. Can. Biosyst. Eng. 44, 23–26. Kay, B.D., Grant, C.D., Groenevelt, P.H., 1985. Significance of ground freezing on soil and bulk density under zero tillage. Soil Sci. Soc. Am. J. 49, 973–978. Kladivko, E.J., Griffith, D.R., Mannering, J.V., 1986. Conservation tillage effects on soil properties and yield of corn and soybeans in Indiana. Soil Tillage Res. 8, 277–286. Letey, J., 1995. Relationship between soil physical properties and crop production. Adv. Soil Sci. 1, 227–294.
171
Lindstrom, M.J., Reicosky, D.C., 1997. Carbon dioxide loss from soil: a comparison between till and no-till management systems. In: Proceeding of 19th Annual Workshop, Manitoba–North Dakota Zero Tillage Farmers Association, Box 40, Isabella, MB, Canada, . Marshal, T.J., Holmes, J.W., 1988. Soil Physics, 2nd ed. Cambridge University Press, Cambridge, England. Materechera, S.A., Mloza-Banda, H.R., 1997. Soil cone index, root growth and yield of maize as influenced by tillage system on ridges in Malawi. Soil Tillage Res. 41, 13–24. MNZTFA, 1998. Zero Tillage. Manitoba-North Dakota Zero Tillage Farmers Association. Leech Printing Ltd., Brandon, MB Canada. Schumacher, T.E., Smucker, A.J.M., 1981. Mechanical impedance effects on oxygen uptake and porosity of drybean roots. Agronomy J. 73, 51–55. Smucker, A.J.M., McBurney, S.L., Srivastava, A.K., 1982. Quantitative separation of toots from compacted soil profiles by the hydropneumatic elutriation systems. Agronomy J. 74, 500– 503. Tessier, S., Lachance, B., Lague¨ , C., Chen, Y., Chi, L., Bachand, D., 1997. Soil compaction reduction with a modified one-way disker. Soil Tillage Res. 42, 63–77. Tessier, S., Saxton, K.E., Papendick, R.I., Hyde, G.M., 1991. Zerotillage furrow opener effects on seed environment and wheat emergence. Soil Tillage Res. 21, 347–360. Unger, P.W., Fulton, L.J., 1990. Conventional and no-tillage effects on upper root zone soil conditions. Soil Tillage Res. 16, 337– 344. Voorhees, W.B., 1983. Relative effectiveness of tillage and natural forces in alleviating wheel-induced soil compaction. Soil Sci. Soc. Am. J. 47, 129–133. Wilkins, D.E., Siements, M.C., Albrecht, S.L., 2002. Changes in soil physical characteristics during transition from intensive tillage to direct seeding. Trans. ASAE 45, 877–880. Xu, D., Mermoud, A., 2001. Topsoil properties as affected by tillage practices in North China. Soil Tillage Res. 60, 11–19.
Short-term tillage effects on soil cone index and plant development in a poorly drained, heavy clay soil Y. Chena,*, C. Caversb, S. Tessierc, F. Moneroa, D. Lobbd a
Department of Biosystems Engineering, University of Manitoba, Winnipeg, MB, Canada R3T 5V6 Manitoba Agriculture and Food, Soil and Crop Branch, Box 1149, Carman, MB, Canada R0G 0J0 c Manitoba Conservation, Headquarters Operations, 200 Saulteaux Crescent, Winnipeg, MB, Canada R3J 3W3 d Department of Soil Science, University of Manitoba, Winnipeg, MB, Canada R3T 5V6 b
Received 6 August 2003; received in revised form 11 June 2004; accepted 22 June 2004
Abstract Soil compaction is a big challenge in managing poorly drained clay soils. An on-farm field study was conducted over 2 years in a poorly drained, heavy clay soil, Red River Valley, Manitoba, Canada, where soil compaction, crop growth and root development were perceived as serious concerns. To address these concerns, no-tillage and sub-soiling tillage were proposed and compared with the traditional tillage system in which light-duty field cultivators were used at tillage depths ranging from 50 to 75 mm. Measurements of soil cone index indicated that a hardpan existed at approximately 175 mm soil depth in each fall as a result of wheel traffic during the growing season. It may not be necessary to break the hardpan with fall tillage operations in the studied region, as the hardpan was naturally removed over winter. Effects of tillage practices were evaluated using seeding performance and plant development. No-tillage resulted in the similar speed of emergence, plant population and crop yield, but more uniform seeding depth and more roots in the topsoil layer (0–75 mm), when compared with the conventional tillage. Subsoiling promoted much faster crop emergence, higher plant populations and crop yield as well as deeper root penetration than the conventional tillage. However, the draft force required for sub-soiling was four times that of the conventional tillage. # 2004 Elsevier B.V. All rights reserved. Keywords: Compaction; No-tillage; Sub-soiling; Root; Cone index; Crop
1. Introduction In the Canadian Prairies, producers have tendencies to till their soils at shallow depths (75–100 mm) so that * Corresponding author. Tel.: +1 204 474 6292; fax: +1 204 474 7512. E-mail address: [email protected] (Y. Chen).
they can use wide tillage equipment (10–20 m wide) for their large land base. Such a tillage practice in the Red River clay results in poor water infiltration and plant root development. No-tillage and subsoiling have emerged as solutions for solving these problems. No-tillage means less traffic, and in turn, less soil compaction, lower fuel and labour costs. Furthermore,
0167-1987/$ – see front matter # 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.still.2004.06.006
162
Y. Chen et al. / Soil & Tillage Research 82 (2005) 161–171
no-tillage has many other advantages such as controlling wind and water erosion, reducing soil moisture loss and greenhouse gas (carbon) emissions (Lindstrom and Reicosky, 1997). When compared with other tillage practices, long-term no-tillage increases soil organic matter (MNZTFA, 1998) and tends to have greater soil aggregate stability (Kladivko et al., 1986), which increases the resistance to compaction (Ball et al., 1990). However, no-tillage has not yet caught on in areas that have poorly drained heavy clay soils such as in Red River Valley. When switching to no-tillage (NT) from conventional tillage (CT) in such soil conditions, poor water infiltration and crop root development are major initial obstacles. The long-term benefit from no-tillage cannot be achieved easily, unless producers see that the system works in a short term. Sub-soiling can mechanically aerate soil at sub-soil layers, which promotes better water infiltration and absorption, and encourages crop root development (Xu and Mermoud, 2001). Increased yields have been reported when using deep tillage in a compacted soil (Camp and Sadler, 2002). However, sub-soiling requires great tractor power, especially in heavy clay soils, which limits the implement’s working width. This is a major obstacle for the adaptation of subsoiling tillage (ST) in the Red River Valley. The draft force required for sub-soiling needs to be explored for producers to select the appropriate width of implement so that the tractor power can be used to its maximum efficiency. This information can also be used for producers to make the justification between the benefit and the cost. Soil cone index (CI) is an empirical measure of soil strength and is widely used for assessment of the compacting and loosening effects of agricultural implements (Be´ dard et al., 1997; Tessier et al., 1997). Soil cone index can also be used to assess root growth and penetration. The higher is the cone index, the greater is the amount of energy that must be expended by the root to widen the soil pores. Some researchers (Gerard et al., 1982) have shown that increases in soil cone index decrease root elongation and growth. The threshold level at which soil strength hinders root elongation varies with plant species, but usually ranges between 2000 and 3000 kPa (Atwell, 1993). Letey (1995) reported a lower threshold value (1800 kPa).
The objective of this study was to investigate alternative tillage practices that could reduce soil compaction and promote crop performance in a Red River clay soil. Specifically, this study was to investigate the short-term effects of conventional tillage, no-tillage and sub-soiling tillage on soil compaction and plant development.
2. Material and methods 2.1. Site description Field trials were conducted over 2 years at a farm in Elm Creek, Manitoba, Canada. The soil type was poorly drained Red River clay (609 g kg1 clay, 365 g kg1 silt and 26 g kg1 sand, by weight) and is classified as Rego Humic Gleysol of the Osborne soil series. The normal field operations included spring seeding, post-emergence spraying, harvesting, and fall tillage. Prior to the study, the producer performed the tillage operations with a light-duty field cultivator working at fairly shallow tillage depths (50–75 mm). In the first year study, canary-seed crop was sown on barley straw, followed by canola in the second year. The row spacing was 0.20 m for both years. Crops were fertilized to soil test recommendations. The closest weather stations are the Starbuck and Carman Weather Stations that were located 26 km east and 17 km south of the experimental site, respectively. The weather data from these two stations were averaged and are listed in Table 1. The weather data indicated that experimental site experienced a dryer, colder spring, and the month of July was drier, while June and August were wetter, when compared to the 30-year averages. The air temperature during the summer generally conformed to the 30-year averages. 2.2. Equipment description The field cultivator (Fig. 1a) used featured furrower type (or hoe opener) tillage tools that were mounted on light-duty shanks with small tool spacing. The producer had used this cultivator for his conventional shallow tillage. The sub-soiling tillage was performed with a sub-soiler (Fig. 1b) having reversible straight spikes mounted on heavy-duty C-shanks with large
Y. Chen et al. / Soil & Tillage Research 82 (2005) 161–171
163
Table 1 Monthly air temperatures, precipitations and degree-days averaged from two nearby weather stations, 2002 Month
May June July August September
Precipitation
Degree days at 18 8C
Temperature
Total
30 Year normal
% of normal
Maximum
Minimum
Mean
30 Year normal
Cooling
Heating
49.4 136.6 55.3 112.2 25.8
60.6 81.2 76.3 68.2 51.3
81 168 72 165 50
30.4 34.5 33.7 31.4 31
8.2 1.3 7.4 5.4 5.3
8.4 17.7 20.6 18.1 14.0
3.35 0.75 1.15 0.05 1.6
5.1 46.8 90.4 40.0 12.0
303.1 55.6 10.8 36.8 183.7
tool spacing. A 315 kW John Deere tractor (Model 9400) was used to pull all the field equipment during field operations. More details about the field cultivator and sub-soiler are given in Table 2.
2.3. Experimental design In fall 2000, two tillage treatments: conventional tillage and no-tillage were established. In fall 2001, a new treatment, sub-soiling tillage, was added to the field plots. Treatments and equipment parameters are summarized in Table 2. Each treatment was replicated four times. The length of the plots was 90 m. The widths of the CT and ST plots were 12.2 and 3.3 m, respectively, being one pass of the respective tillage implement. The width of the NT plots was 12.2 m. Seeding was performed perpendicular to the plots with a 20 m wide hoe airseeder (John Deere 1820). 2.4. Measurements
Fig. 1. Tillage implements used; (a) side view of the field cultivator for the conventional tillage treatment (CT) in falls 2000 and 2001; (b) the rear view of the sub-soiler for the sub-soiling tillage treatment (ST) in fall 2001.
2.4.1. Soil cone index Soil CI was measured to quantify the level of soil compaction. The Rimik cone penetrometer (Model CP 20, Agridy Rimik Pty. Ltd., Toowoomba, Australia) used was comprised of an in-built data logger, an 800mm long shaft, a cone with a base area of 129 mm2 and an apex angle of 308. The penetrometer was pushed into the soil by hand at a speed of approximately 0.30 mm s1 (ASAE, 2000). Measurements of CI were made at 18 random locations over the entire field before the initiation of the field trials in 2000, and at 12 locations per plot before fall tillage in 2001 and spring seeding in 2001 and 2002. At each location, three measurements were taken to a soil depth of 400 mm at 25 mm increment. Since CI is strongly related to the water content (Materechera and Mloza-Banda, 1997), CI measurements were performed after a heavy rainfall event whenever possible, to maximize uniformity of soil moisture content through the depth profile.
164
Y. Chen et al. / Soil & Tillage Research 82 (2005) 161–171
Table 2 Description of the treatments and the equipment Treatment
NT CT ST
Description
No-tillage Conventional tillage Sub-soiling tillage
Tillage implement
Tillage tool
Type
Width (m)
Tool spacing (m)
Type
Working width (m)
Field cultivator Sub-soiler
12.2 3.3
0.2 0.6
Furrower Narrow point
0.1 0.06
2.4.2. Soil moisture content At the same day of tillage and seeding operation, 10 soil samples were taken randomly on each plot to a depth of 400 mm with 100 mm intervals. Soil samples were weighed, oven-dried at 105 8C for 24 hours, and weighed again to determine the gravimetric moisture content.
2.4.4. Tillage depth In fall 2001, immediately following the tillage operations, tillage depth was measured at 10 random locations on each plot. Loose soil was removed from the soil furrow created by the tillage tools. A board was placed across the furrow on the original soil surface. The tillage depth was measured from the furrow bottom to the board.
2.4.3. Draft force A custom-made DEOR dynamometer was used to measure the draft force of the tillage implement in fall 2001. The dynamometer was installed between the tractor and the implement (Fig. 2) and was connected to a data logger (ProDAS, Michigan Scientific Corporation, 321E Huron St., Mifford MI 48381) in the tractor cab. The force signal was recorded at 100 Hz for 40 s while the tillage implement passed the middle section of the plot. A constant tractor travel speed of 1.7 m s1 was maintained for the tillage operations.
2.4.5. Speed of emergence (SE) and plant population In spring 2002, plant counts were made in a 0.6-m long crop row at 15 random locations on each plot, 4, 7 and 10 days after the first seedling emergence, and weekly thereafter until a stable count was obtained. The speed of emergence (Tessier et al., 1991) was calculated by P ðNi =di Þ SE ¼ A
Fig. 2. The DEOR Dynamometer installed between the tractor and tillage implement hitches to measure the draft forces of the tillage implements in fall 2001.
where SE is the speed of emergence per unit area (plants d1 m2), Ni, the number of newly emerged seedlings counted per day di and A (m2) is the area calculated by the length of the row counted and the airseeder’s row spacing. The final plant count was used as the final plant population (plants m2). 2.4.6. Seeding depth (SD) It was not possible to determine the seeding depth of canola by measuring the CFL (chlorophyll-free length, from the seed remnants to the onset of green stem; Tessier et al., 1991) of the seedlings because this plant does not maintain its seed remnant below the soil surface. Therefore, canary-seed (4.5 kg ha1), having similar size, was mixed and planted with the canola seed (4.5 kg ha1). After the final plant count was completed in spring 2002, five canary-seed seedlings were uprooted from each row used for plant counting, and their CFL were measured, and considered as the effective seeding depths of the canola. After seeding
Y. Chen et al. / Soil & Tillage Research 82 (2005) 161–171
depth measurements, the canary-seed plants were destroyed using herbicide. 2.4.7. Crop yield In 2002, the canola was swathed with the producer’s 8-m swather first. Crop yields for the NT and CT plots were measured with the producer’s combine and a weigh wagon. The combine picked up a 10-m-long swath in the middle of each plot. Only one 10-m-long swath was picked up over the four ST plots. Thus, there were no replications for the measurement of the yield for the ST treatment. Grain samples were oven-dried at 60 8C for 72 hours to determine the dry matter yield. 2.4.8. Root distribution After harvest in 2002, trenches were dug across a crop row to obtain a soil cross-section with exposed crop roots (Fig. 3). The face of each trench was trimmed with shovels and trowels to get a vertical face. A 300-mm ruler was put on the soil surface as a scale reference. A digital image of the trench’s crosssection was taken. The measurements were performed at five random locations per plot. The digital images were processed with the grid method where square
165
grids (25 mm 25 mm) were overlapped on the image (Fig. 3). The major root penetration depth (d) and the lateral root spread (L) (Fig. 3) were estimated using the square grids as reference. Root distribution in the soil profile was assessed by counting the number of intersections with the vertical lines of the grids in each 25 mm vertical layer (layer divided by grid lines), which was defined as the root distribution index of that layer. 2.5. Data analysis Analysis of variance (ANOVA) was performed on the data. Means between treatments were compared with Duncan’s multiple range tests. The statistical inferences were made at a 0.1 level of significance.
3. Results and discussion 3.1. Soil moisture content and bulk density The soil dry bulk density in fall 2000 at tillage (Table 3) represented initial soil condition before the
Fig. 3. Typical image showing the soil cross-section with roots and grids overlapped on the image, used for root measurements in 2002; d = major root penetration depth and L = lateral root spread.
166
Y. Chen et al. / Soil & Tillage Research 82 (2005) 161–171
Table 3 Average gravimetric soil moisture content (%, dry basis) and dry bulk density (mg m3) at the tillage and seeding times Depth (mm)
0–100 100–200 200–300 300–400 a b c
Fall 2000 at tillage
Spring 2001 at seeding
Fall 2001 at tillage
Spring 2002 at seeding
ra
MCb
ra
MCb
ra
MCb
ra
MCc NT
CT
ST
1.27 1.46 1.53 –
32 34 35 –
0.90 1.06 1.16 1.41
47 30 34 25
0.79 1.10 1.35 1.23
31 34 20 44
0.79 1.10 1.35 1.23
39 37 32 34
36 31 34 32
29 29 29 30
Average value of soil dry bulk density over the entire plot area. Average value of soil moisture content over the entire plot area. Average value of soil moisture content for each tillage treatment.
tillage treatments were established. Those values were associated with the producer’s conventional tillage. Those initial densities were greater than those obtained in the 2001 and 2002. This implied that the introduction of the NT and ST reduced the overall soil density. Gravimetric soil moisture at the tillage times in falls 2000 and 2001 was desirable for tillage operations (Table 3). Soil moisture contents were fairly uniform along the soil profile. At spring 2001 seeding time, the soil moisture content on the topsoil layer (0–100 mm) was quite high (47%). At spring 2002 seeding time, the precipitation was below the 30 year normal (Table 1). However, the soil moisture content at the seedbed layer (0–100 mm), ranging from 29 to 39%, was adequate for seeding due to the high field capacity of the clay soil. At that time, the NT increased the soil moisture content by 8%, while the ST decreased by 11%, as compared with the CT. The higher residue cover in the no-tilled plots likely reduced soil moisture loss and the sub-soiling promoted water evaporation loss (Jolata et al., 2001; Xu and Mermoud, 2001). 3.2. Soil cone index 3.2.1. Hardpans in soil Data prior to the initiation of the tillage trials in fall 2000 showed that the CI increased continuously, reached a peak of 1088 kPa at 175 mm, and then decreased (Fig. 4a). According to the concept of the profile analysis method (Chen and Tessier, 1997), a hardpan existed at the 175 mm depth. A hardpan was also identified in fall 2001 at the same depth (175 mm; Fig. 4b). The peak CI value, 1775 kPa, was close to the
agronomical threshold of 1800 kPa (Letey, 1995). Hence, this hardpan could be a potential limiting factor for plant root development, especially if the soil is drier, as soil strength increases as the soil dries (Francis et al., 1987). 3.2.2. Cause of the hardpans CI values measured in spring 2001 (Fig. 4c) increased linearly from the 0 to 175 mm depth and slowly increased at lower depths. A similar trend was observed in the spring 2002 (Fig. 4d). The values of CI in spring were approximately 34% lower on average than those observed in the previous fall, possibly due to the effects of soil freezing-thawing cycles on soil strength. Voorhees (1983) also observed that the soil strength decreases after winter. In addition, no hardpan was detected in either spring, as indicated by the smooth CI curves along the soil depth profile (Fig. 4c,d). The expansion of water upon freezing can alleviate compacted soils through the formation of vertical and horizontal microfractures (Kay et al., 1985; Marshal and Holmes, 1988). Tillage operations can result in a hardpan at a depth immediately or other than immediately below the tilled layer in the soil profile, as grousers of tractor tires can penetrate the tilled layer and shear the soil under the tilled layer (Chen and Tessier, 1997). However, whether or not a hardpan formed as the result of the tillage operations is not a concern in the studied region, because tillage is performed in fall and a hardpan would disappear over winter. The CI results also imply that the hardpans detected each fall were the results of wheel traffics from seeding, spraying, harvesting and any other field operations during the growing season. Contrary to what
Y. Chen et al. / Soil & Tillage Research 82 (2005) 161–171
167
Fig. 4. Soil cone index (CI) versus depth under different tillage treatments; (a) fall 2000; (b) fall 2001; (c) spring 2001; (d) spring 2002.
producers think, fall tillage operations would not be necessary to break hardpans. Efforts for reducing soil compaction should be devoted to field operations during the growing season, such as minimizing wheel traffic and using wide tractor tires. It would be useful to monitor the changes in soil cone index as affected by each field operation during the growing season, so as to find out the exact time when the hardpan occurs. 3.2.3. Effects of tillage treatments As tillage effects most likely pertain to the tilled layer (Unger and Fulton, 1990), the following discussion focuses on trends within the tilled layer. CI values in spring 2001 showed that the CT had reduced soil strength in the tilled layers when compared to the NT (Fig. 4c). Wilkins et al. (2002) also reported that a short-term no-tilled soil had higher soil strengths than a tilled soil. However, the statistically significant difference in this regard was observed only at one depth (50 mm). There were no
differences in CI found between the NT and the CT in fall 2001 (Fig. 4b). In spring 2002, the ST resulted in the same level of CI as the CT and NT, although the sub-soiled plots were expected to have lower PR. This may be due to the lower soil moisture content of the sub-soiled soil (Table 3). The large shank spacing of the sub-soiler could also have been responsible for this observation because the undisturbed area was greater in the subsoiled plots than the conventionally tilled plots. Data showed that tillage effects on CI were less pronounced than weather effects in this clay soil condition. Bullock et al. (1988) have observed that the disruption of soil aggregates by freezing can be more pronounced than a single pass of most tillage implements. 3.3. Draft forces It was the intention to set the tillage depth as deep as possible to enhance root penetration. However, due to the limitation of the shank trip force, the actual
168
Y. Chen et al. / Soil & Tillage Research 82 (2005) 161–171
Fig. 5. Total draft force (Total F), draft force per tool (F/tool) and draft force per meter of the implement width (F/m) for two different tillage treatments measured in fall 2001 and predicted according to ASAE Data (ASAE Standards, 2000); bars with the same letter are not different within the same variable according to Duncan’s multiple range test at P < 0.1.
tillage depth of the CT was only 88 mm and that of the ST was 264 mm. When operated at those depths, the 12.2-m field cultivator and the 3.3-m sub-soiler had similar total draft force (Fig. 5). Furthermore, subsoiling would consume more field time and create more tractor wheel tracks in the field. Specific forces were defined as the total draft force divided by the working width of the implement or the number of tools on the implement. Due to the greater tillage depth, the ST required four times more draft force per meter of implement width than the CT (Fig. 5), although the tool spacing of the ST was much larger. As for the force per tool, the ST gave a value 12 times higher because of its three-fold greater tillage depth. This information can be used to match the implement with tractor power to ensure that the drawbar pull of the tractor is efficiently used. Note that draft force of implement changes with its operational speed. However, speed effects on draft are less pronounced than depth effects (Chen, 2002). Predictions of draft force were made with model parameters listed in Agricultural Machinery Management Data (ASAE Standard, 1999) for narrow point sub-soiler and field cultivator in a fine soil. As compared with the measurements, the predicted values for the CT are 30% lower and those for the ST were 20% lower at the travel speed and tillage depth used in the field trial (Fig. 5). Chen (2002) also found that the ASAE Agricultural Machinery Management Data underestimated draft forces of a winged tillage tool under a clay soil.
Fig. 6. Seeding depth (SD), seed scatter index (SSI), speed of emergence (SE), plant population (PP), and crop yield (CY) for three tillage treatments in 2002; bars with the same letter are not different within the same variable measured, according to Duncan’s multiple range test, at P < 0.1. Statistical analysis was not performed for the CY data due to lack of measurement replications.
3.4. Seeding performance As compared with the CT, the NT had a similar seeding depth and the ST had 6% greater seeding depth (SD; Fig. 6). The latter observation was attributable to the more loosened seedbed of the ¨ zmerzi (2002) also sub-soiled plots. Karayel and O found that loosened seedbed promoted greater seeding depth. For the same reason, the ST resulted in slightly less uniform seeding depth as indicated by its seed scatter index (SSI) that was greater than the CT (Fig. 6). As compared with the CT, the NT slightly favoured more uniform seeding depth due to its firm seedbed. 3.5. Speed of emergence, plant population and crop yield The NT had a slightly higher speed of emergence, plant population (PP) and crop yield (CY) than the CT (Fig. 6). However, the differences were not statistically significant due to the high variations of the data. Plots that had been sub-soiled in the fall showed much faster emergence and higher plant populations than the no-tilled and conventionally tilled plots. Statistical comparisons in crop yield could not be done due to the lack of measurement replications for the ST treatments. However, the value of the crop yield for the ST was higher than that for the NT and CT. The higher soil moisture content of the NT and CT (Table 3) in the dry spring did not have any advantage over the ST in terms of speed of emergence and plant population. These
Y. Chen et al. / Soil & Tillage Research 82 (2005) 161–171
169
advantages of the sub-soiling in this regard were possibly due to the better aeration and higher temperature of the ST plots in the cold spring. The higher value of the yield for the ST could be attributable to its better drainage during a wet period and better water adsorption during a dry period. 3.6. Plant root characteristics The grid method used appears to provide a rapid, quantitative and inexpensive approach for assessing plant root distribution in soil when comparing with imaging and mechanically washing methods used in the literature (Smucker et al., 1982; Harries and Campbell, 1989). However, root mass cannot be quantified using this method. Rooting system could be influence by the amount and distribution of rainfall, which was not investigated in this study. 3.6.1. Major root penetration depth and lateral root spread Major roots of canola could penetrate to as deep as 254 mm, observed in the ST plots, and roots could laterally spread as wide as 297 mm, observed in the CT plots. Most roots in the CT and NT were concentrated above the hardpan (above the 175 mm). On average, roots in the CT penetrated 170 mm deep, and those in the ST penetrated 7% deeper (Fig. 7a) due to its greater tillage depth. Deep root penetration of the ST treatment could have contributed to the higher yield of this treatment (Fig. 6). As compared with the CT, the NT did not hinder root penetration, as indicated by their similar major root penetration depths. The average value of the lateral root spread in the CT was 187 mm, while those of the NT and ST were 11% and 4% smaller, respectively. Statistical significant differences in major root penetration depth and lateral root spread were not detected due to the high variations of the data. 3.6.2. Root distribution index Root distribution indices at different soil layers are shown in Fig. 7b. The root distribution index increased below the surface and reached to its peak at the 75 mm depth for all the tillage treatments. The root index decreased below that depth, which might be due to the development pattern of canola root. Little plant roots
Fig. 7. Canola root characteristics for three tillage treatments, measured in 2002; (a) major root penetration depth, d (S.E. = 7.1 mm) and lateral root spread, L (S.E. = 10.43 mm); (b) root distribution index along soil depth profile; (c) accumulated root distribution index at three depth intervals (S.E. = 1.0, 1.4 and 1.9 mm for 0–75, 75–200 and 0–200 mm, respectively). Values followed by the same letter within the same variable measured are not statistically different according to Duncan’s multiple range test, at P < 0.1.
were found below the hardpan located at the 175 mm depth. Differences in root distribution index between treatments were significant at the 25, 50, 175 and 200 mm depths, and no significant treatment effects were detected at the remaining layers. At the 25 and 50 mm depths, the ST had smallest indices than the CT and NT, which were not statistically different. At the 175 and 200 mm, the ST had the highest index, the NT the least and the CT intermediate.
170
Y. Chen et al. / Soil & Tillage Research 82 (2005) 161–171
The accumulated root distribution index within the normal tilled layer (0–75 mm) followed the order: NT > CT > ST (Fig. 7c), which appears as the reverse trend of the tillage intensity. In the no-tilled and conventionally tilled soils, plants tried to compensate for the restricted rooting depth by increasing lateral root production, as explained by Schumacher and Smucker (1981). The accumulated root distribution index over the 75–200 mm depth followed the trend: NT = CT < ST. This could be explained by the greater tillage depth (264 mm) of the ST, which allowed for easier root penetration to a greater depth. The depth 75–200 mm was untilled layer of the CT plots, which might have been the reason why the CT had similar accumulated root indices to the NT, within this soil depth. When compared the accumulated root distribution indices over the entire soil profile (0–200 mm), there was a particular trend: NT > CT > ST which was, however, not statistically significant.
4. Conclusions In spring before planting, the soil strength was reduced significantly and the hardpan detected in the previous fall vanished. Therefore, it is unnecessary to remove hardpans by any fall tillage in the studied region. The formation of the hardpans in the clay soil may be the result of field operations such as seeding, spraying and harvesting. Reducing the number of field operations during the growing season, reducing the ground contact pressure of tractor and increasing implement width, will reduce the occurrence of hardpan. A more uniform seeding depth was observed when seeding in the firm seedbed of the no-tilled plots than the conventionally tilled plots. No-tillage showed crop emergence, population and crop yield similar to the conventional tillage. Sub-soiling resulted in a 6% greater seeding depth than the other tillage treatments. Sub-soiling dramatically improved crop emergency, plant population and crop yield in spite of its less uniform seeding depth. This was possibly due to its improved drainage, and absorption of water as well as deep root penetration. Sub-soiling required four times higher tractor drawbar pull when working at 264 mm depth than field cultivation at 88 mm depth.
Most major roots of canola in the no-tillage and conventional tillage plots penetrated to a depth above the hardpan identified at 175 mm depth, while those in the sub-soiling tillage penetrated 7% deeper. Roots for the conventional tillage spread wider when compared to those for the no-tillage and sub-soiling tillage. As compared with the conventional tillage, the no-tilled soil contained more roots, especially in the topsoil layers, demonstrated by its 21% higher root distribution index in the 0–75 mm depth, and the sub-soiled soil contained more roots in the bottom layers as indicated by its 15% higher root distribution index in the 75–200 mm depth. Considering its low cost and comparative performance, no-tillage is a feasible tillage alternative and can be practiced in a heavy clay soil. Considering the significantly higher drawbar pull requirement of a subsoiling, one may perform sub-soiling only when needed. No-tillage and sub-soiling tillage should be further studied to confirm their effects on the performance of plant development and yield in a different year, and weather effects should be also taken into account. It would be of particular interest to study if the beneficial effects of sub-soiling can be maintained in a practice such as no-tillage following sub-soiling.
Acknowledgement The authors wish to express their sincerest gratitude and appreciation to Manitoba Agricultural and Food (Covering New Ground program) for providing the financial support to this project; the producer, Carl Classen and his family, for their collaboration; Mr. Dan Caron of Manitoba Agriculture and Food for his support to the project; graduate students Jean Louis Gratton, Mofta Mohamed and Bereket Assefa for their help on fieldwork. Special thanks are given to Sophie Zhang for her editorial assistance. References ASAE Standards, 2000. EP542 Feb99. Procedures for Using and Reporting Data Obtained with the Soil Cone Penetrometer. ASAE, St. Joseph, Mich. Atwell, B.J., 1993. Response of roots mechanical impedance. Environ. Exp. Bot. 33, 27–40.
Y. Chen et al. / Soil & Tillage Research 82 (2005) 161–171 Ball, B.C., Bickerton, D.C., Robertson, E.A.G., 1990. Residue incorporation and tillage for winter barley: soil structural effects. Soil Tillage Res. 15, 309–327. Be´ dard, Y., Tessier, S., Lague¨ , C., Chen, Y., Chi, L., 1997. Soil compaction by manure spreaders equipped with standard and oversized tires and multiple axles. Trans. ASAE 40, 37–43. Bullock, M.S., Kemper, W.D., Nelson, S.D., 1988. Soil cohesion affected by freezing water content, time and tillage. Soil Sci. Soc. Am. J. 52, 770–776. Camp, C.R., Sadler, E.J., 2002. Irrigation, deep tillage, and nitrogen management for a corn-soybean rotation. Trans. ASAE 45, 601–608. Chen, Y., 2002. A liquid manure injection tool adapted to different soil conditions. Trans. ASAE 45, 1729–1736. Chen, Y., Tessier, S., 1997. Techniques to diagnose plow and disk pans. Can. Agric. Eng. 39, 143–147. Francis, G.S., Cameron, K.C., Swift, R.S., 1987. Soil physical conditions after six years of direct drilling or conventional cultivation on silt loam soil in New Zealand. J. Soil Res. 25, 517–520. Harries, G.H., Campbell, G.S., 1989. Automated quantification of roots using a simple image analysis. Agronomy J. 81, 935–938. Gerard, C.J., Sexton, X., Shaw, G., 1982. Physical factors influencing soil strength and root growth. Agronomy J. 74, 875–879. Jolata, S.K., Khera, R., Chabal, S.S., 2001. Straw management and tillage effects on soil water storage under field conditions. Soil Use Manage. 17, 282–287. ¨ zmerzi, A., 2002. Effect of tillage methods on sowing Karayel, D., O uniformity of maize. Can. Biosyst. Eng. 44, 23–26. Kay, B.D., Grant, C.D., Groenevelt, P.H., 1985. Significance of ground freezing on soil and bulk density under zero tillage. Soil Sci. Soc. Am. J. 49, 973–978. Kladivko, E.J., Griffith, D.R., Mannering, J.V., 1986. Conservation tillage effects on soil properties and yield of corn and soybeans in Indiana. Soil Tillage Res. 8, 277–286. Letey, J., 1995. Relationship between soil physical properties and crop production. Adv. Soil Sci. 1, 227–294.
171
Lindstrom, M.J., Reicosky, D.C., 1997. Carbon dioxide loss from soil: a comparison between till and no-till management systems. In: Proceeding of 19th Annual Workshop, Manitoba–North Dakota Zero Tillage Farmers Association, Box 40, Isabella, MB, Canada, . Marshal, T.J., Holmes, J.W., 1988. Soil Physics, 2nd ed. Cambridge University Press, Cambridge, England. Materechera, S.A., Mloza-Banda, H.R., 1997. Soil cone index, root growth and yield of maize as influenced by tillage system on ridges in Malawi. Soil Tillage Res. 41, 13–24. MNZTFA, 1998. Zero Tillage. Manitoba-North Dakota Zero Tillage Farmers Association. Leech Printing Ltd., Brandon, MB Canada. Schumacher, T.E., Smucker, A.J.M., 1981. Mechanical impedance effects on oxygen uptake and porosity of drybean roots. Agronomy J. 73, 51–55. Smucker, A.J.M., McBurney, S.L., Srivastava, A.K., 1982. Quantitative separation of toots from compacted soil profiles by the hydropneumatic elutriation systems. Agronomy J. 74, 500– 503. Tessier, S., Lachance, B., Lague¨ , C., Chen, Y., Chi, L., Bachand, D., 1997. Soil compaction reduction with a modified one-way disker. Soil Tillage Res. 42, 63–77. Tessier, S., Saxton, K.E., Papendick, R.I., Hyde, G.M., 1991. Zerotillage furrow opener effects on seed environment and wheat emergence. Soil Tillage Res. 21, 347–360. Unger, P.W., Fulton, L.J., 1990. Conventional and no-tillage effects on upper root zone soil conditions. Soil Tillage Res. 16, 337– 344. Voorhees, W.B., 1983. Relative effectiveness of tillage and natural forces in alleviating wheel-induced soil compaction. Soil Sci. Soc. Am. J. 47, 129–133. Wilkins, D.E., Siements, M.C., Albrecht, S.L., 2002. Changes in soil physical characteristics during transition from intensive tillage to direct seeding. Trans. ASAE 45, 877–880. Xu, D., Mermoud, A., 2001. Topsoil properties as affected by tillage practices in North China. Soil Tillage Res. 60, 11–19.