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Crop responses to applied soil compaction and to compaction repair treatments
Soil & Tillage Research 61 (2001) 157–166
Crop responses to applied soil compaction and to compaction repair treatments B.J. Radforda,*, D.F. Yuleb, D. McGarryb, C. Playfordc a
Queensland Department of Natural Resources and Mines, Locked Mail Bag No. 1, Biloela, Qld 4715, Australia b Queensland Department of Natural Resources and Mines, Meiers Road, Indooroopilly, Qld 4068, Australia c Queensland Department of Primary Industries, P.O. Box 6014, Rockhampton, Qld 4702, Australia Received 4 September 2000; received in revised form 7 February 2001; accepted 25 February 2001
Abstract Crop responses to annual compaction treatments (applied to whole plots) and management treatments to ameliorate compacted soil were determined in a field experiment on a Vertisol. Initially, all treatments except a control were compacted with a 10 Mg axle load on wet soil (26% gravimetric water content compared with a plastic limit of 22%). Annually applied axle loads of 10 and 6 Mg on wet soil (25–32% soil water) tended to reduce seedling emergence, grain yield (wheat, sorghum and maize), soil water storage and crop water use efficiency (WUE). Annual applications of an axle load of 6 Mg on dry soil (<22% soil water) had little effect on crop performance. Mean reductions in the yield of five crops (three wheat, one sorghum and one maize) in comparison with the uncompacted control were 23% or 0.79 Mg ha1 (10 Mg on wet soil), 13% or 0.44 Mg ha1 (6 Mg on wet soil) and 1% or 0.03 Mg ha1 (6 Mg on dry soil). Maize grown in the fifth year of treatment application was most affected by compaction of wet soil, its WUE being reduced from 14.3 to 9.7 kg ha1 mm1 in response to an axle load of 10 Mg. Reduced WUE was associated with delayed soil water extraction at depth. A 3-year pasture ley was the most successful amelioration treatment. A wheat and a maize crop grown after the ley outyielded the control by 0.33 and 0.90 Mg ha1, respectively. So the pasture not only ameliorated the initial compaction damage, with respect to crop performance, but resulted in improvements in two subsequent crops. # 2001 Elsevier Science B.V. All rights reserved. Keywords: Soil compaction; Grain crops; Crop emergence; Grain yield; Ley pasture
1. Introduction Compaction-induced soil degradation affects about 68 million hectares of land globally (Flowers and Lal, 1998). A component of progressive subsoil damage is the increase in weight of farm machinery in recent decades (Alakukku, 1996a). In the Australian context,
*
Corresponding author. Tel.: þ61-749-929106; fax: þ61-749-923468. E-mail address: [email protected] (B.J. Radford).
soil structural decline has been ranked as Australia’s greatest problem in terms of damage to the soil resource used for cropping (Williams, 1998; McGarry et al., 1999). The vast majority of soil compaction in modern agriculture is caused by vehicular traffic (Flowers and Lal, 1998). Damage from high axle loads increases when the soil is wet because wet soil has reduced strength (Kirby and Kirchhoff, 1990). Tillage and harvest operations commonly have to be carried out when the surface soil is wetter than optimal for wheel traffic. High tyre inflation pressures also increase soil
0167-1987/01/$ – see front matter # 2001 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 7 - 1 9 8 7 ( 0 1 ) 0 0 1 9 4 - 5
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damage (Soane et al., 1981; Rickman and Chanasyk, 1988). The first pass of a wheel causes the greatest amount of soil compaction (Rickman and Chanasyk, 1988; Alakukku, 1996b). In any one crop cycle, more than 30% of ground area is trafficked by the tyres of heavy machinery under zero tillage, 60% under minimum tillage and more than 100% under conventional tillage (Tullberg, 1990). Considerable evidence exists to show that soil compaction, originating from either anthropogenic or natural causes, exerts an enormous impact on the establishment, growth and yield of crops in tropical regions (Kayombo and Lal, 1994). Factors affecting crop yield response to compaction by wheel traffic are not easily defined (Voorhees et al., 1989). When wheel traffic does reduce yield, mechanisms for response should be thoroughly examined (Logsdon et al., 1992). A confounding factor in relating the visible or measured presence of compaction to yield loss is the known interaction between growing season rainfall (or irrigation intensity) and yield (Ha˚ kansson et al., 1988; McGarry, 1993). Compaction in the plough layer (surface soil compaction) can be alleviated by tillage and natural processes, while subsurface compaction is usually alleviated only by natural processes such as freezing/thawing, drying/wetting and biological activity (Ha˚ kansson et al., 1987). Subsurface compaction thus often persists for a long time, and has been measured 3–11 years after heavy loading (Alakukku, 1996b). However, the natural processes of compaction amelioration can be enhanced with judicious management. For example, the number of wet–dry cycles can be increased by growing a crop or pasture on a clay soil with swell-shrink potential (Pillai and McGarry, 1999). The introduction of suitable earthworm species may also hasten amelioration (Zund et al., 1997; Fragoso et al., 1997), particularly when combined with management practices (such as conservation tillage) which increase worm populations (Rovira et al., 1987; McGarry et al., 2000). The objective of the work reported in this paper was to determine the effects of applied soil compaction on crop performance (wheat, sorghum and maize) and to assess management treatments designed to help ameliorate compaction damage.
2. Materials and methods The study was conducted for 6 years at a single site in a semi-arid environment. All treatments except a control received an initial compaction treatment with harvester wheels on the entire plot areas. Further compaction treatments were applied annually to whole plots with harvester or tractor wheels on soil at varying water contents. Cultural operations were carried out using a system of controlled traffic farming so that wheel traffic was confined to the permanent wheel tracks, which were spaced 3 m apart. Crops grown were wheat (four crops), sorghum (1) and maize (1). Row spacing was 0.3 m for wheat and 0.75 m for sorghum and maize. 2.1. Site The site at Biloela, Qld, Australia (latitude 248220 S, longitude 1508310 E, altitude 173 m) is relatively level ðslope ¼ 0:2%Þ. The soil is a black cracking clay (a Vertisol) developed on an alluvial deposit. Details of selected soil physical properties are shown in Table 1. The liquid limit (drop cone), plastic limit (rolling bead) and 1.5 MPa (wilting point of <2 mm sieved soil by pressure plate) values in the 0–0.1 m layer were 56, 22 and 17% gravimetric water content, respectively. The mean annual rainfall is 685 mm and mean annual evaporation (from a class ‘‘A’’ pan) is 1868 mm. 2.2. Design We used a split-plot design with two replications of two irrigation (I) treatments (raingrown and supplementary irrigation of 75 mm at crop anthesis) with each main plot split into 14 subplots: seven compaction amelioration (C) treatments two fertiliser (F) treatments (control and fertilised). Each plot measured 30 9 m. 2.3. Treatments The two irrigation treatments were included to measure interactions between water supply and yield. The irrigated treatment received one application of 75 mm of water at crop anthesis in all years except 1998 when no irrigation treatment was imposed.
Depth (m)
Soil property PSAa
0–0.05 0.05–0.1 0.1–0.2 0.2–0.3 0.3–0.4 0.4–0.5 0.5–0.6 0.6–0.9 0.9–1.2 1.2–1.5 a
CS (%)
FS (%)
S (%)
C (%)
3 3 2 2 2 1 3 3 3 7
19 19 19 18 17 21 22 25 30 37
31 28 27 27 22 24 24 26 21 20
45 48 53 51 55 53 51 47 43 35
R1b pHc
EC (dS m1)d
Cl (mg kg1)e
CEC (meq%)f
ESP (meq%)g
Organic C (%)h
Total N (%)i
P (mg kg1) j
0.39 7.3 0.40 7.3 0.59 7.8 0.58 7.9 0.63 8.0 0.63 8.2 0.66 8.3 0.65 8.5 0.68 8.4 0.73 8.3
0.157 0.152 0.126 0.128 0.145 0.167 0.189 0.270 0.351 0.386
7 6 18 33 50 65 85 146 269 373
30 34 36 33 35 – – – – –
0.64 0.67 1.30 1.50 1.70 – – – – –
1.7 1.6 1.2 0.9 1.0 – – – – –
0.12 0.11 0.07 0.06 0.06 – – – – –
96 94 70 57 52 – – – – –
Particle size analysis by disaggregating the soil in an aqueous solution by means of chemical reagents and mechanical dispersion, and determining coarse and fine sand fractions gravimetrically and the silt and clay fractions using a hydrometer: CS, coarse sand (>200 mm); FS, fine sand (20–200 mm); S, silt (2–20 mm); C, clay (<2 mm). b Dispersion ratio: % ðsilt þ clayÞ dispersed in water=% total ðsilt þ clayÞ (Bruce and Rayment, 1982). c 1:5 pH (water). d 1:5 electrical conductivity. e 1:5 extractable chloride. f Cation exchange capacity (pH 8.5). g Exchangeable sodium percentage (pH 8.5). h Organic carbon (Walkley and Black, 1934). i Total nitrogen (Kjeldahl digest). j Bicarbonate extractable P (Colwell, 1963).
B.J. Radford et al. / Soil & Tillage Research 61 (2001) 157–166
Table 1 Selected physical and chemical properties of the soil profile (0–1.5 m)
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The initial compaction treatment was applied in April 1993 with the lugged rubber tyres of a Ford New Holland 8060 harvester. Axle loads were 10 and 2 Mg on the front and rear axles, respectively. Inflation pressures were high to maximise compaction: 235 kPa (front) and 205 kPa (rear). The mean gravimetric soil water content at 0–0.1 m during compaction was 25.9%. Harvesting on such wet soil is a short-term economic necessity when summer storms threaten crops. For this study we compacted the entire plot with a single pass of front and rear header wheels. This experimental treatment is not unrealistic because random wheel traffic during a fallow typically covers most of the ground area. The seven compaction/amelioration treatments were: C0
C1
C2
C3
C4 C5
C6
No applied compaction/reduced (dry) tillage (i.e. the soil was tilled only at gravimetric water contents <22%, the plastic limit, to the depth of tillage). Initial compaction; annual wet compaction with a header (10 Mg maximum axle load) at soil water contents of 25–32% (0–0.1 m); frequent tillage to 1995 at soil water contents varying from 14 to 24% (0– 0.1 m), no tillage after 1995. Initial compaction; annual wet compaction with a tractor (6 Mg maximum axle load) at soil water contents of 25–32% (0–0.1 m); frequent tillage at soil water contents varying from 14 to 24% (0–0.1 m). Initial compaction; annual dry compaction with a tractor (6 Mg maximum axle load) at soil water contents <22% to a depth of 0.08 m; reduced (dry) tillage. Initial compaction; no tillage. Initial compaction; cropping/deep ripping (with a chisel plough) and scarifying at soil water contents <22% to the depth of tillage; no tillage. Initial compaction; pasture ley of lucerne (Medicago sativa cv. Trifecta) and Gatton panic (Panicum maximum Jacq. cv. Gatton) for 3 years (cut 10 times and returned to the soil); reduced (dry) tillage; cropping.
The fertilised treatment received nitrogen as urea on four occasions and zinc as a foliar spray of 1%
zinc sulphate heptahydrate on three occasions (Table 2). The timing of all compaction and tillage treatments is shown in Table 2. 2.4. Management Crops were grown utilising water stored in the soil during a fallow, as well as in-crop rainfall. The crops grown were wheat (Hartog) in 1993, wheat (Hartog) in 1994, sorghum (MR31) in 1995, wheat (Hartog) in 1996, wheat (Sunstate) in 1997 and maize (DK689) in 1998. Sowing dates for the crops and pasture are shown in Table 2. Chlorpyrifos (500 g a.i. l1) insecticide was applied at 1 l ha1 on 20 August 1996 to control armyworm, Mythimna convecta (Walker), in wheat. Herbicides were used when necessary to control weeds in treatments with no or reduced tillage. The herbicides used were glyphosate, 2,4-D, paraquat, diquat, oxyfluorfen, atrazine, haloxyfop (in the pasture plots only), glyphosate trimesium, fluroxypyr and chlorsulfuron. 2.5. Measurements 2.5.1. Soil water content Soil water contents were determined in each plot by neutron moisture meter (Campbell Pacific Nuclear Model 503 DR Hydroprobe) in 0.1 m increments from 0 to 1.5 m at sowing, at weekly intervals during the growth of each crop and at harvest. Soil water contents were also measured in the pasture plots at the same times. 2.5.2. Crop emergence Total numbers of emerged seedlings were counted in 10 m of row per plot for wheat and 50 m for sorghum and maize. From these data, the percentage of emerged seedlings was determined using the number of seeds sown per meter of row. 2.5.3. Grain yield The grain was harvested with a small plot header (fitted with a corn front for the maize harvest) and weighed. Grain moisture content was measured with a grain moisture meter, and grain yields were adjusted to 12% moisture content.
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Table 2 Timing of compaction, tillage, fertiliser application and the sowing of crops and pasture Date
Wet compaction
19/04/1993 19/05/1993 01/06/1993 07/06/1993 24/06/1994 16/11/1993 08/12/1993 20/12/1993 06/01/1994 13/01/1994 24/01/1994 27/01/1994 18/03/1994 10/05/1994 22/08/1994 24/06/1994 23/11/1994 14/12/1994 20/12/1994 21/12/1994 24/01/1995 22/02/1995 16/11/1995 14/12/1995 19/01/1996 07/02/1996 26/06/1996 20/12/1996 02/01/1997 07/01/1997 13/03/1997 30/04/1997 04/06/1997 26/06/1997 05/12/1997 11/12/1997 18/12/1997 13/01/1998 16/02/1998 09/03/1998 19/03/1998
C1–C6
a b
Dry compaction
Tillage
Nitrogen (kg N ha1)
Zinc (spray)
Crop/pasture sowings
C1, C2 C6 (pasture) C0–C5 (wheat) 50 in C0–C6 C1, C2 C1, C2, C5a C0, C3b C3 C1, C2 C1, C0, C1, C1,
C2 C3, C5b C2 C2 C0–C5 C0–C5 (wheat)
C1, C2 C1, C2 C3 C0, C3b C0–C5 (sorghum) 25 in C0–C6 C1, C2 C1, C2 C0, C2, C3b C0, C3b C0–C5 (wheat) C1, C2 C0, C2, C3, C6b C3 C0, C2, C3, C6b C0, C2, C3, C6b 50 in C0–C6 C0–C6 (wheat) C0, C2, C3, C6b C3 C1, C2 C0, C2, C3, C6b C0–C6 (maize) 25 in C0–C6
C0–C6 C0–C6
Deep ripping in C5 (in soil drier than the plastic limit). Dry tillage (in soil drier than the plastic limit).
2.5.4. Water use efficiency The water use efficiency (WUE) for grain production was determined from grain yield/soil water use, where soil water use was the difference between soil water contents (0–1.5 m) at sowing and harvest þ in-crop rainfall þ supplementary irrigation.
(Thus ‘‘soil water use’’ included runoff water and deep drainage.) 2.5.5. Depths of soil water extraction The depth of soil water removal at a particular time was taken as the mid-point of the shallowest 0.1 m
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anthesis had no significant effects on yield, due to only the 1 degree of freedom for error, but reduced WUE from 10.5 to 9.5 in 1996. This was a result of low error variance.
depth increment without any decline in neutron count. Values were determined for each plot at each time of sampling. 2.6. Statistical analyses
3.3. Effect of fertiliser Standard analysis of variance was carried out for all data. When factors were significant ðP < 0:05Þ, pairwise comparison of means was tested using least significant differences. All significant differences in the text are for P < 0:05 unless otherwise stated.
Fertiliser application had only one significant ðP < 0:05Þ effect — a reduction in wheat yield from 2.59 to 2.36 Mg ha1 in 1994 (after 50 kg N ha1 was applied as urea at sowing and a 1% solution of zinc sulphate heptahydrate was applied 59 days after sowing).
3. Results 3.4. Effect of compaction/amelioration on soil water storage
3.1. Interactions (I: irrigation, C: compaction/ amelioration, F: fertiliser)
Annual compaction on wet soil significantly reduced total soil water at sowing (Table 3). Treatment C1 (10 Mg on wet soil) had less soil water than control (C0) in 1994, 1997 and 1998, and C2 (6 Mg on wet soil) less than control in 1995 and 1998. Annual compaction with 6 Mg on dry soil (C3) caused no reductions in soil water at sowing. Mean reductions in soil water storage from 1994 to 1998 due to the three annually applied compaction treatments were 9% (C1), 6% (C2) and 1% (C3).
There were no I F or C F interactions for the measurements reported (soil water, emergence, yield and WUE) and few I C and I C F interactions. For grain yield, the I C interaction was significant in 1995 and 1997. In 1995, C2 had lower yield than C0 in the irrigated but not the raingrown treatment. In 1997, both the I C and I C F interactions were significant, largely because the irrigated pasture (C6) treatments outyielded all other treatments. For WUE, I C in 1995 and I C F in 1997 were significant, reflecting similar interactions for yield in those crops.
3.5. Effect of compaction/amelioration on crop emergence
3.2. Effect of irrigation
Treatment C1 reduced emergence in 1993, 1994, 1995 and 1998 (Table 4). The annual compaction in C2 and C3 from 1994 to 1998 generally caused no reductions in emergence.
Supplementary irrigation had no effect on soil water content at sowing in the following years. Irrigation at
Table 3 Effect of compaction/amelioration treatments on amounts of stored soil water at sowing (values followed by the same letter within columns are not significantly ðP > 0:05Þ different) Treatment
C0 C1 C2 C3 C4 C5 C6
Total amount of stored soil water, 0–1.5 m (mm) 1993
1994
1995
1996
1997
1998
556 536 527 555 568 534 561
561 ab 528 c 546 ab 567 ab 583 a 549 bc Pasture
474 b 448 bc 416 c 472 b 542 a 470 b Pasture
563 ab 537 b 551 ab 571 a 574 a 539 b Pasture
565 500 536 556 571 540 562
547 456 500 526 554 533 563
ab bc c ab a bc a
ab c b ab a ab ab
a c b ab a ab a
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Table 4 Effect of compaction/amelioration treatments on crop emergence (values followed by the same letter within columns are not significantly ðP > 0:05Þ different) Treatment
C0 C1 C2 C3 C4 C5 C6
Total emergence (%) 1993 wheat
1994 wheat
1995 sorghum
1996 wheat
1997 wheat
1998 maize
93 a 71 bc 71 bc 77 b 65 c 77 b Pasture
76 ab 59 c 73 ab 82 a 67 bc 76 ab Pasture
35 b 22 c 39 ab 39 ab 41 ab 46 a Pasture
55 56 51 53 38 50 Pasture
53 56 55 60 56 65 57
87 79 85 78 80 86 84
a c ab c c ab b
Table 5 Effect of compaction/amelioration treatments on grain yield at 12% moisture content (values followed by the same letter within columns are not significantly ðP > 0:05Þ different) Treatment
C0 C1 C2 C3 C4 C5 C6
Grain yield at 12% moisture content (Mg ha1) 1993 wheat
1994 wheat
1995 sorghum
1996 wheat
1997 wheat
1998 maize
5.32 5.18 5.38 5.16 5.29 5.12 Pasture
2.55 2.40 2.41 2.61 2.35 2.52 Pasture
2.56 bc 2.53 bc 1.99 c 2.97 ab 3.43 a 3.09 ab Pasture
3.51 a 3.04 c 3.32 ab 3.45 ab 3.30 ab 3.25 bc Pasture
3.25 2.33 3.10 3.31 3.01 3.21 3.58
5.52 3.14 4.39 4.93 5.79 5.85 6.42
3.6. Effect of compaction/amelioration on grain yield Treatment C1 reduced grain yield in 1996, 1997 and 1998, C2 in 1997 and 1998, and C3 in 1998 only (Table 5). Mean yield reductions due to annual
b e cd b d bc a
b d c c b b a
compaction from 1994 to 1998 were 23% (C1), 13% (C2) and 1% (C3). The pasture ley treatment had significantly ðP < 0:05Þ higher yield than all other treatments in 1997 (wheat) and 1998 (maize).
Table 6 Effect of compaction/amelioration treatments on WUE (values followed by the same letter within columns are not significantly ðP > 0:05Þ different) Treatment
C0 C1 C2 C3 C4 C5 C6
WUE (kg ha1 mm1) 1994 wheat
1995 sorghum
1996 wheat
1997 wheat
1998 maize
6.6 7.0 7.7 7.7 6.9 6.9 Pasture
7.4 9.1 8.1 9.2 9.4 9.5 Pasture
10.5 ab 8.5 c 10.1 b 10.8 a 9.8 b 10.3 ab Pasture
9.9 9.7 10.0 10.8 9.8 9.6 10.1
14.3 ab 9.7 d 12.4 c 13.9 bc 15.2 ab 14.1 bc 16.1 a
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Fig. 1. Depths of soil water extraction for four compaction treatments at eight sampling times during growth of the maize crop (1998).
3.7. Effect of compaction/amelioration on water use efficiency There was reduced WUE compared with the control in C1 in 1996 and 1998, and in C2 in 1998 (Table 6). 3.8. Depths of soil water extraction For maize, the control treatment dried the soil to significantly greater depths than C1 (36–120 days), C2 (36–73 days) and C3 (43–73 days) (Fig. 1). The control also dried the soil to greater depths than C1 in the 1997 wheat (46–60 days) and than C1 and C2 in the sorghum (44–52 days) (data not shown).
4. Discussion Reduced grain yields due to applied wheel compaction on wet surface soil (treatments C1 and C2) were due to reduced soil water storage and/or reduced WUE. Reduced soil water storage in response to compaction is attributed to reduced hydraulic conductivity (Radford et al., 2000) and a lower population density of earthworms and other soil macrofauna (Radford et al., unpublished). Reduced WUE of maize
in response to compaction was associated with delayed soil drying at depth or reduced extraction front velocity (see Fig. 1), which we attribute to slower growth of roots down the profile. The basis for comparison was the control treatment (C0), which received no initial compaction and no wheel traffic throughout the experiment, and was tilled only in soil that was drier than the plastic limit. Treatment C0 therefore represents the performance of a well-managed controlled traffic farming system (Yule, 1998). Yield reductions caused by compaction were not due to reduced plant populations as a result of reduced emergence. Compaction of wet soil with tractor wheels (C2) caused no changes in emergence, and the other compaction treatments (C1 and C3) caused statistically significant, but only small, reductions in emergence. The effect of compaction on emergence would have been a problem if traditional wide points on spring-loaded tines had been used. The sowing machines used in this experiment had smooth coulters, narrow spearpoint openers, tines with high breakout force, and press wheels. Wheel traffic and tillage operations on surface soil drier than the plastic limit (C3) had no effect on soil water storage and little effect on crop performance (emergence and grain yield). By conducting these operations when the surface soil is dry, growers can minimise compaction damage. Tillage operations for weed control can be delayed by using herbicides until the surface soil dries. The initial compaction damage was apparently ameliorated during the growth of the first wheat crop as no adverse effect on that crop’s performance was recorded. More than three wet–dry cycles are needed to initiate measurable repair of Vertisols (PillaiMcGarry and Collis-George, 1990). After two wheat crops in 18 months without any tillage operations (in C4), the initial compaction damage was not only repaired with respect to crop productivity but yield exceeded the uncompacted control. Lablab and mungbean have improved soil structure to greater depths and more rapidly than wheat (Pillai and McGarry, 1999). Following the 3-year pasture ley in C6, grain yields in the subsequent wheat and maize crops were higher in C6 than in any other treatment. Soil structure (with respect to crop production) was not only ameliorated but improved. In a commercial pasture, however, the
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hooves of grazing animals continue to cause soil compaction (Packer, 1988). Also economic analysis showed that this treatment was the least profitable during the course of the experiment (F.C. Chudleigh, personal communication). Annual compaction of wet soil resulted in large reductions in maize yield in 1998 (43% in C1 and 20% in C2). These may have been due to the rainfall pattern, the cumulative effect of six successive compaction treatments, or a sensitivity of maize to compaction damage. Maize appears to be particularly susceptible to compaction (Kayombo and Lal, 1994). Gameda et al. (1987) reported that axle loads of 10 and 20 Mg decreased maize yield by 20–50%, though Voorhees et al. (1989) found that maize yield was not consistently affected by surface layer compaction. In the current experiment, the extraction front velocity of maize was sensitive to compaction (Fig. 1). In contrast, the extraction front velocities of sorghum and sunflower appear insensitive to soil properties (Robertson et al., 1993; Meinke et al., 1993). Maize root numbers in the subsoil were reduced after applied compaction with an 18 Mg axle load but soybean root numbers were not (Logsdon et al., 1992).
5. Conclusions Soil compaction caused by axle loads of 6–10 Mg on a wet Vertisol (25–32% soil water) reduced grain yields (wheat and maize) by reducing soil water storage and/or crop WUE. Reduced WUE of maize was attributed in part to reduced velocity of the soil water extraction front down the profile. Annual applications of an axle load of 6 Mg on dry soil (<22% soil water) had little effect on crop performance. We conclude that trafficking the soil at low soil water contents minimises yield decline. Tillage operations to control weeds can be delayed by using herbicides until the surface soil dries. Compaction can be avoided completely by using a controlled traffic farming system. Crop and pasture roots ameliorated the initial compaction damage by creating wet–dry cycles. Such biological amelioration was as effective as mechanical amelioration by tillage. After a 3-year pasture ley, grain yield exceeded control in subsequent wheat and maize crops. However, pasture production is generally
165
less profitable than cropping, and a commercial pasture would include further compaction by animal hooves.
Acknowledgements We thank the Land and Water Resources Research and Development Corporation (LWRRDC) and the Grains Research and Development Corporation (GRDC) for funding; Alan Key, Alexandra WilsonRummenie and Rebecca Sunnerdale for their technical assistance; and Jeff Morris and his farm staff at Biloela Research Station for performing the cultural operations. References Alakukku, L., 1996a. Persistence of soil compaction due to high axle load traffic. II. Long-term effects on the properties of finetextured and organic soils. Soil Till. Res. 37, 223–238. Alakukku, L., 1996b. Persistence of soil compaction due to high axle load traffic. I. Short-term effects on the properties of clay and organic soils. Soil Till. Res. 37, 211–222. Bruce, R.C., Rayment, G.E., 1982. Analytical Methods and Interpretation Used by the Agricultural Chemistry Branch for Soil and Land Use Surveys. Queensland Department of Primary Industries Publication QB82004, No. 5. Colwell, J.D., 1963. The estimation of the phosphorus fertilizer requirements of wheat in southern New South Wales by soil analysis. Aust. J. Exp. Agric. Anim. Husb. 3, 190–198. Flowers, M.D., Lal, R., 1998. Axle load and tillage effects on soil physical properties and soybean grain yield on a mollic ochraqualf in northwest Ohio. Soil Till. Res. 48, 21–35. Fragoso, C., Brown, G.G., Patro´ n, J.C., Blanchart, E.W., Lavelle, P., Pashanasi, B., Senapati, B., Kumar, T., 1997. Agricultural intensification, soil biodiversity and agroecosystem function in the tropics: the role of earthworms. Appl. Soil Ecol. 6, 17–35. Gameda, S., Raghavan, E., McKyes, E., Theriault, R., 1987. Subsoil compaction in a clay soil. II. Natural alleviation. Soil Till. Res. 10, 123–130. Ha˚ kansson, I., Voorhees, W.B., Elonen, P., Raghavan, G.S.V., Lowery, B., van Wijk, A.L.M., Rasmussen, K., Riley, H., 1987. Effect of high axle load traffic on subsoil compaction and crop yield in humid regions with annual freezing. Soil Till. Res. 10, 259–268. Ha˚ kansson, I., Voorhees, W.B., Riley, H., 1988. Vehicle and wheel factors influencing soil compaction and crop responses in different traffic regimes. Soil Till. Res. 11, 239–282. Kayombo, B., Lal, R., 1994. Responses of tropical crops to soil compaction. In: Soane, B.D., van Ouwerkerk, C. (Eds.), Soil Compaction in Crop Production, Elsevier, Amsterdam, pp. 287–316.
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Kirby, J.M., Kirchhoff, G., 1990. The compaction process and factors affecting soil compactibility. In: Hunter, M.N., Paull, C.J., Smith, G.D. (Eds.), Proceedings of Queensland Department of Primary Industries Soil Compaction Workshop, Toowoomba, Australia, pp. 28–31. Logsdon, S.D., Allmaras, R.R., Nelson, W.W., Voorhees, W.B., 1992. Persistence of subsoil compaction from heavy axle loads. Soil Till. Res. 23, 95–110. McGarry, D., 1993. Degradation of soil structure. In: Land Degradation Processes in Australia. Longman Cheshire, Melbourne. McGarry, D., Sharp, G., Bray, S.G., 1999. The Current Status of Soil Degradation in Queensland Cropping Soils. Queensland Department of Natural Resources, DNRQ990092. McGarry, D., Bridge, B.J., Radford, B.J., 2000. Contrasting soil physical properties after zero and traditional tillage of an alluvial soil in the semi-arid tropics. Soil Till. Res. 53, 105–115. Meinke, H., Hammer, G.L., Want, P.J., 1993. Potential soil water extraction by sunflower on a range of soils. Field Crops Res. 32, 59–81. Packer, I.J., 1988. The effects of grazing on soils and productivity — a review. Soil Conservation Service of NSW Technical Report No. 4. Pillai, U.P., McGarry, D., 1999. Structure repair of a compacted Vertisol with wet–dry cycles and crops. Soil Sci. Soc. Am. J. 63, 201–210. Pillai-McGarry, U.P.P., Collis-George, N., 1990. Laboratory simulation of the surface morphology of self-mulching and non self-mulching Vertisols. I. Materials, methods and preliminary results. Aust. J. Soil Res. 28, 129–139. Radford, B.J., Bridge, B.J., Davis, R.J., McGarry, D., Pillai, U.P., Rickman, J.F., Walsh, P.A., Yule, D.F., 2000. Changes in properties of a Vertisol and responses of wheat after compaction with harvester traffic. Soil Till. Res. 54, 155–170.
Rickman, J.F., Chanasyk, D.S., 1988. Traction effects on soil compaction. In: Proceedings of Agricultural Engineering Conference, Hawkesbury, Australia, pp. 103–108. Robertson, M.J., Fukai, S., Ludlow, M.M., Hammer, G.L., 1993. Water extraction by grain sorghum in a sub-humid environment. I. Analysis of the water extraction pattern. Field Crops Res. 33, 81–97. Rovira, A.D., Smettem, K.R.J., Lee, K.E., 1987. Effect of rotation and conservation tillage on earthworms in a red-brown earth under wheat. Aust. J. Agric. Res. 38, 829–834. Soane, B.D., Blackwell, P.S., Dickson, J.W., Painter, D.J., 1981. Compaction by agricultural vehicles: a review. II. Compaction under tyres and other running gear. Soil Till. Res. 1, 21–35. Tullberg, J.N., 1990. Why control field traffic? In: Hunter, M.N., Paull, C.J., Smith, G.D. (Eds.), Proceedings of Queensland Department of Primary Industries Soil Compaction Workshop, Toowoomba, Australia, pp. 41–42. Voorhees, W.B., Johnson, J.F., Randall, G.W., Nelson, W.W., 1989. Corn growth and yield as affected by surface and subsoil compaction. Agron. J. 81, 294–303. Walkley, A., Black, I.A., 1934. An examination of the Degtjareff method for determining soil organic matter and a proposed modification of the chromic acid filtration method. Soil Sci. 37, 29–38. Williams, J., 1998. Australia needs a true blue land system. CSIRO Land and Water News 2: 1–3, CSIRO, Australia. Yule, D.F., 1998. Controlled traffic farming — the future. In: Proceedings of Second National Controlled Traffic Conference, Gatton, Australia, pp. 6–12. Zund, P.R., Pillai-McGarry, U., McGarry, D., Bray, S.G., 1997. Repair of a compacted Oxisol by the earthworm Pontoscolex corethrurus (Glossoscolecidae, Oligochaeta). Biol. Fert. Soils 25, 202–208.
Crop responses to applied soil compaction and to compaction repair treatments B.J. Radforda,*, D.F. Yuleb, D. McGarryb, C. Playfordc a
Queensland Department of Natural Resources and Mines, Locked Mail Bag No. 1, Biloela, Qld 4715, Australia b Queensland Department of Natural Resources and Mines, Meiers Road, Indooroopilly, Qld 4068, Australia c Queensland Department of Primary Industries, P.O. Box 6014, Rockhampton, Qld 4702, Australia Received 4 September 2000; received in revised form 7 February 2001; accepted 25 February 2001
Abstract Crop responses to annual compaction treatments (applied to whole plots) and management treatments to ameliorate compacted soil were determined in a field experiment on a Vertisol. Initially, all treatments except a control were compacted with a 10 Mg axle load on wet soil (26% gravimetric water content compared with a plastic limit of 22%). Annually applied axle loads of 10 and 6 Mg on wet soil (25–32% soil water) tended to reduce seedling emergence, grain yield (wheat, sorghum and maize), soil water storage and crop water use efficiency (WUE). Annual applications of an axle load of 6 Mg on dry soil (<22% soil water) had little effect on crop performance. Mean reductions in the yield of five crops (three wheat, one sorghum and one maize) in comparison with the uncompacted control were 23% or 0.79 Mg ha1 (10 Mg on wet soil), 13% or 0.44 Mg ha1 (6 Mg on wet soil) and 1% or 0.03 Mg ha1 (6 Mg on dry soil). Maize grown in the fifth year of treatment application was most affected by compaction of wet soil, its WUE being reduced from 14.3 to 9.7 kg ha1 mm1 in response to an axle load of 10 Mg. Reduced WUE was associated with delayed soil water extraction at depth. A 3-year pasture ley was the most successful amelioration treatment. A wheat and a maize crop grown after the ley outyielded the control by 0.33 and 0.90 Mg ha1, respectively. So the pasture not only ameliorated the initial compaction damage, with respect to crop performance, but resulted in improvements in two subsequent crops. # 2001 Elsevier Science B.V. All rights reserved. Keywords: Soil compaction; Grain crops; Crop emergence; Grain yield; Ley pasture
1. Introduction Compaction-induced soil degradation affects about 68 million hectares of land globally (Flowers and Lal, 1998). A component of progressive subsoil damage is the increase in weight of farm machinery in recent decades (Alakukku, 1996a). In the Australian context,
*
Corresponding author. Tel.: þ61-749-929106; fax: þ61-749-923468. E-mail address: [email protected] (B.J. Radford).
soil structural decline has been ranked as Australia’s greatest problem in terms of damage to the soil resource used for cropping (Williams, 1998; McGarry et al., 1999). The vast majority of soil compaction in modern agriculture is caused by vehicular traffic (Flowers and Lal, 1998). Damage from high axle loads increases when the soil is wet because wet soil has reduced strength (Kirby and Kirchhoff, 1990). Tillage and harvest operations commonly have to be carried out when the surface soil is wetter than optimal for wheel traffic. High tyre inflation pressures also increase soil
0167-1987/01/$ – see front matter # 2001 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 7 - 1 9 8 7 ( 0 1 ) 0 0 1 9 4 - 5
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damage (Soane et al., 1981; Rickman and Chanasyk, 1988). The first pass of a wheel causes the greatest amount of soil compaction (Rickman and Chanasyk, 1988; Alakukku, 1996b). In any one crop cycle, more than 30% of ground area is trafficked by the tyres of heavy machinery under zero tillage, 60% under minimum tillage and more than 100% under conventional tillage (Tullberg, 1990). Considerable evidence exists to show that soil compaction, originating from either anthropogenic or natural causes, exerts an enormous impact on the establishment, growth and yield of crops in tropical regions (Kayombo and Lal, 1994). Factors affecting crop yield response to compaction by wheel traffic are not easily defined (Voorhees et al., 1989). When wheel traffic does reduce yield, mechanisms for response should be thoroughly examined (Logsdon et al., 1992). A confounding factor in relating the visible or measured presence of compaction to yield loss is the known interaction between growing season rainfall (or irrigation intensity) and yield (Ha˚ kansson et al., 1988; McGarry, 1993). Compaction in the plough layer (surface soil compaction) can be alleviated by tillage and natural processes, while subsurface compaction is usually alleviated only by natural processes such as freezing/thawing, drying/wetting and biological activity (Ha˚ kansson et al., 1987). Subsurface compaction thus often persists for a long time, and has been measured 3–11 years after heavy loading (Alakukku, 1996b). However, the natural processes of compaction amelioration can be enhanced with judicious management. For example, the number of wet–dry cycles can be increased by growing a crop or pasture on a clay soil with swell-shrink potential (Pillai and McGarry, 1999). The introduction of suitable earthworm species may also hasten amelioration (Zund et al., 1997; Fragoso et al., 1997), particularly when combined with management practices (such as conservation tillage) which increase worm populations (Rovira et al., 1987; McGarry et al., 2000). The objective of the work reported in this paper was to determine the effects of applied soil compaction on crop performance (wheat, sorghum and maize) and to assess management treatments designed to help ameliorate compaction damage.
2. Materials and methods The study was conducted for 6 years at a single site in a semi-arid environment. All treatments except a control received an initial compaction treatment with harvester wheels on the entire plot areas. Further compaction treatments were applied annually to whole plots with harvester or tractor wheels on soil at varying water contents. Cultural operations were carried out using a system of controlled traffic farming so that wheel traffic was confined to the permanent wheel tracks, which were spaced 3 m apart. Crops grown were wheat (four crops), sorghum (1) and maize (1). Row spacing was 0.3 m for wheat and 0.75 m for sorghum and maize. 2.1. Site The site at Biloela, Qld, Australia (latitude 248220 S, longitude 1508310 E, altitude 173 m) is relatively level ðslope ¼ 0:2%Þ. The soil is a black cracking clay (a Vertisol) developed on an alluvial deposit. Details of selected soil physical properties are shown in Table 1. The liquid limit (drop cone), plastic limit (rolling bead) and 1.5 MPa (wilting point of <2 mm sieved soil by pressure plate) values in the 0–0.1 m layer were 56, 22 and 17% gravimetric water content, respectively. The mean annual rainfall is 685 mm and mean annual evaporation (from a class ‘‘A’’ pan) is 1868 mm. 2.2. Design We used a split-plot design with two replications of two irrigation (I) treatments (raingrown and supplementary irrigation of 75 mm at crop anthesis) with each main plot split into 14 subplots: seven compaction amelioration (C) treatments two fertiliser (F) treatments (control and fertilised). Each plot measured 30 9 m. 2.3. Treatments The two irrigation treatments were included to measure interactions between water supply and yield. The irrigated treatment received one application of 75 mm of water at crop anthesis in all years except 1998 when no irrigation treatment was imposed.
Depth (m)
Soil property PSAa
0–0.05 0.05–0.1 0.1–0.2 0.2–0.3 0.3–0.4 0.4–0.5 0.5–0.6 0.6–0.9 0.9–1.2 1.2–1.5 a
CS (%)
FS (%)
S (%)
C (%)
3 3 2 2 2 1 3 3 3 7
19 19 19 18 17 21 22 25 30 37
31 28 27 27 22 24 24 26 21 20
45 48 53 51 55 53 51 47 43 35
R1b pHc
EC (dS m1)d
Cl (mg kg1)e
CEC (meq%)f
ESP (meq%)g
Organic C (%)h
Total N (%)i
P (mg kg1) j
0.39 7.3 0.40 7.3 0.59 7.8 0.58 7.9 0.63 8.0 0.63 8.2 0.66 8.3 0.65 8.5 0.68 8.4 0.73 8.3
0.157 0.152 0.126 0.128 0.145 0.167 0.189 0.270 0.351 0.386
7 6 18 33 50 65 85 146 269 373
30 34 36 33 35 – – – – –
0.64 0.67 1.30 1.50 1.70 – – – – –
1.7 1.6 1.2 0.9 1.0 – – – – –
0.12 0.11 0.07 0.06 0.06 – – – – –
96 94 70 57 52 – – – – –
Particle size analysis by disaggregating the soil in an aqueous solution by means of chemical reagents and mechanical dispersion, and determining coarse and fine sand fractions gravimetrically and the silt and clay fractions using a hydrometer: CS, coarse sand (>200 mm); FS, fine sand (20–200 mm); S, silt (2–20 mm); C, clay (<2 mm). b Dispersion ratio: % ðsilt þ clayÞ dispersed in water=% total ðsilt þ clayÞ (Bruce and Rayment, 1982). c 1:5 pH (water). d 1:5 electrical conductivity. e 1:5 extractable chloride. f Cation exchange capacity (pH 8.5). g Exchangeable sodium percentage (pH 8.5). h Organic carbon (Walkley and Black, 1934). i Total nitrogen (Kjeldahl digest). j Bicarbonate extractable P (Colwell, 1963).
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Table 1 Selected physical and chemical properties of the soil profile (0–1.5 m)
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The initial compaction treatment was applied in April 1993 with the lugged rubber tyres of a Ford New Holland 8060 harvester. Axle loads were 10 and 2 Mg on the front and rear axles, respectively. Inflation pressures were high to maximise compaction: 235 kPa (front) and 205 kPa (rear). The mean gravimetric soil water content at 0–0.1 m during compaction was 25.9%. Harvesting on such wet soil is a short-term economic necessity when summer storms threaten crops. For this study we compacted the entire plot with a single pass of front and rear header wheels. This experimental treatment is not unrealistic because random wheel traffic during a fallow typically covers most of the ground area. The seven compaction/amelioration treatments were: C0
C1
C2
C3
C4 C5
C6
No applied compaction/reduced (dry) tillage (i.e. the soil was tilled only at gravimetric water contents <22%, the plastic limit, to the depth of tillage). Initial compaction; annual wet compaction with a header (10 Mg maximum axle load) at soil water contents of 25–32% (0–0.1 m); frequent tillage to 1995 at soil water contents varying from 14 to 24% (0– 0.1 m), no tillage after 1995. Initial compaction; annual wet compaction with a tractor (6 Mg maximum axle load) at soil water contents of 25–32% (0–0.1 m); frequent tillage at soil water contents varying from 14 to 24% (0–0.1 m). Initial compaction; annual dry compaction with a tractor (6 Mg maximum axle load) at soil water contents <22% to a depth of 0.08 m; reduced (dry) tillage. Initial compaction; no tillage. Initial compaction; cropping/deep ripping (with a chisel plough) and scarifying at soil water contents <22% to the depth of tillage; no tillage. Initial compaction; pasture ley of lucerne (Medicago sativa cv. Trifecta) and Gatton panic (Panicum maximum Jacq. cv. Gatton) for 3 years (cut 10 times and returned to the soil); reduced (dry) tillage; cropping.
The fertilised treatment received nitrogen as urea on four occasions and zinc as a foliar spray of 1%
zinc sulphate heptahydrate on three occasions (Table 2). The timing of all compaction and tillage treatments is shown in Table 2. 2.4. Management Crops were grown utilising water stored in the soil during a fallow, as well as in-crop rainfall. The crops grown were wheat (Hartog) in 1993, wheat (Hartog) in 1994, sorghum (MR31) in 1995, wheat (Hartog) in 1996, wheat (Sunstate) in 1997 and maize (DK689) in 1998. Sowing dates for the crops and pasture are shown in Table 2. Chlorpyrifos (500 g a.i. l1) insecticide was applied at 1 l ha1 on 20 August 1996 to control armyworm, Mythimna convecta (Walker), in wheat. Herbicides were used when necessary to control weeds in treatments with no or reduced tillage. The herbicides used were glyphosate, 2,4-D, paraquat, diquat, oxyfluorfen, atrazine, haloxyfop (in the pasture plots only), glyphosate trimesium, fluroxypyr and chlorsulfuron. 2.5. Measurements 2.5.1. Soil water content Soil water contents were determined in each plot by neutron moisture meter (Campbell Pacific Nuclear Model 503 DR Hydroprobe) in 0.1 m increments from 0 to 1.5 m at sowing, at weekly intervals during the growth of each crop and at harvest. Soil water contents were also measured in the pasture plots at the same times. 2.5.2. Crop emergence Total numbers of emerged seedlings were counted in 10 m of row per plot for wheat and 50 m for sorghum and maize. From these data, the percentage of emerged seedlings was determined using the number of seeds sown per meter of row. 2.5.3. Grain yield The grain was harvested with a small plot header (fitted with a corn front for the maize harvest) and weighed. Grain moisture content was measured with a grain moisture meter, and grain yields were adjusted to 12% moisture content.
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161
Table 2 Timing of compaction, tillage, fertiliser application and the sowing of crops and pasture Date
Wet compaction
19/04/1993 19/05/1993 01/06/1993 07/06/1993 24/06/1994 16/11/1993 08/12/1993 20/12/1993 06/01/1994 13/01/1994 24/01/1994 27/01/1994 18/03/1994 10/05/1994 22/08/1994 24/06/1994 23/11/1994 14/12/1994 20/12/1994 21/12/1994 24/01/1995 22/02/1995 16/11/1995 14/12/1995 19/01/1996 07/02/1996 26/06/1996 20/12/1996 02/01/1997 07/01/1997 13/03/1997 30/04/1997 04/06/1997 26/06/1997 05/12/1997 11/12/1997 18/12/1997 13/01/1998 16/02/1998 09/03/1998 19/03/1998
C1–C6
a b
Dry compaction
Tillage
Nitrogen (kg N ha1)
Zinc (spray)
Crop/pasture sowings
C1, C2 C6 (pasture) C0–C5 (wheat) 50 in C0–C6 C1, C2 C1, C2, C5a C0, C3b C3 C1, C2 C1, C0, C1, C1,
C2 C3, C5b C2 C2 C0–C5 C0–C5 (wheat)
C1, C2 C1, C2 C3 C0, C3b C0–C5 (sorghum) 25 in C0–C6 C1, C2 C1, C2 C0, C2, C3b C0, C3b C0–C5 (wheat) C1, C2 C0, C2, C3, C6b C3 C0, C2, C3, C6b C0, C2, C3, C6b 50 in C0–C6 C0–C6 (wheat) C0, C2, C3, C6b C3 C1, C2 C0, C2, C3, C6b C0–C6 (maize) 25 in C0–C6
C0–C6 C0–C6
Deep ripping in C5 (in soil drier than the plastic limit). Dry tillage (in soil drier than the plastic limit).
2.5.4. Water use efficiency The water use efficiency (WUE) for grain production was determined from grain yield/soil water use, where soil water use was the difference between soil water contents (0–1.5 m) at sowing and harvest þ in-crop rainfall þ supplementary irrigation.
(Thus ‘‘soil water use’’ included runoff water and deep drainage.) 2.5.5. Depths of soil water extraction The depth of soil water removal at a particular time was taken as the mid-point of the shallowest 0.1 m
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anthesis had no significant effects on yield, due to only the 1 degree of freedom for error, but reduced WUE from 10.5 to 9.5 in 1996. This was a result of low error variance.
depth increment without any decline in neutron count. Values were determined for each plot at each time of sampling. 2.6. Statistical analyses
3.3. Effect of fertiliser Standard analysis of variance was carried out for all data. When factors were significant ðP < 0:05Þ, pairwise comparison of means was tested using least significant differences. All significant differences in the text are for P < 0:05 unless otherwise stated.
Fertiliser application had only one significant ðP < 0:05Þ effect — a reduction in wheat yield from 2.59 to 2.36 Mg ha1 in 1994 (after 50 kg N ha1 was applied as urea at sowing and a 1% solution of zinc sulphate heptahydrate was applied 59 days after sowing).
3. Results 3.4. Effect of compaction/amelioration on soil water storage
3.1. Interactions (I: irrigation, C: compaction/ amelioration, F: fertiliser)
Annual compaction on wet soil significantly reduced total soil water at sowing (Table 3). Treatment C1 (10 Mg on wet soil) had less soil water than control (C0) in 1994, 1997 and 1998, and C2 (6 Mg on wet soil) less than control in 1995 and 1998. Annual compaction with 6 Mg on dry soil (C3) caused no reductions in soil water at sowing. Mean reductions in soil water storage from 1994 to 1998 due to the three annually applied compaction treatments were 9% (C1), 6% (C2) and 1% (C3).
There were no I F or C F interactions for the measurements reported (soil water, emergence, yield and WUE) and few I C and I C F interactions. For grain yield, the I C interaction was significant in 1995 and 1997. In 1995, C2 had lower yield than C0 in the irrigated but not the raingrown treatment. In 1997, both the I C and I C F interactions were significant, largely because the irrigated pasture (C6) treatments outyielded all other treatments. For WUE, I C in 1995 and I C F in 1997 were significant, reflecting similar interactions for yield in those crops.
3.5. Effect of compaction/amelioration on crop emergence
3.2. Effect of irrigation
Treatment C1 reduced emergence in 1993, 1994, 1995 and 1998 (Table 4). The annual compaction in C2 and C3 from 1994 to 1998 generally caused no reductions in emergence.
Supplementary irrigation had no effect on soil water content at sowing in the following years. Irrigation at
Table 3 Effect of compaction/amelioration treatments on amounts of stored soil water at sowing (values followed by the same letter within columns are not significantly ðP > 0:05Þ different) Treatment
C0 C1 C2 C3 C4 C5 C6
Total amount of stored soil water, 0–1.5 m (mm) 1993
1994
1995
1996
1997
1998
556 536 527 555 568 534 561
561 ab 528 c 546 ab 567 ab 583 a 549 bc Pasture
474 b 448 bc 416 c 472 b 542 a 470 b Pasture
563 ab 537 b 551 ab 571 a 574 a 539 b Pasture
565 500 536 556 571 540 562
547 456 500 526 554 533 563
ab bc c ab a bc a
ab c b ab a ab ab
a c b ab a ab a
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163
Table 4 Effect of compaction/amelioration treatments on crop emergence (values followed by the same letter within columns are not significantly ðP > 0:05Þ different) Treatment
C0 C1 C2 C3 C4 C5 C6
Total emergence (%) 1993 wheat
1994 wheat
1995 sorghum
1996 wheat
1997 wheat
1998 maize
93 a 71 bc 71 bc 77 b 65 c 77 b Pasture
76 ab 59 c 73 ab 82 a 67 bc 76 ab Pasture
35 b 22 c 39 ab 39 ab 41 ab 46 a Pasture
55 56 51 53 38 50 Pasture
53 56 55 60 56 65 57
87 79 85 78 80 86 84
a c ab c c ab b
Table 5 Effect of compaction/amelioration treatments on grain yield at 12% moisture content (values followed by the same letter within columns are not significantly ðP > 0:05Þ different) Treatment
C0 C1 C2 C3 C4 C5 C6
Grain yield at 12% moisture content (Mg ha1) 1993 wheat
1994 wheat
1995 sorghum
1996 wheat
1997 wheat
1998 maize
5.32 5.18 5.38 5.16 5.29 5.12 Pasture
2.55 2.40 2.41 2.61 2.35 2.52 Pasture
2.56 bc 2.53 bc 1.99 c 2.97 ab 3.43 a 3.09 ab Pasture
3.51 a 3.04 c 3.32 ab 3.45 ab 3.30 ab 3.25 bc Pasture
3.25 2.33 3.10 3.31 3.01 3.21 3.58
5.52 3.14 4.39 4.93 5.79 5.85 6.42
3.6. Effect of compaction/amelioration on grain yield Treatment C1 reduced grain yield in 1996, 1997 and 1998, C2 in 1997 and 1998, and C3 in 1998 only (Table 5). Mean yield reductions due to annual
b e cd b d bc a
b d c c b b a
compaction from 1994 to 1998 were 23% (C1), 13% (C2) and 1% (C3). The pasture ley treatment had significantly ðP < 0:05Þ higher yield than all other treatments in 1997 (wheat) and 1998 (maize).
Table 6 Effect of compaction/amelioration treatments on WUE (values followed by the same letter within columns are not significantly ðP > 0:05Þ different) Treatment
C0 C1 C2 C3 C4 C5 C6
WUE (kg ha1 mm1) 1994 wheat
1995 sorghum
1996 wheat
1997 wheat
1998 maize
6.6 7.0 7.7 7.7 6.9 6.9 Pasture
7.4 9.1 8.1 9.2 9.4 9.5 Pasture
10.5 ab 8.5 c 10.1 b 10.8 a 9.8 b 10.3 ab Pasture
9.9 9.7 10.0 10.8 9.8 9.6 10.1
14.3 ab 9.7 d 12.4 c 13.9 bc 15.2 ab 14.1 bc 16.1 a
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Fig. 1. Depths of soil water extraction for four compaction treatments at eight sampling times during growth of the maize crop (1998).
3.7. Effect of compaction/amelioration on water use efficiency There was reduced WUE compared with the control in C1 in 1996 and 1998, and in C2 in 1998 (Table 6). 3.8. Depths of soil water extraction For maize, the control treatment dried the soil to significantly greater depths than C1 (36–120 days), C2 (36–73 days) and C3 (43–73 days) (Fig. 1). The control also dried the soil to greater depths than C1 in the 1997 wheat (46–60 days) and than C1 and C2 in the sorghum (44–52 days) (data not shown).
4. Discussion Reduced grain yields due to applied wheel compaction on wet surface soil (treatments C1 and C2) were due to reduced soil water storage and/or reduced WUE. Reduced soil water storage in response to compaction is attributed to reduced hydraulic conductivity (Radford et al., 2000) and a lower population density of earthworms and other soil macrofauna (Radford et al., unpublished). Reduced WUE of maize
in response to compaction was associated with delayed soil drying at depth or reduced extraction front velocity (see Fig. 1), which we attribute to slower growth of roots down the profile. The basis for comparison was the control treatment (C0), which received no initial compaction and no wheel traffic throughout the experiment, and was tilled only in soil that was drier than the plastic limit. Treatment C0 therefore represents the performance of a well-managed controlled traffic farming system (Yule, 1998). Yield reductions caused by compaction were not due to reduced plant populations as a result of reduced emergence. Compaction of wet soil with tractor wheels (C2) caused no changes in emergence, and the other compaction treatments (C1 and C3) caused statistically significant, but only small, reductions in emergence. The effect of compaction on emergence would have been a problem if traditional wide points on spring-loaded tines had been used. The sowing machines used in this experiment had smooth coulters, narrow spearpoint openers, tines with high breakout force, and press wheels. Wheel traffic and tillage operations on surface soil drier than the plastic limit (C3) had no effect on soil water storage and little effect on crop performance (emergence and grain yield). By conducting these operations when the surface soil is dry, growers can minimise compaction damage. Tillage operations for weed control can be delayed by using herbicides until the surface soil dries. The initial compaction damage was apparently ameliorated during the growth of the first wheat crop as no adverse effect on that crop’s performance was recorded. More than three wet–dry cycles are needed to initiate measurable repair of Vertisols (PillaiMcGarry and Collis-George, 1990). After two wheat crops in 18 months without any tillage operations (in C4), the initial compaction damage was not only repaired with respect to crop productivity but yield exceeded the uncompacted control. Lablab and mungbean have improved soil structure to greater depths and more rapidly than wheat (Pillai and McGarry, 1999). Following the 3-year pasture ley in C6, grain yields in the subsequent wheat and maize crops were higher in C6 than in any other treatment. Soil structure (with respect to crop production) was not only ameliorated but improved. In a commercial pasture, however, the
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hooves of grazing animals continue to cause soil compaction (Packer, 1988). Also economic analysis showed that this treatment was the least profitable during the course of the experiment (F.C. Chudleigh, personal communication). Annual compaction of wet soil resulted in large reductions in maize yield in 1998 (43% in C1 and 20% in C2). These may have been due to the rainfall pattern, the cumulative effect of six successive compaction treatments, or a sensitivity of maize to compaction damage. Maize appears to be particularly susceptible to compaction (Kayombo and Lal, 1994). Gameda et al. (1987) reported that axle loads of 10 and 20 Mg decreased maize yield by 20–50%, though Voorhees et al. (1989) found that maize yield was not consistently affected by surface layer compaction. In the current experiment, the extraction front velocity of maize was sensitive to compaction (Fig. 1). In contrast, the extraction front velocities of sorghum and sunflower appear insensitive to soil properties (Robertson et al., 1993; Meinke et al., 1993). Maize root numbers in the subsoil were reduced after applied compaction with an 18 Mg axle load but soybean root numbers were not (Logsdon et al., 1992).
5. Conclusions Soil compaction caused by axle loads of 6–10 Mg on a wet Vertisol (25–32% soil water) reduced grain yields (wheat and maize) by reducing soil water storage and/or crop WUE. Reduced WUE of maize was attributed in part to reduced velocity of the soil water extraction front down the profile. Annual applications of an axle load of 6 Mg on dry soil (<22% soil water) had little effect on crop performance. We conclude that trafficking the soil at low soil water contents minimises yield decline. Tillage operations to control weeds can be delayed by using herbicides until the surface soil dries. Compaction can be avoided completely by using a controlled traffic farming system. Crop and pasture roots ameliorated the initial compaction damage by creating wet–dry cycles. Such biological amelioration was as effective as mechanical amelioration by tillage. After a 3-year pasture ley, grain yield exceeded control in subsequent wheat and maize crops. However, pasture production is generally
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less profitable than cropping, and a commercial pasture would include further compaction by animal hooves.
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