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Soil compaction control — Objectives, possibilities and prospects
SOIL T E C H N O L O G Y
vol. 3, p. 231-239
Cremlingen 1990
SOIL C O M P A C T I O N C O N T R O L OBJECTIVES, POSSIBILITIES A N D P R O S P E C T S I. Hhkansson, Uppsala Summary
2
Experimentalbackground
Based mainly on a summary of the resuits of soil compaction experiments in Machinery traffic in arable fields causes Sweden, the demands for and the im- formation of ruts and soil compaction, portance of a program for control of the which may result in reduced crop yield, machinery induced compaction is formu- greater risk of erosion, poorer utilisation lated. Some possibilities to reduce com- of plant nutrients and increased leakpaction are discussed, such as reducing age, increased energy requirement for the traffic intensity on wet soil and de- tillage and increased need of ploughing creasing the ground pressure and axle (HAKANSSON et al. 1988). Among the load of the vehicles. Examples of present various consequences of soil compaction trends in Swedish farming are given. Es- the crop yield effects seem to be the most timations of the economic consequences wellknown. Even these, however, canof soil compaction are supposed to lead not be easily quantified, since they are to major changes of the technique for very variable and complex. A review of field operations, especially in wet regions. some experimental work on physical soil degradation in Swedish agriculture was made by JOHANSSON (1988). From I Introduction this it may be concluded that physical soil degradation of various types often The author's view of some soil comreduces crop yield by 20%. Machinery paction problems associated with the use induced soil compaction is one of the of heavy machines in agriculture is summajor reasons. marized. An attempt is made to make a In a short perspective, crop response general discussion, although the author's own experience originates from Sweden to compaction is not exclusively negand reference is made mainly to Swedish ative. Ploughing loosens the soil too experimental work. Comprehensive lit- much, and a moderate recompaction erature reviews have been published by normally increases yield (HAKANSSON SOANE et al. (1981a, b, 1982), TAYLOR 1966, F E R G E D A L 1971, E D L I N G & & G I L L (1984), KAYOMBO (1986) and F E R G E D A L 1972). Too intensive recompaction, however, again reduces the H/~KANSSON et al. (1988). yield. Thus, the crop yield as a funcISSN 0933-3630 tion of the state of compactness of the (~1990 by CATENA VERLAG, plough layer generally follows some type D-3302 Cremlingen-Destedt, W. Germany of maximum curve (fig. la). The op0933-3630/90/5011851/US$ 2.00 + 0.25 SOIL TECHNOLOGY--A cooperating Journal of CATENA
H~kansson
232
a) y 100 80
fl- ~ -
6O
70
b)
8'5
I ,/ /
-
~6o.
(soil moisture content)
(gr°und ) )y (traffic iPrffnStenSUs~t
80 r
1
5Time(years)
c)
d)
80~- ~
I
1
5
I ~
l°°r~ ....
80 I-, 1
F i g . 1"
!
10 Time (years)
,
, "T~ffi~ t~i.a~d
5
10
15 Time (years)
Schematic illustration of the effects of soil compaction on crop yield (Y).
a) Yield of spring barley under normal Swedish weather conditions as a function of the degree of compactness (D) of the plough layer as determined according to H/~KANSSON (1990). b) Residual effects of compaction of the plough layer on one occasion, shortly before ploughing, as a function of clay content, soil moisture content at time of traffic, ground pressure or traffic intensity. Annual ploughing is assumed. c) Residual effects of intensive traffic on one occasion as a function of the axle load of the vehicles. Annual ploughing is assumed. d) Cumulative effects of annually repeated traffic of moderate intensity as a function of the axle load of the vehicles used. The residual effects after terminating the traffic are also indicated. Annual ploughing is assumed.
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Soil Compaction Control
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Traffic intensity Trailer wheels Normal conditions (Mg km ha-1) 100 300 300
wide wide narrow
98 93 89
Wet conditions 94 88 --
Tab. 1: Average relative grain yield of small grain cereals during the first four years
in three long-term compaction experiments on clay or clay loam soils. Rel. yield in plots without experimental traffic = 100. Traffic with tractor and trailer (axle loads <5 Mg) was carried out annually, just before autumn ploughing. The tractor had standard tyres with normal inflation pressures, the trailer had wide wheels with an inflation pressure of 200 kPa or narrow wheels with an inflation pressure of 500 kPa. Traffic was carried out when soil water content was at or slightly above field capacity (wet) or a few percent lower (normal). During the rest of the year all plots were treated uniformly. The experiments were in the initial phase and the crop response increased with time (compare fig.ld).
timum state o f compactness, however, varies with several factors, two important ones being the moisture situation during the growing season ( H , ~ K A N S S O N 1966, E D L I N G & F E R G E D A L 1972) and the type o f crop ( H ] k K A N S S O N 1973, 1983). The state o f compactness o f the plough layer can be characterized in such a way that m a x i m u m crop yield is obtained at the same "degree o f compactness" irrespective o f soil type ( H / ~ K A N S S O N 1988, 1990). A single ploughing c a n n o t completely alleviate the effects o f previous compaction o f the ploughed layer except on soils with very low clay content ( H ~ K A N S S O N & D A N F O R S 1981, H A K A N S S O N et al. 1988). The higher the clay content the larger and the more persistent are the residual negative effects on crop growth (fig. lb). In clay soils they m a y persist for 4-5 years, in spite o f annual ploughing and frost action. The higher the traffic intensity, the g r o u n d pressure o f the wheels, or the soil moisture content at the time o f traffication the greater are the effects (tab.l). In tab. 1 the traffic intensity is quantified by the n u m b e r o f M g k m ha -l
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(the weight o f the machines times the distance driven). As a c o m p a r i s o n it m a y be mentioned that the normal annual traffic intensity in the production o f small grain cereals and sugar beets in Sweden has been estimated to 150-200 M g k m ha -1 and a b o u t 300 Mg km ha -1, respectively. The tractor traffic during mouldb o a r d ploughing to a depth o f 25 cm normally contributes about 50 M g k m ha -t , the traditional sequence o f 5-6 separate operations for seedbed preparation and sowing about 60, and the harvest o f sugar beets a b o u t 150. There m a y be m a n y reasons for the adverse residual effects o f soil compaction, an important one being a coarser structure o f the seedbed ( H ] k K A N S S O N 1983, H / k K A N S S O N et al. 1985 b). The residual effects and the one-year effects o f the actual degree o f compactness o f the plough layer seem to be purely additive (unpublished results by the author). In a reduced tillage system where ploughing is omitted, soil c o m p a c t i o n o f the topsoil is m u c h more persistent than in a system with ploughing. W h e n using normal farm machinery, c o m p a c t i o n is probably the greatest obstacle to plough-
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less tillage, at least on sandy soils (RYD B E R G 1987). Thus, the more compaction can be reduced the more feasible is a ploughless system. Compaction of the subsoil, mainly caused by vehicles with high axle load and tractor traffic in the open furrow when ploughing, is very persistent, perhaps permanent, even in a climate with annual freezing (HAKANSSON 1985, H A K A N S S O N et al. 1987, 1988). Effects of subsoil compaction on crop yield are illustrated in fig. lc. Compaction of the subsoil has been estimated to be the greatest physical threat to the productivity of Swedish arable soils, provided the trend of increasing axle load of farm machinery is not broken (HAKANSSON 1987). Alleviation of compaction by subsoiling is expensive and sometimes appears to be impossible. In regions with higher rainfall intensity and a demand for higher infiltration capacity than in northern Europe, subsoil compaction may be even more detrimental. When trafficking a field with a crop stand, e.g. when harvesting a forage crop, direct damage to the plants may be more harmful than soil compaction. H,~KANSSON et al. (1988) reviewed some of the literature on the effects of this type of traffic. Great damage is associated with factors such as high ground pressure and wheel slip, wheels with an unsuitable tread pattern, high traffic intensity and an unsuitable traffic pattern.
3
However, some general rules can be formulated. In a tillage system with annual ploughing the objective of compaction control would be as follows. For minimizing the detrimental long-term effects, which are important especially on clay soils, soil compaction throughout the year should be minimized. However, there is one important exception. During secondary tillage and sowing the plough layer should be moderately re-compacted so that a degree of compactness close to that which can be expected to give maximum yield of the actual crop under the local climatic conditions is obtained. With regard to the residual effects, the degree of compactness aimed at should be slightly below the optimal one for the crop sown. If ploughless tillage (shallow tillage or no-tillage) is practiced, or is being introduced, soil compaction should always be minimized. The less compaction the more competitive is the reduced tillage system compared to a system with ploughing. Another objective is to completely avoid deep subsoil compaction rather than attempt to cure it after it has occurred. Otherwise the soil productivity may be permanently impaired. This implies that the axle load must be restricted to an acceptable limit. For traffic in growing crops the essential point is to reduce the damage to the plants rather than to control soil compaction.
Objectives 4
The demands for and the importance of a program for soil compaction control varies considerably with the situation, and can be quantified only on the basis of local experiments and experience.
Possibilities
There are many possibilities to reduce detrimental soil compaction (H/~KANSSON et al. 1988). By means of "controlled traffic" (TAYLOR
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Soil Compaction Control
1985) soil compaction can be completely avoided for the major part of the area. This may be a useful system, especially where no need for recompaction after ploughing exists. Another possibility would be to modernize the old system with cable-towed implements ( L E P O R I et al. 1985). This system was utilized about one hundred years ago when heavy steam engines were used as power sources. The engines only trafficked the headlands. The implements were towed back and forth by cables and the main parts of the fields were non-trafficked. The potential crop yield effects of a cable-farming system were studied in Sweden in two long-term experiments on heavy clay soils very sensitive to compaction ( H A K A N S S O N et al. 1985a). The cable-farming plots outyielded the control plots where tractors with standard wheels with an inflation pressure of 100-120 kPa were used by 26%. When utilizing some of the possible timeliness effects of the cable-farming by sowing earlier, crop yield was increased still more. Sometimes the need for recompaction of a loosened plough layer exists, as in northern Europe when small grains are sown with narrow row-spacing, after mouldboard ploughing to a depth of about 25 cm. In such situations a frequently practised method for compaction control during seedbed preparation and sowing is the use of dual wheels or wide tyres with low inflation pressures. Here, the normal approach is to use several separate operations and a random traffic pattern, which leads to the moderate recompaction desired over a large part of the field, although other parts m a y be uncompacted or too intensively compacted ( F E R G E D A L 1971). Combining harrowing, sowing and fer-
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235
tilizing into one operation and using a machine with low-pressure wheels spread over the whole working width (DANF O R S 1987), gives a still more uniform and suitable state of compactness all over the field. A standard tractor as power unit for such a combination, however, leaves the area between the tractor wheels uncompacted, unless a specific arrangement for compaction of this area is made. This may lead to lower crop yield than a system with separate operations ( H U H T A P A L O 1985). A seedbed preparation and sowing combination based on traditional components seems to be more compatible with a no-ploughing than with a ploughing system. For all other field traffic it is essential to minimize soil compaction. As much as possible, therefore, traffic on wet soil must be avoided, and this may be facilitated by flexible planning of the work, high machinery capacity and a crop production and soil management system such that many of the field operations can be carried out during dry seasons. For instance, in Sweden, tillage and sowing is normally carried out under drier conditions for autumn-sown than for spring-sown crops. Thus, a large percentage of autumn-sown crops helps to control compaction. The use of low-pressure tyres also decreases compaction. At present there is a considerable activity among tyre manufacturers to develop such tyres. In the same Swedish experiments where cablefarming was tested, use of dual rear wheels on the tractor and an inflation pressure of 50-60 kPa throughout the year resulted in 6% higher yield than the standard wheels ( H A K A N S S O N et al. 1985a). In three new long-term experiments, a system in which the tractors have dual wheels and an inflation pres-
2 36
sure of 80 kPa and the other machines have wheels of traditional standard, is compared with a system where only lowpressure tyres with a maximum inflation pressure of 50 kPa is used. Already during the first three years, the low-pressure tyres resulted in a crop yield increase of 4%. For harvesting and transport operations a low traffic intensity is essential. This can be achieved by large working widths, a good organization of the field traffic, many entries to the fields, and matching the size of the loads to the length of the fields. In order to avoid subsoil compaction the axle load should be restricted. In Sweden (H/~KANSSON 1987) and G D R ( P E T E L K A U 1984), axle load limits of 6 Mg and 4 Mg, respectively, have been recommended. Such restrictions, of course, face no technical problems, only practical and economical ones, such as redesign of heavy vehicles. To decrease damage by traffic in growing crops such as harvest traffic in forage crops, control measures would normally be a low ground pressure and wheel slip, wheels with a suitable tread pattern, a suitable traffic pattern, a traffic intensity as low as possible, and multiple use of the tracks ( A R M B R U S T E R 1989, M. TUVESSON, unpublished results). For spreading and spraying operations in growing annual crops, on the other hand, narrow wheels may often be the best solution. Some examples of present trends in Sweden will be given. Many farmers regard soil compaction as one of their largest problems and are trying various counter-measures. In one region a noploughing system together with combination of seedbed preparation, fertilizing and sowing into one operation is
H~kansson
presently becoming increasingly popular, and the farmers strive at carrying out all remaining field operations with lowground-pressure machinery and with a low number of Mg km ha l. On one farm with about 1000 ha of arable land, heavy machines are still used, but the axle loads are restricted to 6 Mg and the inflation pressures in all tyres to 50 kPa. This has required reconstruction of some of the machines, such as mounting steered triple axles on a 15 m 3 slurry tanker and rebuilding some other machines to make space for larger wheels. A crop yield increase of about 3% would pay for this, but probably the increase will be twice as high. Another farmer has built his own tractor with eight wide tyres, and in most field operations he can use an inflation pressure below 50 kPa. When ploughing, he mounts one plough on each end of the tractor. Thus, the tractor does not have to be turned, which saves about 20% time, driving distance, and compaction on his irregular fields. In a region with severe soil compaction problems in combination with timeliness and drainage problems, a group of farmers is now seriously discussing the development of a modern "cable-farming" system for practical use. This would completely solve the compaction problems, but various timeliness effects and reduced need of ploughing might possibly be the greatest benefits. Some measures tbr compaction control, such as changes of the traffic pattern, adapting the tyre inflation pressure to the prevailing situation and arranging new entries to the fields, may often be taken without investments. Introducing low-pressure tyres, buying powered harrows in order to facilitate combination of seedbed preparation and sowing or
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increasing the number of axles on heavy vehicles in order to reduce the axle load require moderate investments. Complete avoidance of compaction is possible only by major changes of the whole machine or production system.
5
Prospects
In a long perspective, major changes of the technique for field operations can be foreseen. Significant activities to reduce compaction are in progress. The present machinery sytem was originally developed for regions with the largest farms, and these regions have a dry climate. So far, only minor changes have been made to adapt the machines to wetter situations. A more independent machinery development for wet regions seems necessary. The limits for traffic intensity, axle load and ground pressure are lower and, therefore, they are reached earlier, the wetter the climate. However, at present detrimental effects of soil compaction seem to be observed even in dry areas. The identification of critical machines or operations and technical improvements would be facilitated by estimations of the economic consequences of soil compaction. Therefore, as soon as enough data are available models for such estimations should be developed. However, an economic model must consider many effects of compaction, and data applicable to the local situation must be available. Therefore, an extensive local experimentation is required, and the model must be adapted to the available data. However, in some regions sufficient data for reasonably good economic estimations exist. The author is presently developing a model for calculating the economic SOIL T E C H N O L O G Y - A cooperating Journal of CATENA
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consequences of soil compaction under Swedish conditions. These consequences, and the optimal choice of methods and machinery for field operations, vary considerably between farms, and thus, to become an aid in practical farming, the model must be developed for use on individual farms. Furthermore, it needs to be very detailed in order that effects of individual operations, machines, axles or wheels can be identified. So far, the one-year effects of recompaction of the ploughed layer, the long-term effects of plough layer compaction, and the effects of subsoil compaction and traffÉc in forage crops are being considered. Later, effects on draft requirement and need of tillage will be included. Effects on water infiltration, runoff and erosion or on leaching of plant nutrients cannot presently be included, because local data are missing. Parts of the model have been tested on some farms. The experience indicates that an economic optimization of the techniques for field operations with regard to soil compaction may result in a considerable improvement of the efficiency of the farming system. It will result in the use of more varying methods and a better adaptation to local conditions. Sometimes reduced compaction may facilitate a significant reduction of production costs by reducing the need of ploughing. The consequences of soil compaction are less intensively studied in tropical regions than in temperate regions, one reason being the lower level of mechanization. However, in many tropical countries the farming is gradually becoming mechanized. Since compaction may have detrimental effects on infiltration, runoff and erosion, its effects may be more harmful than in a temperate
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region. Furthermore, there is no freezing. Therefore, in these countries the risks caused by machinery traffic may be greater. In order to facilitate the choice of a suitable technique, the consequences of various machinery systems should be studied before major investments are made. Once large investments are made, changes will take a long time and during that time the productivity of the soils may be permanently impaired. References ARMBRUSTER, K. (1989): Untersuchungen an Reifen zum boden- und pflanzenschonenden Befahren yon Griinland. In: V.A. Dodd & EM. Grace (Eds.), Agricultural Engineering, Balkema, Rotterdam, Vol. 3, 1723-1728. DANFORS, B. (1987): Equipment for seed placement below a removed and replaced surface tilth. J. agric. Engng. Res. 38, 167 172. EDLING, P. & FERGEDAL, L. (1972): Model experiments on soil compaction 1968-69. Swedish Univ. Agric. Sci., Uppsala, Div. Soil Management, Report 31, 71 pp. (In Swedish). EERGEDAL, L (1971): Soil compaction by tractor at different times for spring sowing of small grain cereals. Swedish Univ. Agric. Sci., Uppsala, Div. Soil Management, Report 26, 140 pp. (In Swedish). H.~KANSSON, I. (1966): Experiments with different degrees of compaction in the topsoil and upper part of the subsoil. Grundf6rb~ittring 19, 281 332. (In Swedish with English summary). H/~KANSSON, I. (1973): The sensitivity of different crops to soil compaction. Summaries from Sixth International Conference on Soil Tillage, September 24-29, 1973, Wageningen, The Netherlands, 14:1-14:4. H~KANSSON, I. (1983): About the reasons for influences of machinery traffic on crop yield. Proceedings of Symposium "Zmeny pudniho prostredi ve vztahu k intenzifikacnim faktorum" 1983, Brno, Czechoslovakia, 57-66. (In German). H~KANSSON, I. (1985): Swedish experiments on subsoil compaction by vehicles with high axle load. Soil Use and Management 1, 113-116. H/~KANSSON, I. (1987): Long-term effects of modern technology on productivity of arable
land. K. Skogs- o. Lantbruksakad. Tidskr. 126, 35~40. (In Swedish with English summary). H~,KANSSON, L (1988): A method for characterizing the state of compactness of an arable soil. CATENA SUPPLEMENT 11, 101 105. H~KANSSON, I. (1990): A method for characterizing the state of compactness of the plough layer. Soil & Tillage Research. (In press). H.~KANSSON, I. & DANFORS, B. (1981): Effects of heavy traffic on soil conditions and crop growth. Int. Society for Terrain-Vehicle Systems, Hannover, NH, U.S.A., Proceedings of 7th Int. Conf., 16 20 Aug. 1981, Calgary, Alb., Canada, 239--253. H~KANSSON, I., ttENRIKSSON, L. & GUSTAFSSON, L. (1985a): Experiments on reduced compaction of heavy clays and sandy soils in Sweden. Proceedings of Int. Conf. on Soil Dynamics, Auburn University, Auburn, AL. U.S.A., 995 1009. H~kKANSSON, 1., WIKLERT, P. & THUNHOLM, B. (1985b): Long-term effects of compaction by farm machinery on some ecologically important physical properties of soils. University of Georgia, Athens, GA, U.S.A., lntecol Bulletin 1985:12, 119 125. H,~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 & Tillage Research 10, 259-268. HA,KANSSON, 1., VOORHEES, W.B. & RILEY, H. (1988): Vehicle and wheel factors influencing soil compaction and crop response in different traffic regimes. Soil & Tillage Research 11, 239-282. HUHTAPALO, A,. (1985): Combined harrowing and sowing. Swedish Univ. Agric. Sci., Uppsala, Research Information Centre, Report A63, 21:1 21:6. (In Swedish). JOHANSSON, W. (1988): Physical soil properties, plant production and environment. Swedish. Univ. Agric. Sci., Uppsala, Research Information Centre, Report 136, 11 27. (In Swedish). KAYOMBO, B. (1986): Soil compaction from tropical agricultural lands and its control. Inst. Agric. Eng., Royal Vet. and Agric. Univ., Tf.strup, Denmark, Report 54, 74 pp.
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Soil Compaction Control
LEPORI, W.A., MIZRACH, A. & SHMULEVICH, I. (1985): Soil tillage and cultivation using non-tractive power transmission methods. Proceedings of Int. Conf. on Soil Dynamics, Auburn University, Auburn, AL, U.S.A., 10461054. PETELKAU, H. (1984): Effects of harmful compaction on soil properties and crop yields and measures to reduce compaction. Tagungsber. Akad. Landwirtsch.-Wiss. DDR, Berlin, 227, 25-34. (In German with English summary). RYDBERG, 1". (1987): Studies in ploughless tillage in Sweden 1975-1986. Swedish Univ. Agric. Sci., Uppsala, Div. Soil Management, Report 76, 132 pp. (In Swedish with English summary). SOANE, B.D., BLACKWELL, P.S., DICKSON, J.W. & PAINTER, D.J. (1981a): Compaction by agricultural vehicles: a review. I. Soil and wheel characteristics. Soil & Tillage Research 1, 207-237. SOANE, B.D., BLACKWELL, P.S., DICKSON, J.W. & PAINTER, D.J. (1981b): Compaction by agricultural vehicles: a review. II. Compaction under tyres and other running gear. Soil & Tillage Research 1, 373-400. SOANE, B.D., DICKSON, J.W. & CAMPBELL, D.J. (1982): Compaction by agricultural rehicles: a review. III. Incidence and control of compaction in crop production. Soil & Tillage Research 2, 3-36. TAYLOR, J.H. (1985): Controlled traffic: a spinoff of soil dynamics research. Proceedings of Int. Conf. on Soil Dynamics, Auburn University, Auburn, AL, U.S.A., 1101-1111. TAYLOR, J.H. & GILL, W.R. (1984): Soil compaction: state-of-the-art report. J. Terramech. 21, 195-213.
Address of author: Inge Hikansson Swedish University of Agricultural Sciences Dept. of Soil Sciences P.O. Box 7014 S-750 07 Uppsala, Sweden
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vol. 3, p. 231-239
Cremlingen 1990
SOIL C O M P A C T I O N C O N T R O L OBJECTIVES, POSSIBILITIES A N D P R O S P E C T S I. Hhkansson, Uppsala Summary
2
Experimentalbackground
Based mainly on a summary of the resuits of soil compaction experiments in Machinery traffic in arable fields causes Sweden, the demands for and the im- formation of ruts and soil compaction, portance of a program for control of the which may result in reduced crop yield, machinery induced compaction is formu- greater risk of erosion, poorer utilisation lated. Some possibilities to reduce com- of plant nutrients and increased leakpaction are discussed, such as reducing age, increased energy requirement for the traffic intensity on wet soil and de- tillage and increased need of ploughing creasing the ground pressure and axle (HAKANSSON et al. 1988). Among the load of the vehicles. Examples of present various consequences of soil compaction trends in Swedish farming are given. Es- the crop yield effects seem to be the most timations of the economic consequences wellknown. Even these, however, canof soil compaction are supposed to lead not be easily quantified, since they are to major changes of the technique for very variable and complex. A review of field operations, especially in wet regions. some experimental work on physical soil degradation in Swedish agriculture was made by JOHANSSON (1988). From I Introduction this it may be concluded that physical soil degradation of various types often The author's view of some soil comreduces crop yield by 20%. Machinery paction problems associated with the use induced soil compaction is one of the of heavy machines in agriculture is summajor reasons. marized. An attempt is made to make a In a short perspective, crop response general discussion, although the author's own experience originates from Sweden to compaction is not exclusively negand reference is made mainly to Swedish ative. Ploughing loosens the soil too experimental work. Comprehensive lit- much, and a moderate recompaction erature reviews have been published by normally increases yield (HAKANSSON SOANE et al. (1981a, b, 1982), TAYLOR 1966, F E R G E D A L 1971, E D L I N G & & G I L L (1984), KAYOMBO (1986) and F E R G E D A L 1972). Too intensive recompaction, however, again reduces the H/~KANSSON et al. (1988). yield. Thus, the crop yield as a funcISSN 0933-3630 tion of the state of compactness of the (~1990 by CATENA VERLAG, plough layer generally follows some type D-3302 Cremlingen-Destedt, W. Germany of maximum curve (fig. la). The op0933-3630/90/5011851/US$ 2.00 + 0.25 SOIL TECHNOLOGY--A cooperating Journal of CATENA
H~kansson
232
a) y 100 80
fl- ~ -
6O
70
b)
8'5
I ,/ /
-
~6o.
(soil moisture content)
(gr°und ) )y (traffic iPrffnStenSUs~t
80 r
1
5Time(years)
c)
d)
80~- ~
I
1
5
I ~
l°°r~ ....
80 I-, 1
F i g . 1"
!
10 Time (years)
,
, "T~ffi~ t~i.a~d
5
10
15 Time (years)
Schematic illustration of the effects of soil compaction on crop yield (Y).
a) Yield of spring barley under normal Swedish weather conditions as a function of the degree of compactness (D) of the plough layer as determined according to H/~KANSSON (1990). b) Residual effects of compaction of the plough layer on one occasion, shortly before ploughing, as a function of clay content, soil moisture content at time of traffic, ground pressure or traffic intensity. Annual ploughing is assumed. c) Residual effects of intensive traffic on one occasion as a function of the axle load of the vehicles. Annual ploughing is assumed. d) Cumulative effects of annually repeated traffic of moderate intensity as a function of the axle load of the vehicles used. The residual effects after terminating the traffic are also indicated. Annual ploughing is assumed.
SOIL TECHNOLOGY
A cooperating Journal of CA'lENA
Soil Compaction Control
233
Traffic intensity Trailer wheels Normal conditions (Mg km ha-1) 100 300 300
wide wide narrow
98 93 89
Wet conditions 94 88 --
Tab. 1: Average relative grain yield of small grain cereals during the first four years
in three long-term compaction experiments on clay or clay loam soils. Rel. yield in plots without experimental traffic = 100. Traffic with tractor and trailer (axle loads <5 Mg) was carried out annually, just before autumn ploughing. The tractor had standard tyres with normal inflation pressures, the trailer had wide wheels with an inflation pressure of 200 kPa or narrow wheels with an inflation pressure of 500 kPa. Traffic was carried out when soil water content was at or slightly above field capacity (wet) or a few percent lower (normal). During the rest of the year all plots were treated uniformly. The experiments were in the initial phase and the crop response increased with time (compare fig.ld).
timum state o f compactness, however, varies with several factors, two important ones being the moisture situation during the growing season ( H , ~ K A N S S O N 1966, E D L I N G & F E R G E D A L 1972) and the type o f crop ( H ] k K A N S S O N 1973, 1983). The state o f compactness o f the plough layer can be characterized in such a way that m a x i m u m crop yield is obtained at the same "degree o f compactness" irrespective o f soil type ( H / ~ K A N S S O N 1988, 1990). A single ploughing c a n n o t completely alleviate the effects o f previous compaction o f the ploughed layer except on soils with very low clay content ( H ~ K A N S S O N & D A N F O R S 1981, H A K A N S S O N et al. 1988). The higher the clay content the larger and the more persistent are the residual negative effects on crop growth (fig. lb). In clay soils they m a y persist for 4-5 years, in spite o f annual ploughing and frost action. The higher the traffic intensity, the g r o u n d pressure o f the wheels, or the soil moisture content at the time o f traffication the greater are the effects (tab.l). In tab. 1 the traffic intensity is quantified by the n u m b e r o f M g k m ha -l
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(the weight o f the machines times the distance driven). As a c o m p a r i s o n it m a y be mentioned that the normal annual traffic intensity in the production o f small grain cereals and sugar beets in Sweden has been estimated to 150-200 M g k m ha -1 and a b o u t 300 Mg km ha -1, respectively. The tractor traffic during mouldb o a r d ploughing to a depth o f 25 cm normally contributes about 50 M g k m ha -t , the traditional sequence o f 5-6 separate operations for seedbed preparation and sowing about 60, and the harvest o f sugar beets a b o u t 150. There m a y be m a n y reasons for the adverse residual effects o f soil compaction, an important one being a coarser structure o f the seedbed ( H ] k K A N S S O N 1983, H / k K A N S S O N et al. 1985 b). The residual effects and the one-year effects o f the actual degree o f compactness o f the plough layer seem to be purely additive (unpublished results by the author). In a reduced tillage system where ploughing is omitted, soil c o m p a c t i o n o f the topsoil is m u c h more persistent than in a system with ploughing. W h e n using normal farm machinery, c o m p a c t i o n is probably the greatest obstacle to plough-
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less tillage, at least on sandy soils (RYD B E R G 1987). Thus, the more compaction can be reduced the more feasible is a ploughless system. Compaction of the subsoil, mainly caused by vehicles with high axle load and tractor traffic in the open furrow when ploughing, is very persistent, perhaps permanent, even in a climate with annual freezing (HAKANSSON 1985, H A K A N S S O N et al. 1987, 1988). Effects of subsoil compaction on crop yield are illustrated in fig. lc. Compaction of the subsoil has been estimated to be the greatest physical threat to the productivity of Swedish arable soils, provided the trend of increasing axle load of farm machinery is not broken (HAKANSSON 1987). Alleviation of compaction by subsoiling is expensive and sometimes appears to be impossible. In regions with higher rainfall intensity and a demand for higher infiltration capacity than in northern Europe, subsoil compaction may be even more detrimental. When trafficking a field with a crop stand, e.g. when harvesting a forage crop, direct damage to the plants may be more harmful than soil compaction. H,~KANSSON et al. (1988) reviewed some of the literature on the effects of this type of traffic. Great damage is associated with factors such as high ground pressure and wheel slip, wheels with an unsuitable tread pattern, high traffic intensity and an unsuitable traffic pattern.
3
However, some general rules can be formulated. In a tillage system with annual ploughing the objective of compaction control would be as follows. For minimizing the detrimental long-term effects, which are important especially on clay soils, soil compaction throughout the year should be minimized. However, there is one important exception. During secondary tillage and sowing the plough layer should be moderately re-compacted so that a degree of compactness close to that which can be expected to give maximum yield of the actual crop under the local climatic conditions is obtained. With regard to the residual effects, the degree of compactness aimed at should be slightly below the optimal one for the crop sown. If ploughless tillage (shallow tillage or no-tillage) is practiced, or is being introduced, soil compaction should always be minimized. The less compaction the more competitive is the reduced tillage system compared to a system with ploughing. Another objective is to completely avoid deep subsoil compaction rather than attempt to cure it after it has occurred. Otherwise the soil productivity may be permanently impaired. This implies that the axle load must be restricted to an acceptable limit. For traffic in growing crops the essential point is to reduce the damage to the plants rather than to control soil compaction.
Objectives 4
The demands for and the importance of a program for soil compaction control varies considerably with the situation, and can be quantified only on the basis of local experiments and experience.
Possibilities
There are many possibilities to reduce detrimental soil compaction (H/~KANSSON et al. 1988). By means of "controlled traffic" (TAYLOR
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1985) soil compaction can be completely avoided for the major part of the area. This may be a useful system, especially where no need for recompaction after ploughing exists. Another possibility would be to modernize the old system with cable-towed implements ( L E P O R I et al. 1985). This system was utilized about one hundred years ago when heavy steam engines were used as power sources. The engines only trafficked the headlands. The implements were towed back and forth by cables and the main parts of the fields were non-trafficked. The potential crop yield effects of a cable-farming system were studied in Sweden in two long-term experiments on heavy clay soils very sensitive to compaction ( H A K A N S S O N et al. 1985a). The cable-farming plots outyielded the control plots where tractors with standard wheels with an inflation pressure of 100-120 kPa were used by 26%. When utilizing some of the possible timeliness effects of the cable-farming by sowing earlier, crop yield was increased still more. Sometimes the need for recompaction of a loosened plough layer exists, as in northern Europe when small grains are sown with narrow row-spacing, after mouldboard ploughing to a depth of about 25 cm. In such situations a frequently practised method for compaction control during seedbed preparation and sowing is the use of dual wheels or wide tyres with low inflation pressures. Here, the normal approach is to use several separate operations and a random traffic pattern, which leads to the moderate recompaction desired over a large part of the field, although other parts m a y be uncompacted or too intensively compacted ( F E R G E D A L 1971). Combining harrowing, sowing and fer-
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tilizing into one operation and using a machine with low-pressure wheels spread over the whole working width (DANF O R S 1987), gives a still more uniform and suitable state of compactness all over the field. A standard tractor as power unit for such a combination, however, leaves the area between the tractor wheels uncompacted, unless a specific arrangement for compaction of this area is made. This may lead to lower crop yield than a system with separate operations ( H U H T A P A L O 1985). A seedbed preparation and sowing combination based on traditional components seems to be more compatible with a no-ploughing than with a ploughing system. For all other field traffic it is essential to minimize soil compaction. As much as possible, therefore, traffic on wet soil must be avoided, and this may be facilitated by flexible planning of the work, high machinery capacity and a crop production and soil management system such that many of the field operations can be carried out during dry seasons. For instance, in Sweden, tillage and sowing is normally carried out under drier conditions for autumn-sown than for spring-sown crops. Thus, a large percentage of autumn-sown crops helps to control compaction. The use of low-pressure tyres also decreases compaction. At present there is a considerable activity among tyre manufacturers to develop such tyres. In the same Swedish experiments where cablefarming was tested, use of dual rear wheels on the tractor and an inflation pressure of 50-60 kPa throughout the year resulted in 6% higher yield than the standard wheels ( H A K A N S S O N et al. 1985a). In three new long-term experiments, a system in which the tractors have dual wheels and an inflation pres-
2 36
sure of 80 kPa and the other machines have wheels of traditional standard, is compared with a system where only lowpressure tyres with a maximum inflation pressure of 50 kPa is used. Already during the first three years, the low-pressure tyres resulted in a crop yield increase of 4%. For harvesting and transport operations a low traffic intensity is essential. This can be achieved by large working widths, a good organization of the field traffic, many entries to the fields, and matching the size of the loads to the length of the fields. In order to avoid subsoil compaction the axle load should be restricted. In Sweden (H/~KANSSON 1987) and G D R ( P E T E L K A U 1984), axle load limits of 6 Mg and 4 Mg, respectively, have been recommended. Such restrictions, of course, face no technical problems, only practical and economical ones, such as redesign of heavy vehicles. To decrease damage by traffic in growing crops such as harvest traffic in forage crops, control measures would normally be a low ground pressure and wheel slip, wheels with a suitable tread pattern, a suitable traffic pattern, a traffic intensity as low as possible, and multiple use of the tracks ( A R M B R U S T E R 1989, M. TUVESSON, unpublished results). For spreading and spraying operations in growing annual crops, on the other hand, narrow wheels may often be the best solution. Some examples of present trends in Sweden will be given. Many farmers regard soil compaction as one of their largest problems and are trying various counter-measures. In one region a noploughing system together with combination of seedbed preparation, fertilizing and sowing into one operation is
H~kansson
presently becoming increasingly popular, and the farmers strive at carrying out all remaining field operations with lowground-pressure machinery and with a low number of Mg km ha l. On one farm with about 1000 ha of arable land, heavy machines are still used, but the axle loads are restricted to 6 Mg and the inflation pressures in all tyres to 50 kPa. This has required reconstruction of some of the machines, such as mounting steered triple axles on a 15 m 3 slurry tanker and rebuilding some other machines to make space for larger wheels. A crop yield increase of about 3% would pay for this, but probably the increase will be twice as high. Another farmer has built his own tractor with eight wide tyres, and in most field operations he can use an inflation pressure below 50 kPa. When ploughing, he mounts one plough on each end of the tractor. Thus, the tractor does not have to be turned, which saves about 20% time, driving distance, and compaction on his irregular fields. In a region with severe soil compaction problems in combination with timeliness and drainage problems, a group of farmers is now seriously discussing the development of a modern "cable-farming" system for practical use. This would completely solve the compaction problems, but various timeliness effects and reduced need of ploughing might possibly be the greatest benefits. Some measures tbr compaction control, such as changes of the traffic pattern, adapting the tyre inflation pressure to the prevailing situation and arranging new entries to the fields, may often be taken without investments. Introducing low-pressure tyres, buying powered harrows in order to facilitate combination of seedbed preparation and sowing or
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increasing the number of axles on heavy vehicles in order to reduce the axle load require moderate investments. Complete avoidance of compaction is possible only by major changes of the whole machine or production system.
5
Prospects
In a long perspective, major changes of the technique for field operations can be foreseen. Significant activities to reduce compaction are in progress. The present machinery sytem was originally developed for regions with the largest farms, and these regions have a dry climate. So far, only minor changes have been made to adapt the machines to wetter situations. A more independent machinery development for wet regions seems necessary. The limits for traffic intensity, axle load and ground pressure are lower and, therefore, they are reached earlier, the wetter the climate. However, at present detrimental effects of soil compaction seem to be observed even in dry areas. The identification of critical machines or operations and technical improvements would be facilitated by estimations of the economic consequences of soil compaction. Therefore, as soon as enough data are available models for such estimations should be developed. However, an economic model must consider many effects of compaction, and data applicable to the local situation must be available. Therefore, an extensive local experimentation is required, and the model must be adapted to the available data. However, in some regions sufficient data for reasonably good economic estimations exist. The author is presently developing a model for calculating the economic SOIL T E C H N O L O G Y - A cooperating Journal of CATENA
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consequences of soil compaction under Swedish conditions. These consequences, and the optimal choice of methods and machinery for field operations, vary considerably between farms, and thus, to become an aid in practical farming, the model must be developed for use on individual farms. Furthermore, it needs to be very detailed in order that effects of individual operations, machines, axles or wheels can be identified. So far, the one-year effects of recompaction of the ploughed layer, the long-term effects of plough layer compaction, and the effects of subsoil compaction and traffÉc in forage crops are being considered. Later, effects on draft requirement and need of tillage will be included. Effects on water infiltration, runoff and erosion or on leaching of plant nutrients cannot presently be included, because local data are missing. Parts of the model have been tested on some farms. The experience indicates that an economic optimization of the techniques for field operations with regard to soil compaction may result in a considerable improvement of the efficiency of the farming system. It will result in the use of more varying methods and a better adaptation to local conditions. Sometimes reduced compaction may facilitate a significant reduction of production costs by reducing the need of ploughing. The consequences of soil compaction are less intensively studied in tropical regions than in temperate regions, one reason being the lower level of mechanization. However, in many tropical countries the farming is gradually becoming mechanized. Since compaction may have detrimental effects on infiltration, runoff and erosion, its effects may be more harmful than in a temperate
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region. Furthermore, there is no freezing. Therefore, in these countries the risks caused by machinery traffic may be greater. In order to facilitate the choice of a suitable technique, the consequences of various machinery systems should be studied before major investments are made. Once large investments are made, changes will take a long time and during that time the productivity of the soils may be permanently impaired. References ARMBRUSTER, K. (1989): Untersuchungen an Reifen zum boden- und pflanzenschonenden Befahren yon Griinland. In: V.A. Dodd & EM. Grace (Eds.), Agricultural Engineering, Balkema, Rotterdam, Vol. 3, 1723-1728. DANFORS, B. (1987): Equipment for seed placement below a removed and replaced surface tilth. J. agric. Engng. Res. 38, 167 172. EDLING, P. & FERGEDAL, L. (1972): Model experiments on soil compaction 1968-69. Swedish Univ. Agric. Sci., Uppsala, Div. Soil Management, Report 31, 71 pp. (In Swedish). EERGEDAL, L (1971): Soil compaction by tractor at different times for spring sowing of small grain cereals. Swedish Univ. Agric. Sci., Uppsala, Div. Soil Management, Report 26, 140 pp. (In Swedish). H.~KANSSON, I. (1966): Experiments with different degrees of compaction in the topsoil and upper part of the subsoil. Grundf6rb~ittring 19, 281 332. (In Swedish with English summary). H/~KANSSON, I. (1973): The sensitivity of different crops to soil compaction. Summaries from Sixth International Conference on Soil Tillage, September 24-29, 1973, Wageningen, The Netherlands, 14:1-14:4. H~KANSSON, I. (1983): About the reasons for influences of machinery traffic on crop yield. Proceedings of Symposium "Zmeny pudniho prostredi ve vztahu k intenzifikacnim faktorum" 1983, Brno, Czechoslovakia, 57-66. (In German). H~KANSSON, I. (1985): Swedish experiments on subsoil compaction by vehicles with high axle load. Soil Use and Management 1, 113-116. H/~KANSSON, I. (1987): Long-term effects of modern technology on productivity of arable
land. K. Skogs- o. Lantbruksakad. Tidskr. 126, 35~40. (In Swedish with English summary). H~,KANSSON, L (1988): A method for characterizing the state of compactness of an arable soil. CATENA SUPPLEMENT 11, 101 105. H~KANSSON, I. (1990): A method for characterizing the state of compactness of the plough layer. Soil & Tillage Research. (In press). H.~KANSSON, I. & DANFORS, B. (1981): Effects of heavy traffic on soil conditions and crop growth. Int. Society for Terrain-Vehicle Systems, Hannover, NH, U.S.A., Proceedings of 7th Int. Conf., 16 20 Aug. 1981, Calgary, Alb., Canada, 239--253. H~KANSSON, I., ttENRIKSSON, L. & GUSTAFSSON, L. (1985a): Experiments on reduced compaction of heavy clays and sandy soils in Sweden. Proceedings of Int. Conf. on Soil Dynamics, Auburn University, Auburn, AL. U.S.A., 995 1009. H~kKANSSON, 1., WIKLERT, P. & THUNHOLM, B. (1985b): Long-term effects of compaction by farm machinery on some ecologically important physical properties of soils. University of Georgia, Athens, GA, U.S.A., lntecol Bulletin 1985:12, 119 125. H,~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 & Tillage Research 10, 259-268. HA,KANSSON, 1., VOORHEES, W.B. & RILEY, H. (1988): Vehicle and wheel factors influencing soil compaction and crop response in different traffic regimes. Soil & Tillage Research 11, 239-282. HUHTAPALO, A,. (1985): Combined harrowing and sowing. Swedish Univ. Agric. Sci., Uppsala, Research Information Centre, Report A63, 21:1 21:6. (In Swedish). JOHANSSON, W. (1988): Physical soil properties, plant production and environment. Swedish. Univ. Agric. Sci., Uppsala, Research Information Centre, Report 136, 11 27. (In Swedish). KAYOMBO, B. (1986): Soil compaction from tropical agricultural lands and its control. Inst. Agric. Eng., Royal Vet. and Agric. Univ., Tf.strup, Denmark, Report 54, 74 pp.
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LEPORI, W.A., MIZRACH, A. & SHMULEVICH, I. (1985): Soil tillage and cultivation using non-tractive power transmission methods. Proceedings of Int. Conf. on Soil Dynamics, Auburn University, Auburn, AL, U.S.A., 10461054. PETELKAU, H. (1984): Effects of harmful compaction on soil properties and crop yields and measures to reduce compaction. Tagungsber. Akad. Landwirtsch.-Wiss. DDR, Berlin, 227, 25-34. (In German with English summary). RYDBERG, 1". (1987): Studies in ploughless tillage in Sweden 1975-1986. Swedish Univ. Agric. Sci., Uppsala, Div. Soil Management, Report 76, 132 pp. (In Swedish with English summary). SOANE, B.D., BLACKWELL, P.S., DICKSON, J.W. & PAINTER, D.J. (1981a): Compaction by agricultural vehicles: a review. I. Soil and wheel characteristics. Soil & Tillage Research 1, 207-237. SOANE, B.D., BLACKWELL, P.S., DICKSON, J.W. & PAINTER, D.J. (1981b): Compaction by agricultural vehicles: a review. II. Compaction under tyres and other running gear. Soil & Tillage Research 1, 373-400. SOANE, B.D., DICKSON, J.W. & CAMPBELL, D.J. (1982): Compaction by agricultural rehicles: a review. III. Incidence and control of compaction in crop production. Soil & Tillage Research 2, 3-36. TAYLOR, J.H. (1985): Controlled traffic: a spinoff of soil dynamics research. Proceedings of Int. Conf. on Soil Dynamics, Auburn University, Auburn, AL, U.S.A., 1101-1111. TAYLOR, J.H. & GILL, W.R. (1984): Soil compaction: state-of-the-art report. J. Terramech. 21, 195-213.
Address of author: Inge Hikansson Swedish University of Agricultural Sciences Dept. of Soil Sciences P.O. Box 7014 S-750 07 Uppsala, Sweden
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