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Providing evidence to improve practice

Action: Control traffic and traffic timing Soil Fertility

Key messages

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Biodiversity: One randomized, replicated study from Poland found higher numbers and bacterial activity under controlled traffic. One replicated site comparison study from Denmark found higher microbial biomass when farm traffic was not controlled

Erosion: Five trials from Europe and Australia (including three replicated trials, one controlled before-and after-trial, and one review) found a higher number of pores in the soil, less compaction, reduced runoff and increased water filtration into the soil under controlled traffic. One controlled, replicated trial from India found increased soil crack width when traffic was not controlled.

Yield: Two replicated trials from Australia and the USA found increased yield under controlled traffic.

SOIL TYPES COVERED: clay, loamy-sandloamy-silt, sandy loamsilty, silty-clay, silt loam.


Supporting evidence from individual studies


A randomized, replicated experiment in 1990-1991 on silt loam soil in Shoreham, UK (Robinson & Naghizadeh 1992) found lower runoff in uncompacted ground (3 l/h) compared to compacted ground in tractor wheelings (8 l/h). There were two sites with 100 x 18 m cultivated plots (number not specified). Plots had three different cultivation practices (shallow cultivation, conventional deep cultivation, and deep cultivation followed by heavy rolling). A rainfall simulator was used to test runoff, with each treatment subjected to three simulated rainfall events, lasting one hour at 42.5 mm/h. Runoff and eroded soil was caught in a trap immediately downslope of the rainfall simulator. The volume of runoff and weight of eroded soil were measured.



A replicated experiment in 1990-1991 on loamy sand in the USA (Torbert and Reeves 1995) found 10% high plant nitrogen uptake in the dry year under no traffic compared to under traffic. Plant nitrogen uptake in the wet year was higher under no traffic and tillage (186 kg N/ha) than when under combined traffic and tillage treatments (161 kg N/ha). Corn Zea mays grain yield was higher under no traffic with residue incorporated (6.1Mg/ha) compared to under traffic (5.2Mg/ha). The experimental area was split into two with corn Zea mays planted in one half, and soybean Glycine Max. Treatments included: no-tillage, annual subsoiling (deep tillage to 44 cm depth), and one-time complete disruption (subsoiling the middle 25cm of each strip plot). Plots were 21.3 x 6.1 m strips. Within each treatment, two further treatments were applied: no traffic, and traffic (plots driven over by a 4.6 Mg tractor). Within the traffic treatments were two residue management treatments: no-tillage and crop residue in corporation (using a disc). Nitrogen fertilizer was added to 2.3 x 1.8 m of each treatment. Soils were sampled to 90 cm depth.



A controlled before-and-after trial in 1995-1997 on a loamy silt soil in Lower Saxony, Germany (Langmaack et al. 2002) found 70-85% more soil pores in unwheeled compared to soil compacted by heavy machinery. Earthworms Lumbricus terrestris were not affected by compaction. Burrows made by earthworms Aporrectodea caliginosa were still lower in length (9 mm/g/day), volume (68 mm3/g/day), and windiness (17%) compared to uncompacted soil two years after the compaction event. One part of the field was compacted six times in spring 1995 by repeated wheeling by heavy four-wheel-drive machinery with a 5 Mg wheel load, the other, uncompacted. Undisturbed soil monoliths (a vertical sample showing several soil horizons) were taken from fields in 1997 under conventional tillage or conservation tillage. X-ray computed 2D images were used to analyse soil structure.



A controlled, replicated experiment in 2000 on a non-chalky clay soil in Bhopal, India (Bandyopadhyay et al. 2003) found that increased compaction increased soil crack width. The smallest cracks were found in uncompacted plots (0.027 m) compared to low (0.037 m) or high compaction plots (0.040 m). Within a rotation of rice Oryza sativa and wheat Triticum aestivum there were three compaction or puddling treatments:  low (four passes by power tiller), high (eight passes by power tiller) and no compaction. There were three replicates in plots of 5 x 8 m. Crack length, depth and width, and soil water content and soil density were measured.



A review of 37 studies covering countries in the European Union (Chamen et al. 2003) found that controlled traffic with precision guidance can avoid compacting soil in a cropped area. Changing tyre load and tyre inflation achieved reduced risk of compaction. Studies showed that compaction was reduced on-farm by avoiding working the soil in wet conditions, adjusting to out-of-furrow ploughing (i.e. not ploughing repeatedly along the same lines), confining the compaction to particular areas (such as tracks outside the cropping area), reduced loosening of topsoil and subsoil, and the use of equipment with low ground pressure.



A replicated experiment in 1994-1999, on a clay soil in Queensland, Australia (Li et al. 2007) found that runoff decreased by 36% and yield increased by 9% in controlled traffic plots compared to compacted plots. Soil water content was higher in compacted plots at 0-500 mm depth. Controlled traffic and zero tillage combined decreased runoff by 47.% and increased yield by 14.5 %. Reduced tillage also reduced runoff regardless of traffic. Tillage plots of 90 m2 were arranged in pairs (one plot had zero tillage and the other plot had stubble mulch tillage), within which were two traffic treatments:  non-wheeled and wheeled. This was replicated in four blocks. Compacted areas were wheeled annually using a 100 kW tractor. Crops included: wheat Triticum aestivum, sorghum Sorghum bicolor, maize/sweet corn Zea mays and sunflower Helianthus annus. Yield was determined from harvested transects in the plots. Runoff was recorded and soil moisture content was measured by taking soil cores to 5 cm depth.



A replicated, site comparison study in 2001-2003 on sandy loam soil in Denmark (Schjønning et al. 2007) found 25% lower microbial biomass at Flakkebjerg in uncompacted compared to compacted soil across all three cropping systems. No difference was found at Foulum. There were three 4-year crop rotations at two sites: cereal (oats Avena sativa, barley Hordeum vulgare, lupin Lupinus angustifolius and wheat Triticum aestivum) without manure; cereal plus manure; and cereal-grass Lolium perenne-clover Trifolium repens and Trifolium pratense rotation without manure. Part of each plot was compacted by a medium-sized tractor. There were two replicates of 216 m2 plots at Foulum and 169 m2 plots at Flakkebjerg. Soils were sampled to 13 cm depth at Foulum and 10 cm depth at Flakkebjerg in spring in the wheat plots, from compacted and uncompacted plots.



A replicated design in 2001-2006 on a silty-clay soil in Lower Saxony, Germany (Koch et al. 2008) found that subsoil structure was improved with no traffic/wheeling compared to repeated wheeling with present-day heavy agricultural machinery. The number of soil pores decreased under wheeling. Three adjacent fields were used, with sugar beet Beta vulgaris planted at a density of about 90,000 plants/ha. Cultivation of crops followed regional standards of good professional practice. Wheeling was carried out with a six-row self-propelled sugar beet tanker harvester and compared with an unwheeled control treatment. Soil penetration resistance was measured to 0.65 m in depth. After sugar beet sowing, undisturbed and disturbed soil core samples were taken in spring 2004-2006, from 0.05m to 0.6 m in depth. Water infiltration rate in the field was measured in May 2005 and 2006.



A randomized, replicated experiment in 2008 on silty soils in Lublin, Poland (Siczek & Frąc 2012) found fewer bacteria (1,700 million colonies/kg) and lower bacterial activity in strongly compacted soil, but higher numbers and activity in moderately compacted soil (4,650 million colonies/kg) compared to an uncompacted treatment (2,600 million colonies/kg). Bulk density was 22.5% and 15.5% higher in the strongly and moderately compacted soil respectively, compared to uncompacted soil (1.3 Mg/m3). There were three compaction treatments in a soybean Glycine max crop obtained using a wheel tractor: strongly (5 passes), moderately (3 passes) and uncompacted (0 passes) soil. There were six replicates, total area for each compaction was not specified. Within each treatment were 1.8 x 2.1 m plots with no mulch, or mulched with straw. Fertilizer was applied uniformly to all plots at 54-70-80 kg/ha NPK. Soil was sampled three times during crop development from the centre of the soybean rows. Microbial parameters including bacterial number and enzyme activities were measured.


Referenced papers

Please cite as:

Key, G., Whitfield, M., Dicks, L.V., Sutherland, W.J. & Bardgett, R.D. (2019) Enhancing Soil Fertility. Pages 627-648 in: W.J. Sutherland, L.V. Dicks, N. Ockendon, S.O. Petrovan & R.K. Smith (eds) What Works in Conservation 2019. Open Book Publishers, Cambridge, UK.