In the previous article about soil compaction we discussed briefly the causes of soil compaction, the different levels and various ways of detecting a compacted soil. In this article we will discuss the effects of compaction as well as methods of prevention and control.
Effects of soil compaction
• Soil structure: Soil is made up of sand, silt, clay and organic material. The way in which these particles are arranged is what makes the soil structure. Compaction disturbs the natural arrangement of these particles, by increasing the soil density. This limits the movement of air, water, and plant nutrients in the soil. Furthermore, a damaged soil structure creates a denser soil with higher bulk density (soil dry weight per unit volume) decreasing the ability of plant roots to penetrate the soil.
• Reduced water infiltration/drainage in soils: Compacted soils increase the soils vulnerability to water logging and water run-off, resulting in nutrient losses and possible contamination of neighbouring water bodies.
• Global warming: Previous studies have shown that compacted soils can contribute to global warming, by increasing the release of greenhouse gases such as methane and nitrous oxide.2,3 As soil compaction results in poor drainage and water logging, it creates favourable conditions for anaerobic bacteria decomposition. This means that applied nitrogen fertilizers are subjected to denitrification; a process in the nitrogen cycle where nitrate is reduced to nitrous oxide and nitrogen gas by denitrifying bacteria. Methane emissions have also been linked to compacted soils.
Research has shown an increase in methanogens (anaerobic bacteria responsible for the release of methane) in compacted soils compared to uncompacted soils. 4
• Poor, nutrient uptake and crop yield: Plant roots find it difficult to penetrate compacted soil layers because of their high density and reduced porosity. The consequences of this are shallow root growth, nutrient deficient crops and low crop yield.
Aside from the above negative effects it has been noted that slightly compacted soils are beneficial in corn seed germination. It reduces soil water loss due to evaporation; therefore maintaining the soil moisture level around the germinating seed (read more about how this happens). 1
Ways of preventing compaction include:
• Avoid the use of heavy machineries or equipment on wet soils as the soil in this condition is vulnerable to compaction.
• Enrich the soil with organic matter. Organic matter in soils improves soil structure and aggregation. This forms a greater resistance to the force from compaction causing agents. Organic matter in soils can be increased by adding green manure, or animal manure to the soil.
Removing or controlling compaction
When avoiding the use of heavy machinery on wet clay soils is not feasible, crop growers or scientist resort to either curing the soil of compaction or reducing the damaging effects of this process.
• Use of ploughing: Mouldboard and chisel ploughing are often used to remove surface compaction in soils.
• Use controlled traffic: This method minimizes compaction on soils. The farmer confines the traffic of heavy-drawn machinery to certain lanes of the field on a yearly basis. This way, only the traffic lanes are at risk of compaction. The soil around the lanes remains undisturbed. The success of this approach depends on careful matching of machine equipments used on the farm, so that compaction caused by all equipments is restricted to a given area.1
• Use the right equipments or machinery: Choosing the right equipment will minimize compaction. For example, choose machines with less axle weight, choose machines with wider tires and dual tires, use low tire inflation pressure, choose track wheels or tires accordingly.5
Bibliography and further reading
1. Dejong-Hughes et al (2001) Soil compaction causes, effects and control. Retrieved from: www.extension.umn.edu.
2. Ball et al (1999) Field N2O, CO2 and CH4 fluxes in relation to tillage, compaction and soil quality in Scotland. Soil and Tillage Research 53: 29-39.
3. Bessou et al (2010) Modelling soil compaction impacts on nitrous oxide emissions in arable fields. European Journal of Soil Science 61: 348-363.
4. Frey et al (2011) Heavy-machinery traffic impacts methane emissions as well as methanogen abundance and community structure in oxic forest soils 77: 6060-6068.
5. Wolkowski R and Lowery B (2008) Soil compaction: causes, concerns and cures. Retrieved from: https://www.soils.wisc.edu/extension/pubs/A3367.pdf.