Randy L. Raper, Oklahoma State University
Warren J. Busscher, USDA-ARS
Alan D. Meier, North Carolina State University
Kipling S. Balkcom, USDA-ARS
Until the 1880s, agricultural vehicles were relatively light, horse-drawn and not particularly damaging to soils. Mass production of tractors began in 1902 [15] and these heavy vehicles caused excessive compaction, especially if operated across wet soils. In addition, integration of livestock grazing with crop management in conservation production systems showed that plant growth decreases as cattle traffic increases. Above-ground signs of compacted soils include ponding and erosion as well as decreased crop productivity. Below ground, compaction crushes soil pores, resulting in reduced rainfall infiltration, water-storage capacity and root growth.
At some distance below the soil surface, excessive forces from surface traffic combined with naturally occurring soil-profile formation can cause a layer of extreme compaction referred to as a hardpan. These dense layers restrict rooting within and below their depths. This limits root extraction of moisture and nutrients, resulting in reduced yields. Some hardpans occur naturally and are often caused by small silt and clay particles amassing in larger pore spaces between sand particles. The presence of all three particle sizes in problematic proportions can lead to reduced porosity and increased soil density.
Tillage is often used to disrupt compacted layers. Conventional deep tillage disrupts compacted soil layers but has negative effects because valuable crop residues are buried. In the 1960s, some considered residue a problem and felt burying it was desirable [14]. This is indicative of an era that valued a clean soil surface for unimpeded planting operations. At the time, most agriculturalists did not recognize that crop residue protects the soil from wind and water erosion. Excessive tillage was also responsible for decreasing soil organic matter over time throughout the soil profile, thus limiting water-storage and carbon-storage capacities. However, there are tillage strategies designed to disrupt soil compaction while minimally disturbing the soil surface and maintaining surface-residue cover.
This chapter reviews published research to illustrate that (1) soil compaction can be managed with deep tillage while conserving soil and water resources; and (2) even though deep tillage is an energy-intensive process, several steps can be taken to reduce fuel consumption. The conclusions drawn in the research reviews are applicable to the soil types, management strategies and other local conditions specific to the research project. Seek out local Extension professionals and others with knowledge of local practices when developing a farm plan.