Editing Tilth (section)

== Aggregation ==
Good tilth shares a balanced relation between soil-aggregate tensile strength and [[friability]], in which it has a stable mixture of aggregate soil particles that can be readily broken up by shallow, non-abrasive tilling. A high tensile strength will result in large cemented clods of compacted soil with low friability. Proper management of agricultural soils can positively affect soil aggregation and improve tilth quality.<ref name=":2">{{Cite journal|last1=Schjønning|first1=Per|last2=Munkholm|first2=Lars J.|last3=Elmholt|first3=Susanne|last4=Olesen|first4=Jørgen E.|date=October 2007|title=Organic matter and soil tilth in arable farming: Management makes a difference within 5–6 years|journal=Agriculture, Ecosystems & Environment|language=en|volume=122|issue=2|pages=157–172|doi=10.1016/j.agee.2006.12.029}}</ref>

Aggregation is positively associated with tilth. With finer-textured soils, aggregates may in turn be made up of smaller aggregates. Aggregation implies substantial pores between individual aggregates.<ref name=":1">{{Cite web|url=http://www.sare.org/Learning-Center/Books/Crop-Rotation-on-Organic-Farms/Text-Version/Physical-and-Biological-Processes-In-Crop-Production/Crop-Rotation-and-Soil-Tilth|title=Crop Rotation and Soil Tilth|last=Van Es|first=Harold|website=www.sare.org|accessdate=2015-09-10}}</ref>

Aggregation is important in the subsoil, the layer below tillage. Such aggregates involve larger (2- to 6-inch) blocks of soil that are more angular and not as distinctive. These aggregates are less affected by biological activity than the tillage layer. Subsurface aggregates are important for root growth deep into the profile. Deep roots allow greater access to moisture, which helps in drought periods. Subsoil aggregates can also be compacted, mainly by heavy equipment on wet soil. Another significant source of subsoil compaction is the practice of plowing with tractor wheels in the open furrow.<ref name=":1" />