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R horizon

Hard, consolidated bedrock beneath the soil. The bedrock commonly underlies a C horizon but can be directly below an A or a B horizon.


Rural Development Programme.

Reduced tillage

A tillage without inversion at a reduced depth (about 30% crop residues remaining on the surface), with specific machines (often with grubber/cultivator), more than once a year.


The addition of hydrogen, removal of oxygen, or the addition of electrons to an element or compound. Under anaerobic conditions (where there is no dissolved oxygen present) such as in

Reference soil condition

The condition of the soil to which functional capacity is compared. . Soil quality is usually assessed by comparing a soil to a reference condition. The reference condition may be data from a comparable benchmark soil, baseline measurements taken previously on the same soil, or measurements from a similar soil under undisturbed vegetation, or under similar management.


The unconsolidated mantle of weathered rock and soil material on the Earth's surface, sometimes considered to be loose earth materials above solid rock.

Regulating services

The benefits obtained from the regulation of ecosystem processes, including, for example, the regulation of climate, water, and some human diseases.

Relative normalized density

Texture-corrected dry bulk density: ratio of actual dry bulk density and a reference value which is dependent on clay content (RECARE).

Relay intercrop



The elevations or inequalities of a land surface, considered collectively.

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