Topsoil Information

What is topsoil?

Good topsoil is a mixture of mineral particles‭, ‬water‭, ‬nutrients‭, ‬organic matter‭, ‬air and living organisms‭.‬

Understanding the source and make-up of a topsoil will help you select the right product for your project. If importing a topsoil for landscaping then compliance to BS3882:2015 should be a minimum requirement.

British Standard for topsoil ❯ Topsoil Terminology ❯ Topsoil Facts ❯

Technical Support

Essential Guide

Nutrients

Nitrogen

Required for the growth of leaves and stems, its deficiency causes weak, stunted growth and yellowing of older leaves. However, excess nitrogen can also be detrimental causing such effects as disproportionate leaf growth at the expense of other parts of the plant (e.g. flowers).

Phosphorous

Principle nutrient for root growth and development, deficiencies may be seen through stunted root systems whilst the leaves on some plants may also exhibit a dull green or purple coloration.

Magnesium

A constituent of chlorophyll, the green pigment which enables plants to photosynthesise, magnesium deficiency may be noted by the interveinal yellowing of the plant’s older leaves.

Organic Matter pH Electrical Conductivity Potentially Toxic Elements (PTEs) Leaching

Organic Matter

Organic matter consists of living organisms and is very important to soil function and plant growth as it influences soil structure (and hence aeration, drainage and root growth), water-holding capacity and soil fertility. It binds mineral particles into granular or crumb structures and the proportion of water that is available for plant uptake. It is a major source of essential plant nutrients including nitrogen, phosphorus, potassium and sulphur; it is also the food for soil organisms, and without it, biochemical activity, which is essential for ecosystem functioning, would cease.

pH

pH is the measure of the acidity or alkalinity of a soil. It affects nearly all soil properties and is a major factor in determining where trees, shrubs and grasses will grow. It influences structural stability, plant nutrient availability, microbe activity and soil pollutant mobility.

Electrical Conductivity

General measure of the soluble salt content or salinity of a soil, a good quality topsoil should have an electrical conductivity value within the range of 100-1500uS/cm (soil : water extract).

Potentially Toxic Elements (PTEs)

Excessive concentrations may be hazardous to health and inhibit plant growth. Laboratory analysis is necessary to indicate the levels of PTEs.

Leaching

The removal of materials in solution from the soil, often as a result of excessive rainfall.

British Standard for topsoil‭ (‬BS3882:2015‭)‬

Topsoil is an important aspect of many civil engineering, public and private landscaping projects where it should support healthy plant growth.

There are two grades:

Multipurpose grade

This is a grade suited to most situations where topsoil is required.

Specific Purpose

This grade comprises characteristics appropriate for specialist applications, e.g. low fertility, acidic or alkaline.

The Standard gives up-to-date advice on correct soil sampling, handling, storage, subsoil preparation and depth of topsoil.

The Standard also draws attention for the need for potentially toxic elements analysis and to the possibility that Site Specific Assessment Criteria (SSAC) or Generic Assessment Criteria (GAC) might have been set for the intended recipient site.

Note 4 in table 1 of the standard references the Contaminated Land Exposure Assessment (CLEA) model (EA/DEFRA:2009) Soil Guidelines Values and Charted Institute of Environment Health (CIEH) / Land Quality Management (LQM) Generic assessment criteria for human health risk assessment.

Topsoil suppliers are required to provide a Declaration of Analysis to include:

Location of topsoil source
Previous and current land use for Natural Soils
Date of Sampling and Analysis
BS3882:2015 compliant topsoil must be sampled every 5000 cubic metres (8000t) traded
Test results including Contamination Parameters
Written confirmation of compliance with BS3882:2015.

All purchasers and users of topsoil should ask their topsoil supplier for a copy of the following:

BS3882:2015 Declaration of Analysis
Analysis Certificate
Sampling Protocol

Copies of BS3882:2015 are available from:
BSI Customer Services Department
Tel: (0845 086 9001)

Topsoil Terminology

Well structured soil

Soil structure is the aggregation of soil particles (sand, silt, clay and organic matter) into granules, crumbs or blocks. It is the shape that the soil takes based on its physical, chemical and biological properties; it is very important since (along with texture) it affects drainage and aeration capacity of the soil.

Without structure a soil collapses and compacts, resulting in a number of problems for landscaping and civil projects. It can be considered as the “framework” of a Soil Profile.

Typical soil profile

Soils develop over long periods of time and generally become deeper and develop distinct layers or horizons.

A soil profile is made up of three layers:

Topsoil

Subsoil

Parent Material

This thin layer (usually less than 30cm) is normally the most fertile because of the organic matter that has accumulated from plant and biological activity.

In this layer, the majority of a plant’s feeder roots are present which take up nutrients.

Usually lighter in colour as it does not contain as much organic matter as topsoil. This layer can be composed of varying proportions of clay, sand, silt and stones.

This is the original material from which the soil is developed. This layer has deposits of sand, gravel, pebbles, boulders and rock in various mixtures.

Poorly-structured, cloddy soil

Virtually all soils need an open structure through the soil profile in order to function effectively as a growing medium. In particular, soil structure influences the main soil and
plant root functions, aeration, drainage and
root development.

Without structure, soils will suffer from anaerobism, waterlogging and nutrient lock-up and, ultimately, plants will die!

Trial pit showing anaerobism (grey colour)

Compaction destroys soil structure because it increases the density of the soil by packing the particles closer together; this causes a layer within the soil profile that is impregnable to plant roots, water and air. It can occur in the topsoil and the subsoil layers.

Topsoil is easier to restore than subsoil but the latter cannot be ignored as rooting alone will not break up or restructure a compacted subsoil.

Main causes of compaction	Danger signs of compaction	How you can detect compaction
Misuse of heavy equipment Trampling or trafficking over soils Handling soils when wet and plastic Stockpiling soils inappropriately	Anaerobism and waterlogging are the biggest soil-related causes of plant failures in landscaping projects but both can be avoided with the right ground preparation.	Ponding of water on the surface Resistance experienced when pushing a soil probe or spade into a soil Black, anaerobic layer with a sour odour in a turf-rooting layer Uneven plant growth Yellowing leaves Waterlogging Poor root development and shallow root systems Anaerobism