Soil Amendment

Compiled by:
Beat Stauffer (seecon international gmbh), Nina Carle (seecon international gmbh), Dorothee Spuhler (seecon international gmbh)

Executive Summary

Soil amendment includes all inorganic and organic substances mixed into the soil for achieving a better soil constitution regarding plant productivity. Soil amendment does not include mulching, which includes substances lying on top of the soil. There are different substances for different soils and plants to optimise the soil conditions. A very common amendment is the addition of organic matter like compost, due to its low production costs.
In Out

Compost/Biosolids

Food Products

Introduction

The reason for soil amendment is to provide a better environment for roots and plant growth: this includes the improvement of the soil structure and water holding capacity, the availability of nutrients, and the living conditions for soil organisms, which are important for the plants to grow. Furthermore, a better soil texture and better root growth avoids soil degradation during heavy rains or in windy regions. It also supports the nutrient cycle when organic amendments are used (e.g. manure). Beside soil amendment, there are several methods to provide soil moisture conservation such as soil cover and reforestation (living plants), mulching or several tillage techniques. Of course it is also very important that a crop is planted which is suitable for the given climate. Basically, any organic or inorganic material that is added to the soil and improves its quality can be considered as soil amendment. The type of amendment chosen depends entirely on how the soil needs to be changed. By using soil amendment, almost every type of soil can be made fertile (WEST COAST SEEDS 2011).

Amendments

Both  inorganic and organic substances can be added into the soil. Organic substances consist of material derived from living things (e.g. plants), whereas inorganic substances are mined or man-made.

Inorganic Amendments

Inorganic substances are vermiculite, perlite, tire chunks, pea gravel and sand. In general, they must be bought, which makes them more expensive than organic amendments. Additionally, the industrial production process needs a great deal of energy. Therefore, these substances do not have the same degree of sustainability as organic amendments. Most are relatively sterile (with regard to plant pathogens) and many are relatively inert. Inorganic amendments are used to (REED 2007):

Organic Amendments

Organic growing medium amendments usually are derived from plants or plant products that occur naturally (peat moss from peat bogs), or are the by-products of processing plants or mills (sawdust, cedar chips, bark, bagasse, rice hulls) or waste disposal plants (compost, processed sewage sludge, biosolids). The main purpose of using organic amendments is to loosen the soil and create large pores to increase (REED 2007):

By far, the most important organic soil amendments worldwide are compost and animal dung (e.g. chicken, cow). Compost and animal dung are most often easily available and economically affordable.

In professional agriculture, the most commonly used organic amendment is peat moss (e.g. sphagnum peat moss which is the highest quality, but also hypanaceous or domestic peat). Other organic amendments include wood chips, grass clippings, straw, compost in general (produced in large or small scale facilities), manure (see also use of compost, use of dehydrated faeces or terra preta), processed sewage sludge (biosolids), sawdust, etc. Normally, there are more organic substances available than inorganic substances and generally they are cheaper (REED 2007; GIZ 2010). Practising good crop rotations and choosing the correct crop improves soil amendment.

Before incorporating into ground beds, most organic amendments, especially sawdust, cedar chips, bark and bagasse, should be composted or aged, and sterilised before use if possible. All of these amendments have a high C:N ratio. Use of amendments which are not composted and have a high C:N ratio will deplete N from the soil, may cause a salt or an ammonia/ammonium burn, or may cause damage due to heat build up.

Amendments with a low C:N ratio will release N upon further decomposition, thus act as an organic fertiliser. However, organic matter with a low C:N ratio also should be composed to avoid rapid ammonia/ammonium release and toxicity (adapted from REED 2007).

Advantages of Organic Amendments

Humic acid is a principal component of humic substances, which are the major organic constituent of organic soil amendments. Organic soil amendments (humus) have been known by farmers to be beneficial to plant growth for longer than recorded history. It was supposed that humus was used directly by plants, but it was shown later that plant growth depends upon inorganic compounds. Therefore, many soil scientists held the view that organic matter was useful for fertility only as it was broken down with the release of its constituent nutrient elements into inorganic forms. At the present time, soil scientists hold a more holistic view and at least recognise that humus influences soil fertility through its effect on the water-holding capacity of the soil: the spongy structure of organic matter is able to bind water and some inorganic molecules which act as micro- or macro-nutrients. Consequently, humic acids also slow water evaporation from soils. This is especially important in soils where clay is not present or in a low concentration, in arid areas, and in sandy soils without the capability to hold water. The oxygen end of another water molecule bonds with the hydrogen end of another, until the evaporation rate is reduced by 30% (NUTRANETICS 2000).

An additional benefit of organic amendments is also the fact that organic matter feeds soil microbes, which in turn release nutrients into the soil, thereby increasing soil fertility.

Factors to Consider When Choosing an Amendment

(Adapted from DAVIS & WILSON 2005)

There are at least four factors to consider in selecting a soil amendment:

  • How long the amendment will last in the soil
  • Soil texture
  • Soil salinity and plant sensitivities to salts
  • Salt content and pH of the amendment

Laboratory tests can determine the salt content, pH and organic matter of organic amendments. The quality of bulk organic amendments for large-scale landscape uses can then be determined. The amendment you choose depends on your goals.

  • Are you trying to improve soil physical properties quickly? Choose an amendment that decomposes rapidly.
  • Do you want a long-lasting improvement to your soil? Choose an amendment that decomposes slowly.
  • Do you want a quick improvement that lasts a long time? Choose a combination of amendments.

Soil texture

Permeability

Water Retention

Sand

high

low

Loam

medium

medium

Silt

low

high

Clay

low

high

Table 1: Permeability and water retention of various soil types. This can be changed by adding an amendment (see table 2). Source: DAVIS & WILSON (2005)

Amendment

Permeability

Water Retention

Fibrous:

Peat

Wood chips

Hardwood bark

 

low-medium

high

high

 

very high

low-medium

low-medium

Humus:

Compost

Aged manure

 

low-medium

low-medium

 

medium-high

medium

Inorganic:

Vermiculite

Perlite

 

high

high

 

high

low

Table 2: Depending on crops, permeability and water retention of soils (table 1) can be adjusted. Source: Davis & Wilson (2005)

Cost Considerations

Most inorganic amendments are mined from natural deposits and further processed to yield the final product. Heavy machinery and technical know-how is necessary to produce such amendments. These facts cause higher costs in production. In the other hand, organic amendments have high self-help compatibility, because farmers can produce them on-site. There are numerous methods that help to produce organic amendments and support a sustainable handling of the local nutrient and water cycle. Composting toilets, terra preta toilets, fossa alternas or arborloos, UDDT are toilet systems that generate organic amendments. According to GIZ (2010), there are more organic substances available than inorganic, and they are generally cheaper.

Environmental Effects

Soil amendments have to be handled carefully. Soil does not have the capacity to bind substances ad infinitum without releasing them. If too many nutrients or organic matter are put into the soil, they can be released and cause an outflow into the groundwater and surrounding rivers and lakes, which can cause water pollution (GIZ 2010).

At a Glance

Working Principle

Organic or inorganic substances are mixed into the soil to improve the physical properties. The goal is a better environment for roots, water infiltration, and holding capacity.

Capacity/Adequacy

Each soil type has different needs for soil amendments.

Performance

Intelligent management leads to moisture conservation and a good harvest. Too much addition of amendments leads to polluted water due to nutrient wash-out.

Costs

Depending on the infrastructure, it can either be more or less expensive to buy inorganic substances than to produce organic substances.

Self-help Compatibility

Organic substances can be produced by oneself from animal waste, plant debris or with the approach of different toilet systems.

O&M

It can be very time consuming to mix soil amendments with the soil. If organic amendments are produced locally or on-site, the adopted technique (e.g. composting toilet) must be used properly.

Reliability

Reliable, old method. Carefully applied, regular soil amendment can improve soil quality immensely.

Main strength

Even minor improvement of the physical properties of the soil can generate a much better soil condition for plants.

Main weakness

Too much input of substances results in an output mainly in surrounding water bodies, which is an environmental damage.

Applicability

Soil amendments, if managed carefully, can be applied everywhere. Care has to be taken in choosing the appropriate soil amendment depending on the initial soil conditions. Especially organic amendments can be produced locally. Mixture into the soil can be time consuming

Advantages

  • Soil amendments improve the physical properties resulting in better con-ditions for water storage, root development and soil ecosystems
  • Soil amendments enhances soil aeration
  • Soil amendments can be produced locally, especially organic amendments (e.g. compost), which are cheap to produce
  • Soil amendments can be applied almost everywhere by almost anybody

Disadvantages

  • Wood products can tie up nitrogen in the soil
  • The incorporation of the soil amendment (especially of organic amendments) can be time consuming
  • If too many nutrients or organic matter are put into the soil, they can be released and cause an outflow of nutrients into the groundwater and sur-rounding rivers and lakes, which can result in water pollution

References Library

DAVIS, J.G.; WILSON, C.R. (2005): Choosing a Soil Amendment. Fort Collins: Colorado State University. URL [Accessed: 15.11.2011].

GIZ (Editor) (2010): Resource-Saving Fertiliser Use. Eschborn: German Agency for International Cooperation (GIZ). URL [Accessed: 15.11.2011].

NUTRANETICS (Editor) (2000): Humic Acid Structure and Properties. Stockton: Nutranetics ProBio Solutions. URL [Accessed: 16.02.2012].

WEST COAST SEEDS (Editor) (2011): Soil Amendments and How to Use Them. Ladner: West Coast Seeds. URL [Accessed: 15.11.2011].

Further Readings Library

Reference icon

AGRESOURCE (Editor) (2012): Protecting Local Water Resources by Amending Soil with Compost. Amesbury: Agresource Inc. URL [Accessed: 12.01.2012].

Communities can protect water resources by instituting minimum requirements for organic matter in soil. Compost, much of which is generated locally, when incorporated into soil improves water holding capacity and soil quality. By incorporating compost into soil for establishment of lawns and landscape plantings, water used for irrigation is conserved and the potential for groundwater contamination is reduced. Read more about it in this paper.


Reference icon

AGWE, J.; MORRIS, M.; FERNANDES, E. (2007): Africa’s Growing Soil Fertility Crisis: What Role For Fertilizer? . Washington, D.C.: The World Bank. URL [Accessed: 25.04.2012].

This document draws upon the material prepared for fertiliser strategy as-sessment, summarises the information on the approaches to enhancing fertiliser supply and use in Africa, and identifies some future steps.


Reference icon

DAVIS, J.G.; WILSON, C.R. (2005): Choosing a Soil Amendment. Fort Collins: Colorado State University. URL [Accessed: 15.11.2011].

This factsheet gives an overview how to choose a soil amendment. It talks about the application rate, organic or inorganic amendments, salt and pH content of the soil and if biosolids are safe to use as an amendment.


Reference icon

GIZ (Editor) (2010): Resource-Saving Fertiliser Use. Eschborn: German Agency for International Cooperation (GIZ). URL [Accessed: 15.11.2011].

World population growth and changing consumption patterns, along with limited capacity to expand arable land and pasture, require the intensification of agriculture. There is much potential for such intensification in developing countries: the soils are often nutrient-poor as a result of both natural conditions (climate, geology) and human activity, while at the same time use of external inputs is limited. One way of improving land productivity is to provide better plant nutrition, for which both organic and inorganic fertilisers are available options.


Reference icon

HUE, H.V.; SILVA, J.A. (2000): Organic Soil Amendments for Sustainable Agriculture: Organic Sources of Nitrogen, Phosphorus, and Potassium. In: SILVA, J.A.; UCHIDA, R. (): Plant Nutrient Management in Hawaii’s Soils, Approaches for Tropical and Subtropical Agriculture. Honolulu, 133-144. URL [Accessed: 25.04.2012].

Sustainable agriculture, which is characterised by farming profitably while minimising damage to the environment, is not easy to practice. “Conventional” agriculture in the USA is commonly considered to involve practices that have potential to damage the environment. These include tilling the soil excessively, over applying readily soluble inorganic fertilisers (“chemical fertilisers”), and over applying pest-control formulations (herbicides, insecticides, fungicides, etc.). “Sustainable” agriculture attempts to find alternatives to such practices, alternatives that are economically feasible but have less potential to cause environmental damage.


Reference icon

ROY, R.N.; FINCK, A.; BLAIR, G.J.; TANDON, H.L.S. (2006): Plant Nutrition for Food Security: A Guide for Integrated Nutrient Management. Rome: Food and Agriculture Organization of the United Nations (FAO). URL [Accessed: 25.05.2012].

This guide on integrated plant nutrient management, dealing with various aspects of plant nutrition, is an attempt to provide support to the ongoing efforts directed at enhanced and sustainable agricultural production. It seeks to bridge the scientific knowledge gap, and it presents updated information on plant nutrition with emphasis on INM. In helping stakeholders to improve their ability to identify and resolve constraints relating to plant nutrition – be they of a technical, economic, social or policy nature – and to demonstrate on the field practical ways of increasing production through efficient plant nutrition, the guide should assist in achieving the goal of food security.


Reference icon

SULLIVAN (n.y.): Sustainable Soil Management - Soil System Guide. Fayetteville: Appropriate Technology Transfer for Rural Areas (ATTRA). URL [Accessed: 25.04.2011].

This publication covers basic soil properties and management steps toward building and maintaining healthy soils. The publication is divided into three distinct sections, each with its own purpose. Section 1 deals with basic soil principles and provides an understanding of living soils and how they work. In section 1 you will find answers to why soil organisms and organic matter are important. Section 2 covers management steps to build soil quality on your farm. The last section covers farmer stories of people who have successfully built up their soil. A large resource section of other available information concludes the publication.


Reference icon

TRAUNFELD, J.; NIBALI, E. (2009): Soil Amendments and Fertilizers. ELLICOT CITY: Home and Garden Information Center. URL [Accessed: 25.04.2012].

Fertilisers and soil amendments are a wide array of materials added to soils to improve plant growth. They can be organic, such as bone meal, or inorganic, such as 10-10-10 fertiliser. Some must be purchased, while others are free for the taking from your landscape. Many are dual purpose—they serve as both fertilisers and soil amendments.


Reference icon

U.S. EPA (Editor) (2006): The Use of Soil Amendments for Remediation, Revitalization, and Reuse. Washington DC: United States Environmental Protection Agency (U.S. EPA). URL [Accessed: 12.01.2012].

This paper is a product of a workshop, which was hosted by the U.S. EPA in 2006. Soil amendments of interest consist of waste residuals such as municipal biosolids, animal manures and litters, sugar beet lime, wood ash, coal combustion products, log yard waste, neutralising lime products, and a variety of composted agricultural by-products, as well as traditional agricultural fertilisers.


Reference icon

WEST COAST SEEDS (Editor) (2011): Soil Amendments and How to Use Them. Ladner: West Coast Seeds. URL [Accessed: 15.11.2011].

A short article about soil amendments and some tips how some different amendments can be used and its benefits.


Case Studies Library

Reference icon

GYA (Editor) (2010): Profiting from Soil Organic Matter. Harpenden: GY Associates Ltd.. URL [Accessed: 10.02.2012].

A corporation located in the United Kingdom focuses on soil organic matter research and practical advices for farmers. There was a case study and a bro-chure released in 2010.


Important Weblinks

http://www.ext.colostate.edu/ [Accessed: 15.11.2011]

More general information about plants, soil, fertiliser and insect Colorado State University, basic knowledge about garden management

http://www.westcoastseeds.com/ [Accessed: 15.11.2011]

Soil amendments and how to use them; an overview about different soil amendments and their advantages.