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How to Choose Soil Amendments

How to Choose Soil Amendments

Soil amendments are additives, which are added to the soil to make it fertile so that plants are provided with all the necessary nutrients. They can improve soil properties like water retention, infiltration, permeability, and aeration. This article tells you how to choose them.
Gardenerdy Staff
It is necessary to mix the amendments well with soil, for effective movement of air and water, thereby increasing the nutrient dispersal. The basic purpose of this technique is to increase the absorption rate of nutrients by the roots, and to maintain the plants as healthy as possible. Certain methods like mulching involve just placing the additives on soil, instead of mixing them. This is done mainly to prevent evaporation, decrease growth of unwanted weeds, decrease the runoff rate, create an attractive appearance, etc. You must add them in appropriate quantities to avoid adverse effects of their overuse.

There are two types of soil amendments- organic and inorganic. The former are made from natural products. The most common ones are sphagnum peat, wood chips, straw, sawdust, compost, and manure. Wood chips are mainly used as mulches. They increase the organic constituents of soil, thus providing a favorable environment for bacteria and earthworms for soil enrichment. Inorganic amendments are of two types: manufactured (man-made) and mined, and they include certain chemicals that make the soil fertile. However, they can also reduce the percentage of natural nutrients in the long run, if used for a long time and in large quantities. Vermiculite, perlite, sand, diatomaceous earth, clinolite (composed of mineral clinoptilolite), etc., are some examples of this type.

Factors to Consider while Choosing
While selecting a particular type of soil conditioner for use, it is important to consider certain factors like type of soil, nature of the conditioner, and their compatibility with one another. Provided below are the main criteria, according to which the type of amendment can be chosen.

Soil Texture

This parameter depends on the size of the soil particles, i.e., the coarseness or fineness of the grains. Sandy soils that have a coarse texture, are amended to increase their moisture-retaining capacity. Hence, for increasing the nutrient recycling, fast-acting conditioners like vermiculite and peat can be used. Clayey soils that have a fine-grained texture, are amended to increase the permeability, drainage, and aeration capacity of soil. Hence, you can use organic conditioners like wood chips, tree bark, perlite, etc. Loamy soils are perfect for agricultural plantations, as they consist of the right proportion of sand, silt, and clay fragments. Though addition of amendments is not required for such soils, they can be mixed only under certain conditions like decrease in nutrients due to overuse of fertilizers and pesticides, barren or wasteland topography, etc.

Effect on Nutrient Recycling

The conditioners that have a slow effect on nutrient cycling lead to an increase in the soil life, thereby making them usable for several years. The physical properties of soil (texture, porosity, color, grain size, etc.) can be improved by adding materials that can rapidly decompose, thereby helping in fast nutrient dispersal. When several types of conditioners are used in fixed proportions (combination to be used with organic types, as far as possible), both physical and chemical properties of soil improve in a short time, and this change remains constant for many years. A good knowledge of the soil types required for different crops is important before deciding the type of amendment to be used.

Soil salinity

The salinity of soil may increase naturally, or due to excessive usage of chemical fertilizers and pesticides. The former occurs in swamp and mangrove areas (because of proximity to the coastal regions), while the latter can occur in any agricultural regions (where chemical fertilizers or pesticides are heavily used). For highly saline soil types, conditioners like sphagnum peat, organic composts, gypsum, sulfur-based products, etc., are the best ones for use. Gypsum does not affect the pH level of soil, and helps to dissociate the sodium ions, which are further leached out of the soil system. These materials can help reduce the percentage of salts, thereby increasing the nutrient flow and water circulation in the soil. Also, plantation of salt-resistant crops like carrot, strawberry, maple, pine, etc., can help in maintaining a constant nutrient recycling in saline soil.

Salt Percentage and pH of the Conditioner

Most biosolids, wood ash, mountain peat, etc., are characterized by a high amount of salts and pH levels. Such conditioners should not be used for nutrient cycling management of soil. Grade 1 biosolids can be used, as they have a significantly low salt content. But these chemicals should not be used for the crops whose roots are edible, as they can directly come in contact with the underground portions of the crop. Fresh manure can be avoided, as it often contains high levels of ammonia that may affect the plant. Properly composted wood ash, sphagnum peat, and plant-based composts are the best options, as they have low salt content, as well as optimum pH levels.

Different soil amendments have their own merits and demerits. Their choice depends on basic factors like soil texture, nutrient recycling, soil salinity, and pH level of the conditioners. As organic amendments do not cause any long-term damage to the soil, they are preferred over the inorganic ones. It is not advisable to use inorganic conditioners unless availability or affordability are a concern.