Salts in Soil/Dirt and Compost

SALTS IN SOIL/Dirt is a 'big deal' - because sooner or later, almost all composters - and most gardeners who use compost in gardens will have this issue - sooner for those living in arid and semi-arid locations. The question is: will you be able to recognize the symptoms and know what to do? True, salt build-up is only ONE of the many issues that should be 'watched for' in soils - pH being another 'biggie' as well as elevated levels of phosophorous and potassium from use of 'balanced' (x-x-x) synthetic fertilizers.

Now let's be realistic. Salts exist. Commonly. And are not an issue until they become elevated. Above 10 uhmos/mg is generally considered the level to watch for, so it's wise to have a plan to deal with the condition.

It is my experienced opinion as a Master Organic Gardener Instructor and Master Composter Instructor, that gardeners (and particularly composters) GUESS way too often, when attempting to implement solutions - simply because they have no base of reference, and because they have not done their 'homework' online. Salts are usually measured by conductivity. Testing for salts is fairly easy, including the making of a conductivity meter to test salt levels.

It is quite easy to make a problem worse by adding too much of what is "generally" considered a 'good thing'. A soil test is such a reliable base, and is an effectively means of qualifying and quantifying judgements IF the soil testing lab is "transparent" in identifying the procedures they use to qualify reported information, AND you know how to read the results of the test.

Some recommended reading: (cut and paste links into a browser if the link does not work)

Under irrigated conditions in arid and semi-arid climates, the build-up of salinity in soils is INEVITABLE. The severity and rapidity of build-up depends on a number of interacting factors such as the amount of dissolved salt in the irrigation water and the local climate. However, with proper management of soil moisture, irrigation system uniformity and efficiency, local drainage, and the right choice of crops, soil salinity can be managed to PROLONG field productivity.

Actively growing vegetable crops requires a continuous supply of balanced nutrients in the soil. Unfortunately, these are usually provided by the application of synthetic fertilizers which include soluble salts - urea being a particular 'salty' product. When the concentration of any soluble salt in the soil (including those from fertilizers), becomes too high, the roots (and later the plant tops) are injured. Leaching with clean irrigation water is the best solution.

Salts also come from any fertilizers we apply to our gardens and landscapes. But probably the biggest source of salts in the soil is our irrigation water. Yes, the water we drink and use to irrigate our plants has salts. Certainly the levels are small, only about 350 parts per million in tap water - salty ocean water has 20,000+ ppm. However, over time, these small amounts of salt can accumulate in the soil and can cause harm to many potted, garden and landscape plants. Pay attention to what your plants are telling you. Learn how to 'listen' to your plants - they NEVER lie.

Salt levels increase from adding nitrogen and potassium fertilizers, and from DECOMPOSITION OF SOIL ORGANIC


NOTE: this is a 3-part .pdf document - click the arrows to view all pages... Soluble salt levels in the soil are important, because high soluble salts can reduce water uptake by plants, restrict root growth, cause burning of the foliage, inhibit flowering, and limit fruit and vegetable yields.

Salty soils usually contain several types of salt. One of these is sodium salt. Where the concentration of sodium salts is high relative to other types of salt, a sodic soil may develop. Sodic soils are characterized by a poor soil structure: they have a low infiltration rate, they are poorly aerated and difficult to cultivate.

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Salts in COMPOST

Principal uses of compost are to mix it into soil (amendment) or to use it as a mulch or as potting media.

However, if purchasing a "compost" product from a store, just because an organic (biologic) material has undergone "some kind" of a composting process and is designated a "compost" on the bag, doesn't necessarily mean that its use will be beneficial. Check product information on the bag's label for salt content. If there isn't any product information about the feedstock it was made from, or if information is scant, best advice I can give is: DON'T buy it!!.

Salts that become soluble and commonly found in commercial compost products are potassium chloride; sodium chloride; various nitrates; compounds involving sulfates; and calcium, magnesium, and potassium carbonates. The kinds of feedstock influence which salt will be predominant. Feedstock that has a rich nutrient source, such as animal manure, will result in compost with a bit higher soluble salt levels than those not containing animal manure, but is usually a negligible difference, depending on age of the manure when it was used. If animal fluids make up part of the feedstock, then the compost can be higher in the soluble salts of sodium chloride and potassium chloride, but aged trampled hay is usually not an issue, particularly if annual rainfall has been at normal levels to leach salts from the material (which also means that some nitrogen was leached also).

Salts tend to build up in large stockpiled materials of commercial vendors that do not get turned/aerated and watered appropriately.

Soluble nutrients, particularly potassium, calcium and nitrogen typically account for most of the salinity in compost products. Sodium salt is an undesirable soluble salt. This element should ideally account for less than 25% of the total soluble salts in compost.

Because North Carolina has a large poultry industry, large amounts of turkey litter is composted, and the compost is readily available in stores without salt information on bag labels. North Carolina State University tests have found that turkey litter compost has high electrical conductivity (soluble salts level)...higher than those of commercial potting mixes.

A MUST-READ FOR COMPOST-BUYERS !! If compost production is not managed properly, or if a large amount of poultry manure is used, salts can

 sometimes accumulate in the product to a level high enough to injure plants upon application (right out of the 

bag - especially seedlings.

Thousands more links say the same thing in different ways... Google for "soil salts" and "compost salts" to see other such references. Main point: Learn to 'read' what your plants are telling you. LEARN THEIR LANGUAGE !!

© Robert C. Moore ~ All Rights Reserved

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