SOIL SALINITY

The Creeping Menace

White crust formations in extreme salt situations. This photo was taken near the beach in our local area

Tomatoes show moderate tolerance to soil salinity

Salt tolerant myoporum plants to be used on the hobby farm

One of the most difficult problems found in many parts of Australia is the presence of excess salt in the soil. Soil salinity is an indication of the level of soluble chemical compounds present.

Salinity And Natural Salts

Salts are released naturally when rocks break down, the most predominant being sodium chloride or common salt. Other salts include compounds of magnesium, potassium and calcium. When salt levels become elevated soils are damaged and crop production is diminished.

Salt problems occur naturally in the landscape, but many areas become saline due to excess clearing of vegetation, over cultivation and poor irrigation practices. The end result is that plants find it more difficult to absorb water from the soil; plants wilt more readily, produce less growth and in severe cases tissues are damaged. Eventually sensitive plants will die and salt affected areas show a greatly reduced variety of plant growth.

Salt Crystals And Soil Test

In extreme cases a white crust of dried salt forms on the soil surface and very few plants are able to survive.

The standard unit used when measuring salt levels is deciSiemens per metre (ds/m). This is measured using an electrical conductivity meter (EC meter). The greater the level of dissolved salt, the higher the reading These readings can be converted into a measure which is easier to visualise known as parts per million (ppm). A 1000 ppm water sample contains 1 gram of dissolved salt in each litre of water. Few crops are productive if salt levels are in excess of 2500 ppm. or 2.5 grams of dissolved salt per litre of water.

Hobby Farm Irrigation

Sadly, salt accumulation has become a concern on my hobby farm due to the dry conditions and lack of fresh irrigation water. Reduced rainfall has resulted in the build up of salt near the soil surface. This occurs as water evaporates from the soil surface and salt crystals form. Irrigation restrictions mean I am unable to wash excess salt from near the root system of the young trees and these young plants are showing signs of stress. I expect many of the young trees to be damaged and not survive the next summer. Increased levels of salt are also causing the formation of a crust or hardening of the soil surface. This is damaging the basic structure of the soil and affecting the germination of some plant seeds.

Soil Salinity Mangement

These methods include:

• Raising soil levels by mounding the soil before planting,
  
• Adding organic matter such as compost,
  
• Not over cultivating soil and planting salt tolerant crops.

There is however no substitute for a good rain as this will wash away much of the salt which accumulates near the soil surface during times of drought.

Salt control is one of the more important problems to be faced if the hobby farm is to sustain a diverse range of plants and animals. Rainwater collection and storage will be vital if this threat is to be overcome.

Salt is an essential requirement for life, but in excess it is a sure recipe for disaster.