“Soil is the great connector of lives, the source and destination of all. It is the healer and the restorer, and the resurrector by which disease passes into health, age into youth, death into life. Without proper care for it, we can have no community, for, without proper care for it, we can have no life.” – Wendall Berry
Our relationship to the soil is absolute – It provides us with our food, building materials, medicine, filters our waters and stores carbon. It is composed of organic and inorganic material, gases, liquid and organisms that together support life.
But over the last 50 odd years, our soils have not been faring so well. Research has shown that the nutrient availability in our soils is declining and this, in turn, has had an effect on our food.
Dr David Thomas provides a comprehensive analysis of historical changes in food nutrient levels.
By comparing data available from 1940 with that in 1991, Thomas was able to show a substantial loss in mineral and trace element content in every group of foods investigated.
Mineral depletion in vegetables 1940 – 1991
Average of 27 kinds of vegetables
Mineral depletion in meat 1940 – 1991
Average of 10 kinds of meat
The nutrient depletion summarized in Thomas’s review represents an average of mineral and trace element changes in 27 kinds of vegetables and 10 types of meat.
With this in mind, understanding how the minerals in the soil affect the plants we eat is critical from the macro nutrients to the ever essential micro nutrients. What functions does that mineral form in the plant, how can we assess the plants to see what they are deficient in, what are the conditions that can attribute to this reduction in nutrient availability, and typically, what crops may be affected. The information provided below can help show the relationship between the different minerals in our soils and the effects they have on our plants and in turn, us.
Some nutrient is also moves more freely than others
Nutrient mobility in soil
Very Mobile – (prone to leaching) nitrate Nitrogen, sulfate Sulfur, Boron
Moderately Mobile – ammonium Nitrogen ( ammonium Nitrogen is temporarily immobile), Potassium, Calcium, Magnesium, Molybdenum
Immobile – organic Nitrogen, Phosphorus, Copper, Iron, Manganese, Zinc (Chelated forms of Copper, Iron, Manganese and Zinc are mobile and resistant to leaching)
Nutrient mobility in plants
Very mobile – Nitrogen, Phosphorus, Potassium, Magnesium (Deficiency symptoms appear first in older leaves and quickly spread throughout the plant)
Moderately mobile – Sulfur, Copper, Iron, Manganese, Molybdenum, Zinc (Deficiency symptoms first appear in new growth but do not readily translocate to old growth)
Immobile – Boron, Calcium (Calcium is very immobile)
When high levels of Nitrogen induce accelerated growth rates, levels of micro nutrients that would normally be marginal can become deficient. High soil levels of Nitrogen can assist Phosphorus, Calcium, Boron, Iron and Zinc but an excess can dilute these elements. Low soil levels can reduce Phosphorus, Calcium, Boron, Iron and Zinc uptake. Ammonium Nitrogen can make Molybdenum deficiency appear less obvious.
High levels of Phosphorus reduce Zinc and, to a lesser degree, Calcium uptake. It is antagonistic to Boron in low pH soils.
High levels of Potassium reduce Magnesium and to lesser extent Calcium, Iron, Copper, Manganese and Zinc uptake. Boron levels can either be low or toxic. Low levels can accentuate Iron deficiency.
High levels of Calcium can accentuate Boron deficiency. Liming can decrease the uptake of Boron, Copper, Iron, Manganese and Zinc by raising soil pH.
High levels of Copper can accentuate Molybdenum and to a lesser degree Iron, Manganese and Zinc deficiency.
Iron deficiency can be accentuated by liming, low Potassium levels or high levels of Copper, Manganese or Zinc.
High levels of Copper, Iron or Zinc can accentuate Manganese deficiency – especially repeated soil applications of Iron. Uptake can be decreased by liming or increased by Sulfur applications (because of the affects on pH)
Deficiencies can be accentuated by high levels of Copper and to a lesser degree Manganese. Uptake can be adversely affected by sulfates. Uptake can be increased by phosphates and liming. Molybdenum can increase Copper deficiencies in animals.
Uptake can be decreased by high Phosphorus levels, liming or high levels of Copper, Iron or Manganese. Zinc deficiencies are often associated with Manganese deficiencies, especially in citrus.
What to read next?
This deck of cards helps you plan which vegetable to grow where, when and how using techniques from our Serious Backyard Abundance Workshop
Seed Raising Mix – While you can spend a lot of money on seed raising mix, it is much easier and cheaper to be able to do it yourself.
Our Urine is high in nitrogen, moderate in phosphorus and low in potassium. It is an excellent high nutrient liquid fertiliser in our gardens