Soil

The nutritional analysis in PC software packages and in the USDA website may well be dated. I believe this will be significant with respect to minerals particularly for two reasons. 

1.  Australia, for example, being the oldest continent, has depleted and leached soils. Selenium is present in most of our soils at lower proportions than it is in North America. If it is not in the soils, It is not going to get into the crops nor into the flesh of the animals that eat those crops. Even when minerals like selenium are present in the soils, they still need to be made bio-available through the interaction of moisture and soil microbes (mainly fungi) breaking down stable compounds into substrate for bacteria and plants.

2.  Australian soils are also relatively poor in some of the more significant minerals used for crops and as feed for domesticated animals - we rely on imported phosphatic fertilizers for example.  Let me quote from Weston Price (page 490) who puts the problem graphically and succinctly in the US context: "[P]hosphorous ... constitutes only about one part in 1,000 of the earth's crust.  Plants, dry weight, require about 30 parts per thousand; while animals with skeletons, dry weight, require it in the ratio of 100 parts per 1,000. The only source of phosphorous is the soil on which the plants grow, and we must realize that the top 7 inches of an acre of ground contains only about 1,000 pounds of phosphorous in a chemical form in which plants can use it. Now when we realize that a 60 bushel crop per acre of wheat or corn will remove from the soil about 25 pounds of phosphorous per acre, or one fortieth of the total content in the top 7 inches, we are immediately confronted with the fundamental, controlling problem that we have, accordingly, only enough phosphorous in the average soil for forty excellent crops ..."  We are now sixty years after Price was writing and we may be coming up to thresholds in many agricultural areas. Older nutrient analyses may be in need of frequent rerunning to check their currency.

Evfit home  See also the effect of rising atmospheric CO2 on the micronutrient content of food crops