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Iodine (I) is an essential trace element commonly deficient in agricultural systems. Whereas there is much information on I in food crops, there is a lacuna of knowledge on the environmental factors that affect pasture I concentrations. We aimed to identify the most important environmental factors affecting the concentration of I in New Zealand pastures, and the consequences to agricultural systems. Soil and pastoral samples were collected throughout the country and analyzed for I and other elements. The soils contained 1.1 to 86 mg I kg−1, with 0.005 to 1.4 mg kg−1 in the pasture. In 26% of pastures, I concentrations were insufficient for sheep nutrition, whereas 87% contained insufficient I for cattle nutrition. Pasture I concentrations were negatively correlated with the distance from the sea, and the concentration of oxalate‐extractable amorphous Al, Fe, and Si oxides, which immobilize soil I. Soil organic C and clay increased I retention in soil but did not significantly affect pasture I concentrations. Future work should investigate how soil properties affect pasture I uptake in inland areas. Core Ideas 87% of New Zealand pastures contained insufficient iodine for cattle. Pasture I levels are higher close to the sea. Pasture I levels are lower in soil that is high in Fe and Al (oxyhydr)oxides.

In four out of ten Danish soils, varying in texture, pH, and forms of inorganic phosphate, phosphate solubility in dilute CaCl, solution corresponded to the solubility of one or other of six phosphate minerals presumed to exist in soils. On adding moderate rates of phosphate, only one of the soils sustained phosphate activities corresponding to such a mineral (octocalcium phosphate). Consequently, removal of added phosphate from solution, as in the determination of the differential phosphate potential buffering capacity was the result of an adsorption type of mechanism rather than precipitation of crystalline phosphate compounds.