The influence of variation in copper content of an organic soil on the mineral nutrition of oats grown in situ

Oats (Avena sativa L. cv. 3C‐W) were grown on a 2‐ha field of an organic soil, the 0–20 cm layer of which varied in Cu content from 91 to 248 ppm. Analyses of samples of the soil and the mature crop revealed that soil Cu content did not correlate with Cu concentrations in the grains or straw. The EDTA‐soluble or ‘available’ Cu content of the soil was ‘abundant’ all over the field, ranging from 200 to 1100 times the total uptake of Cu by the crop. In spite of this, soil concentration of Cu was positively correlated with grain yield, and consequently with grain uptakes of Cu, Fe and P. The results suggest that (a) large proportions of native and residual fertilizer Cu in organic soils are not available to plants, and (b) that there is little luxury consumption of Cu by oats growing on an organic soil even when sufficient soil Cu is available and its concentration correlates with grain yield.