Manganese and Soil Fertility

variety of crops. Pot tests indicated that addition of about 200 p.p.m. of copper from copper sulfate produced a toxic reaction in soils low in copper, but otherwise comparable to Alsatian vineyard soils, which were found to contain as much as 400 p.p.m. of copper. Among the crops tested, vines were most resistant to copper toxicity; clover and alfalfa were most sensitive. Symptoms of copper poisoning were found in southern France in spinach and gladiolus grown in a field once occupied by a peach orchard that had been sprayed heavily for many years with Bordeaux mixture. Only the parts of the field having quite acid soil (pH 4.5 to 4.7) were affected; the copper content of that soil was 98 to 130 p.p.m. Future research in disease control and soil fertility with copper-containing compounds should evaluate the residual effects, because nearly all the copper applied to crops will normally be fixed in the few inches near the surface of the soil.