Response of Corn and Soybeans to Field Applications of Copper

Copper deficiencies have been recognized on muck soils for over 35 years. Cu deficiencies and responses under a wide range of growing conditions and soil types in Indiana have been identified by several workers. This study was initiated to establish the need for copper fertilization on certain Indiana soils and to investigate the utility of tissue analyses as a diagnostic tool for identifying such situations. Spectrographic analysis of corn (Zea mays L.) and soybean (Glycine max (L.) Merr.) tissue samples submitted by farmers and dealers in 1966 to the Purdue Soil and Plant Analysis Laboratory, were used to locate fields producing crops with copper levels below 5 ppm in the leaf tissue. In the spring of 1967, 44.8 kg Cu/ha was applied at 12 locations. These treatments were effective in increasing the leaf tissue copper level in both corn and soybeans. Corn yields were increased 3 to 12% on all five harvested locations and soybean yields 1.3% and 14.2% on both harvested locations. In 1968 and 1969, increased copper uptake was indicated by higher tissue copper levels and by increased yields. Differences in treatments were more evident in corn tissue sampled 1 month prior to tasseling than when sampled at tasseling time. Yield increases as high as 22.5% in 1968 and 17.9% in 1969 were obtained even though tissue copper levels were not below the “critical level” of 5 ppm. Corn yields in 1968 on a “Chalmers” silty clay loam were increased an average of 6.7% with copper applied in 1968, while yields of corn grown on the same plots with no additional treatment were depressed 6.4% in 1969. In this instance, yields decreased more with cupric sulfate than with cuprous oxide. The largest and most consistent yield increases were obtained on sandy loam and high organic matter soils. It was concluded that corn and soybean yields could be significantly increased with copper additions on selected mineral soils of northwestern and north central Indiana.