Copper fertilizer practices in Manitoba

Abstract

Soil testing criteria for copper (Cu) in Manitoba were established in the mid-1980s and were primarily based on growth chamber studies for a range of crop species. A multitude of Cu products and fertilizer placement methods are practiced with insufficient research in support of them. Hence, we attempted to develop agronomic and economic Cu fertilizer management practices for soils of Manitoba through a series of experiments for crop species at two locations with DTPA-extractable Cu levels of 0.12 and 0.25 mg kg-1 soil, respectively. These experiments involved broadcast and incorporation of CuSO4·5H2O (25% Cu), CuEDTA (7% Cu), and a low (<1%) and a high (>60%) water solubility Cu oxysulphate (12.5 and 12% Cu, respectively). Four rates of side-banded liquid CuEDTA (0, 0.28, 0.56 or 1.12 kg Cu ha-1) or seedrow-placed granular products (0, 1.12, 2.24 and 4.48 kg ha-1) as above, were either superimposed or were compared directly with broadcast and incorporation of the same rates. This study confirmed that DTPA extractable Cu levels of less 0.2 mg kg-1 soil are deficient, whereas DTPA-extractable Cu levels of greater than 0.2, but less than 0.4 mg kg-1 are marginal. Broadcast and incorporation of CuSO4·5H2O at rates as low as 2 kg Cu ha-1 or side banding of 0.28 to 0.56 kg Cu ha-1 of liquid CuEDTA provide maximum economic grain yield increases in soils with either deficient or marginal Cu levels. Seedrow applied granular Cu products may provide a maximum agronomic and economic yield increase only in soils with marginal soil Cu levels. Low solubility Cu products do not correct Cu deficiency, whereas CuEDTA, although agronomically equal to CuSO4·5H2O and high solubility oxysulphates, may have a disadvantage due to its high cost. Key words: Deficient, marginal, sulphate, oxysulphate, chelate, seedrow, side band, broadcast