A field experiment was carried out on a clay-sand-loamy Red-Yellow Latosol (Typic Acrustox) in Planaltina, Federal District, Brazil, during the cropping seasons of 1995/96, 1996/97 and 1997/98, to compare the effect of three methods of copper application (soil, foliar spray and seed treatment) on soybean (cv. Doko RC) grain yield and to determine the soil and leaf critical levels of that nutrient. There were no significant differences among the treatments in the first crop, probably due to a dry spell during the grain filling pod stage. In the second and third crops, 1.2 and 2.4 kg ha-1 of copper, either broadcasted, in the first crop, or in the row, i.e, 0.4 and 0.8 kg ha-1 per crop, gave maximum grain yields. The level of 2.4 kg ha-1 of copper mixed with the seeds and the level of 0.6 kg ha-1 of copper sprayed on the leaves, twenty days after emergence, also gave maximum grain yields in the second and third crops. The soil critical levels determined by the 0.1 mol L-1 HCl, Mehlich-1, Mehlich-3 and DTPA pH 7,3 extracting solutions were 0.6, 0.5, 0.5 and 0.6 mg dm-3 of copper, respectively. The critical leaf copper concentration was 3.9 mg kg-1.
Glycine max (L.) Merr.; copper placement; foliar spray; seed treatment; extractant solutions; critical level