Part of the swine manure from confined production is still improperly disposed into water streams and small rivers in southern Brazil. An alternative disposal method would be to use this animal residue as a soil fertilizer. However, repeated applications in the same area may cause nutrient build up to phytotoxic levels and could lead to surface and subsurface water pollution. The objective of this study was to evaluate the effect of Zn addition to the soil on corn dry matter production. Zinc was added as ZnO or as solid swine manure from animals temporarily fed with a diet enriched with Zn. Three experiments, each lasting 30 days, were carried out in a greenhouse in 1998/1999 using the same experimental units. Each pot contained 5.0 kg (dry base) of a Hapludox soil with pH 5.9 and 590 g kg-1 of clay. Rates of Zn were 0, 6.25, 12.5, 25 and 50 mg kg-1, which were mixed with the soil before each planting. Corn dry matter and Zn concentration in the plant tissue and soil, extracted with HCl 0.1 mol L-1 were determined. Zn concentration in soil and corn tissue, and the amount taken up by plants increased in proportion to the rate of Zn applied. Zn concentration in soil was greater for treatments with swine manure than with ZnO. Corn dry matter was not affected by Zn addition in any experiment, regardless of the Zn source. The cumulative addition of Zn to soil at rates up to 150 mg kg-1, raised Zn concentration in soil and plant tissue to levels greater than 160 and 250 mg kg-1, respectively. These levels, however, did not cause Zn toxicity to corn at the early stages of development, which shows that there is a wide range between sufficiency and toxicity of Zn in soil and in the plant tissue.
soil zinc; sources of zinc; swine manure