Tillage, lime, and poultry litter effects on plant concentrations of zinc, manganese, and copper

Minimum tillage cropping systems and the use of animal manures on cropland are becoming more prevalent. An experiment was initiated to determine the effects of tillage and lime/gypsum variables on uptake of zinc (Zn), manganese (Mn), and copper (Cu) by corn (Zea mays L.) and to show correlations between plant uptake of these metals and soil pH and Mehlich 1-extractable soil metals where poultry litter was used as a nitrogen (N) source. Surface soil samples were taken in the spring and fall for two years from a long-term tillage experiment that had been in place for nine years. There were two tillage treatments [conventional (CT) and no-tillage (NT)] and six lime/gypsum treatments (control, 8,960 kg gypsum ha-1 every fourth year, 4,480 kg lime ha-1 every fourth year, and three treatments of 8,960 kg lime ha-1 in a four-year period divided by application times into 1, 2, and 4 treatments). Poultry litter was applied each year of the two-year experiment at a rate of 8.96 Mg ha-1 on a dry weight basis. Soil samples were analyzed for pH and Mehlich 1-extractable Zn, Mn, and Cu, and plant tissue (small plant, ear leaf, stalk, and grain) was analyzed for Zn, Mn, and Cu concentrations. Lime treatments resulted in lower Zn in the small plant and ear leaf for CT, but not for NT. Plant Mn was decreased by lime and gypsum rates for small plant, ear leaf stalk and grain for both years for CT and NT. Correlations for plant Zn versus soil pH were generally non-significant, except for one year for ear leaf Zn (R=-0.413**). Correlations for soil pH and plant tissue Cu were all nonsignificant. Correlations for plant Mn and soil pH were strong with R values over 0.80. Plant Mn response to treatments was found at a pH range of 4.2 to 5.8 for ear leaf and pH 5.2 to 6.2 for stalks. Plant Mn and Zn versus Mehlich 1-extractable soil Mn and Zn, respectively, were negative. This response was possibly due to oxidation-reduction and non-incorporation of the lime for Mn and non-incorporation of the lime for Zn. Also, the poultry litter was high in Zn (447 mg kg-1), which could have masked pH effects. It was concluded that soil sampling for plant micronutrients for NT, especially where a waste material high in micronutrients is applied, can give erratic and even erroneous results. However, lime and tillage treatments had a predictable effect on micronutrient uptake as related to soil pH.