The effect of residual zinc and its chemical forms on growth and zinc concentration in wheat

Zn deficiency has been reported for some crops in Iran. The published reports indicated that Zn recovery from fertilizers is very low. This means that a considerable portion of applied Zn is not absorbedly by the first plant and thus could be used by sub sequence crops. The objectives of the present experiment were to study: (i) The effects of residual Zn on growth and Zn concentration and uptake by wheat (Triticum aestivum L.), (ii) Growth and Zn concentration and uptake as affected by Zn chemical forms. Based on the last study twenty surface soil samples (0-30cm) from major paddy rice fields in Fars province were used and treated with 3 levels of Zn (0, 5, 10 mg/kg soil as ZnSO4.7H2O) then planted to rice (first crop). Pots were replanted to rice (second crop) and the wheat (third crop), respectively. Shoot dry weight, relative growth and Zn concentration and uptake were used as plant responses. Soil samples were taken before wheat and extracted. In addition, chemical forms of native and applied Zn were determined by sequential fractional method. The results indicated that although residual Zn had no significant effect on dry matter of wheat, it markedly increased Zn concentration and uptake by this crop. The results of present study also shown that 33 – 42% of applied Zn was converted to carbonate form. It indicated that this form is responsible for the observed residual effect of ZnSO4 in these calcareous soils. Multiple regression equations revealed that the carbonate form was significantly correlated with dry matter, Zn concentration and uptake and relative yield of wheat. The regression equations were also run in soil samples before the third crop.