Effect of nitrogen application on concentration of cadmium and nutrient ions in soil solution and in durum wheat

A growth chamber experiment was conducted to study the effect of nitrogen fertilizer on the chemical composition of the soil solution over time, and to determine Cd uptake as a function of rates of nitrogen fertilizer application and transpiration. Sceptre durum wheat was grown in a fine sandy loam soil, in pots with treatments of 0, 50, 100, 200, 400, and 800 mu g N g(-1) as urea. The soil solution was removed by water displacement and analyzed for Cd and other nutrient ions at time of seeding, 10, 20, 30, and 40 d after seeding, and at the time of crop maturity. Soil samples were analyzed at each sampling time, and aboveground plant material was also harvested at these times and analyzed for Cd and other nutrient ions. Behaviour of Cd was compared to that of the nutrient ions to gain a better understanding of patterns of ion behaviour. Conductivity measurements were taken as estimators of ionic strength. Both solution Cd concentration and DTPA-extractable soil Cd increased significantly with increasing nitrogen rate. The increases in Cd concentration with N fertilization were greatest immediately after fertilization and appeared to be related to an increase in soil and solution conductivity, with pH also having an influence on DTPA-extractable Cd. The soil solution concentration of all nutrients, with the exception of phosphate, increased with N rate. The effects of N fertilization on the amounts of extractable nutrients in the soil were more variable. Plant Cd concentrations increased with increasing N application rate to 800 mu g g(-1), but dry matter yield and transpiration only increased with N rate to 200 mu g g(-1). Cadmium was the element most affected by increasing the N rate, and there were minor changes in uptake of other elements such as N, P, K, Ca, Mg, Mn, Zn, and Cu with N application rate and time. This study clearly illustrated the effect of nitrogen fertilization on the concentration of Cd in the soil solution and its uptake by durum wheat.