Concentration of cadmium in durum wheat as affected by time, source and placement of nitrogen fertilization under reduced and conventional-tillage management

Cadmium concentration in durum (Triticum durum L.) grain may be influenced by fertilizer management. A three year field study was conducted at two locations in southwestern Manitoba, Canada, to determine the effect of source, timing and placement of N fertilizer on grain Cd concentration of durum wheat under reduced-tillage (RT) and conventional-tillage (CT) management. There was a significant year-to-year variation in grain yield and grain Cd concentration, indicating a strong effect of environment on phytoavailability of Cd. Soil type also had a dominating effect on Cd in durum grain. Grain Cd concentration and accumulation were always lower at the Newdale clay loam (CL) location than the Stockton fine sandy loam (FSL) location. Compared to CT, RT management decreased grain Cd concentration and accumulation. Application of N fertilizer significantly increased grain Cd concentration and decreased grain Zn concentration. The increase in grain Cd could be due to the increasing Cd concentration in soil solution, the improved crop growth, or a competitive interaction between Cd and Zn for binding sites in the soil system and for uptake sites in the roots, following the application of N fertilizer. Time, source and placement of N fertilization showed inconsistent effect on grain yield and grain Cd concentration. The effects when observed were minor compared to effects of year and soil type on grain Cd concentration. Application of anhydrous ammonia (NH₃) generally resulted in higher Cd concentration in durum grain than application of same level of other N sources including urea ammonium nitrate (UAN), urea and ammonium nitrate (AN), probably due to greater N efficiency from the NH₃ as compared to the other sources. Where differences due to placement occurred, banded application of fertilizers generally resulted in higher Cd concentration in durum grain than did dual-banded placement, indicating a higher fertilizer availability. Soil type, year and N fertilization greatly affected concentration of Cd in durum grain. Selection of a suitable source, timing and placement combination of N fertilization is important in optimizing crop yield and minimizing grain Cd concentration.