The effect of organic amendment composition on zinc and cadmium availability and uptake in wheat crops

Organic amendments provide crops with nutrients, but can also add pollutants. Yet the fate of micronutrients such as zinc (Zn) and pollutants such as cadmium (Cd) in soil-crop systems is difficult to predict because of the complexity of amendments added to soils. We performed pot and incubation experiments to determine whether the soil availability, uptake and transfer to grain of Zn and Cd in wheat (Triticum aestivum) are linked to the composition of amendments. Three amendments with highly diverse chemical properties, including varied organic matter (OM) degradability, were applied to a non-contaminated, arable soil. Stable isotopes of 70Zn and 106Cd were used to trace metals taken up from inputs versus soil in wheat biomass. We found the amendment most enriched in rapidly degradable OM (poultry manure) led to the highest wheat uptake of input-derived Zn i.e., 87{+/-}14 mg Zn (kg soil)-1. This was 2.5 times higher than input-derived Zn uptake from the most degraded amendment (compost). We did not observe an increase in soil available Zn with amendment application. Thus, biotic processes resulting from soil-plant-microbial interactions led to the increase in wheat uptake of input-derived Zn with amendment enrichment in rapidly degradable OM. Amendments led to minimal uptake of input-derived Cd in wheat and did not increase soil available Cd. Furthermore, we found no significant increase in grain Zn and Cd concentrations with amendments compared to the control. Our results highlight how amendment OM composition affects soil availability and wheat uptake of Zn and Cd with organic amendment application.