Biofortification of zinc in wheat grain by the application of sewage sludge

Abstract

Increasing the concentrations of the essential micronutrient Zn in staple crops like grain is desirable for human nutrition. We investigated the long-term ability of municipal treatment works sewage sludge, liquid sewage sludge and ZnCO3 applied to soils to increase Zn in in wheat grain (Triticum aestivum L.) in a number of field experiments conducted on different soils. We used six long-term field experiments that were set up on contrasting soils in England and the target applications were built up between 1994 and 1997. Topsoil samples and harvested grain samples were taken and air dried in 1999, 2001, 2003 and 2005. Relationships between grain Zn concentrations and soil properties and changes with time were examined. Wheat grain Zn concentrations increased with soil Zn concentrations in a similar log-log relationship with all of the Zn sources tested. Comparing total or extractable Zn in soil as explanatory factors showed little benefit of using extractable Zn measurements to predict grain concentrations over total Zn. Additional factors such as soil pH or organic carbon did not explain much more of the variation in grain Zn in our experiments. However, grain Zn concentrations did not respond at all at a site with pH 7.7. Sewage sludge applications to soil can increase grain Zn concentrations for at least 2 to 8 years after application and has similar effectiveness to ZnCO3.