Productivity and heavy metal pollution management in a silage maize field with reduced recycled wastewater applications with different irrigation methods

Using wastewaters in irrigated agriculture can cause heavy metal accumulation as well as salinity in soil. A practical way of minimizing accumulation in soil is to use irrigation techniques that require less water and consequently introduce less heavy metals into the feeding chain in silage maize cultivation with wastewater irrigation. The objective of this study is to address this issue. A factorial field experiment was carried out for two years in a completely randomized design with three replicates. Experimental plots were irrigated with three different irrigation methods (subsurface and surface drip, and furrow) applying three different levels (full irrigation and 33 and 67% deficit irrigations) of recycled wastewater and freshwater. The results showed that soil heavy metal contents, salinity, macro nutrients, organic matter, cation exchange capacity, porosity and wet aggregate stability were significantly higher in full irrigation with wastewater, while pH, carbonates, bulk and particle densities were significantly lower. Drip methods reduced salinity and heavy metal contents significantly. Heavy metal pollution indexes also indicated that drip methods are more effective in reducing metal pollution in soil. However, considerable accumulations of Cd and Ni were found with all methods while deficit irrigation decreased accumulations. The highest cation exchange capacity and K2O contents and the lowest exchangeable sodium percentage were determined with the subsurface drip method. The subsurface drip method saved 20.7 and 49% more irrigation water than the surface drip and furrow methods under fully irrigated conditions. Therefore, it can be concluded that using the subsurface drip method with recycled wastewater can be used in silage maize cultivation because soil productivity and water savings increased while metal pollution and salinity in soil decreased. Moreover, using 33% less wastewater can be a useful practice to decrease Cd and Ni accumulation.

Automated summary

The study found that drip irrigation methods significantly reduced salinity and heavy metal contents in the soil, while deficit irrigation decreased heavy metal accumulations. The subsurface drip method showed significant water-saving effects, increased soil productivity, and reduced metal pollution and salinity.