Combined land application of treated wastewater and biosolids enhances crop production and soil fertility

Abstract

Land application of treated wastewater (TWW) and biosolids is considered a cost-effective reuse method and valuable source of organic matter and nutrients. However, it may pose an adverse impact on the environment and human health. The main objective of this study is to determine the ability of land application of TWW and biosolids to enhance crop production and soil fertility. The study compared the effect of biosolids, commercial fertilizer, and manure on forage crop production (Zea mays). The soil and applied materials were analyzed before the experiment for major characteristics. Application rates were determined and calculated based on the crop nitrogen requirement, which is approximately 135 kg ha−1. Applied materials were incorporated uniformly in the top soil. Drip irrigation system was installed and Z. mays were sowed, and the plants were irrigated weekly with TWW to reach field capacity water content. At harvest, the crop yield and yield components were determined. Soil and plant samples were taken at the end of the experiment. Soil samples were analyzed for physical, chemical, and microbiological parameters. Plant samples were analyzed for essential nutrients, heavy metals, and biological analysis. The results have shown that, compared with the control, the crop yield increased similarly with the application of biosolids, commercial fertilizer, or manure. The yield increase was attributed to the increase in both leaves number and plant height that were affected similarly as the yield did. Plant macronutrient and micronutrient concentrations were not significantly affected by the treatments. However, the plant uptake of macronutrients and micronutrients similarly increased with biosolids, commercial fertilizer, and manure. On the other hand, Cd and Pb levels were below the detection limits. The results of soil analysis indicated that soil pH, EC, and SAR were not significantly affected by the treatments. However, CEC and OM significantly increased in the top soil with the application of biosolids, commercial fertilizer, or manure. DTPA-extractable micronutrients were not affected by the treatments. Soil and plant microbiological analysis indicated that Salmonella spp., IPN, and total fecal coliform count were not affected by the treatments and all samples were tested negative for enteric viruses. It can be concluded from this study that combined land application of TWW and biosolids improves crop production and enhances soil fertility level without significant impact on the environment and human health.