Effect of hydrogel based soil amendments on yield and growth of wastewater irrigated potato and spinach grown in a sandy soil

Abstract

Increased food production, required for a growing population, would place additional stress on freshwater resources. Since agriculture is the largest freshwater consumer, supplementation of irrigation water with wastewater could be beneficial. However, wastewater contains contaminants such as heavy metals, which can adversely affect plant growth. Thus, it is necessary to develop techniques to minimize this adverse impact of wastewater irrigation. The objective of this study was to determine the effect of super absorbent polymer (SAP), as well as a mixture of SAP and plantain peel biochar as soil amendments, on growth and yield of wastewater (WW) irrigated potatoes ( Solanum tuberosum L.) and spinach ( Spinacia oleracea L.). The proposed amendments are known to adsorb these contaminants and reduce their uptake by plants, thus promoting plant growth and yield. In the mixed amendment, gasified biochar (GBC) was used for potatoes, whereas pyrolyzed biochar (PBC) was used for spinach plants. In 2015 and 2016, potatoes were grown in sandy soil filled lysimeters, with treatments: SAP+WW, SAP+GBC+WW, WW (no amendment, wastewater irrigation) and FW (no amendment, freshwater irrigation). In 2016, spinach plants were grown in different lysimeters with treatments SAP+WW, SAP+PBC+WW, WW and FW. The amendments were incorporated in soil at the rate of 1% (w/w) for both the plants. Plants were irrigated with laboratory prepared, highly contaminated synthetic wastewater, and were harvested at maturity. Observations on yield and plant health parameters, viz. photosynthetic activity, stomatal conductance, normalized difference vegetative index (NDVI), relative chlorophyll content index (RCCI), leaf temperature and root structure were recorded. Results indicated that irrigating potato and spinach plants with the wastewater, had no adverse effects on yield and growth of the plants. Potato tuber yield was the lowest with treatment SAP+GBC+WW during both years, and no significant differences were found in yield amongst other treatments. Spinach yield in SAP+PBC+WW treatment was significantly higher than that in other treatments (p<0.05). No significant effect of treatments on the plant growth parameters was observed. The study indicates that the proposed amendments can be used to promote growth and yield of crops grown with contaminated wastewater, however, the effect of these amendments are dependent on the type of crop. • Hydrogel–biochar mix soil amendment increased wastewater irrigated spinach yield. • Wastewater irrigation did not cause yield reduction for potato and spinach plants. • Wastewater irrigated potato exhibited higher leaf greenness for hydrogel treatment.