Effects of Biochar and Biochar-Compost Mix as Soil Amendments on Soil Quality and Yield of Potatoes Irrigated with Wastewater

This study evaluated the impact of biochar, compost, and a biochar-compost mix on soil properties and yield of potatoes irrigated with wastewater. In each year of a 2-year (2017, 2018) field lysimeter study conducted under wastewater (WW) irrigation, a thrice-replicated completely randomized design (CRD) tested the effect of a factorial combination of 3 levels of barley (Hordeum vulgare L.) straw biochar amendment (none, 1%, and 3%) and 2 levels of mixed green and table waste compost amendment (none, 7.5%) on soil physicochemical properties, along with potato (Solanum tuberosum L.) plant growth, physiology, and yield components. Relative to the non-amended control, all amendment treatments had a significant positive effect (p ≤ 0.05) on soil physicochemical properties and crop yield; however, amendments did not affect plant growth or plant physiological parameters. Higher temperatures in the second year led to significantly lower yields than in the first year. In 2017, compost alone increased potato yield under wastewater irrigation, whereas in 2018, yield was greater at the 3% biochar amendment rate than at the 1% amendment rate. We conclude that amending soils with biochar and biochar-compost mix is a feasible way to grow potatoes under wastewater irrigation, but application rate and biochar-compost mixing ratio should be properly selected to achieve a high potato yield. Biochar and biochar-compost amendments improved conditions for potato growth under wastewater irrigation, suggesting that wastewater irrigation of crops grown in amended soil may prove a feasible approach to reducing the need to treat wastewater destined for use as irrigation water, while increasing water and nutrient cycling to improve food security.