Watering techniques and zero-valent iron biochar pH effects on As and Cd concentrations in rice rhizosphere soils, tissues and yield.

• Brown rice Cd and yield was highly dependent on amendment's pH and watering amount. • Both ZVIB 6.3 and 9.7 amendments reduced >50% grain As in all watering treatments. • ZVIB 6.3 with 3/72 watering reduced grain As and Cd by increasing grain yield efficiently. • ZVIB 9.7 could reduce grain As and Cd, but proper watering is required for expected grain yield. Image, graphical abstract Zero-valent iron amended biochar (ZVIB) has been proposed as a promising material in immobilizing heavy metals in paddy fields. In this study, the impacts of pH of ZVIB (pH 6.3 and pH 9.7) and watering management techniques (watering amount in the order of CON (control, 5/72)>3/72>1–3/72>3/100>1/72, with 5/72, for example, representing irrigation given to 5 cm above soil surface in 72 hr regular interval) on As and Cd bioavailability for rice and its grain yield (Yield BR) were investigated in a pot experiment. Brown rice As (As BR) content was irrelative to the watering treatments, while significantly decreased (>50%) with the addition of both ZVIB materials. The diminutions of brown rice Cd (Cd BR) content as well as the Yield BR were highly dependent on both the soil amendment materials' pH and watering amount. Among all the watering treatments, 3/72 treatment (15% less irrigation water than the CON) with ZVIB 6.3 amendment was the optimum fit for simultaneous reduction of As BR (50%) and Cd BR contents (19%) as well as for significant increment (12%) of the Yield BR. Although high pH (9.7) ZVIB application could also efficiently decrease As and Cd contents in brown rice, it might risk grain yield lost if appropriate (e.g. 3/72 in our study) watering management technique was not chosen. Therefore, ZVIB would be an environmentally friendly option as an amendment material with proper selection of watering management technique to utilize As and Cd co-contaminated arable soils safely for paddy cultivation. [ABSTRACT FROM AUTHOR]