Effect of biochar and compost on cadmium bioavailability and its uptake by wheat–rice cropping system irrigated with untreated sewage water: a field study

The cadmium (Cd) uptake and accumulation in the cereal crops like wheat and rice are a serious concern in recent years. Application of various organic amendments in Cd-contaminated soil is an effective technique in management of crop growth and health as organic amendments not only promote plant’s growth but also check Cd translocation in plants. For this purpose, 3 organic amendments (wheat straw biochar (WSB), cotton stick biochar (CSB), and compost comp) were applied @ 0.5% (under randomized complete block design with 4 replicates) in sewage water fed Cd-contaminated soil for effective locking of Cd in soil being cultivated with wheat and rice. The experiment was completed in almost 1 year (December 2014 to November 2015). Our results revealed that all amendments can enhance plant growth and physiology and decrease soil bioavailable Cd contents, but WSB was most prominent among 3 applied. Our results conclude that WSB can enhance straw yield (29.20 and 26.78% for wheat and rice) and grain yield (22.69% and 26.70%) and boast all physiological attributes (chlorophyll contents, stomatal/substomatal conductance, photosynthetic and transpiration rate). Application of WSB decreased post-harvest bioavailable soil Cd contents after wheat and rice crops to 56.37, 48.99% and 7.63, 26.78% in 0–15-cm and 15–30-cm soil depths, respectively. The WSB also decreased Cd translocation in grain, thus helping in decreasing the health risk index (HRI) associated with Cd-contaminated grain consumptions. For economics, amendment application in wheat crops increases its cost, so the benefit–cost ratio was observed to be less than 1. But for upcoming cropping seasons, residues of amendments will still be actively influencing plant growth and yield, so we expect a net higher benefit–cost ratio proving long-lasting use of amendments (especially WSB) a net beneficial approach.