Composite organic amendment boosts soil remediation and Cd detoxification to rape under different nitrogen level

Cadmium (Cd) contamination in soil has posed a great threat to the safety of vegetable production and human health, especially under high nitrogen (N) level. This study investigated the efficacy of composite organic amendment (spent mushroom substrate (SMS) and its biochar) on soil remediation and Cd detoxification to rape under 0.6 mg kg-1 Cd contaminated soil, different N fertilizer (urea, calcium nitrate, ammonium sulfate, and ammonium nitrate) and level (0.1 g kg -1 as the normal N-supply level, 0.2, 0.4, and 0.8 g kg -1 as the excessive N-supply level). The results showed that the application of excessive N deteriorated the soil physicochemical properties, increased the bioavailable Cd, and inhibited the rape growth. With the application of composite organic amendment, the soil pH was increased by 0.58-0.98, the proportion of EXE (exchangeable) Cd was reduced by 13.52%-18.70%, and the Cd contents of rapes were decreased below 0.2 mg kg -1. According to Pearson correlation analysis, the coefficient of N level and pH value of soil was decreased with the application of organic amendment (from-0.30 to-0.31) as well as N level of soil and Cd content of rapes (from 0.62 to 0.61), indicating organic amendment can effectively counteract the negative effects of excessive N fertilizer. Concisely, the application of composted organic amendment is helpful to recover soil properties, microbial activities and rape growth, and can be potentially used to ensure the safety of rape production under Cd contamination and high N level.