Accumulation of potentially toxic elements under long-term application of different organic amendments

There are few assessments and predictions of the accumulation of potentially toxic elements (PTEs) under long-term application of different organic amendments. A 37-year fertilization experiment was conducted with mineral fertilizers alone or with wheat straw, pig and cattle manure to evaluate soil Cu, Zn, Cd and Pb pollution risks. Compared with mineral fertilizers, livestock manure application significantly (p < 0.05) increased soil total or available Cu, Zn and Cd accumulation rates and activities, thereby increasing soil Cu, Zn and Cd accumulation risk. Pig manure had a high risk of soil Cu and Zn pollution, whereas cattle manure had a high soil Cd pollution risk and high comprehensive pollution and potential ecological risk indexes. The recommended safe maximum values for pig and cattle manure application to guarantee 100 years of clean production are 6.2 and 40.4 t ha−1 year−1, respectively. Livestock manure should be applied long term in an appropriate amount to improve soil fertility and maintain soil health simultaneously. Crop straw incorporation is recommended as a clean practice maintaining crop yield without compromising soil health. In future, a Gaussian process regression model should be given priority to simulate and predict the PTE pollution risk after organic amendments are returned to croplands.