Morphological transformation of heavy metals and their distribution in soil aggregates during biotransformation of livestock manure

Abstract

Untreated livestock and poultry manure have become important pollution sources in rural environments because of their potential risks to the surrounding water and soil. Aerobic fermentation has been widely used as the main technique for the biological transformation of livestock and poultry manure. In this study, exogenous additives (zeolite powder, maifanitum, rock phosphate, biochar, straw) and different combinations of these additives were added to the manure of livestock and poultry to produce organic fertilizer by aerobic fermentation. The morphological changes in heavy metals and their redistribution characteristics in soil aggregates were investigated in soils treated with different amendment strategies. The results showed that all treatments increased the soil total nitrogen (TN), alkalinity (AN), available phosphorus (AP) and available potassium (AK) and decreased the total cadmium (Cd) content to varying degrees. Biotransformation of livestock waste had a great impact on the soil residual states of copper (Cu), zinc (Zn) and Cd, and the organic matter-bound Cd was also affected. Zn, Cu and Cd were commonly found in macroaggregates (1–2 mm) and were positively correlated with the content of organic matter in soil aggregates. Organic fertilizers did not affect the contents of Cu, Zn or Cd in aggregates of particle size 0.05 mm in soil but had an effect or significant effect on contents of these metals in particles of 0.05–0.25 mm, 0.25–1 mm or 1–2 mm. This study provides a theoretical basis and practical significance for the remediation of heavy metal pollution and the preparation of organic fertilizer from livestock and poultry waste, and made an important contribution to the field of agriculture.