Abstract
Cattle and pig manure contain useful mineral nutrients (N, P, and K) and are therefore used as organic fertilizer. However, excessive applications of manure can cause environmental problems and threaten animal and human health because these materials also hold significant amounts of heavy metals, particularly Cu and Zn. To assess the potential risk due to the increased concentrations of heavy metals (Cu, Mn, Zn, and Cr) in a harvested crop, two maize hybrids were grown in pots on four different soils with three different fertilisers (urea, pig manure, and cattle manure). Both soil and manure characteristics influenced the heavy metal concentrations in the plant shoots. Organic fertilisation strongly interacted with the soils and, in general, reduced the shoot content of Cu, Mn, and Zn. A preliminary assessment of the heavy metal balance of the agricultural systems based on the intensive livestock production and maize cultivation showed that the potential soil enrichment of the long-term application of livestock manure arises mainly from the application of pig slurries that have a high content of Cu and Zn. The time required to apply an amount of metal that is equal to the initial soil content is 60–300 years for Zn and 240–450 years for Cu, depending on the soil type and the initial heavy metal content.
Highlights
Livestock manure is traditionally recognised as a valuable fertiliser and until the beginning of the 20th century, manure application was the only method for enriching the soil
The results of this study show that the absorption of Cu, Mn, Zn, and Cr by maize is a variable phenomenon and is influenced by several factors
Many authors have suggested that the application of organic fertilizers, such as livestock manure and slurries, greatly increases the amount of nutrients available to crops and that this is a reason for the greater maize absorption of heavy metals (HM) when organic fertilizer is applied [10,30,31]
Summary
Livestock manure is traditionally recognised as a valuable fertiliser and until the beginning of the 20th century, manure application was the only method for enriching the soil. Livestock manure is recognised as valuable fertiliser, the application of the manure to meet a particular nutrient demand may lead (in long-term applications) to excessive accumulations of other elements in the soil, heavy metals (HM) such as copper (Cu), zinc (Zn), and manganese (Mn) [5,6] At adequate concentrations, these elements are essential for the plant life cycle, in excess of specific threshold ranges, the metals become toxic for the edaphic organisms and crops. Prolonged application of HM can lead to a reduction of soil buffering capacity causing permanent contamination of the soil and the leaching of HMs towards the groundwater [8] It has been reported [10] that organic amendments such as cattle manure can serve as soil HM ameliorants. The results were to be used to evaluate the soil enrichment of HM in an intensive livestock area that was based on the possible higher input of HMs in the food chain due to slurry application
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