Abstract
Organic waste products (OWP) application to crop lands makes possible nutrients recycling. However, it can result in long-term accumulation of trace elements (TE) in soils. The present study aimed at (i) assessing the impact of regular applications of urban composts and manure on the TE contents of topsoils and crops in a long-term field experiment, (ii) comparing the TE mass balances with the stock variations of TE in soils, and (iii) proposing a prospective evaluation of this practice, based on estimated soil safe threshold values and simulations of soil TE accumulation for 100 years. In the long-term field experiment, physico-chemical properties and TE contents (Cd, Cr, Cu, Hg, Ni, Pb and Zn) have been measured in OWP, soils, plants and leaching waters for the period 1998–2015, and used for mass balance calculations and long-term simulations of TE accumulations. The composts of green wastes and sludge (GWS) and of municipal solid waste (MSW) were the OWP with the largest TE contents, while the farmyard manure tended to have the lowest. Repeated application of OWP led to significant accumulation of Zn and Cu in the topsoil layer (not for Cr, Cd, Hg, Ni, Pb), especially with GWS, without overpassing calculated protective threshold values. No effect of repeated application of OWP has been observed on TE contents in grains (wheat, maize, barley). The positive mass balance has been dominated by the input flux of TE through OWP and resulted in the observed increases of soil stocks for Cu and Zn. Prospective simulation of soil content evolution until 2100 showed that soil content reached 0.4 mg Cd kg−1 soil (GWS, MSW), 38 mg Cu kg−1 soil (GWS) and 109 mg Zn kg−1 soil (GWS), which remained lower than protective threshold values.
Highlights
The biggest challenge that agriculture faces is to produce food enough in quantity and quality to feed increasing population, in the complex context of climate change
As already stressed by Obriot et al (2016), the largest pH was found in farmyard manure (FYM) and biowaste compost (BIOW), largest content in carbonates in BIOW, largest organic carbon content in FYM, largest organic nitrogen content in green waste (GWS) and FYM, and largest content in phosphorus and potassium were found in GWS and FYM, respectively
Results confirmed that repeated application of organic waste products (OWP), even in large amounts such as those applied in the QualiAgro experiment, did not alter the soil quality in terms of trace elements (TE) contents since they remained far below the calculated protective threshold value for Cd, Cu, Ni, Pb and Zn
Summary
The biggest challenge that agriculture faces is to produce food enough in quantity and quality to feed increasing population, in the complex context of climate change. Nutrient recycling has been neglected due to the worldwide increased use of mineral fertilizers (Richard et al 2019), manure application on soils has traditionally contributed to the recycling of nutrients they contain. Recycling of organic waste products (OWP) in agriculture contributes to circular economy through the recycling of nutrients and organic matter and represents a valuable alternative to their landfilling or incineration (Houot et al 2014; Noirot-Cosson et al 2016; Alvarenga et al 2017). The use of OWP from urban and industrial origin may replace the traditional use of manure in areas where animal breeding is lacking and may be used as a substitute to chemical fertilizers (Noirot-Cosson et al 2016; Sharma et al 2017)
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