Mineralizable carbon in biosolids/fly ash/sugar beet lime treated soil under field conditions

• Plant roots contribute to mineralizable carbon in biosolid treated soils.
• This contribution is enhanced when plant growth is favored.
• Sugar beet lime could be effectively used for biosolid stabilization in the field.

Fly ash (FA) from coal burning power plants is generally used for biosolids stabilization to reduce numbers of pathogens and availabilities of heavy metals contained in biosolids. The objective of this study was to determine the suitability of sugar beet lime (SBL) from sugar beet processing factories as fly ash substitute. Post-harvest soil samples were employed in a 180 d incubation study for each of two year field experiments. A first order logistic model was used to estimate sizes of labile and delayed logistic C pools. All treatments with one exception significantly (P < 0.05) reduced plant biomass compared to the mineral fertilization treatment in the first year under maximum water stress conditions. However, biosolids (7.5 Mg ha−1), biosolids + FA (7.5 Mg ha−1), and biosolids + SBL (7.5 Mg ha−1) significantly (P < 0.05) raised plant biomass compared to the mineral fertilization in the second year under minimum water stress. Applications of biosolids together with either FA (7.5 and 15 Mg ha−1) or SBL (7.5 and 15 Mg ha−1) significantly (P < 0.05) increased sizes of labile and delayed logistic pools in the first year, but they did not in the second year. The sizes of potentially mineralizable carbon pools were bigger in the second year probably due to increased accumulation of wheat root biomass originating from enhanced soil water regime. Carbon mineralization in soils treated with biosolid/fly ash/sugar beet lime at agronomic application rates depends also on plant biomass accumulation, which affects total root biomass and rhizodeposition. Sugar beet lime containing 70% CaO and 5% organic carbon seems to be a good biosolids stabilizing agent compared to fly ash in terms of plant biomass accumulation and mineralizable carbon.