Andrea Ferrarini

Impacts of willow and miscanthus bioenergy buffers on biogeochemical N removal processes along the soil-groundwater continuum

In this article, the belowground and aboveground biomass production in bioenergy buffers and biogeochemical N removal processes along the soil–groundwater continuum was assessed. In a sandy loam soil with shallow groundwater, bioenergy buffers of miscanthus and willow (5 and 10 m wide) were planted along a ditch of an agricultural field (AF) located in the Po valley (Italy). Mineral N forms and dissolved organic C (DOC) were monitored monthly over an 18‐month period in groundwater before and after the bioenergy buffers. Soil samples were measured for inorganic N, DOC, microbial biomass C (MBC) and N (MBN), and potential nitrate reductase activity (NRA). The results indicated that bioenergy buffers are able to efficiently remove from groundwater the incoming NO3‐N (62% – 5 m and 80% – 10 m). NO3‐N removal rate was higher when nitrate input from AF increased due to N fertilization. Willow performed better than miscanthus in terms of biomass production (17 Mg DM ha−1 yr−1), fine root biomass (5.3 Mg ha−1) and N removal via harvesting (73 kg N ha−1). The negative nonlinear relationship found between NO3‐N and DOC along the soil–groundwater continuum from AF to bioenergy buffers indicates that DOC:NO3‐N ratio is an important controlling factor for promoting denitrification in bioenergy buffers. Bioenergy buffers promoted soil microbial functioning as they stimulated plant–microbial linkages by increasing the easily available C sources for microorganisms (as DOC). First, willow and miscanthus promoted high rates of biological removal of nitrate (NRA) along the soil profile. Second, rhizosphere processes activated the soil microbial community leading to significant increases in MBC and microbial N immobilization. Herbaceous and woody bioenergy crops have been confirmed as providing good environmental performances when cultivated as bioenergy buffers by mitigating the disservices of agricultural activities such as groundwater N pollution.

Biomass production and energy balance of herbaceous and woody crops on marginal soils in the Po Valley

A wealth of data and information on the cultivation of perennial biomass crops has been collected, but direct comparisons between herbaceous and woody crops are rare. The main objective of this research was to compare the biomass yield, the energy balance and the biomass quality of six perennial bioenergy crops: Populus spp., Robinia pseudoacacia, Salix spp., Arundo donax, Miscanthus × giganteus, and Panicum virgatum, grown in two marginal environments. For giant reed and switchgrass, two levels of nitrogen fertilization were applied annually (0–100 kg ha−1). Nitrogen fertilization did not affect biomass or energy production of giant reed; thus, it significantly reduced the energy return on investment (EROI) (from 73 to 27). In switchgrass, nitrogen fertilization significantly increased biomass production and the capacity of this crop to respond to water availability, making it a favorable option when only biomass production is a target. Net energy gain (NEG) was higher for herbaceous crops than for woody crops. In Casale, EROI calculated for poplar and willow (7, on average) was significantly lower than that of the other crops (14, on average). In Gariga, the highest EROI was calculated for miscanthus (98), followed by nonfertilized giant reed and switchgrass (82 and 73, respectively). Growing degree days10 during the cropping season had no effect on biomass production in any of the studied species, although water availability from May to August was a major factor affecting biomass yield in herbaceous crops. Overall, herbaceous crops had the highest ranking for bioenergy production due to their high biomass yield, high net energy gain (NEG), and biomass quality that renders them suitable to both biochemical and thermochemical conversion. Miscanthus in particular had the highest EROI in both locations (16 and 98, in Casale and Gariga), while giant reed had the highest NEG on the silty‐loam soil of Gariga.

Development of a soil health index based on the ecological soil functions for organic carbon stabilization with application to alluvial soils of northeastern Italy

There is a need to assess soil health quantitatively to assist with sustainable soil management in agroecosystems. The objective of this research was to develop a farmlevel soil health index (SHI) to help identify the most sustainable management practices including C sequestration and agroecosystem resilience to climate change. For all indexing phases we used the Soil Management Assessment Framework. The SHI was created using a minimum data set (MDS) of physical, chemical and biochemical soil indicators chosen via expert opinion (EO-MDS) (24 indicators) and via the results of PCA (PCA-MDS) (16 indicators). Each observed value was converted into a score (0 to 1) by using site-specific non-linear scoring algorithms. Indicator scores were incorporated into a composite SHI which quantified the ecological performance of 5 soil functions: habitat and biodiversity, water movement and availability, filtering and buffering, nutrient cycling, physical stability and support, and long-term C stabilization. For both MDS evaluations, we assessed agroecosystems managed organically (OS) or conventionally (CS). Results from our study showed that OS had significantly higher ( P<0.05) SHI scores compared to the CS. SHI, with EO-MDS, was more efficient ( P=0.028) than the PCA-MDS (P=0.039) when determining the effect of soil management practices on soil health. Non-linear transformation was a useful technique and represented soil ecological functionality effectively. Five out of six soil functions had significantly greater ( P<0.05) ecosystem performance in OS compared to CS, except for water movement and availability. The benefit for OS lead to a greater soil health status, allowing the system to be more resilient to climate change, to efficiently provide nutrients to plants, and to sustain an active soil food web for