Pyroligneous acid (PA) is produced during the combustion of woody biomass and is a complex aqueous fraction resulting from the thermochemical rupture of the components of vegetable biomass. We evaluated the effect of PA on the soil microbial community and activity in order to assess the applicability of this acid in soil and to gather further information on the mechanisms of its toxicity or stimulation. Five concentrations of PA solution (0, 0.5, 1, 2 and 5%) were selected to monitor the biochemical parameters of the soil. The respirometric test showed that the increase in the evolved carbon dioxide-carbon (C) was not due to a release of the native organic C from the soil, but only from the organic compounds of PA. The highest values of microbial biomass content were found in the soil treated with the lowest PA doses, but decreased with increased doses. At higher application doses (2 and 5%), there was a decrease in most enzymatic activities and a loss of soil quality. When PA was applied in doses of up to 1%, our results indicated no negative effects on soil biology and that there was even an improvement.

Biochar (Bc) and liquid vermicompost extracts (LVEs) are increasingly being used as biofertilizers in agriculture to promote soil-microbe-crop interactions. However, although both these products can potentially act synergistically due to their complementary characteristics, their co-application in different soils has not yet been investigated. Therefore, firstly, an LVE-activated biochar (B_LVE) was experimentally formulated and the persistence of LVE bacteria over a 60-day storage period was determined. The total number of LVE bacteria increased by 10-fold after 7 days and was stable throughout the entire biochar storage period. In addition, changes in the composition of the bacterial community were observed after 30 days of storage, indicating that taxa less represented in pure LVE may be advantaged upon biochar colonization. Secondly, a microcosm experiment was performed to evaluate whether the biological fertility and enzyme activities of two soils, differing in organic matter content, could be enhanced by the addition of LVE-activated biochar. In this experiment, three different doses of Bc, LVE, and B_LVE against the carbon-related biological fertility index (i.e., biological fertility index, BFI) and three enzyme activities over a 21-day incubation period were tested. The B_LVE treatment yielded the best results (i.e., BFI +32%, enzyme activities +38%). This indicates that Bc and LVEs can act synergistically to promote soil fertility, quality, and microbial activity. By integrating LVE-activated biochar into their soil management practices, farmers could achieve higher crop yields and healthier products.

Changes in the chemical and biological characteristics of a calcareous soil by the addition of green compost (GC), vermicompost (VC), biochar, biochar + GC, and biochar + VC were evaluated during a 360-day laboratory incubation. The GC and the VC treatments lowered the soil pH and increased the total and dissolved organic C, microbial biomass C, microbial quotient, alkaline phosphatase (AP-ase) and specific AP-ase, dehydrogenase (DH-ase) and specific DH-ase, and metabolic potential. The improvement in the biological activity of the soil was more notable and permanent with VC than GC. The biochar treatment temporarily increased the pH of the calcareous soil (pH 8.2) up to a maximum of 8.57, showed the greatest increase of total organic C, did not change dissolved organic C and microbial biomass C, and induced small effects on soil biological activities. When mixed with biochar (biochar + GC and biochar + VC), composts led to higher organic C mineralization; dissolved organic C, biomass C, and DH-ase activity; and did not change the metabolic quotient, specific AP-ase, and specific DH-ase activities. The AP-ase activity of biochar was enhanced only by the addition of VC, although in a nonadditive way. Metabolic potential was more than halved by the GC and was not changed by the VC. Overall, our study shows that the incorporation of both composts, particularly VC, into calcareous soils may improve soil quality, whereas biochar could have benefits for C sequestration. In addition, the mixing of GC, and especially VC with biochar, increased some soil quality parameters compared with the biochar-only treatment.

Natural products such as wood distillate (WD) are promising alternatives to xenobiotic products in conventional agriculture and are necessary in organic farming. A field study gave insight into the effectiveness of WD applied as foliar spray (F-WD), soil irrigation (S-WD), and their combination as growth promoters for field beans. The soil fertility and quality parameters, plant growth, nutrient uptake, and resource partitioning within plants were evaluated. In a pot trial, we tested the effect of S-WD on root nodule initiation and growth. S-WD increased DOC and microbial biomass by approximately 10%, prompted enzyme activities, and increased nitrate and available phosphorus in soil, without affecting the number and growth of nodules in field beans. In contrast, the F-WD slightly reduced the DOC, exerted a lower stimulation on soil enzymes, and lowered the soil effect in the combined distribution. In field beans, the F-WD reduced the stem height but increased the number of pods per stem; S-WD increased the N and P concentrations of leaves and the N concentration of the pods. Moreover, all WD treatments retarded plant senescence. The WD revealed itself to be promising as a growth promoter for grain legumes, but further research is needed to understand the interference between the combined soil and foliar applications.

The recycling of key nutrients and bioenergy from waste materials is a goal of sustainable agriculture. The co-application of biochar and a vermicompost solution (vermiwash) could enhance the positive effects of both materials on soil biomass and biological activities. Tomato plants were grown in soil amended with biochar, mixed at a rate of 2% w/w, and vermiwash, applied through fertigation at a rate of 25 mg per plant, alone (B and V) and in combination (BV). Organic C, dissolved organic C (DOC), soil biomass C, and some enzymatic activities were determined at the start (T0) and the end (T100) of the cultivation period in bulk soil and rhizosphere soil. B and V significantly increased the organic C and soil biomass contents. In addition, B retained the DOC species derived from the soil and, in the BV treatment, also the humic substance of the vermiwash. Generally, all the parameters achieved higher values in the rhizosphere than in the bulk soil. The altered soil index three (AI3) of enzyme activities suggests that applying V and B is helpful for the soil microorganisms. Synergisms between B and V were low in the bulk soil and clearly evident in the rhizosphere.