Substitution of mineral fertilizers with organic soil amendments is postulated to improve productivity‐relevant soil properties such as aggregation and organic matter (OM) content. However, there is a lack of studies analyzing the effects of biochar and biogas digestate versus mineral fertilizer on soil aggregation and OM dynamics under temperate field conditions. To address this research gap, a field experiment was sampled four years after establishment on a sandy Cambisol in Germany where mineral fertilizer or liquid biogas digestate was applied with or without 3 or 40 Mg biochar ha−1 (produced at 650°C). Soil samples were analyzed for soil organic carbon (SOC) content, pH, cation exchange capacity, bulk density, water‐holding capacity, microbial biomass, aggregate size class distribution, and the SOC content associated with these size classes. 40 Mg biochar ha−1 significantly increased SOC content in all fractions, especially free particulate OM and the 2–0.25 mm fraction. The yield of small macroaggregates (2–0.25 mm) was increased by biochar, but cation exchange capacity, water‐holding capacity, and pH were not consistently improved. Thus, high‐temperature biochar applied to a sandy soil under temperate conditions is primarily recommended to increase SOC content, which could contribute to climate change mitigation if this C remains sequestered over the long‐term. Fertilizer type did not significantly affect SOC content or other measured properties of the sandy Cambisol, suggesting that replacement of mineral fertilizer with digestate has a neutral effect on soil fertility. Co‐application of biochar with digestate provided no advantages for soil properties compared to co‐application with mineral fertilizer. Thus, independent utilization of these organic amendments is equally suitable.
In recent years, biochar has been discussed as an opportunity for carbon sequestration in arable soils. Field experiments under realistic conditions investigating the CO 2 emission from soil after biochar combined with fertilizer additions are scarce. Therefore, we investigated the CO 2 emission and its 13 C signature after addition of compost, biogas digestate (originating from C4 feedstock) and mineral fertilizer with and without biochar (0, 3, 10, 40 Mg biochar/ha) to a sandy Cambisol in Northern Germany. Biomass residues were pyrolized at~650°C to obtain biochar with C3 signature. Gas samples were taken biweekly during the growing season using static chambers three years after biochar substrate addition. The CO 2 concentration and its d 13 C isotope signature were measured using a gas chromatograph coupled to an isotope ratio mass spectrometer. Results showed increased CO 2 emission (30%-60%) when high biochar amount (40 Mg/ha) was applied three years ago together with mineral fertilizer and biogas digestate. On average, 59% of the emitted CO 2 had a C3 signature (thus, deriving from biochar and/or soil organic matter), independent of the amount of biochar added. In addition, our results clearly demonstrated that only a small amount of released CO 2 derived from biochar. The results of this field experiment suggest that biochar most likely stimulates microbial activity in soil leading to increased CO 2 emissions derived from soil organic matter and fertilizers mineralization rather than from biochar. Nevertheless, compared to the amount of carbon added by biochar, additional CO 2 emission is marginal corroborating the C sequestration potential of biochar.
Abstract. Microplastic and microglass particles from different sources enter aquatic and terrestrial environments. The complexity of their environmental impact is difficult to capture, and the consequences for ecosystem components, for example, the soil microorganisms, are virtually unknown. To address this issue, we performed an
incubation experiment by adding 1 % of five different types of impurities
(≤100 µm) to an agriculturally used soil (Chernozem) and simulating a
worst-case scenario of contamination. The impurities were made of
polypropylene (PP), low-density polyethylene (LDPE), polystyrene (PS),
polyamide 12 (PA12) and microglass. After 80 d of incubation at
20 ∘C, we examined the soil microbial community structure by using
phospholipid fatty acids (PLFAs) as markers for bacteria, fungi and protozoa.
The results showed that soil microorganisms were not significantly affected
by the presence of microplastic and microglass. However, PLFAs tend to
increase with LDPE (28 %), PP (19 %) and microglass (11 %) in treated soil
in comparison with untreated soil, whereas PLFAs in PA12 (32 %) and PS
(11 %) in treated soil decreased. Interestingly, PLFAs revealed significant
differences in PA12 (−89 %) and PS (−43 %) in comparison with LDPE.
Furthermore, variability of bacterial PLFAs was much higher after
microplastic incubation, while fungi seemed to be unaffected from different
impurities after 80 d of incubation. Similar results were shown for
protozoa, which were also more or less unaffected by microplastic treatment as indicated by the minor reduction in PLFA contents compared to the control group. In
contrast, microglass seems to have an inhibiting effect on protozoa because
PLFAs were under the limit of determination. Our study indicated that high
amounts of different microplastics may have contrary effects on soil
microbiology. Microglass might have a toxic effect for protozoa.
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