Use of Digestate as Organic Amendment and Source of Nitrogen to Vegetable Crops

Anaerobic digestion is a valuable process to use livestock effluents to produce green energy and a by-product called digestate with fertilising value. This work aimed at evaluating the fertilising value of the solid fraction (SF) of a digestate as an organic amendment and as a source of nitrogen to crops replacing mineral N. A field experiment was done with two consecutive vegetable crops. The treatments were: a control without fertilisation; Ni85 mineral fertilisation with 85 kg ha−1 of mineral N; fertiliser with digestate at an increasing nitrogen application rate (kg N ha−1): DG-N85 DG-N170, DG-N170+85, DG-N170+170; fertilisation with digestate together with Ni: DG-N85+Ni60, DG-N170+Ni60, DG-N170+Ni25. The results showed a soil organic amendment effect of the SF with a beneficial effect on SOM, soil pH and exchangeable bases. The SF was able to replace part of the mineral N fertilisation. The low mineralisation of the stable organic matter together with some immobilisation of mineral N from SF caused low N availability. The fertilisation planning should consider the SF ratio between the organic N (NO) and total N (TKN). Low NO:TKN ratios (≈0.65) needed lower Ni addition to maintaining the biomass production similar to the mineral fertilisation.

Biochar-manure changes N mineralization in a Gray Luvisol used for agricultural production

Biochar is a source of stable organic matter being explored as a manure additive. A 64-day incubation experiment was conducted to quantify the short-term effect of manure (RM), biochar-manure (BM), raw biochar (BC), RM + BC, and BM + BC amendment on soil carbon (C) and nitrogen (N) mineralization. Manure increased CO2-C emission rates, with the highest cumulative CO2-C emissions being observed for RM + BC. Treatments with BM halted soil C mineralization, indicating manure-C stabilization. By contrast, neither RM nor BM affected soil N mineralization. Applying BM might benefit soil C sequestration by lowering CO2-C emissions over the long-term.

Origin, distribution, and characteristics of Archaeological Dark Earth soils – A review

Archaeological Dark Earth (ADE) is a layer of anthrosol (syn. anthroposol) visually characterized by dark color mainly due to homogenous charcoal inclusion, and substantial enrichment by nutrients in comparison to surrounding soils. ADE is distributed from the tropics (Amazonian Terra preta, African ADE), moderate climatic zones (European ADE) up to the Arctic (kitchen middens). Although ADE soils have been studied also in other regions of the world, they have no special regional names. All types of ADE developed as a result of deliberate and/or unintentional deposition of domestic/occupational wastes, charred residues, bones, shells, and biomass ashes from prehistoric up to recent times. ADEs have optimum C : N ratio for effective mineralization, stable organic matter content, reduced acidity, higher CEC and C, N, P, Ca, Mn, Cu, Zn, Mn, Mg, Fe, Sr, and Ba content in comparison to surrounding soils. The unclear remains the level of ADEs enrichment by these elements as enrichment factors for different elements are based on different analytical approaches from plants-available up to total contents in the soil. Although generally highly productive, comparison of herbage production and crop yields between ADEs and natural soils are still rare. The distribution and persistence of anthropogenic activities leading to the formation of ADEs indicate that they are subject to the continual formation.

Dissipation and sorption processes of polycyclic aromatic hydrocarbons (PAHs) to organic matter in soils amended by exogenous rich-carbon material

Purpose The aim of the research was to assess the effect of biochar addition on aging, degradation, and sorption processes of polycyclic aromatic hydrocarbons (PAHs) to soil organic matter. The study was carried out as a sorption experiment in strictly controlled water and air conditions, which allowed for the accurate observation and prediction of PAH behavior in soils. Materials and methods Four soils were fortified with a PAH mixture (Fluorene-Flu, Anthracene-Ant, Phenanthrene-Phe, Pyrene-Pyr, Chrysene-Chry) at 20 mg kg−1 of single-compound concentration level. The experiment was carried out in two trials: soils + 5PAHs amended with biochar and soil + 5PAHs without biochar addition with incubation times of 0, 1, 3, 6, and 9 months. After each interval time, the extractable (E-SOM) and stable organic matter (S-SOM) were measured as well as PAHs determined in two forms: total concentration (PAH-tot) and residual concentration (PAH-rest) after E-SOM extraction. The PAH loss and half-life times were estimated according to pseudo first-order kinetics equation. Results and discussion The amounts of PAH-tot in the soils without biochar decreased by an average of 92%, while in soil with biochar, this was 41% after 9 months of aging. The amount of PAHs-rest bounded with S-SOM after 9 months of incubation varied from 0.9 to 3.5% and 0.2 to 1.3% of the initial PAH concentration, respectively, for soils non-induced and induced by biochar. In soils without biochar, Flu, Ant, Phe, and Pyr exhibited similar T1/2 (43–59 days), but Chry was characterized by a much higher and broader T1/2 than other hydrocarbons (67–280 days). Biochar addition to the soils significantly influenced the half-life changes for all PAHs. The highest changes were noted for Phe (14-fold increase), and the lowest was for Flu (7-fold increase). Conclusions The addition of exogenous-rich carbon material such as biochar to the soil significantly changes the behavior and sorption potential of PAHs in the soil. Soils enriched with biochar are characterized by a higher persistence of PAHs, longer aging time, and lower affinity for sorption by native organic matter structures. Soils freshly polluted by PAH are mainly sorbed by E-SOM, which significantly increases their accessibility and reduces formation of bound-residues in the soil.

Short-Term Effects of Maize Rhizosphere and N-Fertilization on Stable Organic Matter in a Tropical Soil

The objective of this study was to investigate the effect of maize rhizosphere in the dynamics of soil organic matter (SOM) fractions (particulate organic matter—POM and mineral associated organic matter—MAOM) under different soil nitrogen (N) availability. The experiment was laid out as a factorial scheme 2 × 2: (i) without (-Plant) and with maize plant (+Plant); (ii) without (-N) and with N fertilization (+N) throughout 56 d under greenhouse conditions. Soil surface CO2-C efflux was monitored by static PVC chambers, and soil- and root-derived CO2-C efflux was determined using the mass-balance approach. In the absence of plants, N addition reduced total soil CO2-C efflux over the 56-d experiment and increased MAOM-C. This was followed by an increase of 366% in microbial biomass (MB-C), indicating a high C assimilation by soil microbes. In the presence of plants, there was evidence of positive rhizosphere priming effect (RPE) at 42-d after planting when N was applied. The new C input by rhizodeposition promoted an increase of 495% and 50% in MB-C under -N and +N addition, respectively. The short-term effect of maize rhizosphere appeared to preserve native SOM and allowed higher incorporation of microbial residues-derived C into the MAOM.

EFFECT OF THE SYMBIOSIS BETWEEN LOLIUM MULTIFLORUM AND THE ENDOPHYTE EPICHLOË OCCULTANS ON NUTRITIONAL QUALITY OF PASTURE IN BIOSOLIDS´ AMENDED SOIL

<p>Biosolids have a high content of stable organic matter, which may be used for the remediation of marginal non-agricultural soils used for pasture production. In Argentina, the aerial biomass of <em>Lolium multiflorum</em> Lam., species is highly infected with the endophyte <em>Epichloë occultans</em>. Endophytes establish a symbiotic relationship with host plants, providing protection and resistance against different stress factors. Since land application of biosolids may rise plant stress, the objective of this work was to analyze the growth and concentration of copper (Cu) and zinc (Zn) in aerial biomass of <em>L. multiflorum</em> in symbiosis (or not) with the endophyte <em>E. occultans</em> on a sandy textured soil amended with biosolids. The association of <em>L multiflorum</em> with the endophyte produced an increase in aerial biomass only in the biosolids´ amended soil. However, the presence of the endophyte did not modify the concentration of Cu or Zn in the aerial biomass of the pasture under the experimental conditions.</p>

Soluble salts, copper, zinc, and solids constituents in surface runoff from cattle manure compost windrows

Larney, F. J., Olson, A. F., Miller, J. J. and Tovell, B. C. 2014. Soluble salts, copper, zinc, and solids constituents in surface runoff from cattle manure compost windrows. Can. J. Soil Sci. 94: 515–527. Composting has become widely adopted by the beef cattle feedlot industry in southern Alberta. Compost windrows subjected to heavy rainfall can lead to runoff whose properties may vary with compost maturity. A rainfall simulator generated runoff on days 18, 26, 40, 54, 81, 109 and 224 of manure composting. Runoff was collected in timed 5-L increments to 30 L, creating the variable “time during runoff event” (TDRE). Calcium, K and S showed significant maturity×TDRE interactions, especially earlier in the composting process, e.g., on day 18, Ca values increased from 34 mg L−1 for the initial 0- to 5-L runoff increment to 43 mg L−1 for the final 25- to 30-L increment. Most significant changes in runoff concentrations occurred between days 26 and 40, e.g., Cu levels fell by 67% and Zn levels by 78%. Even though compost Cu and Zn concentrations were higher during the latter stages of composting, their transport potential in runoff was curtailed due to binding with stable organic matter (OM). The C:N ratio of runoff solids decreased from 10.5 on day 18 to only 4.9 on day 224, suggesting the transport of very stable OM after compost curing. The study showed that runoff quality was influenced by compost maturity, which has implications for the timing of rainfall events relative to the maturity spectrum and the potential risk to surface water quality if runoff is not contained.