Effect of carbon-enriched digestate on the microbial soil activity

Objectives As a liquid organic fertilizer used in agriculture, digestate is rich in many nutrients (i.e. nitrogen, phosphorus, sulfur, calcium, potassium); their utilization may be however less efficient in soils poor in organic carbon (due to low carbon:nitrogen ratio). In order to solve the disadvantages, digestate enrichment with carbon-rich amendments biochar or humic acids (Humac) was tested. Methods Soil variants amended with enriched digestate: digestate + biochar, digestate + Humac, and digestate + combined biochar and humic acids—were compared to control with untreated digestate in their effect on total soil carbon and nitrogen, microbial biomass carbon, soil respiration and soil enzymatic activities in a pot experiment. Yield of the test crop lettuce was also determined for all variants. Results Soil respiration was the most significantly increased property, positively affected by digestate + Humac. Both digestate + biochar and digestate + Humac significantly increased microbial biomass carbon. Significant negative effect of digestate + biochar (compared to the control digestate) on particular enzyme activities was alleviated by the addition of humic acids. No significant differences among the tested variants were found in the above-ground and root plant biomass. Conclusions The tested organic supplements improved the digestate effect on some determined soil properties. We deduced from the results (carbon:nitrogen ratio, microbial biomass and activity) that the assimilation of nutrients by plants increased; however, the most desired positive effect on the yield of crop biomass was not demonstrated. We assume that the digestate enrichment with organic amendments may be more beneficial in a long time-scaled trial.

Productivity of coastal Douglas-fir and western redcedar in response to species mixture, planting density, and soil carbon:nitrogen ratio

Mixed-species plantations have been suggested as ecologically and economically viable alternatives to monocultures. We examined the growth response of coastal Douglas-fir (Pseudotsuga menziesii var. menziesii (Mirb.) Franco) and western redcedar (Thuja plicata Donn ex D. Don in Lamb.) to different species mixtures (Douglas-fir : western redcedar mixtures of 1:0, 1:1, 1:3, and 0:1) and planting densities (500, 1000, and 1500 stems·ha−1) in a dry maritime forest on eastern Vancouver Island, Canada. Twenty-two years postplanting, species mixture significantly affected diameter and height growth (p < 0.001), with stand diameter and height generally decreasing with increasing redcedar composition. Inherent variation in soil productivity across the plantation (carbon:nitrogen ratio) equally constrained stand growth. The widest spacing had larger diameter than the closest spacing (p = 0.025) but the least stand basal area compared with the other spacing treatments (p = 0.003–0.031). Stand volume was significantly affected by mixture × density interaction (p = 0.024) and generally declined with increasing proportion of redcedar and decreasing stand density. In the first decades after plantation establishment, inherent species growth traits and soil fertility were most important in dictating stand productivity. Because of the differences in resource utilization of both species, stand dynamics may change as competition for light and soil resources increases. Evaluation of silvicultural recommendations regarding mixtures of both species will continue with plantation development.

A comparison of composting and vermicomposting for the disposal of poultry waste

Context Poultry products, mostly meat and eggs, provide affordable quality foodstuffs to human populations in Nepal. However, the poultry industry’s by-products, such as litter and offal, also generate potential environmental and human health issues and need a sustainable method of management. Aims The present study compared the effectiveness of vermicomposting by using an exotic earthworm species Eisenia fetida, or effective microorganism-based (EM) composting, of poultry litters in the Terai region of Nepal. Methods Four types of poultry litter, namely, broiler cage litter (parent stock litter), broiler deep litter, commercial layer cage litter and layer deep litter, each combined with earthworms (vermicompost) or effective microorganisms, were subjected to decomposition in beds. A completely randomised design in a 4 × 2 factorial arrangement (poultry litters by Eisenia fetida or effective microorganism) with three replicates per treatment was applied. Key results Macronutrient concentrations, and reduction of the carbon:nitrogen ratio were significantly greater in vermicompost than EM compost. In addition, reduction of the carbon:nitrogen ratio was more significant following vermicomposting for broiler and layer cage litter than in other treatments. The highest initial concentration of N was found in layer cage litter (2.1%) and the lowest in layer deep litter (1.3%) and these increased to 1.5–3.4% and 1.7–1.8% in vermicompost and EM compost respectively. Available phosphorus increased by two- to three-fold in most vermicomposted poultry litters in comparison to initial poultry litters, and a two-fold increase in potassium was likewise achieved. Consistent with these results, worm biomass was significantly higher in layer cage litter and broiler cage litter than in deep litter. More cocoons were evident in layer cage litter, and lowest numbers of cocoon formation were observed in broiler deep litter. Conclusions This comparative study showed that vermicomposting is superior to EM composting for bioconversion of poultry litters into value-added compost. Implications With the adoption of this result, the poultry industry in Nepal could become more sustainable.