Andreas de Neergaard

Potential of aeration flow rate and bio-char addition to reduce greenhouse gas and ammonia emissions during manure composting.

Aeration is an important factor influencing CO2, CH4, N2O and NH3 emissions from the composting process. Both CH4 and N2O are potent greenhouse gases (GHG) of high importance. Here, we examined the effects of high and low aeration rates together with addition of barley straw with and without bio-char on GHG and NH3 emissions from composting cattle slurry and hen manure in small-scale laboratory composters. Depending on treatment, cumulative C losses via CO2 and CH4 emissions accounted for 11.4-22.5% and 0.004-0.2% of initial total carbon, while N losses as N2O and NH3 emissions comprised 0.05-0.1% and 0.8-26.5% of initial total nitrogen, respectively. Decreasing the flow rate reduced cumulative NH3 losses non-significantly (by 88%) but significantly increased CH4 losses (by 51%) from composting of cattle slurry with barley straw. Among the hen manure treatments evaluated, bio-char addition to composting hen manure and barley straw at low flow rates proved most effective in reducing cumulative NH3 and CH4 losses. Addition of bio-char in combination with barley straw to hen manure at both high and low flow rates reduced total GHG emissions (as CO2-equivalents) by 27-32% compared with barley straw addition alone. Comparisons of flow rates showed that low flow could be an alternative strategy for reducing NH3 losses without any significant change in N2O emissions, pointing to the need for well-controlled composting conditions if gaseous emissions are to be minimised.

Decomposition of white clover (Trifolium repens) and ryegrass (Lolium perenne) components: C and N dynamics simulated with the DAISY soil organic matter submodel

Using data from a decomposition study, we aimed to test the parameterisation of the soil organic matter module of the DAISY model, and link measurable plant litter fractions (lignin, water-soluble) with the model defined plant litter pools. Shoot and root material from perennial ryegrass and white clover was incubated in a sandy loam soil at 9 °C for 94 days. Accumulated CO2 evolution, soil mineral nitrogen (N) and soil microbial biomass-N were measured during the incubation. Marked differences in decomposition rates between above- and below-ground material as well as between the two plant species were observed. The DAISY model was used to interpret the incubation results. Decomposition rates and utilisation efficiencies were modified, under the constraint that rates of specific pools were independent of the type of material, to obtain good agreement between observed and simulated values. Measurable quality parameters were evaluated against the sizes of pools in the model and measured fluxes. The size of the slowest decomposing fraction of the DAISY model was proportional to the lignin content of the plant material, but twice as large. The easily decomposable fraction in the model was well correlated with the water-soluble fraction of the plant material (r2=0.84). The size of this pool in the model was larger than the water-soluble fraction of the plant material in three of the five plant materials. The initial carbon mineralisation was correlated with water-solubility of the plant material and total mineralisation with the lignin:N ratio. Net N mineralisation was well correlated with the C:N ratio and the N content of the added material. At the end of the experiment, the mineral N content was overestimated by the DAISY model for all treatments, except one. A soil microbial residual pool, consisting of undecomposed microbial tissue is suggested as a possible N-sink during the incubation. The study demonstrated a correlation between the model-defined pools and chemical plant fractions, but also that the pools in the model were larger than their measured counterparts.

Distribution of assimilated carbon in plants and rhizosphere soil of basket willow (Salix viminalis L.)

Willow is often used in bio-energy plantations for its potential to function as a renewable energy source, but knowledge about its effect on soil carbon dynamics is limited. Therefore, we investigated the temporal variation in carbon dynamics in willow, focusing on below-ground allocation and sequestration to soil carbon pools. Basket willow plants (Salix viminalis L.) in their second year of growth were grown in pots in a greenhouse. At five times during the plants growth, namely 0, 1, 2, 3 and 4 months after breaking winter dormancy, a subset of the plants were continuously labelled with 14CO2 in an ESPAS growth chamber for 28 days. After the labelling, the plants were harvested and separated into leaves, first and second year stems and roots. The soil was analysed for total C and 14C content as well as soil microbial biomass. Immediately after breaking dormancy, carbon stored in the first year stems was relocated to developing roots and leaves. Almost half the newly assimilated C was used for leaf development the first month of growth, dropping to below 15% in the older plants. Within the second month of growth, secondary growth of the stem became the largest carbon sink in the system, and remained so for the older age classes. Between 31 and 41% of the recovered 14C was allocated to below-ground pools. While the fraction of assimilated 14C in roots and root+soil respiration did not vary with plant age, the amount allocated to soil and soil microbial biomass increased in the older plants, indicating an increasing rhizodeposition. The total amount of soil microbial biomass was 30% larger in the oldest age class than in an unplanted control soil. The results demonstrate a close linkage between photosynthesis and below-ground carbon dynamics. Up to 13% of the microbial biomass consisted of carbon assimilated by the willows within the past 4 weeks, up to 11% of the recovered 14C was found as soil organic matter.

Alternate partial root-zone irrigation induced dry/wet cycles of soils stimulate N mineralization and improve N nutrition in tomatoes

Given the same amount of irrigation volume, applying alternate partial root-zone irrigation (PRI) has improved crop N nutrition as compared to deficit irrigation (DI), yet the mechanisms underlying this effect remain unknown. Therefore, the objective of this study was to investigate whether PRI induced soil dry/wet cycles facilitate soil organic N mineralization hereby contributing to the improvement of N nutrition in tomatoes. The plants were grown in split-root pots in a climate-controlled glasshouse and were subjected to PRI and DI treatments during early fruiting stage. 15N-labeled maize residues were incorporated into the soils. Results showed that PRI resulted in 25% higher net 15N mineralization than did DI, indicating that the enhanced mineralization of soil organic N alone could account for the 16% increase of N accumulation in the PRI than in the DI plants. The higher net N mineralization under PRI was coincided with an intensified soil microbial activity. In addition, even though soil chloroform fumigation labile carbon (CFL-C, as an index of microbial biomass) was similar for the two irrigation treatments, a significant increase of chloroform fumigation labile nitrogen (CFL-N) was found in the PRI wetting soil. Consequently, the C:N ratio of the chloroform fumigation labile pool was remarkably modified by the PRI treatment, which might indicate physiological changes of soil microbes or changes in labiality of soil organic C and N due to the dry/wet cycles of soils, altering conditions for net N mineralization. Moreover, in both soil compartments PRI caused significantly less extractable organic carbon (EOC) as compared with DI; whilst in the PRI wetting soil significantly higher extractable organic nitrogen (EON) was observed. A low EOC:EON ratio in the PRI wetting soil may indicate an increasing net mineralization of the organic N as a result of microbial metabolism. Conclusively, PRI induced greater microbial activity and higher microbial substrates availability are seemingly responsible for the enhanced net N mineralization and improved N nutrition in tomato plants.

Alternate partial root-zone irrigation improves fertilizer-N use efficiency in tomatoes

The objective of this study was to investigate the comparative effects of alternative partial root-zone irrigation (PRI) and deficit irrigation (DI) on fertilizer-N use efficiency in tomato plants under mineral N and organic N fertilizations. The plants were grown in split-root pots in a climate-controlled glasshouse and were subjected to PRI and DI treatments during early fruiting stage. When analyzed across the N fertilizer treatments, PRI treatment led to significantly higher N yield, agronomic N use efficiency (ANUE), and apparent N recovery efficiency (ANRE) as compared with the DI treatment, indicating significantly higher fertilizer-N use efficiency and soil N availability as well as enhanced plant’s N acquisition ability in the PRI treatment. Analysis across the irrigation treatments showed that the mineral N fertilizer treatment (MinN) significantly increased N yield, ANUE and ANRE relative to the organic N fertilizer treatment (OrgN). Compared with DI, the rhizosphere and bulk soil mineral N content in the soil were significantly lowered in the PRI treatment, indicating the enhanced root N uptake efficiency. It is suggested that PRI-enhanced soil water dynamics may have increased soil nitrate mass/diffusive flow to the root surfaces and root N uptake efficiency in the wetting soil and stimulated soil N mineralization and plant N demand, contributing to the improved fertilizer-N use efficiency in the PRI relative to the DI treatment.

Organic farm conventionalisation and farmer practices in China, Brazil and Egypt

Certified organic agriculture stipulates a range of principles and standards, which govern farmer practices. The recent global expansion of organic agriculture has raised new challenges for organic agriculture, particularly whether management practices in organic farms are subject to the forces of conventionalisation. We studied changes in agroecological practices in certified organic farms in China, Brazil and Egypt. The study takes departure in the conventionalisation hypothesis and the analysis is framed using organic and agroecological principles. The study focuses on agroecological design principles, inherent to organic agriculture, of diversity in crop production, pest, disease and weed management, and soil fertility management. The research design was as a multiple case study of five cases in China, Brazil and Egypt. We show that the adoption of organic agriculture has induced fundamental changes in organic farmer management practices, although agroecological practices of organic farmers do not fulfil organic principles. The forces of conventionalisation exert a strong influence on changes in organic farmer practices. Organic ‘niche’ market crops with a high-value influence organic farmers’ management decisions, particularly regarding the prioritisation of diversity in the cropping systems for agroecological purposes. The farming systems have therefore not undergone major changes of their cropping patterns. Furthermore, there was a general heavy reliance upon input substitution for pest and soil fertility management. This study thus presents new data and a novel analysis of the implications at the farm scale of the global expansion of organic agriculture, and the influence of conventionalisation on farmers practices.

A comparative study of farm nutrient budgets and nutrient flows of certified organic and non-organic farms in China, Brazil and Egypt

Increased demand for certified organic products has led to an increase in the number of certified organic farms in developing countries. Knowledge of farmer nutrient management practices on certified organic farms in developing countries is limited. Thus, the aim of this study was to investigate the impact of the adoption of certified organic agriculture on farm nutrient flows and nutrient budgets, and evaluate to which degree organic farms comply with organic principles relating to nutrient management. The study is based on five case studies of different types of certified organic farming systems in Brazil, Egypt and China. Farm nutrient flows and nutrient budgets for nitrogen, phosphorous and potassium were created for each farm. Four of the five organic systems studied had nutrient surpluses on the farm budget. The surpluses were of varying magnitude. The main difference between organic and non-organic farm nutrient flows was the replacement of mineral fertilizers with organic inputs. However, the magnitude of nutrient flows were generally similar for organic and non-organic farms. Certified organic farms with positive nutrient budgets had a heavy reliance on external inputs. Continued high dependence on an external supply of nutrients, which typically originate from mineral sources, poses a significant challenge to organic farmers’ fulfilment of the principles of organic agriculture.

Greenhouse gas emissions from passive composting of manure and digestate with crop residues and biochar on small-scale livestock farms in Vietnam

This study investigated the effects of different mixing ratios of crop residues and biochar with liquid digestate from anaerobically treated pig manure on CH4, CO2, and N2O emissions over 84 days in a system of passive aeration composting, resembling typical Vietnamese solid manure storage conditions. Two treatments with solid manure were included for comparison. The results showed that C losses through CH4 and CO2 emissions accounted for 0.06–0.28% and 1.9–26.7%, respectively, of initial total C. CH4 losses accounted for just 0.4–4.0% of total C losses. Total N losses accounted for 27.1–40% of initial total N in which N2O emissions corresponded to 0.01–0.57% of initial total N, and hence accounted for only 0.1–1.8% of total N losses. It is assumed that the remainder was either the result of denitrification losses to N2 or ammonia volatilization. The composting of biochar (B) or crop residue with digestate (D) showed significantly lower CH4 and N2O emissions compared with composting manure (M) (p < .05). The composting of digestate with biochar showed significantly lower CO2 and CH4 emissions and significantly higher N2O emissions compared to the composting of digestate with rice straw (RS) (p < .05). The combined composting of digestate with biochar and rice straw (D + B + RS5:0.3:1) showed significantly reduced N2O emissions compared with composting digestate with biochar with alone (p < .05). Composting sugar cane bagasse (SC) with digestate (D + SC) significantly reduced CH4 and N2O emissions compared with the composting of rice straw with digestate (D + RS3.5:1 and D + RS5:1) (p < .05).

Effect of 15n-labeled hairy vetch and nitrogen fertilization on maize nutrition and yield under no-tillage¹

This study evaluated the effect of hairy vetch (Vicia villosa Roth) as cover crop on maize nutrition and yield under no tillage using isotope techniques. For this purpose, three experiments were carried out: 1) quantification of biological nitrogen fixation (BNF) in hairy vetch; 2) estimation of the N release rate from hairy vetch residues on the soil surface; 3) quantification of 15N recovery by maize from labeled hairy vetch under three rates of mineral N fertilization. This two-year field experiment was conducted on a sandy Acrisol (FAO soil classification) or Argissolo Vermelho distrofico arenico (Brazilian Soil Classification), at a mean annual temperature of 18 oC and mean annual rainfall of 1686 mm. The experiment was arranged in a double split-plot factorial design with three replications. Two levels of hairy vetch residue (50 and 100 % of the aboveground biomass production) were distributed on the surface of the main plots (5 x 12 m). Maize in the sub-plots (5 x 4 m) was fertilized with three N rates (0, 60, and 120 kg ha-1 N), with urea as N source. The hairy vetch-derived N recovered by maize was evaluated in microplots (1.8 x 2.2 m). The BFN of hairy vetch was on average 72.4 %, which represents an annual input of 130 kg ha-1 of atmospheric N. The N release from hairy vetch residues was fast, with a release of about 90 % of total N within the first four weeks after cover crop management and soil residue application. The recovery of hairy vetch 15N by maize was low, with an average of 12.3 % at harvest. Although hairy vetch was not directly the main source of maize N nutrition, the crop yield reached 8.2 Mg ha-1, without mineral fertilization. There was an apparent synergism between hairy vetch residue application and the mineral N fertilization rate of 60 kg ha-1, confirming the benefits of the combination of organic and inorganic N sources for maize under no tillage.

Potential of three microbial bio-effectors to promote maize growth and nutrient acquisition from alternative phosphorous fertilizers in contrasting soils

BackgroundAgricultural production is challenged by the limitation of non-renewable resources. Alternative fertilizers are promoted but they often have a lower availability of key macronutrients, especially phosphorus (P). Biological inoculants, the so-called bio-effectors (BEs), may be combined with these fertilizers to improve the nutrient use efficiency.MethodsThe goal of this study was to assess the potential of three BEs in combination with alternative fertilizers (e.g., composted manure, biogas digestate, green compost) to promote plant growth and nutrient uptake in soils typical for various European regions. Pot experiments were conducted in Czech Republic, Denmark, Germany, Italy, and Switzerland where the same variety of maize was grown in local soils deficient in P in combination with alternative fertilizers and the same set of BEs (Trichoderma, Pseudomonas, and Bacillus strains). Common guidelines for pot experiment implementation and performance were developed to allow data comparison, and soils were analyzed by the same laboratory.ResultsEfficiency of BEs to improve maize growth and nutrient uptake differed strongly according to soil properties and fertilizer combined. Promising results were mostly obtained with BEs in combination with organic fertilizers such as composted animal manures, fresh digestate of organic wastes, and sewage sludge. In only one experiment, the nutrient use efficiency of mineral recycling fertilizers was improved by BE inoculation.Conclusions These BE effects are to a large extent due to improved root growth and P mobilization via accelerated mineralization.Graphical abstractPossible modes of action of bio-effectors.