Soil Incorporation Research Articles

Deriving Environmental Life Cycle Inventory Factors for Land Application of Garden Waste Products Under Northern European Conditions

The amount of waste which is being recycled is increasing in Europe. Garden waste is increasingly composted and land applied. However, composting to full maturity requires resources in terms of space, equipment and labour. Alternatives could include a simple shredding, or composting for a shorter time. Finally, an option could be to remove trunks and large branches which are not easy to compost and incinerate them to recover energy. In order to assess these options and the associated environmental impacts, it is necessary to have good estimates of emissions and other inventory factors during the different steps of the life cycle of the compost products. Especially, the impacts occurring after land application are difficult to estimate. The objective of the current paper is to estimate environmental inventory factors for land application of four garden waste products: shredded garden waste, shredded garden waste after removal of the woody fraction, immature garden waste compost and mature garden waste compost. Soil incubations of the materials were conducted in order to assess the carbon (C) and nitrogen (N) dynamics occurring after incorporation in soil. Subsequently, the results were used to calibrate the mineralisation kinetics of the materials in the agroecosystem model Daisy. Subsequently, the model was used to simulate C and N dynamics under different environmental conditions and emissions to the environment and used to derive inventory factors. Nine soil and climate combinations were included in the simulation study to cover local conditions commonly found in Northern Europe. The degradability of the garden waste products increased when the woody fraction of garden waste was removed and generally the degradability of the product was decreased by composting. All four products showed initial immobilisation of N in soil, but it was clear that removal of the woody fraction and composting reduced the length and severity of the immobilisation phase. The approach taken in the current paper using soil incubations to estimate decomposition parameters for the materials and subsequently an agroecosystem model to extrapolate the observations proved efficient at estimating inventory factors under various environmental conditions and fertilisation levels. Under low N availability conditions, the harvest factor, which estimates the fraction of N harvested in response to application of an amount of compost ranged between 0.10 and 0.18 for a sandy loam soil and medium precipitation conditions for Northern European while it ranged from negative values to 0.12 under conditions of ample N supply. These results were also clearly reflected in the emission factors for N leaching to the groundwater and losses to surface water, which were higher under high N availability than under low. The harvest factor, emission factors for ammonia, N leaching to ground water and loss to surface water proved to be very dependent on the local conditions like the soil type, precipitation regime and general fertilisation level, whereas the biochemical composition of the materials was of less importance for these factors. In contrast, the C sequestration factor was almost unaffected by the environmental conditions but depended to a large extent on the degradability of the added material.

An Investigation into the Fertilizer Potential of Slaughterhouse Cattle Paunch

Abstract. In Australia, recycling of paunch waste to farmland has been suggested as a cost-effective and practicable environmental option, but little is known about its agronomic value. Experimental work was undertaken to assess potential risks due to weed seed contamination, determine the agronomic response of ryegrass ( L.) to soil incorporation of paunch, and investigate short-term greenhouse gas (GHG) emissions. Five types of paunch with compost ages between 2 and 16 weeks were compared with urea (46% N) and applied at field equivalent rates of 0 (control), 150, and 300 kg ha-1 N. The risk of weed contamination from paunch applied to soil appeared to be negligible; however, techniques that enable seed viability to be determined may be required to fully discard such risk. Average dry matter yield with paunch was ~30% higher than untreated grass, but ~35% lower than with urea. Dry matter yield in paunch-treated grass was between 2500 and 3250 kg ha-1 over five cuts conducted at 25-day intervals. Paunch N responses were between 1.12 and 3.25 kg DM kg-1 N depending on compost age, but lower than with urea N (~6.5 kg DM kg-1 N). Nitrogen use efficiency of paunch ranged between 3% and 20%, compared to about 35% with urea. Nitrogen fertilizer replacement value (NFRV) of paunch was highest in the 6-week-old compost (~60%) and ranged between 20% and 55% across all other organic materials. Short-term N2O emissions were similar (p > 0.05) with both mineral and organic amendments; however, CH4 emissions were higher (p < 0.05) from paunch compared with urea-treated soil. Overall, there appears to be potential for paunch-derived products to be used as a source of C and nutrients in crop production. Industry quality specifications for compost are available, but they need to be expanded to incorporate guidelines relevant to paunch. There is a requirement for the value proposition to industry to be determined, including reduced cost of paunch disposal via gate fees. Keywords: Byproducts, Composting, Fertilizer replacement value, Nutrient recovery, Nutrient use efficiency, Recycling of abattoir-derived waste.

Allelopathic Effects of Three Sweet Potato Cultivars (Ipomoea batatas) on the Invasive Plant Mikania micrantha.

Sweet potato [Ipomoea batatas (L.) Lam] is an important locally grown cash crop in China; it was demonstrated to suppress the invasive plant Mikania micrantha (M. micrantha) H.B.K through strong competitiveness, but its allelopathic effects on this weed were unknown. The present study aimed to explore the allelopathic potential of sweet potato on M. micrantha. The allelopathic effects of water extracts and soil incorporation from leaves of three sweet potato cultivars (SP1, SP0 and SP9) on the sprout seedling growth of invasive plant M. micrantha in Yunnan Province, China, were studied under laboratory and greenhouse conditions. Stem length, root biomass, aboveground biomass and total biomass of M. micrantha were significantly reduced with increasing concentration in both leaf water extracts and leaf soil incorporation of three sweet potato cultivars. Among these, SP1 had the strongest inhibition and the next highest impact was from SP0 with the lowest effect from SP9. The highest inhibition rates were seen for root biomass, followed by total biomass, whereas the lowest impact was on aboveground biomass. The strong correspondence between results for both leaf water extracts and leaf soil incorporation provided a good demonstration that compounds produced by sweet potato have allelopathic effects on M. micrantha. The general inhibition of M. micrantha by sweet potato followed the order among the three sweet potato cultivars tested as SP1, SP0 and SP9. Moreover, the synthetical allelopathic indices of leaf soil incorporation of three cultivars on M. micrantha were generally higher than these of leaf water extracts. Competition and allelopathy have primarily been seen as separate ecological weed management tools, but as these have demonstrated in the case of sweet potato where both mechanisms inhibit weed growth, there is potential for synergism between competition and allelopathy in the reduction of weed infestations.

Litter dynamics of Olea europaea subsp. Europaea residues related to soil properties and microbial N-biomass in a Mediterranean agroecosystem

Residues decomposition is an important process for plant nutritional demands. The present work was conducted in order to investigate the olive tree residues decomposition (leaves and shoots: buried in a horizontal and a sloping site of an organic olive grove) and its impact on soil properties and microbial N-biomass as affected by soil slope. Mean mass loss and C, N, K, and Mg release rates were higher in leaf than in shoots residues in both soil slopes. The incorporation of leaves and shoots in the soil of the olive grove contributed to its enrichment in certain nutrients such as N, K, Ca, and Mg. Soil organic carbon losses were compensated by the residue released soluble C compounds. The macroaggregates formed by fungal hyphae were not stable in water as Water Aggregate Stability tended to decline in the horizontal site and showed no change in the sloping site. The added amounts of N, P, and K by olive tree residues soil incorporation were 6.1, 0.4, and 7.2 kg ha−1 y−1 (sloping site) and 6.8, 0.3, and 8.8 kg ha−1 y−1 (horizontal site), respectively. These amounts are lower than the needed ones for olive trees (15–35 N, 8 P, ≤50 K kg ha−1 y−1), so olive tree growers should use additional fertilization in order to have strong and productive olive trees.

Linking organic matter chemistry with soil aggregate stability: Insight from 13C NMR spectroscopy

Soil aggregation is considered as a crucial process in agro-system sustainability due to the role in soil physical, chemical and biological dynamics. Here we tested the hypothesis that the initial chemical traits of organic matter (OM) may help to explain the variability of soil aggregation dynamics after organic amendment. We characterized ten OM types (alfalfa litter, biochar, cellulose, glucose, green compost, maize litter, manure compost, meat powder, sawdust, and solid digestate) by 13C-CPMAS NMR and elemental chemical features to investigate the effects of amendment quality on soil aggregation. In a manipulative factorial experiment, dry samples (200 g) of three soil types (S1, S2 and S3) with different texture, high pH (7–9), and similar OM content, were incorporated with 4 g (2% w/w) of dry, 2 mm-grounded OM, incubated in mesocosms for 300 days under controlled temperature (18 ± 2 °C night and 24 ± 2 °C day), and sampled at 4 dates for measuring aggregation index (AI), based on water stability of soil aggregates (WSA). We found that meat powder and alfalfa litter induced a rapid initial increase of AI, exceeding that of the controls by one to two orders of magnitude, likely acting as a C source for microbes. Biochar incorporation in soil barely affected AI, with intermediate effects with other OM types. Considering C bond types corresponding to OM 13C-CPMAS NMR spectral regions, carbonyl C was only correlated to early AI, possibly due to overlapping signals of amide structures; O-alkyl C and di-O-alkyl C (carbohydrate fraction) were positively associated to AI, indicating a promoting effect on soil structure, while aromatic C fractions showed an opposite pattern, possibly related to aggregate protection by coatings associated to water repellency, or to direct aggregate internal binding. This study demonstrates that OM chemical quality plays an important role in soil aggregation process, with the molecular composition defined by 13C-CPMAS NMR spectroscopy being more predictive of aggregation dynamics compared to classical elemental features. As such, this study provides a significant novel contribution to clarify the relationships between OM chemistry and soil aggregation.

Fertilizer value and greenhouse gas emissions from solid fraction pig slurry compost pellets

SUMMARYConversion of pig slurry to pellets is a desirable fertilizer option for farmers who want to mitigate environmental pollution from slurry accumulation. The goals of the current investigation were to determine the fertilizer properties of pig slurry solid fraction (SF) pellets and to assess its potential to enhance soil properties in order to reduce ammonia (NH3) volatilization and greenhouse gas (GHG) emissions. Various parameters influence SF-based pellet fertilizer effectiveness: bulking agent use during composting, pellet diameter sizing and soil application type (superficially or incorporated into the soil). Two composts from the same pig slurry SF obtained from a screw press separator were prepared: pig SF compost without a bulking agent (SSFC) and pig SF compost with wood chips as the bulking agent (wood chip compost (WCC)). For each compost type, pellets of two different diameters (6 and 8 mm) were produced. A mesocosm experiment, conducted with maize plants, was used to test the fertilizer value of the considered pellets. In total, three compost fertilizers – SSFC, WCC and nitrogen: phosphorus: potassium mineral fertilizer 15 : 15 : 15, plus one unfertilized control treatment – were applied at the same N rate (equivalent to 200 kg/ha) using two different methods (surface and soil incorporation). After 65 days, above-ground biomass, roots and soil samples were collected and analysed. Subsequently, a second mesocosm study was undertaken to measure NH3and GHG emissions released from pellet fertilization. Ammonia volatilization was determined immediately after pellet application, while carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) emissions were monitored for 57 days. Study results indicated that both pellet types were effective slow-release fertilizers for maize. Additionally, three actions seemed to make the nutrients contained in pig SF compost pellets more available to plants: addition of a bulking agent before composting, use of small diameter pellets and soil incorporation of the fertilizer.

Impacts of wheat straw addition on dissolved organic matter characteristics in cadmium-contaminated soils: Insights from fluorescence spectroscopy and environmental implications

Incorporating straw in soil can change the dissolved organic matter (DOM) content and also affect the mobility and solubility of soil pollutants. However, few studies have focused on the spectral features of DOM released by soil after amendment with crop residues. In this study, excitation-emission matrix (EEM) fluorescence and UV–visible absorbance spectroscopy were used to monitor the quality and quantity of the DOM derived from wheat straw incorporation in the soil. We found remarkable changes in the dissolved organic carbon (DOC) concentration (0.10–0.34 g kg−1). But the mean DOC concentrations were lower in the cadmium (Cd2+) added treatments compared with the control treatment due to additional Cd2+. The specific UV–visible absorbance at 254 nm was positively correlated with Cd2+ content, thereby suggesting a strong relationship between aromatic materials and heavy metals. Three fluorescent components were identified by EEM fluorescence combined with parallel factor analysis (PARAFAC) modeling, i.e., UVC humic-like, fulvic acid-like, and tryptophan-like. The relative abundances of these three components and dynamic variations in fluorescent indices predicted the changes in DOM composition during the wheat straws decomposition process. Therefore, the findings obtained in this study can be utilized to evaluate the variations in DOM for soil incorporated with straws in order to support agricultural production and overcome the heavy metal pollution.

Biochar amendment changes temperature sensitivity of soil respiration and composition of microbial communities 3 years after incorporation in an organic carbon-poor dry cropland soil

Topsoil samples were collected from plots in a dry cropland in the North China Plain 3 years after a single incorporation of biochar at 20 and 40 t ha−1 and analyzed for abundances and composition of microbial community and for respiration under controlled laboratory conditions at 15, 20, and 25 °C. The addition of biochar generally reduced soil respirations at the three temperatures and the temperature sensitivity (Q10) at 15–20 °C. Biochar amendment significantly increased bacterial 16S rRNA gene abundances and fungal ITS gene diversity and induced clear changes in their community compositions due to improvements in soil chemical properties such as soil organic C (SOC) and available N contents and pH. Illumina Miseq sequencing showed that the relative abundances of Actinobacteria, Gammaproteobacteria, Firmicutes, and Alternaria within Ascomycota, capable of decomposing SOC, were significantly decreased under biochar at 40 t ha−1. The Q10 values at 15–20 °C were significantly correlated with fungal diversity and dehydrogenase activity. Our results suggest that after 3 years a single biochar amendment could induce a shift in microbial community composition and functioning towards a slower organic C turnover and stability to warming, which may potentially reduce soil C loss in dryland under climate warming in the future.

The Effect of Alfalfa Residue Incorporation on Soil Bacterial Communities and the Quantity of Verticillium dahliae Microsclerotia in Potato Fields in the Columbia Basin of Washington State, USA

Verticillium wilt, caused by the soil-borne fungus Verticillium dahliae, is one of the most important diseases of potato in North America. Soil incorporation of alfalfa residues prior to planting potato could be a nonchemical Verticillium wilt management tactic by reducing the number of viable microsclerotia in field soil. Verticillium dahliae microsclerotia were quantified in field soils where organic material from alfalfa was incorporated, and numbers of microsclerotia were compared to fields where alfalfa residue was not incorporated. In addition, bacterial metagenomics was utilized to characterize soils where organic material from alfalfa was or was not incorporated to determine if alfalfa residue incorporation facilitates the formation of soils that suppress or kill V. dahliae microsclerotia. The number of V. dahliae microsclerotia in soil was greater (P = 0.0003) in fields where crop residue was incorporated than fields without incorporation when chloropicrin was used as a fumigant. Conversely, the number of V. dahliae microsclerotia observed in potato plants did not differ (P = 0.4020) between fields where residues were or were not incorporated if chloropicrin was used. Alfalfa residue incorporation did not significantly alter the soil bacterial metagenome compared to fields not subject to residue incorporation in both years of study. Despite these conclusions, the method can be employed to analyze the effect of grower practices with the intent of linking a field practice to increasing soil bacterial diversity and decreasing Verticillium wilt severity on potato.

Reliability of Soil Sampling Method to Assess Visible Biodegradable Mulch Fragments Remaining in the Field after Soil Incorporation

Biodegradable mulches (BDMs) provide a unique advantage to growers in that they can be tilled into the soil after use, eliminating disposal costs that include time, labor, and equipment needs. Biodegradation of BDMs in the soil can be assessed by the presence of visible mulch fragments; although this is not a direct measure of biodegradation, it provides an initial estimation of mulch biodegradation. We carried out three field experiments to develop a protocol for quantifying BDM fragments in the soil after soil incorporation of mulch. Expt. 1 was done at Mount Vernon, WA, and Knoxville, TN, using five BDMs in four replications, including a polyethylene (PE) mulch reference treatment (three replications and at Mount Vernon only), and a ʽCinnamon Girl’ pumpkin (Cucurbita pepo) test crop. At the end of the growing season, mulches were tilled into the soil to a depth of 6 inches and within 16 days, five soil samples were collected with a golf hole cutter (4 inches diameter and 6 inches deep). Fifty-nine percent of the PE mulch fragments were recovered from the reference treatment. Among the remaining treatments, there was a high plot-to-plot variation as to the percent of the BDM recovered (3% to 95% at Mount Vernon, 2% to 88% at Knoxville). To exclude the possibility of mulch degradation impacting mulch recovery, in Expts. 2 and 3 (at Mount Vernon only), one BDM was laid, then tilled into the soil and sampled using the same sampling core as in Expt. 1, but all in 1 day. In Expt. 2, 15 soil samples were collected per plot, which recovered 70% of the mulch, and in Expt. 3, the entire plot was sampled by collecting 128 soil samples per plot, which recovered 62% of the mulch. In summary, sampling with a relatively large core recovered less than 70% of tilled-in mulch, there was high variability between plots within each treatment because of uneven distribution of the mulch fragments in the plot, and even 50 samples per plot did not provide an accurate estimate of the amount of mulch remaining in the field. Thus, soil sampling with a large core was ineffective, and new sampling methods are needed to assess the amount of BDM remaining in the field after soil incorporation.

Nitrogen mobility, ammonia volatilization, and estimated leaching loss from long-term manure incorporation in red soil

Nitrogen (N) loss from fertilization in agricultural fields has an unavoidable negative impact on the environment and a better understanding of the major pathways can assist in developing the best management practices. The aim of this study was to evaluate the fate of N fertilizers applied to acidic red soil (Ferralic Cambisol) after 19 years of mineral (synthetic) and manure fertilizer treatments under a cropping system with wheat-maize rotations. Five field treatments were examined: control (CK), chemical nitrogen and potash fertilizer (NK), chemical nitrogen and phosphorus fertilizer (NP), chemical nitrogen, phosphorus and potash fertilizer (NPK) and the NPK with manure (NPKM, 70% N from manure). Based on the soil total N storage change in 0–100 cm depth, ammonia (NH3) volatilization, nitrous oxide (N2O) emission, N plant uptake, and the potential N leaching loss were estimated using a mass balance approach. In contrast to the NPKM, all mineral fertilizer treatments (NK, NP and NPK) showed increased nitrate (NO3−) concentration with increasing soil depth, indicating higher leaching potential. However, total NH3 volatilization loss was much higher in the NPKM (19.7%) than other mineral fertilizer treatments (≤4.2%). The N2O emissions were generally low (0.2–0.9%, the highest from the NPKM). Total gaseous loss accounted for 1.7, 3.3, 5.1, and 21.9% for NK, NP, NPK, and NPKM treatments, respectively. Estimated N leaching loss from the NPKM was only about 5% of the losses from mineral fertilizer treatments. All data demonstrated that manure incorporation improved soil productivity, increased yield, and reduced potential leaching, but with significantly higher NH3 volatilization, which could be reduced by improving the application method. This study confirms that manure incorporation is an essential strategy in N fertilization management in upland red soil cropping system.

Surface application of acidified cattle slurry compared to slurry injection: Impact on NH3, N2O, CO2 and CH4 emissions and crop uptake

Intensive cattle production has a severe environmental impact due, partly, to ammonia (NH3) and greenhouse gas emissions resulting from handling of the large amounts of slurry (liquid manure) produced. The present study aimed to compare, in terms of NH3, N2O, CH4 and CO2 emissions and crop yield, slurry injection in soil (reference technique) and a combined approach of slurry (S) treatment (by separation and/or acidification) followed by surface application. A pot experiment was performed over 67days with an oat forage crop amended with S or the separated liquid fraction (LF), with and without acidification to pH5.5. Injection of S was compared with surface application of treated S followed or not by soil incorporation. Soil injection reduced NH3 emissions to insignificant levels and did not increase N2O emissions, while maintaining oat yields similar to those for the surface application of S. Surface application of acidified S or acidified LF led to NH3 emissions <7% of applied NH4+-N, with no increase of N2O emissions relative to surface application of S. Furthermore, a stronger decrease of N losses can be achieved by surface application of acidified S followed by soil incorporation. However, surface application of LF without incorporation led to significant NH3 emissions and therefore is not recommended. Significantly lower (p<0.05) CH4 emissions were observed with application of acidified slurry and LF, relative to the respective non-acidified treatments. These results show that surface application of acidified slurry is a good alternative to slurry injection when the latter technique cannot be used.

Effects of rate and application method on the efficacy of metam sodium to reduce clubroot (Plasmodiophora brassicae) of canola

Clubroot, caused by Plasmodiophora brassicae, has become a serious threat to canola (Brassica napus) production in western Canada. Experiments were conducted to evaluate the effect of rate of metam sodium fumigant (dithiocarbamate; sodium N-methyldithiocarbamate; trade name Vapam) and application methods including watering, soil surface covering, and soil incorporation on clubroot of canola. At higher rates (0.4–1.6 mL−1 L soil) metam sodium increased canola seedling emergence and plant health, and reduced root hair infection, gall weight and clubroot severity under greenhouse conditions. Metam sodium application improved subsequent plant growth and reduced clubroot severity, but land preparation and volume of water applied did not affect efficacy. The incorporation of metam sodium into the soil and plastic covering after application improved fumigant efficacy. The study showed that soil fumigation with metam sodium can reduce clubroot severity and improve plant health in the subsequent canola crop.

Deterioration pattern of six biodegradable, potentially low-environmental impact mulches in field conditions

Polyethylene plastic mulches are widely used in agriculture due to the countless advantages they have. However, the environmental problems associated with their use have led us to look for alternative mulch materials which degrade naturally and quickly, impact the environment less and function satisfactorily. To this end, biodegradable plastics and paper mulches are being used, but aspects related to their degradation should be studied more in-depth. This work provides the deterioration pattern of six biodegradable mulch materials (i.e. vegetable starch, polylactic acid plastic films or paper mulches) in horticultural crop in the edaphoclimatic conditions of Central Spain in two situations: over the lifetime of the mulches and after being incorporated into the soil. In the first situation, the deterioration levels were evaluated by recording the puncture resistance, weight and area covered in the above-soil and the in-soil part, and after soil incorporation by the number of fragments, their surfaces and weight. In the above-soil part, biodegradable plastics experienced further deterioration, particularly with no crop, while the paper mulch remained practically intact. However, the in-soil paper experienced complete and rapid degradation. At 200 days after soil incorporation, mulch residues were scarce, with the environmental effects it entails. These findings offer practical implications regarding the type of crop. The measurement of the surface covered, rather than the weight, was shown to be a more reliable indicator of the degradation of mulches. Furthermore, visual estimation was found to underestimate the functionality of mulches in comparison to that of the measurement of the surface covered.

Simulating the Transport and Fate of Trifluralin in Soil

Understanding herbicide dynamics in agricultural soils is crucial to evaluate herbicide application efficiency and its environmental consequences. A model for herbicide trifluralin (α,α,α-reifluoro-2,6-dinitro-N,N-dipropyl-ρtoluidine) dynamics namely runoff, erosion, leaching, volatilization, and degradation losses in agricultural soils was developed using the software package Structural Thinking and Experiential Learning Laboratory with Animation (STELLATM). The model was calibrated using field data with a good agreement between model predictions and field measurements before its applications. A simulation scenario was then performed to predict trifluralin dynamics in a 1.26 ha soybean field. Simulation results showed that in general, the rate of water runoff decreased with the rate of rainfall; however, the rates of trifluralin and sediment losses in runoff depended not only on the rate of rainfall but also on the content of trifluraline in the liquid and solid phases. The rates of trifluralin leaching and volatilization decreased sharply within the first couple of days following the surface spray of trifluralin due to its strong adsorption and soil incorporation. Simulation results further revealed that the rate of trifluralin degradation in the soil decreased exponentially with time. About 6% of the total applied trifluralin remained in the soil at the end of the simulation period (120 days). This study suggests that the model, developed with STELLATM, is a useful tool for estimating herbicide dynamics in agricultural soils.

Nitrogen losses to the environment following food-based digestate and compost applications to agricultural land

The anaerobic digestion of food waste for energy recovery produces a nutrient-rich digestate which is a valuable source of crop available nitrogen (N). As with any ‘new’ material being recycled to agricultural land it is important to develop best management practices that maximise crop available N supply, whilst minimising emissions to the environment. In this study, ammonia (NH3) and nitrous oxide (N2O) emissions to air and nitrate (NO3−) leaching losses to water following digestate, compost and livestock manure applications to agricultural land were measured at 3 sites in England and Wales. Ammonia emissions were greater from applications of food-based digestate (c.40% of total N applied) than from livestock slurry (c.30% of total N applied) due to its higher ammonium-N content (mean 5.6 kg/t compared with 1–2 kg/t for slurry) and elevated pH (mean 8.3 compared with 7.7 for slurry). Whilst bandspreading was effective at reducing NH3 emissions from slurry compared with surface broadcasting it was not found to be an effective mitigation option for food-based digestate in this study. The majority of the NH3 losses occurred within 6 h of spreading highlighting the importance of rapid soil incorporation as a method for reducing NH3 emissions. Nitrous oxide losses from food-based digestates were low, with emission factors all less than the IPCC default value of 1% (mean 0.45 ± 0.15%). Overwinter NO3− leaching losses from food-based digestate were similar to those from pig slurry, but much greater than from pig farmyard manure or compost. Both gaseous N losses and NO3− leaching from green and green/food composts were low, indicating that, in these terms, compost can be considered as an ‘environmentally benign’ material. These findings have been used in the development of best practice guidelines which provide a framework for the responsible use of digestates and composts in agriculture.

除草剤(レナシル)の土壌混和処理に対する2・3の作用特性(年次講演会要旨)

除草剤(レナシル)の土壌混和処理に対する2・3の作用特性(年次講演会要旨)

Assessment of N2O emissions from a fertilised vegetable cropping soil under different plant residue management strategies using 15N tracing techniques

Combined application of plant residues and N fertilisers strongly affect soil mineral N dynamics and N2O emissions depending on the quality of the plant residues, their application methods and other management strategies. We investigated the effect of combined application of two vegetable plant residues (cauliflower and sweet corn) and 15N fertiliser on N dynamics and N2O emission in a glasshouse pot study. The experiment was conducted under two residue management practices (soil incorporation vs surface mulching) over 98days with growing basil (Ocimum basilicum) plants. We also assessed the efficacy of applying the nitrification inhibitor, 3,4-dimethylpyrazole phosphate (DMPP) to the plant residues, for reducing N loss and mitigating N2O emissions. Application of plant residues, both on the soil surface or into soil, resulted in net N mineralisation and increased cumulative N2O emission compared with the application of N fertiliser alone. Soil surface mulching of sweet corn decreased total and residue-induced cumulative N2O emission compared with the incorporation method, while it showed opposite effect on N2O emissions from cauliflower residue. The application of DMPP with sweet corn residue reduced total, residue- and fertiliser-induced N2O emissions; however its application with cauliflower residue did not show any mitigating effect on the N2O emissions. The residue application methods and the use of DMPP did not significantly affect 15N recovery by the basil plants. In contrast, soil incorporation of these residues doubled the microbial immobilisation of applied 15N into soil organic matter. Linear regression analysis of N2O emission during the experimental period indicated that in the treatments without DMPP application, soil NO3−-N concentration was the most important factor in controlling the magnitude of N2O emissions, while the application of DMPP changed the dominant regulating factor from NO3−-N to NH4+-N concentration.

Co-ensiling, co-composting and anaerobic co-digestion of vegetable crop residues: Product stability and effect on soil carbon and nitrogen dynamics

Nitrogen (N)-rich vegetable crop residues left in the field may result in a high risk for N losses during autumn. Removal and conservation of these residues followed by reuse in the field could contribute to improved recycling of nutrients, but some form of processing is required to allow storage before re-application. We have compared co-ensiling, co-composting and anaerobic co-digestion as conservation and valorization options for fresh crop residues. We studied (1) the product quality and stability and (2) the short-term effects of application of these silages, composts and digestates on soil C and N mineralization and N2O emissions. Ensiling resulted in highly biodegradable products with a low pH (4.2-5.2) and more NH4+-N compared to composts. Consequently, soil incorporation of silages resulted in higher net C mineralization (up to 47% after 82days) and microbial biomass C (up to 93μgCg−1 soil after six weeks), and temporary N immobilization (up to 42mgkg−1 soil). Digestates and composts led to lower C mineralization rates (between 2 and 27%) and microbial biomass C (max. 51μgCg−1 soil) and no net N immobilization nor mineralization. Application of digestates resulted in high mineral N contents (47–192mgkg−1 soil) and a decrease of the soil pH. In all three treatments, short-term N2O losses after soil application were very small (<0.11kgNha−1 after 12days). Growers can choose the most appropriate treatment option and application moment and location, depending on the local soil and crop requirements and the on-farm facilities. Furthermore, we conclude that the parameters biodegradation potential (based on the biochemical composition) and oxygen uptake rate have potential as less time-consuming proxies for C mineralization to assess the product stability.

Coupling sorghum biomass and wheat straw to minimise the environmental impact of bioenergy production

The reform of the European sugar market in 2006 paved the way for the development of new agricultural value chains in the Po Valley (Italy). A value chain based on the use of biomass sorghum (Sorghum bicolor (L.) Moench) to produce electricity in a medium-scale power plant was investigated. A Life Cycle Assessment was carried out to explore the environmental impact and energy performance of power generation from three biomass sorghum genotypes characterized by different earliness (early, medium-late and late) in the Po Valley (Italy). To fully cover the plant needs, sorghum was complemented by winter wheat straw. Productivity and losses of sorghum for the past 39 years as simulated in Serra et al. (2017) were used to produce a probability distribution of environmental impacts. Soil organic carbon change relative to the straw removal and sorghum incorporation in soil as well as indirect land use change CO2 emissions for the substitution of sugar crops with energy crops were also accounted for. To test the influence of the assumptions an extensive sensitivity analysis over several parameters was performed. The lowest average GHG emissions (68.9 g CO2eq.MJ−1) were achieved with the late genotype while medium-late and early genotypes emitted 73.5 g CO2eq. MJ−1 and 76.8 g CO2eq.MJ−1, respectively. Despite the conservative assumptions, the bioenergy system contributed on average 47.7% less GHG than a natural gas power plant. In the lowest productivity years the sorghum based energy system emitted 52% less GHG than the Italian electricity mix.Overall, when harvesting and bailing failed due to unfavourable weather conditions, the lowest GHG emissions were found, thanks to the increased replacement of sorghum with straw. In fact, soil incorporation of sorghum biomass resulted in more nutrients added to the soil than with incorporation of wheat straw. Considering that GHG emissions decreased linearly when sorghum biomass yield increased, the highest reductions of GHG were found with late genotypes, that produced the highest yields. The lowest GHG emissions were found when harvesting failed, as the fertilizer debit of straw is lower than the fertilizer credit of sorghum. However, since carbon and nutrients storage in the soil is not rewarded monetarily, this option will not correspond to an optimal profit as the risk of failures are highest with late genotype.All other environmental impacts assessed were higher for the sorghum based system than for the fossil alternatives. It was found that the presence of DeNOx SNCR (Selective Non-Catalytic Reduction) technology achieved the expected mitigation of acidification potential and photochemical oxidant formation but at the expenses of an increased climate change impact, due to additional N2O emissions.