Digested Pig Slurry Research Articles

Composting of the solid fraction of digestate derived from pig slurry: Biological processes and compost properties

The aim of this paper was to assess the characteristics of the solid fractions (SF) obtained by mechanical separation of digestate, their compostability and compost quality. To do so, the SF of digestates obtained from anaerobic digestion of pig slurry, energy crops and agro-industrial residues were sampled in five plants located in Northern Italy. Results obtained indicated that anaerobic digestion by itself promoted the high biological stability of biomasses with a Potential Dynamic Respiration Index (PDRI) close to 1000mgO2kgVS−1h−1. Subsequent composting of digestates, with an added bulking agent, did not give remarkably different results, and led only to a slight modification of the characteristics of the initial non-composted mixtures; the composts obtained fully respected the legal limits for high quality compost. Chemical studies of organic matter composition of the biomasses by using CP MAS 13C NMR, indicated that the compost was composed of a high relative content of O-alkyl-C (71.47% of total C) (cellulose and hemicelluloses) and a low alkyl-C (12.42%) (i.e. volatile fatty acids, steroid-like molecules, aliphatic biopolymers and proteins).

Greenhouse gas emissions and characteristics of wheat (Triticum ssp. L) amended with anaerobically digested pig slurry for biogas production

Greenhouse gas emissions and characteristics of wheat (Triticum ssp. L) amended with anaerobically digested pig slurry for biogas production

Multi-residue analysis of pharmaceuticals in aqueous environmental samples by online solid-phase extraction–ultra-high-performance liquid chromatography-tandem mass spectrometry: Optimisation and matrix effects reduction by quick, easy, cheap, effective, rugged and safe extraction

The aim of this study was to develop and optimise an analytical method for the quantification of a bactericide and 13 pharmaceutical products, including 8 antibiotics (fluoroquinolones, tetracyclines, sulfonamides, macrolide), in various aqueous environmental samples: soil water and aqueous fractions of pig slurry, digested pig slurry and sewage sludge. The analysis was performed by online solid-phase extraction coupled to ultra-high performance liquid chromatography with tandem mass spectrometry (online SPE–UHPLC-MS–MS). The main challenge was to minimize the matrix effects observed in mass spectrometry, mostly due to ion suppression. They depended on the dissolved organic carbon (DOC) content and its origin, and ranged between −22% and +20% and between −38% and −93% of the signal obtained without matrix, in soil water and slurry supernatant, respectively. The very variable levels of these matrix effects suggested DOC content cut-offs above which sample purification was required. These cut-offs depended on compounds, with concentrations ranging from 30 to 290mgC/L for antibiotics (except tylosine) up to 600–6400mgC/L for the most apolar compounds. A modified Quick, Easy, Cheap, Effective, Rugged and Safe (QuEChERS) extraction procedure was therefore optimised using an experimental design methodology, in order to purify samples with high DOC contents. Its performance led to a compromise, allowing fluoroquinolone and tetracycline analysis. The QuEChERS extraction salts consisted therefore of sodium acetate, sodium sulfate instead of magnesium sulfate, and sodium ethylenediaminetetraacetate (EDTA) as a ligand of divalent cations. The modified QuEChERS procedure employed for the extraction of pharmaceuticals in slurry and digested slurry liquid phases reduced the matrix effects for almost all the compounds, with extraction recoveries generally above 75%. The performance characteristics of the method were evaluated in terms of linearity, intra-day and inter-day precision, accuracy and limits of quantification, which reached concentration ranges of 5–270ng/L in soil water and sludge supernatant, and 31–2400ng/L in slurry and digested slurry supernatants, depending on the compounds. The new method was then successfully applied for the determination of the target compounds in environmental samples.

Effects of acidification during storage on emissions of methane, ammonia, and hydrogen sulfide from digested pig slurry

The effects of acidification reduction on methane (CH4), ammonia (NH3) and hydrogen sulphide (H2S) emissions from digested pig slurry during storage were investigated. Pilot-scale experiments designed with three different pH levels including one control and two acidified treatments were conducted. Digested pig slurry was stored and tested in nine mechanically ventilated reactors. An online and continuous monitoring system was used to acquire gas emissions data during the whole storage period. Temperatures and pH in digested slurry were continuously measured with sensors. Off-gas from the reactors and air from room environment were sampled alternately then supplied to gas analysers for CH4 and H2S determination. Headspace NH3 from the 9 reactors were regularly sampled by an air sampling instrument and then determined for concentration by spectrophotometer. The study found that digested pig slurry characteristics still didn't satisfy the national standards after 95 days treatments. Both temperature and pH were crucial factors to influence CH4 and NH3 emissions from digested pig slurry. In the control group (Gn) CH4 and H2S emissions mainly occurred in the first 20 days and 12 days, respectively; while no predictable NH3 emission patterns were found in the experiment. Comparing with Gn, adjustment of initial pH to 5.5 significantly reduced CH4 emissions by 80.8% and NH3 emissions by 40.2%, but increased H2S emissions by 11,324% (average increasing emission flux was 4.1 μg m−2 min−1). Acidification with pH adjusted to 6.5 reduced CH4 emissions by 31.2%, but did not affect NH3 and H2S emissions significantly.

Potential use of anaerobically digested manure slurry to suppress Phytophthora root rot of chilli pepper

Anaerobic digestion is a promising way to treat the large amounts of animal manures produced from animal husbandry in terms of efficient recovery of energy by the anaerobic digestion and of more sustained use of the slurries. Side effects such as suppression of soil borne diseases are not yet well investigated and understood. The objective of the study was to evaluate the potential use of anaerobically digested slurry (ADS) to suppress Phytophthora capsici, the causative agent of Phytophthora root rot of chilli pepper. Mycelial growth and zoospore germination of P. capsici were inhibited by ADS and application of ADS significantly reduced the disease incidence under bioassay conditions. The percentage of reduction in zoospore germination of P. capsici and disease incidence by anaerobically digested pig slurry (ADP) were significantly greater than anaerobically digested dairy slurry (ADD). Filter-sterilization reduced disease suppression only to a certain degree. Exogenous applied ammonium and humic substances (HS) isolated from ADS suppressed P. capsici and the percentages of inhibition of hyphal growth and zoospore germination by HS extracted from ADP were greater than those derived from ADD. It is hypothesized that that the better control of Phytophthora root rot by ADP was attributed to the higher concentration of ammonium and the particular structure of HS.

Chemical and spectroscopic characterization of organic matter during the anaerobic digestion and successive composting of pig slurry

In this work, anaerobic digestion of pig slurry and successive composting of the digestate after centrifugation were studied by means of chemical analysis, FTIR and fluorescence spectroscopy as excitation–emission matrix (EEM). Chemical analysis highlighted the organic matter transformation occurring during the processes. A decrease of volatile solids and total organic carbon were observed in the digestate with respect to the fresh pig slurry as a consequence of the consumption of sugars, proteins, amino acids and fatty acids used by microorganisms as a C source. Water Extractable Organic Matter (WEOM) was obtained for all samples and fractionated into a hydrophilic and a hydrophobic fraction. The highest WEOM value was found in the pig slurry indicating a high content of labile organic C. The digestate centrifuged and the digestate composted showed lower hydrophilic and higher hydrophobic contents because of the decrease of labile C. Total phenolic content was lower in the digestate with respect to fresh pig slurry sample (36.7%) as a consequence of phenolic compounds degradation. The strong decrease of total reducing sugars in the digestate (76.6%) as compared to pig slurry confirmed that anaerobic process proceed mainly through consumption of sugars which represent a readily available energy source for microbial activity. FTIR spectra of pig slurry showed bands indicative of proteins and carbohydrates. A drop of aliphatic structures and a decrease of polysaccharides was observed after the anaerobic process along with the increase of the peak in the aromatic region. The composted substrate showed an increase of aromatic and a relative decrease of polysaccharides. EEM spectra provided tryptophan:fulvic-like fluorescence ratios which increased from fresh substrate to digestate because of the OM decompostion. Composted substrate presented the lowest ratio due to the humification process.

Effects of water saving irrigation and rice variety on greenhouse gas emissions and water use efficiency in a paddy field fertilized with anaerobically digested pig slurry

Proper floodwater management during the cultivation period of paddy rice is essential for regulating the trade-off between methane and nitrous oxide emissions, as well as for saving irrigation water resource and maintaining crop productivity. To elucidate the effects of water saving irrigation (WS) and rice variety on different agro-environmental parameters such as CH4 and N2O emissions, global warming potential (GWP), greenhouse gases intensity (GHGI), carbon efficiency ratio, water use efficiency (WUE), rice growth and yield, a field experiment was conducted with two factors of split-plot design consisting of (1) main factor; WS (WS in which irrigation was withdrawn at soil Eh < −150 mV and kept 0–1 cm floodwater afterward) and continuous flooding (CF), and (2) sub-factor; a forage rice variety Leaf Star (LS) and a normal rice variety Kinuhikari (KN). Results showed that WS irrigation significantly (P < 0.05) mitigated CH4 emission by 65 % and \( {\text{GWP}}_{{{\text{CH}}_{ 4} + {\text{N}}_{ 2} {\text{O}}}} \) by 60 %, and enhanced WUE significantly (P < 0.01) by 180 % from that of CF. Carbon use efficiency of the grain and aboveground biomass carbon increased by 2.4 and 2.5 times, respectively, and GHGI was reduced by 3.1 times in WS. No significant differences were observed in the plant height, tiller number, rice biomass, N uptake and C accumulation between water treatments but the rice varieties: LS showed significantly (P < 0.05) higher values in these parameters than KN. This study highlighted that the WS is an effective measure for mitigating GWP, saving water while sustaining crop productivity.

Control mechanism of phytophthora blight of chilli pepper by anaerobically digested pig slurry— The roles of ammonium and humic acid in biogas slurry

为探明猪粪沼液对作物土传病害的防治效果与机制, 设纯化肥处理为对照, 采用盆栽试验比较了猪粪沼液(ADP1)、外源添加铵沼液(ADP2)、除铵沼液(ADP3)、除腐殖酸沼液(ADP4)施用对辣椒疫病的防治效果。结果表明, 猪粪沼液(ADP1)可以显著降低辣椒疫病的发病率(防效40.8%), 去除沼液中的铵或腐殖酸后, 对辣椒疫病的防治效果显著下降, 其发病率与病原菌对照(PC)无显著差异。定量PCR检测结果表明, ADP2处理土壤疫霉数量最少(2.51×10³ copies·g^-1), ADP3、ADP4沼液处理的辣椒根际疫霉数量较多, 分别为8.19×10³ copies·g^-1、1.38×10⁴ copies·g^-1; 土壤中辣椒疫霉菌的数量低于9.54×103 copies·g 1时, 辣椒疫病发病率与土壤中病原菌数量有较好的对应关系。不同沼液处理对细菌、真菌和放线菌数量的影响不同。病原菌存在下, ADP1处理的细菌、真菌、放线菌数量均最多, ADP2处理的真菌数量最少。孢子萌发试验表明, 随着铵和腐殖酸处理浓度的增加, 对疫霉菌游动孢子萌发的抑制率均逐渐增大。浓度为500 mg·L^-1、1 000 mg·L^-1、1 500 mg·L^-1 NH₄⁺对疫霉菌孢子萌发的抑制率分别为77.6%、81.8%、95.4%。用浓度为25 mg(C)·L^-1、50 mg(C)·L^-1、75 mg(C)·L^-1、150 mg(C)·L^-1的猪粪沼液腐殖酸处理疫霉菌游动孢子6 h, 游动孢子萌发率分别比无菌水对照下降了27.8%、54.5%、70.0%、87.5%。研究表明铵和腐殖酸可能是沼液的主要抑菌因子, 沼液作为土传病害抑制剂具有一定的应用前景。

The impact of activated carbon on NO3−‐N, NH4+‐N, P and K leaching in relation to fertilizer use

SummaryThe ability of light‐textured soils to retain nutrients and water is small. In agriculture such soils pose a risk of nutrient leaching when amended with fertilizers. This study investigated the effects of the incorporation of activated carbon (AC) into the soil to determine (i) if it would decrease leaching of major nutrient ions and (ii) if its effect on leaching is influenced by fertilizer use. Nitrate nitrogen (NO3−‐N), ammonium nitrogen (NH4+‐N), phosphorus (P) and potassium (K) leaching through two substrates (sandy loam soil (S) and a sandy loam soil mixed with activated carbon (S + AC), which were unfertilized (NF or control) or fertilized with inorganic fertilizer (F), pig slurry (PS), pig slurry digestate (PD) or sewage sludge digestate (SD) was studied using mini‐lysimeters. In soil enriched with AC mark K‐835, water percolation and NO3−‐N and P leaching were significantly reduced, and K leaching was increased. Ammonium nitrogen leaching was not influenced by the AC amendment. The impact of AC on NO3−‐N and P leaching and water percolation did not change during the two‐year period, from which it is concluded that AC mark K‐835 prevents the leaching of NO3−‐N and P and increases soil water retention ability, and thus it is beneficial for light‐textured soils.

Integrated Waste Management Combining Anaerobic and Aerobic Treatment: A Case Study

The aim of this work was to study the feasibility of composting, as a post-treatment option, to manage the solid fraction of anaerobically digested pig slurry (SFP) produced in an industrial waste treatment plant, together with other wastes processed in the facility (sewage sludge (SS), paper mill sludge (PS) and pig hair waste (PW), and two bulking agents [maize straw (MS) and wheat straw (WS)]. Six composting mixtures were prepared (percentage on fresh weight basis): P1 (100 % SFP), P2 (80 % SFP + 20 % MS), P3 (60 % SFP + 40 % MS), P4 (35 % SFP + 35 % SS + 30 % mixture of MS and WS), P5 (35 % SFP + 35 % PS + 30 % mixture of MS and WS) and P6 (35 % SFP + 35 % PW + 30 % mixture of MS and WS). Throughout the composting process, temperature evolution was monitored and physico-chemical and chemical parameters were determined. Furthermore, the evolution of the microbial community structure was assessed by the real time PCR technique. The use of the bulking agents influenced positively the composting development, especially in the mixtures P2 and P5. In general, all the composts showed a good degree of maturity and absence of phytotoxicity, but the use and proportions of determined raw materials (PS, SS and SFP) produced composts with several limiting aspects (high salinity and/or notable contents in Cu and Zn) for their agricultural use. The increase of the ratio fungi/eubacteria by the end of the process was consistent with the maturity of the produced compost and the good performance of the process.

Recycling of anaerobic digestates by composting: effect of the bulking agent used

Digestate, the by-product of the anaerobic digestion, can present characteristics which would limit its recycling by direct use in agricultural soils. Composting can be a feasible treatment to stabilise digestate and thus, to improve its properties for using as a soil conditioner or substrate. The aim of this work was to study the viability of composting for the recycling of digestates after solid–liquid separation and the effect of the bulking agent used in the characteristics of the end-products obtained. For this, five piles were elaborated by mixing the solid fraction of a pig slurry digestate (SD) with different bulking agents (wheat straw (WS), vine shoot prunings (VP), exhausted grape marc (EGM) and pepper plant prunings (PP)). Also, one of these piles was watered with the liquid fraction of the pig slurry digestate (LD). Throughout the composting process, the temperature of the mixtures was monitored and physico-chemical, chemical, physical properties and maturity degree were determined. Also, factorial analysis (FA) was used for interpreting the data set of compost characteristics. The composts obtained showed a suitable degree of stability and maturity and suitable physical properties for their potential use as growing media. Also, the type of bulking agent strongly influenced the development of composting and the final properties of the composts, showing the mixtures with WS and VP the most suitable characteristics.

Sulphur fate and anaerobic biodegradation potential during co-digestion of seaweed biomass (Ulva sp.) with pig slurry

Seaweed (Ulva sp.) stranded on beaches were utilized as co-substrate for anaerobic digestion of pig slurry in three-month co-digestion tests in pilot scale anaerobic digesters in the laboratory. The methanogenic potential of Ulva sp. was low compared to that of other potential co-substrates available for use by farmers: 148Nm3CH4/t of volatile solids or 19Nm3CH4/t of crude product. When used as a co-substrate with pig manure (48%/52% w/w), Ulva sp. seaweed did not notably disrupt the process of digestion; however, after pilot stabilisation, biogas produced contained 3.5% H2S, making it unsuitable for energy recovery without treatment. Sequentially addition of the sulphate reduction inhibitor, potassium molybdate, to a final concentration of 3mM, temporarily reduced H2S emissions, but was unable to sustain this reduction over the three-month period. According to these pilot tests, the use of seaweed stranded on beaches as co-substrate in farm-based biogas plants shows some limitations.

Methane and N2O emissions, nitrate concentrations of drainage water, and zinc and copper uptake by rice fertilized with anaerobically digested cattle or pig slurry

We have examined the effects of different types of slurry on CH4 and N2O emissions, Zn and Cu contents of rice, and nitrate content of the drainage water. The experiment included four treatments: (1) anaerobically digested cattle slurry (ADCS), (2) ADCS filtered to remove the coarse organic matter fraction, (3) anaerobically digested pig slurry (ADPS), and (4) chemical fertilizer (CF). The application rate was 30 g NH4–N m−2. Different amounts of C were incorporated with fertilization: 725 g C m−2 in ADCS, 352 g m−2 in filtered ADCS, and 75 g m−2 in ADPS. The average CH4 emissions during a growing period were 304, 359, 452, and 579 mg m−2 day−1 in the CF, ADPS, filtered ADCS, and ADCS treatments, respectively. The CH4 emission was significantly higher in ADCS than in CF and ADPS. Negligible N2O emissions were observed during the growing period. Comparable concentrations of Zn and Cu were observed in the rice grain among the treatments. In contrast, their concentrations in the stems and leaves were significantly higher in ADPS than in CF treated rice, although the values were lower than the upper limit of feed additives. Nitrate concentrations in the drainage water were consistently low (0.5 mg N L−1). The present study suggested that ADPS, containing a lower amount of C than ADCS, might be an organic fertilizer in paddy field with comparable environmental impacts to chemical fertilizers (CF), but long-term field studies are needed to better understand the effects of these organic fertilizers.

Laboratory assessment of ammonia emission after soil application of treated and untreated manures

SUMMARYAmmonia (NH3) volatilization from soil-applied manure not only causes environmental pollution but also reduces the fertilization value of the manure. Anaerobic digestion and solid/liquid separation alter the physical and chemical characteristics of slurry, which affect NH3 emissions after application. The present study measured potential laboratory NH3 losses from different manures, untreated pig slurry and the liquid fractions of each untreated and digested slurry, after their application to two different soil types. The experiment was carried out in dynamic chambers using a photoacoustic infrared gas analyser to determine the NH3 concentration in the air stream directly.The estimated values of nitrogen (N) emitted for surface-applied, untreated pig slurry were 0·26±0·064 mg per mg of applied total ammoniacal nitrogen (TAN). For the liquid fractions of pig slurry and digested pig slurry, results were 0·13±0·064 and 0·16±0·064 mg/mg, respectively. Initial NH3–N emission rates from surface-applied, untreated pig slurry were higher than those measured for either liquid fraction; in the case of the untreated pig slurry, half was emitted in the first 4·9 h of measurement. Silty-loam soil showed a higher N emission than loam soil with surface-applied slurries. This result was probably due to the higher infiltration rate of loam soil, even offsetting the effect of its high soil pH. Immediate manure incorporation into the soil was shown to reduce NH3 emissions by 82%. Results demonstrated that a method combining dynamic chambers with a photoacoustic gas analyser was as reliable as the widely used acid traps method. Moreover, direct measurement with the gas analyser permits an increasing temporal resolution that gave a high-quality description of the NH3 emission dynamic.

Combination of batch experiments with continuous reactor data for ADM1 calibration: application to anaerobic digestion of pig slurry

Modelling anaerobic digestion processes is a key aspect of studying and optimizing digesters and related waste streams. However, for the satisfactory prediction of biogas production and effluent characteristics, some parameters have to be calibrated according to the characteristics of the substrates. This article describes a calibration procedure for the IWA 'Anaerobic Digestion Model no. 1' applied to the modelling of a digester for treatment of pig slurry. The most sensitive parameters were selected and calibrated combining results from a continuous digester and from batch trials run with the sludge sampled from the digester and the addition of specific substrates. According to the sensitivity analysis, acetoclastic methanogenesis, acetogenesis of propionate and acidogenesis of sugars were identified as the main sensitive steps in our case. The calibration procedure led us to modify slightly acetogenesis of propionate kinetic. However, acetoclastic methanogenesis and acidogenesis of sugars kinetics were significantly reduced by decreasing km and increasing Ks. Indeed, for instance, a decrease of km_ac from 8 to 7 day(-1) combined with an increase of Ks_ac from 0.15 to 1.5 kgCOD/m3 was necessary. After calibration, ADM1 provides an accurate simulation of the continuous reactor results.

Changes in mineral nitrogen, soil organic matter fractions and microbial community level physiological profiles after application of digested pig slurry and compost from municipal organic wastes to burned soils

Abstract In this study, mineralization of digested pig slurry and compost from municipal organic wastes in burned soils was followed for 60 days. The effects of amendments on organic matter fractions and microbial community level physiological profiles (CLPP) were also investigated at the end of the incubation period. Soil from a forest 10 days after a fire had a greater basal respiration, and more organic matter that a nearby soil that was not affected by fire, presumably as a consequence of black ash addition following the wildfire. Nitrification was inhibited in soils treated at 105 and 250 °C in the laboratory, but amendment application allowed nitrification to take place in the latter soil, and led to significant flushes of mineralization. Slurry amendment resulted in greater increases in mineral N compared with compost. Soil treated at 250 °C had the greatest content of water-extractable compounds (WE) at the expense of acid-extractable compounds (AE), but during the incubation the variations in these two fractions had an opposite trend, i.e. soil gained AE and lost WE fractions. The variation in N-acetyl-glucosamine-induced respiration was different between compost- and slurry-amended soils, with the greater values in the former. The effect of amendments could be further differentiated by principal component (PCA) and cluster analyses based on the variations in organic matter fractions and CLPP between the beginning and the end of the incubation period. Amendment application led to shifts on the PCA maps that depended both on the amendment and soil treatment. In fresh soil and in that treated at 250 °C, the unamended, compost- and slurry-amended treatments remained relatively close on the PCA maps and had linkage distances 1.0. Pig slurry led to the greatest changes in burned soil, while compost induced the greatest shifts in soil treated at 105 °C. This study suggests that an application of organic amendments after a severe fire event may contribute to a faster recovery of soil functions.

Combined anaerobic and activated sludge anoxic/oxic treatment for piggery wastewater

A process combining anaerobic digestion and anoxic/oxic treatment was developed to treat pig slurry in-order-to partially convert organic matter (OM) into a valuable energy and simultaneously to comply with the environmental constraints as regards to nitrogen removal. However, OM content of digested pig slurry is insufficient to allow a further complete denitrification of the mineral nitrogen content. Hence, four different configurations were designed and evaluated to manage the OM requirements and achieve denitrification. Partial nitrification (PN) of ammonium to nitrite was also applied by regulating oxygen inflow time. Thus, the combined process could remove 38-52% of CODt, 79-88% of CODs, 66-75% of TN and 98-99% of NH(4)(+)N concentrations depending on the slurry characteristics. Anaerobic digestion was able to produce 5.9 Nm(3) of CH(4)/m(slurry added)(3). PN allowed a reduction in the oxygen and OM requirements respectively for nitrification and denitrification. Thus, this process trims-down the energy costs at the farm scale.

Plant-availability to barley of phosphorus in ash from thermally treated animal manure in comparison to other manure based materials and commercial fertilizer

Phosphorus (P) is an essential nutrient and a limited resource, yet excess P is applied to agricultural land and can cause environmental problems in areas with intensive animal farming. In this study, the fertilizing effects of P in several animal manure-based products (including thermal treatment) were tested after application to two agricultural soil types (Jyndevad soil: clay 5.1%, silt 4.1%, sand 88.9%, organic matter 2.1%, total C 1.2% soil dry matter (DM), total P 266 mg kg −1 soil DM, pH 6.3; Rønhave soil: clay 15.4%, silt 32.6%, sand 49.6%, organic matter 2.3%, Total C 1.3% soil DM, total P 488 mg kg −1 soil DM, pH 6.6). The first-year effect of P application was tested in a spring barley crop ( Hordeum vulgare L.) and residual P effects were tested in a perennial ryegrass ( Lolium perenne L.) crop the following year. Untreated ash from thermally gasified animal manure biogas residue (GA) and a corresponding neutralized acid extract of the ash (ExL) in liquid form were the products in focus. Other products in use were: pelletized pig manure biogas residue (PEL), incinerated PEL (IA), anaerobically digested pig slurry (DS), dried ExL, dried fraction of separated pig slurry (SS), thermally gasified SS (GAs), thermally gasified poultry manure (GAp), crushed triple super phosphate (TSP) and disodium phosphate (DSP) was used as reference P fertilizer. For application of 20 kg P ha −1 mineral P fertilizer replacement value (RV) in the second year in the sandy soil was 76% and 99% for GA, 79% and 123% for IA, 95% and 155% for PEL, 94% and 73% for ExL, 55% and 15% for ExD, 64% and 82% for SS, 104% and 109% for DS, 60% and 95% for GAp, 73% and 111% for GAs, where the first value is based on barley DM yield and the second on barley total P uptake. Tripling the GA application rate to 60 kg P ha −1 in both soils had no significant effect on barley DM yield and P uptake. The overall efficiency for liquid fertilizers was much higher than for solid ones and relative effectiveness (RE) of ExL was comparable to RE of DSP. Despite the low P level in soils, the ryegrass crop grew very well on both soils in the second year, and there was no detectable residual effect of the treatments on grass yield and P uptake. In conclusion, untreated ash and solid manures used in this study were not suitable as starter P fertilizer, but could be used to maintain the level of available P in soil, as there were indications that ash/manure P contributed significantly to plant P uptake during the growing season of barley.

The importance of the fallow period for N2O and CH4 fluxes and nitrate leaching in a Mediterranean irrigated agroecosystem

The aim of this study was to evaluate the pattern of nitrous oxide (N2O) and methane (CH4) fluxes, and leaching losses of nitrate (NO3−) and dissolved organic C (DOC), during a fallow–onion crop–fallow cycle in a Mediterranean area. The importance of the fallow (intercrop) period and the type of fertilizer were also evaluated. Goat and chicken manure (M) from an organic farm, digested pig slurry (DPS) and urea (U) were applied at a rate of 110 kg N ha−1 and compared with a zero N treatment (Control). The crop period contributed more than each fallow period to the total N2O emission (ranging from 70 to 85% of the total emission, depending on the treatment). The variability of rainfall during fallow periods affected N2O emissions, with the highest fluxes observed in the second fallow, which was the wetter. Negative net fluxes of N2O (0 to −0.4 mg N2O‐N m−2 day−1) were mainly observed during the irrigation period and in fallow periods. The type of fertilizer had no effect on N2O fluxes, but influenced the CH4 oxidation. The largest CH4 emission was from the manure treatment (2.4 mg CH4‐C m−2 day−1) during the irrigation period. The lowest NO3− but highest DOC leaching rates were measured during the second fallow period from the manure treated plots (0.2 kg NO3−‐N ha−1 and 3.9 kg C ha−1), which also had the highest drainage. The use of OM, therefore, seems to be a suitable method to reduce the environmental impacts associated with N leaching as well as increase the potential to denitrify NO3− in groundwater.

Combination of drip irrigation and organic fertilizer for mitigating emissions of nitrogen oxides in semiarid climate

Fertilizer and irrigation management are two of the most important factors which directly influence nitrification and denitrification processes from agricultural soils and, therefore, emissions of nitrous oxide (N 2O) and nitric oxide (NO). To date, the effect of combining organic fertilizer (applied before planting) with a drip irrigation system (DI) on the emissions of these nitrogen (N) oxides has not been evaluated. The different distribution and amount of water applied with this irrigation system should produce less favourable conditions for denitrification than other irrigation systems, such as furrow irrigation (FI), and this could be used to mitigate emissions of N 2O, especially following organic fertilizer application. In order to test this hypothesis, a field experiment was carried out to compare the influence of FI and DI on N 2O and NO emissions using digested pig slurry (DPS) as organic fertilizer during a melon crop ( Cucumis melo L. cv. Sancho) season. Plots without any N fertilizer were used as a control (control). The irrigation system influenced the water distribution pattern, producing significantly higher ammonium-N (NH 4 +-N) and nitrate-N (NO 3 −-N) concentrations in the soil under DI than under FI. Moreover, the differences observed in water filled pore space (WFPS) and mineral N also favoured a different pattern of emissions of N oxides. Only one large pulse of N 2O (106.9 mg N m −2 d −1) and NO (0.81 mg N m −2 d −1) were observed for FI after the first irrigation event while several pulses were observed for DI during the entire experimental period. As a consequence, nitrous oxide emissions were 75% and 28% lower from control and DPS, respectively under DI than under FI. In contrast, NO emissions were higher for DI on some sampling dates in both treatments, but without significant differences in the cumulative NO emissions between both irrigation systems. In conclusion, this work shows that combining drip irrigation with organic fertilizer for horticultural crops in semiarid climates could be a good management strategy for three reasons: it saves water; it re-uses organic residues and it mitigates N 2O emissions.