Influence of homogenized residues of anaerobic digestate on the physicochemical properties of differently textured soils

Because of the focus on renewable energy, new biogas digesters are being built with the consequence of an increased production of anaerobic digestates (AD) as a by‐product. Although they can be used as organic fertilizer on arable fields, negative impacts of these digestates also may occur. Therefore, it was the aim of this laboratory study to investigate the effect of a normally applied volume of 30 m³ ha^?1 of anaerobic digestates derived from a ground input substrate of maize (Zea mays L.) , sugar beet (Beta vulgaris L.), and wheat (Triticum aestivum L.) in different ratios (100 /80 / 20%) on the properties of two soils. The soils, which were homogenized (sieved to ≤ 2 mm) and placed in columns with a defined bulk density of 1.45 g cm^?3, were a Cambic Luvisol (sandy loam) derived from glacial till and a Podzol (sandy sand) derived from glazial outwash. Physicochemical parameters [pH, electrical conductivity (EC)] and the wetting behavior of the soils were analyzed by measuring the contact angle (CA) by using the Wilhelmy–Plate‐Method (WPM) and the Repellency Index (RI) from the sorptivity of water and ethanol. To determine the risk of soil dispersion as a consequence of digestate amendment, the amount of readily dispersible clay (RDC) was determined by detecting the turbidity of a soil suspension. The application of 30 m³ ha^?1 of AD decreased the wettability of the sandy sand as compared to the untreated soil, while the wettability of the loamy sand remained unaffected by the digestate amendment. The amount of RDC was higher in the loamy sand compared to the sandy sand, but the AD‐amended soil did not exhibit a significant change in dispersibility. While the loamy soil exhibited acidification of the soil after digestate application, the sandy soil showed an alkalinization of soil columns. Overall, the soil texture was identified to be a main factor controlling the effect of the digestates on soil properties. The results of this lab study showed that this study can be used as a first approach for the quantification of digestate amendment under practical conditions.     

Anaerobic co‐digestion of perennials: Methane potential and digestate nitrogen fertilizer value

Co‐digestion of crop biomass improves the traditional manure‐based biogas yield due to an increased content of easily degradable carbon compounds. In this study, the methane potential of three perennials (grass, legumes, and grass+legume) was determined using various amounts together with animal manure. The nitrogen (N) mineralization dynamics in soil and the N‐fertilizer value of the derived digestates were subsequently tested in both a soil incubation study and a pot experiment with spring barley. Digestion of all tested perennials together with a manure‐based inoculum increased the cumulative methane yield four to five times compared to digestion of the inoculum alone, with the highest increases observed with pure grass. However, the methane potential decreased along with increasing grass biomass concentration. In the plant pot experiment, all tested digestates increased barley shoot biomass by 40–170%, to an extent statistically comparable to mineral N fertilizer. However, the application of the digestate originating from fermentation with pure grass resulted in lower plant growth and a more fluctuating soil mineral N content throughout the incubation study compared to the other digestates. Considering the high dry matter and methane yield ha^?1, the possibility to substitute mineral N fertilizer inputs by leguminous biological N₂ fixation capacity, and the digestate fertilizer value, the integration of grass–legume mixtures or sole legumes into anaerobic digestion systems as co‐substrate for manure seems to be promising. This could furthermore contribute to the diversification of cropping systems for bioenergy production.     

Biogas digestates based on lignin-rich feedstock – potential as fertilizer and soil amendment

With advances in biogas technology, lignocellulosic material may be increasingly included in feedstock due to the abundance of raw materials. The main goal of this study was to evaluate fertilizing and soil amendment effects of digestates based on lignin-rich feedstock. The digestates originated from reactors fed with manure co-digested with Salix, wheat straw or sugarcane bagasse, respectively. In pot experiments with three different soils, Italian ryegrass and reed canary grass were grown with 120 kg ha^?1 total nitrogen or 150 kg ha^?1 available nitrogen, respectively, given as either mineral fertilizer or digestate. Soil chemical and physical characteristics were determined after ended experiments. Additionally, an incubation study was carried out to estimate N mineralization from one digestate over time. Digestate addition resulted in similar yields compared to mineral fertilizer, varying from 0.5 (loam) to 1 kg dry matter m^?2 (silt) for Italian ryegrass and 1.2 (loam) to 2.3 kg m^?2 (silt) for reed canary grass. Digestates contributed to a favourable pH for plant growth, reduced bulk density in the loam and improved water retention characteristics in the sand. Biogas digestates based on lignin-rich feedstock appear promising as fertilizers and for soil amelioration but results have to be verified in field experiments.     

不同有机物料接种蚯蚓对设施菜地土壤 培肥及作物生长的影响

设施蔬菜栽培长期施用过量化肥,往往导致土壤质量退化及作物产量降低等问题。因此,采用生态友好的农业生产方式已成为农业可持续发展的趋势。本研究在野外调控试验的第3年采集作物和土壤,研究了施用不同有机物料条件下,接种赤子爱胜蚓(Eisenia foetida)对设施菜地土壤性质和作物生长的影响。结果表明,在不同有机物料施用下接种赤子爱胜蚓均显著地提高了黄瓜和菠菜的产量,其中在施用腐熟牛粪+食用菌渣条件下接种赤子爱胜蚓效果最显著。此外,在腐熟牛粪和腐熟牛粪+食用菌渣施用条件下,接种赤子爱胜蚓显著地提高土壤的硝态氮(NO3–-N)、团聚体平均重量直径(MWD)、微生物生物量碳(MBC)、微生物生物量氮(MBN)和代谢熵(q CO2),而在施用商品有机肥的处理中,接种赤子爱胜蚓仅显著地提高了土壤NO3–-N和q CO2。本研究促进了对蚯蚓在设施农业生态系统中服务功能的理解,并为设施农业生产提供了理论基础。     

C and N dynamics of a range of biogas slurries as a function of application rate and soil texture: a laboratory experiment

Digestates vary in composition and studies regarding their impact on C and N dynamics in soils are scarce. The objective was to analyse the C and N dynamics of digestates originating from various substrates applied to a sandy Cambisol and a silty Anthrosol. In three laboratory experiments (4–6 weeks), the effects of digestate properties, N rate and water content were tested. Averaged over both soils, 21% of the C supplied was emitted as CO₂. Potential NH₃ emissions during the first week ranged between 6% and 12% of NH₄⁺ present in the digestates. The emission factors in the sandy Cambisol were on average 1.2 and 2 times higher for CO₂ and potential NH₃, respectively, compared to the silty Anthrosol. Similarly, net nitrogen mineralization in the sandy Cambisol was approximately twice the N mineralized in the silty Anthrosol. Net nitrification was not influenced by soil texture or different digestates, but increased with increasing application rates and had highest values at 75% of water holding capacity. Our results indicate that the type of substrate input for anaerobic digestion influences the properties of the digestate and therefore the dynamics of C and N. However, soil texture can affect these dynamics markedly.     

土壤添加沼渣对温室气体排放及小麦生长的影响

Digestate, the product obtained after anaerobic digestion of organic waste for biogas production, is rich in plant nutrients and might be used to fertilize crops. Wheat(Triticum spp. L.) was fertilized with digestate, urea, or left unfertilized and cultivated in the greenhouse for 120 d. Emissions of greenhouse gasses(carbon dioxide(CO_2), methane(CH_4), and nitrous oxide(N_2O)) were monitored and plant growth characteristics were determined at harvest. The digestate was characterized for heavy metals, pathogens, and C and N mineralization potential in an aerobic incubation experiment. No Salmonella spp., Shigella spp., or viable eggs of helminths were detected in the digested pig slurry, but the number of faecal coliforms was as high as 3.6 × 10~4colony-forming units(CFU) g-~(1)dry digestate. The concentrations of heavy metals did not surpass the upper limits established by US Environmental Protection Agency(EPA). After 28 d, 17% of the organic C(436 g kg~(-1)dry digestate) and 8% of the organic N(6.92 g kg~(-1)dry digestate)were mineralized. Emissions of CO_2 and CH_4 were not significantly affected by fertilization in the wheat-cultivated soil, but digestate significantly increased the cumulative N_2O emission by 5 times compared to the urea-amended soil and 63 times compared to the uncultivated unfertilized soil. It could be concluded that digestate was nutrient rich and low in heavy metals and pathogens, and did not affect emissions of CH_4 and CO_2 when applied to a soil cultivated with wheat, but increased emission of N_2O.     

Preliminary Evaluation of Seaweed Application Effects on Soil Quality and Yield of Sweet Corn (Zea mays L.)

The practice of applying seaweed to agricultural fields may provide plant nutrients and improve soil quality in coastal agroecosystems, but little is known about its effects on soil properties or crop production. We conducted a preliminary evaluation of changes in soil biological and chemical properties and sweet corn (Zea mays L.) production using seaweed as a partial source of nitrogen (N) (40–55%) for one growing season, using a preformulated organic fertilizer treatment for comparison. Soil electrical conductivity, potassium (K⁺), sulfate (SO₄^2-), and active carbon (C) increased with seaweed addition relative to the organic fertilizer, whereas potentially mineralizable N and pH decreased, with effects varying over time. Sweet corn yield and quality were either equivalent to that with the organic fertilizer or improved. The short-term positive (e.g., increased active C) and negative (e.g., increased salt levels) effects on soil quality suggest further evaluation of this practice is justified.     

ARE ORGANIC N FERTILIZING STRATEGIES ABLE TO IMPROVE LETTUCE YIELD,USE OF NITROGEN AND N STATUS?

Despite the importance of fertilizing practices in the crop yield improvement, nitrogen (N) utilization, and N status, their management by farmers is still rather empirical, especially when new organic materials are applied. Therefore, the aim of this research was to study the possible bio-products (anaerobic digestates and on-farm compost) applications and to evaluate their effects on lettuce performance, N efficiency and soil properties. The plant and soil N indicators were also investigated to reduce the N supply in lettuce production. To accomplish these objectives a three-year field experiment was carried out comparing the following N fertilization strategies: organic, with anaerobic digestates, based on stabilized wine distillery wastewater (SAD) and not stabilized wine distillery wastewater (NSAD) and on-farm compost, based on olive pomace compost (OPC); mineral (MIN), with ammonium sulfate and ammonium nitrate; mineral-organic, with a slow N release commercial fertilizer (CORG). All treatments received 140 kg N ha^?1 and they were compared with an unfertilized control (CONTR). The organic material application increased the marketable yield of 25.6, 20.3 and 10.1% for SAD, NSAD, and OPC treatments, respectively, in comparison with the CONTR. No significant reduction was found for both anaerobic digestates in respect to conventional fertilizers, while the OPC application significantly decreased the crop yield compared to MIN and CORG treatments. Moreover, the marketable head weight showed no significant difference among MIN, CORG, and SAD treatments, while a significant reduction of the weight was observed for NSAD and OPC. These findings highlighted the importance of organic fertilizer choice to sustain lettuce yield. The anaerobic digestates also enhanced head weight of 18.9 and 11.9% for SAD and NSAD, respectively, compared to CONTR, pointing out that the by-products application could be a valid agricultural practice to provide nutrients. Besides, no significant difference in N utilization parameters was found between SAD, MIN and CORG, indicating the effectiveness of the stabilized wine wastewater. Among the plant and soil N indicators tested, our results suggested that the leaves green index and nitrate contents in the leafstalks not only were the most reliable methods for evaluating N status, but they also offered potential advantages of both an easier sampling and a higher positive correlation with lettuce performance. Finally, since the agro-industrial residues did not significantly increase the soil potentially toxic elements level, the findings of this research pointed out that the organic materials can be usefully applied, at least in the short-term period.     

Effects of irrigation volumes and organic fertilizers on eggplant grown in Mediterranean environment

A three-year field experiment was carried out in Mediterranean conditions to study the effects of different irrigations and organic fertilizers on yield, quality and nitrogen utilization of eggplant crop and on soil properties. In a split-plot design, two irrigation treatments (re-establishing 100% and 50% of the calculated maximum evapotranspiration) and four fertilizer treatments (mineral fertilizer, commercial stable manure, anaerobic digestate and municipal solid waste compost) were compared. The highest water volume increased significantly the total and marketable yield, the number of marketable fruits, the dry matter of fruits and the nitrogen-use efficiency with respect to the treatment with the lowest irrigation. Nevertheless, the same treatment decreased significantly the fruit dry matter percentage and total soluble solid content. The lowest water volume led to an improvement of fruit quality. Anaerobic digestate increased significantly the total and marketable yield and dry matter compared with compost. Harvest index, nitrogen harvest index, pH, acidity and total soluble solids did not show significant differences among all fertilizer treatments. N translocation ability of plants and fruit quality were not influenced by the type of fertilizer. At the end of experiment, anaerobic digestate and compost reached the highest levels of soil total organic carbon and humic and fulvic acids content. Besides, anaerobic digestate increased the total extractable carbon, phosphorus and nitrogen content compared to all other treatments. Soil copper, nickel and lead content in all treatments enhanced compared to that at the beginning of experiment, but this accumulation did not represent a possible environmental risk. The content of heavy metals in the soil, after 3 years of application, did not exceed the limits imposed by the Italian law. This study showed that the organic wastes, after being adequately processed, could be applied successfully in agriculture especially in arid environments, characterized by quick mineralization and very low organic matter content.     

Manioc peel and charcoal: a potential organic amendment for sustainable soil fertility in the tropics

In tropical areas, where crop production is limited by low soil quality, the development of techniques improving soil fertility without damage to the environment is a priority. In French Guiana, we used subsistence farmer plots on poor acidic soils to test the effect of different organic amendments, bitter manioc peel (M), sawdust (Sw) and charcoal (Ch), on soil nutrient content, earthworm abundance and yard-long bean (Vigna unguiculata sesquipedalis) production. The peregrine Pontoscolex corethrurus was the only earthworm species found. Pod production and plant growth were lowest in unamended soil. The application of a mixture of manioc peel and charcoal (M + Ch) improved legume production compared with other organic mixtures. It combined the favourable effects of manioc peel and charcoal. Manioc peel improved soil fertility through its low C:N ratio and its high P content, while charcoal decreased soil acidity and exchangeable Al and increased Ca and Mg availability, thus alleviating the possible toxic effects of Al on plant growth. The M + Ch treatment was favourable to P. corethrurus, the juvenile population of which reached a size comparable to that of the nearby uncultivated soil. The application of a mixture of manioc peel and charcoal, by improving crop production and soil fertility and enhancing earthworm activity, could be a potentially efficient organic manure for legume production in tropical areas where manioc is cultivated under slash-and-burn shifting agriculture.     

木质纤维素生物质厌氧发酵沼渣热化学转化利用研究进展

厌氧发酵技术可以将木质纤维素生物质转化为沼气,并伴随副产物沼渣产生。随着大型沼气工程的发展,大量沼渣排放已成为厌氧发酵技术推广应用的主要限制因素之一,亟须对沼渣进行快速有效处理。其中,沼渣的热化学转化利用符合大型沼气工程发展趋势,是当前的研究热点之一。首先分析木质纤维素沼渣的原料特性与热化学转化潜力;再对沼渣成型燃料、热解以及水热炭化等领域的研究现状进行分析,着重对沼渣衍生产物特性、热化学转化过程中存在的问题以及与厌氧发酵结合的潜在优势等方面进行讨论;最后,对沼渣热化学转化的发展趋势进行了展望。木质纤维素生物质厌氧发酵与沼渣热化学转化结合的应用模式研究对大型沼气工程推广应用具有一定的科学意义。     

Yield and Performance and Soil Properties of Organically Fertilized Fodder Crops

The aim of this study was to evaluate the effects of experimental amendments on yields of Trifolium subterraneum L., Pisum arvense L., and Lolium multiflorum Lam., and on soil characteristics. A two-year research was carried out comparing anaerobic digestate (AD) and olive-pomace compost (OPC) with mineral fertilizer (Min), commercial organic-mineral fertilizer (Org-min), and unfertilized control (Cont). Anaerobic digestate and OPC were firstly analyzed for their chemical characteristics. The most important parameters were recorded and soil properties were investigated. Anaerobic digestate showed the highest dry weight for ryegrass, the best yield in pea, and good level of dry matter in clover. Good responses were achieved by OPC. Anaerobic digestate increased total soil organic carbon by 14.4, 8.1 and 7.6% than Min, Org-min and Cont, respectively. Olive-pomace compost increased the same parameter by 16.3, 10.0, and 9.5%. The findings indicated the possibility to substitute mineral fertilizers with organic ones without decreasing yields and support soil fertility.     

Transfer of carbon incubation parameters to model the SOC and SON dynamics of a field trial with energy crops applying digestates as organic fertilizers

The fertilization with organic amendments and digestates from biogas plants is increasingly used to increase carbon stock and to improve the soil quality, but little is still known about their long-term effects. A common method to analyse organic amendments and their mineralization is incubation experiments, where amendments get incubated with soil while CO₂ release is measured over time. In a previous study, carbon models have been applied to model the carbon dynamics of incubation experiments. The derived parameters describing the carbon turnover of the CCB model (CANDY Carbon Balance) are used to simulate the SOC and SON dynamics of a long-term field trial. The trial was conducted in Berge (Germany) where organic amendments like slurry, farmyard manure or digestates were systematically applied. To grant a higher model flexibility, the amounts of crop residues were calculated for roots and stubble separately. Furthermore, the mineralization dynamics of roots and stubble are considered by the model parameters for each crop. The model performance is compared when using the dry matter and carbon content received from the field trial and the incubation experiments, to evaluate the transferability. The results show that the incubation parameters are transferable to the field site, with rRMSE < 10% for the modelled SOC and rRMSE between 10% and 15% for the SON dynamics. This approach can help to analyse long-term effects of unexplored and unusual organic fertilizers under field conditions, whereat the model is used to upscale the C dynamics from incubation experiments, considering environmental conditions.     

Does acidification increase the nitrogen fertilizer replacement value of bio‐based fertilizers?

Acidification of manure, digestate and their processed derivatives has been proposed as a technique to, amongst others, mitigate ammonia emissions related to application in the field. The current study investigated whether acidification of (1) pig slurry (PS), (2) liquid fraction of pig slurry (LFPS), (3) digestate (DIG), and (4) liquid fraction of digestate (LFDIG) increases their nitrogen (N) fertilizer replacement value (NFRV) as compared to non‐acidified counterparts, a synthetic N fertilizer (calcium ammonium nitrate; CAN) and an unfertilized control. Product performance was evaluated from the perspective of (1) crop development (yield, nutrient uptake, and crop quality assessment) via a pot experiment with Lactuca sativa L. and (2) soil N dynamics [net N release (N_rel,net) and net N mineralization] via a soil incubation experiment. Crop yield of pots receiving bio‐based fertilizers performed ‘on par' with CAN as compared to unfertilized control, implying that bio‐based fertilizers derived from digestate or manure could potentially play a role in replacing synthetic N fertilizers. However, our findings also suggest that acidification did not result in an increased use efficiency of applied N. NFRVs of acidified products were below those of non‐acidified products and CAN, with crop yield on average 6–13% and 11–18% lower compared to non‐acidified products and the CAN treatment, respectively. A possible explanation for lower performance as compared to non‐acidified products could be an inhibitory delay in the N_rel,net, which in our experimental design proved to be negative for crops with short production cycles. This pattern was revealed in the incubation experiments in which N_rel,net in acidified products remained below that of non‐acidified, in this study tentatively attributed to immobilization of mineral N. However, this negative effect on N availability should be reaffirmed in crops with longer production cycles. Finally, some interesting findings with regard to plant composition also warrant further in‐depth investigation, e.g ., Zn uptake by lettuce in acidified treatments was significantly higher than that of non‐acidified treatments. This implies that product pre‐treatment may play a future role in biofortification and amelioration of (trace) element composition of crops (arguably for crops with longer production cycles). Improving crop nutritional value by increased uptake of micronutrients is receiving increasing attention.     

Effect of selected organic materials and inorganic fertilizer on the soil fertility of a Humic Nitisol in the central highlands of Kenya

The effect on soil fertility of applying particular organic resources to a humic Nitisol in the central highlands of Kenya was studied. The organic resources (Calliandra calothyrsus, Leucaena trichandra, Tithonia diversifolia, Mucuna pruriens, Crotalaria ochroleuca and cattle manure) were either applied solely or along with inorganic fertilizer in a cropping trial using maize as the experimental crop. After 4 years of continuous cultivation and manuring, soil fertility effects varied among treatments. Cattle manure proved to be the most effective and improved soil fertility by increasing pH, cations (Ca, K and Mg), and C. Calliandra, Leucaena, Tithonia and herbaceous legumes generally reduced soil pH, C and N but increased Ca, K and Mg. Cattle manure is therefore an important resource for maintaining soil organic matter (SOM) in the area and in other similar areas with arable‐livestock systems. Reduction of soil C and N by the high quality organic materials suggests that their role in maintaining SOM in the long‐term is limited in this area. A sound nutrient management system should strive to make a balance between maximizing crop production and sustaining soil quality.     

Potential Use of a Poultry Manure Digestate as a Biofertiliser: Evaluation of Soil Properties and Lactuca sativa Growth

Anaerobic digestion is a process that is widely used for the treatment of organic wastes. The digestate can be used as a soil amendment or crop fertiliser. The aims of our work were to evaluate 1) the physicochemical composition and pathogen content in a digestate from poultry manure, according to international regulations, and 2) the effect of its soil application on the major chemical and biological soil properties and on the growth of Lactuca sativa. The experiment consisted of two groups of pots(with and without crop). Treatments applied to each group were as follows: low and high doses of digestate and inorganic fertiliser, and no application(control)(low dose: 70 kg nitrogen(N) ha~(-1) and 21 kg phosphorus(P) ha~(-1); high dose: 210 kg N ha~(-1) and 63 kg P ha~(-1)). Soil samples were taken 7 and 34 d(harvest) after treatment applications. Heavy metal and pathogen contents in the digestate were below the upper limit values. Despite the high pH and electrical conductivity values of the digestate, both soil parameters presented acceptable values for crop growth. Although there were no initial increases in total inorganic N and available P in soil with digestate application, an increase in the fresh weight of crop was observed with the high dose application. This is probably associated with the slow nutrient release from the digestate during the development of the crop. Changes in the microbial community were temporary and occurred at the initial sampling stage of the experiment.     

Effects of Organic Matter-Rich Amendments on Selenium Mobility in Soils

Soil organic matter (SOM) plays an important role in the Se dynamics in soil. The potential effects of vermicompost and digestate as important sources of SOM on selenium (Se) mobility were assessed in this study. Three soils differing in their physicochemical parameters, fluvisol, chernozem, and luvisol, were chosen, and three types of vermicomposts based on various bio-waste materials as digestate (vermicompost 1), kitchen waste with woodchips (vermicompost 2), and garden bio-waste (vermicompost 3) were used due to their high organic matter content. Additionally, digestate samples alone were applied. To evaluate the potential effect of vermicompost application on sorption characteristics of soils, batch sorption experiments were performed. The results showed a predominant effect on Se species in the soils, where selenite sorbed more intensively compared to selenate, regardless of the soil and ameliorative material applied. In the control, the soil sorption ability of selenite tended to decrease in the order:fluvisol > luvisol > chernozem. However, these differences were not significant. Moreover, the effects of the ameliorative materials depended on both soil and amendment used. In fluvisol, all the amendment applications resulted in a decrease in distribution coefficient (K_d values) of Se, whereas in chernozem, this effect was observed only for the digestate-based vermicompost 1. Increasing K_d levels were reported in luvisol treated with digestate; the application of garden bio-waste-based vermicompost 3 tended to decrease the K_d values. Further studies are required on long-term effects of these amendments on Se mobility in soils and the role of individual organic matter fractions in this context.     

Amount and speciation of N leached from a sandy soil fertilized with urea,liquid digestate,struvite and NH4-enriched chabazite zeolite-tuff

The large use and the bad management of fertilizers that are applied to soil for improving crop production have dramatically impaired soil, water, and air quality. To meet the requirements to reduce nitrogen (N) losses and all the related negative impacts on the environment and food production, it is mandatory to substitute or at least partially substitute the use of inefficient and unsustainable fertilizers with more efficient alternatives. The aim of this paper was to address the amount and speciation of the N released by a sandy soil fertilized with “slow-release fertilizers” and traditional fertilizers (urea and liquid digestate) by means of a series of column leaching experiments. The slow-release alternatives were represented by NH₄-enriched zeolitic tuff and struvite, both obtained by recovering the N from liquid digestate. The treatments consisted of sandy soil fertilized with (i) urea (U) (ii) liquid digestate (LD), (iii) NH₄-enriched zeolitic tuff (N-CHA) and (iv) struvite (STRV). Eight different flushing events were performed over 38 days, leachates were collected and analysed for total Kjeldahl N, organic-N, NH₄⁺-N, NO₃⁻-N, NO₂⁻-N and pH. U and LD lost the majority of N within the first 2 flushing events as organic N and NH₄⁺-N, respectively. On the other hand, STRV and N-CHA lost less N over the whole course of the experiment and with more balanced speciation. The mass balance outlined that after the experiment, native soil N was mined in U and LD treatments while in N-CHA and STRV a fraction of N from the fertilizers was still present. The results showed a slow release of N which can be used more efficiently in agricultural applications, minimizing the N losses.     

Impact of Digestate Application on Chemical and Microbiological Properties of Two Different Textured Soils

Agricultural application of anaerobic digestates can play an important role in plant nutrition. The effects of digestate treatment were studied in pot experiments, using sandy and loamy textured soils with distinct characteristics. Three different treatments were studied and compared: control, digestate, and irrigation treatments. Nitrogen loading was calculated on the bases of the digestate analysis. The same amounts of digestate and irrigation water were applied in the different treatments before sowing and at the V4–V6 stages of maize. Besides the conventional soil chemical analysis, invertase, dehydrogenase, catalase, and the abundance of some cultivable microbes were measured in two consecutive years. According to our results, irrigation and digestate treatments had greater impact in the case of sandy soils than in loamy textured soils. Digestate provides more effective phosphorus and potassium sources than nitrogen. Based on the results of discriminant analysis, the digestate application had a greater influence on soil chemical properties, followed by microbiological parameters.     

PREVIOUS CROPS AND ORGANIC FERTILIZERS IN LETTUCE: EFFECTS ON YIELDS AND SOIL PROPERTIES

The use of organic amendments in agriculture could sustain crop production and preserve the agroecosystem, due to their importance in the conservation of organic matter in soil. The objective of this research was to evaluate the effects of differing organic fertilizers and of previous crops on lettuce growth, nutritional status and yields. The effects on soil characteristics were further investigated. The research was carried out during two years (2006 and 2007) at Metaponto (MT) in southern Italy, on lettuce crops cultivated after eggplant and melon to avoid their continuous cropping. The effects of application of a mineral fertilizer (MF), and of three treatments with organic fertilizers (commercial stable manure - OM; anaerobic digestate based on wine distillery wastewater - AD; composted municipal solid organic wastes coming from the separate collection - MSW) were studied. Head average weight, leaf area index, nitrate content and SPAD readings during the cropping cycles did not show significant differences among fertilizer treatments. On the contrary, marketable yield and head average weight at the harvest presented significantly different among the three organic fertilizers. The average marketable yield and head average weight of organic fertilizers experimental (AD and MSW treatments) decreased of 16 and 17%, respectively, compared to OM treatment. The previous melon crop influenced positively all analyzed parameters of the lettuce compared with previous eggplant crop. The previous melon crop reached the highest marketable yield with an increase of 59% compared with previous eggplant crop. Compared to the mineral fertilizer, the organic ones significantly increased the extracted fraction of soil organic carbon (6.9, 10.7 and 14.9% for OM, AD and MSW, respectively), without significant changes for the humic and fulvic content.