Biochar + AD exerts a biostimulant effect in the yield of horticultural crops and improves bacterial biodiversity and species richness in the rhizosphere

[EN] Organic fertilisers are gaining prominence in advanced agri-systems due to the need for alternatives to the most pollutant agricultural inputs, contributing to sustainable agriculture. The objective of this study was to analyse the agronomic effect of a biochar non-additivated and additivated with anaerobic digestate (AD) on the soil microbiome in melon and pepper crops at the field scale, hypothesising that the synergy between biochar and the additive confers additional benefits to the crop. Two doses of biochar (250 and 500 kg ha−1) and two doses of additive with respect to biochar (5 and 10% v:w) were tested. The highest yield was observed for a reduced dose of mineral fertilisation (NPK −20%) with biochar + AD at the highest dose of additive: a biochar dose of 250 kg/ha with 10% AD for the melon crop and a biochar dose of 500 kg ha−1 with 10% AD for the pepper crop. Specifically, the yield increase compared with the control, which only received NPK, was a 33% increase in melon and 18% in pepper. The microbiome of the bulk soil was not modified by biochar + AD, but the composition of the rhizosphere microbiome changed, emerging plant growth-promoting rhizobacteria (PGPR) or increasing its relative abundance (e.g. Arthrobacter, Mitsuaria or Bacillus genus). We have demonstrated a positive correlation between yield and fruit quality parameters, and the presence of cluster of bacteria with predominance of known PGPR genera, that have been boosted by the treatments with biochar + AD. Thus, we hypothesize that the improved yield and fruit quality is in part due to the rhizosphere bacteria community enhancement.S

Improved Organic Fertilisers Made from Combinations of Compost, Biochar, and Anaerobic Digestate: Evaluation of Maize Growth and Soil Metrics

[EN] Treated bio-residues can be used as biostimulants in crops within the circular economy approach to reduce the use of traditional fertilisers. In this work, we optimised the combination rates for three types of treated bio-residues (compost, biochar, and anaerobic digestate (AD)) in two microcosm trials, one with a combination of compost and biochar and other with biochar and AD. The crop used was maize, and the variables analysed were plant growth, and soil chemical and biological properties. The combination of bio-residues improved plant growth and soil biological activity to a greater extent than one product alone; that is, compost and biochar performed better than compost alone and biochar, and AD performed better than biochar alone. However, while the concentration in the plant biomass of several essential nutrients for crops increased in the treatments with compost and biochar, and with biochar and AD, compared to the untreated controls, the nitrogen concentration was reduced. This was due to the competition for nitrogen between the plant and the soil microbiome, whose activity was activated. Due to the importance of nitrogen in plant growth, the increase in biomass production could be explained not only by the higher availability of other nutrients but also by the plant-growth-promoting activity exerted by the more active soil microbiome. Further research should focus on validating this hypothesis and unravelling the mechanisms involved. From the environmental site, the presence of biochar in the mixtures of organic residues reduced the soil nitrogen at risk of lixiviation and sequestered carbon, which partially compensated for the increased CO2 emissions because labile forms of carbon were present in the remaining organic residues.S

Fertilising Maize with Bio-Based Mineral Fertilisers Gives Similar Growth to Conventional Fertilisers and Does Not Alter Soil Microbiome

[EN] The production of mineral fertilisers relies heavily on mineral deposits that are becoming depleted or is based on processes that are highly energy demanding. In this context, and in line with the circular economy and the European Green Deal, the recovery of nitrogen (N), phosphorus (P), and potassium (K) from organic wastes using chemical technologies is an important strategy to produce secondary raw materials for incorporation into mineral fertilisers, partially replacing the traditional sources of N, P, and K. However, there are very few studies on the agronomic and environmental effects of such substitution. The aim of this work was to evaluate plant growth under microcosm conditions and the effect on the soil microbiome of mineral fertilisers in which part of the N, P, or K content comes from bio-based materials (BBMFs), namely ash, struvite, and a patented chemical process. The crop was maize, and a metataxonomic approach was used to assess the effect on the soil microbiome. The BBMF treatments were compared with a control treated with a conventional mineral fertiliser. The conventional fertiliser performed significantly better than the biobased fertilisers in terms of maize biomass production at the first sampling point 60 days after sowing (DAS), but at the last sampling point, 90 DAS, the BBMFs showed comparable or even better biomass production than the conventional one. This suggests that BBMFs may have a slightly slower nutrient release rate. The use of fertiliser, whether conventional or BBMF, resulted in a significant increase in microbiome biodiversity (Shannon index), while it did not affect species richness. Interestingly, the use of fertilisers modulated the composition of the bacterial community, increasing the abundance of beneficial bacterial taxa considered to be plant-growth-promoting bacteria, without significant differences between the conventional mineral fertilisers and the BBMFs. The predominance of PGPRs in the rhizosphere of crops when BBMFs are used could be part of the reason why BBMFs perform similarly or even better than conventional fertilisers, even if the rate of nutrient release is slower. This hypothesis will be tested in future field trials. Thus, BBMFs are an interesting option to make the food chain more sustainable.SIThis research was funded by European Commission—BBI JU project “Bio-based FERtilising products as the best practice for agricultural management SusTainability (BFERST)”. H2020-BBI-JTI- 2018, Grant agreement ID: 837583. NO-L was granted a fellowship from the FPU program by the Spanish Ministry of Education with code (FPU 17/04201)

Mechanisms involved in drought stress tolerance triggered by rhizobia strains in wheat

Rhizobium spp. is a well-known microbial plant biostimulant in non-legume crops, but little is known about the mechanisms by which rhizobia enhance crop productivity under drought stress. This work analyzed the mechanisms involved in drought stress alleviation exerted by Rhizobium leguminosarum strains in wheat plants under water shortage conditions. Two (LBM1210 and LET4910) of the four R. leguminosarum strains significantly improved the growth parameters (fresh and dry aerial weight, FW and DW, respectively), chlorophyll content, and relative water content (RWC) compared to a non-inoculated control under water stress, providing values similar to or even higher for FW (+4%) and RWC (+2.3%) than the non-inoculated and non-stressed control. Some other biochemical parameters and gene expression explain the observed drought stress alleviation, namely the reduction of MDA, H2O2 (stronger when inoculating with LET4910), and ABA content (stronger when inoculating with LBM1210). In agreement with these results, inoculation with LET4910 downregulated DREB2 and CAT1 genes in plants under water deficiency and upregulated the CYP707A1 gene, while inoculation with LBM1210 strongly upregulated the CYP707A1 gene, which encodes an ABA catabolic enzyme. Conversely, from our results, ethylene metabolism did not seem to be involved in the alleviation of drought stress exerted by the two strains, as the expression of the CTR1 gene was very similar in all treatments and controls. The obtained results regarding the effect of the analyzed strains in alleviating drought stress are very relevant in the present situation of climate change, which negatively influences agricultural production.This project has been financially supported by European Commission - BBI JU project “Bio-based FERtilising products as the best practice for agricultural management SusTainability (BFERST)”. H2020-BBI-JTI-2018, Grant agreement ID: 837583. NO-L was granted a fellowship from the FPU program by the Spanish Ministry of Education with code (FPU 17/04201)

Combined application of N-fixing PGPB and rice straw mulch compensates N immobilization by straw, improving crop growth

[EN] Background Rice straw, often treated as waste, provides many benefits to crops when used as a mulch. However, straw degradation promotes nitrogen immobilisation due to its high C:N ratio, causing N competition between soil microorganisms and the crop. Currently, sustainable practices to remedy nitrogen immobilisation are hardly being implemented. In microcosm conditions we assessed whether the inoculation with N-fixers could offset the transient nitrogen deficiency caused by straw mulch, thereby harnessing the benefits of straw while mitigating its negative impact on nitrogen depletion and exerting a synergistic effect on crop growth. Results Inoculation with N-fixers increased the nitrogen content in the soil (the increase ranged from 14% up to 90% for NH4 + and from 20% to 60% for NO3 −) and, in most cases, also the nitrogen content in the plant (ranging from 10% to 15% increase), compared to the non-inoculated control. Therefore, inoculation would compensate for the lack of nitrogen caused by nitrogen immobilisation, and this resulted in an increased biomass production by the crop compared with the uninoculated control (the increase ranged from 25% to 85%). In addition, inoculation with N-fixers did not lead to a permanent change in the bacterial community composition, whereas straw addition increased the biodiversity of the soil microbiome. Conclusions The results obtained in microcosm conditions are a first indication that complementing straw mulching with the inoculation of N-fixers could avoid the transient N immobilisation produced during straw degradation. Thus, the benefits of the combination would be a yield increase, while improving the biodiversity of the soil microbiome, stabilising soil temperatures and increasing water soil content.SIThis work was supported by the Spanish Ministry of Science, Innovation and Universities (project RTC-2017-6249-2

Scaling-Up of the Production of Biochar from Olive Tree Pruning for Agricultural Use: Evaluation of Biochar Characteristics and Phytotoxicity

[EN] Due to the large acreage of olive trees in the Mediterranean basin, the biochar from olive tree pruning may become an important resource as part of circular economy strategies. However, so far, there is not much knowledge on whether the same characteristics are repeated in biochar once production is up-scaled to an industrial level. Accordingly, this study aimed to scale up the production of olive tree pruning biochar with three reactors (semi-pilot, pilot and industrial) to ascertain the production parameters that determine the characteristics of the obtained biochar and its possible toxicity to use in agriculture or environmental applications. First, the production conditions in the semi-pilot reactor were optimised by testing three temperatures (400, 500 and 600 °C), with the result that 600 °C was the optimal production temperature because of a high carbon content (70.88%), moderate pH (8.1), good carbon sink (R50 > 0.5) and low contents of PAHs (<6 mg/kg) and heavy metals, resulting in a phytostimulanting effect for all the crops studied. Then, the production was upscaled, using 600 °C as pyrolysing temperature. At the industrial scale, accurate temperature control is essential because when temperatures above 650 °C were reached, the biochar showed a pH above 11, resulting in severe phytotoxicity. The longer retention time of the material in the industrial pyrolysers improved the carbon stability and, therefore, the biochar’s role as a carbon sink. Consequently, it was proven that it is possible to produce olive tree pruning biochar adequate for agriculture and environmental applications with large-scale equipment, and the two most important factors needing control are the temperature and retention time.SIThis research was co-funded by the research project “Desarrollo de fertilizantes avanzados a partir de subproductos del olivar y bioestimulantes microbianos” (BIFEROLIVA) [IDI-20191225] co-funded by Cortijo de Guadiana S.A. and CDTI (Spanish Ministry of Science and Innovation)

Evaluación de la fitotoxicidad y toxicidad en microorganismos de diversos productos con biorresiduos tratados

Los productos obtenidos del proceso de pirólisis y de la carbonización hidrotermal, permiten la valorización de la biomasa residual además de resultar atractiva su aplicación en el ámbito agronómico. Sin embargo, los efectos producidos en las primeras fases de crecimiento de los cultivos y en microorganismos del suelo promotores del crecimiento radicular, son poco conocidos. En este trabajo, se produjeron trece productos diferentes derivados de estos procesos, y se evaluó su fitoxicidad y su toxicidad en tres microorganismos, mediante diferentes ensayos. Los resultados obtenidos indican que los productos evaluados presentan un riesgo de fitotoxicidad distinto según la especie a la que se aplique, y que existen diferencias significativas entre los mismos, para los distintos índices de fitotoxicidad y especies. Los productos de carácter sólido y líquido muy diluidos, son los menos fitotóxicos e incluso, producen estimulación en el crecimiento radicular, en la mayoría de las especies. Por otra parte, ninguno de los productos utilizados provoca toxicidad o inhibición en el crecimiento de los microorganimos empleados, por lo que aquellos productos libres de fitotoxicidad y a su vez estimulantes, podrían utilizarse como enmienda en cultivos.Departamento de Ingeniería Agrícola y ForestalMáster en Tecnologías Avanzadas para el Desarrollo Agroforestal2028-07-202028-07-2

Diseño y evaluación agronómica y ambiental de abonos agrícolas avanzados basados en biorresiduos, rizobacterias y en los principios de la economía circular

122 p.[EN] To reduce the negative environmental consequences of agriculture intensification and to achieve sustainability, the European Commission has fostered strategies based on the circular economy to reduce dependence on non-renewable sources. The use of bio-residues is a leading strategy to provide nutrients to crops and improve nutrient use efficiency. The objective of this work was to design and evaluate advanced fertilisers based on different combinations of bio-residues and rhizobacteria, as part of a global strategy based on a circular economy aimed at reducing the use of conventional mineral fertilisers in agriculture. Two families of advanced fertilisers were designed: the first based on compost and the second based on biochar. The first one consisted of two products: i) compost + biochar; and ii) compost inoculated with Bacillus siamensis (SCFB3-1 strain) formulated with biochar as a carrier (‘doped compost’). The second family consisted of one product, namely biochar + anaerobic digestate (AD). The aqueous extracts of the designed products were analysed for phytotoxicity and toxicity in three species of soil rhizobacteria. All products were phytostimulants at the dilution ratio of 1:25 (w:v), whereas for the ratio 1:10, they had either no phytotoxic or moderately phytotoxic effects. Conversely, more concentrated ratios were phytotoxic. No toxicity to rhizosphere bacteria was observed. The products compost + biochar and biochar + AD were preliminary tested in microcosm conditions; in such a trial, maize plants treated with either of the two products produced higher biomass than the non-fertilised control, although the N content in the biomass decreased. In commercial fields, the ‘doped compost’ worked better in terms of crop yield than the combination of compost and biochar. Moreover, a reduced dose (minus 20%) of mineral fertiliser combined with ‘doped compost’ (2 t ha−1) produced a higher yield in melon and pepper than the control that received a full mineral fertiliser dose (24% to 33% higher in melon and 2% to 4% in pepper). Furthermore, the same reduced dose of mineral fertiliser combined with biochar + AD (250 to 500 t ha−1) produced a higher melon yield (2% to 16% higher) and a similar pepper yield compared with the control that received the full mineral dose. In addition to the positive agronomic effects on crop yield from the environmental side, the first advantage is the reduction in the dose of mineral fertilisers. However, more relevant environmental benefits have been encountered in the soil microbiome, as revealed by the metataxonomic approach. Foremost, the composition of the bulk soil microbiome remained unaltered by the treatments. However, the treatments increased the soil microbiome activity, which consumed soil nitrogen (N); thus, the risk of N lixiviation was reduced, although it resulted in a lower N content in the crop biomass. We have demonstrated that the increased yield, even for less N available, is positively correlated with the enhanced microbiome activity but also with the presence of certain bacteria clusters considered plant growth promoting rhizobacteria (PGPR), whose relative abundance in the rhizosphere has been increased by the treatments. Moreover, microbiome diversity and species richness were also enhanced by the treatments, which theoretically has a positive effect on crop yield. We finally hypothesised that not only does the inoculated B. siamensis exert a direct effect on the crop, but it also causes changes in the rhizosphere. Further research is needed to understand the process involved in such a mechanism.[ES] Para reducir las consecuencias medioambientales negativas de la intensificación de la agricultura y lograr la sostenibilidad, la Comisión Europea ha fomentado estrategias basadas en la economía circular para reducir la dependencia de las fuentes no renovables. El uso de biorresiduos es una estrategia puntera para aportar nutrientes a los cultivos y mejorar la eficiencia en el uso de nutrientes. El objetivo de este trabajo fue diseñar y evaluar fertilizantes avanzados basados en diferentes combinaciones de biorresiduos y rizobacterias, como parte de una estrategia global basada en la economía circular dirigida a reducir el uso de fertilizantes minerales convencionales en la agricultura. Se diseñaron dos familias de fertilizantes avanzados: la primera basada en compost y la segunda en biochar. La primera constaba de dos productos: i) compost + biochar; y ii) compost inoculado con Bacillus siamensis (cepa SCFB3-1) formulado con biochar como soporte (‘compost dopado’). La segunda familia constaba de un solo producto, concretamente, biochar + digerido anaerobio (DA). Los extractos acuosos de los productos diseñados fueron utilizados para analizar la fitotoxicidad y la toxicidad en tres especies de rizobacterias del suelo. Todos los productos fueron fitoestimulantes en la proporción de dilución 1:25 (p:v), mientras que en la proporción 1:10 no tenían efectos fitotóxicos o los tenían moderadamente. Por el contrario, las proporciones más concentradas resultaron fitotóxicas. No se observó toxicidad para las bacterias de la rizosfera. Los productos compost + biochar y biochar + AD se ensayaron preliminarmente en condiciones de microcosmos; en dicho ensayo, las plantas de maíz tratadas con cualquiera de los dos productos produjeron una biomasa superior a la del control no fertilizado, aunque el contenido de N en la biomasa disminuyó. En campo, el "compost dopado" funcionó mejor en términos de rendimiento de los cultivos que la combinación de compost y biochar. Además, una dosis reducida (menos 20%) de fertilizante mineral combinada con "compost dopado" (2 t ha-1) produjo un mayor rendimiento en melón y pimiento que el control que recibió una dosis completa de fertilizante mineral (entre un 24% y un 33% mayor en melón y entre un 2% y un 4% en pimiento). Además, la misma dosis reducida de fertilizante mineral combinada con biochar + AD (250 a 500 t ha-1) produjo un mayor rendimiento en melón (2% a 16% mayor) y un rendimiento similar en pimiento en comparación con el control que recibió la dosis mineral completa. Además de los efectos agronómicos positivos sobre el rendimiento de los cultivos, desde el punto de vista ambiental, la primera ventaja es la reducción de la dosis de fertilizantes minerales. Sin embargo, se han encontrado beneficios ambientales más relevantes en el microbioma del suelo, como revela el enfoque metataxonómico. En primer lugar, la composición del microbioma del suelo permaneció inalterada por los tratamientos. Sin embargo, los tratamientos aumentaron la actividad del microbioma del suelo, que consumió nitrógeno (N) del suelo; por lo tanto, se redujo el riesgo de lixiviación de N, aunque resultó en un menor contenido de N en la biomasa del cultivo. Hemos demostrado que el aumento del rendimiento, incluso para menos N disponible, está positivamente correlacionado con la mayor actividad del microbioma, pero también con la presencia de ciertos grupos de bacterias consideradas rizobacterias promotoras del crecimiento vegetal (PGPR), cuya abundancia relativa en la rizosfera se ha visto incrementada por los tratamientos. Además, la diversidad del microbioma y la riqueza de especies también aumentaron con los tratamientos, lo que teóricamente tiene un efecto positivo en el rendimiento de los cultivos. Finalmente, nuestra hipótesis es que B. siamensis inoculado no sólo ejerce un efecto directo sobre el cultivo, sino que también provoca cambios en la rizosfera. Es necesario seguir investigando para comprender el proceso implicado en dicho mecanismo

An Organic Fertilizer ‘Doped’ with a Bacillus Strain Improves Melon and Pepper Yield, Modifying the Rhizosphere Microbiome with Negligible Changes in the Bulk Soil Microbiome

[EN] Doped compost consists of compost inoculated with Bacillus siamensis SCFB3-1 that is formulated in biochar and then mixed with the compost. The study objective was to analyze, at field scale, the effect of doped compost on the melon and pepper yield and on the soil microbiome, hypothesizing that the synergy between the components of doped compost confers additional benefits to the crop. Two doses of compost (2 and 5 t/ha) and two doses of the inoculant (biochar+SCFB3-1) with respect to the compost (3% and 6% w:w) were tested. The highest yield was observed for a reduced dose of mineral fertilization (NPK -20%) with a compost dose of 2 t/ha with 6% of the inoculant. Specifically, the yield increase compared with the control, which only received NPK, was a 47% increase in melon and 28% in pepper. The microbiome of the bulk soil was not modified by the doped compost, but the composition of the rhizosphere microbiome changed, increasing in the abundance of Bacillus (the inoculated strain), but also changing the relative abundance of other genera in the bacterial community. Future works will be focused on unravelling the possible effects of phytohormones on the observed results.SIThis research was funded by the Spanish Ministry of Economy and Competitiveness (project ‘LIGNOxBIOp’ RTC 2016-5834-5), and by University of León, León, Spai