Biodiesel Co-Product (BCP) amendment drives beneficial soil microbiome assembly promoting acid soil health

Biodiesel Co-Product (BCP) amendment has been shown to decrease both nitrate leaching and nitrous oxide (N2O) emissions in acidic soil; however, the effects of BCP on the soil microbiome have not been investigated thoroughly. In this study, we investigated the response of prokaryotic and fungal communities in aspects of structure, diversity, and co-occurrence network to the BCP amendment following complete mixing application (0–18-cm depth) of 1.5 mg BCP-C g−1 and surface application (0–6-cm depth) of 4.5 mg BCP-C g−1 via high-throughput 16S rRNA and internal transcribed spacer (ITS) amplicon sequencing. The amendment altered microbial communities significantly by increasing the relative abundances of Proteobacteria (Burkholderia) and Ascomycota (Trichoderma) in prokaryotic and fungal communities, respectively. Only a higher rate application (4.5 mg BCP-C g−1) decreased prokaryotic alpha diversity, whereas all rates of amendment decreased fungal diversity. The co-occurrence network of prokaryotes had more nodes and links and a higher average degree and clustering coefficient than the fungal network with BCP addition. The majority of keystone species in prokaryotic and fungal networks were from Proteobacteria and Ascomycota taxa. Of note, the BCP amendment significantly increased the OTU numbers of potential biocontrol agents, including Trichoderma (T.) spirale, T. koningiopsis, and T. virens, etc., while decreased OTU numbers related to plant pathogens species, particularly in the complete mixing application. Our work highlights the potential for BCP amendments to promote the assembly of a healthy soil microbiome by enhancing the abundance of potential biocontrol microbes while reducing plant pathogens species, which may contribute to soil health

Integrated application of bacterial carbonate precipitation and silicon nanoparticles enhances productivity, physiological attributes, and antioxidant defenses of wheat (Triticum aestivum L.) under semi-arid conditions

The use of calcium carbonate-precipitating bacteria (CCPB) has become a well-established ground-improvement technique. However, the effect of the interaction of CCPB with nanoparticles (NPs) on plant performance is still meager. In this study, we aimed at evaluating the role of CCPB and/or silicon NPs (Si-NPs) on the growth, physio-biochemical traits, and antioxidative defense of wheat (Triticum aestivum L.) under semi-arid environmental conditions. A 2-year pot experiment was carried out to determine the improvement of the sandy soil inoculated with CCPB and the foliar application of Si-NPs on wheat plants. We tested the following treatments: spraying plants with 1.0 or 1.5 mM Si-NPs (control = 0 mM Si-NPs), soil inoculated with Bacillus lichenforms (MA16), Bacillus megaterium (MA27), or Bacillus subtilis (MA34), and the interaction of individual Bacillus species with Si-NPs. Our results showed that soil inoculation with any of the three isolated CCPB and/or foliar application of Si-NPs at the rates of 1.0 or 1.5 mM significantly improved (p ≤ 0.05) the physiological and biochemical attributes as well as the enzymatic antioxidant activities of wheat plants. Therefore, the combined treatments of CCPB + Si-NPs were more effective in enhancing physio-biochemical characteristics and enzymatic antioxidant activities than the individual treatments of CCPB or Si-NPs, thus achieving the best performance in the treatment of MA34 + 1.5 mM Si-NPs. Our results demonstrated that the co-application of CCPB and Si-NPs, particularly MA34 + 1.5 mM Si-NPs, considerably activated the antioxidant defense system to mitigate the adverse effects of oxidative stress, thus increasing tolerance and enhancing the production of wheat plants in sandy soils under semi-arid environmental conditions

Genome-Wide identification and expression analysis of metal tolerance protein gene family in Medicago truncatula under a broad range of heavy metal stress

Metal tolerance proteins (MTPs) encompass plant membrane divalent cation transporters to specifically participate in heavy metal stress resistance and mineral acquisition. However, the molecular behaviors and biological functions of this family in Medicago truncatula are scarcely known. A total of 12 potential MTP candidate genes in the M. truncatula genome were successfully identified and analyzed for a phylogenetic relationship, chromosomal distributions, gene structures, docking analysis, gene ontology, and previous gene expression. M. truncatula MTPs (MtMTPs) were further classified into three major cation diffusion facilitator (CDFs) groups: Mn-CDFs, Zn-CDFs, and Fe/Zn-CDFs. The structural analysis of MtMTPs displayed high gene similarity within the same group where all of them have cation_efflux domain or ZT_dimer. Cis-acting element analysis suggested that various abiotic stresses and phytohormones could induce the most MtMTP gene transcripts. Among all MTPs, PF16916 is the specific domain, whereas GLY, ILE, LEU, MET, ALA, SER, THR, VAL, ASN, and PHE amino acids were predicted to be the binding residues in the ligand-binding site of all these proteins. RNA-seq and gene ontology analysis revealed the significant role of MTP genes in the growth and development of M. truncatula. MtMTP genes displayed differential responses in plant leaves, stems, and roots under five divalent heavy metals (Cd2+, Co2+, Mn2+, Zn2+, and Fe2+). Ten, seven, and nine MtMTPs responded to at least one metal ion treatment in the leaves, stems, and roots, respectively. Additionally, MtMTP1.1, MtMTP1.2, and MtMTP4 exhibited the highest expression responses in most heavy metal treatments. Our results presented a standpoint on the evolution of MTPs in M. truncatula. Overall, our study provides a novel insight into the evolution of the MTP gene family in M. truncatula and paves the way for additional functional characterization of this gene family

Plant growth-promoting microorganisms as biocontrol agents of plant diseases: Mechanisms, challenges and future perspectives

Plant diseases and pests are risk factors that threaten global food security. Excessive chemical pesticide applications are commonly used to reduce the effects of plant diseases caused by bacterial and fungal pathogens. A major concern, as we strive toward more sustainable agriculture, is to increase crop yields for the increasing population. Microbial biological control agents (MBCAs) have proved their efficacy to be a green strategy to manage plant diseases, stimulate plant growth and performance, and increase yield. Besides their role in growth enhancement, plant growth-promoting rhizobacteria/fungi (PGPR/PGPF) could suppress plant diseases by producing inhibitory chemicals and inducing immune responses in plants against phytopathogens. As biofertilizers and biopesticides, PGPR and PGPF are considered as feasible, attractive economic approach for sustainable agriculture; thus, resulting in a “win-win” situation. Several PGPR and PGPF strains have been identified as effective BCAs under environmentally controlled conditions. In general, any MBCA must overcome certain challenges before it can be registered or widely utilized to control diseases/pests. Successful MBCAs offer a practical solution to improve greenhouse crop performance with reduced fertilizer inputs and chemical pesticide applications. This current review aims to fill the gap in the current knowledge of plant growth-promoting microorganisms (PGPM), provide attention about the scientific basis for policy development, and recommend further research related to the applications of PGPM used for commercial purposes

Mitigate nitrate contamination in potato tubers and increase nitrogen recovery by combining dicyandiamide, moringa oil and zeolite with nitrogen fertilizer

Potato is considered a nitrogen (N) intensive plant with a low N use efficiency (NUE). The current study introduced an excellent approach by combining dicyandiamide (DCD), moringa seed oil (MSO), or zeolite (ZE), with N fertilizer for maximizing potato tuber yields and NUE as well as minimizing tubers nitrate (NO3−) accumulation. The impact of these materials on soil N availability and gaseous emissions (NH3, and N2O) was investigated under incubation conditions. A 2-year field experiment were carried out with seven treatments [without N (control), N fertilizer (350 kg N-urea ha−1 as a recommended dose; UreaRD), 75% of N recommended dose with DCD (Urea75%RD+DCD), Urea75%RD with 2% MSO (Urea75%RD+MSO2%), Urea75%RD with 4% MSO (Urea75%RD+MSO4%), Urea75%RD with 0.5 Mg ZE ha−1 (Urea75%RD+ZER1), and Urea75%RD with 1.0 Mg ZE ha−1 (Urea 75%RD+ZER2)]. We also conducted a 40-days incubation trial with the same treatments; however, urea was added at the rate of 200 mg N kg−1 soil for all treatments, excluding the control. The addition of DCD, MSO, and ZE with urea under incubation conditions delayed the nitrification process, thereby causing a rise in NH4+-N content and a decrease in NO3−-N content. Ammonia-oxidizing bacteria (AOB) was inhibited (p ≤ 0.01) in treatments Urea+DCD, Urea+MSO4%, and Urea+ZER2. The highest NUE indexes were recorded in treatment Urea75%RD+DCD. The highest NO3- accumulation (567 mg NO3− kg−1) in potato tubers was recorded in treatment UreaRD. Whilest, the lowest NO3- content (81 mg NO3− kg−1) was in treatment Urea75%RD+DCD. The lowest cumulative N2O emissions and highest cumulative NH3 volatilization were observed in the treatment Urea+DCD under incubation conditions. Our findings demonstrated that N fertilizer rate could be reduced by 25%, while the tuber yields increased with an acceptable limit of NO3− content, resulting in economical, agronomical, and environmental benefits

Spatial trends in the nitrogen budget of the African agro-food system over the past five decades

Low nitrogen (N) fertilization is a dominant cause of malnutrition in Africa, but the spatial and temporal variability of N cycling patterns in Africa remain unclear. This study is the first to perform a detailed analysis of the N cycling patterns of 52 African countries from 1961 to 2016. We calculated the N use efficiency (NUE) in crop production, country-specific N fertilization trends, and the impacts of N fertilization on human protein demand and the environment. Over the past five decades, total N input to African croplands increased from 20 to 35 kg N ha ^−1 yr ^−1 , while the application of synthetic N fertilizers (SNF) increased from 4.0 to 15 kg N ha ^−1 yr ^−1 . N contributions from animal manure and biological N fixation remained lower than 10 kg N ha ^−1 yr ^−1 and 20 kg N ha ^−1 yr ^−1 , respectively. The total N crop production increased from 15 to 22 kg N ha ^−1 yr ^−1 from 1961 to 2016. Total N surplus in Africa increased from 5 to 13 kg N ha ^−1 yr ^−1 , while estimated gaseous losses increased from 4.0 to 11 kg N ha ^−1 yr ^−1 . However, NUE declined from 74% to 63% during the past five decades, and protein consumption increased from 2.99 to 3.78 kg N capita ^−1 yr ^−1 . These results suggest that Africa suffers from extremely low N input and that N loss is increasing in agricultural land. We recommend the implementation of an effective N management strategy incorporating the use of locally available organic material along with the balanced application of SNF. Such measures will require effective policy development and cooperation between all stakeholders

Modelling and mapping soil nutrient depletion in humid highlands of East Africa using ensemble machine learning : A case study from Rwanda

Soil nutrient depletion is one of the major causes of high yield gaps and nutrient deficiencies in East Africa highlands, including Rwanda. This research sought to determine the current soil nutrient balance and its spatial variation in 10 Rwandan agro-ecological zones. Soil nitrogen (N), phosphorus (P) and potassium (K) depletion in croplands were calculated using data from 455 field trials of the Optimizing Fertilizer Recommendations in Africa (OFRA) project in Rwanda. Calculated soil nutrient balances (NPK) and 15 environmental covariates were used to calibrate soil nutrient depletion models using ensemble machine learning (EML) and 10-fold cross-validation. In the 2019–2020 growing season, annual N and K depletions were 33.6 kg N ha−1 yr−1 and 71.0 kg K ha−1 yr−1, with a positive P balance of 2.30 kg P ha−1 yr−1. High soil nutrient uptake and high soil nutrient loss due to erosion and leaching were two main causes of NPK depletion. Spatial variations of NPK balance were influenced by soil nutrient stocks, soil erosion, elevation, rainfall, soil texture, and soil bulk density. The 10-fold cross-validation showed that coefficients of determination (R2) of NPK models were 62%, 58%, and 58%, respectively. Compared to single models, ensemble machine learning improved NPK model accuracy up to 5%. Our research revealed that soil nutrient depletion was highest in the northwest and lowest in the southeast of the study area. We conclude that increasing soil nutrient inputs without reducing soil nutrient loss due to soil degradation will not decrease soil nutrient depletion in Rwanda and ensemble machine learning outperforms single models in predicting soil nutrient balance. The solution to reduce high soil nutrient depletion in all agro-ecological zones of Rwanda would be to prioritize soil and water conservation measures and increase soil nutrient inputs