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Background and aims: Entomopathogenic mitosporic ascomycetes Beauveria, Metarhizium and Isaria sp. are commonly used for pest control but can also serve other, lesser known functions such as increasing nutrient bioavailability or promote plant growth. The objective of this work was to identify the doses of entomopathogenic fungi (EF) to be applied to soil in order to modify iron (Fe) uptake by plants and promote their growth. Methods: We used an in vitro assay to assess the ability of Beauveria bassiana, Metarhizium brunneum and Isaria farinosa to mobilize Fe from nine Fe oxides differing in composition, particle size and crystallinity, including ferrihydrite, hematite, goethite and magnetite. We also conducted an in vivo assay by applying five different doses (viz., 0, 5 × 102, 5 × 104, 5 × 106 and 5 × 108 conidia ml−1) of a conidial suspension of M. brunneum to the surface of a calcareous soil, which induced Fe chlorosis and a non–calcareous soil which did not induce chlorosis to explore the ability of the fungus on improving Fe nutrition and plant growth of sorghum and sunflower plants. Results: In the in vitro assay, all three EF increased Fe availability differently depending on particle size and crystallinity, and I. farinosa and B. bassiana increased the pH of the culture medium, whereas M. brunneum did not produce a great effect. In the in vivo assay, the highest dose (5 × 108 conidia ml−1) of M. brunneum alleviated Fe chlorosis symptoms of sorghum plants grown in the calcareous soil, and the two highest doses (5 × 106 and 5 × 108 conidia ml−1) increased plant height and inflorescence production of sunflower grown in both soils. Conclusions: The observed benefits of EF on plant growth and nutrition provide support for more sustainable and cost–effective use of these biocontrol agents.

Aims A field experiment was conducted to investigate the effect of biochar on maize yield and greenhouse gases (GHGs) in a calcareous loamy soil poor in organic carbon from Henan, central great plain, China. Methods Biochar was applied at rates of 0, 20 and 40 tha−1 with or without N fertilization. With N fertilization, urea was applied at 300 kg N ha−1, of which 60% was applied as basal fertilizer and 40% as supplementary fertilizer during crop growth. Soil emissions of CO2, CH4 and N2O were monitored using closed chambers at 7 days intervals throughout the whole maize growing season (WMGS). Results Biochar amendments significantly increased maize production but decreased GHGs. Maize yield was increased by 15.8% and 7.3% without N fertilization, and by 8.8% and 12.1% with N fertilization under biochar amendment at 20 tha−1 and 40 tha−1, respectively. Total N2O emission was decreased by 10.7% and by 41.8% under biochar amendment at 20 tha−1 and 40 tha−1 compared to no biochar amendment with N fertilization. The high rate of biochar (40 tha−1) increased the total CO2 emission by 12% without N fertilization. Overall, biochar amendments of 20 tha−1 and 40 tha−1 decreased the total global warming potential (GWP) of CH4 and N2O by 9.8% and by 41.5% without N fertilization, and by 23.8% and 47.6% with N fertilization, respectively. Biochar amendments also decreased soil bulk density and increased soil total N contents but had no effect on soil mineral N. Conclusions These results suggest that application of biochar to calcareous and infertile dry croplands poor in soil organic carbon will enhance crop productivity and reduce GHGs emissions.

In concert with oxygen, soil alkalinity strongly restricts the availability of iron, an essential nutrient with a multitude of functions in living organisms. In addition to its role in mitochondrial energy metabolism and as a cofactor for enzymes, in plants iron also plays key roles in photosynthesis and is required for chlorophyll biosynthesis. The ability to thrive in calcareous soils, referred to as calcicole behaviour, is the readout of an amalgam of traits of which efficient foraging of iron is a decisive factor. Recently, the well-established concept of two distinct iron uptake strategies, phylogenetically separating grasses from other land plants, was expanded by the discovery of auxiliary mechanisms that extend the range of edaphic conditions to which a species can adapt. Secretion of a tailor-made cocktail of iron-mobilising metabolites into the rhizosphere, the composition of which is responsive to a suite of edaphic and internal cues, allows survival in calcareous soils through a competitive iron acquisition strategy, which includes intricate interactions with the consortium of associated microorganisms in, on, and around the roots. This versatile, reciprocal plant-microbiome interplay affects iron mobilisation directly, but also collaterally by impacting growth, fitness, and health of the host. Here, we review the mechanisms and the multifaceted regulation of iron acquisition in plants, taking into consideration the specific constraints associated with the uptake of iron from alkaline soils. Knowledge on how plants extract iron from such soils sets the stage for a better understanding of essential ecological processes and for combatting iron malnutrition in humans.

Many agricultural soils worldwide in their natural state are deficient in phosphorus (P), and the production of healthy agricultural crops has required the regular addition of P fertilisers. In cropping systems, P accumulates almost predominantly in inorganic forms in soil, associated with aluminium, calcium and iron. In pasture soils, P accumulates in both inorganic and organic forms, but the chemical nature of much organic P is still unresolved. The P use efficiency (PUE) of fertilisers is generally low in the year of application, but residual effectiveness is important, highlighting the importance of soil P testing prior to fertiliser use. With increasing costs of P fertiliser, various technologies have been suggested to improve PUE, but few have provided solid field evidence for efficacy. Fluid fertilisers have been demonstrated under field conditions to increase PUE on highly calcareous soils. Slow release P products have been demonstrated to improve PUE in soils where leaching is important. Modification of soil chemistry around the fertiliser granule or fluid injection point also offers promise for increasing PUE, but is less well validated. Better placement of P, even into subsoils, also offers promise to increase PUE in both cropping and pasture systems.

Purpose Plants growing in the soils of karst forests associate with arbuscular mycorrhizae (AM) or ectomycorrhizae (ECM) to acquire nutrients. We researched how these different mycorrhizal associations affect rhizosphere soil nutrient economy in these calcareous soils. Methods Bulk and rhizosphere soils were sampled beneath 25 AM and 9 ECM plants growing in primary forests at the Puding Karst Critical Zone Observatory. Nutrient contents and potential enzyme activities were analyzed to test the effect of different types of mycorrhizal association on rhizosphere soil nitrogen (N) and phosphorus (P) economies. Results The contents of nitrate-N and available-P were markedly lower in the rhizospheres of ECM plants compared to AM plants. Ectomycorrhizal plants promoted relatively greater investment in N-acquisition enzymes, in contrast, AM plants caused relatively greater investment in P-acquisition enzymes. The decreased pH in the rhizospheres of AM plants likely promoted the greater P availability. Conclusion Our results revealed how plants that form contrasting mycorrhizal associations have fundamentally different effects on rhizospheric nutrient economies in the low fertility karst soils of southwest China. Differentiation in N- and P-acquisition capacity of these plants have implications for species coexistence and the high levels of plant biodiversity observed in these forests.

In calcareous soil, the significant portion of applied phosphorus (P) fertilizers is adsorbed on the calcite surface and becomes unavailable to plants. Addition of organic amendments with chemical fertilizers can be helpful in releasing the absorbed nutrients from these surfaces. To check out this problem, a field experiment was conducted for two years to determine the effect of P fertilizers and humic acid (HA) in enhancing P availability in soil and their ultimate effect on growth, yield and P uptake of wheat in calcareous soils. The experiment was comprised of five levels of P (0, 45, 67.5, 90 and 112.5 kg P2O5 ha−1) as a single superphosphate (SSP) and 2 levels of locally produced humic acid (with and without HA) arranged in a two factorial randomized complete block design (RCBD) with three replications. Wheat plant height, spike length, number of grains per spike, 1000-grain weight, grain, straw and biological yield were significantly improved by the addition of HA with SSP. Very often, the performance of 67.5 kg P2O5 ha−1 with HA were either similar or better than 90 or even 112.5 kg P2O5 ha−1 applied without HA. Post-harvest soil organic matter, AB-DTPA extractable and water-soluble P, plant P concentration and its uptake were also significantly improved by the addition of HA with SSP compared to sole SSP application. It was evident that P efficiency could be increased with HA addition and it has the potential to improve crop yield and plants P uptake in calcareous soils.

Cadmium (Cd) contamination of wheat fields is a major environmental problem. Sulfhydryl-grafted palygorskite (SGP) has been used as an efficient amendment to immobilize Cd in calcareous wheat fields. However, information on the long-term effects of SGP on soil Cd immobilization and accumulation in wheat remains limited. In this study, wheat pot and freeze–thaw (F/T) cycle experiments were conducted to explore the remediation stability of SGP during winter wheat growing. The wheat pot experiments showed that applying 0.1–0.2%SGP significantly decreased Cd in wheat grains by 21.57–57.85% in the second year. The application of 0.2%SGP decreased diethylenetriaminepentaacetic acid (DTPA) extractable Cd by 33.84–39.70%, increased DTPA extractable Mn by 11.22–15.86%, and promoted the conversion of exchangeable Cd into carbonate-bound and Fe/Mn oxide-bound Cd fractions in the soil in the second year. The composition and function of soil bacteria differed under the SGP treatment for two consecutive years. F/T cycle experiments showed that F/T cycles did not affect soil pH but converted exchangeable Cd and carbonate-bound Cd to the residual Cd fraction (6%) and increased the mass fraction of > 2 mm soil aggregates. Under 0.2%SGP application, F/T cycles further decreased the available soil Cd concentration and increased the immobilization efficiency of SGP on Cd by 9.37–11.82% in various aggregates. Although SGP can reduce Cd accumulation in wheat for two consecutive years, the remediation efficiency decreased compared to that in the first year, which is unrelated to seasonal F/T cycles; the specific reasons for this reduction must be further explored. Overall, SGP displayed long-term immobilization effects on Cd in wheat fields and showed higher efficiency under F/T cycle conditions, with the potential for long-term remediation of Cd-contaminated calcareous soils in cold regions.

Background and aims The current paradigm for phosphorus (P) fertilizers applied to calcareous soil is that almost entirely water soluble P fertilizers are efficient and sparingly soluble P fertilizers are not efficient P sources for crops. We hypothesize that this paradigm does not apply to recycled P fertilizers and that other P pools can explain the plant use of recycled P fertilizers on calcareous soil. Methods We applied 33P isotopic dilution method to evaluate recycled P fertilizers based on plant P uptake from fertilizer relative to plant uptake from a water soluble P reference fertilizer. The predictability of fertilizer effectiveness based on sequentially extracted P forms and X-ray diffraction pattern of recycled fertilizers derived from sewage sludge, human urine and organic waste was evaluated. Results The plant experiments showed that tested recycled P fertilizers including compost were more effective than rock phosphate. The water insoluble P contained in urine based products was almost as effective as a fully water soluble P fertilizer. The tested recycled P fertilizers are characterized by complex P compounds differing in solubility which were so far not considered in the water and citric acid extraction methods. The fraction of resin- and NaHCO3 extractable fertilizer P explained effectiveness of P fertilizer applied to the calcareous and to an acidic soil. Conclusion We concluded that water solubility is not required when P forms in recycled products are comparable to reactions products of rock phosphate based fertilizers in soil. Alternatives to fully water soluble P fertilizers are available to supply P to crops grown on calcareous soil efficiently.

Purpose Salinity severelyconstrains viticulture in calcareous soils by disrupting rhizosphere microbial community, nutrient availability, and physio-biochemical homeostasis, thereby reducing fruit yield. This study aimed to (i) assess the effects of soil-applied citric acid (CA) and halotolerant/halophilic citrate-utilizing plant growth-promoting rhizobacteria (CU-PGPR; Bacillus spizizenii and Halobacillus marinus ) on the microbial community and chemical properties of saline-calcareous soil, (ii) evaluate vine physio-biochemical responses to the individual and combined treatments, and (iii) determine their impacts on yield and fruit quality. Methods A 2-field experiment (2023/2024 and 2024/2025) on Vitis vinifera at the Faculty of Agriculture’s Experimental Farm (32°42′ N, 29°75′ E), Fayoum University, Egypt. This study evaluated three CA rates: 0 (CA 0 ), 100 (CA 100 ), and 200 (CA 200 ) g vine⁻¹ season⁻¹ and three inoculation treatments: non-inoculated (NI), H. marinus , or B. spizizenii . Measurements included rhizospheric bacterial counts, soil chemistry (pH, electrical conductivity; EC e , and macro- and micro-nutrient availability), leaf and petiole nutrients, physio-biochemical traits, yield, and fruit quality. Results Co-application of CA 200 × B. spizizenii exhibited the strongest synergistic effects. Total bacterial count and specific functional groups markedly increased. Soil pH declined by 6.1%, while available N, K⁺, Fe²⁺, and Zn²⁺ increased by 817%, 105%, 659%, and 720%, respectively. The CA 200 × H. marinus resulted in the highest available P (310% above CA 0 × NI), though EC e was unaffected. Enhanced nutrient bioavailability improved ionic balance, raising the leaf K⁺/Na⁺ ratio by 78% and the Ca²⁺/Na⁺ ratio by 74.7%, while reducing Na⁺ by 31% compared with CA 0 × NI. Physio-biochemically, CA 200 × B. spizizenii boosted vine water content, osmotic adjustment, antioxidant capacity, and photosynthetic efficiency over CA 0 × NI. Consequently, grape yield, pruning weight, fruit TSS/acid ratio, and firmness increased by 97%, 81%, 99%, and 24%, respectively, averaged across both seasons, over CA 0 × NI. Conclusion Co-application of 200 g CA vine − 1 season⁻¹ with B. spizizenii inoculation effectively revitalizes microbial activity and enhances nutrient bioavailability, offering a promising strategy for sustaining viticulture under saline-calcareous soil conditions. Graphical Abstract

Sustainable agricultural production is mainly attributed to healthy soils. Calcareous soils, especially in arid and semiarid areas, suffer from low organic matter and nutrient availability. Low organic matter could degrade soil with reducing the crop productivity. Thus, the present study aimed to assess the integrated effect of soil mulch and irrigation on soil activity, nutrient availability, and potentiality of corn yield under calcareous soil conditions. In a calcareous soil, two mulching soil treatments (mulch and non-mulch) as well as three irrigation regimes, applied as ratio of crop evapotranspiration (60, 80, and 100%, denoted I60, I80, and I100, respectively), were arranged in a strip plot design based on completely randomized block arrangement using 3 replicates. Mulching soil plus irrigation by I80 achieved the maximum increases in organic carbon, organic matter, and soil activity. Higher values of NH 4 + –N form were detected with non-mulch and irrigation by I100 or I60. Lower Zn content was obtained in soil due to mulch or non-mulch plus irrigation I100. With lowering irrigation level by 20% (I80) and by application of mulch, the increases in weight of ear, weight of 100 kernels, and kernel yield of corn amounted to 5.4, 4.6, and 16.1%, respectively. Results from the present study conclude that adoption of soil mulching in corn production system plus moderate irrigation (80% of crop evapotranspiration) is considered a promising management practice for amending calcareous soils, saving irrigation water, and sustaining/boosting soil productivity in arid zones.