Changes in canopy microclimate of faba bean under intercropping at controlled nitrogen levels and their correlation with crop yield

BACKGROUND

The relationship between the microclimate of the intercropping faba bean canopy and yield, and its response to nitrogen application, was studied in the crop canopy to clarify that intercropping and nitrogen application changed the microclimate of the faba bean canopy and affected the yield.

RESULTS

In field experiments in Eshan and Xundian, the growth index, light transmittance, interception rate of photosynthetic effective radiation, temperature, relative humidity, and yield of the faba bean were determined using three planting methods (wheat monoculture, faba bean monoculture, and wheat-faba bean intercropping) and four nitrogen application levels, N0 (0 kg/hm² ), N1 (45 kg/hm² ), N2 (90 kg/hm² ), and N3 (180 kg/hm² ). The results showed that the application of nitrogen improved the growth index of monoculture and intercropping broad beans significantly, reduced the canopy light transmittance and temperature significantly, and increased the interception rate and relative humidity of photosynthetic effective radiation significantly. Compared with N0, the yield of broad bean in both places was the highest in N1, which increased by 14% (Eshan) and 15% (Xundian).

CONCLUSION

Multiple linear stepwise regression and path analysis showed that the decrease in canopy light transmittance during the faba bean pod-setting stage and the interception rate of photosynthetic effective radiation during pod-bulging stage, caused by excessive nitrogen application, were the main climatic and ecological factors limiting the increase in the intercropping faba bean yield in Eshan and Xundian respectively. The optimum nitrogen application rate recommended in production is 45 kg/hm² , to reduce the nitrogen application rate and maximize the productivity of the wheat and faba bean system. © 2023 Society of Chemical Industry.

Apple-marigold intercropping improves soil properties by changing soil metabolomics and bacterial community structures

Marigold can protect crops against soil-borne diseases. However, the effects of intercropping with marigold on apple rhizosphere soils are not known. In this study, we investigated the metabolite profiles and bacterial community structures in rhizosphere soils of the apple-marigold intercropping system by high-throughput sequencing and soil metabolomics. The results show that intercropping marigold could significantly enhance soil moisture, nitrogen, and enzyme activities compared with clean tillage. The soil metabolite profiles and the soil bacterial community structures in the rhizosphere soils were different between the inter-and mono-cropping systems. Among nine metabolites, carbohydrates were more increased in the intercropping system than in the monocropping system. Pathway enrichment analysis revealed that the greatest differential, in terms of metabolic pathway, was starch and sucrose metabolism. Moreover, intercropping marigold significantly increased the relative abundance of plant growth promoting bacteria in rhizosphere soils, such as Rhizobiales, Pseudomonadales, and Bacillales. These results indicate that marigold intercropping positively affected the apple orchard's soil quality and may provide a new intercropping technique to improve soil fertility in orchards and promote plant growth.

Photosynthetic Acclimation of Shade-Grown Soybean Seedlings to a High-Light Environment

Soybean in relay intercropping is initially exposed to a shade environment, followed by exposure to full sunlight after the harvesting of primary crops, e.g., maize. Therefore, soybean's ability to acclimate to this changing light environment determines its growth and yield formation. However, the changes in soybean photosynthesis under such light alternations in relay intercropping are poorly understood. This study compared the photosynthetic acclimation of two soybean varieties with contrasting shade tolerance, i.e., Gongxuan1 (shade-tolerant) and C103 (shade-intolerant). The two soybean genotypes were grown in a greenhouse under full sunlight (HL) and 40% full sunlight (LL) conditions. Subsequently, after the fifth compound leaf expanded, half of the LL plants were transferred to a high-sunlight environment (LL-HL). Morphological traits were measured at 0 and 10 days, while chlorophyll content, gas exchange characteristics and chlorophyll fluorescence were assayed at 0, 2, 4, 7 and 10 days after transfer to an HL environment (LL-HL). Shade-intolerant C103 showed photoinhibition 10 days after transfer, and the net photosynthetic rate (P_n) did not completely recover to that under a high light level. On the day of transfer, the shade-intolerant variety, C103, exhibited a decrease in net photosynthetic rate (P_n), stomatal conductance (G_s) and transpiration rate (E) in the low-light (LL) and low-light-to-high-light (LL-HL) treatments. Additionally, intercellular CO₂ concentration (C_i) increased in low light, suggesting that non-stomatal factors were the primary limitations to photosynthesis in C103 following the transfer. In contrast, the shade-tolerant variety, Gongxuan1, displayed a greater increase in P_n 7 days after transfer, with no difference observed between the HL and LL-HL treatments. Ten days after transfer, the shade-tolerant Gongxuan1 exhibited 24.1%, 10.9% and 20.9% higher biomass, leaf area and stem diameter than the intolerant C103. These findings suggest that Gongxuan1 possesses a higher capacity to adapt to variations in light conditions, making it a potential candidate for variety selection in intercropping systems.

Cereal-Pea Intercropping Reveals Variability in the Relationships among Yield, Quality Parameters, and Obligate Pathogens Infection in Wheat, Rye, Oat, and Triticale, in a Temperate Environment

Widespread usage of intercropping systems has been limited because of a lack of knowledge about the key factors that affect the performance of intercrop components. We used general linear modelling to explain the effect of different cropping systems on the relationships among yield, thousand kernel weight (TKW), and crude protein of cereal crops under the same agro-ecological conditions and naturally occurring inocula of obligate pathogens. The results of our study showed that the yield variation under extreme fluctuations in climatic conditions could be lowered through intercropping cultivation. The disease indices of leaf rust and powdery mildew were highly dependent on the type of cultivation. The relationships among the levels of pathogenic infection and yield performances were not straightforward and were highly dependent on the yielding potentials of the cultivars. Our study indicated that changes in yield, TKW, and crude protein, as well as their relationships during intercropping cultivation, were cultivar specific and, therefore, not the same among all cereal crops exposed to the same agro-ecological conditions.

Soybean Yield and Nutrition Grown on the Straw of Grain Sorghum Inoculated with Azospirillum brasilense and Intercropped with BRS Paiaguás Grass

The adoption of diversified agricultural systems that employ integrated cultural practices appears to be the way to sustainably intensify tropical agriculture. Our objectives were to evaluate the dry matter (DM) accumulation of sorghum inoculated with Azospirillum brasilense, with or without a nitrogen fertilization split, intercropped with palisade grass (Urochloa brizantha cv. BRS Paiaguás), and how these practices influenced the nutrition and development of soybean in succession. The design was a randomized complete block in a 2 × 2 × 3 factorial, consisting of sorghum monoculture cropped or intercropped with palisade grass, sorghum either inoculated or not with A. brasilense, and nitrogen applied at 120 kg ha-1 N only at sowing, only at topdressing, or split-30% at sowing and 70% at topdressing at the beginning of the panicle initiation stage. The residual impacts of these treatments on the following soybean crop were also evaluated. Higher DM yield occurred in sorghum inoculated with A. brasilense, however, this result varied by year. The sorghum-palisade grass intercrop produced a higher amount of straw than sorghum monoculture. The nutrition of soybean was adequate regardless of treatments, but grain yield was higher when the sorghum residue was inoculated. The inoculation of A. brasilense in sorghum intercropped with palisade grass increased yield. The nutrition of soybean was adequate regardless of the treatments, while grain yield was higher on the inoculated sorghum residues. The inoculation of A. brasilense in sorghum intercropped with palisade grass increased DM yield. The intercropping increased the production of biomass for animal grazing and DM for soil coverage. The inoculation of sorghum by A. brasilense and its intercropping with palisade grass contributed to higher soybean yield in succession.

Remediation effect and mechanism of low-As-accumulating maize and peanut intercropping for safe-utilization of As-contaminated soil

Phytoremediation by intercropping is a potential method to realize both production and remediation. Maize and peanut are the main crops planted in arsenic(As) contaminated areas in south China and vulnerable to As pollution. Experiments were conducted on arsenic-polluted soil with low As-accumulating maize monoculture (M), peanut monoculture (P), and intercropping with different distances between the maize and peanut (0.2 m, 0.35 m, and 0.5 m, recorded as MP0.2, MP0.35, and MP0.5, respectively). The results indicated that the As content in the maize grains and peanut lipids in the intercropping system decreased significantly, meeting the food safety standard of China (GB 2762-2017). Moreover, the land equivalent ratio (LER) and heavy metal removal equivalence ratio (MRER) of all intercropping treatments were greater than 1, indicating that this intercropping agrosystem has the advantage of production and arsenic removal, among which the yield and LER of MP0.35 treatment were the highest. Additionally, the bioconcentration factors (BCF) and translocation factor (TF) of MP0.2 increased by 117.95% and 16.89%, respectively, indicating that the root interaction affected the absorption of As in soil by crops. This study preliminarily demonstrated the feasibility of this intercropping system to safely use and remedy arsenic-contaminated farmland during production.

Interspecific plant interaction via root exudates structures the disease suppressiveness of rhizosphere microbiomes

Terrestrial plants can affect the growth and health of adjacent plants via interspecific interaction. Here, we studied the mechanism by which plant root exudates affect the recruitment of the rhizosphere microbiome in adjacent plants-with implications for plant protection-using a tomato (Solanum lycopersicum)-potatoonion (Allium cepa var. agrogatum) intercropping system. First, we showed that the intercropping system results in a disease-suppressive rhizosphere microbiome that protects tomato plants against Verticillium wilt disease caused by the soilborne pathogen Verticillium dahliae. Second, 16S rRNA gene sequencing revealed that intercropping with potatoonion altered the composition of the tomato rhizosphere microbiome by promoting the colonization of specific Bacillus sp. This taxon was isolated and shown to inhibit V. dahliae growth and induce systemic resistance in tomato plants. Third, a belowground segregation experiment found that root exudates mediated the interspecific interaction between potatoonion and tomato. Moreover, experiments using split-root tomato plants found that root exudates from potatoonion, especially taxifolin-a flavonoid compound-stimulate tomato plants to recruit plant-beneficial bacteria, such as Bacillus sp. Lastly, ultra-high-pressure liquid chromatography-mass spectrometry analysis found that taxifolin alters tomato root exudate chemistry; thus, this compound acts indirectly in modulating root colonization by Bacillus sp. Our results revealed that this intercropping system can improve tomato plant fitness by changing rhizosphere microbiome recruitment via the use of signaling chemicals released by root exudates of potatoonion. This study revealed a novel mechanism by which interspecific plant interaction modulates the establishment of a disease-suppressive microbiome, thus opening up new avenues of research for precision plant microbiome manipulations.

Aromatic Plants and Their Associated Arbuscular Mycorrhizal Fungi Outcompete Tuber melanosporum in Compatibility Assays with Truffle-Oaks

The high value of black truffle recompenses the slow growth of the fungus when established in the field. Adding a secondary crop, such as medicinal and aromatic plants (MAPs), could further enhance the sustainability of truffle production agro-forest systems. The dual cultures of ectomycorrhizal truffle-oak seedlings and MAPs (lavender, thyme, and sage) previously inoculated and non-inoculated with native arbuscular mycorrhizal fungi (AMF), were established to evaluate plant-fungi relationships. After 12 months in a shadehouse, plants' growth, mycorrhizal colonization, and extraradical soil mycelium (both of Tuber melanosporum and AMF) were measured. Overall, truffle-oaks' growth was negatively affected by the presence of MAPs, especially when inoculated with AMF. In turn, the presence of truffle-oaks barely affected the co-cultured MAPs, and only lavenders showed a significant growth reduction. All AMF-inoculated MAPs showed higher shoot and root biomass than non-inoculated ones. Compared to truffle-oaks growing alone, the presence of co-cultured MAPs, especially when they were AMF-inoculated, significantly decreased both the ectomycorrhizas and soil mycelium of T. melanosporum. These results reveal the strong competition between AMF and T. melanosporum and warn about the need for the protection of intercropping plants and their associated symbiotic fungi to avoid reciprocal counterproductive effects in mixed truffle-oak-AMF-MAP plantations.

Predacious Natural Enemies Associated With Suppression of Onion Thrips, Thrips tabaci (Thysanoptera: Thripidae), in Intercropped Onion-Barley Agroecosystems

The effects of two possible factors, prevention of pest immigration and enhancement of natural enemies, in suppressing onion thrips, Thrips tabaci L., were estimated in a small-scale experimental system of spring-planted onions intercropped with barley. The population dynamics of the thrips and their potential predatory natural enemies were investigated in four treatments: control (bare ground), insect net barrier, and onion-barley intercropping with or without trimming. We found that intercropping significantly suppressed onion thrips. It is unlikely that this effect was due to the prevention of thrip immigration because they seemed to move over the camouflage and/or physical barriers of the barley and the net barrier surrounding the onions easily. Intercropping with barley significantly increased hoverfly (Syrphidae) larvae numbers on onion leaves, and that of some groups of ground-dwelling predators such as large carnivorous ground beetles (Carabidae), ants (Formicidae), and wolf spiders (Lycosidae). We conclude that the suppression of thrips in this system was associated with the enhancement of hoverfly larvae abundance, mainly Sphaerophoria macrogaster (Thomson) (Syrphidae: Diptera) because they were observed together with thrips on onions and have been reported to predate thrips as well as aphids. Some hoverfly larvae on barley might move to nearby onions to search for new food sources and attack thrips.

Comparative analyses of functional traits based on metabolome and economic traits variation of Bletilla striata: Contribution of intercropping

The intercropping practice has been regarded as a practical land-use selection to improve the management benefits of Bletilla striata plantations. The reports about the variety of economic and functional traits of Bletilla pseudobulb under intercropping systems were limited. The present study investigated the variation of economic and functional traits of Bletilla pseudobulb under different intercropping systems (the deep-rooted intercropping system: B. striata - Cyclocarya paliurus, CB; and the shallow-rooted intercropping system: B. striata - Phyllostachys edulis, PB). The functional traits were analyzed through non-targeted metabolomics based on GC-MS. The results indicated that the PB intercropping system significantly decreased the yield of Bletilla pseudobulb while significantly increasing the total phenol and flavonoids compared with the control (CK). However, there were no significant differences in all economic traits between CB and CK. The functional traits among CB, PB, and CK were separated and exhibited significant differences. Under different intercropping systems, B. striata may adopt different functional strategies in response to interspecific competition. The functional node metabolites (D-galactose, cellobiose, raffinose, D-fructose, maltose, and D-ribose) were up-regulated in CB, while the functional node metabolites (L-valine, L-leucine, L-isoleucine, methionine, L-lysine, serine, D-glucose, cellobiose, trehalose, maltose, D-ribose, palatinose, raffinose, xylobiose, L-rhamnose, melezitose, and maltotriose) were up-regulated in PB. The correlation between economic and functional traits depends on the degree of environmental stress. Artificial neural network models (ANNs) accurately predicted the variation in economic traits via the combination of functional node metabolites in PB. The correlation analysis of environmental factors indicated that Ns (including TN, NH₄ ⁺-, and NO₃ ^--), SRI (solar radiation intensity), and SOC were the main factors that affected the economic traits (yield, total phenol, and total flavonoids). TN, SRI, and SOC were the main factors affecting the functional traits of the Bletilla pseudobulb. These findings strengthen our understanding of the variation of economic and functional traits of Bletilla pseudobulb under intercropping and clarify the main limiting environmental factors under B. striata intercropping systems.

[Effects of Earthworm, Straw, and Citric Acid on the Remediation of Zn, Pb, and Cd Contaminated Soil by Solanum photeinocarpum and Pterocypsela indica]

Regulation of exogenous substances and intercropping are effective methods to improve the efficiency of phytoremediation of heavy metal contaminated soil. A pot experiment was used to study the effects of earthworms, straw, and citric acid on the remediation of Zn, Pb, and Cd contaminated soil by monocropping and intercropping of Solanum photeinocarpum and Pterocypsela indica. The results showed that the bioaccumulation factors (BCF) of earthworms for Zn, Pb, and Cd were 0.07-0.13, 0.10-0.26, and 5.64-15.52, respectively. The addition of straw in the soil increased the biomass of earthworms by 22.29%-223.87% but reduced the heavy metal concentrations by 8.15%-62.58%. Straw and citric acid showed passivation and activation effects, respectively, but earthworms had no significant effect on the available concentrations of heavy metals in the soil. Earthworms had no significant effect on the heavy metal concentrations of P. indica but reduced the heavy metal concentrations of S. photeinocarpum. Straw showed an inhibitory effect on the concentrations of heavy metals in P. indica but promoted the concentrations of Cd in S. photeinocarpum. Citric acid had no significant effect on the heavy metal concentrations in S. photeinocarpum but significantly increased the Pb concentrations in P. indica. Intercropping significantly reduced the soil available heavy metal concentrations and increased the heavy metal concentrations in plant roots; however, it had no significant effect on heavy metal concentrations in plant shoots. The total extraction amounts of Zn, Pb, and Cd by plants were mainly manifested as P. indica>intercropping>S. photeinocarpum. The addition of earthworms increased the total extraction amounts of Zn, Pb, and Cd by 12.49%, 35.89%, and 29.01%, respectively, and the addition of straw+earthworms increased the total extraction amounts of Pb by 87.21%. The results indicated that straw significantly promoted the growth of earthworms and reduced their accumulation of heavy metals, and the addition of earthworms alone or in combination with straw can effectively improve the remediation potential of P. indica of Zn, Pb, and Cd contaminated soil.

An integrated remediation approach using combinations of biochar, Rhizobium leguminosarum, and Vigna radiata for immobilizing and dissipating cadmium contaminants from the soil-mustard plant system

Cadmium (Cd) contamination of soils is an environmental concern, as cadmium harms food crops and can therefore impact human health. The use of combinations of biochar (seeded with Rhizobium leguminosarum) and Vigna radiata (as an intercrop) has the potential to reduce the mobilization of Cd from soil via mustard plants (Brassica juncea). Mustard plants are grown as a food and oil production crop that is consumed worldwide. However, this plant has the property of hyperaccumulation; thus, it bioaccumulates Cd in its tissues, which in turn, if eaten, can become part of the human food chain. Hence, reducing Cd bioaccumulation in mustard plants is crucial to making these plants a reliable and safe source of food for consumption. To improve soil sorption capacity and immobilization efficiency, biochar (in the form of wheat husk) was mixed with R. leguminosarum and intercropped (using V. radiata) with mustard plants for further investigation. Sampling was performed at an early growth stage (i.e., at 30 days) and at maturity (i.e., at 60 days) to determine the impact of Cd on a plant's morphophysiological attributes. Data were analyzed in two ways: first by analysis of variance (ANOVA) and then by the post hoc Tukey's honestly significant difference (HSD) test. The statistical analysis concluded that combinations effectively improved plant traits by 65%-90% in the early growth stage and by 70%-90% in the maturity stage. The T6 treatment combination [i.e., biochar + R. leguminosarum + V. radiata (BC + RL + VR)] provided the most effective results in terms of growth, biomass, pod yield, and pigmentation content. In addition, this combination reduced the translocation of Cd in mustard plants by 70%-95%. The combination of BC + RL + VR effectively reduced Cd contamination of mustard tissue and provided a suitable growing environment for the plants. A post-harvesting soil analysis using X-ray diffraction (XRD) found that Cd was undetectable in soil. This provides clear confirmation that these approaches can lead to Cd soil remediation. Moreover, this study provided insight into the responses of different morphophysiological attributes of mustard plants to Cd stress and could aid in developing Cd stress tolerance in mustard plants.

Daylily intercropping: Effects on soil nutrients, enzyme activities, and microbial community structure

The daylily (Hemerocallis citrina Baroni)/other crop intercropping system can be a specific and efficient cropping pattern in a horticultural field. Intercropping systems contribute to the optimization of land use, fostering sustainable and efficient agriculture. In the present study, high-throughput sequencing was employed to explore the diversity in the root-soil microbial community in the intercropping of four daylily intercropping systems [watermelon (Citrullus lanatus)/daylily (WD), cabbage (Brassica pekinensis)/daylily (CD), kale (Brassica oleracea)/daylily (KD), watermelon/cabbage/kale/daylily (MI)], and determine the physicochemical traits and enzymatic activities of the soil. The results revealed that the contents of available potassium (2.03%-35.71%), available phosphorus (3.85%-62.56%), available nitrogen (12.90%-39.52%), and organic matter (19.08%-34.53%), and the urease (9.89%-31.02%) and sucrase (23.63%-50.60%) activities, and daylily yield (7.43%- 30.46%) in different intercropping soil systems were significantly higher compared to those in the daylily monocropping systems (CK). The bacterial Shannon index increased significantly in the CD and KD compared to the CK. In addition, the fungi Shannon index was also increased significantly in the MI, while the Shannon indices of the other intercropping modes were not significantly altered. Different intercropping systems also caused dramatic architectural and compositional alterations in the soil microbial community. A prominently higher relative richness of Bacteroidetes was noted in MI compared to that in CK, while Acidobacteria in WD and CD and Chloroflexi in WD were pronouncedly less abundant compared to those in CK. Furthermore, the association between soil bacteria taxa and soil characteristic parameters was stronger than that between fungi and soil. In conclusion, the present study demonstrated that the intercropping of daylily with other crops could significantly improve the nutrient levels of the soil and optimize the soil bacterial microflora composition and diversity.

Effects of Hevea brasiliensis Intercropping on the Volatiles of Pandanus amaryllifolius Leaves

Pandanus amaryllifolius Roxb. is a special tropical spice crop resource with broad development prospects. It is widely cultivated under a Hevea brasiliensis (Willd. ex A. Juss.) Muell. Arg. canopy to improve the comprehensive benefits to Hevea brasiliensis plantations in Hainan Provence, China. However, the effects of intercropping with Hevea brasiliensis on the component number and relative contents of volatile substances in different categories in the Pandanus amaryllifolius leaves are still unknown. Therefore, a Hevea brasiliensis and Pandanus amaryllifolius intercropping experiment was set up to clarify the differences between several cultivated patterns on volatile substances in the Pandanus amaryllifolius leaves, and the key regulatory factors of volatile substances. The results showed that the soil pH was significantly decreased, while soil bulk density, alkali-hydrolyzable nitrogen and available phosphorus contents were significantly increased under the intercropping pattern. The component numbers of esters in volatile substances were increased by 6.20%, while the component numbers of ketones were decreased by 4.26% under the intercropping pattern. Compared with the Pandanus amaryllifolius monoculture, the relative contents of pyrroles, esters and furanones were significantly increased by 8.83%, 2.30% and 8.27%, respectively, while the relative contents of ketones, furans and hydrocarbons were decreased by 1.01%, 10.55% and 9.16% under the intercropping pattern, respectively. The relative contents of pyrroles, esters, furanones, ketones, furans and hydrocarbons were associated with changes in soil pH, soil available phosphorus content and air temperature. The results indicated that the reduction in soil pH and enhancement in soil-available phosphorus may be the main reasons for promoting the relative content of pyrroles and reducing the relative content of hydrocarbons under an intercropping pattern. Overall, Hevea brasiliensis intercropping with Pandanus amaryllifolius could not only improve soil properties, but also significantly increase the relative contents of the main volatile substances in Pandanus amaryllifolius leaves, which could provide a theoretical basis for the application and promotion of high-quality production patterns of Pandanus amaryllifolius.

Phytoremediation Competence of Composite Heavy-Metal-Contaminated Sediments by Intercropping Myriophyllum spicatum L. with Two Species of Plants

A variety of remediation approaches have been applied to reduce the harm and diffusion of heavy metals in aquatic sediments; however, phytoremediation in co-contaminated soils is still not clear. In order to explore the phytoremediation of sediments contaminated by Cu and Pb, two submerged plants with different characteristics, Vallisneria natans and Hydrilla verticillata, were interplanted with Myriophyllum spicatum. By simulating a submerged plant ecological environment, medium-scale-simulated ecological remediation experiments were carried out. The results showed that the two planting patterns were effective in repairing the sediments in the Cu and Pb contaminated sediments. The intercropping of Myriophyllum spicatum and Vallisneria natans can be used as the plant stabilizer of Cu because of the TF > 1 and BCF < 1, and the intercropping with Hydrilla verticillata can regulate the enrichment efficiency of Myriophyllum spicatum. The removal rates of Cu and Pb in sediments reached 26.1% and 68.4%, respectively, under the two planting patterns. The risk grade of the restored sediments was RI < 150, indicating a low risk.

Intercropping of Cyphomandra betacea with Different Ploidies of Solanum Sect. Solanum (Solanaceae) Wild Vegetables Increase Their Selenium Uptakes

Selenium (Se) deficiency causes various diseases in humans. Se can be obtained from fruits and vegetables. In this study, the fruit tree Cyphomandra betacea was intercropped with three Solanum sect. Solanum (Solanaceae) wild vegetables [diploid (S. photeinocarpum), tetraploid (colchicine-induced S. photeinocarpum), and hexaploid (S. nigrum)], respectively, and Se uptakes of these plants were determined by a pot experiment. Intercropping decreased the biomass, photosynthetic pigment content, and superoxide dismutase activity of C. betacea, but increased the peroxidase (POD) activity, catalase (CAT) activity, and soluble protein content of C. betacea. These indicators' values of sect. Solanum increased after intercropping. The contents of Se increased in C. betacea and sect. Solanum after intercropping. Intercropped with diploid, tetraploid, and hexaploid increased the shoot Se contents in C. betacea by 13.73%, 17.49%, and 26.50%, respectively, relative to that of C. betacea monoculture. Intercropped with C. betacea increased the shoot Se contents in diploid, tetraploid, and hexaploid by 35.22%, 68.86%, and 74.46%, respectively, compared with their respective monoculture. The biomass and Se content of intercropped sect. Solanum showed linear relationships with the biomass and Se content of their monocultures. The biomass and Se content of intercropped C. betacea also exhibited linear relationships with that of sect. Solanum monocultures. Correlation and grey relational analyses revealed that the CAT activity, POD activity, and soluble protein content were the top three indicators closely associated with the C. betacea shoot Se content. The POD activity, soluble protein content, and translocation factor were the top three indicators closely associated with sect. Solanum shoot Se content. Therefore, intercropping can promote the Se uptake in C. betacea and sect. Solanum wild vegetables.

Bio-Intensive Tactics for the Management of Invasive Fall Armyworm for Organic Maize Production

Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae) is an invasive pest native to the American continent. The present study focused on bio-intensive tactics like intercropping, using natural enemies, botanical insecticides and biopesticides for managing S. frugiperda for the organic production of maize in Indian conditions. A total of eight different parasitoids attacking the different stages of S. frugiperda viz., eggs and larvae were found in the study area. The total parasitism rate due to all the parasitoids ranged from 28.37 to 42.44%. The egg-larval parasitoid, Chelonus formosanus Sonan (Hymenoptera: Braconidae) was the dominant parasitoid (12.55%), followed by Chelonus nr. blackburni (Hymenoptera: Braconidae) (10.98%) and Coccygydium sp. (4.85%). About 36.58 percent of the egg masses collected was parasitized by egg parasitoids, among which Telenomus remus (Nixon) (Hymenoptera: Scelionidae) was the dominant parasitoid. The botanicals insecticides such as citronella and annona extract were most effective, resulting in 100% mortality of FAW larvae (168 h after treatment). The essential oil of garlic (100%) was found highly effective in inhibiting egg hatching, followed by geraniol (90.76%). The maize intercropped with lady's finger (okra) recorded significantly the lowest pest infestation and recorded higher grain yield (6.17 q/ha) than other intercropping systems and control (5.10 q/ha). The overall bioefficacy of commercial biopesticides against the larvae of S. frugiperda was in the following order azadirachtin > Metarhizium anisopliae (Metch.) Sorokin (Hypocreales: Clavicipitaceae) > Beauveria bassiana (Balsamo) Vuillemin (Hypocreales: Clavicipitaceae) at 168 h after treatment.

Responses of the fall armyworm (Spodoptera frugiperda) to different host plants: Implications for its management strategy

BACKGROUND

The selection of suitable host plants for oviposition is critical for herbivorous insects to maximise survival of their offspring. Olfaction plays an important role in this process. However, little is known about how olfaction shapes the interaction between the fall armyworm (Spodoptera frugiperda) and host plants. In this study, we tested the hypothesis that olfaction guides the host selection process in the fall armyworm using oviposition and wind tunnel bioassays.

RESULTS

In no-choice and dual-choice assays, female moths oviposited on all seven host plants that were tested (maize, sorghum, wheat, bean, cowpea, tomato and cabbage). However, in multiple-choice assays, no eggs were deposited on cowpea and cabbage. We found that maize, sorghum and wheat were most preferred for oviposition, whereas cowpea was least preferred. Wind tunnel assays confirmed these divergent oviposition preferences, with maize, sorghum and wheat odours being the most attractive. Gas chromatography-mass spectrometry analysis followed by random forest classification identified terpenes as the potential host-plant attractants.

CONCLUSION

Our results improve our understanding of the chemical ecology of the fall armyworm and suggest that some of these host plants could offer potential for use in an intercropping strategy to manage S. frugiperda. © 2022 Society of Chemical Industry.

The productive performance of intercropping

Crop diversification has been put forward as a way to reduce the environmental impact of agriculture without penalizing its productivity. In this context, intercropping, the planned combination of two or more crop species in one field, is a promising practice. On an average, intercropping saves land compared with the component sole crops, but it remains unclear whether intercropping produces a higher yield than the most productive single crop per unit area, i.e., whether intercropping achieves transgressive overyielding. Here, we quantified the performance of intercropping for the production of grain, calories, and protein in a global meta-analysis of several production indices. The results show that intercrops outperform sole crops when the objective is to achieve a diversity of crop products on a given land area. However, when intercropping is evaluated for its ability to produce raw products without concern for diversity, intercrops on average generate a small loss in grain or calorie yield compared with the most productive sole crop (-4%) but achieve similar or higher protein yield, especially with maize/legume combinations grown at moderate N supply. Overall, although intercropping does not achieve transgressive overyielding on average, our results show that intercropping performs well in producing a diverse set of crop products and performs almost similar to the most productive component sole crop to produce raw products, while improving crop resilience, enhancing ecosystem services, and improving nutrient use efficiency. Our study, therefore, confirms the great interest of intercropping for the development of a more sustainable agricultural production, supporting diversified diets.

[Potential of Intercropping Pennisetum purpureum Schum with Melia azedarach L. and Broussonetia papyrifera for Phytoremediation of Heavy-metal Contaminated Soil around Mining Areas]

In order to study the potential of intercropping Pennisetum purpureum Schum with Melia azedarach L. and Broussonetia papyrifera for phytoremediation of heavy-metal contaminated soil around mining areas, a pot experiment was conducted to investigate the effects of intercropping on plant biomass, heavy metal accumulation, dynamic changes in heavy metal content in soil solution, and response characteristics of the rhizosphere microbial community. The results indicated that the shoot biomass of P. purpureum and M. azedarach from their intercropping system (KX) was increased by 26.5% and 13.2%, respectively, and the shoot biomass of B. papyrifera from the intercropping system of P. purpureum and B. papyrifera (GX) was increased by 13.5% compared with their corresponding monoculture systems. The shoot Cd content of M. azedarach in the KX treatment was significantly increased by 24.9% (P<0.05), and their Cd and Pb accumulation in shoots were also significantly increased. The shoot contents and accumulations of Cd and Pb from P. purpureum in the GX treatment were significantly increased; however, those in B. papyrifera shoots were decreased. The total accumulations of Cd and Pb in each pot from intercropping systems were higher than that from the monoculture treatment, with that from the KX treatment being the highest at 1065 μg·pot^-1. During the 150-day cultivation process, the pH value and dissolved organic carbon (DOC) content in the soil solution under the intercropping systems of KX and GX were higher than those of original soil (CK). After 150 d cultivation, the DOC contents of the soil solution under the KX and GX treatments were significantly increased by 40.5% and 33.1% in comparison with that under CK (P<0.05), respectively. Compared with those from CK and P. purpureum and B. papyrifera monoculture treatments, the Cd content in soil solution from the KX treatment was significantly decreased by 56.1%, 35.5%, and 46.5%, and that in the GX treatment was decreased by 54.5%, 33.2%, and 44.6% (P<0.05), respectively. The Shannon and Chao1 indices of rhizosphere microorganisms under the intercropping systems were significantly higher than those under CK. The number of unique OTUs in intercropping systems was significantly higher than that in CK and the M. azedarach and B. papyrifera monocultures. Intercropping improved the abundance of dominant bacteria such as Actinobacteriota and Acidobacteriota, and the abundance of Actinobacteriota increased by 31.6%, 20.9%, and 25.3% in the KX treatment and by 32.3%, 21.5%, and 25.9% in the GX treatment, respectively, in comparison with those in CK and the P. purpureum and M. azedarach monocultures. It was concluded that intercropping P. purpureum with wood plants could increase their shoot biomass and the accumulations of Cd and Pb, as well as soil environmental quality, whereas the availability and migration risk of heavy metals in soil were reduced. Moreover, the intercropping of P. purpureum and M. azedarach was more beneficial to the remediation of polymetallic-contaminated soil around mining areas.

Intercropping enhances microbial community diversity and ecosystem functioning in maize fields

Background and aims

Intercropping, a widely used planting pattern, could affect soil physicochemical properties, microbial community diversity, and further crop yields. However, its impacts on soil microbial diversity and ecosystem functioning and further soil sustainability are poorly understood.

Methods

We conducted field experiments by intercropping maize with four important crops (i.e., sesame, peanut, soybean, and sweet potato), and examined soil microbial community diversity and ecosystem functioning such as microbial biomass and enzyme activities under monocropping and intercropping. We quantified their intercropping effects on microbial diversity and ecosystem functions with effect size metric Cohen d by comparing to the monocropping of maize.

Results

We found that the four intercropping systems significantly increased soil aggregates in respective of the 2-0.25 mm grain size. Intercropping consistently elevated ecosystem functioning, such as soil enzyme activities of urease, phosphatase, and catalase, soil microbial biomass carbon and soil microbial biomass nitrogen. The Cohen d of bacterial richness also increased from 0.39 to 2.36, the latter of which was significant for maize/peanut intercropping. Notably, these ecosystem functions were strongly associated with the diversity of bacteria and fungi and the relative abundance of their ecological clusters identified with network analysis.

Conclusion

Together, our findings indicate that intercropping generally affected soil physicochemical properties, ecosystem functions, and promoted microbial community diversity. More importantly, our findings highlight the important roles of microbial diversity of ecological clusters (that is, network modules) in maintaining ecosystem functioning after intercropping. These results will help to better understand the microbial diversity and ecosystem function in intercropping systems and guide agricultural practice.

Temporal stability of productivity is associated with complementarity and competitive intensities in intercropping

Year-to-year stability in crop production is a crucial aspect of feeding a growing global population. Evidence from natural ecosystems shows that increasing plant diversity generally increases the temporal stability of productivity; however, we have little knowledge of the mechanisms by which diversity affects stability. In fact, understanding the drivers of stability is a major knowledge gap in our understanding of biodiversity and ecosystem function in general. We varied resource inputs into crop monocultures and intercropping of maize/pea and maize/rapeseed for 3 years in field experiments to create a wide range of values for temporal stability, complementarity effects, selection effects, competition, and facilitation. We correlated whole-system temporal stability in productivity with these values and the stability of competitively subordinate species and competitively dominant species in the intercrops. We then used structural equation modeling (SEM), which combines complex path models with latent variables, to estimate how interspecific interactions for water, nitrogen, and phosphorus affected the relationships between stability and these values. Intercropping treatments did not increase stability, but the wide range of stability created by our experiments allowed us to explore the relationship of many factors with stability. Complementarity correlated positively with the temporal stability of grain yield and aboveground biomass, suggesting that either facilitative interactions or niche partitioning shifted over time in ways that promoted stability. Furthermore, the temporal stability of total productivity of intercropping relied most on the stability of more productive species. However, facilitation tested by relative interaction index independently did not correlate with stability, but the temporal stability of the whole system increased as the competitive effects of competitively dominant species (pea and rapeseed) on competitively subordinate species (maize) decreased and was highest when these competitive effects were virtually zero. SEM indicated that as competition for soil nitrogen from competitively dominant species on competitively subordinate species decreased, the overall temporal stability of whole-system aboveground biomass increased. This stability then led to greater stability in grain production. Our findings indicate that complex shifts in complementarity and competitive intensities are likely to be key mechanisms that maintain temporal stability in species-diverse agriculture and, potentially, in natural systems.

Aromatic border plants in early season berries do not increase parasitism of spotted wing drosophila, Drosophila suzukii

BACKGROUND

The spotted wing drosophila, Drosophila suzukii Matsumura, is a South-East Asian vinegar fly that is a serious worldwide economic threat to the small fruit industry. Typical control consists of weekly pesticide applications, which can have nontarget effects, increase residual pesticides and lead to the development of resistance within pest populations. One potential alternate method of control is the planting of aromatic intercrops to attract the natural enemies of D. suzukii and/or repel the flies directly. We intercropped strawberry rows with flowering sweet alyssum or ryegrass-clover (control) to evaluate their efficacy at mitigating D. suzukii infestation through the attraction of two specialized larval parasitoids, Leptopilina japonica (Novkovic and Kimura) and Ganaspis brasiliensis (Ihering).

RESULTS

Our study did not demonstrate any significant effect of sweet alyssum intercropping on the infestation rate of D. suzukii in strawberries or parasitism level. However, we found that advanced sampling date and recorded numbers of D. suzukii larvae and parasitoids were positively correlated, indicating higher populations at the end of the strawberry-growing season.

CONCLUSIONS

Sweet alyssum intercrops did not reduce D. suzukii infestation rates or increase parasitism levels, likely due to low population numbers in early season berry varieties. Aromatic intercrops may be more effective for increasing pest control in later season crops. © 2022 Society of Chemical Industry.