Competition at the soybean V6 stage affects root morphology and biochemical composition

• The experiment was conducted in the 2016/17 crop season in a greenhouse at Passo Fundo University, Brazil. We hypothesised that the morphological characteristics and biochemical and anatomical composition of soybean roots and shoots, when competing with weeds during different growth periods, are negatively affected, so current concepts of competition between plants should also consider changes in plant roots.
• The soybean cultivar P 95R51 and horseweed (Conyza bonariensis) were used. The treatments consisted of the presence or absence of weeds during different coexistence periods of soybean with horseweed. The periods were V0–V3, V0–V6, V0–R2, V3–R6, V6–R6 and R2–R6, where V0 was the date of soybean sowing and V3, V6, R2 and R6 were phenological stages of the crop. Two fresh roots were used to examine morphological traits. Four roots were used for quantification of dry matter and secondary metabolites.
• Root length was reduced by 21%, 14% and 20% when competing with a weed in the V0–V3, V0–V6 and R2–R6 coexistence periods, respectively. Total phenol content in the V0–V6 and V0–R2 periods was reduced when plants were in competition with weeds; a similar trend was found for flavonoids in the V0–V6 period.
• Soybean–horseweed competition from crop emergence to the V6 stage, in general, affects shoot and root morphological traits and the biochemical composition of the soybean roots. The presence of horseweed at the V3, V6 and R2 stages does not negatively alter the traits evaluated. Root anatomical composition is not modified during all coexistence periods with horseweed.

     

Physiological and growth responses of Centaurea maculosa (Asteraceae) to root herbivory under varying levels of interspecific plant competition and soil nitrogen availability

Summary Centaurea maculosa seedlings were grown in pots to study the effects of root herbivory by Agapeta zoegana L. (Lep.: Cochylidae) and Cyphocleonus achates Fahr. (Col.: Curculionidae), grass competition and nitrogen shortage (each present or absent), using a full factorial design. The aims of the study were to analyse the impact of root herbivory on plant growth, resource allocation and physiological processes, and to test if these plant responses to herbivory were influenced by plant competition and nitrogen availability. The two root herbivores differed markedly in their impact on plant growth. While feeding by the moth A. zoegana in the root cortex had no effect on shoot and root mass, feeding by the weevil C. achates in the central vascular tissue greatly reduced shoot mass, but not root mass, leading to a reduced shoot/root ratio. The absence of significant effects of the two herbivores on root biomass, despite considerable consumption, indicates that compensatory root growth occurred. Competition with grass affected plant growth more than herbivory and nutrient status, resulting in reduced shoot and root growth, and number of leaves. Nitrogen shortage did not affect plant growth directly but greatly influenced the compensatory capacity of Centaurea maculosa to root herbivory. Under high nitrogen conditions, shoot biomass of plants infested by the weevil was reduced by 30% compared with uninfested plants. However, under poor nitrogen conditions a 63% reduction was observed compared with corresponding controls. Root herbivory was the most important stress factor affecting plant physiology. Besides a relative increase in biomass allocation to the roots, infested plants also showed a significant increase in nitrogen concentration in the roots and a concomitant reduction in leaf nitrogen concentration, reflecting a redirection of the nitrogen to the stronger sink. The level of fructans was greatly reduced in the roots after herbivore feeding. This is thought to be a consequence of their mobilisation to support compensatory root growth. A preliminary model linking the effects of these root herbivores to the physiological processes of C. maculosa is presented.     

Influence of root density on the critical soil water potential

Estimation of root water uptake in crops is important for making many other agricultural predictions. This estimation often involves two assumptions: (1) that a critical soil water potential exists which is constant for a given combination of soil and crop and which does not depend on root length density, and (2) that the local root water uptake at given soil water potential is proportional to root length density. Recent results of both mathematical modeling and computer tomography show that these assumptions may not be valid when the soil water potential is averaged over a volume of soil containing roots. We tested these assumptions for plants with distinctly different root systems. Root water uptake rates and the critical soil water potential values were determined in several adjacent soil layers for horse bean (Vicia faba) and oat (Avena sativa) grown in lysimeters, and for field-grown cotton (Gossypium L.), maize (Zea mays) and alfalfa (Medicago sativa L.) crops. Root water uptake was calculated from the water balance of each layer in lysimeters. Water uptake rate was proportional to root length density at high soil water potentials, for both horse bean and oat plants, but root water uptake did not depend on root density for horse bean at potentials lower than −25 kPa. We observed a linear dependency of a critical soil water potential on the logarithm of root length density for all plants studied. Soil texture modified the critical water potential values, but not the linearity of the relationship. B E Clothier Section editor     

Cluster Roots: A Curiosity in Context

Cluster roots are an adaptation for nutrient acquisition from nutrient-poor soils. They develop on root systems of a range of species belonging to a number of different families (e.g., Proteaceae, Casuarinaceae, Fabaceae and Myricaceae) and are also found on root systems of some crop species (e.g., albus, Macadamia integrifoliaandCucurbita pepo). Their morphology is variable but typically, large numbers of determinate branch roots develop over very short distances of main root axes. Root clusters are ephemeral, and continually replaced by extension of the main root axes. Carboxylates are released from cluster roots at very fast rates for only a few days during a brief developmental window termed an ‘exudative burst’. Most of the studies of cluster-root metabolism have been carried out using the crop plant L. albus, but results on native plants have provided important additional information on carbon metabolism and exudate composition. Cluster-root forming species are generally non-mycorrhizal, and rely upon their specialised roots for the acquisition of phosphorus and other scarcely available nutrients. Phosphorus is a key plant nutrient for altering cluster-root formation, but their formation is also influenced by N and Fe. The initiation and growth of cluster roots is enhanced when plants are grown at a very low phosphate supply (viz. ≤1 μM P), and cluster-root suppression occurs at relatively higher P supplies. An important feature of some Proteaceae is storage of phosphorus in stem tissues which is associated with the seasonality of cluster-root development and P uptake (winter) and shoot growth (summer), and also maintains low leaf [P]. Some species of Proteaceae develop symptoms of P toxicity at relatively low external P supply. Our findings with Hakea prostrata (Proteaceae) indicate that P-toxicity symptoms result after the capacity of tissues to store P is exceeded. P accumulation in H. prostrata is due to its strongly decreased capacity to down-regulate P uptake when the external P supply is supra-optimal. The present review investigates cluster-root functioning in (1) L.albus (white lupin), the model crop plant for cluster-root studies, and (2) native Proteaceae that have evolved in phosphate-impoverished environments.     

Growth Respiration of a Flood-Tolerant and a Flood-Intolerant Senecio Species: Correlation between Calculated and Experimental Values

Root growth respiration of Senecio aquaticus Hill (flood-tolerant) and Senecio jacobaea L. (flood-sensitive) was calculated, assuming different P: O ratios. The growth respiration values were calculated on the basis of the chemical composition of root and shoot dry matter, in combination with published data on the energy costs of biosynthetic and transport processes. The comparison between calculated and experimental values suggests a relatively low efficiency of ATP utilization in the roots of the flood-tolerant species. Root growth respiration of S. congestus (R.Br.)DC., which is also flood-tolerant, and Plantago lanceolata L. were also determined. The data showed that not all the flood-tolerant species investigated had high root growth respiration values. An “overflow model’ is proposed to explain observed differences in root growth respiration between species.     

Seasonal variation of growth and development of the roots of five second year conifer species in the nursery

Every other week over their second growing season, stem height, collar diameter, shoot and root dry masses, number of lateral roots and length of the tap root were measured on nursery grown seedlings ofAbies balsamea L. Mill.,Pinus banksiana Lamb.,Pinus resinosa Ait.,Picea mariana Mill. BSP andPicea glauca Moench Voss. Root elongation, branching and mycorrhizal development were also recorded.Given species showed distinct seasonal growth patterns. The rate and timing of maximum root growth (mg/dry weight/week) differed markedly between species.Except for the increase in height ofPinus banksiana, root and shoot growth were not negatively correlated.The results are discussed in relation to the performance of tree seedlings in the nursery.     

Root plasticity in Mediterranean herbaceous species

Abstract

Root plasticity has been largely studied on herbaceous species of north European temperate flora and is defined as the ratio between root depth in dry soils and root depth in wet soils. In summer dry habitats such as Mediterranean environments, the soil water deficit is a common feature to which root systems of plant species should adapt to improve their ecological efficiency. The aim of this study was to compare root plasticity in annual Mediterranean species that regenerate exclusively from seeds, and herbaceous perennial Mediterranean species that use dual regeneration strategies. Root plasticity of ten herbaceous species, six perennials and four annuals, was compared in this study. The annuals species studied occur in lowland Mediterranean grasslands referred to Tuberarietea guttatae class (Dasypyrum villosum, Lophochloa pubescens, Ornithopus compressus, Rumex bucephalophorus), while the perennial species occur in montane sub-Mediterranean grasslands referred to Festuco brometea (Bromus erectus, Festuca ovina., Lotus corniculatus., Minuartia verna, Sanguisorba minor, Thymus longicaulis). The examined species were subjected to water stress according to standard methods applied in comparative ecology, i.e., half of the seedlings of each species received 20 ml de-ionized water daily for three weeks, while the other half did not. After seedling harvesting the following parameters were analysed: (i) total root length; (ii) root length in the first 10 cm of soil; (iii) shoot height; (iv) root biomass in the first 10 cm of soil; (v) shoot biomass; (vi) shoot and root plasticity. Results show that root plasticity increased significantly in dual-regenerator sub-Mediterranean mountain species.     

Efficiency of Root Respiration in Relation to Growth Rate, Morphology and Soil Composition

Root growth respiration and root maintenance respiration rate of the following species were determined: Hypochaeris radicata L. ssp. radicata L., H. radicata ssp. ericetorum Van Soest, Plantago lanceolata L., P. major L. ssp. major, P. major ssp. pleiosperma Pilgcr, P. maritime L., Senecio viscosus L., S. vulgaris L. and Urtica dioica L. A high root growth respiration (i.e. the amount of oxygen consumed for synthesis of a given weight of root material) implied a high maintenance respiration rate (i.e. the amount of oxygen consumed per unit of time and dry weight, but not connected with growth). High values of both components reflect a low efficiency of root respiratory processes. The efficiency of root respiration, as determined by the values for root growth respiration and root maintenance respiration rate could not be demonstrated to be of advantage in adaptation to soil conditions, as e.g. nitrogen content, moisture content and pH. It is concluded that (he degree of ‘wasteful utilization of sugars’ in roots, i.e. such consumption of sugars as cannot be related to structural growth, storage of carbohydrates or maintenance processes, depends on imbalance of transport of sugars from the shoot to the roots with utilization of sugars for synthesis of root material. The results are discussed in relation to Brouwer's explanation for the equilibrium between the growth of shoots and of roots. Root growth rate in the present species appears limited by a factor produced in the shoot under light conditions, and which factor is distinct from carbohydrates. The evidence presented shows that relatively inefficient root respiration does not imply a low growth rate. In regulation of plant growth the growth rate itself and also the shoot to-root ratio may be more important than the regulation of the efficiency of energy metabolism.     

Zoosporangial root infection of tomato by Spongospora subterranea in hydroponic and glasshouse culture results in diminished plant growth

Tomato plants are highly susceptible to root infection by Spongospora subterranea and are commonly used as bioassay hosts. The impacts of root infection with S. subterranea on plant productivity and yield have been debated. Recent experiments with potato, the major economic host of S. subterranea, have indicated significantly reduced plant growth and potato yield following heavy infection. However, there have been very few similar studies that have examined the possible impacts of S. subterranea infection on tomato plant growth. Three tomato cultivars, “Grape,” “Roma” and “Truss,” were challenged with S. subterranea inoculum in hydroponic culture. Moderate to severe zoosporangial infections were observed with minor but statistically significant differences in susceptibility among the three tomato cultivars. Zoosporangial root infection in the absence of root gall formation resulted in significantly diminished shoot lengths and plant fresh weights in pathogen challenge tests conducted both in hydroponic culture and glasshouse‐grown plants in potting mix. Root lengths were reduced, but the differences were statistically significant in a single trial only. The findings from this study demonstrate that, as with potato, root infection by S. subterranea can result in reduced tomato plant growth and that root gall production associated with root infection was not necessary for this retardation of growth response. This further suggests that possible yield impacts in other crop species that are hosts for S. subterranea root infection are worthy of examination.     

Quantifying relationships between rooting traits and water uptake under drought in Mediterranean barley and durum wheat

In Mediterranean regions drought is the major factor limiting spring barley and durum wheat grain yields. This study aimed to compare spring barley and durum wheat root and shoot responses to drought and quantify relationships between root traits and water uptake under terminal drought.One spring barley（Hordeum vulgare L. cv. Rum） and two durum wheat Mediterranean cultivars（Triticum turgidum L. var durum cvs Hourani and Karim） were examined in soil‐column experiments under well watered and drought conditions. Root system architecture traits, water uptake, and plant growth were measured. Barley aerial biomass and grain yields were higher than for durum wheat cultivars in well watered conditions. Drought decreased grain yield more for barley（47%） than durum wheat（30%, Hourani）. Root‐to‐shoot dry matter ratio increased for durum wheat under drought but not for barley, and root weight increased for wheat in response todrought but decreased for barley. The critical root length density（RLD） and root volume density（RVD） for 90% available water capture for wheat were similar to（cv. Hourani） or lower than（cv. Karim） for barley depending on wheat cultivar. For both species, RVD accounted for a slightly higher proportion of phenotypic variation in water uptake under drought than RLD.     

Relationships between cell membrane stability, exudate content and infectivity of Bradyrhizobium japonicum strain 639 to boron starved soybean plants

The influence of boron starvation on the root exudates content in soybean seedlings (Glycine max. L. Merr.) and the effect of exudates pretreatment on the pre-infection processes in symbiotic system Br. japonicum strain 636 and soybean were investigated. Root cell membrane stability of boron starved soybean plants (-B) decreased compared to the control. The concentrations of all analyzed metabolites (reducing sugars, free amino acids, organic acids, soluble phenols and total flavonoids) from root exudates of -B plants were lower than the control concentrations. Analysis of polyphenols after HPLC chromatography of root exudates showed significant difference of peak numbers between chromatograms of exudates obtained from boron starved and from control plants. Bacterial culture treatment with root exudates from -B plants showed decreased growth, chemotaxis and attachment ability toward the host root compared to the control exudate treatments. These changes were accompanied by decreased nodulation and acetylene reduction activity of boron starved soybean plants.     

Root, shoot tissues of Brassica juncea and Cereal secale promote potato health

Brassica species are increasingly being used as cover crops to suppress soil-borne diseases in potato cropping systems. Experiments were conducted in controlled environments and in the field to evaluate the effects of cover crop root or shoot or a combination of root and shoot tissues on potato root and tuber health. In a lab assay we examined the extent to which volatile compounds released from tissues of two cover crop species, rye (Cereale secale L.) and oriental mustard (Brassica juncea L.), could inhibit mycelium growth of two important potato diseases, Rhizoctonia solani and Pythium ultimum. Twenty-four hours into the lab assay, volatile compounds from all residues suppressed fungal growth. After 48 h, marked suppression of hyphal growth continued in the presence of mustard residues but not in the presence of rye tissues or the control without tissues. A 75 L volume container experiment evaluated the effect of incorporating different quantities of mustard shoot and root tissues (none, comparable to field level and fourfold field level) into R. solani and P. ultimum infested soil on potato growth, root health and tuber disease. In the container study, incorporating mustard shoots at the highest dose increased potato yield by 54% and reduced disease rating to 2.3 compared to a severe rating of 4.4 in the control. In the field trial, potato growth, root health and tuber disease levels were evaluated in plots where disease management involved either incorporation of mustard or rye cover crop roots, shoots and whole plants (roots plus shoots) or standard farmer practice of a fumigated fallow as a control. White root tissue was used as a health indicator, and averaged 58 and 78% in the fumigated control and mustard cover crop treatments, respectively. The highest healthy root tissue status (91%) was recorded where whole plants of mustard were incorporated. In contrast to the visual assessment of root and tuber health, tuber yield in the field was not influenced by cover crop treatment. Across experiments, the incorporation of or exposure to whole mustard plants was consistently effective at suppressing soil-borne fungi and promoting healthy roots and tubers, especially at higher rates of biomass. Mustard should be managed so as to maximize incorporated biomass for effective biofumigation. Multipurpose management requiring removal of mustard shoots is incompatible with promoting potato rhizosphere health.     

3D reconstruction and dynamic modeling of root architecture in situ and its application to crop phosphorus research

Root architecture plays important roles in plant water and nutrient acquisition. However, accurate modeling of the root system that provides a realistic representation of roots in the soil is limited by a lack of appropriate tools for the non‐destructive and precise measurement of the root system architecture in situ. Here we describe a root growth system in which the roots grow in a solid gel matrix that was used to reconstruct 3D root architecture in situ and dynamically simulate its changes under various nutrient conditions with a high degree of precision. A 3D laser scanner combined with a transparent gel‐based growth system was used to capture 3D images of roots. The root system skeleton was extracted using a skeleton extraction method based on the Hough transformation, and mesh modeling using Ball‐B spline was employed. We successfully used this system to reconstruct rice and soybean root architectures and determine their changes under various phosphorus (P) supply conditions. Our results showed that the 3D root architecture parameters that were dynamically calculated based on the skeletonization and simulation of root systems were significantly correlated with the biomass and P content of rice and soybean based on both the simulation system and previous reports. Therefore, this approach provides a novel technique for the study of crop root growth and its adaptive changes to various environmental conditions.     

Primary Root Growth and the Pattern of Root Apical Meristem Organization are Coupled

Root apical meristems (RAMs) in dicotyledonous plants have two organizational schemes; closed (with highly organized tiers) and open (tiers lacking or disorganized). These schemes are commonly believed to remain unchanged during the growth of the root axis. Individual roots are commonly thought to have indeterminate growth. We challenge these two generalizations through the study of five species with closed apical organization: Clarkia unguiculata L., Oxalis corniculata L., Dianthus caryophyllus L., Blumenbachia hieronymi Urb., and Salvia farinaceae Benth. cv. Strata. These roots have phased growth patterns where early growth is followed by deceleration, after which the initial cells stop dividing, elongation ceases, and the root reaches its determinate length. At or before reaching determinacy, the root apical meristem stops maintaining its closed organization and becomes less organized. These observations will be placed in context with observations from the literature to suggest two new generalizations, namely, that apical organization does change over the growth phases of roots, and that roots are determinate.     

Root-shoot signalling in sunflower plants with confined root systems

Sunflower plants were grown hydroponically under controlled conditions with the root systems confined in small containers. Root confinement inhibited the growth of sunflower plants as indicated by reduction in both leaf and cotyledon area and root and shoot fresh weight. This effect was more pronounced in shoots. Root confinement favored the accumulation of potassium in the roots and shoots, and the exudation of potassium and water in excised roots. Xylem sap from root confined plants inhibited cotyledon expansion as revealed by bioassay with decapited sunflower seedlings. In addition decapited control plants incubated in ABA solution also showed cotyledon growth reduction. Xylem sap ABA analysis indicated a 7-times higher concentration in root confined than control plants. Our results suggest the synthesis of a chemical signal in the roots of plants subjected to mechanical stress which can be responsible for the inhibition of plant growth.     

Allelopathic Substance Exuded from a Serious Weed, Germinating Barnyard Grass (Echinochloa crus-galli L.), Roots

The allelopathy of a serious weed, barnyard grass (Echinochloa crus-galli L.), was investigated. Root exudates of young barnyard grass showed allelopathic effects and plant-selective activity and inhibited root elongation of all plants tested. With respect to shoot growth, the exudates did not show inhibition of barnyard grass only. The allelopathic substance was isolated and identified as p-hydroxymandelic acid by NMR. p-Hydroxymandelic acid strongly inhibited shoot growth and root elongation of all plants tested. The effects of three congeners of p-hydroxymandelic acid were tested on rice shoot growth. In the biological activity exhibited in rice, shoot growth was related to the hydroxyl groups. Received October 7, 1998; accepted March 29, 1999     

The effect of rhizoctonia root disease and applied nitrogen on growth,nitrogen uptake and nutrient concentrations in spring wheat

Root disease caused by Rhizoctonia solani is a common problem of spring wheat in South Australia. There are reports that nitrogen applications can reduce the incidence and severity of the disease. A glasshouse trail in pots examined the effects of disease and of applied nitrogen on wheat growth, and evaluated the utility of the basal stem nitrate concentration in diagnosing deficiency in plants with and without root disease. Plants were harvested at the mid-tillering stage. Shoot growth was increased by applied nitrogen until a maximum yield was attained, after which additional N had no effect on shoot yield. Root growth, however, responded positively only to low levels of applied N, after which it declined, and in the highest N treatment root mass was less than in the plants without applied N. Root disease caused severe reductions in plant growth, and both root and shoot mass were affected similarly. Even though growth of diseased plants responded positively to applied nitrogen the response was less than that of disease-free plants. The critical concentration of basal stem nitrate-N did not appear to be affected by root disease, and was estimated at 1200 mg kg^-1, consistent with other glasshouse data. The basal stem nitrate-N concentration, either in fresh or dried tissue, appeared a better diagnostic tool of N stress than did total shoot N concentration or content, because of sharper definition of critical concentrations. Concentrations of other nutrients in shoot tissue were affected differentially by both applied nitrogen and root disease, but generally did not reach critical levels, although phosphorus and magnesium appeared deficient in very disease-stressed plants.     

In vitro induction of lipo-chitooligosaccharide production in Bradyrhizobium japonicum cultures by root extracts from non-leguminous plants

Bradyrhizobium japonicum can form a N2-fixing symbiosis with compatible leguminous plants. It can also act as a plant-growth promoting rhizobacterium (PGPR) for non-legume plants, possibly through production of lipo-chitooligosaccharides (LCOs), which should have the ability to induce disease resistance responses in plants. The objective of this work was to determine whether non-leguminous crop plants can induce LCO formation by B. japonicum cultures. Cultures treated with root extracts of soybean, corn, cotton or winter wheat were assayed for presence and level of LCO. Root extracts of soybean, corn and winter wheat all induced LCO production, with extracts of corn inducing the greatest amounts. Root washings of corn also induced LCO production, but less than the root extract. These results indicated that the stimulation of non-legume plant growth by B. japonicum could be through the production of LCOs, induced by materials excreted by the roots of non-legume plants.     

Genotype and Planting Density Effects on Rooting Traits and Yield in Cotton （Gossypium hirsutum L,）

Root density distribution of plants is a major Indicator of competition between plants and determines resource capture from the solh This experiment was conducted in 2005 at Anyang, located in the Yellow River region, Henan Province, China. Three cotton （Gossyplum hlrsutum L.） cultivars were chosen： hybrid Btcultlvar CRI46, conventional Btcultlvars CRI44 and CRI45. Six planting densities were designed, ranging from 1.5 to 12.0 plants/m^2. Root parameters such as surface area, diameter and length were analyzed by using the DT-SCAN Image analysis method. The root length density （RLD）, root average diameter and root area Index （RAI）, root surface area per unit land area, were studied. The results showed that RLD and RAI differed between genotypes; hybrid CRI46 had significantly higher （P 〈0.05） RLD and RAI values than conventlonal cultlvars, especially under low planting densities, less than 3.0 plants/m^2. The root area index （RAI） of hybrid CRI46 was 61% higher than of CRI44 and CRI45 at the flowering stage. The RLD and RAI were also significantly different （P = 0.000） between planting densities. The depth distribution of RAI showed that at Increasing planting densities RAI was Increasingly distributed in the soil layers below 50 cm. The RAI of hybrid CRI46 was for all planting densities, obviously higher than other cultivars during the flowering and boll stages. It was concluded that the hybrid had a strong advantage in root maintenance preventing premature senescence of roots. The root diameter of hybrid CRI46 had a genetically higher root diameter at planting densities lower than 6.0 plants/m^2. Good associations were found between yield and RAI In different stages. The optimum planting density ranged from 4.50 plants/m^2 to 6.75 plants/m^2 for conventional cultlvars and around 4.0-5.0 plants/m^2 for hybrids.     

Colonization preference of Euschistus servus and Nezara viridula in transgenic cotton varieties,peanut, and soybean

Producers of Bt cotton, Gossypium hirsutum L. (Malvaceae), in the southeastern USA face significant losses from highly polyphagous stink bug species. These problems may be exacerbated by crop rotation practices that often result in cotton, peanut, Arachis hypogaea L., and soybean, Glycine max (L.) Merrill (both Fabaceae), growing in close proximity to one another. Because all of these crops are hosts for the major pest stink bug species in the region, we experimentally examined colonization preference of these species among the crops to clarify this aspect of their population dynamics. We planted peanut, soybean, Bt cotton, and glyphosate‐tolerant (RR) non‐Bt cotton at three sites over 3 years in replicated plots ranging from 192 to 1 323 m² and calculated odds ratios for colonization of each crop for Nezara viridula (L.) and Euschistus servus (Say) (both Hemiptera: Pentatomidae). In four of five experiments, both E. servus and N. viridula preferred soybean significantly more often than Bt cotton, non‐Bt cotton, and peanut. Neither N. viridula nor E. servus showed any preference between non‐Bt and Bt cotton in any experiment. Both species had higher numbers in Bt and non‐Bt cotton relative to peanut; this was not significant for any single experiment, but analyses across all experiments indicated that N. viridula preferred Bt and non‐Bt cotton significantly more often than peanut. Our results suggest that soybean in the landscape may function as a sink for stink bug populations relative to nearby peanut and cotton when the soybean is in the reproductive stage of development. Stink bug preference for soybean may reduce pest pressure in near‐by crops, but population increases in soybean could lead to this crop functioning as a source for later‐season pest pressure in cotton.