Pod-filling Stage Research Articles

Responses of field-grown soybean (cv. Essex) to elevated SO 2 under two atmospheric CO 2 concentrations

The objective of this research was to determine the effects of elevated concentrations of carbon dioxide (CO 2) and sulfur dioxide (SO 2) on field-grown soybean. Soybeans ( Glycine max L. Merr. cv. ‘Essex’) were grown a full-season in open-top field chambers exposed to either ambient (350 μl L −1) or elevated CO 2 (500 μl L −1) levels under two levels of SO 2 (0.00 and 0.12 μl L −1). Enriched CO 2, with or without SO 2 treatments, significantly increased net photosynthesis rates, leaf area index (LAI; in R4 growth stage) and leaf dry weight, but did not significantly affect stomatal resistance, transpiration rates, leaf area, plant height, total biomass or grain yield. Elevated SO 2 treatments significantly decreased photosynthesis and LAI during pod fill stages, but did not significantly affect stomatal resistance, transpiration, total biomass, plant height or grain yield. Sulfur dioxide inhibited growth and development (i.e., LAI) during canopy coverage before any effects on photosynthesis were detected. The interactive effects of CO 2 and SO 2 treatments on the gas exchange parameters were significant during pod fill, where high SO 2 reduced photosynthesis at ambient CO 2 but not under elevated CO 2. Leaf area index values were likewise reduced by SO 2 exposure under ambient CO 2 during late flowering and pod fill stages. Thus, enriched CO 2 under high SO 2 exposure partially compensated for the negative impact of SO 2 stress on PS and LAI during the pod fill stages.

Effects of Timing of Drought Stress on Leaf Area Development and Canopy Light Interception of Short‐duration Pigeonpea

AbstractLeaf area index (LAI), fractional canopy light interception (F) and plant mortality at maturity, were determined for nine short‐duration pigeonpea (Cajanus cajan [L.] Millsp.) genotypes in response to drought during the late‐vegetative and flowering (stress 1), the flowering and early podfill (stress 2), or podfill (stress 3) stages. LAI and F were reduced, but plant mortality did not increase under drought. Stress 2 reduced LAI to the greatest extent, consistent with the effects on seed yield. At the end of stress 1, seed yield was closely related to LAI for the different genotypes in stressed but not in unstressed (control) plots. Reductions in LAI due to reproductive growth were as great or greater than those due to water stress. Indeterminate genotypes had smaller but more leaves per plant compared to the determinate genotypes. The importance of these differences to drought resistance was not apparent. Production of leaves with decreasing specific leaf area throughout plant growth may be advantageous, especially when drought is likely to occur during reproductive growth. Values of F during and following water stress gave an indication of genotypic drought resistance, with the most drought‐sensitive genotype showing the largest reduction in F under water stress and the slowest rate of recovery following rewatering. For short‐duration pigeonpea, where plant mortality is not a factor under water stress, the maintenance of both LAI and F appears to indicate genotypic drought resistance.

Analysis of factors controlling dinitrogen fixation and nitrogen release in soybean using pod removal, stem girdling, and defoliation

Abstract We studied the factors controlling nitrogen (N) release from roots and nodules of soybean (Glycine max L. Merr. cv. Kurosengoku). Plants were subjected to pod removal, stem-girdling and defoliation at the pod-filling stage and the effects on nitrogen fixation and release of nitrogenous compounds from the roots were monitored under water culture conditions. Nitrogen fixation was significantly reduced in all the treated plants. In spite of the reduction in the concentration of sugar in the roots and nodules of defoliated and stem-girdled plants, only the latter treatment promoted sustained exudation of total N and ureides. Pod removal did not affect the root and nodule sugar concentration, nor promote the release of nitrogenous compounds. Based on these results, it is suggested that low nitrogen fixation activity as well as low sugar concentration in root and nodules may not be the only factors responsible for N exudation.

Growth and N 2-fixation of soybeans inoculated with strains of Bradyrhizobium japonicum differing in energetic efficiency and PHB utilization

The hypothesis, that accumulation of poly-hydroxybutyrate (PHB) in bacteroids of soybean root nodules and utilization of this polymer during pod-filling, are factors in N 2 fixation during seed development, was tested in a glasshouse experiment. Lincoln soybeans, inoculated with strains of B. japonicum of different energetic efficiency (Hup + or Hup −), were grown under bacteriologically-controlled conditions in open pots of combined-N-free medium, until the pod-filling stage. Nitrogen fixation was measured as accumulation of total N in shoots (including seeds). Bacteroids, prepared from tap-root nodules at intervals during growth, were assessed for PHB and protein content. During vegetative growth, all of the strains were of similar symbiotic effectiveness but during pod-filling, plants inoculated with the three Hup + strains fixed N 2 and grew at about twice the rates of plants inoculated with the three Hup − strains. Bacteroids of all three Hup + strains accumulated PHB (from 40 to >50% dry wt) during vegetative plant growth and utilized it during pod-filling. Two of three Hup − strains accumulated little PHB in the bacteroids and all three utilized little or none of it during pod-filling. These results are discussed in relation to a supply of energy-yielding substrates to nodules during pod-filling, to the influence of energetic efficiency of the bacteroids on PHB accumulation and to the role of PHB utilization in sustaining nodule O 2-demand during seed development.

Maturity and Environntental Effects on Soybeans Resistant to Mexican Bean Beetle (Coleoptera: Coccinellidae)

Entomologists and breeders have met with limited success in the development and release of insect resistant soybean cultivars. Although numerous germplasm lines resistant to defoliating insects have been released, only three cultivars have been made available to growers over the past 20 yr. Researchers have examined potential limitations of insect resistant soybeans, with most of the studies examining the negative impact of plant maturity. This study examined the relative resistance levels of four advanced germplasm lines during the vegetative, flowering, and pod-fill growth stages of soybean development. Resistance was measured by rearing Mexican bean beetle, Epilachna varivestis Mulsant, on excised, field-grown leaves and comparing larval mortality and developmental periods. The study was conducted in two locations for 2 yr. In the 1st yr, mortality was significantly greater, and developmental periods lengthened, on the four resistant soybean lines compared with two susceptible cultivars during the vegetative and flowering stages; however, these differences were slight to nonexistent during the pod-fill stage. Although similar differences were evident the 2nd yr, the levels of resistance were greatly lowered. This reduction in resistance as the plants matured is comparable to that found by other researchers. The loss of resistance in the 2nd yr was unexpected and was attributed to much higher than normal rainfall in July at both locations. We discuss the consequences of lower levels of resistance in maturing plants and under conditions of high rainfall, both for breeding programs and field resistance as required by growers.

Control of Lepidopterans in Canola, 1994

Abstract Plots were planted 9 May on the Washington State University campus, Pullman, WA, with a small plot drill at a seeding rate of 6 lb/acre in 7 rows 6 inches apart. Plots were 20 × 20 ft, replicated 4 times in a randomized complete block design. Six treatments of Biobit were applied on 22 Jul to water stressed plants in the pod-fill stage, with a CO2-powered backpack sprayer. It was equipped with a 6.75 ft boom and 6 XR Teejet 8002 flat fan nozzles with 100 mesh screen on 19 inch spacing and calibrated to deliver 21.3 gpa at 30 psi. Applications were applied at 7 am and the maximum temperatures during the sampling interval were 88-90°F. Efficacy was evaluated at 3 and 10 DAT with 2 (180°) sweeps with a standard 15 inch diam sweep net. Data were analyzed using ANOVA and means separated by Fisher’s LSD.

Growth and Adaptation of Soybean Cultivars under Water Stress Conditions. III. Yield response and dry matter production.

Yield and dry matter production were examined under water-stress conditions. Two cultivars (Zhengzhuta 2 and Heinong 33) were grown in a concrete-framed field. From the flowering to the pod-filling stage, four levels of irrigation treatments were carried out (Treatment I, II, III and IV-from the severst, Treatment I to the non water stressed, Treatment IV). The growing periods were shorter with increasing amount of irrigation. Zhengzhuta 2 had larger shoot dry weight than Heinong 33 in every irrigation treatment. Dry weight of each organ tended to increase with increasing amount of irrigation during the treatment. Shoot dry weight ceased to increase in Treatment IV, but increased in the other treatments after the treatment. Percentage dry weight were higher in leaf and root of Zhengzhuta 2, and in pod of Heinong 33. Crop growth rates (CGRs), leaf area indices (LAIs), net assimilation rates (NARs) and pod growth rates (PGRs) were generally higher with increasing irrigation for both cultivars. CGR was closely related to LAI during the treatment. Pod, seed number and seed yield were greater in the plots with greater amount of irrigation. Zhengzhuta 2 had 540O kg ha-1 in Treatment IV. It's high-yielding potential seemed to be related to it's efficient leaf epansion and radiation interception ability.

Response of short-duration pigeonpea to nitrogen application after short-term waterlogging on a Vertisol

Short-duration pigeonpea suffers from waterlogging damage following heavy rainfall at the pre-flowering stage on soils with high clay content, such as Vertisols. Effects of short-term waterlogging (3 d) on shoot and root growth of short-duration pigeonpea grown on a Vertisol field were quantified, and the alleviation of waterlogging damage by top-dressing of nitrogen fertilizer was examined. Reduced leaf chlorophyll, increased senescence and abscission of lower leaves were observed within 3 d of the initiation of waterlogging. Root growth and symbiotic N 2 fixation were also severely impaired. Root distributions of waterlogged plants were shallower than those of the control during the subsequent recovery period because new adventitious roots were formed in the shallow rather than deep soil layer. Yield of waterlogged crops was significantly smaller than the control. Top-dressing of nitrogen at one day after the termination of waterlogging alleviated waterlogging damage either completely or partially. Leaf chlorophyll and shoot dry mass of waterlogged plants were 78 and 84% of the values in control plants immediately after waterlogging but recovered to 92 and 98% of the control values at the pod-filling stage with a top-dressing of 50 kg N ha −1 . Nitrogen application promoted root growth in the shallow soil layers during the first 11 d after application, and in the deeper soil layers during the subsequent 16 d. Total nodule activity was significantly reduced by 100 kg N ha −1 , but increased by 50 kg N ha −1 around one month after the top-dressing. The reduction in seed yield was largely compensated for by 50 kg N ha −1 , because of recovery from waterlogging damage to shoot and root growth involving increased nodule activity.

Pest Status of Aphids and Other Insects in Winter Canola in Georgia

Canola, Brassica napus L., is being evaluated as a winter grain crop in the southeastern United States. The damage potential of insect pests was studied during three growing seasons in the Piedmont and coastal plain regions of Georgia by controlling insects with insecticides at the rosette, beginning bloom, or pod-fill stages of plant development. Canola pod infestations by the cabbage seedpod weevil, Ceutorhynchus assimilis Paykull, reached 60% at some sites in northern Georgia indicating that this insect will be an important pest of canola in this area. However, C. assimilis was not collected in any year in southern Georgia. Yield responses to insecticide treatments were associated with a complex of aphids, primarily the turnip aphid, Lipaphis erysimi (Kaltenbach), and green peach aphid, Myzus persicae (Sulzer), which caused direct injury to leaves and stems. Aphid injury reduced plant height and winter survival and delayed plant development. Comparison of untreated and season-long treated plots indicated that aphid injury reduced yield by 9.9, 30.4, and 34.8% in 3 yr in the coastal plain region. In northern Georgia, yield losses caused by aphids were ≤2.0% in three of four trials, but aphid injury reduced yield by 32.7% in one trial. Insecticidal control of aphids had the greatest effect on yield during the rosette stage with treatments at first bloom also enhancing yield in some trials. Insecticide treatments at pod-fill stage did not affect canola growth and yield in any trial. Aphids most likely will be a limiting factor in canola production in the southern United States, particularly in the coastal plain region. Aphid management activities should be directed at seedling and rosette stages of plant development.

Seasonal accumulation and partitioning of nitrogen by lentil

Although wheat (Triticum aestivum L.) is the dominant crop of the semi-arid plains of Canada and the western United States, lentil (Lens culinaris Medik.) has become an important alternative crop. Sources and seasonal accumulation of N must be understood in order to identify parameters that can lead to increased N2-fixing activity and yield. Inoculated lentil was grown in a sandy-loam soil at an irrigated site in Saskatchewan, Canada. Wheat was used as the reference crop to estimate N2 fixation by the A-value approach. Lentil and wheat received 10 and 100 kg N ha−1 of ammonium nitrate, respectively. Crops were harvested six times during the growing season and plant components analyzed. During the first 71 days after planting the wheat had a higher daily dry matter and N accumulation compared to lentil. However, during the latter part of the growing season, daily dry matter and N accumulation were greater for lentil. The maximum total N accumulation for lentil at maturity was 149 kg ha−1. In contrast, wheat had a maximum N accumulation of 98 kg ha−1 in the Feekes 11.1 stage, or 86 days after planting. The maximum daily rates of N accumulation were 3.82 kg N ha−1 day−1 for lentil and 2.21 kg N ha−1 day−1 for wheat. The percentage of N derived from N2 fixation (% Ndfa) ranged from 0 at the first harvest to 92 % at final harvest. Generative plant components had higher values for % Ndfa than the vegetative components which indicates that N in the reproductive plant parts was derived largely from current N2 fixation and lentil continued to fix N until the end of the pod fill stage. At final harvest, lentil had derived 129 kg N ha−1 from N2 fixation with maximum N2-fixing activity (4.4 kg N ha−1 day−1) occurring during the early stages of pod fill. Higher maximum rates of N2-fixing activity than net N accumulation (3.82 kg N ha−1 day−1) may have been caused by N losses like volatilization. In addition, lentil provided a net N contribution to the soil of 59 kg ha−1 following the removal of the grain.

Changes in growth and yield components ofBrassica napusin response toAzotobacterinoculation at different rates of nitrogen application

SUMMARYInoculation ofBrassica napuscv. ISN–129 withAzotobacter chroococcumfollowing the application of different amounts of nitrogen produced the greatest increase in seed yield and total dry matter when no external nitrogen had been applied. The yield increase in response to inoculation could be attributed to a greater number of primary branches and pods, associated with a higher leaf area index, particularly at the pod-filling stage, and a faster crop growth rate.

The effect of root damage caused by simulated white grub attack on the growth, yield and water-use of groundnut plants

White grubs (larval scarabaeids) are now recognized as being important pests of groundnut (peanut) in many parts of the world because of their ability to damage roots. A method of simulating white grub damage to groundnut plants was developed to obtain an indication of how the feeding activity of these insects influences plant growth. The effect of root cutting and drought stress on water uptake and biomass production was evaluated, with roots being cut at three depths in the late vegetative and early podfilling stages. As groundnut plants are often grown under conditions of drought stress, the effects of which would be accentuated by root damage, this factor was introduced into the experiment. Plant water-use measurements indicated that the root systems of plants cut 30 days after emergence (DAE) and watered twice a week became fully functional again after 40 days. Pod and total biomass production were however significantly less than those of the uncut control plants, with drought stress reducing yields below the well-watered controls, particularly when cut at 10 cm below the soil surface. The root systems of plants cut 51 DAE did not regrow to any appreciable extent, and rates of plant water-use remained less than half of the uncut control plants. Over all treatments, there was a strong positive correlation between total (and pod) biomass and plant water-use. It was concluded that the phenological stage of the plant at which root damage occurred had a profound influence on the subsequent recovery in root growth and function, and ultimately on pod yield.

Field evaluation of N2 fixation and N partitioning in climbing bean (Phaseolus vulgaris L.) using 15N

The common bean (Phaseolus vulgaris L.) is generally regarded as a poor N2 fixer. This study assessed the sources of N (fertilizer, soil, and fixed N), N partitioning and mobilization, and soil N balance under field conditions in an indeterminate-type climbing bean (P. vulgaris L. cv. Cipro) at the vegetative, early pod-filling, and physiological maturity stages, using the A-value approach. This involved the application of 10 and 100 kg N ha-1 of 15N-labelled ammonium sulphate to the climbing bean and a reference crop, maize (Zea mays L.). At the late pod-filling stage (75 days after planting) the climbing bean had accumulated 119 kg N ha-1, 84% being derived from fixation, 16% from soil, and only 0.2% from the 15N fertilizer. N2 fixation was generally high at all stages of plant growth, but the maximum fixation (74% of the total N2 fixed) occurred during the interval between early (55 days after planting) and late podfilling. The N2 fixed between 55 and 75 days after planting bas a major source (88%) of the N demand of the developing pod, and only about 11% was contributed from the soil. There was essentially no mobilization of N from the shoots or roots for pod development. The cultivation of common bean cultivars that maintain a high N2-fixing capacity especially during pod filling, satisfying almost all the N needs of the developing pod and thus requiring little or no mobilization of N from the shoots for pod development, may lead to a net positive soil N balance.

Competitiveness of Rhizobium leguminosarum bv. phaseoli strains in relation to environmental stress and plant defense mechanisms

Six Rhizobium leguminosarum bv. phaseoli strains (Ciat 151, Ciat 895, Ciat 899, CE3, H2C, Kim5s) were tested for nodule occupancy in different bean cultivars at two field sites (one fertile, one acid tropical soil) and in the greenhouse. The effects of several environmental factors such as low pH, high temperature, Al and Mn toxicity, iron deficiency, bean tannins, and bean phytoalexins were tested in vitro. Strain Kim5s was competitive under all tested conditions while strains CE3 and H2C had consistently low nodule occupancy levels. Strain Ciat 151 was superior to the other inoculant strains in the acid soil but competed poorly in the fertile soil. Strain Ciat 895 was more competitive in the fertile soil. There was a decline in nodule occupancy for all strains tested from the first trifoliate leaf stage to the pod-filling stage. No plant genotype effect on nodule occupancy was observed. There were significant (P<0.05) plant genotype and location effects, but no significant strain effect on acetylene reduction activity, plant dry weight, and nodule number. The greenhouse experiments confirmed, at least partially, the results from the field trials. In Leonard jars with an acid soil, strains Ciat 151 and Kim5s were amongst the most competitive strains. In coinoculation experiments, Kim5s was the most competitive strain, followed by Ciat 899 and Ciat 895. The competitiveness of a given strain was affected by the coinoculant strain. Tolerance in vitro to low pH, high growth temperature, Al or Mn toxicity, or Fe limitation was not related to competitiveness of the inoculum strains. The sensitivity of the strains towards bean tannins or bean phytoalexins also was not correlated with their competitiveness.

Effects of elevated CO 2 concentration on the polyamine levels of field-grown soybean at three O 3 regimes

Effects of increased ozone (O 3) and carbon dioxide (CO 2) on polyamine levels were determined in soybean ( Glycine max L. Merr. cv. Clark) grown in open-top field chambers. The chamber treatments consisted of three O 3 regimes equal to charcoal filtered (CF), non-filtered (NF), and non-filtered plus 40 nl litre −1 O 3 and CO 2 treatments equal to 350, 400 and 500 μl litre −1 for a total of nine treatments. Leaf samples were taken at three different times during the growing season. Examination of growth and physiological characteristics, such as photosynthesis, stomatal resistance, and shoot weight, revealed that increasing CO 2 ameliorated the deleterious effects of increased O 3. Results from the initial harvest, at the pre-flowering growth stage (23 days of treatment), showed that increasing O 3 at ambient CO 2 caused increases in putrescine (Put) and spermidine (Spd) of up to six-fold. These effects were lessened with increased CO 2. Elevated CO 2 increased polyamines in plants treated with CF air, but had no effect in the presence of ambient or enhanced O 3 levels. Leaves harvested during peak flowering (37 days of treatment) showed O 3-induced increases in Put and Spd at ambient CO 2 concentrations. However, increased CO 2 levels inhibited this response by blocking the O 3-induced polyamine increase. Leaves harvested during the pod fill stage (57 days of treatment) showed no significant O 3 or CO 2 effects on polyamine levels. Our results demonstrate that current ambient O 3 levels induce the accumulation of Put and Spd early in the growing season and that further increases in O 3 could result in even greater polyamine increases. These results are consistent with a possible antiozonant function for polyamines. The ability of increased CO 2 to protect soybeans from O 3 damage, however, does not appear to involve polyamine accumulation.

Effects of cadmium and nickel on in vivo carbon dioxide exchange rate of pigeon pea (Cajanus cajan L.)

Pigeon pea plants, grown in sand culture and exposed to varying concentrations of Cd2+ and Ni2+ (5, 10, 15 and 20 mM) at different stages of their growth were examined for carbon dioxide exchange rate (CER), stomatal conductance, transpiration, internal CO2 concentration and chlorophyll content. In general, Cd2+ was more inhibitory than Ni2+ at all concentrations. The extent of inhibition increased with duration of exposure. At the vegetative stage, CER was inhibited by 87% and 30% with 20 mM Cd2+ and Ni2+, respectively one day after treatment. Stomatal conductance decreased in parallel with transpiration rate. After 10 days of treatment, wilting occurred in plants receiving 20 mM Cd2+. Reduction in CER was more pronounced at the flowering stage as compared to vegetative and pod-filling stages. However, decrease in chlorophyll content was marked at the pod-filling stage. Reduction of CER in pigeon pea by these metals could not be attributed to any single factor and appeared to be due to the combined effects on stomatal conductance, chlorophyll content and on the functioning of photosynthetic apparatus.

Excretion of ureide and other nitrogenous compounds by the root system of soybean at different growth stages

Direct excretion of nitrogenous compounds into a N-free nutrient solution, which was allowed to drip onto the root system of soybean (Glycine max (L) Merr. cv. Kurosengoku) was examined at different growth stages; vegetative, flowering and pod-filling. Considerable amounts of nitrogenous compounds were excreted at all the growth stages, with the highest amount recorded at the pod-filling stage. The root was found to be the major site of N compound excretion and its dry weight was linearly correlated with N amount excreted. Maximum nitrogen excretion rate during vegetative and flowering stages was recorded during the ‘day’, however at the pod-filling stage, the highest was recorded during the ‘night’. Ureide was excreted at all growth stages, but the highest amount was recorded at the pod-filing stage. The root was found to be the active site of ureide excretion. Composition of the total nitrogen examined i. e. ureide, soluble proteins, ammonia and amino acids, was found to be changing during the growth stages, suggesting possible different major pathways of excretion at different plant age. Among the N compounds monitored, were soluble proteins, ammonia and amino acids. Only a few of the several amino acids found in the root tissues were observed in the ‘excreted solution’, notably phosphoserine and phosphoethanolamine, at all the growth stages, whilst γ-amino-butyric-acid and serine were observed in trace amounts during vegetative and flowering stages. Quantitatively the ammonia found in the ‘excreted solution’ was far greater than in the tissues.

Growth, yield and soil water extraction of irrigated and dryland peanuts in South Sulawesi, Indonesia

Irrigation at 35 and 70 mm of pan evaporation applied during the pre and/or post early podfilling stages increased pod yield of Spanish peanuts (100 day maturity) three fold compared to a dryland crop. There was no difference in pod yield in crops receiving 12 compared to 6 irrigations. Soil water sampling immediately after irrigations on selected treatments revealed that infiltration of irrigation water was probably restricted to less than ca. 20 cm, a response which resulted in poor soil water replenishment and low irrigation efficiency (Fig. 3). Even though roots extracted soil water below the compaction layer which was at 20 cm severe crop water deficits had developed by the end of irrigation cycles during later but not early stages of growth. The dryland crop, which received no rainfall during the season, presumably extracted significant amounts of soil water at depths to and below 1.2 m (Fig. 3). Despite producing ca. 2.9 t ha-1 of total dry matter yield, pod yield was extremely low (0.5 t ha-1) arising from low pod numbers and high percentage of empty pods.

Soybean Yield Response to Benomyl Fungicide Application under Maximum Yield Conditions

AbstractIn 1980, after three consecutive years with soybean [Glycine max. (L.) Merr.] yields in excess of 5000 kg ha−1 in surface‐irrigated, maximum yield, research plots, yields dropped to 3000 kg ha−1 due to severe development of Septoria brown spot (Septoria glycines Hemmi), which caused premature senescence and defoliation of the leaves. The purpose of this research was to determine the effect of benomyl [methyl‐l‐(butylcarbamoyl)‐2‐benzimidazole carbamate] control of natural infection of foliar diseases, primarily Septoria brown spot, on the yield of irrigated, high‐yield soybean. Benomyl was applied at a rate of 2.2 kg ha−1 at 2‐wk intervals beginning in mid July (late flowering stage, R2‐R3) with the last application in early September (late pod fill stage, R6). Two determinate semidwarf cultivars, Hobbit and Sprite, and two indeterminate cultivars, Pella and Williams 82, were grown in two row spacings, (75 and 17 cm) and compared with and without benomyl treatment for 3 yr. Averaged across the 3 yr, the determinate cultivar, Hobbit, and the indeterminate cultivar, Pella, were the most yield responsive to benomyl treatment (15.4 and 7.7% in 75‐cm rows and 13.8 and 15.5% in 17‐cm rows, respectively). The determinate cultivar, Sprite, and the indeterminate cultivar, Williams 82, failed to show a significant yield increase from benomyl treatment. These results indicate that yield reductions due to Septoria brown spot vary by genotype, but are not associated specifically with plant type (determine vs. indeterminate). Yield increases from benomyl treatment tended to be greater in 17‐cm row width than in 75‐cm row width. This research indicates that control of foliar diseases, such as Septoria brown spot, can significantly increase the yield potential of high yielding soybean under conditions of frequent wetting of the foliage, either by frequent rainfall or irrigation, and should be an important component of a maximum‐yield research or production system.

Effect of CO2enrichment and nitrate application on growth and dinitrogen fixation of wild and cultivated soybean plants during pod-filling stage

A wild soybean variety (Glycine soja Sieb. and Zucc. line Nakei-No. 1) and a cultivated soybean variety (Glycine max L. Merr. cv. Tamahomare) were subjected to treatments of CO2 enrichment and/or 50 ppm nitrate (NO3-N) application during the pod-filling period and the growth and dinitrogen fixation of the plants were examined. 1. The whole plant weight of the soybean cultivar was increased by CO2 enrichment and did not change by NO3-N application, whereas the wild soybean variety responded neither to CO2 enrichment nor to NO3-N application. In the wild soybean variety, CO2 enrichment promoted yellowing and death of leaves, while NO3-N application prevented those phenomena from occuring. 2. In the absence of NO3-N in the culture medium, the dinitrogen-fixing activity in the soybean cultivar increased by CO2 enrichment, whereas it decreased in the wild soybean variety. In the soybean cultivar, the adverse effect of NO3-N on the dinitrogen fixation was alleviated by CO2 enrichment. 3. The whole plant N incre...