Effects Of Plant Growth Stage Research Articles

Different responses of root exudates to biochar application under elevated CO2

Biochar application and rising carbon dioxide (CO2) concentrations are likely to influence both aboveground and belowground plant processes. However, little is known about the influence of biochar and CO2 enrichment on root exudation, as well as their interactive effects. The aim of this study was to reveal whether rice paddy root exudates responded to biochar and CO2 enrichment and whether this effect varied at different plant growth stages. Rice was grown in growth chambers with different biochar addition rates (1%, 2%, 3%, 4%, and 5% by weight) under both ambient (aCO2, 400 ppm) and elevated (eCO2, 700 ppm) CO2 levels. Root exudation variables were measured at the tillering and stem elongation stages. Electrical conductivity (EC), amino acid (AA), indole acetic acid (IAA), and abscisic acid (ABA) levels were significantly increased but cytokinin (CYT) concentrations decreased in response to biochar addition rates. In addition, eCO2 increased root and shoot biomass but decreased the root-to-shoot ratio. eCO2 significantly decreased EC, potassium (K+), ABA, and CYT concentrations, while the opposite pattern was found for AA and IAA. Significant interactive effects between biochar addition and eCO2 were only found on CYT and AA concentrations, while no significant interactive effects of plant growth stage, biochar addition, and eCO2 were found on root exudation. These results indicate that the additive effects of biochar and eCO2 should be integrated into assessments of carbon storage ability in the future. Understanding the different responses of these variables within the rhizosphere is crucial for predicting changes in the carbon balance in response to biochar application and climate change.

Susceptibility of Winter Wheat and Triticale to Yellow Rust Influenced by Complex Interactions between Vernalisation, Temperature, Plant Growth Stage and Pathogen Race

Environmental factors influence the disease susceptibility of crop plants. In this study, we established an experimental system to investigate the effects of vernalisation, temperature and plant growth stage on the susceptibility of winter wheat and winter triticale to Puccinia striiformis, the causal agent of yellow (stripe) rust. Two temperature regimes: standard (18 °C day/12 °C night) and low (12 °C day/6 °C night), vernalised and non-vernalised seedlings, vernalised adult plants and two pathogen races were investigated. At low temperatures, vernalisation reduced the susceptibility of seedlings exposed to the ‘Warrior’ race, while this was only the case for five out of eight varieties exposed to the ‘Kranich’ race. Changing from standard to low temperature resulted in increased susceptibility of non-vernalised seedlings of seven varieties inoculated with the ‘Warrior’ race and five varieties inoculated with the ‘Kranich’ race. Increased susceptibility at low temperature was also detected for several varieties at the adult plant growth stage. Comparisons between vernalised seedlings and adult plants revealed an effect of plant growth stage on disease susceptibility (e.g., Adult Plant Resistance) in five varieties at standard temperature for the ‘Warrior’ race and in five and four varieties at standard and low temperature respectively, for the ‘Kranich’ race. The complex and unpredictable interactions between environment and pathogen influencing yellow rust susceptibility of individual varieties stress the importance of phenotyping for disease resistance under different environmental conditions and pathogen populations. The environmental impact on rust susceptibility should also be taken into account in early-warning systems targeting wheat and triticale breeding programmes and growers.

Nitrogen Uptake and Allocation at Different Growth Stages of Young Southern Highbush Blueberry Plants

Southern highbush blueberry (SHB, Vaccinium corymbosum L. interspecific hybrid) is the major species planted in Florida because of the low-chilling requirement and early ripening. The growth pattern and nitrogen (N) demand of SHB may differ from those of northern highbush blueberry (NHB, V. corymbosum L.). Thus, the effect of plant growth stage on N uptake and allocation was studied with containerized 1-year-old SHB grown in pine-bark amended soil. Five ‘Emerald’ plants were each treated with 6 g 10% 15N labeled (NH4)2SO4 at each of 12 dates over 2 years. In the first year, plants were treated once in late winter, four times during the growing season, and once in the fall. In the second year, treatment dates were based on phenological stages. After a 14-day chase period following each 15N treatment, plants were destructively harvested for dry weight (DW) measurements, atom% of 15N, and N content of each of the plant tissues. Total DW increased continuously from mid-May 2015 to Oct. 2015 and from Mar. 2016 to late Sept. 2016. From August to October of both years, external N demand was the greatest and plants absorbed more N during the 2-week chase period, about 0.53 g/plant in year 1 and 0.67 g/plant in year 2, than in chase periods earlier in the season. During March and April, N uptake was as low as 0.03 g/plant/2 weeks in year 1 and 0.21 g/plant/2 weeks in year 2. Nitrogen allocation to each of the tissues varied throughout the season. About half of the N derived from the applied fertilizer was allocated to leaves at all labeling times except the early bloom stage in 2016. These results suggest that young SHB plants absorb greater amounts of N during summer and early fall than in spring.

Effects of plant growth stage and leaf aging on the response of transpiration and photosynthesis to water deficit in sunflower.

Water deficit influences leaf transpiration rate and photosynthetic activity. The genotype-dependent response of the latter has not been assessed in sunflower (Helianthus annuus L.), particularly during the reproductive period when grain filling and lipogenesis depend greatly on photosynthate availability. To evaluate genotypic responses to water deficit before and after flowering, two greenhouse experiments were performed. Four genotypes-two inbred lines (PSC8, XRQ) and two cultivars (Inedi, Melody)-were subjected to progressive water deficit. Non-linear regression was used to calculate the soil water deficit threshold (FTSWt) at which processes (transpiration and photosynthetic activity) were affected by water deficit. In the vegetative growth stage, photosynthetic activity was affected at a lower mean value of FTSWt (0.39) than transpiration (0.55). However, in the reproductive stage, photosynthetic activity was more sensitive to soil water deficit (FTSWt=0.45). We found a significant (P=0.02) effect of plant growth stage on the difference between photosynthesis and transpiration rate thresholds and, a significant (P=0.03) effect of leaf age on transpiration. Such results will improve phenotyping methods and provide paths for integrating genotypic variability into crop models.

Positional difference in potassium concentration as diagnostic index relating to plant K status and yield level in rice (Oryza sativa L.)

ABSTRACTPlant tissue testing is used as a guide for rice (Oryza sativa L.) fertilization and has been extensively used in the diagnosis of potassium (K) deficiency. However, little attention has been paid to the variation in the diagnostic index of K status in different parts of the rice plant. Here, we assessed the feasibility by testing K concentrations of whole plants, leaf blades and leaf sheaths to develop a suitable diagnostic index of plant K status and yield level in rice under different K application rates. The results showed that this research could satisfy the requirements of K status diagnosis, based on the quadratic-plus-plateau relationship between K application rates and grain yield. The K concentrations of the leaf blades and leaf sheaths on the main stem showed differences based on position. Leaf blade K concentrations significantly decreased from the top of the plant to the bottom in the effective tillering and jointing stages. Conversely, K concentrations in the lower leaf blades exceeded those in the upper leaf blades in the booting and full heading stages. K concentrations in the leaf sheath were significantly reduced with declining leaf position except during the jointing stage under high K treatments. Leaf sheath/leaf blade K concentration ratios increased significantly more in lower tissues than in upper plant tissues. Correlation analysis showed that the K concentrations of all sampled plant tissues were positively correlated to plant K uptake and grain yield. However, K concentrations of the whole plant were more useful as a diagnostic index at the effective tillering stage than at other growth stages. Leaf sheaths in lower positions were preferable to upper leaf sheaths and all leaf blades for evaluating plant K status, although their K concentrations were greatly influenced by plant growth stage. Furthermore, this study demonstrated that the ratio between the K concentrations of the first and fourth leaf blades (LBKR1/4) was grouped into significantly exponential curves (P < 0.01) to describe the relationship between plant K uptake and relative grain yield. Thus, LBKR1/4 could be an ideal indicator of rice plant K status and yield level, as it eliminated the effects of plant growth stage.

Artemisia arborescens L.: essential oil composition and effects of plant growth stage in some genotypes from Sicily

Essential oils from aerial parts of several Artemisia arborescens L. populations, collected in five different localities of Sicily, were analyzed by gas chromatograph–flame ionization detector (GC–FID) and GC–mass spectrometry (GC–MS) in order to study the chemical composition and its variability due to phenological stage. Forty-three compounds, accounting for more than 92% of the oil, were identified. Monoterpene fraction with the exception of Petru population was higher than the sesquiterpene fraction. β-Thujone (20.5–55.9%), chamazulene (15.2–49.4%), camphor (1.3–10.7%) and germacrene D (2.3–3.4%) were the main compounds. Chemical composition was influenced by phenological stage, with an increase in the monoterpene fraction at flowering stage; both in flowering and vegetative stages, the main compounds were always the oxygenated monoterpene β-thujone and the sesquiterpene hydrocarbon chamazulene.

Common Lambsquarters Response to Glyphosate across Environments

We conducted a series of field experiments to determine the role of several factors that might contribute to the inconsistent control of common lambsquarters with glyphosate. Experiments in 2006 and 2007 determined common lambsquarters response to glyphosate under a wide range of measured environmental conditions. Glyphosate was applied at 0.84 kg ae ha−1plus 3.8 kg ha−1ammonium sulfate (AMS) to 10-cm-tall plants on 18 dates in each year and to 20-cm-tall plants on 18 dates in 2007. Control was less for six application dates relative to control for 48 other dates. Poor control was attributed to rainfall on one of these six dates, but for the other five dates, regression analysis did not identify any significant relationships between environmental conditions (relative humidity, temperature at time of treatment, or minimum and maximum temperature pre- and posttreatment) and control, even though a wide range of conditions occurred. To determine the effects of plant growth stage on control, glyphosate was applied at 0.1 to 3.2 kg ha−1plus 3.8 kg ha−1AMS to 10- and 20-cm-tall plants at four sites. The glyphosate ED50value (the effective dose that reduced shoot mass by 50% relative to nontreated plants) was 1.9 to 3.0 times greater for 20- than 10-cm-tall plants in three site-years, but was not affected by plant height in one site-year. We also conducted experiments to determine the effect of rainfall on glyphosate efficacy. Across years, common lambsquarters control increased from 44 to 75% as the interval between glyphosate application (0.84 kg ha−1+ 3.8 kg ha−1AMS) and simulated rainfall increased from 0.5 to 4.0 h, respectively. Our results did not identify environmental conditions that explained reduced glyphosate efficacy in all cases, but they suggest that rainfall after application and plant height can be important factors contributing to the inconsistent control of common lambsquarters.

Developing Rainfall- and Temperature-Based Models to Describe Infection of Canola Under Field Conditions Caused by Pycnidiospores of Leptosphaeria maculans

Blackleg, also known as Phoma stem canker, caused by Leptosphaeria maculans (Phoma lingam), is one of the most serious diseases of canola worldwide. In this study, the mean disease severity (Ds) and incidence (Di) of canola cv. Westar plants infected at the cotyledon, three-leaf, and six-leaf stages by pycnidiospores of L. maculans were monitored in the greenhouse after infection of the plants under field conditions in two successive years and associated with meteorological data during infection time. Pearson's correlation coefficient showed that total rainfall per week (R) was significantly correlated to Ds on plants infected at the cotyledon, three-leaf, and six-leaf stages, and average maximum temperature per week (Tmax) only showed significant correlation with plants infected at the cotyledon and six-leaf stages. These results also indicated that there is correlation between Di and R for plants infected at all three growth stages. A nonlinear model was developed to evaluate the combined effects of R and Tmax on Ds. The best model comprised monomolecular function and beta probability density function for plants infected at the above three growth stages. Parameters, including maximum potential for Ds at a given rainfall (d(max)), rate of changes with respect to rainfall (k), constant of integration (B), maximum potential for Ds with respect to Tmax (e), rate of increase with increasing Tmax to optimum (n), and rate of decrease as Tmax increased and passed the optimum Tmax (p), were estimated for plants infected at the above three growth stages. The effect of plant growth stage was characterized by differences in the upper limit parameter a. This parameter was greater for the plants infected at the cotyledon stage than for plants infected at the other two stages. The estimate of parameter k was the same for the plants infected at the cotyledon and three-leaf stages. This parameter was much lower for the plants infected at the six-leaf stage compared with two other stages. The logistic model could describe the disease incidence with respect to R slightly better than the other two models in the plants infected at all three growth stages. Based on the model, upper-limit estimate (d(max)) was approximately 100, 94.4, and 88.8% in the plants infected at cotyledon, three-leaf, and six-leaf stages, respectively. Di increased until rainfall reached approximately 18, 10, and 13 mm/week and became constant in the plants at cotyledon, three-leaf, and six-leaf stages, respectively. Effects of plant growth stage on the rate of change with respect to R (parameter k) were lower in the plants infected at cotyledon than at the other two stages. The accuracy of the nonlinear models suggests that they could be used to develop a comprehensive model to evaluate epidemics of blackleg based on pycnidiospores as sources of inoculum. However, additional years of data collection should improve model fit and evaluation of introduced models and contribute to the development of a more robust predictive model.

Endophytic Colonization of Potato ( Solanum tuberosum L.) by a Novel Competent Bacterial Endophyte, Pseudomonas putida Strain P9, and Its Effect on Associated Bacterial Communities

Pseudomonas putida strain P9 is a novel competent endophyte from potato. P9 causes cultivar-dependent suppression of Phytophthora infestans. Colonization of the rhizoplane and endosphere of potato plants by P9 and its rifampin-resistant derivative P9R was studied. The purposes of this work were to follow the fate of P9 inside growing potato plants and to establish its effect on associated microbial communities. The effects of P9 and P9R inoculation were studied in two separate experiments. The roots of transplants of three different cultivars of potato were dipped in suspensions of P9 or P9R cells, and the plants were planted in soil. The fate of both strains was followed by examining colony growth and by performing PCR-denaturing gradient gel electrophoresis (PCR-DGGE). Colonies of both strains were recovered from rhizoplane and endosphere samples of all three cultivars at two growth stages. A conspicuous band, representing P9 and P9R, was found in all Pseudomonas PCR-DGGE fingerprints for treated plants. The numbers of P9R CFU and the P9R-specific band intensities for the different replicate samples were positively correlated, as determined by linear regression analysis. The effects of plant growth stage, genotype, and the presence of P9R on associated microbial communities were examined by multivariate and unweighted-pair group method with arithmetic mean cluster analyses of PCR-DGGE fingerprints. The presence of strain P9R had an effect on bacterial groups identified as Pseudomonas azotoformans, Pseudomonas veronii, and Pseudomonas syringae. In conclusion, strain P9 is an avid colonizer of potato plants, competing with microbial populations indigenous to the potato phytosphere. Bacterization with a biocontrol agent has an important and previously unexplored effect on plant-associated communities.

Control of Volunteer Canola with Herbicides: Effects of Plant Growth Stage and Cold Acclimation

Phenoxy herbicides are frequently used to control volunteer canola populations. However, there have been claims that poor control could be due to cold acclimation of canola plants in the spring. The objective of this study was to determine whether cold acclimation or growth stage affected the response of canola volunteers to herbicides. In a growth room experiment, canola plants were prehardened and cold acclimated or were grown at 20/12 C and treated with one of six 2,4-D doses. Cold acclimation as achieved by this experiment affected upper and lower asymptotes of the dose–response curve but not the herbicide dose required to reduce canola weight by 50% relative to the nontreated control (GR50), indicating limited cold-related effects on canola tolerance to 2,4-D. Field experiments, conducted in the provinces of Québec and Saskatchewan, examined the effects of canola growth stage on the efficacy of 2,4-D, MCPA, and carfentrazone. Comparisons of the estimates from the dose–response curves confirmed that herbicide efficacy was consistently greater when canola plants were treated at an early growth stage, regardless of cultivar or herbicide used. The GR50estimates for canola plants treated at a later growth stage exceeded the recommended rates. Some canola plants grown as volunteers in a wheat crop survived 2,4-D or MCPA treatments at 0.5× and 1× rates and produced up to 148 seeds/m2. Efficient control of canola volunteers will be obtained when plants are sprayed at an early growth stage, but near-total control will be highly desirable in order to restrict seedbank buildup, particularly when dealing with canola cultivars with different herbicide-resistant traits.

根圏土壌におけるＣｓおよびＳｒの可給性に及ぼす植物生育ステージの影響

Cs及びSrの土壌―植物移行における, 植物生育段階の影響について, ダイズを用いたポット栽培試験によって検討した。ダイズ植栽区と無植栽区を設け, 生育期間中のMg, K, Ca, Sr及びCsの土壌溶液中濃度, 植物中濃度, 及び蒸散量を測定した。植物生育にともない, 土壌溶液中のMg, K, Ca, Sr及びCs濃度は減少した。Mg, Ca, K及びSrの濃度低下は植栽区で顕著であり, ダイズによる吸収により, 土壌溶液中の濃度が減少したと考えられる。一方でCsについては, 植栽区と無植栽区との差は少なかった。蒸散量から各元素のマスフローによる根表面への移動量を計算し, 実際の吸収量と比較したところ, Csについては, 根近傍 (根圏) においてCsの吸収が阻害され, それは生育後半においてより顕著となることが示された。根密度の高い小スケール栽培により, 根圏土壌におけるCs, Srの可給性について検討した結果, 根圏において局所的にCsの分配係数 (Ka) が増加することが示された。これらの結果から, 長期的な栽培においては, 栽培にともなう根圏のK濃度減少にともない, 根圏においてCsの固定が促進され, 生育後半にはCsの可給性が減少したものと考えられる。こうした根圏における可給性の低下はSrについては認められなかった。

Relationship between Brassica napus seedling and adult plant responses to Leptosphaeria maculans is determined by plant growth stage at inoculation and temperature regime

Contradictory reports exist in the literature on the relationship of seedling and adult plant resistance to blackleg disease in Brassica napus (oilseed rape, canola) caused by Leptosphaeria maculans. Two repeat experiments were carried out to determine whether adult plant responses in certain cultivars of B. napus to a specific strain of L. maculans are evident in the response of the plants at the seedling stage and to evaluate whether the relationship between seedling and adult plant responses to L. maculans is determined by the growth stage of the plant at inoculation and the temperature of incubation prior to field planting. Point inoculations were made with pycnidiospores (conidia) on to cotyledons or youngest leaves of four B. napus cultivars (Westar, Surpass 400, Dunkeld and Grouse) at different growth stages under two temperature regimes (18/24 and 11/18 °C) which were rated for cotyledon or leaf lesions before they were planted out in the field and the severity of subsequent crown cankers assessed. Results across the four cultivars showed there was a significant effect of plant growth stage at inoculation ( P < 0.001), and cultivars ( P < 0.001) and a significant interaction between growth stage and cultivars ( P < 0.001) in relation to cotyledon lesions, leaf lesions, and crown cankers, with both temperature regimes. Overall, the cultivars differed in resistance to the strain tested in relation to cotyledon, leaf and crown canker symptoms, with cv. Dunkeld more resistant than Grouse > Surpass 400 > Westar. Different temperature regimes during inoculation, and for a minimum of 4 weeks post-inoculation, had significant effects on the growth rate of the plant as well as the development of disease symptoms. There was a high degree of positive correlation between the severity of cotyledon or leaf lesions with subsequent crown canker that developed for inoculations at nearly all growth stages at the 18/24 °C regime and the early growth stages (particularly up to and including growth stage 1,01, the first true leaf exposed) at the 11/18 °C regime. Overall, plant growth stage at inoculation clearly determined the expression of seedling and/or adult plant resistance. For all cultivars tested, at the higher temperature regime, expression of resistance between seedlings and adult plants, for nearly all growth stages at inoculation, could not be distinguished. In contrast, at the lower temperature regime, this relationship did not exist for inoculations carried out after growth stage 1,05 (the fifth true leaf exposed). These findings may explain the variable results obtained in previous studies attempting to define ‘adult plant resistance’ to blackleg and also indicates the need for standardizing screening processes for identification of host resistance.

Physiological basis for cotton tolerance to flumioxazin applied postemergence directed

Previous research has shown that flumioxazin, a herbicide being developed as a postemergence-directed spray (PDS) in cotton, has the potential to injure cotton less than 30 cm tall if the herbicide contacts green stem tissue by rain splash or misapplication. In response to this concern, five-leaf cotton plants with chlorophyllous stems and older cotton, 16-leaf cotton plants, with bark on the lower stem were treated with a PDS containing flumioxazin plus crop oil concentrate (COC) or nonionic surfactant (NIS). Stems of treated plants and untreated plants at the respective growth stage were cross-sectioned and then magnified and photographed using bright-field microscopy techniques. More visible injury consisting of necrosis and desiccation was evident in younger cotton. Also, there was a decrease in treated-stem diameter and an increase in visible injury with COC compared with NIS in younger cotton. The effects of plant growth stage and harvest time on absorption, translocation, and metabolism of14C-flumioxazin in cotton were also investigated. Total14C absorbed at 72 h after treatment (HAT) was 77, 76, and 94% of applied at 4-, 8-, and 12-leaf growth stages, respectively. Cotton at the 12-leaf stage absorbed more14C within 48 HAT than was absorbed by four- or eight-leaf cotton by 72 HAT. A majority (31 to 57%) of applied14C remained in the treated stem for all growth stages and harvest times. Treated cotton stems at all growth stages and harvest times contained higher concentrations (Bq g−1) of14C than any other tissues. Flumioxazin metabolites made up less than 5% of the radioactivity found in the treated stem. Because of the undetectable levels of metabolites in other tissues when flumioxazin was applied PDS, flumioxazin was foliar applied to determine whether flumioxazin transported to the leaves may have been metabolized. In foliar-treated cotton, flumioxazin metabolites in the treated leaf of four-leaf cotton totaled 4% of the recovered14C 72 HAT. Flumioxazin metabolites in the treated leaf of 12-leaf cotton totaled 35% of the recovered14C 48 HAT. These data suggest that differential absorption, translocation, and metabolism at various growth stages, as well as the development of a bark layer, are the bases for differential tolerances of cotton to flumioxazin applied PDS.

Influence of Plant Growth Stage on Grape Phylloxera (Homoptera: Phylloxeridae) Populations

To understand the effects of plant growth stage on the performance of grape phylloxera, Daktulosphaira vitifoliae (Fitch), demographic analyses were done using attached roots in a Vitis vinifera L. ‘Chardonnay’ vineyard during the vegetative, mid-ripening, and postharvest periods of grapevines. Survival of first instars was <30%. First instars coincide with the time of gall formation, and their survival was higher during postharvest than during the vegetative and mid-ripening periods. Survival after the second instar did not decrease with development but was stable, generally above 90% for the postharvest period and below 75% for the other experimental periods. Sucrose levels in root phloem parenchyma tissues were highest during postharvest compared with vegetative and mid-ripening periods and reflect a more rapid development during this period but only by a few days. The limiting step of grape phylloxera population growth appears to occur simultaneously with gall formation and is associated with survival. Survival and developmental rate of a virulent grape phylloxera strain were limiting with greenhouse vines of the resistant rootstocks 5C and SO4. Survival and developmental rates were more limiting for attached than detached roots.

Effect of Soybean Growth Stage at the Time of Inoculation with Diaporthe phaseolorum var. meridionales on Stem Canker Development and Yield.

Infections at early stages of plant development followed by a long incubation period before symptoms appear during reproductive stages is characteristic of the disease cycle of stem canker of soybean, caused by Diaporthe phaseolorum var. meridionales. To determine the effect of plant growth stage at the time of infection on symptom development and yield components, soybean plants (cv. Walters) were grown in microplots and inoculated with a suspension of ascospores (106/ml) at the V1, V4, V6, V10, or R2 growth stage. Noninoculated plants served as controls. Development of foliar symptoms was quantified weekly after flowering (R2), and yields and seed weights were determined. The experiment was conducted twice, in 1992 and 1994. Foliar symptoms of stem canker developed for all treatments except the noninoculated control. Foliar symptoms appeared at the R2 to R5 growth stage and reached 90 to 100% incidence for most treatments. Disease development was delayed for the R2 inoculation, suggesting that a minimum incubation period of 34 to 41 days is necessary before foliar symptoms develop. Disease (area under the disease progress curve) was greater and yield, seed number, and seed weight were less in 1994 than in 1992. Quadratic equations significantly related these variables to time of inoculation and reached maximum or minimum values between 40.9 and 43.3 days after planting. This corresponded to the V6 growth stage. Yield and seed number were affected by disease development during pod formation (R2 to R5) in both years, while yield and seed weight were affected by disease development during seed formation (R5 to R6) in 1992.

Technical note: utilization of sainfoin by grazing steers and a method for predicting daily gain from small-plot grazing data.

Sainfoin (Onobrychis viciaefolia Scop.) is adapted to the calcareous soils of the southern Great Plains and can provide early season forage that does not induce bloating; however, little is known about performance by ruminants grazing sainfoin. Our objective was to determine the effect of plant growth stage and grazing pressures on potential animal production from sainfoin as predicted from energy intake as a multiple of maintenance. Nitrogen-fertilized (100 kg of N/ha) Renumex sainfoin was grown under irrigation on a Pullman clay loam (fine, mixed, thermic Torretic Paleustoll) near Lubbock, TX. Light (L), medium (M), and heavy (H) grazing pressures were applied with steers grazing sainfoin that was at the bud (B), flower (F), and seed shatter (S) stages of growth. The L, M, and H pressures were grazed to remove 50, 75, and 90% of the standing plant height. Across growth stages, L, M, and H grazing pressures averaged 52, 69, and 87% removal of pregrazed herbage mass. Dry matter intake as a percentage of BW of steers averaged 3.9, 2.8, and 1.7 for L, M, and H grazing pressures. Across growth stages, predicted live weight gain for L, M, and H grazing pressures averaged .86, .67, and .03 kg/d. Our findings indicate that the multiple of maintenance method may be useful for evaluating treatments from small-plot grazing experiments.

Persistence of Sainfoin under Different Grazing Regimes

AbstractSainfoin (Onobrychis viciaefolia Scop.), a non‐bloat inducing legume, is well adapted to the calcareous soils of the Southern Great Plains. Poor persistence under some managements has limited its; use for grazing. Our objectives were to determine the effect of plant growth stage at defoliation and defoliation intensity on persistence of sainfoin. Nitrogen fertillized (100 kg N ha−1) ‘Renumex’ sainfoin was grown under irrigation on a Pullman clay loam (fine, mixed, thermic Torretic Paleustolll) near Lubbock, TX. Light (L), medium (M), and heavy (H) grazing intensities were applied at the bud (B), flower (F), and seed shatter (S) stages of growth. Across growth stages, L, M, and H intensities averaged 52, 69, and 87% removal of pre‐graze herbage mass, respectively. Over the 2 yr, sainfoin stands declined 20 and 43% when defoliated at the B and F stages under H defoliation intensity. Stands remained above 80% for the L and M intensities. Stands increased from reseeding in the S treatments by 35, 31, and 16% for the L, M, and H defoliations, respectively. Root concentrations of total nonstructural carbohydrates (TNC) began to decrease with the initiation of spring growth reached their seasonal low in June, and then increased into late summer and autumn. Average TNC for H (130 g kg−1) was less than TNC in roots of L and M (155 g kg−1). Our findings indicate thaf sainfoin defoliated at the B or F stages of growth under L or M intensities of defoliation may have acceptable stand persistence when grown under irrigation in the Southern Great Plains.

Influence of Simulated Early Lodging upon Soybean Seed Yield and its Components1

AbstractEarly lodging of soybeans [Glycine max (L.) Merr.] in highly productive environments has been observed throughout the midwestern United States. It has been established that soybean seed yields are decreased when severe lodging occurs sometime prior to physiological maturity. The objective of this 2‐year field study was to examine the effect of plant growth stage at the time of lodging on soybean seed yield and its primary components; pods per plant, seeds per pod, and seed size.The study was conducted at Tipton, Ind., in 1972 on a Crosby silt loam soil (member of the fine mixed mesic family of Aeric Ochraqualfs) and at Lafayette, Ind., in 1973 on a Chalmers silty clay loam soil (member of the fine loamy mixed mesic family of Typic Haplaquolls.) Two Group II soybean cultivars (‘Wells’ and ‘Corsoy’), representing distinct degrees of lodging resistance, were subjected to a simulated lodging treatment at 2‐week intervals in the early reproductive growth stages. Controls were: a) plants supported by a 10 ✕ 10 cm plastic grid system, and b) no treatment or support which permited natural lodging to occur. Depending upon the time of simulated lodging, seed yields of both cultivars were reduced from 11 to 32% in 1972 and from 12 to 22% in 1973. The reproductive growth stage, R5, normally reached during the first 2 weeks of August in central Indiana, was found to be the most critical time for lodging to occur. Neither seeds per pod nor seed size was significantly reduced when lodging occurred at stage R5. The reduction in yield was due almost entirely to a reduced number of pods per plant, especially those on the central stem. When lodging occurred after flowering had commenced apical dominance was lost, resulting in lateral branches assuming central stem characteristics.