V3 Growth Stage Research Articles

Effect of glyphosate on Macrophomina phaseolina in vitro and its effect on disease severity of soybean in the field

Laboratory and field studies were conducted to assess the effects of glyphosate on Macrophomina phaseolina culture growth in vitro and the disease severity of charcoal rot in soybean fields at Stoneville, MS and Jackson, TN. Glyphosate inhibited M. phaseolina growth in a linear dose dependent manner when technical grade glyphosate acid (GlyCry) was used; however, growth was inhibited in an exponential dose dependent manner when a commercial formulation of glyphosate-potassium salt (Gly-K salt) was used. The glyphosate GR50 values (glyphosate concentration required to cause a 50% reduction) in culture radial growth ranged from 0.25 to 9.94 mM among the M. Phaseolina isolates, temperatures, and formulations. The three isolates differed in response to various concentrations across the three temperature regimes. Among the three isolates, TN 410 was the most sensitive for both GlyCry (GR50 = 7.74 mM) and Gly-K salt (GR50 = 0.25 mM) at 30 °C. This research indicates that glyphosate has the ability to inhibit growth of M. phaseolina in culture in vitro. The preliminary field studies demonstrated that application of glyphosate to glyphosate-resistant soybeans did not enhance or reduce the severity of charcoal rot in a no-till field in TN but had some suppressing effect in a tilled environment in MS when single applications were made at growth stage V3 and V6.

Aggressiveness of Fusarium Species and Impact of Root Infection on Growth and Yield of Soybeans

Fusarium spp. are commonly isolated from soybean roots but the pathogenic activity of most species is poorly documented. Aggressiveness and yield impact of nine species of Fusarium were determined on soybean in greenhouse (50 isolates) and field microplot (19 isolates) experiments. Root rot severity and shoot and root dry weights were compared at growth stages V3 or R1. Root systems were scanned and digital image analysis was conducted; yield was measured in microplots. Disease severity and root morphology impacts varied among and within species. Fusarium graminearum was highly aggressive (root rot severity >90%), followed by F. proliferatum and F. virguliforme. Significant variation in damping-off (20 to 75%) and root rot severity (<20 to >60%) was observed among F. oxysporum isolates. In artificially-infested microplots, root rot severity was low (<25%) and mean yield was not significantly reduced. However, there were significant linear relationships between yield and root symptoms for some isolates. Root morphological characteristics were more consistent indicators of yield loss than root rot severity. This study provides the first characterization of aggressiveness and yield impact of Fusarium root rot species on soybean at different plant stages and introduces root image analysis to assess the impact of root pathogens on soybean.

Landscape Features Impact on Soil Available Water, Corn Biomass, and Gene Expression during the Late Vegetative Stage

Crop yields at summit positions of rolling landscapes often are lower than backslope yields. The differences in plant response may be the result of many different factors. We examined corn (Zea mays L.) plant productivity, gene expression, soil water, and nutrient availability in two landscape positions located in historically high (backslope) and moderate (summit and shoulder) yielding zones to gain insight into plant response differences. Growth characteristics, gene expression, and soil parameters (water and N and P content) were determined at the V12 growth stage of corn. At tassel, plant biomass, N content, 13C isotope discrimination (Δ), and soil water was measured. Soil water was 35% lower in the summit and shoulder compared with the lower backslope plots. Plants at the summit had 16% less leaf area, biomass, and N and P uptake at V12 and 30% less biomass at tassel compared with plants from the lower backslope. Transcriptome analysis at V12 indicated that summit and shoulder‐grown plants had 496 downregulated and 341 upregulated genes compared with backslope‐grown plants. Gene set and subnetwork enrichment analyses indicated alterations in growth and circadian response and lowered nutrient uptake, wound recovery, pest resistance, and photosynthetic capacity in summit and shoulder‐grown plants. Reducing plant populations, to lessen demands on available soil water, and applying pesticides, to limit biotic stress, may ameliorate negative water stress responses.

Effect of Fungicide Seed Treatments, Cultivars, and Soils on Soybean Stand Establishment.

Seedling diseases are one of the major production problems for soybean. The primary control of soybean seedling diseases is by fungicide seed treatments but comparisons of seed treatments are difficult because stand responses are often erratic in the field. The objective of this study was to determine the efficacy of soybean fungicide seed treatments in naturally infested soils under controlled environments at three temperatures. Seed of three soybean cultivars were treated with six fungicide treatments or not treated and planted in two soil types collected from two fields in April, May, and June 2008 and 2009. Tests were conducted in growth chambers at 21°C (April planting), 25°C (May planting), or 28°C (June planting). Stands were determined when at least 25% of the seedlings reached the V4 growth stage. Seed treatments improved stands at all three temperatures, in both soils, and in both years. In general, the broad-spectrum fungicides trifloxystrobin + metalaxyl and mefenoxam + fludioxonil + azoxystrobin resulted in the highest stands. The selective fungicide treatments metalaxyl and pentachloronitrobenzene + carboxin were effective at all three temperatures, implying that Pythium spp. and Rhizoctonia solani, respectively, were involved in seedling disease and active over a range of temperatures. The efficacy of fungicides was not consistently associated with the cultivars used in this study.

Inoculação de sementes com bactéria diazotrófica e aplicação de nitrogênio em cobertura e foliar em milho

Considering the importance of nitrogen management and its biological fixation with diazotrophic bacteria, this study was carried out aiming to evaluate the agronomic performance of maize, in response to seed inoculation with Azospirillum brasilense and nitrogen application in side-dressing and leaf. The experiment was conducted in Selvíria, Mato Grosso of Sul State, Brazil, during the growing season 2010/2011, on a clayey Rhodic Haplustox (20º 20’ S and 51º 24’ W, with altitude of 340 m). Sixteen treatments were established with four replications, in randomized blocks with the combination of the factors A. brasilense (with and without inoculante), nitrogen rate (0 and 90 kg ha-1, in V5 growth stage) and urea leaf application (0, 4, 8 and 12%: application in V5 and V8 growth stage). The maize hybrid used was the DKB 390 YG®, sowed in the row spacing of 0.9 m. Parameters measured were productive and morphological components of culture and crop yield. Increase in maize yield by seed inoculation with A. brasilense was observed. The application of 90 kg ha-1 of nitrogen in side-dressing provided higher chlorophyll leaf index, stalk diameter and prolificacy, however, the yield not was increased. The application of urea leaf did not agronomic efficiency and, therefore, should not be used as the unique form of supply and alternative to nitrogen addition to crop.

A Comparison of Two Models to Evaluate Soil Physical Property Effects on Corn Root Growth

Two models for evaluating soil physical condition effects on root growth were compared. The first model, called the Jones model, is a submodel for root growth limitations used by several complex soil–plant–atmosphere models. The second model uses soil physical limitations as identified by the least limiting water range (LLWR). Root surface area density (Rsa) and bulk density (ρb) were determined at the V6, V12, and R1 growth stages of corn in 2004. Water contents (θ) throughout the growing season were determined twice per week with a neutron probe. The cumulative predicted relative root growth suitability (PRGS) was determined using soil physical limitations to root growth defined by each model. Significant plot‐to‐plot variability was observed in ρb and θ. The LLWR resulted in a wider range of PRGS for all sampling times and soil depths. Regressions using the LLWR criteria for soil physical limitations resulted in significant correlations between Rsa with PRGS at the expanding zone of root exploration, indicating more root surface area with better soil conditions. Regressions using the Jones criteria for soil physical limitations resulted in either a nonsignificant correlation between Rsa with PRGS or a linear, negative correlation, indicating less root surface area with better soil conditions. Using limitations of soil physical properties as identified by the LLWR in larger, more comprehensive plant and root growth models may provide a better response of these models to variable soil conditions.

Soybean yield and yield components as influenced by the single and repeated flaming

Field experiments were conducted to study the impact of single and multiple flaming on crop injury, yield components, and yield of soybean. The goal of this experiment was to determine the number of the maximum flaming treatments which soybean could tolerate without any yield loss. The treatments consisted of a non-flamed control, and broadcast flaming conducted one time (at VC-unfolded cotyledon, V2-second trifoliate, and V5-fifth trifoliate), two times (each at VC and V2, VC and V5, and V2 and V5 stages), and three times (at VC, V2, and V5 stages) resulting in a total of eight treatments. All plots were kept weed-free for the entire growing season by hand hoeing. A propane dose of 50 kg ha−1 was applied with torches parallel to the crop row and at an operating speed of 4.8 km h−1 for all treatments. The response of soybean was measured as visual injury ratings (at 7 and 28 days after treatment – DAT) as well as effects on yield components and yield. Broadcast flaming conducted once (at VC or V5 stage), as well as twice (at VC and V5 stages) exhibited the lowest injury of about 8% at 28 DAT. Any treatment that contained flaming at V2 stage resulted in more than 70% injury at 28 DAT. The highest crop yields were obtained from the non-flamed control (3.45 t ha−1) and the plots flamed once at VC (3.35 t ha−1), V5 (3.32 t ha−1), and two times at VC and V5 (3.24 t ha−1), which were all statistically similar. Soybean flamed at V2 stage had lower yields (1.03 t ha−1 at V2, 0.46 t ha−1 at VC and V2, and 0.38 t ha−1 at V2 and V5). The lowest yields were in soybean flamed three times (VC, V2, and V5 stages), which yielded only 0.36 t ha−1. These results indicate that soybean could tolerate a maximum of two flaming treatments at VC and V5 growth stages per season without any yield reduction.

Automatic corn plant location and spacing measurement using laser line-scan technique

Identifying corn plant location and/or spacing is important for predicting yield potential and making decisions for in-season nitrogen application rate. In this study, an automatic corn stalk identification system based on a laser line-scan technique was developed to measure stalk locations during corn mid-growth stages. A laser line-scan technique is advantageous in this application because the line-scan data sets taken from various points of view of a plant stalk results in less interference and higher probability of plant recognition. Data were collected for two 10-meter-long corn rows at the growth stages of V8 and V10 using a mobile test platform in 2011. Each potential stalk cluster was identified in a scan and registered with the same stalks in previous scans. The final location of a stalk was the average of the measured locations in all scans. The current system setup with data processing algorithms achieved 24.0 and 10.0 % of mean total errors in plant counting at the V8 and V10 growth stages, respectively. The root-mean-squared error (RMSE) between system measured plant locations and manually measured ones were 2.3 and 2.6 cm at the V8 and V10 growth stages, respectively. The interplant spacing measured by the developed system had a good correlation with the manual measurement with an R 2 of 0.962 and 0.951 for the V8 and V10 growth stages, respectively. This system can be ultimately integrated in a variable-rate-spraying system to improve real-time, high spatial resolution variable-rate nitrogen applications.

Vapor Movement of Aminocyclopyrachlor, Aminopyralid, and Dicamba in the Field

Vapor movement of synthetic auxin herbicides can injure desirable plants outside the treatment zone. Vapor movement of the synthetic auxin herbicides aminocyclopyrachlor and aminocyclopyrachlor methyl was compared with that of the relatively volatile herbicide dicamba and the low volatile herbicide aminopyralid with a soybean bioassay under greenhouse and field conditions. Soybean is very sensitive to these active ingredients. Under greenhouse conditions, 82 (61 to 104) mg ae ha−1of aminocyclopyrachlor, 26 (18 to 33) mg ae ha−1of aminocyclopyrachlor methyl, 82 (69 to 95) mg ae ha−1of aminopyralid, and 61 (47 to 75) mg ae ha−1of dicamba produced an estimated 25% visual soybean phytotoxicity response when soybean was treated POST at the V3 growth stage (GR25[95% confidence interval]). In field studies, aminocyclopyrachlor, aminocyclopyrachlor methyl, and aminopyralid were applied at 70 g ae ha−1and dicamba was applied at 560 g ae ha−1(labeled application rates) to soybean at the V3 growth stage. All herbicides were applied within an enclosed chamber (3 m by 3 m by 1 m) to mitigate movement of spray droplets. The enclosures were removed shortly after spray application and soybean response immediately surrounding the treated area was recorded in each of eight directions approximately 10 d after treatment. On the basis of bioassay responses, relative amount of vapor movement was dicamba &gt; aminocyclopyrachlor methyl &gt; aminopyralid ≈ aminocyclopyrachlor. Vapor movement of aminocyclopyrachlor was very low indicating that the risk of phytotoxic response of sensitive plants due to volatility of aminocyclopyrachlor is negligible.

Response of Soybean Yield Components to 2,4-D

Soybean plants exposed POST to 2,4-D can have reduced seed yield depending on the dose and time of exposure, but it is unclear how 2,4-D affects specific yield components. Objectives were to quantify soybean injury, characterize changes in seed yield and yield components of soybean plants exposed to 2,4-D, and determine if seed-yield loss can be estimated from visual assessment of crop injury. Ten rates (0, 0.1, 1.1, 11.2, 35, 70, 140, 280, 560, and 2,240 g ae ha−1) of 2,4-D were applied to Becks brand 342 NRR soybean at three soybean growth stages (V2, V5, or R2). The soybeans were planted near Lafayette, IN and Urbana, IL in 2009 and 2010 and near Fowler, IN in 2009. Twenty percent visual soybean injury was caused by 29 to 109 g ha−12,4-D at 14 d after treatment (DAT) and 109 to 245 g ha−1at 28 DAT. Nonlinear regression models were fit to describe the effect of 2,4-D on seed yield and yield components of soybean. Seed yield was reduced by 5% from 87 to 116 g ha−1and a 10% reduction was caused by 149 to 202 g ha−12,4-D at all application timings. The number of seeds m−2, pods m−2, reproductive nodes m−2, and nodes m−2were the most sensitive yield components. Path analysis indicated that seeds m−2, pods m−2, main stem reproductive nodes m−2, and main stem nodes m−2were the most influential yield components in seed-yield formation. Seed-yield loss was significant (P &lt; 0.0001) and highly correlated (R2= 0.95 to 0.99) to visual soybean injury ratings. A 10% seed-yield loss was caused by 35% soybean injury observed at 14 DAT, whereas a 10% seed-yield loss was a result of 40, 19, and 15% soybean injury observed at 28 DAT when soybean was exposed to 2,4-D at the V2, V5, and R2 growth stages, respectively.

Soybean growth under drought stress and foliar manganese

The objective of the present study was to investigate effect of manganese foliar application on soybean growth under drought stress condition. Therefore, a field experiment was conducted as a split split plot based on randomized complete block design with three replicates in Kermanshah province, Iran, 2010. Treatments includes: two irrigation regimes, two foliar treatments, and eight soybean cultivars. At the V4 growth stage, the plants were sprayed twice with 0.5% manganese liquid or distilled water. During the reproductive growth stages, five plants were selected from each plot randomly and leaf area index, stem, leaf, pod, and seed dry weight were measured. The results shown that in stressed plants leaf, stem, pod and seed dry weight was reduced. Total dry weight decreased with irrigation withholding by 12.5%. In addition, soybean plants have lower leaves at the end of growing season under water deficit conditions. Furthermore, in well water condition, Clark, Williams, and DPX cultivars had the highest response to Mn foliar application. Also, Mn application at water deficit condition had significant effect on pod and grain dry weight in all of evaluated cultivars. Total dry weight of M7 cultivar had the lowest response to manganese application in both condition compared the other cultivars.

Response of soybean yield to manganese foliar application under short-term drought stress

This research was done in order to investigate the Response of soybean yield to manganese foliar application under short-term drought stress at flowering stage in climatic condition of Kermanshah, Iran 2010. The experimental design was a split split plot based on Randomized Complete Block design with three replicates. Treatments includes: two irrigation regimes, two foliar treatments, and eight soybean cultivars. At the V4 growth stage, the plants were sprayed twice with 0.5% manganese liquid or distilled water. At the end of growing season, biological yield, grain yield, yield components and harvest index were measured. The results of analysis variance were shown that irrigation regimes, manganese foliar treatments and cultivars had significant effects on number of pod and seed per plant, grain yield and biological yield at 1% level (P<0.01). Irrigation at all of growth stages and manganese foliar application produced the highest number of node per plant, number of sub branch, number of pod and seed per plant, grain yield and biological yield in soybean cultivars. Whereas, maximum 100-seed weight and harvest index were obtained with irrigation withholding at flowering stage. The effect of Mn foliar application in water deficit condition on pod and seed number, grain yield, and biological yield were higher than when manganese was used in Ic treatment.

Could Weed Sensing in Corn Interrows Result in Efficient Weed Control?

At the field scale, weeds generally appear aggregated rather than randomly distributed, and this aggregation is linked to the spatial heterogeneity of biotic and abiotic factors. Crop management practices shape the spatial pattern of weed infestations by modifying certain factors having an impact on weed emergence and growth. Although crop seeding is often the last in-field disturbance before crop and weed emergence, its effect on the distribution of weeds has received little attention in the literature. The purpose of this study was to assess the influence of the planting operation on weed cover and presence in corn fields using digital images to investigate the possibility of sensing the interrow to infer the presence or absence of weeds on the corn row. A total of 18 site-years under conventional tillage treated with a single POST application of herbicide were selected across seven locations. Image analysis, at the V2 to V4 growth stage of corn, was used to compare the weed cover in three zones: the undisturbed interrows, the corn rows, and the interrows compacted by tractor wheel traffic. For 61% of site-years, there was no significant difference among the zones. When there was a significant difference compared with the other two zones, the undisturbed interrow was usually less infested. Point-to-point comparisons of weed presence or absence (based on a threshold of five pixels) between the interrow and the corn row revealed 70 or 73% correspondence, depending on the type of interrow (undisturbed or tracked). However the error of inference of the corn row weed cover generated by sensing only adjacent interrows may be too high for efficient commercial weed control.

Improving evapotranspiration simulations in the CERES-Maize model under limited irrigation

Limitations on water resources for agriculture in places such as Colorado, USA, have caused farmers to consider limited irrigation as an alternative to full irrigation practices, where the crop is intentionally stressed during specific growth stages in an effort to maximize yield per unit water consumed, or evapotranspiration (ET). While crop growth models such as CERES-Maize provide the ability to evaluate numerous management scenarios without the costs associated with multiyear field experiments, recent studies have shown that CERES-Maize performs well under full irrigation but overestimates ET of corn under limited irrigation management. The primary objective of this study was to improve CERES-Maize ET simulation under limited irrigation management while maintaining accuracy of other important model output responses. Field experiments with corn were performed in northern Colorado, USA from 2006 to 2010, where four replicates each of full (ET requirement supplied by irrigation throughout the season) and limited (no irrigation before the V12 growth stage unless necessary for emergence, then full irrigation afterwards) irrigation treatments were analyzed. The local sensitivity of model input parameters affecting ET was evaluated, prompting changes to the model code with a new dynamic crop coefficient (KCD) as a function of the crop leaf area index. The modified CERES-Maize model more accurately represented ET under full and limited irrigation, for example reducing late-season ET potential from a plant with reduced canopy and more closely matched FAO-56 crop coefficient curves under full irrigation. Using the limited irrigation data for evaluation, the modified model showed significant decreases in model error for seasonal cumulative ET (root mean square deviation RMSD from 80.9mm to 49.9mm) and water productivity (RMSD from 5.97kgha−1mm−1 to 2.86kgha−1mm−1) as compared to the original model. The modified model was subsequently applied to several hypothetical irrigation management strategies, indicating that reducing weekly vegetative stage water applications from 20mm to 2.5mm can increase simulated water productivity by over 15%. While these synthetic water production functions may not be feasible in a production field with natural climate variability, the modified ET model indicates promise for limited irrigation management increasing water productivity.

Tillage Effects on Corn Soil-plant-water Continuum in Alfisols of Southern Ohio

Tillage alters soil physical properties and impacts soil water regime, crop’s relative water content (RWC), and root distribution. Thus, a field study was conducted to characterize and correlate root distribution and assess RWC of corn ( Zea mays L.) with soil physical properties under two tillage systems i.e. no-till (NT), and conventional tillage (CT). The RWC, determined four times during a course of the day at two growth stages (V8, i.e. 60 days after planting; and R2, i.e. 90 days after planting), was significantly different (P < 0.05) among two tillage treatments. Corn grown under NT had significantly higher RWC than that under CT during both growth stages. At the V8 growth stage, the RWC ranged from 73.2 to 95.4 % under NT compared with 60.9 to 89.6 % under CT. Further, during the afternoon measurements, RWC was 15 % higher under NT than CT. A similar trend was observed during the R2 growth stage but with lesser RWC values probably due to the lower soil water content at that time. Higher root mass density (RMD) i.e. 0.50 Mg m -3 was measured in 0-10 cm depth under NT than under CT (0.34 Mg m -3 ), and the opposite was true for 10-20 cm depth. Due to the presence of a compacted layer (plow pan) in CT, roots were concentrated mostly in 10-20 cm depth. Further, higher RMD was measured along the row than within row.

Interpreting Relationships between Soil Variables and Soybean Iron Deficiency using Factor Analysis

Iron chlorosis in soybean [Glycine max (L.) Merr.] can be difficult to predict and often depends on various soil factors. The objective of this study was to determine the underlying soil factors that are conducive to Fe chlorosis in soybean using a statistical factor analysis. This study was conducted at seven locations in western Kansas with intensive soil sampling to investigate the relationships between soil variables and the incidence of Fe chlorosis. The soil variables measured were pH, P, Fe, organic matter (OM), Ca, Mg, electrical conductivity (EC), NO3–N, and calcium carbonate equivalent (CCE). Factor analysis was performed using the Varimax rotation and the Heywood convergence to obtain the best possible relationships. The factors were deemed significant if the Eigenvalues were >1. The factor analysis showed that two underlying factors can be selected to explain the incidence of Fe chlorosis in soybean. These factors are “plant chlorosis” (Factor 1) and “soil available Fe” (Factor 2). With regression analysis, these underlying factors were indicative of the chlorophyll meter (CM) readings at the V3 and V6 growth stages and in the grain yield (GY). However, soybean management practices, such as variety selection and the use of seed-applied Fe fertilizers were shown to affect the relationship between latent factors (from factor analysis) and soybean response. When seed-applied Fe fertilizers are used with tolerant and nontolerant soybean varieties, the overall effect of the undelaying soil factors seems irrelevant to soybean response.

First Report of Races 11 and 12 of Cercospora sojina, the Causal Agent of Soybean Frogeye Leaf Spot, in Argentina.

During the growing seasons of 2008 to 2009 and 2009 to 2010, severe outbreaks of soybean (Glycine max (L.) Merr.) frogeye leaf spot, a disease caused by Cercospora sojina Hara, occurred in several areas in Argentina (1). Two surveys were conducted in soybean fields, one in 2008 that included the provinces of Buenos Aires, Córdoba, and Santa Fe, and another that was performed in 2009 in the same provinces plus three others: Entre Ríos, Santiago del Estero, and Tucumán. In both surveys, plants presented circular lesions with reddish brown-to-gray spots and bordered by typical, narrow, reddish purple margins (3). To promote sporulation and to enable identification of the causal agent, leaves of diseased plants were collected and placed in a moist chamber for 24 h with a 12-h light cycle at 25°C. Conidia were plated on potato dextrose agar medium amended with streptomycin and were incubated at 25°C and 12 h of fluorescent light. Isolated cultures sporulated in 10 days and, on the basis of their morphology, were identified as C. sojina. A total of 147 isolates were deposited at the Culture Collection of CEREMIC (Centro de Referencia de Micología). They produced one- to nine-septate hyaline, elongate to fusiform conidia that measured 54.9 ± 16.2 × 5.7 ± 1.0 μm. Six isolates of C. sojina, each representing a province, were inoculated on a set of 12 differential soybean cultivars: Lee, Davis, Hood, Richland, Lincoln, Kent, Tracy, S 100, Palmetto, Peking, CNS, and Blackhawk (2). Fifteen plants of each differential were sprayed at V3 growth stage with a suspension of 6 × 104 conidia/ml. The test was conducted twice in a complete randomized design with three replicates. Control plants were sprayed with sterile distilled water. After inoculation, plants were placed in a greenhouse bench humidity chamber at 26 to 28°C for 72 h. Disease was rated 14 days after inoculation; plants with numerous lesions were considered susceptible and each of the 15 plants was given a score of 1. Plants with small or no lesions were classified as resistant and given a score of 0. Control plants remained healthy. The pathogen was reisolated from symptomatic plants and morphological characteristics were consistent with C. sojina. Based on the response of the differentials to each isolate and on the race designations, the isolates from Buenos Aires, Córdoba, Santa Fe, and Tucumán belong to race 11, while those from Santiago del Estero and Entre Ríos province to race 12. The finding of these two races threatening soybean cultivars in Argentina may be indicative of additional races. Thus, the incorporation of multiple resistance genes may reduce the impact of the disease on soybean. To our knowledge, this is the first report of the identification of races of C. sojina in Argentina.

Acúmulo de nutrientes e matéria seca na parte aérea de dois cultivares de soja RR sob efeito de formulações de glyphosate

O estudo da seletividade e dos efeitos secundários dos herbicidas nas culturas agrícolas é de extrema importância para o sucesso da agricultura. Objetivou-se com este trabalho avaliar o efeito de formulações de glyphosate sobre o acúmulo de nutrientes e produção de matéria seca na parte aérea de dois cultivares de soja resistente ao glyphosate (RR). O experimento foi conduzido em casa de vegetação, em delineamento de blocos ao acaso com seis repetições. Os tratamentos resultaram do arranjo fatorial entre formulações de glyphosate (Roundup Original®, Roundup Ready®, Roundup Transorb®, Roundup WG®, Roundup Ultra® e Zapp Qi®), mais uma testemunha e cultivares de soja RR (CD 225 RR e V Max RR). As aplicações dos herbicidas ocorreram quando as plantas se apresentavam no estádio V3, na dosagem de 960 g e.a. ha-1. O acúmulo de macronutrientes e micronutrientes e a produção de matéria seca na parte aérea das plantas sempre foram maiores no cultivar V Max RR em relação ao CD 225 RR. As formulações Roundup Ready® e Roundup Ultra® não proporcionaram redução no acúmulo de nutrientes e na produção de matéria seca na parte aérea dos cultivares. Por sua vez, Roundup Transorb®, Roundup Original® e Roundup WG® prejudicaram a nutrição dos cultivares e a produção de matéria seca. Conclui-se que o acúmulo de nutrientes e a produção de matéria seca na parte aérea de plantas de soja são alterados em função da aplicação de glyphosate, mesmo para cultivares RR.

EFFECT OF DELAYED NITROGEN FERTILIZATION ON MAIZE (ZEA MAYS L.) GRAIN YIELDS AND NITROGEN USE EFFICIENCY

Maize grain yield potential can be estimated mid-season using NDVI at the V8 growth stage, thus affording delayed sidedress nitrogen (N) application. Several combinations of preplant and sidedress N at various growth stages were evaluated. Maize grain yields were maximized with 90 kg N ha-1 preplant followed by 90 kg N ha-1 sidedress at V6 or V10 (8 of 9 site-years). Delaying N application until V10 growth stage when preplant N was applied did not result in lower yields. Mid-season N supplies fertilizer at the time when crop need and N uptake are at a maximum, and thus facilitates more efficient N use. Lowest nitrogen use efficiencies (NUE) were observed with higher N rates and when all N was applied preplant. Highest NUE's were achieved with 45 kg N ha-1 preplant followed by 45 kg N ha-1 sidedress applied at V6 growth stage (8 of 9 site-years) and at V10 (6 of 9 site-years).

Irrigation and nitrogen effects on the leaf chlorophyll content and grain yield of maize in different crop years

For economic as well as environmental reasons, the determination of optimal nitrogen (N) fertiliser application rates under field conditions is of great importance, especially under irrigated conditions. A two-year field experiment was conducted in Hungary (47°33′N, 21°26′E, 111m) with six N fertiliser rates (0–150kgha−1) under irrigated and non-irrigated conditions with the aim to compare the chlorophyll (Chl) concentration of maize (Zea mays L.) leaves at different growth stages to the soil nitrate-N, the amount of N applied as fertilizer and grain yield. The effect of irrigation and N fertilisation on the soil water and nitrate-N dynamics, grain yield and water use efficiency (WUE) was also examined. In the drought year of 2007, the volumetric soil water content increased from the surface (8.5–9.5, v/v%) to a depth of 1.2m (15–20, v/v%) in both water treatments. In the extremely wet year of 2008, an opposite tendency was observed. In 2007, N applied without irrigation accumulated in the 0–0.2m depth and nitrate-N did not significantly decrease, due to minimal crop N uptake. Under irrigated conditions, nitrate-N was significantly reduced by crop uptake during the growing season of both years. In 2007, chlorophyll meter readings were related to the plant available N at the R1 stage in both water treatments (P<0.001). The CMR value and yield were in close correlation with each other at the R1 growth phase in the drought year in the irrigated treatment (P<0.001; R=0.724), and in the wet year both in the non-irrigated (P<0.001; R=0.735) and the irrigated treatments (P<0.001; R=0.782). The soil nitrate content could be concluded to in the dry year (2007) at the R1 growth stage in both irrigation treatments (R=0.614; R=0.648), and in the wet year (2008) in the non-irrigated treatment at the V12 growth stage (R=0.763).In 2007, the lack of rainfall caused yield stress in the non-irrigated treatment, in contrast to the significantly reduced yield in every N treatment in comparison with the non-irrigated treatment recorded in 2008, due to the extremely high amounts of rainfall. The yield surplus per 1mm irrigation was negative and the level of WUE was also significantly lower.