V3 Growth Stage Research Articles

Foliar and Seed Application of Amino Acids Affects the Antioxidant Metabolism of the Soybean Crop

In recent years, the application of natural substances on crops has been intensified in order to increase the resistance and yield of the soybean crop. Among these products are included plant biostimulants that may contain algae extracts, amino acids, and plant regulators in their composition. However, there is little information on the isolated effect of each of these constituents. The objective of this research was to evaluate the effect of the application of isolated amino acids on the antioxidant metabolism of the soybean crop. Experiments were carried out in a greenhouse and in the field with the application of the amino acids glutamate, phenylalanine, cysteine, glycine in seed treatment, and foliar application at V4 growth stage. Antioxidant metabolism constituents evaluated were superoxide dismutase, catalase, peroxidase, hydrogen peroxide content, proline, and lipid peroxidation. In addition, resistance enzymes as polyphenol oxidase and phenylalanine ammonia-lyase (PAL) were evaluated. In both experiments, the use of cysteine, only in seed treatment and in both seed treatment and foliar application increased the activity of the enzyme PAL and catalase. Also in both experiments, the use of phenylalanine increased the activity of the enzyme PAL when the application was carried out as foliar application or both in seed treatment and foliar application. In the field experiment, the application of glutamate led to an increase in the activity of the catalase and PAL enzymes for seed treatment and foliar application. The use of the set of amino acids was only efficient in foliar application, which led to a greater activity of the enzymes peroxidase, PAL, and polyphenol oxidase. The other enzymes as well as lipid peroxidation and hydrogen peroxide presented different results according to the experiment. Therefore, glutamate, cysteine, phenylalanine, and glycine can act as signaling amino acids in soybean plants, since small doses are enough to increase the activity of the antioxidant enzymes.

Modes of application of cobalt, molybdenum and Azospirillum brasilense on soybean yield and profitability

ABSTRACT The use of cobalt (Co) and molybdenum (Mo) along with the co-inoculation with Azospirillum brasilense on soybean can contribute to biological nitrogen fixation (BNF), allowing higher yields. Thus, this work aimed to study the technical and economic viability of soybean in the Cerrado, according to the mode of application of Co + Mo, and seed or leaf co-inoculation with Azospirillum brasilense. The experiment was conducted in Selvíria-MS, in a no-tillage system in an Oxisol, arranged in a randomized block design with six treatments (seed application of two treatments with Co + Mo, with or without inoculation with A. brasilense, respectively; Foliar application of Co + Mo at soybean V3 stage; Foliar application of Co + Mo together with A. brasilense at V3 growth stage; Foliar application of A. brasilense at V3 growth stage; and the Control, consisting of only inoculation with Rhizobium), and four replicates. Seed application of Co + Mo associated with seed inoculation with A. brasilense promoted the highest leaf N content, hundred-grain weight, yield and profitability with the soybean crop.

English

It is possible to increase nitrogen for wheat productivity by adjusting the single and fractionated dose based on the condition of the agricultural year. The objective of this work is to study the  highest  amount of nitrogen used for the production of wheat using single dose  or fractionation under favorable and unfavorable cultivation years. The study was conducted in  2012, 2013 and 2014 in Augusto Pestana, Rio Grande do Sul, Brazil. The experimental design was a randomized block in a 4 × 3 factorial scheme with four replications. It consists of N-fertilizer rates (0, 30, 60 and 120 kg ha-1), forms of supply [single (100%), growth stage V3 (third expanded sheet); fractionated (70%/30%) growth stage V3/V6 (third and sixth expanded sheet); fractionated (70%/30%) phonological stage V3/E (third expanded leaf and early grain filling)]. In favorable, intermediate and unfavorable years, wheat cultivated with single dose of nitrogen is more effective than the grain fractionated, regardless of the succession system. Nitrogen use efficiency can be substantially reduced or increased in wheat based on  the condition of the year of cultivation and the use of the optimal dose of the nutrient may not necessarily express maximum grain yield with economic efficiency.   Key words: Triticum aestivum, relation C/N, meteorological condition, simulation.

Corn, Soybean, and Wheat Yield Response to Crop Rotation, Nitrogen Rates, and Foliar Fungicide Application

Crop rotations involving corn (Zea mays L.) and soybean [Glycine max (L.) Merr.] are well‐known production systems across the Midwestern United States, but the addition of wheat (Triticum aestivum L.) in the rotation has received less attention. Additionally, the interactive effect of crop rotation with nitrogen (N) fertilizer and foliar fungicide application on yields for these three crops is not yet well understood. Data were collected in Wisconsin from a long‐term crop rotation experiment during 2013 to 2015 to measure corn (grain and silage), soybean, and wheat yield response to crop rotation frequency (seven rotations involving corn, soybean, and wheat), six levels of N, and foliar fungicide use. During the 3 yr of the experiment, minimal interactive effects were detected, which suggested that the examined management decisions can remain separate for growers in Wisconsin. Yearly crop rotation of corn and soybean increased corn grain yields in 2014 by 15 to 18% and soybean yields by 24 to 31% in 2015 compared with continuous cropping. No other crop rotation effect was observed. Fungicide use at the V5 growth stage for corn, at R3 for soybean, and at GS9 for wheat, increased wheat (7.4–16.8%) and soybean yield (3.6–5.4%) but not corn grain or silage yields. Nitrogen application was more beneficial for corn compared with wheat and soybean. The effect of N on soybean was similar across all rotations, and grain yields increased when N rate was higher than 100 kg ha−1. The data suggest that N rate recommendations should be based on crop needs, regardless the rotation system.

The Effect of 2,4-Dichlorophenoxyacetic Acid (2,4-D) on Peanut when Applied During Vegetative Growth Stages

ABSTRACT The development of 2,4-D-resistant cotton and soybean cultivars has created great concern about the potential off-target movement of 2,4-D onto sensitive broadleaf crops. Peanut is often grown in close proximity to cotton and soybean. Therefore, field studies were conducted during 2012 and 2013 at Plains, Ty Ty, and Attapulgus, GA to evaluate peanut response to 2,4-D at 67, 133, 266, 533, and 1066 g ae ha−1 applied at preemergence (PRE), 10, 20, or 30 d after planting (DAP), corresponding to PRE, V2, V3, and V5 peanut growth stages. Nontreated controls (NTC) were included for comparison. Treatment timing by rate interactions were significant (P < 0.0001). As 2,4-D rate increased peanut injury increased. There was variation in yield loss response dependent on peanut growth stage at application timing. Peanut that was treated preemergence and at the V2 growth stage did not have yield loss at any of the 2,4-D evaluated rates (67 to 1066 g ha−1) relative to the NTC. When peanut was treated at V3 and V5 growth stages with 2,4-D, injury estimates were 5 to 32% from the 67 to 1066 g ha−1 rates respectively, and peanut canopy diameter was stunted 5 to 35% at the same rates. The resulting peanut yield loss was 23 and 36% from 533 and 1066 g ha−1 of 2,4-D applied at V3 and V5 growth stages; in part due to reproductive growth being initiated during that time-frame and peanut had less time to recuperate before harvest. Linear regression models were used to evaluate peanut injury and peanut yield results. Significant correlations were established for V3 and V5 treatments between injury and yield, injury and canopy diameter, and canopy diameter and yield (P < 0.0001), with correlation coefficients of − 0.48, − 0.76, and 0.51, respectively. Growers and extension agents will be able to use these peanut injury estimates and canopy diameter data to make improved predictions of potential peanut yield loss where off-target movement of 2,4-D or sprayer contamination has occurred.

Soil Waterlogging and Nitrogen Fertilizer Management Effects on Corn and Soybean Yields

Core Ideas Excessive soil moisture resulting from extreme precipitation events during early spring can often cause decreases in corn grain yields in the midwestern United States. Each day of waterlogging resulted in an average corn grain yield loss of 0.42 Mg ha−1 and 0.72 Mg ha−1 in 2013 and 2014, respectively. Pre‐plant N fertilizer applications of non‐coated urea; polymer coated urea, and non‐coated urea+nitrification inhibitor resulted in 19% higher yields compared to the non‐treated control in 2014. Effects of rescue N fertilizer were seen on soybean yields in the succeeding year after corn, while rescue N affected corn yields only in 2014. Climatic conditions including rainfall and air temperature had a significant role in crop response to waterlogging and N fertilizer treatments. In the midwestern United States, excessive soil moisture resulting from extreme precipitation events during early spring can often cause decreases in corn (Zea mays L.) grain yields and escalate N loss. A field trial was conducted from 2013 to 2015 in Northeast Missouri to determine the effects of soil waterlogging duration, pre‐plant N and rescue N fertilizer applications on corn and succeeding soybean [Glycine max (L.) Merr] production. Plots were either non‐flooded or flooded for durations of 1, 3, or 7 d when corn was at V6 growth stage. Pre‐plant N fertilizer treatments included non‐treated control (CO), urea (NCU), urea plus nitrapyrin (NCU+NI), and polymer coated urea (PCU) applied at 168 kg N ha−1. A rescue N fertilizer application of 0 or 84 kg N ha−1 of urea plus N‐(n‐butyl) thiophosphoric triamide (NBPT) (NCU+UI) was applied at V10 growth stage. Each day of waterlogging resulted in an average corn grain yield loss of 0.42 and 0.72 Mg ha−1 in 2013 and 2014, respectively. Pre‐plant N fertilizer applications of NCU, PCU, and NCU+NI resulted in 19% higher yields compared to CO in 2014. Effects of rescue N fertilizer were seen on soybean yields in the succeeding year after corn, while rescue N positively affected corn yields only in 2014. These results indicated that rescue N fertilizer applications are not effective if drought conditions occur after its application in corn. Climatic conditions including rainfall and air temperature had a significant role in crop response to waterlogging and N fertilizer treatments.

First Report of Soybean Fusarium Wilt Caused by Fusarium oxysporum in Croatia

Soybean (Glycine max [L.] Merr.) is the leading oilseed crop produced and consumed in the world, grown in at least 70 countries in 2013. Wilted soybean plants were observed in May 2014 in commercial fields at Osijek (Slavonia County). Ten symptomatic plants, from each of 14 soybean fields surveyed, were collected at the V3 growth stage (Licht 2014). Plants were wilted with symptoms of external and internal browning at the base of stems, interveinal chlorosis of leaves, and death of shoots. Roots were symptomless. Fourteen soybean fields were observed and Fusarium oxysporum Schlecht. emend. Snyder & Hansen was determined as the causal agent of disease in 11 of them. To isolate the causal agent, the discolored stem tissues selected from symptomatic plants were sterilized with 1% sodium hypochlorite and placed on potato dextrose agar (PDA). Single-spore cultures were used for morphology and molecular analyses. Colony growths were rapid and aerial mycelium was white with hints of purple. The undersurfaces of colonies were cream-colored. Macroconidia were abundant, hyaline, slightly sickle-shaped with a foot-shaped basal cell, and 3- to 5-septations. Microconidia were formed abundantly in false heads. They were generally oval and single-celled. Morphological identification was done according to The Fusarium Laboratory Manual (Leslie and Summerell 2006). Species identity was confirmed on two representative isolates, TFus1 and TF2, by sequencing a portion of the EF1-α gene using the degenerate primers EF1 and EF2 (O’Donnell et al. 1998). The sequence comparison revealed a 100% match with F. oxysporum sequences in GenBank (KP964863) for isolate TFus1 and a 99% homology with GenBank gene sequences (KP710616) for isolate TF2. Greenhouse inoculations were performed to confirm pathogenicity. Two isolates of F. oxysporum (TFus1: KX165288 and FT2: KX165289) were used for preparing inoculum. Sterilized mixtures of wheat and barley seeds (10 g of each) were inoculated with a spore suspension (106 conidia/ml) of selected isolates and incubated for 2 weeks at room temperature. Control inoculum was prepared by applying sterile distilled water only to seed. After 2 weeks, the inoculum (6 g per pot) was placed 3 to 4 cm below the surface of sterile soil in 50 × 20 × 15 cm pots. After 3 days, 30 soybean seeds (cv. Tisa) per treatment (3 replicates) were sown in the pots and maintained at 25/22°C, 14:8 h photoperiod, and 75% relative humidity in a growth chamber. Seven weeks after sowing, stem discoloration was observed on 82.8% (TFus1) and 100.0% (FT2) of soybean plants. Symptoms on infected plants were similar to those observed in the field and the fungus was successfully reisolated. No symptoms were observed on control plants. To our knowledge, this is the first report of F. oxysporum causing soybean wilting in Croatia. In humid and cold springs, the presence of this pathogen could cause economically significant reduction in soybean yield.

The Effects of Stabilized Urea and Split-Applied Nitrogen on Sunflower Yield and Oil Content

Sunflower is an efficient nitrogen (N) accumulator due to its aggressive taproot and extensive root system. While N rate studies in sunflower have shown a yield response, the response is often highly variable and difficult to predict in many instances. Additionally, since most sunflower production is intended for the oil market, surplus nitrogen tends to decrease oil content. Therefore, it is critical to hone nitrogen rates to maximize both yield and oil production and to incorporate alternative approaches to fertilizer application, which includes timing and method of application. The objective of the present study was to assess the efficacy of a split-application of N at either the V4 or R1 growth stage to increase yield and/or oil content in sunflower. A second objective was to examine whether a urease inhibitor could be used to retain soil N longer and achieve a similar effect as a split-application. Studies were conducted at two locations over two growing seasons in South Dakota, USA. A target rate of 90 kg·ha-1 was applied as urea-ammonium nitrate (UAN) either as an at-planting application or split-applied. Overall, N additions did significantly increase yield over a control. On average, the urease inhibitor tended to increase grain yields over split-applying N at either growth stage, however, there was no statistical effect on either grain yield or oil content. Based on 15N analysis, approximately 27% of the N in the grain was derived from the UAN fertilizer, which indicates a relatively large reliance upon soil N for grain N content. The addition of a urease inhibitor significantly increased average fertilizer uptake by nearly 6% to 32.7%.

Variable rate nitrogen management in corn: Response in two crop rotations

Decision-making criteria to accurately predict nitrogen (N) rates in corn (<i>Zea mays</i> L.) would greatly benefit canopy sensor-guided variable rate N (VRN) management with positive implications for water quality. The objectives of this study were to measure corn yield response to VRN applied at the midvegetative corn growth stage and compare yield and agronomic efficiency (AE) between a one-time spring-N application (preplant or early sidedress) and two VRN management strategies, split-N (VRN^S) and rescue-N (VRN^R). Field sites located across Iowa received spring-N fertilizer at six application rates, with additional N potentially applied with each VRN spring-N rate and for the VRN^S and VRN^R strategies at the V10 growth stage based on canopy sensing. Drought conditions were evident during 2012 and 2013 in Iowa, which resulted in reduced corn yield and requirement for N fertilizer at many site-years. The VRN with 0 and 56 kg N ha⁻¹ (50 lb N ac⁻¹) applied in the spring was most closely aligned with calculated economic optimum N rate and AE. The VRN^S and VRN^R strategies applied more N than was needed, compared to spring-N only. Canopy sensors did not detect adequate to excess N, and therefore N applied prior to VRN application should be part of sensing-based algorithm criteria. Mean corn yield with the soybean (<i>Glycine max</i> [L.] Merr.)–corn rotation was not maintained with VRN when no spring-N was applied. Yield comparison showed no differences between spring-N, VRN^S, and VRN^R for both rotations. However, the greatest AE was achieved with spring-N and the VRN^S strategy in the soybean–corn rotation. Weather events that occur during and after canopy sensing and VRN application remain an important factor for successful corn yield response to N rate and timing, and should be considered with canopy sensor VRN. Results from this study provide feedback on how to translate remote sensing data into VRN management.

Sensor-Based Algorithm for Mid-Season Nitrogen Application in Corn

Applying insufficient nitrogen (N) in a highly responsive crop, such as corn, results in lower grain yield, quality, and profits. On the other hand, when nitrogen is applied in excess of crop needs, profit is reduced and negative environmental consequences are likely. The objective of this study was to develop and employ a sensor-based algorithm to determine the mid-season N requirements for deficit-irrigated corn in Coastal Plain soils. The algorithm was developed using varied prescription rate N plot on two soil types. The test plots received nine different rates of N fertilizer, replicated 5 times in plots of each soil type using a Randomized Complete Block design. A 6-row GreenSeeker optical sensor was used to measure plant NDVI, between the V6 to V8 growth stages. The sensor readings were used to develop an algorithm to be used in the estimation of side-dress N application in corn. The NDVI sensor readings were collected at the V6 to V8 growth stage during the 2015 and 2016 growing seasons correlated with actual corn yields (R2 > 0.68, p < 0.001). In-Season Estimated yield (INSEY) was used along with the actual yield to produce a yield potential for each growing season for deficit-irrigated corn crop. In summary, the algorithm developed from the NDVI readings reduced N application rates by 21% and 34% in soil types 1 and 2, respectively, compared to the normal grower practice (226 kg N/ha) with no reduction in corn yields.

Application of foliar fertilizer and fungicides on white spot disease control and development of maize

This study aimed to evaluate the effect of forms of application of foliar fertilizers and fungicides to control fungus causing white maize spot, Phaeosphaeria maydis , and the growth and development of hybrids maize. The design had randomized blocks, with the use two sources hybrids maize with different reaction to white maize spot: resistant and susceptive and application with moisture of foliar chemical fungicide + cobalt foliar + molybdenum foliar + manganese and control treatment, without application consisting of four treatments and five replications. In the treatments with application of moisture were done on vegetative maize growth stage V8 (stage that determine that the number of kernel rows), VT (stage that arrives when the last branch of the tassel is completely visible) and reproductive maize growth stage R2 (kernels are white on the outside and resemble a blister). The evaluation of variables of growth of maize plants: grain dry mass, cob dry mass, leaf dry mass, culm dry mass and modificated leaf ear and total plant dry mass. Harvest was carried out when the grains were 20% humidity. The application of fungicides and foliar fertilizers increased the leaves, culm, ear modificated, cobs and shoot dry mass plants maize. The application of fungicides and foliar fertilizers providing returning of 11.409,5 kg ha -1 of shoot dry mass plants with increased of 1.296 kg ha -1 on soil(12,81%). In the susceptive hybrid maize the application of fungicides and foliar fertilizers provide higher dry mass grains and shoot of plants.

Macro-Nutrient Concentration and Content of Irrigated Soybean Grown in the Early Production System of the Midsouth

ABSTRACTMacro-nutrients in soybean (Glycine max L. Merr.) have not been extensively researched recently. Concentrations and contents of nitrogen, phosphorus, potassium, calcium, magnesium, and sulfur (N, P, K, Ca, Mg, and S) were determined for three irrigated cultivars grown using the early soybean production system (ESPS) on two soils (a sandy loam and a clay) in the Mississippi Delta during 2011 and 2012. Data were collected at growth stages V3, R2, R4, R6, and R8. No change in macro-nutrients due to soil type or years occurred and modern cultivars were similar to data collected >50 years ago. Mean seed yield of 3328 kg ha−1 removed 194.7 kg N ha−1, 16.5 kg P ha−1, 86.0 kg K ha−1, 17.5 kg Ca ha−1, 9.0 kg Mg ha−1, and 10.4 kg S ha−1. Increased yields over the decades are likely due to changed plant architecture and/or pests resistance, improved cultural practices, chemical weed control, and increased levels of atmospheric carbon dioxide (CO2). Yield improvements by genetically manipulating nutrient uptake appear to be unlikely.

Management of Large, Glyphosate-Resistant Palmer Amaranth (Amaranthus palmeri) in Corn

Palmer amaranth is a very problematic weed that has evolved resistance to several classes of herbicides, including 5-enolypyruvylshikimate-3-phosate synthase–inhibiting herbicides and photosystem II–inhibiting herbicides. In recent years, corn producers have had difficulty controlling large Palmer amaranth (&gt; 20 cm) in corn &gt; 30 cm whether it be due to environmental conditions or management failures. Palmer amaranth management in corn this tall is made even more challenging because atrazine is not labeled POST in corn &gt; 30 cm tall. Therefore, a study was conducted in 2013 and 2014 in Jackson, TN, to evaluate herbicide programs in corn &gt; 30 cm tall for the control of glyphosate-resistant Palmer amaranth &gt; 20 cm tall. Treatments consisted of herbicides applied alone and in mixtures with dicamba plus diflufenzopyr. Herbicides were applied POST to corn between the V5 and V6 growth stages. Dicamba plus diflufenzopyr 28 d after application controlled Palmer amaranth &gt; 87%. The herbicides alone or in combinations applied as tank mixtures did not improve control (&lt; 76%) over dicamba plus diflufenzopyr alone. There were no grain-yield differences among treatments because of Palmer amaranth control. This was likely due to the Palmer amaranth competition having already affected corn yield by the V5 to V6 corn growth stages.

Maize intercropped with Urochloa ruziziensis under no-tillage system

ABSTRACT The no-tillage system is a conservation practice that seeks greater sustainability of the production system and can be replicated in large land areas. Maize intercropped with forages of the Urochloa genus has proven to be profitable and suitable for targeting both the straw and grain production. This study aimed at evaluating maize yield and cover plants, using different maize row spacings and forage seeding methods, under a no-tillage system. A randomized blocks design, in a 2 x 3 + 2 factorial scheme, with four replications, was used. The treatments consisted of two maize row spacings (0.45 m and 0.90 m) intercropped with Urochloa ruziziensis, using three different methods (Urochloa sown in the row, Urochloa sown by hauling soon after maize was sown and Urochloa sown during the maize V4 growth stage) + controls (only maize at two spacings). The intercropping between maize spaced 0.90 m with Urochloa ruziziensis in the sowing row provided better grain yield results without interfering with the Urochloa dry matter production.

Corn Yield Loss Due to Volunteer Soybean

The widespread adoption of glyphosate-resistant corn and soybean in cropping rotations often results in volunteer plants from the previous season becoming problem weeds that require alternative herbicides for control. Corn yield losses due to season-long volunteer soybean competition at several densities in two growing seasons were used to define a hyperbolic yield loss function. The maximum corn yield loss observed at high volunteer soybean densities was about 56%, whereas, the incremental yield loss (I) at low densities was 3.2%. Corn yield loss at low volunteer soybean densities was similar to losses reported for low densities of velvetleaf and redroot pigweed, with 10% yield loss estimated to occur at 3 to 4 volunteer soybean plants m−2. Several herbicides, including dicamba with or without diflufenzopyr applied at the V2 growth stage of volunteer soybean, provided &gt; 90% control, demonstrating several economical options to control volunteer glyphosate-resistant soybean in glyphosate-resistant corn. Reevaluation of control recommendations may be needed with commercialization of other genetically modified herbicide-resistant soybean varieties.

The critical period for weed control in three corn (Zea mays L.) types

Knowledge of the crop-weed competition period is vital for designing effective weed management strategies in crop production systems. Field studies were conducted at the Agricultural Research Institute, Kahramanmaras, Turkey in 2013 and 2014 to determine the critical period for weed control (CPWC) in three corn (Zea mays L.) types (field corn, popcorn, and sweet corn). A four parameter log-logistic model described the relationship between relative crop yield to both increasing duration of weed interference and length of weed-free periods. The relative yield of corn was influenced by duration of weed-infested or weed-free period, regardless of corn types. Increasing periods of weed interference significantly reduced corn yields in both years. In field corn, the CPWC ranged from 175 to 788 growing degree days (GDD) in 2013 which corresponded to V2–V12 growth stages, and 165–655 GDD (V1–V10 growth stages) in 2014 based on the 5% acceptable yield loss (AYL) level. In popcorn, the CPWC ranged from 92 to 615 GDD (VE–V10 growth stages) in 2013 and 110–678 GDD (V1–V10 growth stages) in 2014. In sweet corn, the CPWC ranged from 203 to 611 GDD in 2013 (V2–V10 growth stages) and 182–632 GDD (V2–V10 growth stages) in 2014. The practical implication of this study is that weed management should be initiated around V1 stage and maintained weed-free up to V12 stage in all corn types to prevent yield losses greater than 5%. These findings could help corn producers improve the cost effectiveness and efficacy of their weed management programs.

Biological aspects of Bemisia tabaci biotype B and the chemical causes of resistance in soybean genotypes

In Brazil, the silverleaf whitefly (SLW), Bemisia tabaci biotype B, is a serious soybean pest. SLW management is difficult and new control strategies, such as host–plant resistance, are required. Herein, we aimed to evaluate the biology of SLW, from eggs to adults, on seven soybean cultivars. The emergence of adult insects was monitored daily. Defense-related compounds were identified and quantified from the V3 to the V8 stages in SLW-infested and non-infested plants. The rates of emergence of SLW adults were lower in cultivars ‘IAC 17,’ ‘IAC 19’, and ‘IAC 24’ compared with the susceptible cultivar ‘IAC Holambra Stwart’. Rutin, genistin, genistein, and salicylic acid were identified and quantified in plant extracts. The rutin, genistin, and genistein levels decreased after SLW infestation. Rutin concentrations increased in infested plants of ‘IAC 17’ (V6) and ‘IAC 19’ (from V5 to V8). ‘Barreiras’ showed the highest genistein content in non-infested plants; from V5 growth stage, it was not detected in cultivars Doko (infested), Vencedora, ‘IAC 17’, and ‘IAC 24’ (non-infested). High levels of salicylic acid were observed in ‘IAC ‘19’-infested plants (at V3 and V5). The results suggest that rutin can be related to SLW adults’ emergence only when the feeding source was ‘IAC 19’. Consequently, further studies are needed to access the associated gene expressions and the effect of other secondary metabolites, mainly volatile compounds from SA pathway, including its consequences on feeding preference and mostly in relation to IAC cultivars.

Active Optical Sensing of Spring Maize for In-Season Diagnosis of Nitrogen Status Based on Nitrogen Nutrition Index

The nitrogen (N) nutrition index (NNI) is a reliable indicator of crop N status and there is an urgent need to develop efficient technologies for non-destructive estimation of NNI to support the practical applications of precision N management strategies. The objectives of this study were to: (i) validate a newly established critical N dilution curve for spring maize in Northeast China; (ii) determine the potential of using the GreenSeeker active optical sensor to non-destructively estimate NNI; and (iii) evaluate the performance of different N status diagnostic approaches based on estimated NNI via the GreenSeeker sensor measurements. Four field experiments involving six N rates (0, 60, 120,180, 240, and 300 kg·ha−1) were conducted in 2014 and 2015 in Lishu County, Jilin Province in Northeast China. The results indicated that the newly established critical N dilution curve was suitable for spring maize N status diagnosis in the study region. Across site-years and growth stages (V5–V10), GreenSeeker sensor-based vegetation indices (VIs) explained 87%–90%, 87%–89% and 83%–84% variability of leaf area index (LAI), aboveground biomass (AGB) and plant N uptake (PNU), respectively. However, normalized difference vegetation index (NDVI) became saturated when LAI &gt; 2 m2·m−2, AGB &gt; 3 t·ha−1 or PNU &gt; 80 kg·ha−1. The GreenSeeker-based VIs performed better for estimating LAI, AGB and PNU at V5–V6 and V7–V8 than the V9–V10 growth stages, but were very weakly related to plant N concentration. The response index calculated with GreenSeeker NDVI (RI–NDVI) and ratio vegetation index (R2 = 0.56–0.68) performed consistently better than the original VIs (R2 = 0.33–0.55) for estimating NNI. The N status diagnosis accuracy rate using RI–NDVI was 81% and 71% at V7–V8 and V9–V10 growth stages, respectively. We conclude that the response indices calculated with the GreenSeeker-based vegetation indices can be used to estimate spring maize NNI non-destructively and for in-season N status diagnosis between V7 and V10 growth stages under experimental conditions with variable N supplies. More studies are needed to further evaluate different approaches under diverse on-farm conditions and develop side-dressing N recommendation algorithms.

Early‐Season Lactofen Application Fails to Increase Soybean Yield under Weed‐Free Conditions

In an effort to increase soybean [Glycine max (L.) Merr.] yield, growers may consider non‐traditional use of crop inputs. One non‐traditional input use is the application of lactofen {2‐ethoxy‐1‐methyl‐2‐oxoethyl 5‐[2‐chloro‐4‐(trifluoromethyl)phenoxy]‐2‐nitrobenzoate} herbicide to early‐vegetative soybean to promote increased branch development and ultimately increase seed yield. The purpose of this study was to evaluate the effect of early‐season lactofen application and simulated herbicide injury on stands, plant height, light interception, and seed yield. The experiments were conducted at two locations in Kentucky during the 2013 and 2014 growing seasons. Treatments included lactofen herbicide applied at 240 g a.i. ha−1 and fomesafen {5‐[2‐chloro‐4‐(trifluoromethyl)phenoxy]‐N‐methylsulfonyl‐2‐nitrobenzamide} herbicide applied at 600 g a.i. ha−1. A meristem removal treatment was included, where the apical meristem of each soybean was physically removed, and a leaf removal treatment was also performed. All treatments were applied to soybean at V1, V2, V3, and V4 growth stages. The herbicide application timing had no effect on any of the above mentioned agronomic measurements. The apical meristem removal reduced plant stands and plant height in 2 site‐years while lactofen and leaf removal decreased early‐light interception in all site‐years. Meristem removal and leaf removal reduced seed yield in 1 site‐year, while lactofen, leaf removal, and meristem removal reduced seed yield in another site‐year. None of the treatments increased seed yield compared with the untreated control. Despite a limited number of trials, this study suggests that application of lactofen to soybean for non‐weed control purposes is not a viable strategy to increase soybean yield.Core Ideas Leaf removal and lactofen application decrease early‐season light interception in soybean. Destroying the soybean apical meristem either decreases or does not affect soybean yield. Lactofen application to early vegetative soybean does not increase yield under weed free conditions.

Use of corn height measured with an acoustic sensor improves yield estimation with ground based active optical sensors

Corn height measured manually has shown promising results in improving the relationship between active-optical (AO) sensor readings and crop yield. Manual measurement of corn height is not practical in US commercial corn production, so an alternative automatic method must be found in order to capture the benefit of including canopy height into in-season yield estimates and from there into in-season nitrogen (N) fertilizer applications. One existing alternative to measure canopy height is an acoustic height sensor. A commercial acoustic height sensor was utilized in these experiments at two corn growth stages (V6 and V12) along with AO sensors. Eight corn N rate sites in North Dakota, USA, were used to compare the acoustic height sensor as a practical alternative to manual height measurements as an additional parameter to increase the relationship between AO sensor readings and corn yield. Six N treatments, 0, 45, 90, 134, 179, and 224kgha−1, were applied before planting in a randomized complete block experimental design with four replications. Height measurement using the acoustic sensor provided an improved yield relationship compared to manual height at all locations. The level of improvement of the relationship between AO readings multiplied by acoustic sensor readings and yield was greater at V6 growth stage compared to the V12 growth stage. At V12, corn height measured manually and with the acoustic sensor multiplied by AO readings provided similar improvement to the relationship with yield compared to relating AO readings alone with yield at most locations. The acoustic height sensor may be useful in increasing the usefulness of AO sensor corn yield prediction algorithms for use in on-the-go in-season N application to corn particularly if the sensor height is normalized within site before combining multiple locations.