V3 Growth Stage Research Articles

Utility of Interseeded Winter Cereal Rye in Organic Soybean Production Systems

Soybean [Glycine max (L.) Merr.] growers using organic production systems have predominately been limited to mechanical cultivation for weed control. Interseeded cover crops such as winter cereal rye (Secale cereale L.) have been used in conventional soybean production systems in conjunction with herbicides to reduce tillage and cultivation operations. The objective of this study was to determine if high soybean planting populations in drill‐planted (19‐cm row) systems or a single mechanical cultivation in row‐planted (76‐cm row) systems could facilitate the use of interseeded rye in organic soybean production systems. Interseeded winter cereal rye decreased soybean grain yield in 2 of 3 yr in the drill‐planted system by 22 and 17%, respectively, and in all 3 yr of the row‐planted system by 23, 27, and 23%, respectively. Moisture stress from the interseeded rye was a predominate factor in soybean grain yield reduction. In 2000, the soybean planting population was inversely correlated with late‐season biomass of interseeded rye. However, during the drier years of 2001 and 2002, increasing soybean planting density did not significantly reduce late‐season biomass of interseeded rye. The interseeded rye reduced late‐season weed biomass in both the drill‐planted and row systems in 2001. Removal of the interseeded rye with mechanical cultivation in the row system when the soybean was at the V4 growth stage was ineffective in 2000 but increased soybean grain yield by 1142 and 746 kg ha−1, respectively, in 2001 and 2002. These results suggest that some means of controlling winter cereal rye growth is necessary for effective management across a range of precipitation levels.

Utility of Interseeded Winter Cereal Rye in Organic Soybean Production Systems

Soybean [Glycine max (L.) Merr.] growers using organic production systems have predominately been limited to mechanical cultivation for weed control. Interseeded cover crops such as winter cereal rye (Secale cereale L.) have been used in conventional soybean production systems in conjunction with herbicides to reduce tillage and cultivation operations. The objective of this study was to determine if high soybean planting populations in drill-planted (19-cm row) systems or a single mechanical cultivation in row-planted (76-cm row) systems could facilitate the use of interseeded rye in organic soybean production systems. Interseeded winter cereal rye decreased soybean grain yield in 2 of 3 yr in the drill-planted system by 22 and 17%, respectively, and in all 3 yr of the row-planted system by 23, 27, and 23%, respectively. Moisture stress from the interseeded rye was a predominate factor in soybean grain yield reduction. In 2000, the soybean planting population was inversely correlated with late-season biomass of interseeded rye. However, during the drier years of 2001 and 2002, increasing soybean planting density did not significantly reduce late-season biomass of interseeded rye. The interseeded rye reduced late-season weed biomass in both the drill-planted and row systems in 2001. Removal of the interseeded rye with mechanical cultivation in the row system when the soybean was at the V4 growth stage was ineffective in 2000 but increased soybean grain yield by 1142 and 746 kg ha−1, respectively, in 2001 and 2002. These results suggest that some means of controlling winter cereal rye growth is necessary for effective management across a range of precipitation levels.

Dosimetric measurement of the visible and UV exposures on field grown soybean plants

This paper describes a dosimeter system for measuring both the PAP (photosynthetically active photons) (400–700 nm) and ultraviolet-B (UVB) (280–320 nm) exposures in the supplemental UVB irradiation of field grown soybean ( Glycine max [L.] Merr.) plants. At the V2 growth stage, the dosimeters positioned at the same position and orientation as the trifoliate leaves of the plants that were measured received 12–38% more PAP and 5–82% more UVB than the unifoliate leaves. For the crop maturity stage, the plants exposed to high levels of UV irradiance (high UV treatment) received approximately 40% more UVB on a horizontal plane at the top of the plant canopy compared to the control group of plants (control treatments). For the other measurement sites over the plants that were orientated at 45° to the vertical in the north, south, east and west directions, the additional amount of UVB for the supplemental treatment compared to the corresponding sites for the plants in the control treatments varied between −39 and 37%, due predominantly to the shading provided by the other plants. Furthermore, the supplemental UVB changed the natural partitioning of UVB and PAP and the ratio of PAP to UVB over the plants. All these variations to the UVB and PAP over the plant canopy cannot be predicted by exposure measurement in the wavebands on a horizontal plane. Consequently, for the case of the complex topography of plants, the dosimeters described in this paper have the advantage of allowing the exposures to be measured simultaneously at multiple sites that are at any orientation.

Influence of nitrogen and duration of weed interference on corn growth and development

Abstract An improved understanding of the effects of nitrogen (N) on crop–weed interactions is needed for the development of integrated weed management systems where responsible use of N fertilizers is considered. Field experiments conducted in 1999 and 2000 at two locations in eastern Nebraska quantify the effects of N and increasing duration of weed interference on corn growth and development. A naturally occurring population of weeds was allowed to compete with the corn crop for increasing lengths of time and at three rates of N application (0, 60, and 120 kg N ha−1). Weed interference and withholding applied N increased the time to 50% silking by an average of 3.9 and 2.9 d, respectively. Regardless of treatments, relative growth rates of corn leaf area and biomass were maximized between the V1 and V2 growth stages of corn and increased linearly with N rate but were affected to a lesser extent by weed presence. The improvement in early season corn growth with addition of N resulted in greater leaf are...

Changes in Soybean Gas-Exchange After Moisture Stress and Spider Mite Injury

Field experiments were conducted in 1997 and 1998 to understand the physiological responses of soybean, Glycine max (L.) Merrill, to injury from two-spotted spider mite, Tetranychus urticae Koch, and to examine the contribution of soil moisture toward soybean tolerance to spider mite injury. A split-plot treatment design was used consisting of moisture stress as the main plot and spider mite injury as the sub-plot treatments in a randomized complete block design with eight replications. Soybeans were moisture-stressed beginning approximately at V10 growth stage, and spider mites were maintained on soybeans for 10 d, and then physiological responses of soybean were determined. Moisture-stressed soybeans had lower leaf water potentials, photosynthetic rates, stomatal conductances, and transpiration rates. Spider mite injury also caused a significant reduction in photosynthesis, stomatal conductance, transpiration, and chlorophyll content. The lack of a significant impact of spider mite injury on chlorophyll fluorescence and similar light curves, at low light intensities, of soybean leaves with and without spider mite injury, suggest that spider mite injury does not interfere with the light reaction center at the initial stage of photosynthesis. Despite measurable reductions in total chlorophyll content from mite injury, fluorescence data and light curves strongly indicate photosynthetic rate reductions from mite injury were not immediately associated with chlorophyll loss or effects on photosynthetic electron transport. There were significant interactions between moisture stress and spider mite injury for some gas-exchange parameters. Photosynthetic rate reductions by spider mites were greater in moisture-unstressed than stressed soybeans. Superimposing spider mite injury did not reduce photosynthetic rates greatly in moisture-stressed soybeans because of an initially low photosynthetic rate from moisture stress. However, comparison of absolute photosynthetic rates of spider mite-injured soybean leaves with and without moisture stress suggested that soil moisture improved soybean tolerance to spider mite injury.

First Report of Sudden Death Syndrome (Fusarium solani f. sp. glycines) of Soybean in Minnesota.

In August 2002, soybean (Glycine max (L.) Merr.) plants exhibiting foliar and root symptoms typical of sudden death syndrome were observed in Blue Earth and Steele counties in south-central Minnesota. Leaf symptoms ranging from small chlorotic spots to prominent interveinal necrosis were present on soybean plants at the R6 to R7 growth stage. As plants matured, complete defoliation took place with only petioles remaining. Symptomatic plants had necrotic secondary roots, truncated taproots, and discolored cortical tissue at the soil line. Blue sporodochia containing macroconidia were observed on the taproot of affected plants at both locations (3,4). Multiple cultures from both locations were obtained by transferring macroconidia from the sporodochia to potato dextrose agar (PDA) and modified Nash-Snyder Medium (NSM) (3). After 14 days, isolations were made from fungal colonies exhibiting bluish pigmentation and masses of bluish macroconidia (4). The isolates grew slowly, developed a bluish color, and formed sporodochia containing abundant macroconidia on NSM. These isolates were identified as Fusarium solani (Mart.) Sacc. f. sp. glycines based on colony characteristics and morphology of macroconidia (2). Pathogenicity tests were conducted with a single isolate from each location. The isolate from Blue Earth County was inoculated as mycelia in a plug of media onto taproots of plants of susceptible cvs. Williams 82 and Spencer at the V2 growth stage. Chlorotic spots appeared on leaves after 12 days of growth at 22 to 25°C in the greenhouse. Interveinal necrosis appeared after 15 days (4). The isolate from Steele County was used to inoculate the susceptible cv. Great Lakes 3202. Sorghum seed (3 cm3) infested with mycelia of the isolate were placed 2 to 3 cm below soybean seed planted in Cone-Tainers. Noninfested sorghum seed was used as a control. Plants were maintained for 21 days at 22 to 28°C in the greenhouse. Chlorotic spots appeared on leaves of inoculated plants within 21 days after planting followed by the development of interveinal chlorosis and necrosis (1). Molecular analysis further supported the identification of the Steele County isolate as F. solani f. sp. glycines. Polymerase chain reaction with specific primers Fsg1 and Fsg2 of total genomic DNA extracted from the Steele County isolate amplified a 438-bp DNA fragment identical with that extracted from previously identified isolates of F. solani f. sp. glycines (1). In 2002, symptoms of sudden death syndrome were also reported in Olmsted, Freeborn, and Mower counties. Although studies are needed to determine the distribution of sudden death syndrome in the state, the occurrence of the symptoms at multiple locations suggests that F. solani f. sp. glycines is widely distributed in southeast and south-central Minnesota. The counties where sudden death syndrome symptoms were reported are located in the most productive soybean-growing region of Minnesota. Sudden death syndrome could be a serious threat to soybean production in this area since poorly drained, heavy, clay soils are common, and soil temperatures 18°C or less are normal before the end of May.

Field Verification of the Barber–Cushman Mechanistic Phosphorus Uptake Model for Maize

A two‐year field study in southeastern South Dakota examined how phosphorus (P) fertilizer applied to a silt loam soil affected the predictability of P uptake in maize (Zea mays L.) using the Barber–Cushman mechanistic P uptake model. Liquid ammonium polyphosphate was applied to provide 0, 10, 20, and 40 kg P ha−1 comparing a concentrated single or double band application, or comparing a concentrated single band to a fertilizer band diluted with water. Soil, plant tissue, and roots were sampled intensely. The model simulation used observed measurements as well as reasonable estimates and assumptions derived from the literature. Predicted P uptake was affected more by soil solution P (C li ) than applied fertilizer P rate. The agreement of observed with predicted P uptake was improved when their regressions were grouped according to C li ranges rather than applied P rates. In 1991, the model predicted 86–90% of observed P uptake at the high C li range (21–77 µmol L−1) but only predicted 23–44% of observed P uptake at the low C li range (1–16 µmol L−1) at the V6 (6th leaf) and V12 (12th leaf) growth stages. Predicted P uptake was much lower than observed at all C li ranges for the simulation period at the R2 (silking) growth stage. Parameters used in simulating maize P uptake were suitable at the high C li values up to the V12 growth stage. At low C li values at the V12 and R2 growth stages, additional soil factors that may affect maize P uptake (i.e., root hair proliferation, mycorrhizal infection, rhizosphere acidification, root architecture) should be included in a simulation model to improve P uptake predictability.

Relationships Between Reactions of Sweet Corn Hybrids to Stewart's Wilt and Incidence of Systemic Infection by Erwinia stewartii.

Relationships between the reactions of sweet corn hybrids to Stewart's wilt and the incidence of natural, systemic infection by Erwinia stewartii differed among trials in which the prevalence of Stewart's wilt differed. Systemic Stewart's wilt infection was assessed for 262, 296, and 245 hybrids planted in seven trials in central Illinois in June and July 1998, 1999, and 2000, respectively. Incidence of systemic infection was calculated in each trial for all hybrids in each of nine categories of Stewart's wilt reactions (i.e., 1 = resistant and 9 = susceptible). When mean incidence was about 5%, incidence ranged from about 1 to 8% on resistant to moderately susceptible hybrids, but incidence was nearly 30% on susceptible hybrids. When mean incidence ranged from 10 to 16%, the relationships between hybrid reactions and incidence were explained by exponential or polynomial regressions. Incidence was less than 10% for hybrids with resistant and moderately resistant reactions, and incidence was greater than 15% for moderately susceptible to susceptible hybrids. When mean incidence was near 50%, the relationship was linear. Incidence was about 18% for resistant hybrids and about 80% for susceptible hybrids. Incidence increased about 8% for each class of hybrid reaction from 1 to 9. The influence of resistance on the development of systemic infection at very early seedling growth stages also was evaluated in six greenhouse trials. A highly resistant hybrid, Bonus, was systemically infected in two of six greenhouse trials when seedlings were inoculated prior to the V3 growth stage; however, systemic infection was not as severe as on a susceptible hybrid, Jubilee. Systemic infection was more severe on Bonus when plants were inoculated at earlier growth stages between VE and V3. The resistant hybrid Bonus was not systemically infected when inoculated after the V4 growth stage except for one greenhouse trial when all Stewart's wilt ratings were higher than usual. Hybrid reactions to Stewart's wilt affected the incidence of systemic infection in field situations and they affected the growth stage at which resistance effectively prevented systemic movement of E. stewartii within plants in greenhouse trials. This information can be used to determine more effectively when to apply other control measures, such as insecticidal seed treatments.

LOW GROUND-COVER FILTERING TO IMPROVE RELIABILITY OF THE NITROGEN REFLECTANCE INDEX (NRI) FOR CORN N STATUS CLASSIFICATION

Recent advancements in low-cost remote sensing equipment and techniques have proven that crop parameterclassification can be practical in agricultural situations. One problem still remaining is how to account for in-field variabilityof mixed ground-cover areas. This study focused on finding a non-invasive method of screening low ground-cover areasbefore assessing crop nitrogen (N) status. Four years of plot data were used where intense ground sampling was coupled withnadir-viewing remotely sensed data from a ground-based remote sensing system. Data were collected over irrigated corn(Zea mays L.) with both light and dark soil backgrounds to develop a relationship between leaf area index (LAI) and remotelysensed data. An index based on subtracting the red from the green reflectance (green - red) was shown to be strongly relatedto LAI. A concurrent assessment of the N reflectance index (NRI) over the four-year study indicated that the corn N statusclassification improved with increasing LAI. Using the (green - red) index and a screening value corresponding to an LAIof 2.5, the data from the four-year study were screened and the NRI was reassessed. The initial screening removed all bare-soiland many of the measurements collected before the V12 growth stage. In this example, 94.0% of the data associated with LAIbelow 2.5 was correctly filtered out, and 95.4% of the data collected over areas with LAI at or above 2.5 correctly passedthe filter. This method of filtering was shown to be highly effective in screening low ground-cover and bare-soil areas beforeclassification. Future incorporation of this technique into on-the-go filtering algorithms could improve crop parameterclassification from remotely sensed measurements in early-season and mixed vegetative cover situations.

Critical periods of weed control in soybean for full field and in-furrow interference

Abstract Soybean and annual weed competition studies were conducted over 2 yr in Balcarce, Argentina, to define the critical period of weed control and to compare yield losses in soybean, when weeds competed in the total cropping area (row plus furrow) or only in the furrow. In the first year, broad-leaf weeds were more abundant than annual grasses, but in the second year, grasses were more abundant. Critical weed-free periods required to prevent yield losses of 2.5 and 10% were long and consistent for both years and for both types of competition, lasting between 50 and 61 d after crop emergence (DAE) or the V8 to V9 and R2 to R3 soybean growth stages, respectively. No differences in predicted yield for both places of competition was found when weeds grew after the V4 or later crop growth stages (35 DAE). The critical periods of weed removal to prevent equivalent yield losses were different in both years. Varying between 1 DAE in 1986–1987 and 30 DAE in 1988–1989, for 2.5% yield losses, corresponding to g...

HYPERSPECTRAL CHARACTERISTICS OF CORN PLANTS UNDER DIFFERENT CHLOROPHYLL LEVELS

Remote sensing of chlorophyll level in corn at V6 growth stage based on spectral measurements has been limitedby soil background, changes in cloud cover, and solar angles. Chlorophyll levels at V6 growth stage are a strong indicatorof nitrogen status. This article suggests a solution based on an understanding of the hyperspectral characteristics of cornplants at different chlorophyll levels. Hyperspectral characteristics of corn plants with variable chlorophyll levels, undervariable cloud cover, and with variable solar angles are presented. The chlorophyll levels were measured using the Minolta502 chlorophyll meter. Investigation has found that spectral reflectance response patterns (SRRPs) of corn plants at the samechlorophyll level, acquired during cloud cover changes, still show consistent spectral pattern characteristics. The samecharacteristics were observed for SRRPs acquired as solar angles changed between 0950 and 1450 h. The results suggest thatthe SRRPs can be used to develop a robust model for predicting chlorophyll in corn at V6 growth stage. Furthermore, a strongcorrelation was obtained between chlorophyll readings (in SPAD units) and the near infrared/green (NIR/G) ratio (r 2 = 0.94,root mean square error = 1.44 SPAD units) at constant solar irradiance.

HYPERSPECTRAL–BASED NEURAL NETWORK FOR PREDICTING CHLOROPHYLL STATUS IN CORN

The use of spectral reflectance techniques for predicting nitrogen in corn at V6 growth stage has been limited bythe soil background and changes in cloud cover and solar angles. Measurement and prediction techniques, which areindependent of these factors, are needed for fast and accurate prediction of nitrogen deficiency at V6 growth stage forsitespecific sidedressing of nitrogen. Spectral reflectance response patterns (SRRPs) from individual corn plants werecollected under variable cloud cover and solar angles using a fiber optic spectrometer. Chlorophyll levels, which are strongindicators of nitrogen status in plants, were also measured on each corn plant using a SPAD chlorophyll meter. Thebackpropagation neural network model was trained using spectral channels of the SRRPs as inputs and chlorophyll readingsas an output. The model showed strong correlation between predicted and actual chlorophyll meter readings (r 2 = 0.91, rootmean square prediction error = 1.30 SPAD units with validation set) from the same corn variety and soil type as the trainingset.

Variation in Soybean Response to Early Season Foliar Fertilization among and within Fields

Foliar fertilization of crops can complement soil fertilization. Recent research showed that soybean [Glycine max (L.) Merr.] yield response to early season N–P–K foliar fertilization was inconsistent and difficult to predict. This study's objectives were to further evaluate soybean response to early season N–P–K fluid fertilizers with or without S or micronutrients and to assess the within‐field response variation. The mixtures 3–8–15 (N–P–K), 3–8–15–1 (N–P–K–S), 10–4–8, 10–4–8–1, and 10–4–8–1 plus B, Fe, and Zn were evaluated in 18 conventional small‐plot trials. The within‐field variation in response to a 3–8–15 fertilizer mixed with glyphosate [N‐(phosphonomethyl) glycine] herbicide was evaluated in eight strip trials harvested with combines equipped with yield monitors and differential global positioning systems receivers. A fertilizer rate of 28 L ha−1 was sprayed once at the V5 growth stage. There was a yield response to the 3–8–15 and 10–4–8–1 fertilizers in one small‐plot trial (260 kg ha−1) and to 3–8–15 fertilizer in another trial (360 kg ha−1). There was a small response to the 3–8–15 fertilizer across the 18 trials (93 kg ha−1). Soybean responded to 3–8–15 fertilizer only in one strip trial where the yield response was higher in acidic soil areas. No response variation was detected across contrasting soil test values or soil types within other trials. Soybean response to foliar fertilization across all production conditions will seldom offset fertilization costs. The probability of economic yield response could be increased if the fertilizer is mixed with a postemergence herbicide because application costs are reduced.

Response of Glyphosate-Resistant Soybean (Glycine max) to Trimethylsulfonium and Isopropylamine Salts of Glyphosate1

Field studies were conducted from 1998 to 2000 to evaluate the effects of the trimethylsulfonium (Tms) salt of glyphosate on glyphosate-resistant soybean at Belleville, IL. Glyphosate-Tms and glyphosate-isopropylamine (Ipa) at 1,120, 1,680, 2,240, 3,360, and 4,480 g ai/ha were applied at the V4 and R1 growth stages of glyphosate-resistant soybean. Glyphosate-Tms and glyphosate-Ipa caused greater chlorosis when applied at the R1 growth stage when compared with the V4 growth stage, and chlorosis increased with rate. Chlorosis ranged from 0 to 20% depending on the year. In 1998, glyphosate-Ipa at 2,240 and 3,360 g/ha applied at the R1 growth stage caused 4 to 5% more chlorosis than glyphosate-Tms at the same rates. In addition to chlorosis, glyphosate-Tms caused bleaching (white speckling) of soybean leaves, with bleaching increasing as glyphosate-Tms rate increased. Glyphosate-Ipa caused no bleaching, regardless of rate. Glyphosate-Tms and -Ipa caused no visible height reduction at 14 and 28 d after treatment in any year. In 1998 and 1999, glyphosate-Tms and -Ipa, at the highest rate applied at the R1 growth stage, increased days to maturity of soybean. Despite the injury and delay in maturity caused by glyphosate-Tms and -Ipa, there was no difference in grain yield across years because of glyphosate salt, rate, or application timing.Nomenclature: Glyphosate; soybean, Glycine max (L.) Merr. ‘Pioneer 94B01 RR’.Additional index words: Herbicide injury, postemergence, transgenic soybean.Abbreviations: DAT, days after treatment; EPSPS, 5-enolpyruvylshikimate-3-phosphate synthase; Ipa, isopropylamine; Tms, trimethylsulfonium.

Frogeye Leaf Spot of Soybean Caused by Cercospora sojina in Northwestern Argentina

Frogeye leaf spot of soybean (Glycine max (L.) Merr.), caused by Cercospora sojina Hara, was first detected during the 1997-98 growing season at low incidence and severity (<1% of the leaf diseased) levels in the provinces of Tucumán, Salta, Jujuy, Catamarca, and Santiago del Estero in northwestern Argentina. During the 1998-1999 growing season, disease incidence increased and disease severity grew to 10% of the leaf surface diseased on highly susceptible cultivars in a few locations. An outbreak of frogeye leaf spot occurred throughout northwestern Argentina during the 1999-2000 growing season. Frogeye leaf spot was severe on susceptible cultivars in the provinces of Salta, Santiago del Estero and Catamarca with the greatest intensity in the northeastern part of the Province of Tucumán. Symptoms on leaves were circular lesions that ranged in size from 1 to 5 mm, were reddish-brown to gray or tan, and were bordered by a narrow, reddish-brown to purple margin. Conidiophores and conidia of C. sojina developed on the abaxial leaf surface (1,2). Severely diseased leaves were desiccated and dropped during the R6 stage of growth. Lesions also developed on stems, pods, and seeds. Field surveys indicated that this disease reduced the yields of the highly susceptible cultivars Anta 82 RR, Coker 6738, and A 6445 RG by 48, 34, and 25%, respectively. C. sojina was cultured from diseased tissue on PDA acidified with 0.2% lactic acid and maintained on V-8 juice agar amended with streptomycin sulfate (100 mg/l). Conidia were elongated, dark, 38 to 62 × 5 to 9 μm, with 2 to 6 septa, and borne on dark conidiophores with 1 to 4 septa. Pathogenicity tests were conducted on seedlings of the susceptible cultivars A 6445 RG and Coker 6738 and on the resistant cultivars A 8000 RG and Shulka. Seedlings were inoculated at the V3 growth stage by spraying the leaves with a conidial suspension (4 × 104 conidia/ml) using a hand-held atomizer. Control plants were sprayed with sterile distilled water. Plants were placed in a moist chamber at 26°C for 2 days and then transferred to a greenhouse bench where they were kept at 25 to 30°C. Symptoms identical to those observed in the field became visible after 7 to 10 days. Ratings were made 14 days after inoculation by estimating the percentage of leaf area affected using a standard area diagram. Lesions covered 60 to 65% of the leaf area of susceptible cultivars, but less than 2% on resistant cultivars. Control plants remained healthy. C. sojina was reisolated from lesions on leaves of susceptible plants. Above-average rainfall and high relative humidity in northwestern Argentina during the first three months of 2000 may have encouraged the severe outbreak of frogeye leaf spot of soybean. The outbreak was aggravated by the widespread use of notillage systems in the region and the large hectarage planted with susceptible cultivars.

Critical Compositional Nutrient Indexes for Sweet Corn at Early Growth Stage

It would be instrumental to define nutrient norms from small‐size crop databases at the V4–V6 corn (Zea mays L.) growth stage for in‐season N fertilizer recommendations. Our objective was to derive Compositional Nutrient Diagnosis (CND) and Diagnosis and Recommendation Integrated System (DRIS) nutrient index ranges from a sweet corn database and to relate nutrient concentration and indexes to ear yield. A sweet corn database of 240 observations on commercial yields and N, P, K, Ca, and Mg concentrations in 30‐cm high corn seedlings were divided at random between survey (n = 200) and validation (n = 40) subpopulations. The proportion of low‐yield specimens in the survey population was computed at inflection point of a cubic cumulative variance ratio function and was associated with a chi‐square value (CND r2) of 3.9 that was confirmed in the validation subpopulation. Critical CND nutrient indexes were found to be symmetrical about zero as follows: −0.70 to +0.70 for N, −0.45 to +0.45 for P, −1.14 to +1.14 for K, −0.63 to +0.63 for Ca and Mg, and −1.05 to +1.05 for the residual filling value. Summing squared critical nutrient indexes also gave a CND r2 of 3.9, the minimum CND imbalance index for high‐yield targets (&gt;6.7 Mg ha−1). Nutrient concentration values were little to closely related to CND indexes (R2 = 0.34–0.87). The DRIS and CND indexes were highly related to each other (R2 = 0.91–0.99). For N at V4–V6 growth stage, the CND N index was the most closely related to ear yield.

USE OF PRECISION FARMING TO IMPROVE APPLICATIONS OF FEEDLOTWASTE TO INCREASE NUTRIENT USE EFFICIENCY AND PROTECTWATER QUALITY

Spatial variability in crop yields can be caused by many factors, which makes it difficult to determine the most limiting factors. Application of animal wastes to relatively infertile areas offers the potential to supply needed nutrients and improve soil physical properties. The objectives of this study were to test a manure application strategy to reduce spatial variability in corn (Zea mays L) yield and to identify the most limiting nutrients in relatively low yielding areas in a field. Fresh solid beef feedlot manure was applied in 1997 to a strip across areas with variable fertility status. No fertilizer was applied with the manure in 1997. Uniform N fertilizer, but no manure, was applied in 1998. Leaf tissue samples and chlorophyll meter readings were collected along the strips during the growing season and from adjacent strips without manure application. Grain yield was determined at plant maturity. In 1997, chlorophyll meter readings indicated season long N deficiency (<95% sufficiency index) in no-manure plots with sufficiency indices of 93, 88, 85, and 88% for the V10, V17, R2, and R3 growth stages, respectively. Only an early season N deficiency was detected in a few of the no-manure plots in 1998. Leaf tissue analyses indicated N and P were growth limiting factors in 1997, with leaf N concentrations of 25, 26, and 27 mg g−1 for non-manure plots and 30, 33, and 31 mg g−1 for manure plots at V12, R1, and R3 growth stages, respectively. Leaf P concentrations were 2.0, 2.0, and 1.9 mg g−1 for no-manure plots versus 2.5, 2.7, and 2.3 mg g−1 for manure plots, respectively. In 1998, neither N or P were identified as limiting factors. Grain yields in 1997 were 10.2 and 12.2 Mg ha−1, which increased to 11.9 and 12.8 Mg ha−1 in 1998 for no-manure and manure plots, respectively.

Effect of Row Spacing and Herbicides on Burcucumber (Sicyos angulatus) Control in Herbicide-Resistant Corn (Zea mays)1

Abstract: Experiments examining burcucumber management in glufosinate-resistant (GR) and imidazolinone-resistant (IMI) corn were conducted in 1997 and 1998 in southeastern Pennsylvania. GR corn was planted in 38- and 76-cm rows, and postemergence (POST) treatments of glufosinate and glufosinate plus atrazine were applied to corn at the V4 or V5 growth stage. In a second study, IMI corn was planted in 76-cm rows, and 15 preemergence (PRE) and POST herbicide programs were evaluated. Herbicide treatments included RPA-201772, CGA 152005, simazine, imazethapyr plus imazapyr, imazamox, chlorimuron plus thifensulfuron, nicosulfuron plus rimsulfuron plus atrazine, CGA 152005 plus primisulfuron, and combinations with atrazine. Burcucumber germinated throughout the growing season, with greatest emergence occurring in early June, gradually decreasing to minimal emergence by mid-July. Glufosinate alone controlled burcucumber 79 to 90% 7 weeks after planting (WAP) regardless of application timing or row spacing. By 10...

Soybean Growth and Development as Affected by Glyphosate and Postemergence Herbicide Tank Mixtures

Field research was conducted to evaluate the effect of glyphosate [N‐(phosphonomethyl)glycine] and postemergence herbicide tank mixtures applied to soybean [Glycine max (L.) Merr.] at the V5 growth stage on growth, development, and grain yield of glyphosate‐resistant and nonresistant cultivars. Glyphosate at 840 g a.e. ha−1 did not affect vegetative growth, reproductive development, leaf area index (LAI), or grain yield of glyphosate‐resistant soybean compared with nontreated glyphosate‐resistant soybean. Soybean injury 21 d after treatment (DAT) was 14 to 18% when herbicide tank mixture treatments were applied. Soybean injury caused by postemergence herbicide tank mixtures resulted in delayed vegetative development when measured 7 DAT, delayed reproductive development at 20 and 80 DAT, reduced season‐long height of ‘Asgrow A1900’ and ‘Asgrow AG1901’, and reduced aboveground dry weight at 35 and 56 DAT compared with nontreated plants. Leaf area index was reduced by postemergence tank mixtures up to 52 DAT but was greater 70 and 80 DAT, depending on the cultivar. The ratio of red to far red light that reached the soil surface 28 DAT was dependent on cultivar and herbicide selection. Yield of soybean treated with herbicides other than glyphosate timed for weed control and disease suppression was reduced at least 200 and 130 kg ha−1 in 1997 and 1998, respectively, in the absence of weeds and disease.

Variation in Mineral Concentration and Grass Tetany Potential among Russian Wildrye Accessions

Grass tetany or hypomagnesemic tetany in cattle (Bos taurus) is caused by an imbalance of K, Ca, and Mg in the diet. Indications of grass tetany range from reduced milk yield or weight gain to severe convulsions and death. The risk of grass tetany dramatically increases when the K/(Mg + Ca) ratio of forage exceeds 2.2, especially for dams during early lactation. Russian wildrye [Psathyrostachys juncea (Fisch.) Nevski], a valuable forage species, has ratios well above this level. Our objectives were to determine the mineral concentration and ratio values for 65 accessions of Russian wildrye to select germplasm sources with low tetany ratio and to determine the effects of year, location, and their interactions with accessions. Seedlings of each accession and two checks, Syn A and Mankota, were established in replicated space‐plant nurseries at Logan, UT, Mandan, ND, and Swift Current, Saskatchewan, Canada. Years‐within‐location effects generally produced the largest variance component, while the accession variance was larger than location × accession and location × accession × year interaction variances for K, Ca, Mg, K/(Mg + Ca) ratio, and Reduced Tetany Potential (RTP) index. Selection for these traits in Russian wildrye germplasm will require multiple years to characterize adequately accessions, breeding lines, or synthetics. The K/(Ca + Mg) ratio of the accessions tested ranged from 2.2 to 3.0 when averaged across sites and years for V4 growth stage. A similar range of ratio values and ranking of the accessions was observed at the E2 growth stage. The three tetraploid accessions evaluated were among the five accessions with the highest tetany ratios. Previously reported forage yield and seed yield means were significantly correlated with K, Mg, and N concentrations and K/(Ca + Mg) ratio. The RTP index was not correlated with forage yield, seed yield, or N concentration. Therefore, selection in Russian wildrye should be based on increased RTP index rather than K concentration or K/(Ca + Mg) ratio to avoid concomitant unintentional selection of reduced forage yield and seed yield.