bluuebunny/crossref_metadata_2025 huggingface dataset:
Critical Phosphorus Levels for Salicornia Growth
Authors: Alsaeedi Abdullah H. , Elprince Adel M.
Published: July 2010

Basic information is needed to estimate P status ofSalicornia bigeloviiTorr. with increased precision if progress is to be made in adapting this halophyte as a conventional oilseed crop for direct seawater irrigation in coastal areas of arid regions. The P nutrition of salicornia was studied by using the nutrient solution technique in the greenhouse. The culture solutions were seawater, enriched to 1/2‐strength modified Hoagland's solution [pH = 6.2 ± 0.2; electrical conductivity (EC) = 54 ± 2 dSm−1], and P treatments ranging from 0 to adequate amounts of P for full growth. All stages of deficiency symptoms were observed at harvest, ranging from stunted growth, necroses, purplish coloration, chlorosis, and dark bluish‐green coloration to no symptoms. Dry and fresh weight of the tops were plotted against soluble P and total P values to give plant nutrient calibration curves that were fitted to the composite growth model by the least squares procedure. On the basis of the curve sharpness coefficient and range parameter output values and ease of sampling, semiwoody internodes, matured internodes and soluble P concentration were selected from the five plant parts sampled and the two forms of P determined as the best combination to diagnose the P status of Salicornia. About 480 mg kg−1of soluble P in semiwoody internode tissue was tentatively set as the critical concentration for growth of the salicornia. The corresponding value for total P was set at 780 mg kg−1
Site‐Specific Analysis of a Droughted Corn Crop: II. Water Use and Stress
Authors: Sadler E. John , Bauer Philip J. , Busscher Warren J. , Millen Joseph A.
Published: July 2010

In the southeastern USA Coastal Plain, spatial variation in soils causes extreme spatial variation in grain yield, as seen in yield maps. Corn (Zea mays L.) appears to be particularly susceptible to soil variation, especially during periods of drought. Our objectives were to compare variation in water use and stress of corn within and among soil map units. In one field, at two sites in each of four map units, we measured site‐specific effects of soil variation on crop water use from 40 d after planting until after maturity using a time‐domain reflectometer (TDR). On 4 d during vegetative growth, drought stress was evaluated on eight transects using infrared thermometer (IRT) measurements of canopy temperature (Tc). During the most severe drought, visibly stressed areas had canopy‐air temperature differences (Tc − Ta) > 10°C, yet other areas remained <2°C. Two days after a 46‐mm rain, Tc − Ta was near zero over the whole field, indicating little water stress. The time series of TDR measurements produced estimates of daily evapotranspiration, runoff, and infiltration; site‐to‐site differences in these dominated the water balance. Water stress, inferred from water use, matched that inferred earlier from yield components. In sum, corn at the eight sites arrived at final water use via fundamentally different paths. Further, variation between sites within soils was significant, indicating that soil map units are not homogenous with respect to water relations. These results underscore the need for within‐season observations of crop water use and stress to augment interpretation of site‐specific yield maps.
MarkSim: Software to Generate Daily Weather Data for Latin America and Africa
Authors: Jones Peter G. , Thornton Philip K.
Published: July 2010

A software package to generate daily weather data for Latin America and Africa is described. The program is based on a stochastic weather generator that uses a third‐order Markov process to model daily weather data. The model has been fitted to data from more than 9200 stations with long runs of daily data throughout the world. The climate normals for these stations were assembled into 664 groups using a clustering algorithm. For each of these groups, rainfall model parameters are predicted from monthly means of rainfall, air temperature, diurnal temperature range, and station elevation and latitude. The program identifies the cluster relevant to any required point using interpolated climate surfaces at a resolution of 10 min of arc (18 km2) and evaluates the model parameters for that point. The application currently contains surfaces for Latin America and Africa, and other regions will later be added. Use of the software is demonstrated by generating daily weather data files for running one of the DSSAT crop models.
Economics of Cropping Systems Featuring Different Rotations, Tillage, and Management
Authors: Katsvairo Tawainga W. , Cox William J.
Published: July 2010

Economics is the dominant factor influencing the adoption of cropping systems. The objective of this 6‐yr study was to determine profitability of cropping systems featuring four crop rotations (continuous corn (Zea mays L.), soybean [Glycine max (L.) Merr.]–corn, soybean–corn–corn, and soybean–wheat (Triticum aestivum L.)/red clover (Trifolium pratense L.)–corn), three tillage systems (moldboard, chisel, and ridge) and two management input (high and low chemical) systems. The soybean–corn rotation under low chemical management resulted in the greatest net returns in chisel ($100 ha−1) and moldboard plow tillage ($148 ha−1) because the reduction in production costs (∼$110 ha−1), associated with less fertilizer and pesticide costs in corn and less herbicide costs in soybeans, offset the reduction in gross returns ($72 ha−1 in chisel and $38 ha−1 in moldboard plow), associated with lower corn and soybean yields in chisel and lower corn yields in moldboard plow. Continuous corn under high chemical and soybean–corn–corn and soybean–corn rotations under low chemical management had similar net returns in ridge tillage ($33, $26, and $17 ha−1, respectively). Growers who substitute soybean–corn and soybean–corn–corn (in ridge) rotations for continuous corn can maximize profits and reduce starter fertilizer use by 33 to 50%, N fertilizer by 60 to 70%, herbicides by about 60%, and insecticides by 65 to 100%. Growers who use moldboard plow tillage may realize maximum profits by adopting the soybean–wheat/red clover–corn rotation under low chemical management if they market the wheat straw, a common practice in New York.
Effects of Nitrogen and Sulfur on Canola Yield and Nutrient Uptake
Authors: Jackson Grant D.
Published: July 2010

Spring canola (Brassica napus L. var. napus) is becoming a significant oilseed crop adapted to the western USA. Often N and S limit crop growth. Field experiments were established to study the effects of N and S fertilization on seed yield, oil content, and N, P, K, and S uptake of spring canola. Four N rates in combination with three S rates were evaluated on two irrigated and three rainfed locations in the western triangle area of Montana near Conrad. Seed yields ranged from 0.1 to 3.8 Mg ha−1. Seed yield and oil content N responses were closely related to available N (fertilizer N plus soil NO3–N in 90 cm of soil). Seed oil content varied from 370 to 510 g kg−1 and was depressed by increasing N. Optimum seed and oil yield occurred at about 200 kg N ha−1. Two of the experimental sites responded to S. About 20 kg S ha−1 was adequate for optimum seed and oil yields. At the optimal N and S levels, total plant N, P, K, and S uptake averaged 140, 25, 170, and 60 kg ha−1, respectively. Of the total N, P, K, and S accumulation, about 40% of the N, 30% of the P, and 85% of the K and S remained in the postharvest residue.
Leaf and Stem Properties of Alfalfa Entries
Authors: Sheaffer Craig C. , Martin Neal P. , Lamb JoAnn F.S. , Cuomo Greg R. , Jewett Jane Grimsbo , Quering Steven R.
Published: July 2010

Alfalfa (Medicago sativa L.) has been considered as a biofuel feedstock. A system has been proposed to produce electricity from the stems and utilize the leaves as a livestock feed. We determined the effects of harvest regimes on yield and quality of leaf, stem, and total herbage of six alfalfa entries. We applied three harvest regimes involving three harvests per year at bud stage or early flower, or two harvests per year at late flower. An early flower harvest regime had the highest leaf yield (average of 5.6, 4.5, and 4.5 Mg ha−1 for the early flower, late flower, and midbud regimes, respectively), and the late flower harvest regime had the highest stem yield (average of 5.8, 5.3, and 3.9 Mg ha−1 for the late flower, early flower, and midbud regimes, respectively). Leaf concentration decreased with increased herbage maturity (average of 540, 517, and 458 g kg−1 for the midbud, early flower, and late flower regimes, respectively) and was associated with total herbage crude protein (CP) and acid‐detergent fiber (ADF) and neutral‐detergent fiber (NDF) Harvest regime did not affect total seasonal herbage yield or stand persistence. Alfalfa entries differed in herbage quality, leaf concentration, and leaf yield, but did not consistently differ in total herbage or stem yield. Herbage yield and quality differences among entries were similar for all harvest regimes. Producers can affect stem and leaf yields by selection of harvest regime.
Improving Estimates of Individual Leaf Area of Sunflower
Authors: Bange Michael P. , Hammer Graeme L. , Milroy Stephen P. , Rickert Kenneth G.
Published: July 2010

Simple, accurate, and nondestructive methods of determining leaf area of plants are important for many experimental comparisons. Determining individual leaf area (LA) of sunflower (Helianthus annuus L.) can involve measuring leaf length (L) and breadth (B). The objectives of this field study were to compare published and new models to determine the most precise model to predict the area of individual leaves of sunflower plants and to test the applicability of these models between sowing times, with three genotypes differing in maturity and stature, and at different times during crop growth. The best model, which included both the L and B factors (LA = aL + dL + eLB + c), accommodated changing leaf shape during crop development. The relationship between leaf dimensions and LA was significantly improved when sowing time and the times of leaf sampling were included in the relationship; however, no significant differences were found among genotypes. The relative increase in precision with more complex models was considered. Both length and breadth measurements were needed to attain precision for all leaf sizes, and given the availability of computer‐based statistical packages, the use of relatively complex models in the assessment of individual leaf areas would appear to be a practical option.
Soil Type, Climatic Regime, and the Response of Water Use Efficiency to Crop Management
Authors: Gregory Peter J. , Simmonds Lester P. , Pilbeam Colin J.
Published: July 2010

In many rainfed regions of the world, only a small fraction of the total water available for crop production is transpired and water use efficiency (WUE) is low. Changes in crop management practice to reduce evaporation from the soil surface (Es) have been successful in some locations but unsuccessful elsewhere. This paper outlines a conceptual framework for assessing the potential for improved crop management to reduce Es and summarizes results from Syria, Kenya, and Niger. The results show that factors such as evaporative demand, amount and frequency of rainfall, soil texture, and the distribution of roots interact to influence the sensitivity of Es to management practices that modify canopy area and root growth. Using a simulation model we demonstrate the quantitative effect of these interactions and show that the scope for reducing Es is greatest in clay soils in locations with frequent rain and low evaporative demand and least on sandy soils in regions with sporadic rainfall and high evaporative demand. The distribution of roots has a marked influence on the rate of drying of the soil surface and thereby on soil hydraulic conductivity which becomes more important as evaporative demand increases relative to rainfall.
Seasonal Yield Distribution of Cool‐Season Grasses following Winter Defoliation
Authors: Riesterer Janet L. , Casler Michael D. , Undersander Daniel J. , Combs David K.
Published: July 2010

Graziers in southeastern USA often stockpile forage in late summer to extend the grazing season and reduce feeding costs. The effect of winter grazing on the following growing seasons production in the upper Midwest has not been reported. This study was conducted to determine the consequential forage yield and persistence of several cool‐season grasses following various winter defoliation and N fertilization treatments in the upper Midwest. Grass cultivars included early and late‐maturing orchardgrass (Dactylis glomerata L.), quackgrass [Elytrigia repens (L.) Nevski], reed canarygrass (Phalaris arundinacea L.), smooth bromegrass (Bromus inermis Leyss.), tall fescue (Festuca arundinacea Schreb.), and timothy (Phleum pratense L.). October, December, or March defoliation generally did not affect seasonal forage yield except when early spring growth preceded March defoliation, reducing first‐cut forage yields. Without N, timothy, reed canarygrass, and orchardgrass had the highest seasonal forage yields. Both orchardgrass varieties, tall fescue, and reed canarygrass had the greatest response to N whereas timothy had the lowest response. While both spring‐applied N treatments (single and split application of 101 kg ha−1) had carryover effects into the midsummer cuttings, the single N application resulted in higher seasonal forage yield than the split‐N application. Tall fescue had the greatest carryover response to N in both years. Orchardgrass and reed canarygrass provided the highest forage yields throughout the season. Tall fescue and both orchardgrass varieties were most persistent and timothy, smooth bromegrass, and quackgrass were least persistent.
Morphological Development of Alfalfa Cultivars Selected for Higher Quality
Authors: Hall Marvin H. , Smiles W. Scott , Dickerson Robert A.
Published: July 2010

Alfalfa (Medicago sativa L.) maturity at the time of harvest greatly influences forage quality. The objective of this research was to determine if observed quality differences between high quality and other alfalfa cultivars were due to differences in morphological development. Two high‐quality cultivars (‘WL 252HQ’, ‘WL 322HQ’) and two check cultivars (‘5262’, ‘5454’) with similar fall dormancy ratings were established on a Murrill silt loam (fine‐loamy, mixed, mesic Typic Hapludult) in the spring of 1996. During 1997, 1998, and 1999, each cultivar was hand‐sampled weekly for 4 consecutive wk during the spring growth period and for 3 consecutive wk during the three subsequent growth periods. Morphological development and forage quality were determined for each alfalfa cultivar at each sampling. There were no interactions between growth period or sampling times and alfalfa cultivars for either alfalfa maturity or forage quality. Morphological development of the cultivars was not different at any of the sampling times. Averaged across all growth periods and sampling times, crude protein (CP) concentrations and in vitro dry matter digestibility (IVDMD) were 14 and 13 g kg−1, respectively, higher for the high‐quality cultivars (ADF) and neutral‐detergent fiber (NDF) concentrations were 16 and 15 g kg−1, respectively, lower. The data from this research indicates that the difference in quality between the high quality and traditional alfalfa cultivars is not due to differences in morphological development. Selecting for higher‐quality alfalfa was successful and is not an artifact of inadvertently selecting for delayed development.
Evaluation of Seedbed Preparation, Planting Method, and Herbicide Alternatives for Dryland Soybean Production
Authors: Popp Michael P. , Oliver Lawrence R. , Dillon Carl R. , Keisling Terry C. , Manning Patrick M.
Published: July 2010

The current economic situation provides incentives for producers to reduce input costs. Examples include reduced herbicide rates and an array of planting methods that utilize new herbicide and equipment technologies. This study investigated the implications of seedbed preparation (conventional vs. conservation tillage), planting equipment (broadcast, drill, no‐till drill, air seeder, and planter), and herbicide alternatives [full‐rate preplant followed by full‐rate over the top (FRI), reduced‐rate preplant followed by reduced‐rate over the top (RRI), and full‐rate over the top by itself (FROT)] for soybean [Glycine max (L.) Merr] at two locations (Keiser and Pine Tree, AR) with two cropping systems (full season vs. double‐cropped). While some yield differences were observed across seedbed preparation and planting equipment, they did not lead to consistent results. Conventional and conservation tillage were the preferred production strategies for full‐season and double‐cropped systems, respectively. Seasonal labor, weather, and scale of operation are expected to play a major role because planting equipment did not impact yields or cost. Herbicide programs did not affect yields. Lower costs through reduced‐rate herbicide applications led to higher returns and lower financial risk without restricting the planting method. Both the FROT and RRI weed control systems lead to higher returns compared with the FRI system. Producers concerned with the lack of residual herbicide activity afforded by preplant herbicides would be expected to choose the RRI system at the cost of slightly lower net returns in the full‐season system.
Differential Response of Soybean Yield Components to the Timing of Light Enrichment
Authors: Mathew Jomol P. , Herbert Stephen J. , Zhang Shuhuan , Rautenkranz Andreas A. F. , Litchfield Gerald V.
Published: July 2010

Solar radiation is an important environmental factor influencing seed yield in soybean [Glycine max (L). Merr.]. Our objective was to analyze the response of soybean seed yield components to light enrichment initiated at different growth stages. Light enrichment was imposed on the indeterminate soybean cultivars Altona and Evans by installing wire mesh fencing on either side of the center row to push the adjacent rows aside at different growth stages. Fences prevented plants in the neighboring rows from encroaching on the growing space of the center row plants. Pod number per plant and to a lesser extent seed size accounted for variation in seed yield. Light enrichment initiated at late vegetative or early flowering stages increased seed yield 144 to 252%, mainly by increasing pod number, while light enrichment beginning at early pod formation increased seed size 8 to 23%, resulting in a 32 to 115% increase in seed yield. Responses to light enrichment occurred proportionately across all node positions despite the differences in the time (15–20 d) of development of yield components at the different node positions. Although maximum seed size may be under genetic control in soybean plants, our results suggested seed size can still be modified by the environment with some internal control moderating the final size of most seeds in all pods. It indicates that plants are able to redistribute the available resources to components not yet determined, in an attempt to maintain or improve yield.
Winter Establishment of Eastern Gamagrass in the Southern Piedmont
Authors: Mueller J.Paul , Hall Timothy S. , Spears Janet F. , Penny Brenda T.
Published: July 2010

Eastern gamagrass [Tripsacum dactyloides (L.)] has the potential to contribute as a warm‐season component in grazing systems and conservation plantings, but its seeds exhibit a strong dormancy that reduce germination and successful stand establishment. A 3‐yr study was conducted on Typic Hapudult soils to determine the influence of fungicide seed treatment [Captan (N‐trichloromethylthio‐4‐cyclohexene‐1,2‐dicarboximide), 5.6 g a.i. kg−1 seed] and winter planting date (November–February) on germination, stand establishment, and herbage mass of eastern gamagrass. Eastern gamagrass was planted with and without fungicide seed treatment at monthly intervals between November and May. The May plantings (stratified and nonstratified seeds) served as controls. Fungicide seed treatment had no effect on initial or subsequent stands of eastern gamagrass. Winter plantings resulted in initial stands that were equal or superior to stands established from planting stratified seeds in May (5.9 vs. 3.4 plants m−2, respectively). Significant seed carry‐over effects were observed from spring (April and May) plantings, with an average of 8.8 seedlings m−2 germinating in spring of the second year compared with 1.7 seedlings m−2 for winter treatments. Herbage mass for spring plantings (March, April, and May) was depressed up to 75% compared with winter plantings. Planting in November, December, or January is an effective alternative to planting stratified seeds in May in the southern Piedmont.
Diagnostic Efficiency of the Blacklayer Stalk Nitrate and Grain Nitrogen Tests for Corn
Authors: Brouder Sylvie M. , Mengel David B. , Hofmann Brenda S.
Published: July 2010

Protecting water quality and maintaining profitable corn (Zea maysL.) production requires diagnostics that can distinguish between N deficiency, sufficiency, and excess. This study evaluates initial recommendations on blacklayer basal‐stalk NO3–N ranges and critical concentrations for diagnosing N status, and it compares the performance of this test with grain analysis. Observations (428) were collected from 13 N‐response experiments. Linear response and plateau (LRP) and binary logistic regression (BLR) were used to characterize the relationships between yield and tissue‐test values. With the LRP, stalk NO3–N and grain N concentrations separating deficient from sufficient observations were 0.42 and 13.1 g kg−1, respectively, and the success rates of the two tests were comparable (77 and 75%, respectfully). The BLR also identified critical concentrations, but the values increased with decreasing yields, a desirable decision‐rule attribute given that extreme deficiency can result in higher‐than‐expected tissue concentrations. The success rates of multiple BLR functions using yield and stalk or grain analysis as factors were again comparable (88 and 87%, respectively), but they were significantly greater than with the LRP analysis. Stalk analysis was superior to grain analysis for distinguishing sufficiency from excess. A constant stalk NO3–N concentration (1.67 g kg−1) separated sufficient from excessive cases, and fertilizer efficiency approached zero at 2.9 g kg−1. Premature sampling resulted in stalk NO3–N levels that were 40 to 600% greater than levels observed after blacklayer formation, with the greatest error occurring when N fertility was low. When not testing for N excess, the advantages of grain analysis are the ease of sampling during harvest and the reduced risk of error associated with premature sampling.
Variation in Soybean Response to Early Season Foliar Fertilization among and within Fields
Authors: Mallarino Antonio P. , Haq Mazhar U. , Wittry David , Bermudez Manuel
Published: July 2010

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.
Nitrogen Fertilization and Rhizobial Inoculation Effects on Kura Clover Growth
Authors: Seguin Philippe , Sheaffer Craig C. , Ehlke Nancy J. , Russelle Michael P. , Graham Peter H.
Published: July 2010

Kura clover (Trifolium ambiguum M.B.) is a persistent, rhizomatous forage legume; however, its use is currently limited by slow establishment. We determined the effects of rhizobial inoculation and N fertilization on kura clover growth and N2 fixation in the seeding year. Kura clover was seeded with or without a commercial rhizobial inoculant and with and without N fertilization in three environments. Fertilization treatments consisted of 100 kg N ha−1 either applied at seeding or split in 10 kg N ha−1 applications every other week after seeding. Nitrogen fertilization increased seeding‐year herbage accumulation in all locations, but the response to fertilizer N was greater on a loamy sand with low organic matter and available N than on a silt loam with high soil organic matter. Rhizobial inoculation failed to consistently improve seeding‐year herbage accumulation compared with no inoculation; a positive response was observed in only one of three environments. Dry matter accumulation responses of root and rhizome to N fertilization and rhizobial inoculation were similar to that of herbage. Dinitrogen fixation in the seeding year varied between 9 and 25 kg ha−1 fixed N, depending on the environment. Seeding‐year inoculation increased postseeding year herbage yield. Also, when a positive response to N fertilization occurred in the seeding year, the response was maintained in the postseeding year. A commercial rhizobial inoculant was ineffective in establishing adequate nodulation in the seeding year in a N‐limited soil, indicating the need to identify more effective rhizobia for kura clover.
Economic Analysis of Conservation and Conventional Tillage Cropping Systems on Clayey Soil in Eastern Arkansas
Authors: Parsch Lucas D. , Keisling Terry C. , Sauer Patricia A. , Oliver Lawrence R. , Crabtree Nathan S.
Published: July 2010

Conservation tillage offers an alternative approach for managing clayey soils in the midsouthern United States. This study compared conservation tillage seedbed preparation vs. conventional tillage main plots with subplots of (i) nonirrigated soybean (Glycine max L. Merr.), (ii) irrigated soybean, (iii) irrigated grain sorghum (Sorghum vulgare L.), (iv) irrigated soybean followed by irrigated grain sorghum, (v) irrigated soybean followed by irrigated corn (Zea mays L.), and (vi) continuous irrigated cotton (Gossypium hirsutum L.) for the years 1986 to 1991 at Keiser, AR. Cropping practices were similar to those used by producers in the area. Grain sorghum yielded better in a soybean rotation than in monoculture and also in conventionally tilled seedbed than in conservation tillage. For other crops, yield did not differ significantly by tillage. Except for cotton, conventional tillage resulted in higher average net returns (NR) than conservation tillage. Although the most profitable system was continuous cotton with conservation tillage, NR varied widely across years, and there were fewer observations for cotton than for other systems in the study. Among conventional tillage seedbed preparation, nonirrigated continuous soybean was more profitable than any of the irrigated systems, including irrigated soybean. However, irrigated soybean resulted in NR that were less variable than nonirrigated soybean. The study confirmed the increased variable costs and decreased equipment costs that accompany conservation tillage systems. Even with the dramatic changes in burndown herbicide costs that have occurred since the study was conducted, the rankings of the cropping systems for profitability would not change.
Multispectral Reflectance of Cotton Related to Plant Growth, Soil Water and Texture, and Site Elevation
Authors: Li Hong , Lascano Robert J. , Barnes Edward M. , Booker Jill , Wilson L. Ted , Bronson Kevin F. , Segarra Eduardo
Published: July 2010

Radiometric data can be useful to determine the impact of field heterogeneity, irrigation, and fertilization on plant water and N use. A 2‐yr (1998–1999) study was conducted on the South Texas High Plains to investigate cotton (Gossypium hirsutum L.) spectral and agronomic responses to irrigation and N fertilization and to determine the simple and cross correlation among cotton reflectance, plant growth, N uptake, lint yield, site elevation (SE), and soil water and texture. The treatments were irrigation at 50 and 75% of calculated cotton evapotranspiration (ET) and N rates of 0, 90, and 135 kg ha−1 arranged in an incomplete block of size‐2 design. Plant and soil spectral properties were investigated within a wavelength of 447 to 1752 nm. Near‐infrared (NIR) reflectance was positively correlated with plant biomass and N uptake. Reflectance in the red and midinfrared band increased with SE. The mixed‐model analysis showed that cotton NIR reflectance, normalized difference vegetative index (NDVI), soil water, N uptake, and lint yield were significantly affected by irrigation (P < 0.0012). The N treatment had no effect on spectral parameters, and interaction between irrigation and N fertilizer was significant on NIR reflectance (P < 0.0027). All spectral and agronomic parameters measured were associated with SE. The red and NIR reflectance and NDVI were cross‐correlated with soil water, sand, clay, and SE across a distance of 60 to 80 m. Characterization of plant and soil reflectance and their spatial structure can be the basis for variable N application on heterogeneous fields to increase N use efficiency.
Cotton Growth under No‐Till Production in the Lower Mississippi River Valley Alluvial Flood Plain
Authors: Pettigrew William T. , Jones Michael A.
Published: July 2010

Declining profit margins have forced Mississippi Delta cotton (Gossypium hirsutum L.) producers to consider conservation tillage as a means of reducing production inputs. Due to limited experience and research with conservation tillage in the Mississippi Delta, our objectives were to determine how no‐till production affected cotton growth, light interception, dry matter partitioning, yield, and fiber quality compared with conventional tillage. Six cotton genotypes were evaluated in no‐till and conventional tillage systems in 1997 and 1998. Data for dry matter partitioning, light interception, bloom counts, nodes above white bloom (NAWB), lint yield, yield components, and fiber quality were collected. Slower emergence delayed development of the no‐till cotton throughout both seasons. No‐till plants averaged 42% less leaf area index (LAI) during prebloom and 27% less LAI at midbloom than plants in conventional tillage before recovering to have similar late‐season LAI. Conventional tillage plants intercepted 28% more sunlight during prebloom and 17% more sunlight at midbloom before both tillage treatments reached canopy closure late in the season. Flower production and cutout (NAWB = 5) were delayed in no‐till compared with conventional tillage. Lint yield was 11% lower in the no‐till treatment than in conventional tillage due primarily to an 8% reduction in the number of bolls m−2. Fiber quality traits were inconsistently altered by tillage treatments across years. The delayed blooming period of the no‐till plants meant that these plants may have encountered slightly different weather during bloom, possibly contributing to the yield and fiber quality differences between treatments.
In‐Season Prediction of Potential Grain Yield in Winter Wheat Using Canopy Reflectance
Authors: Raun William R. , Solie John B. , Johnson Gordon V. , Stone Marvin L. , Lukina Erna V. , Thomason Wade E. , Schepers James S.
Published: July 2010

Nitrogen fertilization rates in cereal production systems are generally determined by subtracting soil test N from a specified N requirement based on the grain yield goal, which represents the best achievable grain yield in the last 4 to 5 yr. If grain yield could be predicted in season, topdress N rates could be adjusted based on projected N removal. Our study was conducted to determine if the potential grain yield of winter wheat (Triticum aestivum L.) could be predicted using in‐season spectral measurements collected between January and March. The normalized difference vegetation index (NDVI) was determined from reflectance measurements under daytime lighting in the red and near‐infrared (NIR) regions of the spectra. In‐season estimated yield (EY) was computed using the sum of two postdormancy NDVI measurements (Jan. and Mar.) divided by the cumulative growing degree days (GDD) from the first to second reading. A significant relationship between grain yield and EY was observed when combining all nine locations across a 2‐yr period. Our estimates of potential grain yield (made in early Mar.) differed from measured grain yield (mid‐July) at three sites where yield‐altering factors (e.g., late summer rains delayed harvest and increased grain yield loss due to lodging and shattering) were encountered after the final sensing. Evaluating data from six of the nine locations across a 2‐yr period, EY values explained 83% of the variability in measured grain yield. Use of EY may assist in refining in‐season application of fertilizer N based on predicted potential grain yield.
Searching for Rice Allelochemicals
Authors: Rimando Agnes M. , Olofsdotter Maria , Dayan Franck E. , Duke Stephen O.
Published: July 2010

A bioactivity‐guided isolation method was developed with the objective of isolating the allelochemicals in rice (Oryza sativa L.). Roots of the allelopathic rice cultivar Taichung Native 1, grown hydroponically, were extracted and fractionated, with the activity of the fractions followed using a 24‐well culture plate microbioassay. Some of the fractions obtained consisted of pure compounds, but none inhibited the growth of barnyardgrass [Echinochloa crusgalli (L.) Beauv.] at the lower concentration at which they were tested. Identified compounds were azelaic acid; ρ‐coumaric acid; 1H‐indole‐3‐carboxaldehyde; 1H‐indole‐3‐carboxylic acid; 1H‐indole‐5‐carboxylic acid; and 1,2‐benzenedicarboxylic acid bis(2‐ethylhexyl)ester. ρ‐Coumaric acid, a known allelochemical, inhibited the germination of lettuce (Lactuca sativa L.) seedlings at 1 mM However, ρ‐coumaric acid was active against barnyardgrass only at concentrations higher than 3 mM The two most active fractions obtained from the bioassay‐guided isolation were still a mixture of compounds as analyzed by gas chromatography–mass spectrometry (GC‐MS). Further fractionation is being done to isolate and identify the allelochemical(s) in these active fractions. This work has demonstrated the use of bioassay‐guided isolation in identifying allelochemicals in rice and has correlated observed field activity with laboratory experiments.
Peanut Response to Prohexadione Calcium in Three Seeding Rate–Row Pattern Planting Systems
Authors: Jordan David L. , Beam Joshua B. , Johnson P. Dewayne , Spears Jan F.
Published: July 2010

Peanut (Arachis hypogaea L.) in the USA is generally grown in single rows spaced 91 to 102 cm apart. Research suggests that pod yield can be increased by growing peanut in twin rows (18–23 cm spacing) on beds spaced 91 to 102 cm apart. Prohexadione Ca (Ca salt of 3,5‐dioxo‐4‐propionylcyclohexanecarboxylic acid) increases row visibility and in some instances increases pod yield and improves market grade factors. Research was conducted to determine response of peanut grown in three seeding rate–row pattern planting systems (single rows at a seeding rate of 120 kg ha−1 or twin rows spaced 18 cm apart on beds spaced 91 cm apart at seeding rates of 145 and 190 kg ha−1) to prohexadione Ca applied at 50% row closure. Row visibility increased and main stem height was shorter at the end of the season when prohexadione Ca was applied in most environments and for most seeding rate–row pattern combinations when compared with nontreated peanut. Pod yield and gross economic value increased 160 kg ha−1 and $96 ha−1, respectively, when prohexadione Ca was applied irrespective of the seeding rate–row pattern combination or environment. Prohexadione Ca also increased the percentage of extra large kernels (% ELK) but did not affect percentages of sound mature kernels (SMK), other kernels (OK), sound splits (SS), or total sound mature kernels (TSMK). Seeding rate–row pattern combination affected pod yield, market grade, and gross economic value although a consistent trend was not apparent.
The Use of Allelopathic Legume Cover and Mulch Species for Weed Control in Cropping Systems
Authors: Caamal‐Maldonado Jesús Arturo , Jiménez‐Osornio Juan José , Torres‐Barragán Andrea , Anaya Ana Luisa
Published: July 2010

Traditional weed control practices in Mexico use legumes as cover crops or manures. Legumes used in these practices play a dual role in agroecosystems by protecting the soil from erosion and by enriching it with organic matter and N through Rhizobium symbiosis. Farmers in the tropical regions of Mexico use Mucuna spp., Canavalia spp. and other legumes to control weeds in their fields. We conducted in vitro bioassays and greenhouse experiments to evaluate the toxic effect of four legumes velvetbean [Mucuna deeringiana (Bort) Merr.], jackbean [Canavalia ensiformis (L.) DC.], jumbiebean [Leucaena leucocephala (Lam.) de Wit], and wild tamarind [Lysiloma latisiliquum (L.) Benth.] on weed growth, and on the survival of insects and nematodes. The aqueous leachates (1%) of the four legumes were tested on three test plants by seed germination and radicle growth bioassays in petri dishes. The aqueous leachates of all four legumes exhibited strong phytotoxic effect on the radicle growth of the test plants. The effects of velvetbean and jackbean leachates were also evaluated on the survival of phytopathogenic nematodes. Both leachates had nematotoxic effects. Greenhouse experiments were conducted to evaluate the effect of the four legumes dried leaves incorporated as mulches to potting soil, on the number and biomass of weeds, and on the biomass of tomato (Lycopersicon esculentum L.) plants. The decomposition of velvetbean and jackbean leaves in potting soil significantly reduced (>50%) the development of phytopathogenic nematodes in the roots of tomato. A 5‐yr field experiment conducted at the University of Yucatan (UADY) evaluated the effect of velvetbean and jackbean used as living cover crops, and jumbiebean and wild tamarind used as dead mulches incorporated on soil surface, on weed growth, and corn (Zea mays L.) yield. The experimental field was treated with the traditional slash and burn system in February 1994. In July 1994 the experiment was performed using the local agricultural practices in a complete randomized block design with three repetitions. The treatments were: corn+velvetbean, corn+jackbean, corn+jumbiebean, corn+wild tamarind, corn+Paraquat (1,1′‐dimethyl‐4,4′‐bipyridinium ion) herbicide, corn weeded by hand, and plots without corn weeded by hand. The number, biomass, diversity, and relative importance of weeds, as well as corn yield, were evaluated. In addition, taxonomic composition of weeds was determined. All legumes reduced weed growth with velvetbean (as living cover crop) producing the largest weed biomass reduction (68%). These legumes also improved the yield of corn during the first 2 yr of the experiment. For better management of natural resources, the use of legumes as biological tools in agriculture to control weeds and improve soil conditions should be encouraged through coordinated efforts between farmers, academic, and governmental institutions.
Weed Suppression by Release of Isothiocyanates from Turnip‐Rape Mulch
Authors: Petersen Jan , Belz Regina , Walker Frank , Hurle Karl
Published: July 2010

The allelopathic potential of isothiocyanates (ITC) released by turnip–rape mulch [Brassica rapa (Rapifera Group)–Brassica napus L.] was evaluated. Six different ITCs were identified from chopped turnip–rape by HPLC‐DAD/HPLC‐MS. All plant parts contained 2‐phenylethyl‐ITC. In the shoot n‐butyl and 3‐butenyl‐ITC dominated. Younger leaves, flowers, and buds also contained small amounts of benzyl and allyl‐ITC. Furthermore, marginal amounts of 4‐pentenyl‐ITC were detected. In the soil, where turnip–rape mulch was incorporated, only low amounts of ITCs were detected. It was shown that the DT50 of ITCs in soil are very short. Germination tests with weed seeds in aqueous ITC solutions showed, that aryl‐ITCs were the most suppressive compounds. Within the alkyl‐ITCs, the activity decreased with increasing molecular mass. The susceptibility of different weed species to ITCs mainly depended on seed size. Smaller seeds tended to be more sensitive. Further studies demonstrated a high biological activity of ITCs in the vapor phase. n‐Butyl‐ITC was more suppressive in the vapor phase than in aqueous solution, while 2‐phenylethyl‐ITC showed the opposite effect. Results demonstrated that weed suppression observed in the field was probably due to the high amounts of ITCs identified in turnip–rape mulch. Isothiocyanates were strong suppressants of germination on tested species—spiny sowthistle [Sonchus asper (L.) Hill], scentless mayweed (Matricaria inodora L.), smooth pigweed (Amaranthus hybridus L.), barnyardgrass [Echinochloa crusgalli (L.) Beauv.], blackgrass (Alopecurus myosuroides Huds.), and wheat (Triticum aestivum L.)—and probably interact with weed seeds in the soil solution and as vapor in soil pores.
Response of Winter Wheat to Simulated Stand Reduction
Authors: Holen Douglas L. , Bruckner Philip L. , Martin John M. , Carlson Gregg R. , Wichman David M. , Berg James E.
Published: July 2010

Environmental stresses can reduce winter wheat (Triticum aestivum L.) stands to less than optimum densities, forcing producers to assess yield potential from early season plant densities. Our objectives were to assess changes in yield and associated traits resulting from varying spring plant densities, and to determine if these responses varied by cultivar. Three hard red winter wheat cultivars were grown at seven population densities in seven Montana environments. Plant density levels ranging from 10 to 100% of target stand were achieved for each cultivar by planting 215 seeds m−2 in the fall and replacing winter wheat seed with spring wheat seed in proportion to the desired spring survival for each treatment. Cultivars did not differ in mean spring plant density or grain yield but differed for yield components, test weight, and protein concentration. The response to increasing plant density was generally not cultivar specific, as plant density interactions with cultivar were significant only for kernels spike−1. Grain yield increased, as did spikes m−2 and kernels m−2, while kernel weight and kernels spike−1 decreased with increasing spring plant density. Response to increasing spring plant density varied with environment for all traits, but environment effects and linear and quadratic plant density terms accounted for 95% of the variation in interaction means for all traits except tillers plant−1. Maximum grain yield occurred at 140 plants m−2, and 21.5 plants m−2 produced winter wheat grain yield equal to spring wheat grain yield for the same environments.
Soybean Growth and Development as Affected by Glyphosate and Postemergence Herbicide Tank Mixtures
Authors: Nelson Kelly A. , Renner Karen A.
Published: July 2010

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.
Comparison of Late‐Season Diagnostic Tests for Predicting Nitrogen Status of Corn
Authors: Fox Richard H. , Piekielek William P. , Macneal Kirsten E.
Published: July 2010

We compared six late‐season diagnostic tests for determining N adequacy in corn (Zea mays L.) in a 3‐yr study in Pennsylvania. The six tests were: (i) the NO−3–N concentration of stalk sections at black layer; (ii) the NO−3–N concentration of stalk sections at the one‐fourth milk line growth stage (MLGS), which allows corn grown for silage to be tested; (iii) the chlorophyll meter (CM) test at the one‐fourth MLGS; (iv) the relative CM test (normalized values) at the one‐fourth MLGS; (v) a visual test based on the number of green leaves below and including the ear leaf at the one‐fourth MLGS; and (vi) a relative visual test (normalized values at the one‐fourth MLGS). We found that with a critical level of 250 mg kg−1 NO−3–N, the stalk NO−3 test separated N‐sufficient from N‐deficient sites with approximately 93% accuracy when sampling was done at either the one‐fourth MLGS or within several weeks after black‐layer formation. It appears that the 250 mg kg−1 NO−3–N critical level can be used to accurately predict N adequacy for any sampling time between the one‐fourth MLGS and a few weeks after black‐layer formation. When drought‐stressed fields were excluded or the CM readings normalized with a high‐N reference plot in the field, the accuracy of the CM test at the one‐fourth MLGS was approximately 92%. The visual test at the one‐fourth MLGS was an accurate predictor of corn N status only when visual readings were normalized with a high‐N reference plot. These results demonstrate that there are several late‐season N tests that are suitable for making relatively accurate assessments of N sufficiency for corn silage and grain yields.