bluuebunny/crossref_metadata_2025 huggingface dataset:
Timing and Rate of Ethephon Application to Two‐Row and Six‐Row Spring Barley
Authors: Bridger Gregory M. , Klinck Harold R. , Smith Donald L.
Published: July 2010

Ethephon (2‐chloroethyl phosphonic acid) reduces lodging in barley (Hordeum vulgare L.) by shortening straw, but the optimal rate and growth stage of application, both of which may interact with cultivar and environment, are unclear, especially for two‐row barley in North America. Field studies in Quebec in 1985 and 1986 evaluated the response of ‘Leger’ six‐row and ‘Birka’ two‐row barley to ethephon applied at varying rates, growth stages, and times of day. The two‐row cultivars Rodeo and Micmac were also included in one experiment. Lodging was slight or absent in all experiments. The taller Leger was usually shortened more than Birka, largely due to greater shortening of the peduncle. Late boot applications of ethephon consistently shortened straw, but the window of effective application began at the flag leaf stage and extended for more than 1 wk for Birka, while for Leger it was about 4 d, but differed phenologically between years. Heading was delayed by ethephon. In Rodeo and Birka, ethephon often reduced the degree of spike emergence from the flag leaf sheath. Incomplete spike emergence may have contributed to reduced kernel and test weights, particularly with applications from the flag leaf until the late boot stage. Ethephon increased Leger yield by up to 15% in one experiment under the favorable conditions of 1985. In 1986, a wet year, yield in one experiment was reduced by 11% by the higher ethephon rate (480 g a.i. ha−1), due to reduced spikes per square meter. Birka yield was reduced (P = 0.06) by 6% by the higher rate (480 g a.i. ha−1) in the 1986 application date study. Harvest index of Rodeo and Birka was reduced due to reduced tiller survival following application of ethephon at 480 to 500 g a.i. ha−1. Yield component compensation usually occurred between spikes per square meter and kernel weight, particularly for two‐row cultivars. Height was reduced more by applications at 0400 h and 0600 h than later in the day. Birka kernel weight was reduced with morning or evening applications, while Leger kernel weight was little affected by application time of day. In the absence of lodging and under conditions of environmental stress, ethephon applied at rates over 240 g a.i. ha−1 may reduce yields, particularly of two‐row barley, for which spike emergence may be severely reduced.
Dry Matter Partitioning in a True vs. Facultative Annual Forage Legume
Authors: Williams M. J. , Chambliss C. G. , Brolmann J. B.
Published: July 2010

Differential partitioning of photosynthate has been suggested as the reason for low early‐season (8 to 12 wk post planting) dry matter (DM) yield of ‘Savanna’ stylo [Stylosanthes guianensis (Aubl.) Sw.], a facultative annual over much of its Florida range. In a 3‐yr field study (1991–1993), the effect of planting date (April vs. June) on root‐to‐shoot ratio (g g−1), leaf‐to‐stem ratio (g g−1), and total plant weight (g) of Savanna stylo was compared with common alyceclover [Alysicarpus vaginalis (L.) DC.], a true annual, for 16 wk post planting. Only time post planting consistently affected root‐to‐shoot ratio, which declined as time post planting increased. Within years, leaf‐to‐stem ratio also declined with increasing time post planting, but, on average, Savanna stylo had a higher leaf‐to‐stem ratio than alyceclover. There was a planting date × legume × year × time post planting interaction for total plant weight. This was because total plant weights, although similar regardless of planting date or legume in 1991 and 1993, differed in 1992, when April‐planted Savanna stylo plants had greater total plant DM than June‐planted Savanna stylo or either planting date of alyceclover. Across the 16‐wk post‐planting period, there was a consistent legume × planting date interaction each year for total plant weight. This was because both Aprilplanted legumes were vegetative for the full 16‐wk post‐planting period (April–August) and total plant weight remained similar, but only Savanna stylo remained vegetative for the full 16‐wk post June‐planting period (June–October). Total plant weight of June‐planted alyceclover was lower due to flowering and leaf loss in the later part of the 16‐wk post‐planting period. These data indicate that the lower early‐season DM yield of Savanna stylo compared with alyceclover is not due to physiological differences associated with perennial and annual growth habits.
An Inexpensive Silver‐Silver Chloride Reference Electrode
Authors: Shuman Larry M. , Wander Michelle M. , Pitts Ray B.
Published: July 2010

Simple, inexpensive, and rugged reference electrodes are essential for field applications. The objective of this study was to develop an inexpensive, field‐worthy reference electrode. The electrode developed consists of a silver wire coated with AgCl held in a small glass tube filled with 4 M KCl gelled with agar. The glass tube assembly is fitted inside a larger polyvinyl chloride (PVC) tube filled with gelled (NH4)2SO4 solution and capped with a fritted soil‐contacting membrane. The millivolt output compared well (R2 = 0.999) with predicted values and values from commercial reference electrodes when paired with pH and nitratesensing electrodes. Comparisons of commercial and fabricated electrodes in two soils showed that the outputs were statistically the same, and that they were operational within a moisture range from saturation to 0.7 to 0/1 kg kg−1, depending on the soil texture. The fabricated electrodes are low cost, rugged, and stable for months when kept wet.
Windbreak Effect on Biomass and Grain Mass Accumulation of Corn: A Modeling Approach
Authors: Zhang Hehui , Brandle James R.
Published: July 2010

While numerous studies have indicated that field windbreaks both improve crop growing conditions and generally enhance crop growth and yield, especially under less favorable conditions, the relationship between the two is not clearly understood. A simple model is proposed to simulate biomass and grain mass accumulation of corn (Zea mays L.) with a windbreak shelter or without (exposed condition). The model is based on the positive relationship between intercepted solar radiation and biomass accumulation and requires plant population and hourly inputs of solar radiation and air temperature. Using published data, radiation use efficiency (RUE) was related to plant population, and a temperature function was established between the relative corn growth and temperature for pre‐silking stages. Biomass and grain mass simulated by the model agreed well with those measured for both sheltered and unsheltered plants from 1990 to 1992. Windbreaks did not significantly increase biomass or grain mass of corn for this study, even though air temperature was greater with than without shelter, probably indicating that the microclimatic changes induced by windbreaks were not physiologically significant for the 3‐yr period studied. The model has potential use in future studies to relate windbreak effects to crop yield and to evaluate windbreak designs for maximum benefits.
Pasture Soil Surface Temperature Response to Drought
Authors: Feldhake Charles M. , Glenn David M. , Peterson Donald L.
Published: July 2010

Forage persistence during severe drought is dependent on the plant's ability to maintain, at the soil surface, a viable crown from which growth regenerates upon renewed availability of water. The objective of this study was to evaluate the surface soil temperature under a tall fescue canopy during the progression into severe drought. A 2.5‐ by 2.5‐ by 2.0‐m weighing lysimeter was shielded from precipitation during rainy weather from the summer solstice through the fall equinox of 1992 at Kearneysville, WV. As evapotranspiration decreased to 23% of the calculated potential rate, there was no increase in midday soil heat flux relative to net radiation but a 2.3‐fold increase in surface soil temperature relative to levels of net radiation. During severe water stress, daytime surface soil temperatures remained from 0 to 3°C cooler than canopy temperature; however, nighttime surface soil temperatures were typically around 5°C warmer than canopy temperature, suggesting that surface soil temperature was poorly coupled to canopy temperature. Surface soil temperature under complete canopy cover may be useful for quantifying forage water stress by evaluating the magnitude of daytime changes relative to net radiation. The forage canopy provides shielding for the crown from daytime radiation and high temperatures during water stress; however, this is in part offset by the insulation provided and the resultant higher nighttime temperatures.
Influence of Soil Moisture Regimes on Subsequent Soil Manganese Availability and Toxicity in Two Cotton Genotypes
Authors: Weil Ray R. , Foy Charles D , Coradetti Carol A.
Published: July 2010

Differential plant tolerance to high levels of Mn and effects of changing soil aeration on Mn availability and are major factors in the problem of Mn toxicity in acid soils. A pot study was conducted to evaluate the effects of temporary flooding or drying on Mn forms and toxicity during subsequent cotton (Gossypium hirsutum L.) growth. Two acid, high‐Mn Hapludalfs were incubated for 16 d in flooded, air‐dry, or moist conditions, then restored to field moisture content and planted with two cotton genotypes: C‐310,73‐307 (307, Mn‐tolerant) and C‐Sgl,70‐517 (517, Mn‐sensitive). After the incubation period, levels of exchangeable Mn in the Jackland soil (pH 4.8) were 9.0, 2.6, and 0.3 mmol kg2212;1, respectively, for flooded, air‐dry, and moist pretreatments. Corresponding values for the Myersville soil (pH 5.2) were only 4.4, 0.6, and 0.1 mmol kg2212;1. Three days after seedling emergence in the flooded pretreatment, exchangeable Mn declined to 4.4 mmol Mn kg2212;1 in the Jackland soil and 0.2 mmol Mn kg2212;1 in the Myersville soil. Manganese toxicity symptoms (crinkle leaf) for both cotton genotypes developed only on the Jackland soil, with severity of symptoms following the order: flood > air dry > moist. With both soils, flooding pretreatment decreased dry matter production; generally more for 517 than for 307. Tissue Mn concentrations were 20 to 50 times higher in leaves from Jackland soil compared to those from Myersville soil. Where flooding caused toxicity symptoms in both genotypes, lower exchangeable Mn was measured in pots growing Mn‐tolerant cotton. Differential Mn tolerance of cotton genotypes was not associated with differential Mn uptake or tissue concentration.
Root Heave of Alfalfa Cultivars with Differing Levels of Resistance to Aphanomyces Root Rot
Authors: Wiersma Daniel W. , Undersander Daniel J. , Grau Craig R.
Published: July 2010

Aphanomyces root rot (ARR) (caused by Aphanomyces euteiches Drechs.) and phytophthora root rot (PRR) (caused by Phytophthora sojae M.J. Kaufmann & J.W. Gerdemann) are important diseases of alfalfa (Medicago sativa L.) grown in wet soil, but few studies have quantified the effects of ARR on alfalfa performance. An alfalfa cultivar trial of 82 cultivars with differing levels of ARR resistance was seeded in July 1993 in a naturally infested soil at Marshfield, WI. Excessive precipitation in 1993 and 1994 led to widespread expression of ARR and PRR, and large cultivar yield differences were measured. There was differential root heaving among cultivars in the 1993–1994 winter. Fall 1993 forage yield was low, but cultivars with high ARR resistance yielded >400% more than did susceptible cultivars. Root heaving in 1994 was inversely correlated with level of resistance to ARR (r = −0.68), 1993 forage yield (r = −0.72), and 1994 forage yield (r = − 0.81). Resistant and highly resistant cultivars produced 2 Mg ha−1 more forage than susceptible or low resistance cultivars. Forage yields in 1995 (a relatively dry year) did not differ with ARR resistance level. Under wet soil conditions, ARR‐resistant alfalfa cultivars can produce higher forage yields than susceptible cultivars. In addition, resistance to ARR reduces damage due to root heaving.
Increase of CO2 and Climate Change Effects on Iowa Soybean Yield, Simulated Using GLYCIM
Authors: Haskett Jonathan D. , Pachepsky Yakov A. , Acock Basil
Published: July 2010

Increases in atmospheric CO2 concentration are likely to have a significant impact on the climate and to affect the growth and development of crops. The effect of climate change on crops has to be assessed for large areas to provide information for global estimates and regional strategy development. In this study, computer simulations were done using the soybean [Glycine max (L.) Merr.] crop model GLYCIM to assess the effects of these changes on soybean yields in the state of Iowa. The ability of the model to accurately predict the effect of changes in atmospheric CO2 concentration was tested by comparing model results with a curve fit of CO2 concentration yield response derived from measured data. To simulate the effects of climate change, we used projected monthly weather variables for ambient and increased CO2 from three general circulation models (GCMs): Goddard Institute for Space Studies (GISS), Geophysical Fluid Dynamics Laboratory (GFDL), and United Kingdom Meteorological Office (UKMO). The monthly weather variables were converted to the daily weather to simulate soybean crop yields in nine crop reporting districts (CRDs) of Iowa, with and without increases in atmospheric CO2. When climate change was simulated with increasing levels of CO2 (baseline 350, 450, 550, and 650 µL L−1), yields increased. Without increases in atmospheric CO2, yields remained essentially constant in the GFDL and GISS scenarios, while decreasing by 2 to 10% in the UKMO scenario. The variability in yields among nine CRDs increased for all scenarios as climate changed and levels of CO2 increased. Overall, projected climate changes did not substantially alter simulated soybean yields. The increase in CO2 concentration in the atmosphere was the primary determinant of yield response.
Yield and Nitrogen Uptake of Rotated Corn in a Ridge Tillage System
Authors: Iragavarapu Tammiraj K. , Randall Gyles W. , Russelle Michael P.
Published: July 2010

Information is scant on the response of corn (Zea mays L.) following legumes seeded with small grains in reduced tillage systems in the upper Midwest. Our objective was to determine yield and N uptake response of ridge‐tilled corn planted after soybean [Glycine max (L.) Merr.], wheat (Triticum aestivu L.) alone, wheat with alfalfa (Medicago sativa L.), or wheat with hairy vetch (Vicia villosa Roth), compared with continuous corn. Field studies were conducted from 1991 through 1994 at two southern Minnesota locations on a poorly drained Webster clay loam (fine‐loamy, mixed, mesic Typic Endoaquoll) soil. At Freeborn, corn grown in rotation with soybean yielded highest (6.8 Mg ha−1) in 2 of 3 yr, while continuous corn usually yielded less than corn grown after other crops. Corn grown after other crops accumulated 23 to 36 kg ha−1 more N than continuous corn in 2 of 3 yr at all fertilizer‐N rates up to 135 kg N ha−1. At Waseca, corn grain yields and N uptake were generally similar among rotations, except that yields were 1.5 to 1.9 Mg ha−1 lower and total N uptake was 16 to 18 kg ha−1 less following wheat alone in 2 of 3 yr, compared with other rotations at fertilizer‐N rates up to 135 kg N ha−1. Regression analysis indicated that significant, positive, non‐N‐related rotation effects were present at Freeborn, but not at Waseca, where there was a negative effect of wheat alone on subsequent corn yield. The potential fertilizer‐N savings due to including annual alfalfa or hairy vetch could not be calculated because the N rates used in this study were insufficient to determine the economically optimum N rate. However, neither the alfalfa nor hairy vetch provided a consistent source of available N for the subsequent corn crop in this study.
Yield‐Independent Variation in Grain Nitrogen and Phosphorus Concentration among Ethiopian Wheats
Authors: Schulthess Urs , Feil Boy , Jutzi Samuel C.
Published: July 2010

New semidwarf wheat (Triticum aestivum L.) cultivars and new land management practices for Vertisols are being introduced in Ethiopia. Our objectives were to (i) determine the variation of N and P content and concentration in the grain and whether these are related to grain yield, (ii) test cultivar response to different fertility levels, and (iii) assess component traits of N and P yield. Five bread wheat cultivars and three durum wheat (Triticum durum Desf.) cultivars were sown in Exp. 1 at three locations in Ethiopia on two dates. In Exp. 2, seven of these cultivars were grown on a P‐deficient soil at four N levels (0, 20.5, 41, 61.5 kg N ha−1) and four P levels (0, 10, 20, 30 kg P ha−1); in Exp. 3, two cultivars were grown in all possible combinations of the same four N and P levels. Grain yields did not differ among cultivars, but significant variations were found for total shoot N and P, grain N and P yield, and grain N and P concentration. Cultivar differences in these traits were fairly consistent across the treatments and were corroborated by Exp. 3. The N and P concentrations in the grain were not related to grain yield (r = 0.36 NS for N; r = 0.28 NS for P). There was a positive association between grain N and P concentrations in Exp. 1 (r = 0.66; P = 0.07) and in Exp. 2 (r = 0.92; P < 0.01). The N and P grain yields were related to total shoot N and P at maturity (r = 0.99; P < 0.001). However, postanthesis accumulation of N was more closely related to postanthesis dry matter accumulation (r = 0.84; P < 0.05) than to the postanthesis accumulation of P (r = 0.56 NS). Total shoot P varied by as much as 50%. Thus, cultivar choice is an important factor determining removal of P from the soil.
Measures of Validity in Cultivar Performance Trials
Authors: Bowman Daryl T. , Watson Clarence E.
Published: July 2010

The coefficient of variation (CV) has been used for many years by researchers to determine the validity of performance trials. The premise behind the CV, that the standard deviation is proportional to the mean, compromises one of the assumptions of a normal distribution (i.e., that the sample mean and sample variance are independent). If there is a nonnormal distribution, then the data may need to be transformed, which in turn may invalidate the use of the CV. A constant CV across trials implies a relationship between the error variance and the mean such that the slope = 2.0 in the regression of In error variance on ln mean. The purpose of this paper is to stress the relationship between the error variance and mean in the CV, review this relationship in actual yield data, and examine the effects of various transformations on CVs and coefficient of determination (R2). The ln error variance regressed on In mean for several agronomic crops ranged from −0.11 for full‐season corn (Zea mays L.) to 1.31 for oat (Avena sativa L.). Although some crops had a nonzero regression coefficient for this relationship, none approached 2.0, the level that supports the hypothesis that the CV is a viable tool for comparing the relative variation of different trials. Data transformations (e.g., square root, logarithmic, angular, inverse, reverse, and addition of a constant) tend to lower CV values in most cases, but can cause dramatic increases, depending on the nature of the variance and the specific transformation. On the other hand, R2, which is a measure of the amount of variability accounted for in the model, remains relatively unaffected by most transformations. Reasonable R2 values for determining validity of performance trials may vary by location and crop species. Examination of North Carolina data revealed that discarded trials generally had R2 values less than 50%. The R2 may be affected by the size of the dataset, and so adjusted R2 maybe more useful for comparing trials of varying sizes; however, adjusted R2 will tend to be larger where there are larger differences among entries. There is no one perfect measure of the validity of trial data, but the R2 and the adjusted R2 are reasonable alternatives to the CV and should be examined along with other statistical measures when evaluating crop performance data.
Seed Maturity, Storage Time and Temperature, and Media Treatment Effects on Germination of Two Wild Sunflowers
Authors: Seiler Gerald J.
Published: July 2010

Dormancy in achenes (seeds) of wild sunflower (Helianthus) species ensures that they do not germinate in temperate climates until conditions are optimal for seedling survival. However, high achene dormancy results in low germination of achenes, precluding utilization of many wild species for domestic purposes. Interest in the use of native Helianthus species for domestic purpose such as low‐maintenance ornamentals, revegetation, cut flowers, and genetic improvement of cultivated sunflower has recently increased. The objectives of this study were to evaluate germination media to overcome dormancy and enhance germination of two annual species, H. annuus L. and H. petiolaris Nutt., and to evaluate the influence of achene maturity and storage time and temperature on germination. A 1 mM gibberellic acid (GA3) medium was the most effective stimulant in laboratory tests for enhancing germination of H. annuus. Germination of treated achenes was 81%, compared with 38% for the control. Germination of H. petiolaris achenes was 60% with the 1 mM GA3 medium, compared with 9% for the water control. This GA3 medium enhanced germination regardless of achene maturity, storage time, or storage temperature. When averaged over all media, achene maturities, and storage times and temperatures, H. annuus had a germination of 41%, compared with only 21% for H. petiolaris. The age of the achenes at harvest influenced germination. Achenes harvested 20 d after flowering generally had greater germination than those harvested 40 d after flowering, especially for H. petiolaris. Storage time and temperature could not overcome the dormancy imposed prior to germination in either species. Utilization of germination media to enhance germination of wild Helianthus species will facilitate their use for domestic purposes.
Temperature and Sowing Date Affect the Linear Increase of Sunflower Harvest Index
Authors: Bange Michael P. , Hammer Graeme L. , Rickert Kenneth G.
Published: July 2010

The linearity of daily linear harvest index (HI) increase can provide a simple means to predict grain growth and yield in field crops. However, the stability of the rate of increase across genotypes and environments is uncertain. Data from three field experiments were collated to investigate the phase of linear HI increase of sunflower (Helianthus annuus L.) across environments by changing genotypes, sowing time, N level, and solar irradiation level. Linear increase in HI was similar among different genotypes, N levels, and radiation treatments (mean 0.0125 d−1), but significant differences occurred between sowings. The linear increase in HI was not stable at very low temperatures (down to 9°C) during grain filling, due to possible limitations to biomass accumulation and translocation (mean 0.0091 d−1). Using the linear increase in HI to predict grain yield requires predictions of the duration from anthesis to the onset of linear HI increase (lag phase) and the cessation of linear HI increase. These studies showed that the lag phase differed, and the linear HI increase ceased when 91% of the anthesis to physiological maturity period had been completed.
Software for Mapping and Analyzing Weed Distributions: gWeedMap
Authors: Krueger David W. , Coble Harold D. , Wilkerson Gail G.
Published: July 2010

The spatial pattern of weeds in a field is often patchy. This pattern can be visualized with maps created by geographical information system (GIS) software. However, this software is often difficult to use and/or expensive, especially if not all of the GIS functionality is needed. The objective of this project was to develop a means of easily and economically generating weed maps. This was accomplished by creating a PC‐based Windows software tool to generate weed maps from scouting information. The scout enters weed data that has been collected in a gridded, systematic sampling protocol. From this information, the program creates a map for each weed species in the field. Scouting data can be density, percent cover, or any other type of measurement. Five data ranges are displayed on the map, with the user specifying the data values and map colors associated with each range. Various statistics are calculated, such as the average density of each species. Weed diversity in each field is determined with Shannon's diversity index and evenness index. These indices are also calculated with the density data weighted by the competitiveness of each weed species. This gives the weed ecologist a quantitative measure of the competitive diversity, which is related to the impact of the weed population on yield loss.
Thrips Injury Can Reduce Peanut Yield and Quality under Conditions of multiple Stress
Authors: Funderburk Joe E. , Gorbet Dan W. , Teare Iwan D. , Stavisky Julianne
Published: July 2010

Severe injury from tobacco thrips [Frankliniella fusca (Hinds)] to seedling peanut (Arachis hypogaea L.) has not been documented to reduce yield and quality. However, thrips injury may be economically important when combined with another factor, such as postemergence herbicide injury. This note reports results of a field experiment in which control of tobacco thrips during an unusually dry early season greatly increased peanut seed yield and quality. ‘Florunner’ peanut was grown using preplant and postemergence herbicides for weed control. Treatments consisted of an untreated control and four labeled insecticides applied at planting or soon after crop emergence. Populations of adult tobacco thrips were significantly suppressed by aldicarb [2‐methyl‐2‐(methylthio) propionaldehyde O‐(methylcarbamoyl) oxime]; all insecticides significantly suppressed immature thrips. Aldicarb, the most efficacious insecticide treatment, significantly improved peanut yield by 32% and quality as determined by percentage of total sound mature kernels. All but one of the remaining insecticide treatments significantly improved seed yield, with increases ranging from 9 to 31%. Rainfall was extremely low early in the growing season, and (based on 41 yr of records at the site) drier conditions occur 10% of the time. This is a frequency great enough to matter, but low enough to make further research difficult. The observations reported here suggest that early‐season moisture stress intensifies peanut yield and quality losses associated with combined injury from thrips and postemcrgence herbicides.
Medic Planting Date Effect on Dry Matter and Nitrogen Accumulation When Clear‐Seeded or Intercropped with Corn
Authors: Jeranyama Peter , Hesterman Oran B. , Sheaffer Craig C.
Published: July 2010

Intercropping annual forage legumes with row crops has been proposed as a strategy to control erosion, suppress weeds, and contribute biological N to companion or subsequent crops. This experiment evaluated the effect of planting date of two annual medic species [burr and snail medic, Medicago polymorpha L. and M. scutellata (L.) Mill.] on yield and N accumulation of both medic and interseeded corn (Zea mays L.). Medics were either clear‐seeded (i.e., monocropped) or interseeded into corn at five planting dates from 7 May to 13 July in each of two years at East Lansing, MI, on a Capac loam (fine‐loamy, mixed, mesic Aerie Endoaqualf). Clear‐seeded medic produced up to 3 Mg ha−1 of dry matter at 60 d after planting. In the interseeding system, medic dry matter yields were only 50% of yield in a clearseeded system. Average aboveground medic N concentration was 50 and 20 kg ha−1 in clear‐seeded and interseeded systems, respectively. Interseeding at corn planting produced the greatest medic dry matter, but also was associated with the greatest reduction in corn yield. Corn yields were not reduced by interseeding medic 28 d after com planting. Interseeding medic into corn was associated with a positive yield response (3–25%) of subsequent corn grain. Medics reduced fertilizer needs of corn in the subsequent year by 37 kg N ha−1.
Field Validation of Soil Solute Profiles in Irrigated Cotton
Authors: Norton E. Randall , Silvertooth Jeffrey C.
Published: July 2010

Management of water and fertilizer N are important aspects of cotton production in the desert Southwest. GOSSYM, a cotton growth simulation model, has been used extensively to manage these inputs. Our objectives were to further validate GOSSYM by comparing model‐simulated and measured soil NO‐3‐N profiles, to evaluate GOSSYM's potential as a management tool under irrigated growing conditions in the desert part of the U.S. Cotton Belt, and to address questions about the way GOSSYM simulates NO‐3‐N movement through the soil profile in relation to irrigation water management (which in turn affects prediction of plant growth and development). We compared measured profiles of NO‐3‐N with GOSSYM‐simulated profiles. Soil profile samples were obtained from an existing N‐management field study, a split‐plot within a randomized complete block design. Mainplots were upland and pima cotton (G. hirsutum L. cv. DPL 5415 and G. barbadense L. cv. Pima S‐7, respectively). Subplots were a check (0 fertilizer N) and three other N‐management strategies. The cotton was grown on a Casa Grande sandy loam [fine‐loamy, mixed, hyperthermic Typic Natrargid (reclaimed)] near Maricopa, AZ, in 1994 and 1995. Fertilizer N rates ranged from 0 to 350 kg ha−1 in 1994 and 0 to 392 kg ha−1 in 1995. Soil samples taken to a depth of 120 cm in 30‐cm increments were analyzed for NO‐3‐N. Comparisons of simulated and actual NO‐3‐N profiles revealed tendencies in GOSSYM to overestimate NO‐3‐N leaching out of the effective rooting zone, resulting in simulated N stresses midseason. When GOSSYM simulated an N stress, between 50 and 75% of the simulated soil NO‐3‐N values were greater than the measured values, yet the simulated N stress still occurred. This indicates possible limitations in GOSSYM's ability to adequately predict N uptake by plants. The dynamic soil N portion of the model needs further refinement, particularly for cotton production under irrigated desert conditions.
Foliar Fertilization of Soybean at Early Vegetative Stages
Authors: Haq Mazhar U. , Mallarino Antonio P.
Published: July 2010

The yield response of soybean [Glycine max (L.) Merr.] to foliar fertilization during reproductive stages has been inconsistent. This study evaluated soybean responses to foliar applications of a 3–8–15 (N–P–K) fertilizer at early vegetative stages in 48 trials conducted on Iowa soils that tested mostly optimum or above in P and K. In 1994, the treatments were a control, single applications of 19, 28, or 38 L ha−1 at the V5 stage, and 38 or 56 L ha−1 split as one‐half at the V5 stage and one‐half 8 or 9 d later. In 1995 and 1996, only the single rate of 28 L ha−1 and the split rate of 38 L ha−1 were used. The lowest and highest volumes used encompassed N‐P‐K rates of 0.8‐2.1‐3.9 to 2.4‐6.3‐11.7 kg ha−1. All treatments were replicated four times. Some or all treatments increased yields in seven sites and decreased yields at two sites. Mean yield increases were 60 kg ha−1 in 1994 (not significant), 30 kg ha−1 in 1995 (not significant), 60 kg ha−1 in 1996, and 54 kg ha−1 across the 48 sites. Differences between treatments were small and inconsistent, and the single application of 28 L ha−1 (one of the lowest rates used) produced the highest mean yield increase across all responsive sites (375 kg ha−1). In 1994, the higher yield responses occurred on ridge‐till and no‐till fields and when the P concentration of young plants was low. No treatment caused leaf burning. Foliar fertilization seldom increased P and K concentrations of leaves at the R2 growth stage and did not affect plant maturity, grain moisture, or the weight of grains. No simple set of measurements explained the occurrence of yield responses. Results of factor and regression analyses suggested that responses tended to occur in soils with high cation exchange capacity, when plant‐available P was low, and/or when rainfall in spring and midsummer was low. This group of variables explained only 14 to 23% of the responses in different years, however. Effective use of foliar fertilization of soybean at early growth stages in areas with predominantly high‐testing soils requires further research to identify the conditions under which positive responses are more likely.
Mechanisms of Corn Tolerance and Velvetleaf Suppressive Ability
Authors: Lindquist John L. , Mortensen David A. , Johnson Blaine E.
Published: July 2010

Crops that better tolerate weed competition or preempt resources from weeds may reduce dependence on herbicides for weed control and benefit an integrated weed management program. Irrigated field experiments were conducted to identify morphological traits of corn (Zea mays L.) that enhance its tolerance and weed suppressive ability. Two old (circa 1940) and two modern corn hybrids were grown in mixture with five target densities of velvetleaf (Abutilon theophrasti Medik.) in two years. Corn height and leaf area index (LAI) were measured periodically throughout the growing season. Vertical leaf area distribution was measured at corn anthesis. Quantitative estimates of these traits were obtained for each experimental unit using linear and nonlinear regression analysis. Magnitude of the correlation between these trait estimates and corn yield reduction in mixture with velvetleaf or velvetleaf seed capsule production was used as an indicator of the importance of each trait to the enhancement of corn tolerance or velvetleaf suppressive ability. Canopy traits having highest correlation with corn relative yield in 1995 were maximum LAI (r= −0.38) and crop density (r = −0.24). Those with highest correlation in 1996 were crop density (r = ‐0.36), degree days accumulated between emergence and 50% maximum height (r = 0.34) and LAI (r = 0.19), and vertical leaf area distribution (0.49). Corn canopy traits were not correlated with velvetleaf seed production in 1995. However, vertical leaf area distribution (r = 0.60), maximum LAI (r = −0.32), and corn density (r = −0.26) were correlated with velvetleaf seed production in 1996. Results suggest that increasing maximum corn LAI, rate of canopy closure, or height at which leaf area occurs in the canopy can improve corn tolerance and velvetleaf suppressive ability. These traits can be modified by varying cultural practices such as row spacing and population density, or through breeding.
Establishment of Corn in Rotation with Alfalfa and Rye: Influence of Grazing, Tillage, and Herbicides
Authors: Morris Jennifer L. , Allen Vivien G. , Vaughan David H. , Luna John M. , Cochran Michele A.
Published: July 2010

Integrating livestock into crop rotations offers alternatives for grazing and crop management. Grazing, tillage, and herbicides were evaluated in a randomized block design with four replications for transition from alfalfa (Medicago sativa L.) to corn (Zea mays L.). For the control (T1), alfalfa was overseeded with rye (Secale cereale L.) in October, and corn was no‐till established in early May. For alternative treatments, alfalfa was grazed by cattle (Bos taurus) from July until October. Treatments were: T2, disking prior to rye planting, grazing rye for 12.5 d prior to corn planting, with dicamba (3,6‐dichloro‐2‐methoxybenzoic acid) applied after corn planting; T3, no spring grazing, with glyphosate [N‐(phosphonomethyl)glycine] applied before corn planting; T4, same as T3 plus grazing rye for 1.8 d in early spring; T5, autumn application of glyphosate to alfalfa before planting a rye‐hairy vetch (Vicia villosa Roth) cover crop; and T6, autumn disking before planting rye‐hairy vetch with no herbicides used. System T2 increased suppression of alfalfa and corn plant populations compared with shorter grazing periods. System T4 increased corn plant populations compared with no spring grazing (T3; 3.5 vs. 3.0 plants m−1). Autumn disking (T6) generally provided less control of alfalfa than autumn application of glyphosate (T5). Applying glyphosate before corn planting (T3 and T4) improved corn populations and growth, compared with autumn glyphosate or disking (T5 and T6), and resulted in corn forage yield (23 Mg ha−1) similar to conventional no‐till establishment (T1; 22 Mg ha−1). Herbicides completely killed alfalfa, but grazing alfalfa and rye reduced alfalfa persistence. Grazing could provide benefits to corn production systems while providing forage for cattle.
Simulation of Water Uptake in Maize, Using Different Levels of Process Detail
Authors: Jara Jorge , Stockle Claudio O.
Published: July 2010

Daily crop water uptake was simulated using algorithms from three crop simulation models, CropSyst, CERES, and EPIC (listed in order of decreasing process detail). Simulated results were compared with measurements of sap flow and soil water content for maize (Zea mays L.) growing at Prosser, WA, under a wet and a dry irrigation treatment, and with soil water content measurements for nonirrigated maize at Davis, CA. At Prosser, the dry treatment imposed only a mild stress; at Davis, the stress was severe. Simulation variables such as maximum crop evapotranspiration, root density by soil layer, and green leaf area index were provided as daily input. At Prosser, all algorithms performed similarly when simulating crop water uptake. For the wet treatment, the root mean square error (RMSE) was 0.27 to 0.28 mm d−1, and the relative error [RE = 100 (RMSE/Measured average)] was 7.0 to 7.2%. For the dry treatment, simulation accuracy decreased (RMSE = 0.33–0.38 mm d−1; RE = 9.0–10.5%). The time evolution of water uptake simulated by CropSyst better depicted the measured sap flow (water uptake) difference between wet and dry treatments. Simulations of soil water content by layer for the wet treatment, compared with measurements available for 17 d, yielded RMSEs from 0.022 to 0.024 m3 m−3 and REs from 8.5 to 9.2%. For the dry treatment (12 d of measurements), the best simulations were obtained with the water uptake algorithms from CropSyst and CERES, with RMSE = 0.015 m3 m−3 (both models) and RE = 6.4% (CropSyst) and 6.6% (CERES), compared with RMSE = 0.019 m3 m−3 and RE = 8.1% for EPIC. Under the severe water stress at Davis, CropSyst had the best performance. This algorithm simulated changes in soil water content by layer (8 d of measurements available) with RMSE of 0.011 m3 m−3 and RE of 5.0%, while the RMSE and RE values for CERES and EPIC were 0.016 and 0.019 m3 m−3 and 7.6 and 9.0%, respectively. The more process‐oriented algorithm (CropSyst) showed an increasing advantage as water stress severity increased. The EPIC algorithm had the poorest performance under water stress. This could be improved by modifying the value of the water extraction distribution parameter in EPIC, but with this change the wet treatment simulations at Prosser deteriorated substantially, indicative of limitations in EPIC'S simple approach.
Assessing Soil Quality in the Rolling Pampa, Using Soil Properties and Maize Characteristics
Authors: Maddonni Gustavo A. , Urricariet Susana , Ghersa Claudio M. , Lavado Raúl S.
Published: July 2010

Intensive land use in the Rolling Pampa of Argentina appears to be reducing soil quality for crop production. Our objective was to establish the best edaphic and/or plant indicators for assessing soil quality with regard to functioning as a medium for crop production. Nine fields with Typic Argiudoll soils were selected for evaluation based on agriculture history and apparent soil structural stability. Soil chemical and physical properties and maize (Zea mays L.) vegetative and reproductive characteristics were measured. Multivariate statistical analyses were applied to the data to determine potential indicators of soil quality. Soil and crop variables explained more than 70% of the variance in soil quality among agricultural histories. The edaphic indicators that showed the greatest change from pristine conditions were organic C, total N, P, Mg, K, B, Ca, and Zn contents and cation exchange capacity. Using crop variables, leaf length, maximum fraction of intercepted photosynthetically active radiation, grain yield, kernel number, prolificacy, and total dry matter at physiological maturity, served to establish a soil quality gradient. Variation of maize growth was associated with edaphic indicators of soil quality and revealed the importance of soil aggregate stability in determine changes in soil quality for crop production.
Cultivar Effects on Oat–Berseem Clover Intercrops
Authors: Holland J. B. , Brummer E. C.
Published: July 2010

Oat (Avena sativa L.) intercropped with berseem clover (Trifolium alexandrinum L.), an annual forage legume, has economic and biological advantages for use as a rotation crop in the north‐central USA. To investigate the effects of different oat and berseem clover cultivars on the productivity of the intercrop and its components, and to test for interspecific cultivar interactions, we evaluated binary combinations and monocultures of a sample of oat and berseem clover cultivars in three Iowa environments. Oat cultivars varied for oat traits, effects on clover stands and yield, and total intercrop biomass. Berseem clover cultivars varied for forage yield, stand, maturity, damage due to disease and insects, and effects on intercrop biomass. In one environment, only one of seven berseem clover cultivars survived after the first forage harvest. Adding oat to berseem clover reduced total forage and weed yields, clover stands, and relative maturity of clover, but increased total crop biomass and forage plant health. Adding berseem clover to oat did not reduce oat grain or straw yields, and in one year increased oat test weight. Cultivar rankings of each species differed in monoculture vs. intercrop. Interspecific cultivar interactions were not significant for most traits. Greater genetic improvement in the productivity of the oat‐berseem clover intercrop will more likely be achieved by improvement of general agronomic productivity of berseem clover than by trying to enhance specific ecological combining ability of particular oat and berseem clover cultivar combinations.
Weed Population and Crop Yield Response to Recommendations from a Weed Control Decision Aid
Authors: Hoffman Melinda L. , Buhler Douglas D. , Owen Micheal D. K.
Published: July 2010

Selecting among the diverse options available to manage weeds requires varied knowledge. This study field‐tested the performance of a decision aid model that integrates biological and economic factors to make weed control recommendations. The model was parameterized using data from the literature and subjected to sensitivity analysis. Tactics generated from the resulting model were compared with standard‐herbicide weed control in continuous corn (Zea mays L.) having a long‐term history of various tillage and herbicide application regimes. The model recommended preemergent and postemergent weed control based on weed seed and weed seedling densities, respectively. Using standard‐herbicide weed control resulted in fewer weed seeds in the soil each year compared with model‐based weed control. Variation among model‐based weed control treatments applied to plots with different management histories was eliminated over the course of the study as weed populations shifted in response to weed control practices. The result was a 98% relative abundance of foxtail (Setaria spp.) seedlings after 3 yr of model‐based treatments, compared with 70% in standard‐herbicide treatments. In 1994, the model reduced herbicide use and weed control treatment costs, but often reduced corn yields and net economic returns. In 1995, model‐based treatments maintained or increased corn yields and net returns. In 1996, however, model‐based treatments consistently reduced corn yields and net returns. Variability in control treatment effectiveness and weed‐crop interaction greatly affected the performance of the model. The use of decision‐aid models in weed management is still a developing technology. Interactions of the weed seed bank, weed emergence, treatment effectiveness, weed‐crop interference, and environmental conditions are very complex. The model could become a valuable tool for producers if consistency of weed control were improved by better understanding and modeling of threshold levels and accounting for weed seed production and by adding data on weed emergence, seed production, yield loss, and control efficacy.
Residue Management of Perennial Ryegrass and Tall Fescue Seed Crops
Authors: Young William C. , Mellbye Mark E. , Silberstein Thomas B.
Published: July 2010

Regulations on open‐field burning have forced grass seed growers to adopt alternatives for postharvest residue management. Experiments were conducted on fields established by grass seed producers in western Oregon to compare effects of (i) mechanical straw removal and flail‐chopping the stubble (flail‐chop), (ii) mechanical straw removal and propane‐burning the stubble (propane‐burn), and (iii) open‐field burning the residue (open‐burn) on seed yield the following year. Treatments were tested on three consecutive crop years of perennial ryegrass (Lolium perenne L. cv. Regal and Pleasure) and tall fescue (Festuca arundinacea Schreb. cv. Martin and Rebel II). Seed yield components were measured to identify the components through which treatments affect yield. Treatments did not affect seed yield of Regal perennial ryegrass and Martin tall fescue in any crop year. Third‐crop seed yield of Pleasure perennial ryegrass was 15% higher for the open‐burn than for the flail‐chop treatment; fourth‐crop seed yield was 12% higher for the open‐burn treatment than for either flail‐chop or propane‐burn. Across years, seed yields of Rebel II tall fescue for propane‐burn and open‐burn treatments were 8 and 12% greater, respectively, than for flail‐chop. Where seed yields were affected, differences among treatments were through changes in seed number per unit area (seeds m−2), but seed weight was relatively stable. Treatments did not affect the number of fertile tillers in any cultivar. Variations in seed number were apparently due to treatment effects on the number of seeds set per tiller. We conclude that the need for postharvest residue burning in perennial ryegrass and tall fescue is cultivar specific. Mechanical residue removal is apparently as effective as open‐field burning for maintaining high seed yields in some cultivars of these grasses.