bluuebunny/crossref_metadata_2025 huggingface dataset:
Leaf Expansion in Field‐Grown Sunflower in Response to Soil and Leaf Water Status
Authors: Sadras V. O. , Villalobos F. J. , Fereres E.
Published: July 2010

Leaf responses to soil water deficits in controlled environments may be mediated by nonhydraulic root signals (RS). The aim of this study was to evaluate in the field the effects of RS and leaf water potential (Ψ1) on leaf expansion rate (LER) of sunflower (Helianthus annuus L.). Two experiments were performed on a deep sandy‐loam soil (Typic Xerofluvent) in a Mediterranean environment under spring (Exp. 1) and summer conditions (Exp. 2). WET and DRY treatments were established at the 16th‐leaf stage in both experiments. WET plots were irrigated daily with an amount of water equal to the reference evapotranspiration of the previous day. DRY plots received no water during the treatment period which was maintained until LER declined to about 30% of the WET controls. A split‐root (SR) treatment with the root zone divided in dry and wet sections was included in Exp. 2. Soil water content (θa), LER and Ψ1 were measured. Responses of LER to soil drying were better described by Ψ1 than by plant available water (PAW); i.e., the response of LER to PAW depended on evaporative demand, whereas a single regression of Ψ1 on LER fitted all the data (P < 0.001). Leaf expansion rate and Ψ1 of DRY plants began to decline with respect to that of WET plants at similar PAW thresholds. The soil water content in the dry soil zone of the SR plots was similar to that in the DRY plots during the first week of treatment whereas θa in the wet zone allowed SR plants to maintain a water status similar to that of WET controls. Split‐rooted plants did not behave as DRY controls, as expected in the case of a significant root signal effect, but maintained LER similar to the WET plants. It is concluded that, under the conditions of the present experiments, hydraulic effects were probably of more importance than nonhydraulic root signals in the regulation of sunflower leaf expansion.
Seed Quality and Yield of Early‐Planted, Short‐Season Soybean Genotypes
Authors: Mayhew W. L. , Caviness C. E.
Published: July 2010

A new soybean [Glycine max (L.) Merr.] production system, in which early‐maturing indeterminate cultivars are planted in early April, has been used by some growers in Arkansas and other Southern states. The intent is to escape late‐season moisture deficits. This research was conducted to measure seed yield and seed quality (as determined by seed germination and viability) of Maturity Group (MG) III and IV genotypes planted in early April of 1989 and 1990 under nonirrigated conditions at three locations in Arkansas (approximately 34° to 36° N lat). Yields across the six environments averaged 1816 and 1992 kg ha−1 for four MG III and four MG IV cultivars, respectively. ‘Williams 82’ produced the highest average yield (2072 kg ha−1) in MG III and ‘Competitor’ produced the highest (2110 kg ha−1) in MG IV. Seed germination was 32 and 39% for MG III and IV, respectively (average of six environments). Poor seed germination was associated with infection with Phomopsis longicolla T.W. Hobbs, one of the causal organisms of phomopsis seed decay (PSD). PI 417479 had significantly less PSD‐infected seed than the other genotypes in three environments and averaged only 4% infection when all environments were included. Yield of early‐planted, nonirrigated MG III and IV indeterminate cultivars was = 16% greater than for nonirrigated conventional cultivars, but the seed produced had low germination and viability. Highyielding, early‐maturing cultivars with resistance to PSD need to be developed if this new production system is to be a viable management option for growers in the soybean production region of the U.S. South.
Tillage and Weed Management Affects Winter Wheat Yield in an Integrated Pest Management System
Authors: Young F. L. , Ogg A. G. , Papendick R. I. , Thill D. C. , Alldredge J. R.
Published: July 2010

Adoption of conservation practices by U.S. Pacific Northwest growers to meet farm bill legislation for erosion control is limited by the inability to control weeds and other pests in cereal and pulse crops. A 6‐yr, 16‐ha integrated pest management field study was conducted in the subhumid wheat area of the Pacific Northwest from 1985 through 1991 to develop a crop production system that controls weeds effectively and reduces soil erosion. Farm‐size machinery were used to till, plant, and harvest crops grown in either a continuous wheat (Triticum aestivum L.) sequence or a 3‐yr rotation of winter wheat‐spring barley (Hordeum vulgare L.)‒spring pea (Pisum sativum L.) in conservation and conventional tillage systems. Minimum, moderate, and maximum weed management levels were superimposed over each cropping by tillage system. Position of winter wheat within a cropping system influenced yield so that wheat produced more grain following spring pea > spring wheat >> winter wheat. Insects and root diseases were not yield‐limiting factors in either conventionally tilled monoculture wheat or no‐till wheat in the 3‐yr cropping system. Yield of winter wheat in the conventionally tilled, continuous wheat system was similar for all three weed management levels. Yield of winter wheat in conservation tillage systems increased at both the moderate and maximum level of weed management compared with the minimum level. No‐till winter wheat planted after either pea or spring wheat at the moderate and maximum weed management levels yielded a minimum of 605 kg ha−1 more than conventionally tilled wheat at the same management levels.
Water Use by Annual Green Manure Legumes in Dryland Cropping Systems
Authors: Biederbeck V. O. , Bouman O. T.
Published: July 2010

Data on plant water use and soil water depletion by green manure legumes are needed to develop sustainable cropping systems in a semiarid environment. The objectives of this study were to determine: (i) seasonal water use by legumes, (ii) their water use efficiency (WUE), and (iii) residual soil water contents after legume growth compared with summerfallow and continuous spring wheat (Triticum aestivum L.). Black lentil (Lens culinaris Medikus), Tangier flatpea (Lathyrus tingitanus L.), chickling vetch (Lathyrus sativus L.), and feed pea (Pisum sativum L.), were seeded into wheat stubble with snow trap strips on an Orthic Brown Chernozem soil (Aridic Haploborolls) at Swift Current, SK, from 1984 to 1990. Legume water use exceeded that of fallow at 4 to 6 wk after seeding. When legumes were tilled into the soil at full bloom, differences in water content between cropped treatments and fallow were largest and most consistent in the top 0.6 m, suggesting that the legumes extracted water primarily from this depth. In an extreme drought year, substantial water depletion occurred below 0.6 m. Water use efficiency of legumes was 11 to 29 kg ha−1 mm−1, similar to that of spring wheat. Feed pea and chickling vetch used water more efficiently than the other legumes or N‐fertilized wheat. Significant differences in WUE across years were related to differences in DM production. Soil water contents above the 0.6‐m depth in late fall following green manuring were 62 to 82% that of fallow and increased over winter to 79 to 103% of fallow. Subsoil water was, on average, recharged after wheat to only 68% but following green manure to 81% of fallow. Partial fallow replacement with legumes would reduce the risk of erosion and nutrient leaching and minimize the hazard of salinization and eutrophication of downstream ecosystems.
Influence of Residue Removal Method and Herbicides on Perennial Ryegrass Seed Production: I. Weed Control
Authors: Mueller‐Warrant George W. , Young William C. , Mellbye Mark E.
Published: July 2010

Grass seed production in the Pacific Northwest is in transition from reliance on open‐field burning to systems integrating mechanical removal of postharvest crop residues with chemical weed control. Field tests of the ability of these systems to meet current seed certification standards while maintaining normal seed yields were initiated in 1989. Fourteen herbicide treatment sequences plus an untreated check were evaluated under five residue removal systems at two sites during two consecutive growing seasons. Residue removal methods were three nonburn systems varying in thoroughness of residue removal and two methods of burning. Among the nonburn systems, adequate control of volunteer perennial ryegrass (Lolium perenne L.), the most abundant weed in all tests, was most readily achieved in plots where residue was most thoroughly removed. Herbicide treatments providing the best weed control in both years at both sites included preemergence (PRE) metolachlor [2‐chloro‐N‐(2‐ethyl‐6‐methylphenyl)‐N‐(2‐methoxy‐1‐methylethyl) acetamide] followed by postemergen (POST) oxyfluorfen [2‐chloro‐1‐(3‐ethoxy‐4‐nitrophenoxy)‐4‐(trifluoromethlyl)benzene)] plus diuron [N'−3, dichlorophenyl)‐N,N‐dimethylurea], PRE metalochlor followed by POST diuron, and PRE pendimethalin [N‐(1‐ethylpropyl)‐3,4‐dimethyl‐2,6‐dinitrobenzenamine] followed by POST oxyfluorfen plus metribuzin] [4‐amino‐6‐(1,1‐dimethylethyl)‐3‐(methylthio)‐1,2,4‐triazin‐5(4H)‐one]. PRE pendimethalin followed by POST oxyfluorfen plus diuron provided adequate weed control in most residue removal systems, but was marginal in the least thorough residue removal system. With properly chosen herbicide treatments, seed certification standards for perennial ryegrass can be met without field burning.
Growth and Development of Soybean Isolines that Differ for Maturity
Authors: Wilcox John A. , Wiebold William J. , Kephart Kenneth D. , Niblack Terry L.
Published: July 2010

Isolines for maturity within a common background may be useful in research that attempts to determine the effect of maturity group adaptation on soybean [Glycine max (L.) Merr.] growth or yield. Although the effects of maturity genes on soybean phenology have been studied extensively, little is known about their effects on other soybean characteristics. Field experiments were conducted near Columbia, MO, in 1991 and 1992 to determine the effects of three major maturity genes on growth and development of soybean. Four near‐isogenic strains (isolines) were replicated four times in a completely randomized design: L71‐920 (e1e2e3), Clark (e1E2E3), L74‐441 (E1E2e3), and L67‐1474 (E1E2E3). Vegetative and reproductive characteristics were recorded for five plants within each plot. Late‐maturing isolines were taller and had more leaves than early‐maturing isolines, but stem growth and leaf initiation rates were similar. Late‐maturing isolines produced more flowers and pods because they had more nodes than early‐maturing isolines. Late‐maturing isolines produced more than 25% of total yield on branches, whereas early‐maturing isolines produced approximately 10% of total yield on branches. Because the isolines used in this study had consistent differences for plant phenology, they can be useful components of experiments that include maturity as a factor. However, changes in phenology also changed plant morphology.
Production of Prenuclear Minitubers of Potato with Peat‐Based Arbuscular Mycorrhizal Fungal Inoculum
Authors: Niemira Brendan A. , Safir Gene R. , Hammerschmidt Raymond , Bird George W.
Published: July 2010

Prenuclear minitubers of potato (Solanum tuberosum L.) are the source material used to produce field‐grown seed potatoes. Seed potatoes are in turn planted by commercial growers to produce potatoes for fresh packing and processing. Arbuscular mycorrhizae (AM) have been demonslrated to increase yield in low‐input systems. This study was conducted to determine whether and how a commercial AM inoculum influences prenuclear minituber production under high‐input commercial conditions. A peat‐based medium containing the mycorrhizal fungus Glomus intraradix was tested in a commercial minituber greenhouse production facility. This medium increased yields of the most valuable sizes of prenuclear minitubers by 84%, and increased total prenuclear minituber yield by 49% when compared with conventional peat‐vermiculite media under commercial growing conditions. Potato plants grown in this mycorrhizal medium had more uniform stolon development, as well as stolons 39% longer than plants grown in the conventional medium. These yield increases and morphological changes occur in the presence of very low levels of mycorrhizal colonization, and there was no evidence of the enhanced plant P nutrition generally associated with mycorrhizal symbiosis. These effects may indicate the presence of a hormonally mediated plant response to the mycorrhizae that results in more uniform stolon growth and an increase in tuber initiation.
A Portable Electronic Device for Evaluating Root Lodging Resistance in Maize
Authors: Fouéré Alain , Pellerin Sylvain , Duparque Annie
Published: July 2010

Because climatic conditions conducive to natural lodging of maize (Zea mays L.) are sporadic and unreliable, a need exists for methods of evaluating the resistance of genotypes to root lodging. A portable electronic device was built for horizontal pushing resistance measurements on individual plants. The apparatus simultaneously records the angle of inclination and the resistance torque of the plant during an artificial pushing test. The device consists of a support, a force sensor, an angle sensor, and a control head. Data logging is possible by using a microprocessor‐based system. Data may be transferred to a computer using an RS232 serial transfer protocol. The time required for the test in field conditions is approximately 1 min per plant. Preliminary results obtained on 14 maize genotypes grown in three field environments showed that genotypes susceptible to root lodging were characterized by low average values of their maximum resistance torque.
Cover Crops Affect Sorghum Seedling Growth
Authors: Dabney Seth M. , Schreiber Jonathon D. , Rothrock Craig S. , Johnson Joseph R.
Published: July 2010

Recently killed cover crops often interfere with crop seedling growth. Controlled‐environment and field studies were conducted to characterize the nature and persistence of cover crop interference with sorghum [Sorghum bicolor (L.) Moench] seedling growth and to test several seed‐zone management practices that might alleviate detrimental effects. Germination, root and shoot length, and disease incidence of sorghum germinated at 25°C for 5 d in soil collected 2, 4, 7, 14, 23, and 32 d after killing cover crops indicated legume cover crops were more detrimental to seedling growth than were nonlegumes. Surface residues, subsurface residues, and residue leachates contributed to the deleterious effects. Seedling shoot disease incidence of 50% persisted through 32 d when legume residues were mixed into soil or placed on top of soil at planting, but disappeared by 7 to 14 d if residues were removed. Pathogenic organisms isolated from lesions on seedlings indicated legume cover crops increased damage due to Rhizoctonia solani Kühn. In a no‐till field study, stand density was reduced 15% and aboveground seedling dry weight was reduced 45%, from 85 to 45 mg plant−1 28 d after planting, when sorghum was planted 1 d after killing crimson clover (Trifolium incarnatum L.) compared with planting 21 d or longer after killing. Insecticide, activated charcoal, or CaO2 seed coating improved sorghum stand density 15%, but did not affect seedling size. In‐furrow fungicide drench had no effect on stand density, but phytotoxic effects of the fungicide reduced shoot and root growth rates in both field and controlled‐environment studies. Residue removal combined with selected in‐furrow treatments may allow the interval between cover‐crop killing and successful no‐till planting to be reduced to less than 7 d.
Evaluation of a Field Test Kit for Measuring selected Soil Quality Indicators
Authors: Liebig Mark A. , Doran John W. , Gardner John C.
Published: July 2010

A field soil quality test kit was developed to permit rapid assessment of numerous soil characteristics recognized as basic indicators of soil quality. This study was conducted to determine the accuracy and precision of indicator measurements with the field soil quality test kit. Data collected with the test kit were compared with that from standard laboratory analyses using soils from grassland and cropland on two farms in Stutsman County, North Dakota. Results obtained with the test kit for electrical conductivity, soil pH, soil nitrate, and gravimetric water content compared well with those found by standard laboratory analyses. Significant differences in soil respiration between the field and laboratory methods were attributed to the inclusion of root respiration in the test kit measurement and to differences in sampling time, disturbance, and soil depth. Repeated test kit measurements were, for the most part, no more variable than standard laboratory analyses except when the water status of soils neared saturation. This preliminary evaluation demonstrated the field test kit to be an effective screening tool for point‐scale assessment of soil quality by providing accurate and precise data over a range of soil conditions.
Yield Components and Forage Quality of Common Vetch during Pod Filling
Authors: Caballero Rafael , Barro C. , Rebolé A. , Arauzo M. , Hernaiz P. J.
Published: July 2010

Common vetch (Vicia sativa L.) is a high‐quality alternative forage legume in rainfed areas of the Mediterranean basin. Determining harvest strategies to maximize yield of available nutrients must include an assessment of morphological development, forage and grain yields, and changes in forage quality during seed filling. Field studies were conducted near Madrid, Spain, during the 1991–1992 and 1992–1993 growing seasons on a Typic Xerofluvent Entisol soil. Common vetch was sown in November and harvested in May and June of the following year. Maturity stages during pod filling were defined by progressively higher seed dry matter (DM) concentration (full bloom and 250–300, 450–550, and >800 g kg−1 seed DM). Total herbage, seed, and crude protein yields were compared. Measurements of plant partitioning, acid‐detergent fiber, and acid‐detergent lignin were carried out by harvesting individual plants at seven maturity stages, similarly defined, during pod filling (200‐250, 250‐300, 350‐450, 450‐550, 600‐700, 700–800, and >800 g kg−1 seed DM). Before 450–550 g kg−1 seed DM, forage, seed, and crude protein yields increased with advancing maturity. As maturity advanced beyond 450–550 g kg−1 seed DM, negative crop growth rates were found in the two growing seasons. Plant partitioning showed that the seed fraction in the harvested biomass varied from 74 g kg−1 DM at 200‐250 g kg−1 seed DM to 491 g kg−1 DM at 450–550 g kg−1 seed DM. Little change was observed in plant parts or seed weight beyond 450–550 g kg−1 seed DM. This last stage of maturity is recommended for maximizing nutrient yield for common vetch hay production.
Estimating Field Losses of Rice in Asia, Using Small Quadrat Samples
Authors: Bell Mark A. , McLaren Christopher G. , Patena George F. , Mendoza Dionisio C.
Published: July 2010

Field losses of rice (Oryza sativa L.) in small fields of Asia are rarely quantified. In developed countries, loss is often measured using devices attached to large combines. Such harvesting equipment is rarely used in Asia, so quadrat counts are more applicable. We estimated field losses of rice using a 10‐ by 10‐cm rigid quadrat in commercial fields on Luzon in the Philippines. Losses ranged from 66 to 503 kg ha−1. Due to the rapidity of the quadrat counts, sample variability throughout the field was easily assessed. By counting the number of seeds and multiplying by 22 to 25 (typical range for 1000‐kerneI weight), field loss (kg ha−1) was estimated directly. To estimate field losses within ±50 kg ha−1, a rule of thumb of three is suggested (i.e., the total number of samples required is approximately three tunes the average number of grains being counted in the sample). A sequential sampling procedure is presented for efficiently determining whether grain losses are below a specified tolerance. The quadrat method is an option for rapid assessment of losses, especially by farmers, where more sophisticated methods are not available.
Response of Spring Barley to Crop Rotation, Conservation Tillage, and Weed Management Intensity
Authors: Légère Anne , Samson Nathalie , Rioux Romain , Angers Denis A. , Simard Régis R.
Published: July 2010

Constraints to the adoption of conservation tillage in central and eastern Quebec potentially include cool wet springs, short growing seasons, and variable precipitation patterns. This study was conducted to determine the suitability of conservation tillage practices to cereal cropping systems in this area of Quebec. The effects of crop rotation [spring barley (Hordeum vulgare L.) monoculture; spring barley‐red clover (Trifolium pratense L.) rotation], tillage [fall moldboard plow (MP); fall chisel plow (CP), and direct‐seeded no‐till (NT)], and weed management intensity (intensive, moderate, minimum) on populations and dry weights of crop and weeds at midseason, and on grain yields and yield components were examined on a Kamouraska clay and a Saint‐André gravelly‐sandy loam. On the clay site, moderate weed management in NT treatments resulted in crop establishment, growth, and yields comparable to those in MP treatments. Over five years, grain yields in NT treatments averaged 2877 kg ha−1, compared with 2870 and 2260 kg ha−1 in MP and CP, respectively. Grain yields were also consistently but not statistically higher in the rotation (3014 kg ha−1) than in the monoculture (2322 kg ha−1). On the loam site, crop establishment, growth, and yields responded negatively to reductions in tillage and weed management intensity. Barley stand establishment and weed control in CP and NT treatments on the loam site were less successful in the monoculture than in the rotation. No‐till grain yields (1494 kg ha−1) were on average 7% lower than CP yields (1608 kg ha−1), and 29% lower than MP yields (2076 kg ha−1). Rotation had no effect on grain yields on the loam site. Findings confirm the potential of conservation tillage to generate sustained yield returns in spring barley cropping systems, provided that proper attention is given to critical aspects of the cropping system, including crop establishment and weed management.
SAS‐STABLE: Stability Analyses of Balanced and Unbalanced Data
Authors: Magari Robert , Kang Manjit S.
Published: July 2010

Stability concept is often used to analyze genotype × environment interaction (G × E), by partitioning G × E variance into stability variance components for each genotype. A significant stability variance for a particular genotype indicates lack of stability. An existing computer program (STABLE) calculates the yield‐stability (YSi) statistic for balanced data sets only. Therefore, we developed a program (SAS‐STABLE) that calculates stability variances for balanced as well as unbalanced data sets and is based on the restricted maximum likelihood method. Data may be stored in SAS files or other files that can be retrieved by SAS commands and statements used for data management. This program is for the Windows version of SAS for IBM‐PC compatible computers; a mainframe version is also available. Variance components are solved by iterating on some starting values. Prior knowledge of the values of variances would reduce number of iterations to reach convergence and save execution time. SAS‐STABLE can easily incorporate one or more covariates into the model and remove their effects from G × E variances for each genotype. Variances are tested based on the hypothesis H0: σ2 = 0, assuming normal distribution.
A High Oil Pollinator Enhancement of Kernel Oil and Effects on Grain Yields of Maize Hybrids
Authors: Lambert Robert J. , Alexander D. Eugene , Han Z. J.
Published: July 2010

Several attempts to develop high oil (HO) maize (Zea mays L.) hybrids that are competitive in yield have met with limited success, because of the negative association between oil levels and grain yields. Generally, HO hybrids have high oil kernels but with reduced starch levels, smaller endosperm, and reduced kernel size. The objective of the study was to determine if the use of a high oil maize pollinator could reduce the potential grain yield losses associated with high oil maize production. Nine different single‐cross hybrids were grown for 3 yr and pollinated by two different pollinators. To produce maize hybrids with different kernel oil concentrations under open‐pollinated conditions, the nine hybrids were pollinated by a high oil pollinator (HOP) and by a normal oil pollinator (NOP). To control pollinations, all nine hybrids were detasseled. A split‐plot design allowed for a comparison of the effects of the two pollinators. The four normal oil (NO) hybrids produced oil concentrations in the 60 to 70 g kg−1 range on a dry weight basis when pollinated by a HOP, with no reduction in grain yields. These same hybrids produced oil concentrations in the 47 to 55 g kg−1 range and similar yields when pollinated by a NOP. The four HO hybrids produced yields about 15% lower than the NO hybrids when pollinated by a HOP and about 12% lower yields when pollinated by a NOP. The normal fertile check hybrid produced yields differing by only 1% with the two pollinators, but the oil levels showed an increase of 17 g kg−1 for a HOP relative to a NOP. This increase in oil levels of the NO hybrids pollinated by a HOP is the result of a small increase in germ weight, an increase concentration of oil in the germ, and a reduction in the percentage of endosperm. The changes in kernel traits do not appear to reduce grain yields of the NO hybrids, but do increase oil levels. The consequence of this procedure is to trick the sporophyte into producing greater amounts of oil in the germ.
Weed Seedbanks and Corn Growth following Continuous Corn or Alfalfa
Authors: Clay Sharon A. , Aguilar Immer
Published: July 2010

Specific crop rotations may reduce weed problems and supplement agrichemical inputs. This study, conducted from 1991 through 1994, compared weed densities and corn (Zea mays L.) growth in continuous corn rotation (C/C) and in an alfalfa (Medicago sativa L.)/alfalfa/corn rotation (A/C) among different input levels (tillage, herbicide, and fertilizer rates varied to achieve high, intermediate, and low treatments). Alfalfa suppressed weeds. During establishment, grass and broadleaf weeds made up about 36 and 10% of the forage biomass, respectively. During the second year, grass and broadleaf weeds made up no more than 17 and 4% of the forage biomass, respectively. Weed seed density in both A/C and C/C corn low‐input plots averaged about 15 000 seeds m−2 in 1993; however, grass seed comprised 73% of the C/C seedbank, but only 26% of the A/C seedbank. In 1994, weed seed density increased to 38 000 seeds m−2 in the low‐input A/C corn, and grass species made up 55% of the seedbank. However, grass densities in A/C and C/C low‐input corn averaged about 300 and 4000 shoots m−2, respectively, each year. No grain was harvested in C/C low‐input corn, due to intense weed competition. Grain yield in A/C low‐input corn was 37% of the A/C high‐input treatment in 1993, 66% of the yield in A/C high‐input treatment in 1994, and similar to yield in the C/C medium‐input treatment both years. Alfalfa in rotation with corn may be used to reduce weed competition while sustaining yield.
Noncontiguous Replications in Soybean Performance Tests
Authors: Wilcox James R. , Zhang Guodong
Published: July 2010

Soybean [Glycine max (L.) Merr.] performance trials are commonly conducted in randomized complete block designs with contiguous replications. Local environmental hazards such as hail, flooding, or herbicide drift can result in the loss of entire experiments and the included germplasm with contiguous replications. Noncontiguous replications, spatially separated at a location, minimize chances of local hazards affecting all replications. Our objective was to compare the validity of data from noncontiguous vs. contiguous replications of soybean performance trials. Eleven performance tests were conducted over a 3‐yr period in three‐replicate randomized complete block designs using both contiguous and noncontiguous replications. Distance between noncontiguous replications varied from 200 to 800 m. Twenty‐five to 40 lines in either Maturity Group II or III were evaluated in each test. Traits measured were plant maturity, mature plant height, and seed yield. Variability among lines was significant (P = 0.01) using both contiguous and noncontiguous replications in all 11 tests for plant maturity and plant height. Variability among lines was significant (P = 0.05) for seed yield in 7 of 11 tests of contiguous replications and in 9 of 11 tests of noncontiguous replications. Correlation coefficients among line means between the two types of replication varied from 0.83 to 0.98 for maturity, from 0.51 to 0.94 for plant height, and from 0.51 to 0.89 for seed yield in those tests where significant variation was observed among lines. Evaluating soybean lines in tests using noncontiguous replications requires no more effort or space than using contiguous replications. The results demonstrate that noncontiguous replications are an effective and useful alternative to contiguous replications for soybean performance tests.
Plant Determinants of Mycorrhizal Dependency in Soybean
Authors: Khalil Samina , Loynachan Thomas E. , Tabatabai M. Ali
Published: July 2010

Even though the mycorrhizal relationship is thought to be important in nutrient and water uptake by plants, earlier work showed that soybean cultivars differ in responsiveness. The reasons for cultivar differences are unclear. The objective of this growth‐chamber study was to relate plant‐growth parameters and rooting characteristics of three soybean cultivars to mycorrhizal dependency (MD). The soybean cultivars were chosen from a preliminary study to represent a range in MD values from high (Glycine soja Sieb. & Zucc. PI 468916; referred to hereafter as Soja), to intermediate [G. max (L.) Merr. cv. Mandarin] and low (G. max cv. Swift). Shoot weight, P percentage in shoot tissue, total shoot P uptake, P use efficiency, rate of growth, and root acid phosphatase activity were measured at three harvests when plants were grown at three relative P levels, each with and without mycorrhizal fungal (Gigaspora margarita Becker & Hall) colonization. Soja developed an active symbiosis more quickly than Swift or Mandarin, and mycorrhizae clearly aided in P uptake. When averaged across harvests at low P, mycorrhizal Soja had 7.8 times greater total shoot P than nonmycorrhizal Soja. Comparable values were 2.4 for Mandarin and 1.5 for Swift. Soja roots showed higher phosphatase activity and a higher percentage increase in phosphatase activity with mycorrhizal colonization than did the other two cultivars. Nonmycorrhizal Soja root lengths (avg. 1401 cm) at 5‐wk growth were significantly shorter than Mandarin (2303 cm) and Swift (2236 cm) root lengths. The mean diameter of lateral roots of Soja (0.38 mm) was greater than that of Mandarin or Swift (≈0.26 mm). Root lengths and root surface areas were negatively correlated (P < 0.01) with MD.
A Model to Calculate the Vertical Distribution of Grain Number in Pea
Authors: Roche Romain , Jeuffroy Marie‐He´leène
Published: July 2010

In the pea (Pisum sativum L.) as in most grain legume crops, the seeds are located on the reproductive nodes along the stems. The number of nodes varies widely, and this, combined with variations in environmental conditions during the seed set period, creates a high degree of field‐to‐field variability in the distribution of seeds along the stems. To model seed number profiles in pea, we adapted a method initially proposed by Dwyer and Stewart for calculating the vertical distribution of plant leaf area in maize (Zea mays L.). The entire profile can be described by two empirical constants, by the number of the individual node bearing the most seeds, and by the maximum number of seeds on one node. These four inputs vary from one location‐year to another and are calculated from empirical relationships, taking as explanatory variables the main characteristics of the pea stand. The proposed model simulating seed number per node in pea was evaluated on two samples: one with data from the cultivar used to estimate model parameters (18 points with six different locations and six different years), and another using data from nine other cultivars (27 points). The model gives a reasonable account (r2 > 0.80) of the variability in seed number profiles measured in the field. The model uses only one cultivar‐dependent parameter (mean weight per seed), and thus it can be easily used by farmers or advisers for practical purposes such as agronomic diagnosis to explain the lack of seeds on some nodes.
Alfalfa Stand Tolerance to Potato Leafhopper and Its Effect on the Economic Injury Level
Authors: Lefko Stephen A. , Pedigo Larry P. , Rice Marlin E.
Published: July 2010

In 1997, several seed companies released alfalfa (Medicago sativa L.) cultivars that were marketed as resistant to potato leafhopper, Empoasca fabae (Harris), the key pest of this crop in the Midwest and northeastern USA. Our objectives were to investigate the mechanism of insect resistance and determine if potato leafhopper‐resistant alfalfa cultivars would require revised pest management guidelines. Two field experiments were planted in Ames, IA. Four resistant cultivars (initial release) were compared with a susceptible cultivar planted in 1996. Another experiment was planted in 1998 to compare the same susceptible control with three other resistant cultivars (secondary release). Cages were used to create four levels of leafhopper stress, and nymphs were collected from inside cages when the alfalfa was harvested. Estimates of alfalfa dry weight were used to calculate linear yield‐loss models, and model coefficients were used to calculate economic injury levels and economic thresholds. Trials were run on seedling, second‐cutting seeding‐year, second‐cutting second‐year, and second‐cutting third‐year alfalfa growth. There were no measurable differences in nymph production on resistant or susceptible cultivars in any trial, indicating that an antibiotic resistance mechanism was unimportant under production conditions. The potential for resistant alfalfa to outperform susceptible alfalfa under leafhopper stress began after initial seedling growth and continued through Year 3. The mechanism was described as stand tolerance, and appeared to increase as the alfalfa stand matured. The onset of stand tolerance after the initial growth interval of the seeding year raised the economic threshold from 8 to 80 leafhoppers per 10 sweeps.
TFPlan: Software for Restricted Randomization in Field Plot Design
Authors: Bowman Daryl T.
Published: July 2010

Strict computer randomizations of entry/treatment numbers in field plot designs may result in the placement of entries on one side of the field or back‐to‐back. Both situations present a problem if the blocks have not been properly assigned, or errors occur in planting, maintaining, or harvesting the plots. A software program (TFPlan) was developed to avoid the randomizations that resulted in these two types of problems. TFPlan was initially designed for cultivar performance trials in North Carolina and may be useful to breeders, cultivar testing programs, and researchers who have large entry/treatment numbers. It has the capability of adding tests, changing plots, inserting border and irrigation rows, marking fill‐in plots, adding miscellaneous footnotes as well as labeling the tests. TFPlan will make 500 or more attempts to find a randomization that does not have entries occurring only on one side of the field or back‐to‐back.
Temporal Effects of Compost and Fertilizer Applications on Nitrogen Fertility of Golf Course Turfgrass
Authors: Garling Daniel C. , Boehm Michael J.
Published: July 2010

Little information is available regarding the effects of compost topdressings on the fertility of low‐cut fairway turfgrass. The objectives of this research were to assess: (i) the effects of compost and inorganic fertilizer applications on turfgrass color and growth, (ii) the duration and magnitude of compost topdressings on foliar N concentrations, and (iii) the interaction of compost and fertilizer applications on foliar N concentrations. Nitrogen was applied as inorganic fertilizer at rates of 96, 192, and 384 kg N ha−1 in 1997 and at 48, 96, and 192 kg N ha−1 in 1998 and 1999. Compost topdressings were applied every May and September from 1997 to 1999. Compost treatments consisted of: (i) 100% composted biosolids, (ii) a blend of composted biosolids and yard waste, and (iii) a nontopdressed control. Compost topdressings significantly increased turfgrass color, growth, and foliar N concentrations. Color enhancement lasted for up to 8 wk for plots receiving composted biosolids and for up to 5 wk for plots receiving the blend of composts. Composted biosolids increased foliar N concentrations for approximately 50 d following the May topdressings and for 26 d following the September topdressings. Foliar N concentrations following the May topdressings were increased by approximately 50% by the composted biosolids and by approximately 30% by the compost blend compared with the nontopdressed control. Differences in the duration of color enhancement brought about by the composts most likely can be explained by differences in N content of the composts used.
Analysis of Seedbeds and Maturity Groups for Dryland Soybean on Clayey Soil
Authors: Popp Michael P. , Keisling Terry C. , Oliver Lawrence R. , Dillon Carl R. , Manning Patrick M.
Published: July 2010

Soybean [Glycine max (L.) Merr.] production systems on clayey soils are difficult to manage. With improvements in no‐till planting equipment and herbicide technologies in the early 1990s, no‐till production has become a viable alternative to the traditional tilled seedbed. Therefore, the relative economic performance of tilled and no‐till seedbeds with respect to profitability, sensitivity to input price changes, and risk is assessed for maturity group (MG) IV, V, and VI soybean. Field experiments using split plots (main plots were MG and subplots were seedbeds) and a randomized complete block design with four replications were conducted from 1992 to 1994 at Rohwer, AR and from 1990 to 1997 at Keiser, AR on Sharkey and Sharkey silty clay, respectively. The importance of weather conditions is highlighted in the varied seedbed preparation effect on grain yields, with no clear advantage to either method. On average, yields were higher for MG IV at Rohwer and MG VI at Keiser. The breakeven price and yield analysis suggested that MG selection had a larger economic impact than seedbed preparation, regardless of location. This analysis also showed the extent of production cost differences and associated risk of loss by location. Risk analysis revealed that optimal production strategies changed when input costs were added to yield information and further confirmed that MG selection affects profitability more than seedbed preparation. Production practices that better exploit the yield potential of various MG cultivars (as related to weather conditions) therefore deserve further research attention.
Creating Spatially Contiguous Yield Classes for Site‐Specific Management
Authors: Ping J. L. , Dobermann A.
Published: July 2010

Annual yield maps are spatially fragmented because of random variation caused by crop management as well as measurement errors. Two approaches for creating maps of spatially contiguous yield classes were evaluated at two irrigated sites. In the first approach, prior‐classification interpolation (PCI), grid size was increased from 4, 8, 16, and 32 to 64 m by kriging interpolation before cluster analysis used for mapping yield classes. Choosing a coarse resolution (>16 m) for yield interpolation before spatial classification resulted in maps that did not accurately depict yield patterns, significant decline of the yield variance accounted for, and loss of resolution in areas of sharp yield transitions caused by irrigation or near the field borders. In the second approach, postclassification filtering (PCF), cluster analysis of mean relative yield was conducted on the smallest grid size (4 m), and the classification results were postprocessed using a spatial filtering algorithm with window sizes that were equivalent to the 8‐, 16‐, 32‐, and 64‐m grid sizes used in PCI. This procedure removed erroneous map fragmentation and created maps of contiguous yield classes while preserving the class means and general yield patterns at high spatial resolution. Window sizes for spatial filtering of yield maps should be in the 30‐ to 60‐m range. Landscape pattern metrics may offer new potential for assessing mapping techniques as well as comparing agricultural production fields with regard to ranking their relative opportunities for site‐specific crop management.
Recalcitrant Problems in Environmental Instrumentation
Authors: Baker John M.
Published: July 2010

Frontiers in any science are generally defined by measurement limitations, and that is especially true in environmental biophysics. Among the more persistent issues are surface–atmosphere exchange, soil water and solute fluxes, plant water status, and plant/soil nutrient status. Measurement of surface–atmosphere exchange is particularly critical to global climate change research. Despite advances in instrumentation, accuracy of flux measurements, particularly eddy covariance, remains unacceptable, partly because the underlying assumptions of stationarity and surface homogeneity are so restrictive. Even when these assumptions are valid, the method appears to systematically underestimate for reasons that are not yet well understood. Similarly, soil water and solute fluxes cannot yet be measured accurately and routinely, hampering water quality research. Recent advances in tension lysimetry offer hope for improvement, but most field experiments still rely on modeling of water and solute flow, supported by indirect measurements of ancillary variables, e.g., soil water content, soil water potential, and solute concentration, at discrete points in time and space. A third area of ongoing concern is that of plant water status. The major uncertainty here concerns which property should be measured. Nearly all of the effort over the past 30 yr has been directed at measuring water potential, but water potential measurements are equilibrium measurements, and plants operate in dynamic environments. Furthermore, many physiological processes appear to be more related to relative water content than to water potential. Finally, more accurate and more timely (e.g., in situ) measurements of plant/soil nutrient status are sorely needed to take advantage of the promise of precision agriculture.
Evaluation of GPFARM for Dryland Cropping Systems in Eastern Colorado
Authors: Andales Allan A. , Ahuja Lajpat R. , Peterson Gary A.
Published: July 2010

GPFARM is an ARS decision support system for strategic (long‐term) planning. This study evaluated its performance for comparing alternative dryland no‐till cropping systems and established limits of accuracy for eastern Colorado, using data collected in 1987 through 1999 from an ongoing long‐term experiment at three locations along a gradient of potential evapotranspiration (PET) (Sterling, low PET; Stratton, medium PET; and Walsh, high PET). The crop rotations, which included winter wheat (Triticum aestivum L.), corn (Zea mays L.), sorghum [Sorghum bicolor (L.) Moench], proso millet (Panicum miliaceum L.), and varying fallow periods, were wheat–fallow, wheat–corn–fallow, and wheat–corn–millet–fallow at Sterling and Stratton and wheat–fallow, wheat–sorghum–fallow, and wheat–sorghum–millet–fallow at Walsh. The ranges of relative error (RE) of simulated mean and root mean square error (RMSE) were total soil profile water content (RE: 0 to 23%; RMSE: 38 to 76 mm water), dry mass grain yield (RE: −27 to 84%; RMSE: 419 to 2567 kg ha−1), dry mass crop residue (RE: −5 to 42%; RMSE: 859 to 1845 kg ha−1), and total soil profile residual nitrate N (RE: −42 to 32%; RMSE: 26 to 78 kg ha−1). GPFARM simulations agreed with observed trends and showed that productivity and water use efficiency increased with cropping intensification and that Stratton was the most productive and Walsh the least. GPFARM (v. 2.01) was less suited for year‐to‐year grain yield prediction under dryland conditions but has potential as a tool for studying long‐term interactions between environment and crop management system. Future development and applications of GPFARM must account for crop‐specific responses to stress, detailed hydrology, better understanding of root uptake processes, and spatial variability to give more accurate grain yield predictions in water‐stressed environments.
Deep and Shallow Fall Tillage for Irrigated Soybean Grown with Different Weed Management Systems in the Midsouthern USA
Authors: Heatherly Larry G. , Spurlock Stan R. , Elmore C. Dennis
Published: July 2010

Management inputs that maximize economic return from early soybean [Glycine max (L.) Merr.] production system (ESPS) plantings in the midsouthern USA have not been evaluated fully. The objective was to determine the effect of different weed management systems on yield and net return from irrigated ESPS plantings of soybean following deep (DT; 40–45 cm deep) and shallow (ST; <10 cm deep) fall tillage. Adjacent experiments receiving either DT or ST were conducted in 1999 and 2000 on Sharkey clay (very‐fine, smectitic, thermic Chromic Epiaquert) near Stoneville, MS (33°26′ N lat). Weed management systems were (i) glyphosate‐resistant (GR) cultivar with pre‐emergent (PRE) nonglyphosate [N‐(phosphonomethyl)glycine] herbicides followed by one postemergent (POST) application of glyphosate timed to control grasses, (ii) GR cultivar with two POST applications of glyphosate timed to control both grasses and broadleaves, (iii) GR cultivar with PRE nonglyphosate herbicides followed by two POST applications of glyphosate timed to control both grasses and broadleaves, (iv) non‐GR cultivar with PRE herbicides followed by one POST application of a grass herbicide, (v) non‐GR cultivar with POST application of herbicides timed to control both grasses and broadleaves, and (vi) non‐GR cultivar with PRE herbicides followed by POST applications of herbicides timed to control both grasses and broadleaves. Fall DT was more expensive than ST but resulted in taller soybean plants and less weed cover at harvest. Average yields and net returns from DT and ST were 4286 and 4085 kg ha−1 and $364 and $362 ha−1, respectively. Thus, the investment in equipment for fall DT for irrigated ESPS plantings is not justified. Postemergent‐only weed management was the cheapest for both GR and non‐GR cultivars. Weed management that used POST‐only glyphosate resulted in the greatest yield and profit from GR cultivars. With non‐GR cultivars, yields were not affected by weed management, but net returns were lower when the most intensive weed management was practiced.