bluuebunny/crossref_metadata_2025 huggingface dataset:
Row Spacing in the Early Soybean Production System
Authors: Bowers Glenn R. , Rabb James L. , Ashlock Lanny O. , Santini Judith B.
Published: July 2010

In the southern USA, determinate soybean grown in row spacings (RS) of 50 cm or less generally produce higher yields than that grown in RS of 75 to 100 cm. However, the Early Soybean Production System (ESPS) commonly employs indeterminate cultivars in environments with limited rainfall. This study was conducted to determine whether RS affects seed yield in the ESPS. Twenty‐one field experiments were conducted from 1984 to 1997 at sites in Arkansas, Louisiana, and Texas to determine the effect of RS on seed yield in the ESPS. Row spacings of 80 and 40 cm were compared in seven tests; of 75, 50, and 25 cm in six tests; of 75 and 25 cm in one test; of 100, 50, and 25 cm in four tests; and of 100 and 25 cm in three tests. One to five Maturity Group (MG) III and IV indeterminate cultivars were planted in a given test. Based on similarity of treatments and experimental designs, each field test was assigned to one of 10 environmental clusters (EC). Five EC showed a significant (17–36%) yield increase as RS narrowed. Of the other five EC, three had nonsignificant yield increases, one had virtually no yield change, and one had a nonsignificant yield decrease as RS narrowed. Yield was most responsive to RS when the total July and August rainfall ranged from 100 to 270 mm. These results suggest that narrow rows (≤40 cm) should be used to optimize yields from ESPS plantings in the midsouthern USA.
Forage Quality and Production of Small Grains Interseeded into Bermudagrass Sod or Grown in Monoculture
Authors: Moyer Joseph L. , Coffey Kenneth P.
Published: July 2010

Bermudagrass [Cynodon dactylon (L.) Pers.] is productive in summer but dormant for much of the year in the central USA. The grazing season for bermudagrass can be lengthened with fall‐interseeded small grains, which provide forage for early‐season grazing. We compared forage yield and quality of rye (Secale cereale L., two cultivars), wheat (Triticum aestivum L., three cultivars), and barley (Hordeum vulgare L., one cultivar) when interseeded into bermudagrass sod or grown in monoculture. Field plots of each small grain were harvested two to four times each season and analyzed for in vitro dry matter digestibility (IVDMD) and crude protein (CP). Cumulative forage production for early spring (growing degree days [GDD] < 1000) was greater (P < 0.05) for rye than for barley in all but one instance. Late spring (GDD > 1000) production of barley was usually greater than that of rye, but wheat cultivars were more balanced in seasonal production. Total forage production among small grains was often similar within each system, but the monoculture system had an almost threefold advantage. Although cultivars varied for IVDMD in the monoculture system, comparisons of digestible dry matter (DDM) were more consistent among harvests. Early DDM production of barley was usually lowest among the species, but as high or higher than other species for ryes. Concentrations of CP were variable, but relative CP production and yield had similar trends. In this study, rye was the best‐suited species for interseeding in bermudagrass for early‐season forage in grazing systems.
Cropping System Effects on Weed Emergence and Densities in Corn
Authors: Singer Jeremy W. , Cox William J. , Hahn Russell R. , Shields Elson J.
Published: July 2010

The USDA has a goal of implementing integrated pest management (IPM) practices on 75% of the cropland in the USA so growers may adopt weed control practices that emphasize crop rotation and cultivation. Our objectives were to estimate weed densities in corn (Zea mays L.) and to examine weed emergence in an unmanaged weed area of corn following 4 yr of continuous corn, which received preemergence broadcast herbicides, and following soybean [Glycine max (L.) Merr.]–corn and soybean–wheat (Triticum aestivum L.)/red clover (Trifolium pratense L.)–corn cropping systems, which received banded herbicides and cultivation, on four farms in New York. More total weeds emerged at two sites and more perennial weeds emerged at all sites in the unmanaged weed area of corn in the soybean–wheat/red clover–corn cropping system compared with continuous corn because of poor red clover establishment, which resulted in a fallow period after wheat harvest. Weed densities in corn averaged 6.3 and 9.9 weeds m−2 in the soybean–wheat/red clover–corn cropping system, compared with 1.7 and 1.0 weeds m−2 in continuous corn at two of the sites, because of greater weed emergence and unsatisfactory weed control with banded herbicides and a single cultivation in the soybean–wheat/red clover–corn cropping system. When red clover does not establish well, growers should expect increased weed densities in the subsequent corn crop. Growers should then consider fall tillage or herbicide application after wheat harvest, or additional cultivation(s) or herbicide applications in the subsequent corn crop.
Optimizing Crop Water Use in Sparse Stands of Pearl Millet
Authors: Payne William A.
Published: July 2010

Most of current theory on crop water use–yield relations has been developed for intensively managed crops with well‐developed canopies. In most agricultural systems of semiarid West Africa, low input levels and endemic environmental stress predominate. In farmers’ fields, leaf area index (LAI) of the staple grain, pearl millet [Pennisetum glaucum (L.) R. Br.], may never reach 1. In contrast to dense canopied crops, pearl millet yield is little correlated with ET. Reduced LAI decreases ET efficiency (kg dry matter mm−1 evaporation from crop and soil surfaces) because evaporation (E) from the soil surface constitutes a large portion of ET. Additionally, atmospheric water vapor pressure deficit (e∗‐e) increases within sparse canopies due to sensible heat transfer from the soil surface, and small and irregular roughness length of the canopy. Greater (e∗‐e) further decreases crop T efficiency (kg dry matter mm−1 transpiration) and therefore ET efficiency. Under low‐input conditions, pearl millet ET efficiencies are roughly one‐third of those obtained under intensive management, suggesting that T efficiency is also reduced by environmental stress, especially soil nutrient deficiency. Environmental stresses also cause poor root development, which results in reduced crop water supply, and increased resistance to water uptake. Optimizing crop water use of sparse pearl millet stands will require some form of nutrient input. Other appropriate technologies include certain forms of intercropping and agroforestry that have been traditionally practiced in parts of West Africa. These can improve soil nutrient availability, increase effective crop cover, and reduce canopy (e∗‐e).
Precipitation, Temperature and Tillage Effects upon Productivity of a Winter Wheat–Dry Pea Rotation
Authors: Payne William A. , Rasmussen Paul E. , Chen C. , Goller R. , Ramig Robert E.
Published: July 2010

Winter wheat (Triticum aestivum L.) is grown in rotation with fresh pea (Pisum sativum L.) in the wetter (≥450 mm) zones of the inland Pacific Northwest, and with summer fallow in the drier (<450 mm) zones. Typically, this cropping system has been tillage‐intensive. Summer fallow deleteriously affects soil properties, while fresh pea markets have decreased for decades. Alternative wheat‐based cropping systems are needed. The objective of this 6‐yr study was to evaluate the agronomic viability of a winter wheat–dry pea rotation under four tillage systems. Primary tillage operations for wheat and pea residue, respectively, were: (i) fall disk and chisel plow (Fall D‐CH); (ii) fall moldboard plow and moldboard plow (Fall MBD‐MBD); (iii) spring moldboard plow and moldboard plow (Spring MBD‐MBD); and (iv) fall sweep and skew‐tread (Fall SWP‐SKW). Spring precipitation strongly influenced dry pea yield, but tillage had little to no effect. Pea yield could be predicted well by a model combining precipitation distribution with a heat stress index. Wheat yield was more influenced by winter than spring precipitation, and was ∼400 kg ha−1 less for the Fall SWP‐SKW treatment. Wheat protein content was also reduced in the Fall SWP‐SKW tillage treatment. The probable reason for lower wheat yield is poor weed control. Dry pea is agronomically viable as a rotation substitute for summer fallow or fresh pea. The apparent yield decline of wheat yield in the minimum tillage system needs to be evaluated in terms of tillage costs, and improved technologies for weed, residue, and N management.
Early Prediction of Soybean Yield from Canopy Reflectance Measurements
Authors: Ma B. L. , Dwyer Lianne M. , Costa Carlos , Cober Elroy R. , Morrison Malcolm J.
Published: July 2010

Correlations between plant canopy reflectance and aboveground biomass can possibly be used for early prediction of crop yield. Field experiments were conducted in 1998 and 1999 on two soil types to assess whether measurements of canopy reflectance at given stages of development could be used to discriminate high from low potential yields among genotypes with known differences in potential grain yield and whether a consistent relationship between yield and canopy reflectance could be used for screening and predicting soybean [Glycine max (L.) Merr.] yield in a variety trial. A 3‐by‐42 factorial experiment, arranged in a randomized complete block design with three replications, was used on each soil type for both years. Three population densities (25, 50, and 75 seeds m−2) represented low, optimum, and high levels. Forty‐two historical varieties represented nearly six decades (1934–1992) of soybean yield improvement in Canada. Canopy reflectance was measured with a hand‐held multispectral radiometer on three sampling dates (approximately R2, R4, and R5 stages) for each site. Grain yield at harvest was measured. Soybean grain yield was highly positively correlated with canopy reflectance, expressed as normalized difference vegetation index (NDVI), at all sampling dates. Regression analyses showed a positive relationship between NDVI and grain yield, with R2 up to 0.80 (P < 0.01) and progressive improvement from R2 to R5 stages. Population density did not affect the yield–NDVI relationship at the development stages studied. Our data suggest that canopy reflectance measured nondestructively between R4 and R5 stages adequately discriminates high‐ from low‐yielding genotypes and provides a reliable, fast, repeatable indicator for screening and ranking soybean genotypes based on the relationship between NDVI and grain yield (R2 ranged from 0.44–0.80).
Performance of Annual Medic Species (Medicago spp.) in Southeastern Wyoming
Authors: Walsh Michael J. , Delaney Ronald H. , Groose Robin W. , Krall James M.
Published: July 2010

Annual medic (Medicago spp.) pastures that produce high levels of good quality forage are well suited to grazing and are used extensively throughout dryland farming regions of the world. In these regions, they are normally an integral component of cropping rotations because they allow for reductions in weed and disease problems in addition to increasing soil N levels for subsequent crops. The objective of this research was to investigate the performance of 17 annual medic cultivars and experimental lines for their potential use as self‐regenerating annual pastures in the dryland cropping region of southeastern Wyoming. Dry matter and seed production capabilities were recorded over three seasons, 1996 to 1998. Growth phase development following different emergence times was evaluated in two seasons, and the forage quality was assessed for medic cultivars and lines grown in the 1997 season. Results revealed that the M. rigidula (L.) All. line, SA10343, consistently produced the greatest level of dry matter, with more than double the amount of forage than nearly all other cultivars. Dry matter production was related to the period of growth and development where higher yielding cultivars showed extended periods of vegetative growth. In general, the southeastern Wyoming climate substantially reduced the growth and development periods of medic cultivars bred in southern Australia. Given the overall performance of all cultivars, it was determined that the M. rigidula species had the greatest potential for further development in this environment.
Long‐Term Liming Effects on Coastal Plain Soils and Crops
Authors: Gascho Gary J. , Parker Myron B.
Published: July 2010

Most soils in the southern Coastal Plain need liming; however, long‐term data are needed on its value and changes in soil profile pH, Ca, or Mg. Field studies with lime rates have been maintained on a Tifton soil (Plinthic Kandiudult) for 31 yr and on Pelham soil (Arenic Paleaquult) for 24 yr to determine soil chemical changes, rates needed for high yields, and if yield of cotton (Gossypium hirsutum L.) on low‐pH soils can be increased by Ca or Mg fertilization. Total amounts [calcium carbonate (CaCO3) equivalent] of dolomitic lime were 0, 7.5, 15.0, and 30.0 Mg ha−1 for Tifton and 0, 11.7, and 34.0 Mg ha−1 for the Pelham. Liming increased pH, Ca, and Mg to a depth of 90 cm. Decreases in pH, Ca, and Mg were closely related to the amount of ammoniacal N (NH4–N) applied. Application of 15 Mg ha−1 dolomitic lime on the Tifton soil for 31 yr and 34 Mg ha−1 on the Pelham soil for 24 yr maintained surface soil (0–15 cm) pH near 6.0 and provided greatest crop yield. In no‐lime plots, in 2000, exchangeable Al (0–45 cm depth) was >0.3 cmolc kg−1, and Al saturation was >15% of the effective cation exchange capacity on Tifton soil and >20% on Pelham soil. In those plots, low cotton yields were not increased by fertilization with Ca or Mg salts without liming. Providing 5.25 and 14 kg lime kg−1 N for the Tifton and Pelham soils, respectively, decreased soil Al saturation to <7%.
Germination and Seedling Cold Tolerance in Sorghum
Authors: Tiryaki Iskender , Andrews David J.
Published: July 2010

Early planting of sorghum [Sorghum bicolor (L.) Moench] hybrids in temperate agriculture confers numerous advantages but requires genetic variation, both in lines and in parental effects for germination and seedling tolerance to low soil temperatures. The objectives of this study were to examine genetic variation among 12 diverse sorghum lines and their hybrids with two testers for their relative ability to germinate and emerge at low soil temperatures. Rate of germination, final germination level, and rate of shoot growth were measured under normal and constant cold temperature conditions (20–30°C in a greenhouse and 15°C in a growth chamber, respectively) as well as in an early planted field. Two early maturing lines, PI550666 and PI550597 (from Russia), appear to be better sources of germplasm than Shan Qui Red (from China) for germination and early seedling cold tolerance because of fewer undesirable characteristics. There were significant differences among genotypes under normal temperature conditions for both total germination percentage and rate of early shoot growth, whereas no significant differences were found in cold conditions. Of the two testers (female parents), N123A generally showed a negative combining ability for rate of germination in cold conditions, whereas crosses with tester N250A tended to be substantially better than the male parent. Selection for germination cold tolerance in seed parents will be more effective than in male parents. Though only inferred by this research, it is likely that differences in combining ability exist between seed parents for germination cold tolerance.
Variation in the Allelopathic Effect of Rice with Water Soluble Extracts
Authors: Ebana Kaworu , Yan Wengui , Dilday Robert H. , Namai Hyoji , Okuno Kazutoshi
Published: July 2010

The allelopathic effect of rice (Oryza sativa L.) on lettuce (Lactuca sativa L.) and ducksalad [Heteranthera limosa (Sw.) Willd.] was investigated with water soluble extracts. Ducksalad is a major weed in southern USA rice fields. ‘PI312777’ and ‘Rexmont’, which are suppressive and nonsuppressive to ducksalad in the field, were used to establish the bioassay of allelopathic activity in rice. Water soluble compounds, which were extracted from rice seedlings and adult plants, were applied to lettuce seeds. Leaf extract of PI312777 inhibited the root growth of lettuce more strongly than those of Rexmont. Extracts from the leaves of rice seedlings at the six‐leaf stage inhibited the growth of ducksalad and lettuce, and a close relationship existed between the inhibitory effect and the two test plants. A wide range of variation in allelopathic activity among rice cultivars was assessed using water soluble extracts from their leaves and lettuce as a test plant.
Evaluation of Zinc Seed Treatments for Rice
Authors: Slaton Nathan A. , Wilson Charles E. , Ntamatungiro Sixte , Norman Richard J. , Boothe Danny L.
Published: July 2010

Zinc seed treatments for rice (Oryza sativa L.) were previously evaluated as an alternative to soil‐applied Zn. Recommendations concerning the effectiveness of Zn seed treatments were never clearly stated. Our objectives were to evaluate the utility of Zn seed treatments for supplying Zn to rice grown on soils prone to Zn deficiency. In 1998, a study with three cultivars compared Zn‐treated seeds [2.8 g Zn (kg seed)−1] with a control and 11 kg Zn ha−1 as ZnSO4 applied to the soil. Because tissue Zn concentration did not differ among cultivars, a single cultivar, Drew, was used in studies at two locations in 1999. The control and the soil‐applied Zn were compared with seeds that were treated with three rates of ZnSO4 and ZnEDTA (ethylenediaminetetraacetic acid). Analysis showed net seed concentrations of 1.0, 2.2, and 4.7 g Zn (kg seed)−1 as ZnSO4 and 1.4, 2.8, and 5.7 g Zn (kg seed)−1 as ZnEDTA. In 1998, neither visual Zn deficiency symptoms nor significant yield differences were observed among treatments. Soil‐applied Zn and Zn seed treatments increased tissue Zn concentration by 11.9 and 4.7 mg Zn kg−1, respectively, above that of the control (19.7 mg Zn kg −1). In 1999, Zn deficiency occurred at both locations. Measurements of dry matter, tissue Zn concentration, and grain yield showed that Zn‐treated seed performed equal to or better than soil‐applied Zn. These data suggest that seed Zn concentrations between 2.2 to 5.7 g Zn (kg seed)−1 are an economical alternative to soil‐applied Zn.
Nitrogen Fertilization of No‐Till Cotton on Loess‐Derived Soils
Authors: Howard Donald D. , Gwathmey C.Owen , Essington Michael E. , Roberts Roland K. , Mullen Mike D.
Published: July 2010

Information on nitrogen (N) fertilization of no‐till (NT) cotton (Gossypium hirsutum L.) is needed to optimize lint yields and earliness. We evaluated five N rates and three application methods for NT cotton production on Loring silt loam (fine‐silty, mixed, active, thermic Oxyaquic Fragiudalfs) with natural winter annuals as a cover; and on Memphis silt loam (fine‐silty, mixed, active, thermic Typic Hapludalfs) having corn (Zea mays L.) stover as a cover and on Lexington silt loam (fine‐silty, mixed, active, thermic Utlic Hapludalfs) having winter wheat (Triticum aestivum L.) as a cover. Nitrogen rates of 0, 34, 67, 101, and 134 kg ha−1 were either broadcasted as ammonium nitrate (AN) or injected as urea–ammonium nitrate (UAN) at planting. Additional treatments included broadcasting 67 kg N ha−1 as AN at planting with either 34 or 67 kg N ha−1 banded 6 wk later. Relative to no N, broadcasting 67 kg N ha−1 as AN increased 4‐yr average NT lint yields on Loring silt loam from 739 to 1281 kg lint ha−1 and 2‐yr average yields on Lexington silt loam from 1086 to 1535 kg ha−1. A higher N rate (101 kg N ha−1) was needed to increase 2‐yr average yields on Memphis silt loam from 821 to 1169 kg ha−1. Broadcasting AN was a satisfactory placement method producing yields equal to or higher than injecting UAN or splitting AN for NT cotton produced on these loessial soils despite different covers and residues.
Deep Tillage and Crop Rotation Effects on Cotton, Soybean, and Grain Sorghum on Clayey Soils
Authors: Wesley Richard A. , Elmore Carroll D. , Spurlock Stan R.
Published: July 2010

Deep tillage (subsoiling) of clayey soils in the fall when the profile is dry is a new concept that results in increased yields and net returns from soybean [Glycine max (L). Merr.] grown without irrigation. Crop rotation may also result in increased crop yields. Field studies were conducted on Tunica clay (clayey over loamy, smectitic, nonacid, thermic, Vertic Haplaquept) near Stoneville, MS (33°26′ N lat) to determine the individual and combined effects of fall deep tillage and crop rotations on crop yields and net returns. Treatments included monocrop cotton [Gossypium hirsutum (L.)], soybean, and grain sorghum [Sorghum bicolor (L.) Moench], and biennial rotations of cotton with grain sorghum and soybean with grain sorghum grown without irrigation and in either a conventional‐till (CT) or deep‐till (DT) production system. Yields from all cotton and soybean crop sequences grown in the DT respectively averaged 541 kg ha−1 and 525 kg ha−1 greater than comparable cotton (2184 kg ha−1) and soybean (2983 kg ha−1) crop sequences grown in the CT. Net returns from monocrop cotton ($552 ha−1) and soybean ($462 ha−1) in the DT respectively averaged $392 ha−1 and $121 ha−1 more than similar crop sequences in the CT. Rotations increased cotton and soybean yields but not net returns because of the low value of the grain sorghum component. These data indicate that fall deep tillage should be incorporated into monocrop cotton and soybean crop sequences to maximize and stabilize net returns from these crops on Tunica clay.
Black Spruce Growth and Understory Species Diversity with and without Sheep Laurel
Authors: Mallik Azim U.
Published: July 2010

Growth and understory species diversity of black spruce [Picea mariana (Miller) B.S.P.] planted in central Newfoundland at contiguous sites with and without dense cover of sheep laurel (Kalmia angustifolia L.) were compared. Black spruce stem density and volume per hectare were calculated by sampling 10 circular quadrats (50 m2), and the cover of all plant species was determined by sampling 20 quadrats (1 m2) in each site. In addition, 10 randomly sampled planted black spruce samplings from each site were analyzed for stem height, basal diameter, and foliar chemistry. Results showed a significantly lower stem height and basal diameter (65 and 51%, respectively) at the site with dense sheep laurel cover (36%) compared with the site with sparse sheep laurel cover (<1% sheep laurel cover, and henceforth referred to as the non‐sheep laurel site for simplicity). Black spruce grown at the sheep laurel dominated site contained significantly higher quantities of Ca, Al, Fe, and K in the needles than that grown at the non‐sheep laurel site. The sheep laurel dominated site also had a significantly higher mean organic matter depth of 8.3 cm compared with 5.6 cm at the non‐sheep laurel site. Canonical correspondence analysis (CCA) of the species cover data clearly separated the sheep laurel dominated plots from the non‐sheep laurel plots. The sheep laurel dominated site had reduced species richness of vascular plants but increased species richness for lichens compared with the non‐sheep laurel site. Allelopathy associated with phenol‐induced soil nutrient imbalance and nutrient stress is a possible cause for black spruce growth inhibition at the sheep laurel dominated site.
Enhancing Water Use Efficiency in Irrigated Agriculture
Authors: Howell Terry A.
Published: July 2010

Irrigated agriculture is a vital component of total agriculture and supplies many of the fruits, vegetables, and cereal foods consumed by humans; the grains fed to animals that are used as human food; and the feed to sustain animals for work in many parts of the world. Irrigation worldwide was practiced on about 263 Mha in 1996, and about 49% of the world's irrigation occurred in India, China, and the USA. The objectives of this paper are to (i) review irrigation worldwide in its ability to meet our growing needs for food production, (ii) review irrigation trends in the USA, (iii) discuss various concepts that define water use efficiency (WUE) in irrigated agriculture from both engineering and agronomic viewpoints, and (iv) discuss the impacts of enhanced WUE on water conservation. Scarcely one‐third of our rainfall, surface water, or ground water is used to produce plants that are useful to mankind. Without appropriate management, irrigated agriculture can be detrimental to the environment and endanger sustainability. Irrigated agriculture is facing growing competition for low‐cost, high‐quality water. In irrigated agriculture, WUE is broader in scope than most agronomic applications and must be considered on a watershed, basin, irrigation district, or catchment scale. The main pathways for enhancing WUE in irrigated agriculture are to increase the output per unit of water (engineering and agronomic management aspects), reduce losses of water to unusable sinks, reduce water degradation (environmental aspects), and reallocate water to higher priority uses (societal aspects).
A Simple Performance‐Based Index for Assessing Multiple Agroecosystem Functions
Authors: Liebig Mark A. , Varvel Gary , Doran John
Published: July 2010

Evaluating the impact agricultural practices have on agroecosystem functions is essential to determine the sustainability of management systems. This paper presents an approach to determine the relative sustainability of agricultural practices. A simple ranking procedure using a relative scoring method is proposed to discriminate among treatments based on the status of crop and soil parameters within different agroecosystem functions. Summing scores across agroecosystem functions allows for the identification of agricultural practices that are performing optimally based on functions included in the procedure. An example, using data from a long‐term cropping systems experiment in the western Corn Belt, found the indexing procedure to successfully discern differences in overall performance across four agroecosystem functions between conventional [continuous corn (Zea mays L.) cropping sequence at a fertilization rate of 180 kg N ha−1] and alternative {corn–oat (Avena sativa L.) + clover (Trifolium pratense L.)–grain sorghum [Sorghum bicolor (L.) Moench]–soybean [Glycine max (L.) Merr.] cropping sequence at a fertilization rate of 90 kg N ha−1} management systems. The simplicity, inclusiveness, and inherent flexibility of the indexing procedure can be considered benefits and drawbacks, depending on the point of view taken. Data requirements of the approach, however, are stringent. Consequently, its most appropriate use may be with data from long‐term agroecosystem experiments.
Weed Suppression by Annual Legume Cover Crops in No‐Tillage Corn
Authors: Fisk John W. , Hesterman Oran B. , Shrestha Anil , Kells James J. , Harwood Richard R. , Squire John M. , Sheaffer Craig C.
Published: July 2010

Cover crops often reduce density and biomass of annual weeds in no‐till cropping systems. However, cover crops that over‐winter also have the potential to reduce crop yield. Currently, there is an interest in annual medics (Medicago spp.) and other annual legumes that winter‐kill for use as cover crops in midwestern grain cropping systems. A 2‐yr study was conducted at East Lansing and the Kellogg Biological Station, Michigan, to investigate the influence of annual legume cover crops on weed populations. Two annual medic species [burr medic (M. polymorpha cv. Santiago) and barrel medic (M. truncatula Gaertn. cv. Mogul)], berseem clover (Trifolium alexandrinum L. cv. Bigbee), and medium red clover (Trifolium pratense L.) were no‐till seeded as cover crops into winter wheat (Triticum aestivum L.) stubble in a winter wheat/corn (Zea mays L.) rotation system. Density of winter annual weeds were between 41 and 78% lower following most cover crops when compared with no cover control in 2 out of 4 site years, while dry weight was between 26 and 80% lower in all 4 site years. Impact of cover crops on the density of summer annual weeds was infrequent; however, weed dry weights were reduced by 70% in 1995 following burr medic and barrel medic. Dry weight of perennial weeds before corn planting were 35 to 75% lower following annual legumes compared with the control, while weed density was not affected. This study indicated a potential for annual legumes to reduce weed density and growth in no‐till corn grain systems.
Water‐Seeded Rice Cultivars Differ in Ability to Interfere with Watergrass
Authors: Gibson Kevin D. , Hill James E. , Foin Theodore C. , Caton Barney P. , Fischer Albert J.
Published: July 2010

The repeated use of a limited number of herbicides has led to the development of resistant weed species in California rice (Oryza sativa L.). Competitive rice cultivars could help reduce herbicide dependency and decrease selective pressure for resistance. We conducted field experiments to determine if differences in competitive ability existed between two semidwarf cultivars of water‐seeded rice. Cultivars M‐202 and A‐301 were grown on Stockton clay soil at two seed rates (84 and 168 kg ha−1) in 1996 and four seed rates (56, 112, 168, and 224 kg ha−1) in 1997. Molinate (S‐ethyl hexahydro‐1H‐azepine‐1‐carbothioate) and propanil [N‐(3,4‐dichlorophenyl)propanamide] were used to control a mixed infestation of watergrass [Echinochloa oryzoides (Ard.) Fritsch, E. phyllopogon (Stapf) Koss] in 1996 and 1997, respectively. Molinate (0 and 4.5 kg a.i. ha−1) was applied in 1996, and propanil (0, 1, 2 and 4 kg a.i. ha−1) was applied in 1997. M‐202 was taller, produced more leaf dry weight, had greater light interception, and reduced watergrass biomass more than A‐301 in both years of the study. The more competitive M‐202 also had higher yields than A‐301 under weedy and weed‐free conditions. Watergrass growth was not affected by rice seed rates in either year. This study suggests that herbicide rates could be reduced and weed control could be improved if more competitive cultivars were developed for water‐seeded rice.
Glyphosate‐Resistant Soybean Cultivar Yields Compared with Sister Lines
Authors: Elmore Roger W. , Roeth Fred W. , Nelson Lenis A. , Shapiro Charles A. , Klein Robert N. , Knezevic Stevan Z. , Martin Alex
Published: July 2010

Herbicide‐resistant crops like glyphosate resistant (GR) soybean [Glycine max (L.) Merr.] are gaining acceptance in U.S. cropping systems. Comparisons from cultivar performance trials suggest a yield suppression may exist with GR soybean. Yield suppressions may result from either cultivar genetic differentials, the GR gene/gene insertion process, or glyphosate. Grain yield of GR is probably not affected by glyphosate. Yield suppression due to the GR gene or its insertion process (GR effect) has not been reported. We conducted a field experiment at four Nebraska locations in 2 yr to evaluate the GR effect on soybean yield. Five backcross‐derived pairs of GR and non‐GR soybean sister lines were compared along with three high‐yield, nonherbicide‐resistant cultivars and five other herbicide‐resistant cultivars. Glyphosate resistant sister lines yielded 5% (200 kg ha−1) less than the non‐GR sisters (GR effect). Seed weight of the non‐GR sisters was greater than that of the GR sisters (in 1999) and the non‐GR sister lines were 20 mm shorter than the GR sisters. Other variables monitored were similar between the two cultivar groups. The high‐yield, nonherbicide‐resistant cultivars included for comparison yielded 5% more than the non‐GR sisters and 10% more than the GR sisters.
Agroeconomic Analyses of Drip Irrigation for Sugarbeet Production
Authors: Sharmasarkar Florence Cassel , Sharmasarkar Shankar , Held Larry J. , Miller Stephen D. , Vance George F. , Zhang Renduo
Published: July 2010

Sugarbeet (Beta vulgaris L.) is a major cash crop in Wyoming where overuse of water and agrochemicals is a concern in furrow‐irrigated areas. Drip irrigation, an alternative technology, is not well developed for row crops within the state. Therefore, our objective was to evaluate the economic feasibility of implementing drip irrigation practice for sugarbeet production. Capital budgeting analyses, including net present value (NPV) and rate of return (ROR), were used for 10 to 40 ha. Sensitivity analyses were conducted with drip system size and life span, interest rate, water price, and weed control cost. Sugarbeet and sugar yields were higher under drip irrigation than furrow irrigation at P = 0.05. The drip system investment cost decreased with increasing size. Total variable costs for drip irrigation were lower than those for furrow irrigation. Sugarbeet returns were $2080 and $2310 ha−1 for furrow and drip irrigation practices, respectively. Higher returns and shorter payback time were observed for large conversion areas. The sensitivity was more pronounced with small‐scale farming. Increasing interest rates caused delays in positive return and profit and contributed to larger differences in payback time between drip system sizes. For all conversion sizes, ROR increased with system lifetime. Higher profitability was observed for areas with increased water prices and weed control costs. The overall findings indicated that sugarbeet production under drip irrigation would be most profitable for a 40‐ha area with payback periods ranging from 7 to 10 yr.
Weed Community as an Indicator of Summer Crop Yield and Site Quality
Authors: Suárez Susana A. , de la Fuente Elba B. , Ghersa Claudio M. , León Rolando J.C.
Published: July 2010

We studied relationships between weed community characteristics and management practices, soil degradation (reductions of the A horizon, organic matter, total N, and available P) levels, and soybean [Glycine max (L.) Merr.] and corn (Zea mays L.). Our objective was to provide a scale based on floristic information that could be used to evaluate sites in terms of summer crop yields and agroecosystem degradation. Weed surveys were carried out in 1995 and 1999 in corn and soybean fields. Cluster analysis and canonical correspondence analysis (CCA) were used with data from 1995. Regional or gamma diversity, local or alpha diversity, and exchange of species between habitats or beta diversity of weed communities were estimated as well as changes in origin, morphotype, and life cycle for data from both surveys. Four weed communities related to crops and yields were identified. In both corn and soybean fields, the potential for high crop yield (low soil degradation) may be indicated by the presence of the weed groups identifying the weed community of a crop species. Sowing date, agronomic index, mechanical control, and the use of grass herbicide also accounted for weed community structure. Sites with higher than average yield had the highest alpha diversity. The number of native species in the community was related to soil degradation levels. Soil degradation proved to be more important than type of crop in determining the structure of a weed community.
Defoliation Effects on Sunflower Yield Reduction
Authors: Muro Julio , Irigoyen Ignacio , Militino Ana F. , Lamsfus Carmen
Published: July 2010

Quantifying the effect of leaf area loss on sunflower (Helianthus annuus L.) yield caused by hail, pests, and diseases is important in the management of this crop, both from a technical and economic point of view. The effect of defoliation depends, however, on the foliar surface eliminated and on the growth stage at which this takes place. This effect has been quantified in the USA, but these data are lacking for specific conditions of Europe. The aim of this paper was to determine the response of sunflower cultivation to several levels of defoliation that took place at different growth stages under European growth conditions. Four field trials were conducted by applying four defoliation treatments (nondefoliated control, 33, 66, and 100%) at different growth stages ranging from preflowering (R2) to physiological maturity (R9). Crop yield loss increased with increasing level of defoliation. Preflowering stage R3 was the most sensitive. At this stage a 100% defoliation of the leaf surface resulted in 92% yield loss, reducing both the number of seeds per head and 1000‐seed weight. A 100% defoliation at stage R7 (back of head a pale yellow) caused a 50% yield loss, while at stage R9 (physiological maturity) defoliation had no effect on yield. The yield loss caused by defoliation at different plant growth stages under European conditions differed slightly from the one designed for U.S. conditions.
Crop Modeling
Authors: Poluektov Ratmir A. , Topaj Alexandre G.
Published: July 2010

During the last two decades, computer simulation models have become powerful tools for investigating agricultural crop dynamics and solving practical problems. Many models have been developed in various countries, which permits exploration of the influence of weather conditions and agricultural strategies on the fate of a crop. However, some fundamental problems related to the description of agricultural plant growth and development remain unsolved. These primarily concern the totality of biological processes such as ontogenetic development and morphogenesis due partly to the lack of knowledge in plant physiology and the absence of realistic ideas about the origin of plant life. These circumstances have forced modelers to use quite sophisticated heuristic approaches rather than biologically sound descriptions. This paper represents the authors’ vision of this situation.
Simulation of Maize Grain Yield Variability within a Surface‐Irrigated Field
Authors: Cavero Jose , Playán Enrique , Zapata Nery , Faci Jose M.
Published: July 2010

Spatial variability of crop yield within a surface‐irrigated field is related to spatial variability of available water due to nonuniform irrigation and soil characteristics, among other factors (e.g., soil fertility). The infiltrated depth at each location within the field can be estimated by measurements of opportunity time and infiltration rate or simulated with irrigation models. We investigated the use of the crop growth model EPICphase to simulate the spatial variability of maize (Zea mays L.) grain yield within a level basin using estimated or simulated (with the irrigation model B2D) infiltrated depth. The relevance of the spatial variability of infiltration rate, opportunity time, and soil surface elevation in the simulation of grain yield spatial variability was also investigated. The measured maize grain yields at 73 locations within the level basin, ranging from 3.16 to 11.54 t ha−1 (SD = 1.79 t ha−1), were used for comparison. Estimated infiltrated depth considering uniform infiltration rate resulted in poor simulation of the spatial variability of grain yield [SD = 0.59 t ha−1, root mean square error (RMSE) = 1.98 t ha−1]. Simulated infiltrated depth with the irrigation model considering uniform infiltration rate and soil surface elevation resulted in grain yield simulations with lower variability than measured (SD = 0.64 t ha−1, RMSE = 1.58 t ha−1). Introducing both sources of spatial variability in the irrigation model resulted in the best simulation of grain yield spatial variability (SD = 1.68 t ha−1, RMSE = 1.16 t ha−1; regression of calculated vs. measured yields: slope = 0.74, r2 = 0.56).
Tillage and Nitrogen Fertilization Influence Grain and Soil Nitrogen in an Annual Cropping System
Authors: Halvorson Ardell D. , Wienhold Brian J. , Black Alfred L.
Published: July 2010

Increasing the frequency of cropping in dryland systems in the northern Great Plains requires the application of N fertilizer to maintain optimum crop yields. A 12‐yr annual cropping rotation [spring wheat (Triticum aestivum L.)–winter wheat–sunflower (Helianthus annuus L.)] under dryland conditions was monitored to determine the influence of tillage system [conventional till (CT), minimum till (MT), and no till (NT)] and N fertilizer rate (34, 67, and 101 kg N ha−1) on N removed in grain and annual changes in postharvest soil NO3–N. Nitrogen removal in the grain increased with increasing N rate in most years. Total grain N removal was lowest with NT at the lowest N rate and highest with NT at the highest N rate compared with CT. Total grain N removal after 12 cropping seasons was 144, 84, and 61% of the total N applied for the 34, 67, and 101 kg N ha−1 fertilizer rates, respectively. Residual soil NO3–N levels were not affected by N rate or tillage system in the first 3 yr, but they increased significantly following consecutive drought years. Residual NO3–N in the 150‐cm soil profile tended to be higher with CT and MT than with NT. Soil NO3–N movement below the crop root zone may have occurred in 1 or 2 yr when precipitation was above average. Results indicate that NT, with annual cropping, may reduce the quantity of residual soil NO3–N available for leaching compared with MT and CT systems.
Tillage, Cover Crop, and Kill‐Planting Date Effects on Corn Yield and Soil Nitrogen
Authors: Sainju Upendra M. , Singh Bharat P.
Published: July 2010

Tillage and spring kill date may affect cover crop N accumulation and subsequent N release to the soil, thereby influencing corn (Zea mays L.) N uptake and yield. We examined the influence of three tillage practices [no till (NT), chisel plowing (CP), and moldboard plowing (MP)], two cover crop management systems [hairy vetch (Vicia villosa Roth) vs. winter weeds], and two cover crop kill–corn planting dates [early (early April cover crop kill and mid to late April corn planting) vs. late (mid to late April cover crop kill and late April to early May corn planting)] on cover crop N accumulation, soil inorganic N, and silage corn N uptake and yield. An experiment was conducted on a Dothan sandy loam (fine‐loamy, siliceous, thermic, Plinthic Paleudults) from 1997 to 1999 in central Georgia. Cover crop N accumulation was higher with late kill than with early kill (113 vs. 104 kg ha−1). Corn yield was higher with late planting in NT than in CP or MP (19.5 vs. 15.1–16.6 Mg ha−1) and higher in CP or MP with early planting than in MP with late planting (18.1–18.4 vs. 15.1 Mg ha−1). Similarly, corn N uptake was higher in NT with late planting than in CP or MP with early or late planting (217 vs. 133–171 kg ha−1). Soil inorganic N (0− to 30‐cm depth) at corn planting was higher in CP than in NT (18.4–30.2 vs. 9.9–20.5 mg kg−1). Corn yield and N uptake in NT and N concentration and uptake in CP and MP can be increased by delaying cover crop kill by 2 wk, but corn yield in CP and MP can be maintained by killing cover crop early in the spring.
Software for Measuring Root Characters from Digital Images
Authors: Ingram Keith T. , Leers Gary A.
Published: July 2010

Root research methods are often tedious, labor intensive, and prone to large variability. Minirhizotron technology has the potential to greatly enhance root research capabilities, but quantifying minirhizotron data is very time consuming. This note presents new software that allows rapid, accurate measurement of root length from digital images—Root Measurement System (RMS). In addition to measuring root lengths and diameters, RMS records number of roots in an image and calculates their total volume, total surface area, and length density. Ten untrained RMS users averaged 654 ± 42 s to measure the length of a 24 mm s‐shaped line 10 times. The standard error of the mean for repeated length measurements was <0.1 mm for all but one of the operators. In a subsequent test with 10 different operators having various levels of experience, operators averaged a total of 2324 ± 213 s to measure the lengths and diameters of 10 images of pseudo roots made from wires. There was no significant difference among operators for total length measured, but operators did differ in lengths apportioned among 0.1‐mm‐diam. classes. For minirhizotron images collected in a field study, an experienced operator could analyze from 17 to 38 images h−1 depending on number and length of roots in the images. With its speed, accuracy, and versatility, RMS offers the possibility to analyze sufficient numbers of minirhizotron images to allow detection of treatment effects in field research.
Physiological and Harvest Maturity of Canola in Relation to Seed Quality
Authors: Elias Sabry G. , Copeland Larry O.
Published: July 2010

The ability to identify physiological (PM) and harvest maturity (HM) of canola (Brassica napus L.) by phenological characteristics would permit timely harvest to avoid problems of both under‐ and overripe pods. This study was conducted to identify PM and HM of six winter and spring canola cultivars using morphological and physiological markers including seed and pod color, seed dry weight (DWT), seed moisture content (SMC), and to measure seed quality (germination and vigor) at PM and HM. Pods and seeds from each cultivar were sampled at weekly intervals from pod formation until HM. Standard germination, accelerated aging, and cold tests were conducted to assess seed quality. Canola attained PM when pods turned from green to greenish‐yellow or light brown, and contained seeds ranging from brownish green to greenish brown and light brown. The seeds were firm. Seed DWT did not change significantly from PM to HM. Seed MC at maximum DWT ranged from 203 to 360 g kg−1. Pods at HM were yellow to brown and the seeds were brown or dark brown to black, depending on the cultivar. The SMC was near 100 g kg−1 and the seeds were hard and rattled inside the pod. Seeds of all cultivars had greater germination and vigor at HM than at PM. Canola can be harvested 2 wk before reaching HM without affecting yield; however, SMC at this stage is not suitable for direct harvest and seed quality is not at the highest level.
Predicting Preharvest Sprouting Susceptibility in Barley
Authors: Rodríguez M. Verónica , Margineda Martín , González‐Martín Juan F. , Insausti Pedro , Benech‐Arnold Roberto L.
Published: July 2010

Preharvest sprouting (PHS) susceptibility in cereals is a consequence of low grain dormancy before harvest. Dormancy loss rate depends on genotype and may also be affected by environmental conditions during seed formation. To establish a quantitative relationship between temperature and PHS susceptibility, a malting barley (Hordeum vulgare L.) cultivar, ‘Quilmes Palomar’, was sown on different dates over a 3‐yr period to obtain a range of thermal conditions during grain filling (soil type: Aeric Argiudoll). The period from pollination to physiological maturity (PM) was adjusted to a thermal time (TT) scale, which was then divided into 50°C‐day intervals. Mean temperature within each interval was calculated for the different sowing dates. Grain dormancy was monitored using a germination index (GI). We sought a linear relationship between temperature during grain filling and GI at some moment after PM. The strongest correlation (P < 0.0001) was obtained between mean temperature values within the TT interval ranging from 300 to 350°C‐day (Tm300–350) and GI values 12 d after PM (GI12DAPM). This indicates that temperature during this sensitivity window explains variability in dormancy level among years and locations for this cultivar, and may therefore explain differences in PHS susceptibility. A regression model (GI12DAPM = 7.14 × (Tm300–350) − 99; r2 = 0.95, n = 9) was generated for predicting GI values 12 d after PM, and tested on commercial plots. The linear relationship between temperature and GI after PM was confirmed, though the effect of one or more undescribed, environmental factors differing among tested locations was revealed.