bluuebunny/crossref_metadata_2025 huggingface dataset:
Defoliation Effects on Seasonal Production and Growth Rate of Cool‐Season Grasses
Authors: Belesky David P. , Fedders James M.
Published: July 2010

Knowledge of seasonal distribution of herbage growth is essential for design of pasture management schemes that optimize season‐long herbage productivity and nutrients for grazing livestock. Current knowledge of cool‐season grass growth is derived largely from either hay production or high‐input systems. A 3‐yr field study was conducted to determine the productivity and growth rates of cool‐season grasses defoliated according to sward height criteria in a marginal soil environment. Defoliation regimes included hay harvest, lenient (50%) removal of short (10 cm) canopies, and both lenient and intensive (75%) removal of tall (20 cm) canopies. Species included orchardgrass (Dactylis glomerata L.), fescue × perennial ryegrass hybrid (Festuca arundinacea Schreb. × Lolium perenne L.), and prairie grass (Bromus willdenowii Kunth). Cumulative yield curves were fit to the Gompertz growth equation and growth rates were derived from the fitted data. All species had low yields relative to other defoliations and growth rates when managed for removal of 50% of canopy height regardless of height. Managing pastures on the premise of take half, leave half may not always contribute to plant persistence and sustained productivity. Frequent defoliation beginning in spring resulted in a greater portion of annual yield occurring in late than in early season, resulting in more stable distribution but less herbage within a season, compared with canopies managed as hay. High growth rates of prairie grass early in the study were followed by stand degradation, regardless of defoliation treatment, and may indicate unsuitability for use in low‐input or marginal environments. Autumn recovery of herbage production did not occur under any defoliation regime.
Photosynthate Reserves during Grain Filling in Winter Wheat
Authors: Gent Martin P. N.
Published: July 2010

How much does stored or reserve photosynthate contribute to grain growth in winter wheat (Triticum aestivum L.)? Three models were developed to assess this contribution. In Model I, all current photosynthate was used for vegetative or reproductive growth, and there was no reserve. In Model II, photosynthate accumulated in a reserve was used preferentially to support maintenance respiration, while current photosynthate accumulated in the grain. In Model III, the maintenance component extracted from the reserve was continuously replenished from current photosynthate, thus requiring a greater contribution from the reserve for dry matter in the grain. Each model related dry matter accumulation at the whole‐plant level to photosynthesis, respiration, and the distribution and retention of 14C from 14CO2 assimilated photosynthetically. To test the models, these characteristics were measured in four cultivars of New York soft white winter wheat grown in the field in Connecticut in three years. Observations showed that canopy respiration and grain dry matter accumulation were approximately equal sinks for photosynthate and, together, were greater than canopy photosynthesis late in grain filling. Consequently, in two years, Model I (with no reserve) terminated grain filling early and predicted a lower harvest index than was observed. The observed time course of the distribution and retention of radioactivity from a pulse of 14C02 assimilated photosynthetically was most consistent with predictions of Model III (continuous replenishment of the reserve). In this model, preanthesis reserves contributed from 0.2 to 0.5 of grain dry weight of winter wheat in Connecticut, depending on harvest index. This contribution is expected to exceed 0.5 in more stressful climates.
Cereal Grain Yield: Biblical Aspirations and Modern Experience in the Middle East
Authors: Amir J. , Sinclair T. R.
Published: July 2010

Very little information exists on crop yields in antiquity. Examination of some of the earliest yield records may give some insight about crop productivity among ancient peoples and a historical perspective on the progress achieved in modern agronomic practices. The Book of Genesis contains one of the earliest recorded expressions of a concern for the yielding potential of cultivated crops. In this paper, we translate the ambiguous biblical reference to crop yield into a modern expression of crop yield per unit land area. Because the yield aspirations of these ancient people are equivalent to modern yields achieved under rainfed conditions at the same location, we undertook an analysis of the agronomic practices used by these ancient people to determine the likelihood that such yields could be achieved. In fact, it appears possible that maximum cereal yields in the ancient Middle East could have approximated modern yields. This analysis may highlight the great advances in modern agriculture to bring high crop yields to large land areas by overcoming various stresses, but the inherent physiological yielding potential may not have been substantially altered over the millennia.
Soil Temperature Limitation to Water Use by Field‐Grown Winter Wheat
Authors: Wraith J. M. , Ferguson A. H.
Published: July 2010

Modification of crop water use patterns in response to the field soil temperature regime has important agronomic and environmental implications. A 2‐yr field study was conducted to ascertain how soil temperature modification influenced seasonal soil water depletion for a winter wheat (Triticum aestivum L.) crop near Bozeman, MT. Soil surface cover materials including clear plastic, white metal, and styrofoam were applied in the fall after germination and plant establishment. Soil temperature and water content profiles were monitored throughout the winter and spring growing seasons. Soil water depletion was significantly accelerated for those treatments having relatively warmer soil temperatures. Differences of up to 65 mm of cumulative soil water depletion were observed between warm and cool treatments during spring. Significant water extraction from a given depth within the soil profile did not occur until the soil temperature reached 10 to 11 °C during 1985. Repeated rainfall during 1986 obscured any relationship between minimum soil temperature and water uptake in the upper soil profile, but the same relationship as during 1985 was noted at greater depths. Although the nature of our field data does not allow determination of whether cold temperatures constrained root growth, root water uptake, or both of these processes, our field results substantiate conclusions drawn by other investigators using controlled‐environment techniques. It is clear that cultural practices or climatic changes affecting seasonal soil temperature can impact soil water utilization by winter wheat in thermally limited growing areas.
Plot Techniques for Assessment of Bunch Weight in Banana Trials under Two Systems of Crop Management
Authors: Ortiz Rodomiro
Published: July 2010

Banana (Musa spp.) is an important perennial crop in tropical countries. Testing improved germplasm and/or agronomic practices to increase productivity requires accuracy and precision. The objectives of this study were to determine the optimum plot size (i.e., number of plants per experimental plot) and the number of replications to detect significant true mean differences in bunch weight (i.e., commercial yield) between treatments. Three uniformity trials of the cultivar Valery grown in Ultisols under two different management practices (alley cropping of banana with multispecies hedgerows and monocropping of banana in cleared land) and at two locations in the humid forest zone of sub‐Saharan Africa were used. The methods of maximum curvature and comparison of variances were used to determine optimum plot size, while the number of replications was estimated by Hatheway's method. This statistical procedure considered an expected relative magnitude of differences between treatment means at a specific probability level and the relationship between the coefficient of variation and soil heterogeneity. The experimental plot should have a single row of 5 plants for banana in an alley cropping system, whereas single rows of 20 plants plot−1 are required in a monocropping system. This finding indicates that alley cropping of banana with multispecies hedgerows may be an adequate system not only to maintain diversity but also for greater efficiency in testing improved germplasm. A table was developed, indicating the expected detectable true mean differences for bunch weight per plant for different number of treatments tested (5–30), plants per plot (5–40), replications (2–6), and management practices. This table allows musa researchers to select minimum trial sizes, according to their objectives and available resources. For example, when 30 treatments are tested in alley cropping fields, using randomized complete block designs with two replications of 10 plants plot−1, a true bunch weight mean difference of 15% may be found to be significant.
Tillage and Rotation Effects on Corn Yield Response to Fertilizer Nitrogen on Aqualf Soils
Authors: Stecker John A. , Buchholz Darly D. , Hanson Roger G. , Wollenhaupt Nyle C. , McVay Kent A.
Published: July 2010

Fertilizer N recommendations are often increased for no‐till corn (Zea mays L.) relative to conventionally tilled corn. A comparison of relative yield responses to fertilizer N is lacking for continuous corn and corn following soybean [Glycine max (L.) Merr.] when grown with conventional and no‐tillage systems on poorly drained claypan soils. Field studies spanning 5 site‐years were conducted on somewhat poorly (Udollic Ochraqualf) and poorly (Mollic Albaqualf) drained claypan soils in central and northeast Missouri. The experimental design was a split‐split plot, where whole plots were tillage system (chisel‐disk and no‐till) and subplots were rotation (continuous corn and corn following soybean). Subsubplots were N rates of 0, 67, 135, 202, and 269 kg ha−1, applied preplant as either anhydrous NH3 (82‐0‐0 N‐P‐K) or knife‐injected urea‐ammonium nitrate (UAN) solution (32‐0‐0). Corn grain yield response to fertilizer N was described by quadratic and quadraticplateau models that had similar R2 values. With continuous corn, both models predicted no‐till to require 14 to 17 kg ha−1 (5–7%) less fertilizer N for maximum yield and profit than the chisel‐disk system. The predicted maximum no‐till grain yield was 0.34 Mg ha−1 less than the chisel‐disk system. No‐till corn following soybean required an average additional 17 kg N ha−1 (8%) for maximum yield (quadratic model) and 45 kg N ha−1 (35%) for maximum profit (quadratic‐plateau) than the chisel‐disk system. The average maximum yield for no‐till corn following soybean was 0.20 Mg ha−1 less than the chisel‐disk system. Apparent N credit for corn following soybean varied from 0 to 159 kg ha−1. With the quadratic model, the average N credit was 54 kg ha−1 for the chisel‐disk system and 24 kg ha−1 for no‐till. Decreased no‐till corn yields that required equal or greater fertilizer N indicate at least a short‐term economic disadvantage for this tillage system on these poorly drained soils.
Aerodynamic Characteristics of Corn as Determined by Energy Balance Techniques
Authors: Tolk Judy A. , Howell Terry A. , Steiner Jean L. , Krieg Daniel R.
Published: July 2010

Aerodynamic resistance to heat transfer (rah) needed to calculate sensible heat flux (H) used in energy balance modeling can be estimated from momentum aerodynamic resistance with corrections for atmospheric stability. This study compared rah and H modeled by four commonly used resistance methods with rah and H measured indirectly through energy balance techniques. Three momentum aerodynamic parameters were calculated: roughness length, Zom; zero plane displacement, d; and friction velocity, U*. Corn (Zea mays L.) was grown on east‐west rows (0.75 m wide) in 1989 and 1990 at Bushland, TX, in two contiguous 5‐ha fields where two weighing lysimeters were located and micrometeorological measurements were made. Sensible heat flux was indirectly measured as a residual of the energy balance and then used to calculate aerodynamic resistance. Momentum aerodynamic parameters were calculated from near‐neutral condition wind‐speed profiles using a least squares procedure. The momentum parameter relationships to crop height (CH) were d = 0.73 ✕ CH (r2 = 0.59) and Zom = 0.12 ✕ CH (r2 = 0.96). While no rah model performed well, the best linear fit (r2 = 0.75, y = 1.08x + 4.2) between measured (x) and modeled (y) rah occurred under stable atmospheric conditions; for measured and modeled H, the best linear fit (r2 = 0.84, y = 0.93x + 62.1) occurred under all atmospheric conditions. Measured rah in neutral and unstable conditions was not closely associated with wind speed. Performance of a model with a limited stability factor was improved by increasing the magnitude of the factor. These results suggest that rah models may be sensitive to atmospheric stability and local conditions such as fetch and leaf area.
Estimating Leaf Wetness in Dry Bean Canopies as a Prerequisite to Evaluating White Mold Disease
Authors: Deshpande Rohini Y. , Hubbard Kenneth G. , Coyne Dermot P. , Steadman James R. , Parkhurst Anne M.
Published: July 2010

In semiarid regions, wetness of leaves or other plant parts is essential for development of white mold disease [caused by Sclerotinia sclerotiorum (Lib.) de Bary] in dry edible bean (Phaseolus vulgaris L.). Our goal was to monitor leaf wetness in field plots and predict leaf wetness from prevailing meteorological conditions. The dew point within the canopy and the adjacent leaf temperature (infrared) were used to estimate leaf wetness in two dry bean cultivars of highly contrasting canopy architecture. These are simple, direct measurements that do not disturb the canopy. Sensors were calibrated before and after field measurement periods. Results were compared with the saturation air vapor pressure deficit from a nearby weather station to derive an empirical equation for estimating leaf wetness. The measured leaf wetness period in the dense canopy (cv. Tara) exceeded that in the open canopy (cv. Starlight) by 14% (plus an offset of 1.35 h). This corresponded to higher white mold disease (WM) severity in the dense than in the open canopy. The respective WM severity for dense and open canopies was 93 and 32% in 1990, and 73 and 10% in 1991. The empirical relationship for estimating hourly leaf wetness explained 81% of the variance in the open canopy and 70% of the variance in the dense canopy in 1991; in 1992, accuracy approached 90%. Thus, nearby weather station data offer input to a method that in turn offers a means of assessing leaf wetness in Tara and Starlight, with potential for use with other cultivars. Theoretical considerations indicate that the empirical coefficients are a function of canopy microclimate. Further studies should evaluate the relationship between these empirical coefficients and canopy architecture.
Comparison of Limited Irrigated vs. Dryland Cropping Systems in the U.S. Great Plains
Authors: Norwood Charles A.
Published: July 2010

Irrigated hectares in the Great Plains are being converted to dryland because of the declining water table and increasing energy costs for irrigation. A study was conducted in the central Great Plains near Garden City, KS, from 1989 through 1991 to compare limited‐irrigated cropping systems for use on land that would otherwise be converted to dryland. Irrigated continuous winter wheat (Triticum aestivum L.) and grain sorghum [Sorghum bicolor (L.) Moench] were compared with the wheat‐sorghum‐fallow rotation where either one, both, or neither crop was irrigated. Irrigated wheat yields in the rotations averaged 26% more than dryland. Rainfall eliminated any benefits of irrigation on the 1989 and 1990 grain sorghum, but yields in the rotations were increased an average of 168% over dryland in 1991. Average irrigated continuous wheat and sorghum yields were 19 and 8% less than irrigated rotated wheat and sorghum yields, respectively, in 1990 and 1991, but when yields were annualized continuous wheat and sorghum averaged 20 and 59% more than the irrigated rotations. Annualized irrigated rotation yields were similar to dryland in 1990, but 68% more in 1991. Irrigating either crop in the rotation produced similar annualized yields, but irrigating both crops increased yield an additional 13%. Irrigation water use efficiencies were highest for the rotated crops, and lowest for the continuous crops. More grain can be produced with very limited irrigation than with dryland systems, but no single system is best for all conditions. Producers with less water should probably irrigate fallow systems, while those with more water can crop more intensely.
Yields of Alfalfa Varieties Selected for Aphanomyces Resistance in Kentucky
Authors: Vincelli Paul , Lauriault Leonard M. , Henning Jimmy C.
Published: July 2010

Field tests were conducted over 4 yr to investigate whether alfalfa (Medicago sativa L.) varieties and experimental populations selected for resistance to aphanomyces root rot (caused by Aphanomyces euteiches Drechsler) (here termed aphanomyces‐selected varieties) would collectively outyield varieties not selected for resistance (unselected varieties). All entries were resistant to phytophthora root rot (caused by Phytophthora medicaginis E.M. Hans & Maxwell). At the conclusion of the tests, the mean cumulative dry matter yield of aphanomyces‐selected varieties was higher (4.2% increase, P = 0.063) than that of unselected varieties in a site naturally infested with A. euteiches and P. medicaginis. However, total yields of certain unselected varieties equaled or even exceeded (P = 0.10) those of certain aphanomyces‐selected varieties, and there was no correlation among varieties between yield and percentage of Aphanomyces‐resistant plants. No significant difference in mean cumulative yield was observed between aphanomyces‐selected and unselected varieties in two sites infested with A. euteiches alone nor in four sites not infested with either pathogen. Since outbreaks of seedling diseases were minor in all tests, the yield effects observed may be due to differences in plant health manifested after stand establishment. Our data are consistent with the hypothesis that selection for Aphanomyces resistance contributes to an overall improvement of elite alfalfa germ plasm for cultivation in poorly drained soils infested with both A. euteiches and P. medicaginis. However, considered alone, selection for Aphanomyces resistance in individual varieties was not always predictive of high yield in Aphanomyces‐infested sites. These tests do not rule out the possibility of a substantial yield benefit to Aphanomyces resistance under conditions unusually conducive to seedling disease induced by A. euteiches.
Distinguishing Resource Competition and Chemical Interference: Overcoming the Methodological Impasse
Authors: Weidenhamer Jeffrey D.
Published: July 2010

Understanding allelopathy may hold the key to new weed management strategies. However, the difficulty of distinguishing chemical interference from competition has hindered studies of allelopathy in natural and cultivated plant communities. Experimental rigor has increased, but has yet to provide unambiguous proof of allelopathy. The complexities of allelopathic interactions, as illustrated by ongoing investigations in the Florida scrub, make it unlikely that clear examples will be forthcoming. While conclusive proof of chemical interference may not be attainable, the challenge of obtaining strong supportive evidence remains. Progress is needed in bioassay methods that distinguish allelopathy from other interference mechanisms. Phytotoxic effects are density‐dependent in a manner inconsistent with resource competition, suggesting that allelopathy can be distinguished by characteristic growth responses across planting densities. In monoculture, greater phytotoxicity at low plant densities causes deviations from expected yield‐density relationships. In mixed culture, the targetneighbor method, in which differing densities of a neighbor species are planted around a target plant, has been used to study phytotoxic effects. In the presence of an applied phytotoxin, increased growth of sensitive target plants as the density of insensitive neighbors increases is inconsistent with a hypothesis of resource competition and provides compelling, though not conclusive, evidence for chemical interference. Once evidence of allelopathy is obtained from plant growth studies, supportive analytical data must be obtained from analyses of toxin concentrations and flux rates in the soil and rhizosphere. The use of adsorbent materials originally applied to the analysis of organic pollutants should allow the measurement of allelochemical flux rates in addition to static concentrations.
Subsoil Nitrate Uptake and Symbiotic Dinitrogen Fixation by Alfalfa
Authors: Blumenthal Jürg M. , Russelle Michael P.
Published: July 2010

Alfalfa (Medicago sativa L.) is a deeply rooted perennial that may be able to remove NO3 from the subsoil beneath the rooting zone of annual crops. Our main objectives were to characterize the potential of two alfalfa cultivars (Agate and Ineffective Agate, an ineffectively nodulated near isoline of Agate) to remove NO3 from the subsoil and to evaluate the influence of available subsoil NO3 on symbiotic N2 fixation. Low (≈0.3 mM) or high (20 mM) NO3−N concentrations were supplied through a subsoil irrigation system installed in a Hubbard loamy sand soil (sandy, mixed Udorthentic Haploboroll) at Becker, MN. Nitrate uptake and N2 fixation were evaluated during two regrowth periods using 15N. During fall regrowth in the establishment year, supply of 20 mM 15N‐enriched NO3 through subsoil irrigation did not decrease symbiotic N2 fixation; during summer regrowth of the first production year, symbiotic N2 fixation decreased only 40% (from 7.77 to 4.60 g N m−2). Even though it had higher yields, Agate alfalfa removed less subsoil NO3−N (1.52 and 5.51 g N−2) than did Ineffective Agate (3.12 and 7.13 g N m−2) in each of two harvests where 15N was applied. Root length and mass after 2 yr were not altered by NO3 treatment or cultivar. This is the first time that direct measurements of subsoil nitrate removal have been made in the field for an N2‐fixing crop. Because it is unlikely that differences in NO3 uptake efficiency could account for such cultivar differences, we propose that assimilation of atmospheric N2 reduced the capacity of the fixing crop to absorb NO3. These results suggest that non‐N2‐fixing alfalfa cultivars would be more useful for bioremediation of nitratecontaminated sites than standard cultivars.
Plant Morphology and Forage Nutritive Value of Three Bahiagrasses as Affected by Harvest Frequency
Authors: Cuomo G. J. , Corkern D. L. , McCoy J. E. , Walz R. , Blouin D. C.
Published: July 2010

Differences in morphological development have been reported among bahiagrass (Paspalum notatum Flügge) cultivars. Relationships of harvest management to these developmental differences and subsequent forage production and nutritive value have not been characterized. A 2‐yr study was initiated by harvesting ‘Argentine’, ‘Pensacola’, and ‘Tifton 9’ bahiagrass every 20, 30, or 40 d from mid‐May until mid‐September. Objectives were to determine if differences exist among these cultivars for leafiness, morphological development, forage mass, and forage nutritive value, and to determine if differences were affected by harvest frequency and season of growth. Leaf percentage by weight, inflorescence development, forage nutritive value, and forage mass were evaluated for monocultures of the three cultivars. Argentine had a greater (P 0.01) percent leaf (87.2%) than did Pensacola (80.4%) or Tifton 9 (81.0%). In addition, Argentine and Tifton 9 produced fewer (P = 0.01) inflorescences at 20‐ and 30‐d harvest frequencies than did Pensacola. Leaf percentage was greater (P = 0.01) at 20‐ (88.7%) than at 30‐ (78.6%) and 40‐d (81.4%) harvest frequencies. There were cultivar × plant part interactions (P < 0.05) for neutral detergent fiber (NDF) and lignin, but differences were detected only in the stem component. No differences (P ≤ 0.05) were detected among cultivars for other nutritive value variables. Total forage mass was similar (P ≤ 0.05) among cultivars. Differences in forage mass were detected (P = 0.01) only at the first harvest, where Argentine produced less forage (1.9 Mg ha−1) than Pensacola (3.1 Mg ha−1) or Tifton 9 (2.9 Mg ha−1). The combination of greater leaf percentage and fewer inflorescences indicate that Argentine could have potential advantages as a forage over other bahiagrass cultivars.
Effect of Wheat Morphological Stage at Grazing Termination on Economic Return
Authors: Redmon Larry A. , Krenzer Eugene G. , Bernardo Daniel J. , Horn Gerald W.
Published: July 2010

The economic impact of timing of grazing termination in the wheat (Triticum aestivum L.) grain‐stocker cattle (Bos sp.) enterprise has not been elucidated. A 4‐yr study used the first hollow stem stage of growth in ungrazed wheat as a grazing termination indicator and the subsequent effect on net return. First hollow stem is the stage at which hollow stem can first be identified above the crown; it occurs prior to the growing point reaching the soil surface. Net return was maximized when grazing was terminated at first hollow stem. Grain yield decreased (P< 0.05) 83 kg ha−1 d−1 as cattle grazed past first hollow stem. Increased weight gain by cattle was not sufficient to offset grain yield losses. Since hollow stem formation was delayed in grazed wheat, producers who use semidwarf wheat as a dual‐purpose crop should monitor the morphological stage in ungrazed areas of the field to determine the optimum time to terminate grazing.
NEPER‐Weed: A Picture‐Based Expert System for Weed Identification
Authors: Schulthess Urs , Schroeder Kris , Kamel Ahmed , AbdElGhani AbdElGhani M. , Hassanein El‐Hassanein E. , AbdElHady Shaban Sh. , AbdElShafi AbdElMaboud , Ritchie Joe T. , Ward Richard W. , Sticklen Jon
Published: July 2010

Most current expert systems for weed identification are ruled‐based. They use text only and rely on a large number of botanical terms. In rule‐based expert systems, knowledge is not organized in a structured manner. Hence, they are difficult to create and use. This article describes the advantages of the generic task approach to building expert systems. The generic task approach is based on the assumption that certain knowledge and control structures may be common to a particular task across domains. Hence, reusable control structures, or tools, have been developed to solve problems. We developed an expert system that uses a hierarchical classification tool. Text descriptions are replaced with pictures, to minimize the use of technical terms. Hypotheses are established or ruled out on the basis of the user's choices among options presented as pictures. This approach reduces the number of characters required for weed identification and the user does not need to know technical terms. In our system, the classification of grasses is based on the morphologies of the leaf base and leaf surface. Broadleaf weed classification is based on the shapes of the cotyledon and true leaf. The system contains 51 Egyptian weeds. The hierarchical classification tool allowed for a clear separation of the knowledge from the structure in which the knowledge is organized. The object‐oriented nature of this approach simplifies adding or removing weeds. This approach can be readily applied to other domains, such as disease identification, fertilizer recommendation, or cultivar selection.
Soybean Physiology, Regrowth, and Senescence in Response to Defoliation
Authors: Klubertanz Tom H. , Pedigo Larry P. , Carlson Richard E.
Published: July 2010

Recent studies have shown that one component of soybean [Glycine max (L.) Merr.] response to insect defoliation is delayed senescence and increased physiological activity of lower, remaining leaves. The objective of this study was to test the ability of these and other mechanisms of defoliation tolerance to function in drought‐stressed plants. Controlled irrigation rates and artificial defoliation treatments were used in a 2‐yr study. Defoliation significantly increased soil‐moisture percentage in both years, showing that defoliated stressed plants conserve more water than nondefoliated stressed plants. Compensatory regrowth was observed following defoliation, resulting in more leaves in defoliated plants than predicted. Removal of expanding leaves, however, reduced leaf area and also reduced growth potential relative to nondefoliated plants. Senescence of lower leaves was delayed in defoliated plants, as has been found in previous studies. The responses of leaf physiological rates to defoliation were similar in drought‐stressed and well‐irrigated plots. These data suggest that crop models integrating physiological parameters and defoliation rates could add or subtract the effect of drought stress as a constant or simple function.
Water Transport Characteristics of Cotton as Affected by Drip Irrigation Layout
Authors: Moreshet Samuel , Fuchs Marcel , Cohen Yehezkel , Cohen Yefet , Langensiepen Matthias
Published: July 2010

To reduce drip irrigation equipment costs, dripper lines are laid in alternate interrow spaces. This study examined the effect of this practice on cotton (Gossypium hirsutum L.) water relations. Measurements of water uptake and water potential of plants grown in the field were conducted during four rainless summers at two locations. During the first summer, drippers in every interrow space delivered about 50 mm of water, the exact amount depending on estimated evapotranspiration (ET), every 10 d. The following summer, drip lines were laid in alternate interrow spaces, applying frequent (2‐4 d) and small (10‐20 mm) amounts of water, based on estimated ET. Treatments were repeated the following two summers. Measurements included water uptake (F), leaf water potential (ψ1, and soil water content. Whenever a linear relationship between diurnal ψ1 and F was found, we determined the hydraulic conductance (KT) of the plants as the line's slope reciprocal, and the intercept (ψ0) as the water potential at the root‐soil interface. A linear relation was found in the treatment with drippers in every interrow space. Water stress developed toward the end of the irrigation interval, causing KT to decrease without affecting ψ0. Irrigation restored KT to its initial value. With the alternate interrow‐space pattern, the relationship between ψ1 and F remained linear only until midday. Afternoon (ψ1, F) points were below those of the morning, suggesting a lowering of the soil water potential near the roots. It was concluded that drippers laid in alternate interrow spaces expose cotton to frequent short periods of water stress.
Sorghum Response to Saline Industrial Cooling Water Applied at Three Growth Stages
Authors: Ulery April L. , Ernst Frederick F.
Published: July 2010

Saline wastewater from industrial or agricultural sources may be an alternative irrigation supply in arid regions if effective crop and water management strategies for their use are developed. A field experiment was conducted to determine if grain yields of sorghum [Sorghum bicolor (L.) Moench] irrigated with undiluted saline waste‐water from cooling towers of an electrical power generation plant can be significantly increased by applying nonsaline water at a critical growth stage. The wastewater had an average electrical conductivity (EC) of 0.67 S m−1 and was high in CaSO4. Plot studies were conducted for 4 yr using conventional cultural practices and sprinkler irrigation on Tujunga loamy sand—Hanford fine sandy loam soil (mixed, thermic Typic Xeropsamment—coarse‐loamy, mixed, nonacid, thermic Typic Xerorthent). Highest grain yields were obtained from the nonsaline control plots and from treatments that received nonsaline water during either the vegetative or reproductive growth stages. Plant height decreased in response to salinity, and differences between treatments were apparent by 27 d after planting. Plant height and grain yield were both negatively correlated with soil salinity by the 3rd yr of the experiment. Over an extended length of time, the best treatment for maximizing yield and utilizing saline wastewater is the application of nonsaline water early in the season to germinate and establish seedlings, followed by saline water during the grain‐filling stage.
Grass–Legume Bicultures as Winter Annual Cover Crops
Authors: Ranells Noah N. , Wagger Michael G.
Published: July 2010

Grass‐legume bicultures as winter annual cover crops may combine the N scavenging ability of grasses and the biological N2 fixation capacity of legumes to improve N management in crop production systems of the southeastern USA. A 3‐yr field experiment was conducted on a Norfolk loamy sand (fine‐loamy, kaolinitic, thermic Typic Kandiudults). The focus of this research was to examine the differences among legume monocultures and grass‐legume bicultures with regard to early spring dry matter (DM) and N accumulation, and related effects on soil inorganic N levels and subsequent corn (Zea mays L.) yield. Austrian winter pea [Pisum sativum L. subsp, sativum var. arvense (L.) Poir.], crimson clover (Trifolium incarnatum L.), commonve tch (Vicla saava L.), and hairy vetch (Vicla villosa Roth) were grown in monoculture and in bicultures with rye (Secale cereale L.), oat (Arena satira L.), and wheat (Triacum aestivum L.). Aboveground plant material was harvested in early March, late March, and mid‐April. Biomass was separated into component species and analyzed for total N and C concentrations. Averaged over 3 yr, legume component DM accumulation in monoculture and biculture ranged from 0.87 to 2.53 Mg ha−1, with a ranking of Austrian winter pea < hairy vetch < commonv etch < crimson clover. For the same period, the grass component DM accumulation ranged from 1.31 to 2.28 Mg ha−1, in the order rye = oat < wheat. Three‐year mean N accumulation values for the legume component followed the same relative ranking and ranged from 24 to 93 kg N ha−1. Grass factor N content ranged from 18 to 39 kg N ha−1 in the order rye < oat < wheat. For all bicultures, the average C:N ratio over the 3‐yr experiment was >30, suggesting that net N mineralization would occur from the decomposing cover crop residues. Profile soil inorganic N (0 to 90 cm) was greater in legume monoculture than in grass‐legume biculture treatments, indicating the ability of grasses to capture soil N. Corn yield was affected by the treatments in 1 of 3 yr, with greater yields following a legume monoculture than a grass‐legume biculture. Collectively, these results suggest that grass‐legume bicultures as winter annual cover crops have the potential to utilize residual soil NO3 and thereby minimize leaching while adding fixed N to cropping systems in the southeastern USA.
Deep and Shallow Banding of Phosphorus and Potassium as Alternatives to Broadcast Fertilization for No‐Till Corn
Authors: Bordoli José M. , Mallarino Antonio P.
Published: July 2010

Proper P and K management for no‐till crops is uncertain. Potential problems include inappropriate extrapolation of soil test interpretations and fertilizer recommendations from conventional tillage, inappropriate soil sampling techniques, and inefficient fertilizer placement. This study compared broadcast, deep‐band, and planter‐band P and K placements for no‐till corn (Zea mays L.). Long‐term P and K trials were established in 1994 at five Iowa research centers and were evaluated for 3 yr. Eleven short‐term P‐K trials were established in farmers' fields during the same period. Treatments were various P (0 to 56 kg P ha−1) and K (0 to 132 kg K ha−1) rates broadcast, banded with the planter 5 cm beside and below the seeds, and deep‐banded at the 15‐ to 20‐cm depth before planting. Soil samples were collected from the 0‐ to 7.5‐cm and 7.5‐ to 15‐cm depths prior to planting. Soiltest P (PST) at the 0‐ to 15‐cm depth ranged from very low to very high across sites; soil‐test K (KST) ranged from optimum to very high. There were grain yield responses to fertilization at several sites, but no significant differences between the P or K rates and no interactions between rates and placements. Phosphorus increased yields only in soils testing very low or low, and there was no response to P placement at any site. Potassium increased yields in several soils that tested optimum or higher in KST, and yields were higher when K was deepbanded. High rates of broadcast or planter‐banded K did not offset the advantage of deep‐banded K. Responses were better related with deficient rainfall in late spring and early summer than with KST. Current soil‐test P interpretations and P fertilizer recommendations based on chisel‐plow tillage are appropriate for most Iowa soils managed with no‐tillage. Further work is needed to better characterize and predict responses to deep‐banded K. Because yield response was small, the cost‐effectiveness of deep‐band K will be determined largely by application costs.
A Canopied Sprayer for Accurate Application of Herbicides
Authors: Ginn Lawrence H. , Adams E. Ray , Heatherly Larry G. , Wesley Richard A.
Published: July 2010

Preemergent and postemergent herbicides applied to research plots must be confined to the target area and crop. Our objective was to develop an apparatus that could be used to apply herbicides effectively for weed control in randomized field plots of multiple crops with no injury to nontarget crops in adjacent plots. A canopied sprayer that attaches to a row‐crop tractor having a standard Category I or II three‐point hitch and a PTO was designed and constructed. This sprayer delivered broadcast‐ and band‐applied herbicides to small plots without causing drift‐related injury to nontarget crops planted in adjacent plots. Use of this sprayer eliminated wind‐blown drift, and ensured the confinement of herbicides to target plots, alleys, and borders.
Nitrogen Dynamics of Various Green Manure Species and the Relationship to Lowland Rice Production
Authors: Clément Alain , Ladha Jagdish K. , Chalifour François‐P.
Published: July 2010

Green manure (GM) is an alternative to mineral fertilizers, particularly for subsistence farmers whose resource base is small. Published information on the influence of the chemical composition of GM on N dynamics in lowland rice (Oryza sativa L.) is scarce. A field experiment was conducted in the 1992 wet season (WS), the 1993 dry season (DS) and the 1993 wet season to compare GM species and urea as sources of N for rice, to monitor N release and uptake during the season, and to verify the effect of the chemical composition of GM on rice yield (including the residual effect on dry season rice). Ten species were compared, with two controls (with and without deep‐placed urea supergranules). Nitrogen from urea or GM crops was applied at the rate of 80 kg N ha−1. Most GM species performed as well as urea supergranules. Cowpea [Vigna unguiculata (L.) Walp.], soybean [Glycine max (L.) Merr.], and sorghum [Sorghum bicolor (L.) Moench] outyielded the urea control in the 1992 wet season. Residual effects of GM incorporation on rice grain yield during the 1993 dry season were generally modest. Rice grain yield response to GM application was comparable for both the 1992 and 1993 wet seasons (r2 = 0.83**). In microplots without rice plants, there was limited GM‐N mineralization past 30 days after transplanting (DAT). Soil NH+4‐N with rice increased until about 20 DAT, and then decreased sharply, because of rice N uptake. At 50 DAT, soil NH+4‐N reached very low levels in all treatments. Rice N uptake between 31 and 52 DAT was explained by the size of early‐season soil NH+4‐N pool (r2 = 0.83**). Higher N uptake rates by rice with GM than with urea from 52 to 69 DAT indicate a better synchrony between GM‐N availability and rice N uptake. The C/N ratio of GM species influenced rice N uptake, but only early in the season.
Are Simulation Models Ready for Agricultural Research in Developing Countries?
Authors: Mutsaers H. J. W. , Wang Zaoqian
Published: July 2010

As an example of the application of simulation modeling in developing countries, the SARP (Simulation and Systems Analysis for Rice Production) project is reviewed. SARP promoted the ORYZA models for paddy rice (Oryza sativa L.) research in Southeast Asia. The models successfully simulated crop growth as affected by canopy photosynthesis, sink capacity, and N nutrition. The rather crude plant physiology in these and similar models limits their usefulness in simulating the effect of morphological modifications and the response to various stress factors. Modeling skills developed by SARP in Asian research institutes cannot be maintained without continued coordination from advanced institutes. More basic knowledge on the plant's morphogenesis and feedback mechanisms is required for effective simulation of plant adaptation to complex growth environments, including intercropping, as found in many developing countries. A more rigorous modular approach to modeling is advocated, as well as standardization of modules for well‐understood processes, as part of a toolkit for applied research for use in combination with other techniques, including statistical techniques.
Insect Defoliation and Population Dynamics in Blends of Resistant and Susceptible Soybean Cultivars
Authors: Sij John W. , Bowers Glenn R. , Way M. O. , Boykin D. L.
Published: July 2010

Phytophagous insects can cause significant economic yield loss in soybean [Glycine max (L.) Merr.] production areas of the southern United States. Although breeding efforts have resulted in developing insect‐resistant cultivars, the yield potential of these cultivars is generally lower than conventional cultivars under conditions of light insect pressure. The objective of this study was to determine if a blend of insect resistant and insect susceptible cultivars affords some degree of insect control while maintaining high yields under high insect pressure environments. Experiments were conducted on a Labelle soil (Oxyaquic Vertic Argiaquolls) near Beaumont, TX, in 1990 to 1992. The 3‐yr field study included five population ratios of Maturity Group VIII cultivars Dowling (insect susceptible, S) and Crockett (insect resistant, R): 100 S:0 R, 75 S:25 R, 50 S:50 R, 25 S:75 R, and 0 S:100 R. Plots were sampled weekly for insects and percent leaf defoliation when insect populations began to increase in late summer. Data were analyzed with blend treated as a linear trend. Insect counts of six major pests showed that, of 18 possible year‐insect combinations, in only three cases were there significant population differences due to blend. In late season, the percent defoliation of Crockett increased in all 3 yr as the percentage of Crockett in the blend increased. By contrast, as the percentage of Dowling in the blend increased, the percent defoliation of Dowling decreased in 2 of the 3 yr. Therefore, blending Crockett and Dowling did not offer insect defoliation protection for Dowling and may have had an opposite effect. Maximum percent defoliation for Crockett was generally 40 to 50% less than that for Dowling. In 1990 and 1991, blending had no effect on yield or seed quality. In 1992, there was a significant, negative effect on yield (b = −4.46) and seed quality (b = 0.01) as the percentage of Crockett increased in the blend. Blends of these cultivars did not improve yield of Dowling under conditions of insect pressure compared with a pure stand of Dowling. A blend of insect resistant and susceptible cultivars did not appear to be a suitable insect control management strategy in soybean.
Bermudagrass Response to High Nitrogen Rates, Source, and Season of Application
Authors: Osborne Shannon L. , Raun William R. , Johnson Gordon V. , Rogers Jerry L. , Altom Wadell
Published: July 2010

High N rates and source of N have been thoroughly evaluated in bermudagrass [Cynodon dactylon (L.) Pers.] forage production, but less is known concerning season of application and estimated fertilizer N recovery in these systems. Two field studies (Ardmore, OK: Wilson silt loam, Vertic Haplustalfs; Burneyville, OK: Minco fine sandy loam, Udic Haplustolls) were conducted at two locations over two years to evaluate the effects of rate, timing, and source of N on bermudagrass forage yield, total N, NO3 concentration, and estimated fertilizer N recovery. Nitrogen was applied at rates of 112, 224, 448, 672, and 1344 kg N ha−1 as NH4NO3 or urea in early spring (March) and late summer (August). Fertilizer N recovery can be maximized at rates of 112 and 224 kg N ha−1 applied in the early spring and late summer, respectively. Even when N rates of 1344 kg N ha−1 were applied annually, bermudagrass forage NO3‐N was seldom above 2000 mg kg−1, which is below published toxic levels (2400–4500 mg kg−1) for cattle (Bos taurus) consumption. Early‐spring applied N increased yields, N removal, and fertilizer recovery compared with late‐summer applied N. Fertilizer N recovery was higher for NH4NO3 than for urea, especially when applied in late summer. Late‐summer applications of urea should be avoided, due to increased NH3 volatilization losses. Nitrogen applied at 112 kg N ha−1 in early spring can result in fertilizer recoveries in excess of 85%. These high recoveries in forage production systems are possibly a result of continuous preanthesis forage harvesting when gaseous plant N losses are small, but which increase following anthesis.
Modeling Plant Competition with the GAPS Object‐Oriented Dynamic Simulation Model
Authors: Rossiter David G. , Riha Susan J.
Published: July 2010

Modeling interspecies competition is a natural application for dynamic simulation models of agricultural systems. We extended a dynamic simulation model of the soil–plant–atmosphere system, GAPS, to include the case where multiple plant species are growing in competition. The competition model was implemented as an object hierarchy that exchanges information with a crop model hierarchy by means of access procedures. Crop models, atmospheric procedures, and soil–plant water interface procedures required minimal change in order to support the competition model. We implemented two competition models: modified ALMANAC and winner‐takes‐all. The modified ALMANAC model requires that crop models of competing plants simulate leaf area index, single‐crop light interception, and canopy height. Using this information, the ALMANAC model partitions solar radiation among the competitors. GAPS is written in the object‐oriented language Turbo Pascal.
Use of Anhydrous Ammonia in Single‐Pass Seeding Operations of Spring Wheat at Varied Landscape Positions
Authors: Matus Alejandro , Walley Fran , Hnatowich G. , van Kessel Chris , Knight J.D.
Published: July 2010

Adoption of no‐till seeding practices by many farmers has increased interest in using anhydrous ammonia (AA) in single‐pass seeding operations. It is expected that crop response to different fertilizer N sources and fertilizer placement will vary at the landscape level, because of inherent differences in soils related to topography. Two openers (side‐band and sweep wing tip) were evaluated for use in a single‐pass seeding operation of spring wheat (Triticum aestivum L.). The openers differed in fertilizer placement and soil disturbance. The effect of AA on grain yield and protein content as influenced by application rate and opener was investigated at varied landscape positions. The experiment was conducted at six sites in two years using a randomized complete block design. Averaged across year and location, wheat grain yield was higher on footslopes than on shoulders; however, the effect of landscape position was not consistent at all locations. Landscape position did not affect protein content. Application of AA with either opener resulted in grain yields and protein contents comparable to granular urea and ammonium nitrate (AN) fertilizers. Even at the highest AA application rate tested (105 kg N ha−1), no crop damage was expressed in final yield.