bluuebunny/crossref_metadata_2025 huggingface dataset:
Shoot Growth Rate of Soybean as Affected by Drought Stress1
Authors: Hoogenboom Gerrit , Peterson Curt M. , Huck M. G.
Published: July 2010

Shoot size at time of flowering has a strong effect on final yield and can be significantly reduced by drought stress. Studies were performed at the Auburn rhizotron from 1981 through 1983 to investigate the effects of drought stress on daily shoot growth rates of soybean [Glycine max (L.) Merr. ‘Braxton’]. Plants were grown in a Marvyn loamy sand (fine‐loamy, siliceous, thermic Plinthic Paleudult) and received only rainfall (NI) or rainfall and supplemental irrigation (IR) during each growing season. Irrigation was controlled by tensiometers installed 0.4 m deep, and water was added when soil water potential (Ψ soil) fell below −15 kPa. Shoot growth patterns, e.g., stem elongation, leaf formation, and leaf area increase, followed characteristic exponential growth curves during early vegetative development when no moisture stress was evident. Sensitivity to water stress (Ψ soil < −15 kPa) increased as total leaf area and resulting transpiration demand increased. Stem elongation and leaf area expansion rates decreased significantly for the NI treatment during periods of water stress. During periods of moisture stress, leaves formed on NI plants were smaller than leaves at comparable nodes on IR plants (0.0075 vs. 0.010 m2). After periods of rainfall, shoots of NI plants grew more rapidly than those of IR plants (0.025 vs. 0.020 m/day), and most of the growth reduction during the previous stress period was regained. Accumulated growth over time, i.e., total leaf area (0.22 m2), number of nodes (17), final internode lengths (e.g., 0.08 m), and mainstem height (1.15 m), was comparable between NI and IR treatments. Thus, no long‐term differences were observed between IR and NI treatments because significant short‐term reductions in shoot growth rate due to drought stress were followed by compensatory growth during periods of rainfall.
Seeding Rate and Row Spacing Effects on Yield and Yield Components of Ratoon Rice1
Authors: Jones D. B. , Snyder G. H.
Published: July 2010

Ratoon cropping of rice (Oryza sativa L.) has recently received renewed attention as a means to lower unit production costs. However, little information is available on the effect of main crop cultural practices on ratoon yields of drill‐seeded rice. The objective of this study was to determine the effect of main crop seeding rate and row spacing of drill‐seeded rice on yield and yield components of the ratoon crop. Two contrasting plant types, tall (cv. Lebonnet) and semi‐dwarf (cv. Bellemont and Lemont), were drill‐seeded at rates of 50, 100, and 150 kg seed ha−1 in 0.15‐, 0.20‐, and 0.25‐m row spacings in three tests conducted on an organic soil. Ratoon grain yields differed significantly (P<60.01) among tests for both plant types, and were not significantly (P<60.05) correlated to main crop grain yields (r= −0.62). Ratoon grain yields of both cultivars were not significantly (P<0.05) affected by main crop seeding rate, row spacing, or seeding rate X row spacing interaction. Increased seeding rates significantly increased ratoon panicles per square meter (P< 0.01) and decreased ratoon filled grain number per panicle (P<0.01) in all tests for both plant types. Panicles per square meter and filled grain number per panicle accounted for over 85% of the variation in ratoon grain yield. Compensation between these two yield components stabilized ratoon grain yield at relatively low levels.
Atmospheric Carbon Dioxide Enrichment Effects on Cotton Midday Foliage Temperature: Implications for Plant Water Use and Crop Yield1
Authors: Idso S. B. , Kimball B. A. , Mauney J. R.
Published: July 2010

In an experiment designed to determine the likely consequences of the steadily rising carbon dioxide (CO2) concentration of Earth's atmosphere for the foliage temperature, water use, and yield of cotton (Gossypium hirsutum L. var. Deltapine‐61) plants, cotton was grown out‐of‐doors at Phoenix, AZ, in open‐top, clear‐polyethylene‐wall, CO2‐enrichment chambers for three summers under mean daylight CO2 concentrations of 340, 500 and 640 μmol CO2 mol−1 air on an Avondale clay loam soil [fine‐loamy, mixed (calcareous), hyperthermic Anthropic Torrifluvent]. Infrared thermometer measurements of the cotton foliage temperature (TF) indicated that a 330 to 660 μmol CO2 mol−1 air doubling of the atmospheric CO2 content results in a midday TF, increase of 1.1 °C for well‐watered cotton at Phoenix in the summer. This temperature increase was predicted to produce a 9% reduction in per‐unit‐leaf‐area plant transpiration rate and an 84% increase in crop biomass production, which compared favorably with the measured crop biomass increase of 82% for such a doubling of the air's CO2 content. These findings, together with similar findings for a second plant species—water hyacinth [Eichhornia crassipes (Mart.) Solms]—allowed us to develop a technique for assessing the effects of a 330 μmol CO2 mol−1 air CO2 concentration increase on the percentage yield increase (Y) of a crop via infrared thermometry by means of the equation Y = 7.6% × (IJ)−1, where IJ represents the Idso‐Jackson plant water stress index. If this equation holds up under further scrutiny, it could provide a rapid and efficient means for assessing the yield response of crops to atmospheric CO2 enrichment.
Salt Effects on Alfalfa Seedling Emergence1
Authors: Assadian N. Waissman , Miyamoto S.
Published: July 2010

Alfalfa (Medicago sativa L.) is regarded as susceptible to salts at establishment. This study was conducted to evaluate: (i) emergence reduction by irrigation with saline waters; and (ii) the relationship among seed germination, hypocotyl salt injuries, and seedling emergence. Greenhouse experiments were conducted using ‘Moapa’ and ‘Mesilla’ grown in Bluepoint fine loamy sand (calcareous, thermic Typic Torripsamment). In Exp. 1, seedling emergence and salt accumulation near the soil surface were monitored after seeding at three depths (3, 10, and 15 mm) and irrigated with water of 0.8 to 7.6 dS m−1. In Exp. 2, seed germination was measured in sponges moistened with saline solutions (0.8‐32 dS m−1). In Exp. 3, seedling emergence was monitored after placing a 5‐mm layer of salted‐sand having the saturation extract salinity of 0.8 to 45 dS m−1 onto emerging seedlings to evaluate hypocotyl salt injuries. Results indicated that the rate and final emergence of both cultivars declined when salinity of irrigation waters exceeded 4.3 dS m−1, even though the seed germinated well in saline solutions of 28 dS m−1. Soluble salts had accumulated mostly in the top 5‐mm depth where salinity increased to 20 dS m−1 in 4 days when irrigated at 4.3 dS m−1. A significant reduction in emergence occurred in Exp. 3 when the salinity of the surface‐placed sand exceeded 17 dS m−1. Emergence reduction observed from a seeding depth of 3 mm was probably due to the reduction in seed germination, whereas from seeding depths of 10 mm or more, emergence appeared to be limited by hypocotyl salt injuries after germination. Alfalfa could be established with minimal salt damage from water, up to approximately 4 dS m−1, when seeded approximately 10 mm deep.
Nitrogen Utilization from Fertilizer and Legume Residues in Legume‐Corn Rotations1
Authors: Hesterman O. B. , Russelle M. P. , Sheaffer C. C. , Heichel G. H.
Published: July 2010

Legume‐corn (Zea mays L.) rotations are common throughout the U.S. Corn Belt, but little information is available about the efficiency of legume residue N utilization, or about fertilizer‐N use efficiency in different cropping sequences. Our objective was to determine the contribution of N from soil, fertilizer, and legume residues for six legume‐corn sequences. The effect of applied fertilizer N rate was also examined. Field studies were conducted on a Udorthentic Haploboroll and a Typic Hapludoll. First‐phase (Year 1) rotation components included alfalfa (Medicago sativa L.), corn, soybean [Glycine max L. (Merr.)], or fallow. Nitrogen–15‐depleted (NH4)2SO4 was applied to second‐phase (Year 2) corn. Fertilizer‐N use efficiency for second‐phase corn was 51% for the whole plant and 36% for grain, with no effect of first‐phase treatment. Average use efficiency of legume‐N (uptake of legume‐N/legume‐N incorporated) was 43% for the whole corn plant and 30% for grain. Second‐phase corn derived a greater proportion of its N from residue of alfalfa (36%) than soybean (12%). When the rate of N applied to corn was increased from 56 to 168 kg N ha−1, the proportion of N derived from legume residue decreased from 44 to 19% in whole corn plants and from 57 to 23% in grain. Results suggest that the N credit commonly attributed to legumes in crop rotation may be inflated by as much as 132%.
Grazing Effects on the Total Nonstructural Carbohydrate Pools in Caucasian Bluestem1
Authors: Christiansen Scott , Svejcar Tony
Published: July 2010

Total nonstructural carbohydrates (TNC) may be overemphasized relative to other factors governing plant survival in pastures. A grazing study was conducted on established 1‐ha pastures of Caucasian bluestem [Bothriochloa caucasica (Trin.) C.E. Hubb.] during 1983–1984 at the Forage and Livestock Research Laboratory, 2 km west of El Reno, OK. The objective was to compare allocation of TNC to leaf, stem (plus sheath), stem base, and dead components of heavily or lightly grazed Caucasian bluestem. Soils were fine‐silty Pachic Haplustolls of the Dale Series. Put‐and‐take stocking was used to maintain high and low grazing pressures from mid‐May to late September both years. Pastures were sampled four times in 1983 and three times in 1984 by excavating representative plants, separating them into plant parts, and analyzing for TNC. Heavy grazing pressure initially decreased (P<0.1) concentrations of TNC in all living tissues. However, no differences in TNC concentration due to grazing pressure were found the second year. On six of seven sampling dates over 2 yr, grazing pressure did not affect (P>0.1) the amount of TNC located in stem bases. Stem bases contained more than half the total shoot TNC in heavily grazed plants; however, lightly grazed plants contained much more total shoot TNC (as much as seven times greater) compared to heavily grazed plants, due to light utilization by animals. A densely appressed physical arrangement of stem bases provided sites for tiller initiation and protection from grazing. Crown architecture in Caucasian bluestem, together with physiological and morphological adjustments, ensured a nongrazeable mass of stem bases containing sufficient quantities of TNC to sustain plants under heavy grazing.
Corn‐Hybrid Performance under Conventional and No‐Tillage Systems after Thinning1
Authors: Carter P. R. , Barnett K. H.
Published: July 2010

Corn (Zea mays L.) producers question the relative performance: of hybrids under different previous‐crop residue management systems. The objective of this study was to assess tillage system ✕ corn hybrid interactions for hybrids commonly grown in the northern United States. Field experiments were conducted at four locations in Wisconsin during 1984 and 1985, including sites with Plano and Nickin silt loam (Typic Argiudoll) and Meridian loam (Mollic Hapludalf) soils. Fifteen hybrids with a range of maturities (90–115 days based on the Minnesota Relative Maturity System) were compared under conventional (moldboard plowing and disking)(CT) and no‐till (NT) systems, in a corn‐following‐corn sequence. Stands were thinned after emergence. No‐till resulted in cooler soil temperatures (0.8–3.8°C cooler), lower emergence percentage (7–12% lower), delayed vegetative growth [4.4 (NT) vs. 7.9 (CT) g plant−1], later silking (2–5 days later), and increased grain moisture (10–20 g kg−1) compared to CT. For grain yield, differences occurred for all main effects (locations, years, tillage systems, and hybrids), and most interactions were significant. Yields under NT were 92% (cool spring, 1984) and 96% (warm spring, 1985) of CT yields. On silt‐loam soils, NT yields were 92 to 95% of CT yields, but tillage systems had similar yields on the loam soil. Superior‐yielding hybrids under CT were also good choices with NT, although delayed growth under NT limited the yield potential of later‐maturing (100–115 days) hybrids.
In Situ Nuclear Magnetic Resonance Imaging of Roots: Influence of Soil Type, Ferromagnetic Particle Content, and Soil Water1
Authors: Rogers Hugo H. , Bottomley Paul A.
Published: July 2010

The paucity of root information combined with the difficulty in obtaining it make new approaches imperative. The observation of roots is essential to the understanding of plant growth and productivity. Proton (1H) nuclear magnetic resonance (NMR) imaging offers a noninvasive method for the study of both root morphology and function in situ. Herein, NMR imaging of plant root systems was evaluated for southeastern U.S. agricultural soil series from 30 different sites, and eight common artificial soil substrates, as a function of soil type, ferromagnetic particle content, and soil water, using a 1.5‐tesla medical research NMR imaging system and Vicia faba L. seedlings grown in the soils. Roots of about 1 mm in diameter and 1‐mm‐diam capillaries of water were undetectable by NMR imaging and conventional NMR in soils with ferromagnetic particle contents of greater than about 4% by weight. Below 4%, ferromagnetic particle content did not correlate well with NMR image quality, but the presence or absence of NMR signals from water‐containing capillaries embedded in soil samples in a conventional NMR experiment reliably reflected soil suitability for NMR root imaging. Images of seedlings in four of the artificial soils (perlite, Ottawa sand, peatlite, and peat) and seven of the native soils (Wynnville fine sandy loam, Lucy loamy sand, Dothan sandy loam, Lakeland sand, Kinston loamy sand, Blanton loamy sand, and Eustis fine sandy loam) showed excellent spatial resolution and accurate reproduction of the root systems when they were extricated from the soils. However, the results from three of the artificial soils (perlite, Ottawa sand, and peat) were significantly compromised by background NMR signals that derived from soil water. In the seven native soils, soil water to near saturation was rendered essentially invisible by the NMR imaging sequence employed, thereby demonstrating excellent root‐to‐soil image contrast. Several root pathologies apparent in the images were identified. The results reveal that 1H NMR imaging is a practical tool for the nondestructive, noninvasive investigation of plant root systems in many natural agricultural soils at virtually any stage of a water stress cycle.
Yield Responses of 16 Winter Wheat Cultivars to Row Spacing and Seeding Rate1
Authors: Marshall G. C. , Ohm H. W.
Published: July 2010

Grain yields of winter wheat (Triticum aestivum L.) may increase as the spacing between rows is decreased. Results in previous studies have varied with other management variables and environments, however, and only one or a few wheat genotypes were used in any one study. We used a wide genetic base of 16 cultivars to obtain estimates of yield response at two row spacings and two seeding rates to determine if there was a consistent response across cultivars and years. Row spacings of 64 and 192 mm were compared at seeding rates of 377 and 538 kernels m−2. There were large year ✕ row spacing and year ✕ seeding rate interactions. The narrow row spacing treatments averaged 6.8 and 5.3% more grain than the standard spacing in 1983 and 1984, respectively. Cultivar responses to narrow row spacing ranged from 1.1 to 17.4% in 1983, and from −8.0 to 19.7% in 1984. No response to seeding rate was observed in 1983, but the higher seeding rate yielded 7.1% more grain in 1984 when tillering was low. A significant row spacing ✕ seeding rate interaction was detected over both years as 9.1% increase in grain yield was observed with both narrow row spacing and high seeding rate compared to wide row spacing and low seeding rate. We concluded that (i) row spacings narrower than the conventional 192‐mm spacing have the potential to significantly increase grain yields, but the response may vary depending on the cultivar and environmental conditions, and (ii) a combination of increased seeding rate and narrow row spacing is important for increasing grain yield.
Aluminum Effects on Growth, Mineral Uptake, and Efficiency Ratios in Red Clover Cultivars1
Authors: Baligar V. C. , Wright R. J. , Kinraide T. B. , Foy C. D. , Elgin J. H.
Published: July 2010

Red clover (Trifolium pratense L.) is an important hay or pasture crop of the humid region of the United States, and its adaptability to acid infertile soils is still unknown. Research was undertaken to evaluate the effects of five levels of Al (0, 25, 50, 75, and 100 µmol L−1) on growth, uptake, and mineral nutrient efficiency ratios (ER) in 23 red clover cultivars. The ER is defined as milligrams of dry shoot weight produced per milligrams of element in the shoot. The initial solution pH of 4.5 changed due to crop growth, and such effects might have altered the concentrations of Al; however, relative comparisons between cultivar responses were possible. The growth of shoots and roots showed significant differences with respect to Al levels, cultivars, and their interactions. At 50 µmol L−1 Al, the average reduction of shoot and root growth was 73 and 57% of control, respectively. Overall shoot nutrient content showed a significant positive correlation with shoot and root dry weight, and inverse relations with treatment Al levels and shoot Al concentrations. The ER assisted in differentiating cultivars into efficient and inefficient utilizers of the absorbed nutrients. With the exception of the ER for Ca, Mg, and Mn, overall inverse relations were observed between Al levels and ER. The cultivars used in this study showed intraspecific genetic diversity in growth and ER values for the essential elements in the presence or absence of Al. ‘Kuhn’ and ‘Prosper I’ are the recommended cultivars for moderately acidic soils.
Soybean Response to Potassium Fertility under Four Tillage Systems
Authors: Vasilas B. L. , Esgar R. W. , Walker W. M. , Beck R. H. , Mainz M. J.
Published: July 2010

Because tillage affects root growth and activity, it affects the ability of plants to utilize soil and fertilizer nutrients. It has not been determined if K fertility recommendations developed for clean tillage systems are appropriate for reduced tillage systems. Therefore, an experiment was conducted on a Muscatine silt loam (fine‐silty, mixed, mesic Typic Haplaquoll) and a Sable silty clay loam (fine‐silty, mixed mesic Aquic Argiudoll) to determine the response of soybean [Glycine max (L.) Merr.] cultivars Williams 82 and Century to three levels of soil K fertility under four tillage systems over 2 yr. The tillage systems were moldboard plow (fall plowed plus spring disk), chisel plow (fall chisel plowed plus spring disk), spring disk, and no‐till. Soil K treatments were 336 kg exchangeable K ha−1, 336 kg exchangeable K ha−1 plus 73 kg banded K ha−1, and 560 kg exchangeable K ha−1. A corn (Zea mays)‐soybean rotation was used. Grain yields were similar for the moldboard plow, chisel plow, and disk systems. Grain yields were consistently lower for the no‐till system. This response was greatest for the cultivar Century in a year when herbicide carryover and Phytophthora (Phytophthora megasperma) damage under no‐till reduced final plant populations by 44% compared to that with the moldboard plow system. Increasing the exchangeable soil K level from 336 to 560 kg ha−1 increased grain yields of Century during a dry growing season. Tillage did not affect the magnitude of response, and banded K had no effect on grain yield. We concluded that the tillage system should not influence K fertility recommendations for soils such as these.
Effects of Inoculation Rate, Rhizobia1 Strain Competition, and Nitrogen Fixation in Chickpea
Authors: Somasegaran Padma , Hoben Heinz J. , Gurgun Velittin
Published: July 2010

Chickpea (Cicer arietinum L.) is the third most widely cultivated legume in the world, but N‐fixation studies addressing its inoculation response and rhizobial strain competition are limited. We investigated N fixation and competition by three strains of chickpea Rhizobium (TAL numbers 480, 620, and 1148) on ‘Desi’ and ‘Kabuli’ chickpea genotypes grown in vermiculite and two soils (Ultisol and Oxisol) free of chickpea rhizobia. Chickpea grown in vermiculite was inoculated with single and mixed strains. A three‐strain mixture was inoculated at 10, 102, 104, 106, and 108 rhizobia per seed on seeds planted in the two soils. Nodulation and N‐fixing parameters were significantly different for chickpea genotypes and rhizobial strains, with no genotype × strain interaction in the vermiculite experiment. TAL 620 was the most competitive strain in both chickpea genotypes. Maximum N fixation in both genotypes was achieved at 104 and 106 rhizobia per seed in the Ultisol and Oxisol, respectively. Nitrogen fixation by chickpea in response to different inoculation rates was best described by a quadratic model. The three strains of Rhizobium competed differently in the two soils. Competition in the Ultisol was due to significant strain differences and genotype x strain interaction. In the Oxisol, there was no strain competition. Different inoculation rates did not influence strain competition. In general, the Kabuli genotype had a greater N‐fixing potential than the Desi. Maximum N fixation in the two soils was a function of the different inoculation rates for both genotypes. Competition among chickpea rhizobia was influenced by the growth medium, chickpea genotypes, and strain differences but not inoculation rates.
Response of Corn and Tomato Plants to Fluorine Concentration in Solution Culture
Authors: Bar‐Yosef B. , Rosenberg R.
Published: July 2010

To understand and control the delicate balance between beneficial and detrimental contents of F in plants, the functional relationships between F concentration in ambient solutions and F uptake rate by plants must be known. The objectives of the present work were: (i) to study the effect of F solution concentration (CF) on F content in plants and on the rate of dry matter production and root elongation in young corn (Zea mays L.) and tomato (Lycopersicon esculentum L.) plants, and (ii) to define fluxes of F uptake versus CF in the two crops. The growth rate (GR) of corn and tomato plants decreased significantly as CF increased from 0.26 to 0.53 and from 0.05 to 0.26 mmol/L, respectively. The root elongation rate (RER) of corn 2 to 7 d old was maximum at CF = 0.26 mmol/L, and decreased when CF was raised to 2.63 mmol F/L. Tomato RER decreased when CF was increased from 0 to 0.53 mmol/L, and was unaffected when CF was raised further to 2.63 mmol/L. The threshold F shoot content at which the GR started to decline was about 12 mg F/kg in both crops. At any CF, F content in the roots exceeded that in the shoots by a factor that varied between 1.2 and 10. The maximal F content in shoots and roots of corn and tomato plants was 54 and 680, and 126 and 1310 mg F/kg, respectively, obtained at a CF of 2.63 mmol/L. The CF had no effect on N, P, and K contents in tomato, but had a suppressive effect on K content in the shoots of corn plants. At a CF between 0.05 and about 3 mmol F/L in the solution, the rate of F uptake per unit root weight (FF) increased exponentially with CF in both test crops, indicating a diffusive F permeation into the roots. At a CF of about 3 mmol F/L, FF of tomato was nearly twice that of corn.
Prediction of Alfalfa Herbage Mass Using Sward Height, Ground Cover, and Disk Technique
Authors: Griggs T. C. , Stringer W. C.
Published: July 2010

Rapid, nondestructive methods of estimating herbage mass (HM) are vital to experiments involving frequent collection of data, especially where physical sampling may alter growth. Herbage mass estimation techniques are based on double‐sampling, in which clipped HM and corresponding nondestructive sward measurements are used in regression analysis to obtain prediction equations. Our objective was to evaluate the precision and accuracy of sward height (SH), ground cover (GC), and disk height (DH) as predictors of HM in alfalfa (Medicago sativa L.) at weekly intervals after cutting. Sward height was measured with a sliding crossbar on an upright meter stick. Ground cover was estimated using a 0.18‐ by 0.22‐m grid subdivided into 20 cells. Disk height was measured with 0.96‐ and 1.76‐kg, 0.2‐m2 aluminum disks, allowed to settle on the sward canopy. All nondestructive measures were accompanied by clipping ofthe areas measured. Clipped HM ranged from 12 to 794 g m−2. Herbage mass prediction equations were developed following stepwise regression of sample HM on SH, DH, GC, days of growth, and derived variables. The most precise HM prediction models were based on SH and DH, accounting for 79 to 94% of variation in HM of calibration samples. Applying prediction equations to a validation data set generated predicted HM values. Sward height and DH models accounted for 59 to 86%, and 80 to 97%, respectively, of the variation in HM of validation samples. Herbage mass of validation samples was predicted with lower standard errors of validation by DH models (19.5–35.9 g m−2) than by SH models (60.8–65.6 g m−2) on the same stands in the same year. The disk technique provides a rapid, accurate means of nondestructively monitoring growth in alfalfa plots.
Kernel Weight Increase in Response to Decreased Kernel Number in Sorghum
Authors: Kiniry J. R.
Published: July 2010

Processes involved in the increase of individual kernel weight (KWT) in sorghum [Sorghum bicolor (L.) Moench] in response to reduced kernel number per panicle (KNO) have not been investigated. A better understanding of these would aid modelers in predicting grain yield, and crop physiologists in understanding yield component compensation. This study examined whether rate of kernel filling, effective filling period (EFP), or both were responsible for the increase in KWT. A widely used single‐seeded hybrid, ‘ATx399 × RTx430’, and an expermental twin‐seeded hybrid, ‘ATx623 × 77CS256TS’, were grown on a Houston black clay (fine, montmorillonitic, thermic Udic Pellustert) at Temple, TX, in 1985 and 1986. Seventy‐nine percent shading during the 16 d prior to 50% anthesis caused KNO to be reduced by 72%. Kernels from the apical, middle, and basal portions of the panicles were sequentially harvested to determine the rate of filling and the EFP. Kernel weight of these shaded plants was 31% greater than for the control. Effective filling period for shaded plants was not increased significantly compared to the control. Rate of filling was, therefore, the primary means by which the increased KWT was attained. Neither the number of endosperm cells per kernel 10 to 16 d post‐anthesis nor the number of starch granules per kernel 14 to 16 d post‐anthesis were increased significantly by shading. Number of starch granules was three times greater at maturity than at 14 to 16 d post‐anthesis, and was significantly greater for the shaded treatment. While final kernel volume was greater for the shaded plants, a volume limitation did not appear to be the cause for the difference in dry weights. Kernel dry weight was already different between treatments by the time maximum volume was achieved. Further investigation is needed to determine the reasons for the increase in both rate of filling and KWT in response to decreased KNO.
Seasonal and Soil Fertility Effects on the Response of Waterlogged Cotton to Foliar‐Applied Nitrogen Fertilizer
Authors: Hodgson A. S. , MacLeod D. A.
Published: July 2010

The majority of irrigated cotton (Gossypium hirsutum L.) soils in Australia are poorly drained, and the short‐term waterlogging associated with extended furrow irrigation reduces cotton yield, partly by reducing the uptake of N. Foliar application of N before irrigation can overcome a transient shortage, but yield responses have been variable. Seasonal and soil N fertility effects on the response of waterlogged cotton to foliar‐applied N fertilizer were studied over three seasons at Narrabri, N.S.W., Australia. A cracking grey clay soil (Typic Pellustert) was waterlogged by furrow irrigations lasting 4 to 32 h. Climatic and soil fertilizer conditions included a cool, moist season with optimal soil fertilizer N; a hot, arid season with high soil fertilizer N; and a hot, arid season with a wide range of soil fertilizer N. Foliar N was applied at 0, 5, 10, and 20 kg ha−1 in the first season, 0, 15, 30, and 60 kg ha−1 in the second season, and 0, 60, 120, and 180 kg ha−1 in the third season. Increased waterlogging reduced N uptake and lint yield. Nevertheless, there was no response to foliar N in the cool, moist season because factors other than N limited growth and yield whether or not N was supplied to the foliage. Lack of response to foliar N in the hot, arid season with high soil N fertility was attributed to high uptake of N (163 kg N ha−1) by untreated shoots, which compensated for reduced uptake by the roots during waterlogging. A three‐factor interaction in the third season confirmed that more cotton yield was recovered by applying foliar N under more severe waterlogging when soil N levels were not high. At N rates of 120 and 180 kg ha−1, shoots recovered more soil‐applied N than foliar‐applied N. Recoveries were similar at 60 kg N ha−1. The results confirmed that foliar N can ameliorate the effects of waterlogging in cotton, defined some of the conditions under which responses to foliar N occur, and explained some of the variability in response to foliar N found under commercial conditions.
Calibrated Heat Pulse Method for Determining Water Uptake in Cotton
Authors: Cohen Y. , Fuchs M. , Falkenflug V. , Moreshet S.
Published: July 2010

The heat pulse method for measuring sap flow in cotton (Gossypium hirsutum L. cv. SJ‐2) stems was developed and tested to provide a means for investigating transpiration of single plants under field conditions without disturbing the environment. The temperature difference between two radially inserted thermocouples, one 9 mm above and the other 4 mm below a heater piercing the stem, was measured every 0.3 s following emission of a heat pulse. These dimensions are a compromise solution between ideal configuration, ease of probe construction, and resolution of the signal detector. Two data were recorded: the time elapsed from pulse emission to the first re‐occurrence of the initial temperature difference, and the time at which the temperature difference was maximum. At low and moderate convective sap velocities in the stem (0‐0.17 mm s−1), the first datum can be measured with precision to accurately estimate sap velocity. At velocities higher than 0.22 mm s−1 the initial differential temperature change is too small and evolves too rapidly to detect when temperature returns to its initial value, but the temperature wave has a well defined maximum that is related to sap velocity. For convective velocities between 0.17 and 0.22 mm s−1, both data can be used. Calibration against transpiration measurements in potted cotton plants, grown outdoors, showed that the apparent effective conducting stem area is 0.71 of the total cross‐section. This fraction was found to remain constant over the entire range of stem diameters reached by cotton grown as an annual crop. The transpiration rate of a cotton plant is determined by multiplying the effective conducting area by the sap velocity. The study shows how the heat pulse quantifies water uptake of cotton and can be carried out in field conditions.
Late Fall Fertilization of Kentucky Bluegrass
Authors: Wehner D. J. , Haley J. E. , Martin D. L.
Published: July 2010

Many turfgrass managers apply a portion of the total yearly N to cool‐season turfgrasses in the late fall (November). The purpose of this field study was to compare fertilization programs with and without N applications in November using both slow‐release and soluble N sources. Turfs of two different cultivars of Kentucky bluegrass (Poa pratensis L. cv. Baron and cv. Newport) growing on a Flanagan silt loam (fine, montmorillonitic, mesic Aquic Argiudoll) received 10 fertilization programs utilizing urea, isobutylidene diurea (IBDU), or sulfur‐coated urea (SCU). Urea was applied four times per year with either a spring application or a late‐fall application combined with applications in early June, mid‐July, and early September (171–196 kg N ha−1 yr−1). For IBDU and SCU, application dates and N rates (kg ha−1) consisted of June 98 + September 98, June 98 + November 98, and June 49 + September 49 + November 74. The turfs were rated for color for 3 yr, and clipping weights were determined weekly for the final 2 yr of the study. Results were generally similar for both cultivars, except fewer significant differences in spring color ratings were found on Newport. An application of urea in November, without a subsequent spring fertilization, resulted in higher turf color ratings in the early spring but lower turf color ratings in May and June, compared to turf receiving a spring fertilization. Results indicate that a late‐fall application of urea may not eliminate the need for spring fertilization but may allow a reduction in the amount of N applied in spring. Turfs fertilized with SCU in November received higher color ratings in the spring than did turf fertilized with SCU in September. With IBDU, the June + September program resulted in the highest number of ratings with acceptable turf color. November IBDU applications did not result in higher color ratings in the spring and resulted in inefficient use of the N applied.
Response of Alfalfa Grown on Acid Soil to Different Chemical Amendments
Authors: Rechcigl J. E. , Edmisten K. L. , Wolf D. D. , Reneau R. B.
Published: July 2010

Soil acidity is a major cause of reduced yields of alfalfa (Medicago sativa L.) in the southeastern United States. The purpose of this study was to determine if alfalfa could be grown successfully on acid soils if sufficient Ca, N, Mo, and surface lime were provided. ‘Arc’ alfalfa was planted in March 1985 in a split‐plot design on an Aquic Fragiudult soil. Treatments included surface and incorporated dolomitic lime at either 6.5 or 13.0 Mg ha−1, gypsum at 13.0 Mg ha−1. In addition, each plot was split, with half of the plot receiving 224 kg N ha−1 and half receiving no N. Compared to the control, surface application of lime increased yields of alfalfa in both 1985 and 1986. Yields increased in response to addition of either N or Mo, indicating the importance of Mo in establishing the alfalfa nodule system for N assimilation. Soil pH averaged 4.8 and 6.7, and exchangeable AI averaged 2 and 21 mg kg−1 in the surface 5 cm of the limed and unlimed plots, respectively. The results of this study indicate that surface lime application is adequate for alfalfa establishment and production on acid soils, and that reduced N fixation appears to be a major limiting factor to growth of alfalfa on acid soils.
Fall Harvest Management of Alfalfa. I. Date of Fall Harvest aind Length of Growth Period Prior to Fall Harvest
Authors: Edmisten K. L. , Wolf D. D. , Lentner M
Published: July 2010

Alfalfa (Medicago sativa L.) harvest schedules are often interrupted by various factors. Interruptions in ideal alfalfa harvest schedules can delay the final harvest to dates considered critical to winter survival. The objectives of this study were to determine if a critical period for fall harvest management actually exists at 80°25′ W Long., 37°ll′ N Lat., and 610‐m elevation in Virginia, and if length of the growth period prior to final fall harvest (GPPFH) influences plant persistence and succeeding spring yields. Final fall alfalfa harvest was made 10, 20, or 30 September or 10,20, or 30 October for 2 yr in two identical experiments. Alfalfa was managed to achieve a 30‐, 40‐, 50‐, or 60‐d GPPFH. The soil was a mixture of Landisburg silt loam (fine‐loamy, mixed, mesic Typic Fragiudult) and Greendale silt loam (fine‐loamy, siliceous, mesic Fluventic Dystrochrept). Total nonstructural carbohydrates (TNC) in taproots and population of surviving plants were determined in December (214–351 g kg−1) and March (141‐221 g kg−1). Succeeding spring yields in May ranged from 1.0 to 3.1 Mg ha−1 and were a measure of accumulated influence of management treatments. Harvests made at any time during the fall period did not cause stand density reduction. Length of GPPFH was more important than date of fall harvest in making management decisions for fall harvest. Succeeding spring yields and TNC levels were generally high for the 50‐d growth period, and fall harvest yield would offset any reductions in spring yield observed in this study. In addition, fall harvests made with a 50‐d GPPFH maintained quality and leafiness better than the 60‐d GPPFH. With the exception of the 30 October fall harvest date, a critical period was eliminated by increasing the GPPFH to 50 or more days. The 30 October fall harvest required a 60‐d GPPFH for maximum spring production.
Growth of Wheat and Barley Seedlings at Different Matric and Osmotic Potentials
Authors: Hao X. , de Jong E.
Published: July 2010

Since saline and drought conditions often occur together, plant response to the combined stresses is of considerable interest. The effects of matric and osmotic potential on shoot and root growth of wheat (Triticum aestivum, cv. Neepawa) and barley (Hordeum vulgare, cv. Bonanza) were investigated in a growth chamber. An artificially salinized Dark Brown Chernozemic sandy loam soil (Typic Borolls) was used in the study. The plants were germinated in nonsaline soil, transplanted onto columns with different osmotic and matric potentials, and grown for up to 8 d. Osmotic potentials of −0.1 to −1.0 MPa and matric potentials of −0.01 to −2.5 MPa reduced shoot and root growth, but the effects of the matric and osmotic stress were not necessarily quantitatively equal. A marked interaction between the two potentials occurred at high stress levels. In the most saline treatments, root growth was greater in the dry than the wet treatments. It is suggested that the latter is due to increased salt accumulation around the roots caused by more rapid mass flow in the wettest soil.
Interactive Water and Nitrogen Effects on Senescence of Maize. I. Leaf Area Duration, Nitrogen Distribution, and Yield
Authors: Wolfe D. W. , Henderson D. W. , Hsiao T. C. , Alvino A.
Published: July 2010

Stress effects on leaf senescence are important for maize (Zea mays L.), since production of new photosynthetic area is genetically pre‐determined. Interactive effects of water and N deficits on water potential components, green leaf area (GLA) duration, and N and biomass allocation during grain filling were evaluated in a 2‐yr field study conducted on Yolo loam (fine‐silty, mixed, nonacid, thermic Typic Xerorthents) under four treatments: 180 kg N/ha applied at planting, with (NI) and without (ND) irrigation; and no N fertilizer, with (OI) and without (OD) irrigation. Leaves of low N plants had reduced capacity for solute accumulation, and both water and N deficits caused 0.1‐ to 0.5‐MPa reductions in midday leaf turgor. Total GLA was smallest in the OD treatment, but senescence during grain filling was greatest in the ND treatment because of a high transpiration demand and a high reproductive sink demand for N. Ear removal reduced the rate of post‐anthesis leaf N decline of all treatments, and plants in the ND treatment showed a significant reduction in leaf senescence rate when ears were prevented. Grain yield of the OD treatment was <50% of NI yield in both years; ND and OI treatments had intermediate reductions. Although the timing and intensity of stress differed between treatments and years, both water and N deficits reduced leaf longevity, and GLA duration from anthesis to harvest was linearly related (r2 = 0.92) to final grain dry weight.
Wheat Yield Analysis in Relation to Advancing Technology in the Midwest United States
Authors: Feyerherm A. M. , Kemp K. E. , Paulsen G. M.
Published: July 2010

Improving grain yields requires knowledge of sources of gains in the past to point the way to future advances. Our objectives were to analyze technology‐related yield changes of winter wheat (Triticum aestivum L.) in the U.S. Great Plains (a seven‐state region) and the Cornbelt (a four‐state region) since 1954 and to attribute them to major sources of variation. Within each of the 11 states, total yield change due to technology, yield change due to genetic improvement, and yield change due to applied N, were independently estimated. Yield change due to other factors was obtained by subtracting genetic and applied N induced changes from the total. Results were aggregated to regional levels. Wheat yields advanced 30 kg ha−1 yr−1 in the Great Plains and 43 kg ha−1 yr−1 in the Cornbelt from 1954 through 1979. In the Great Plains, 43,22, and 35% of the total increase was attributed to genetic improvement, applied N, and other sources, respectively. Comparable figures for the Cornbelt were 74, 22, and 2%. When the analysis was extended to 1984 for Nebraska, Kansas, and Oklahoma, the rate of increase remained almost the same, but the distribution among genetics, N, and other sources changed from 45, 25, and 30% for 1954 through 1979, to 61, 27, and 13% for 1954 through 1984. We concluded that from 1954 through 1979, genetics and applied N accounted for almost all the yield gain in the Cornbelt, but other factors (irrigation, pesticides, improved tillage, etc.) contributed about one‐third of the gain in the Great Plains. Technology continued to raise yields at the same rate in the central Great Plains during the 1980s, but a larger share was due to genetic improvement than during 1954 through 1979.
Forage Lignins and Their Effects on Fiber Digestibility
Authors: Jung H. G.
Published: July 2010

The lignin fraction of forage cell walls is negatively associated with fiber digestion by ruminants. Lignins can be classified as core lignins, highly condensed polymeric matrices; and non‐core lignins, low molecular weight phenolic monomers. Core lignins are covalently linked to hemicellulose in forage cell walls, with at least some of these linkage being alkali‐labile in grasses. Among the non‐core lignins, p‐coumaric acid is primarily associated with the core lignin fraction of cell walls whereas ferulic acid is generally linked to the hemicellulose fraction. The majority of non‐core lignin moities are esterified to other cell wall components, but ether linkages also seem to exist. Legumes and grasses differ in lignin concentration and composition. Physiological maturity of forages influences lignin content. Genetics and environmental influences have been observed to alter both concentration and composition of forage lignins. Lignification seems to depress digestion of grass cell walls more strongly than in legumes. Composition of core lignin may influence fermentation of forages more than does simply concentration. Non‐core lignins also are negatively correlated with fiber fermentation, but this may just reflect the positive correlation between core and non‐core lignin concentrations. Covalent linkage of lignin to carbohydrate has been shown to be important in model cell wall systems for inhibiting fermentation. Much remains to be learned about lignin structure and the mechanisms by which lignins interfere with ruminal digestion of forages.
Phosphorus Nutritional Requirement of Maize Seedlings for Maximum Yield
Authors: Barry D. A. J. , Miller M. H.
Published: July 2010

In a maximum yield experiment in Ontario, Canada, response of maize (Zea mays L.) to greater than recommended P fertilizer applications seemed to result mainly from improved P nutrition of seedlings. A 2‐yr study was conducted to determine the effect of P nutrition during the seedling stage on final yield. An outdoor, hydroponic system was used to vary P nutrition during growth and provide adequate levels of all other nutrients and water. Plants receiving the greatest or an intermediate P concentration solution had P concentrations of 7.2 and 4.4 g kg−1, respectively, at the 6‐leaf stage, whereas plants receiving the least P concentration solution had a shoot P concentration of 2.8 g kg−1. Plants that received the intermediate or least P solutions until the 6‐leaf stage but then received the greatest P solution to maturity attained shoot P concentrations of at least 5.0 g kg−1 8 d after increasing the P solution concentration. Grain yield was greater on treatments receiving the greatest P solution from the beginning than from the 6‐leaf stage (8.2 vs. 7.2 t ha−1), mainly because of a greater kernel number. Kernel number was most sensitive to P nutrition during the period from planting to the 6‐leaf stage. A shoot P concentration of at least 5.0 g kg−1 at the 6‐leaf stage was required to obtain maximum yield.
Variability in Alfalfa for Growth and Mineral Uptake and Efficiency Ratios under Aluminum Stress
Authors: Baligar V. C. , Elgin J. H. , Foy C. D.
Published: July 2010

Alfalfa (Medicago sativa L.) is an important forage legume that is known to be sensitive to soil acidity. A nutrient solution experiment was conducted under controlled growth conditions to evaluate the effects of Al (0, 75, and 150 µmol L−1) on growth, nutrient uptake, and mineral nutrient efficiency ratios (ER = shoot dry weight produced per unit element in shoot) in 15 selected alfalfa cultivars and lines. Growth of shoots and roots differed with Al levels and cultivars/lines. At 75 µmol L−1 the mean reductions of shoot and root dry matter yield were 29 and 6% of the control, respectively. Shoot nutrient contents showed significant positive correlations with shoot and root weights, and negative correlations with Al level and shoot Al concentrations. The ER values were used to classify cultivars and lines into efficient and inefficient utilizers of absorbed nutrients. With the exception of the ER for Ca, negative correlations were observed between Al level and ER. The cultivars and lines used in this study showed intraspecific genetic diversity for dry matter yield and ER values for the elements when plants were grown with or without AL.
Time of Desiccation Effects on Plant Composition and Subsequent Nitrogen Release from Several Winter Annual Cover Crops
Authors: Wagger M. G.
Published: July 2010

Efficient utilization of N contained in cover crop residues by the subsequent summer crop requires an understanding of temporal patterns of N release as related to specific management strategies. The objective of this research was to determine, under field conditions, changes in plant composition and subsequent patterns of N release resulting from two desiccation dates approximately 2 wk apart (early and late) for rye (Secale cereale L.), crimson clover (Trifolium incarnatum L.), and hairy vetch (Vicia villosa Roth) cover crops. Averaged over 2 yr the late desiccation treatment resulted in increases in cover crop dry matter of 39, 41, and 61% for rye, crimson clover, and hairy vetch, respectively. Corresponding increases in total N content of the respective cover crops were 14, 23, and 41%. Significant differences in cellulose, hemicellulose, and lignin contents were found among cover crop residues between desiccation times. Nitrogen release from decomposing cover crop residues was monitored using nylon mesh (53 µm) bags. In general, the order of N release was hairy vetch > crimson clover > rye. Cover crops desiccated early decomposed faster, however, the relative magnitude of these N release patterns differed sharply between years. The percentage of initial residue N remaining after 16 wk for the early desiccation date in 1984 was 53, 14, and 13% for rye, crimson clover, and hairy vetch, respectively, compared with corresponding values of 59, 42, and 35% in 1985, which was characterized by a relatively dry growing season. Estimates of N released from each cover crop indicated that the potentially larger available N pool resulting from a delay in desiccation was offset by the slower rate of N release, especially for rye and crimson clover.