bluuebunny/crossref_metadata_2025 huggingface dataset:
Tall Fescue Rhizome Production as Influenced by Bermudagrass Competition and Cutting Frequency
Authors: Bouton J. H. , Whitehead F. C. , De Battista J. P.
Published: July 2010

The rhizome trait in tall fescue (Festuca arundinacea Schreb.) should impart better persistence and competitive ability in areas marginal for its adaptation or in mixed swards. This is especially true in the southern range of its adaptation where tall fescue‐bermudagrass [Cynodon dactylon L. (Pers.)] pastures predominate. This study was conducted to investigate the effects of bermudagrass competition and cutting frequency on rhizome production and growth among different tall fescue genotypes on a Cecil sandy loam soil (clayey, kaolinitic, thermic Typic Hapludult). The effects of cutting frequencies of 1 and 6 wk or 2 and 4 wk were evaluated in two separate experiments among three rhizomatous and three non‐rhizomatous genotypes space‐planted into a clean tilled area or into a common or ‘Coastal’ bermudagrass sod. Bermudagrass competition depressed rhizome production, tillering, and plant size across all genotypes. Little effect was recorded for these same characters with frequent cutting unless done weekly. There were significant differences among genotypes for rhizome production. Highly rhizomatous genotypes survived better and grew larger in bermudagrass than non‐ or weakly‐rhizomatous genotypes, indicating the rhizome trait may impart better performance in tall fescue grown in bermudagrass mixtures.
The Impact of Maturity and Genotype on Blend Performance in Group V and Group VII Soybean Cultivars
Authors: Gizlice Ziya , Carter T. E. , Burton J. W.
Published: July 2010

It has been hypothesized that the divergent maturity of blend components is a major factor leading to the positive blend responses sometimes noted in soybean [Glycine max (L.) Merr.]. The objective of this study was to examine the association between cultivar maturity and blend performance in determinate soybean. Eight purelines (four from maturity group [MG] V and VII), and the 28 two‐way blend combinations of these purelines were evaluated for seed yield in eight North Carolina environments. Blend responses (expressed as a deviation of the blend yield from pure‐stand component average) were 0.1, 1.9, and 3.3% for MG V, intermaturity (MG V/ MG VII), and MG VII blends, respectively. The intermediate average response of the intermaturity (MG V/MG VII) blends is an indication that divergent maturity of the blend components has little effect on blend performance. This notion is further substantiated in that individual positive blend responses occurred more frequently in the MG VII blends than in the MG V/MG VII blends. Only the MG VII blend group showed a significant overall blend response (84 kg ha−1). The highest yielding MG V/MG VII blend, that of ‘Coker 237’ (MG VII) with ‘N77‐114’ (MG V), was composed of component cultivars that blended well even when no maturity factors were evident. We conclude that maturity differences may be incidental to better blend performance in determinate soybean. The range of individual blend responses was −9.7 to 9.1%, expressed as deviations from pureline component averages.
Ethephon Application and Nitrogen Fertilization of Irrigated Winter Barley in an Arid Environment
Authors: Pearson C. H. , Golus H. M. , Tindall T. A.
Published: July 2010

Lodging in barley (Hordeum vulgare L.) can result in grain loss, lower seed quality, increased disease, high grain moisture, reduced harvest efficiency, and lower milling grade. Application of N fertilizer to achieve high barley yields often results in increased lodging. Consequently, N applications are often reduced in order to lessen the potential for lodging. Use of plant growth regulators may permit higher N application rates without increased lodging. Field studies were conducted in an irrigated arid environment during 1986 and 1987 on Fruita sandy clay loam (fine‐loamy, mixed, mesic Typic Haplargid) soil. Ethephon [(2‐chloroethyl) phosphonic acid] was applied at 0.42 kg a.i. ha−1 to irrigated winter barley that received 56, 112, 168, and 224 kg ha−1 of spring‐applied N. The 1986 data indicated that, in the absence of lodging, ethephon did not affect barley grain yields. Ethephon increased grain yields in 1987 in association with reduced lodging. Plant height response to ethephon was similar across N rates. Ethephon shortened internode lengths on the upper portion of the culm and reduced lodging of winter barley grown at high N rates. Ethephon did not affect spikes m−2, kernel mass, kernels spike−1, or seed N content in either year. Application of higher N rates than traditionally used in irrigated winter barley increased grain yield and seed N content. In years when lodging occurred, ethephon was effective as an antilodging agent.
Crop Yield as Affected by Rotation and Nitrogen Rate. II. Grain Sorghum
Authors: Peterson Todd Andrews , Varvel G. E.
Published: July 2010

Crop rotation is reported to increase grain sorghum [Sorghum bicolor (L.) Moench] yield in some, but not all cases. This study compares yield of continuous grain sorghum with that of sorghum grown (i) in a 2‐yr rotation with soybean [Glycine max (L.) Merr.]; (ii) in a 4‐yr oat + clover [Avena sativa (L.) + 80% Melilotus officinalis (L.) Lam., 20% Trifolium pratense]‐corn (Zea mays L.)‐soybean—grain sorghum rotation; and (iii) in a 4‐yr soybean—corn—oat + clover—grain sorghum rotation. Interactions between crop rotation and N rate were also determined. The study was conducted for 4 yr on a Sharpsbury silty clay loam (fine, montmorillonitic, mesic Typic Arguidoll). Continuous grain sorghum showed a greater response to fertilizer N than sorghum in rotation. Sorghum following legumes in rotation did not respond to applications of more than 90 kg N ha−1, while continuous sorghum increased with all levels of N applied. Yield of continuous sorghum was 3.4, 5.0, and 5.3 Mg ha−1 with 0, 90, and 180 kg N ha−1, respectively, while sorghum in rotation averaged 5.0, 5.4, and 5.3 Mg ha−1 at the same N rates. Differences between continuous and rotated sorghum were large without applied N, but were minimized or removed with N applications. Sorghum in the 2‐yr sorghum‐soybean rotation produced sustained high yields (5.0 Mg ha−1) without additions of N fertilizer.
Computational Approach to Assess Actual Transpiration from Aerodynamic and Canopy Resistance
Authors: Ben‐Asher J. , Meek D. W. , Hutmacher R. B. , Phene C. J.
Published: July 2010

A simple method for estimating actual transpiration may help to control precise irrigation. The Penman‐Monteith equation can be a useful method, provided data on canopy resistance (rc) and aerodynamic resistance (rav are available. These parameters are complex and hard to obtain. The objective of this study was to estimate rc and rav with infrared thermometers (IRT). Tomato (Lycopersicon esculentum Mill. cv. UC‐82B) grown under various irrigation regimes on a Panoche clay loam soil (fine‐loamy, mixed, thermic Typic Torriorthents) were used to obtain differential values of canopy and air temperatures. With standard climatological data, they were used for the determination of rc and rav. Calculated values of rc and rav were used to estimate actual transpiration rates. A basic assumption is that both rc and rav are crop‐specific coefficients of proportionalities rather than physically measurable parameters. While rc varies according to water availability, rav is not directly affected by soil water status, but is a factor of crop and climatic conditions. Thus, rav determined under conditions approximating potential transpiration (Tp) was also used to evaluate rc under water deficit conditions. Calculated values of rc and transpiration agreed with values measured with a steady state diffusion porometer. A computational link exists between measurements of canopy, air temperature, rc, and rav. Infrared thermometers can be effectively used in irrigation management.
Regional Environment and Cultivar Effects on the Quality of Wheat Straw
Authors: Rao S. C.
Published: July 2010

Cereal grain residues represent a major portion of crop residues produced in the USA, and could be an important source of feed for ruminants if the nutritive value could be improved. A study was conducted to determine the effects of cultivar and regional environment on the fiber concentration, crude protein (CP), and in vitro drymatter digestibility (IVDMD) of wheat (Triticum aestivum L.) straw. Samples of five hard red winter wheat cultivars (Centurk 78, Newton, Vona, Scout 66, and TAMW‐101), grown at four cultivar test centers in Oklahoma, Kansas, Colorado, and Texas, were collected after harvest during 1983–1984, 1984–1985, and 1985–1986 growing seasons. Samples were ground and analyzed for neutral detergent fiber (NDF), acid detergent fiber (ADF), permanganate lignin (LIG), CP, and IVDMD. No significant differences were observed in fiber content among cultivars within location and year. Cultivars did differ in CP and IVDMD with a significant year ✕ cultivar interaction. A combined analysis showed a significant location ✕ year interaction for all the components tested. Average values for NDF, ADF, and LIG content of all cultivars among locations throughout the study period ranged from 703 to 849,495 to 606, and 73 to 115 g kg−1, respectively, whereas CP and IVDMD values ranged from 18 to 53 and 295 to 449 g kg−1 , respectively. Crude protein increased linearly with mean spring temperature, as did ADF concentrations with cumulative precipitation. Digestibility of wheat straw, however, was not affected by environmental conditions. Environmental factors such as spring temperature and precipitation exerted greater influence on CP and fiber contents, whereas cultivars had little effect on the CP and IVDMD of wheat straw.
Grazing Winter Wheat: II. Height Effects on Response to Production System
Authors: Winter S. R. , Thompson E. K. , Musick J. T.
Published: July 2010

Current wheat (Triticum aestivum L.) cultivars are shorter and have more lodging resistance than previous cultivars. Thus, the reduction in height and lodging caused by grazing may be less desirable now than previously. The objective of this research was to compare the growth and yield response to grazing of hard red winter wheat cultivars that vary in height and other traits. Siouxland, a tall cultivar, Vona, a semidwarf, and Q588, a short hybrid, were grown 2 yr in irrigated grain and grazed production systems. In 1986, Siouxland yielded the same in grain and grazed systems and was insensitive to grazing termination date except that severe grazing after 15 March reduced yield 20%. In contrast, Vona and Q588 yielded less in all grazed systems than in the grain system and were more sensitive to grazing termination date than Siouxland because they had lower leaf area and headed earlier. Grazing until 29 March reduced yield of Vona and Q588 two to five times more than Siouxland. In 1987, grazing increased yield of Siouxland and Vona by 41 and 23%, respectively, while reducing yield of Q588 by 8% in a lodging‐prone environment (330 mm spring irrigation) because Siouxland and Vona lodged without grazing and Q588 did not. With 130 mm spring irrigation, lodging was less and all cultivars responded similiarly to grazing. In conclusion, grazing is more likely to reduce the yield of a lodging‐resistant short cultivar with high yield potential than a tall cultivar that is susceptible to lodging.
Water Potential in Sugarcane Measured from Leaf Segments in a Pressure Chamber
Authors: Saliendra Nicanor Z. , Meinzer Frederick C. , Grantz David A.
Published: July 2010

The validity of using sugarcane leaf segments to measure leaf water potential with the pressure chamber technique was assessed. Three pressure chamber protocols: (i) use of leaf tips, (ii) leaf segments sealed inside balloons, and (iii) exposed leaf segments, were compared. Measurements obtained using leaf segments were 0.05 to 0.06 MPa higher than those obtained from leaf tips. These small differences in water potential between leaf tips and nonapical segments could be attributed to transpiration‐induced, water potential gradients existing prior to excision. Sealing the excised segment within a rubber balloon inside the pressure chamber altered the apparent water potential by 0.01 MPa or less, relative to exposed leaf segments. The use of leaf segments was more convenient and less destructive of plant material than the use of leaf tips or entire leaves. This protocol proved to be an accurate and reliable way of measuring water potential in sugarcane using the pressure chamber technique.
A Thermal Stress Index for Cotton
Authors: Burke J. J. , Hatfield J. L. , Wanjura D. F.
Published: July 2010

Thermal stress is difficult to separate from water stress; however, linking enzyme kinetics to plant temperature provides a new description of plant stress. Previous reports have shown that cotton was within its thermal kinetic window (the temperature range over which the value of the apparent Michaelis constant (Km) of enzymes remains within 200% of the minimum observed value) for approximately 30% of the growing season, and that the time the plant temperatures were within the thermal kinetic window (TKW) was related to biomass production. The present study investigated the usefulness of the 27.5 °C midpoint temperature of the TKW of cotton (Gossypium hirsutum L.) as a baseline temperature for a thermal stress index (TSI). Using this biochemical baseline and measurements of foliage temperature, we compared the TSI response with cotton field performance. The study was conducted in the field on an Olton silty clay loam soil (fine mixed, thermic, Aridic PaleustoIIs) during 1984 and 1987. Measurements of foliage temperature were made with a hand‐held 4° field of view (FOV) infrared thermometer and plant biomass measured by destructive sampling. The biochemically based TSI and the physically based crop water stress index (CWSI) were highly correlated (r2 = 0.92) for cotton across a range of environmental conditions. The results indicate that the TSI may be useful in quantifying thermal stress via a procedure related to plant biochemistry.
Branch Dry Weight in Relation to Yield Increases in Narrow‐Row Soybean
Authors: Board J. E. , Harville B. G. , Saxton A. M.
Published: July 2010

Previous studies indicated total dry matter at R5 (TDM,R5) played a more important role in narrow‐row yield increases at late compared to optimal planting dates in soybean [Glycine max (L.) Merr.]. The objective of this study was to test the hypothesis that greater TDM(R5) in narrow vs. wide rows at late plantings stimulates yield by increasing vegetative branch dry matter (BDM,R8), branch yield components, and branch reproductive dry matter (BRDM). Field studies were conducted during 1987 and 1988 at optimal (May) and late (July) planting dates, with two commercial soybean cultivars (Forrest, Maturity Group V and Centennial, Maturity Group VI), and 100‐cm (wide) rows/normal plant population, 50‐cm (narrow) rows/normal plant population, and 50‐cm rows/high plant population. The test was conducted at Baton Rouge, LA on a Mhoon silty clay (fine‐silty, mixed, nonacid, thermic, Typic, Fluvaquents) soil. Narrow compared to wide row spacing resulted in greater BDM(R8) at both planting dates. However, increased BDM(R8) was correlated with whole plot yield (r2 = 0.92***, significant at P = 0.001) only at the late planting. Narrow‐row‐increased BDM(R8) was responsible for greater yield at this planting date because it was associated with increasing branch yield components which are reduced by late planting: branch number, total branch length, branch node number, and branch pod and seed production. In conclusion, data supported the hypothesis that the close association between narrow‐row‐increased TDM(R5) and yield at late plantings is related to increased branch dry matter and branch yield component production.
Tillage and Cover Crop Management for Soil Water Conservation
Authors: Munawar A. , Blevins R. L. , Frye W. W. , Saul M. R.
Published: July 2010

The effectiveness of a conservation tillage system depends on the amount and distribution of plant residues left on the soil surface. We determined effects of tillage systems, N fertilizer rates, and cover crop management on soil temperature, soil moisture, and corn (Zea mays L.) yields. Tillage treatments were chisel‐plow tillage, conventional tillage (moldboard plowing and disking), disk tillage, and notillage. Nitrogen fertilizer at rates of 0, 75, 150, or 225 kg N ha−1 were broadcast on the soil surface. Rye (Secale cereale L.) on one‐half of each split plot was killed 3 wk before corn planting time, while the other half was allowed to grow until the corn was planted. Corn yields in 1986 were 4.41, 4.03, 3.64, and 2.25 Mg ha−1 for notillage, chisel‐plow tillage, disk tillage, and conventional tillage, respectively. The yields were significantly greater with early killed rye (3.85 and 5.05 Mg ha−1 in 1986 and 1987, respectively) than with late‐killed rye (3.32 and 4.58 Mg ha−1 in 1986 and 1987, respectively). Soil temperature tended to be slightly higher under the latekilled rye mulch in 1986 with no significant difference in 1985. Soil moisture content was significantly higher for early killed rye treatment in the early part of the season in 1986 because there was less soil moisture depletion due to the growing rye.
Grain, Dry Matter Yield Relationships for Winter Wheat and Grain Sorghum—Southern High Plains
Authors: Howell Terry A.
Published: July 2010

Grain yield of cereal crops is closely associated to the aerial (above ground) dry matter yield, but predictions of grain yield based on model estimates of dry matter yield are often inaccurate due to variations in the assumed harvest index. This study analyzed the relationship between grain yield and aerial dry matter yield from published studies for winter wheat [Triticum aestivum (L.)] and grain sorghum [Sorghum bicolor (L.) Moench) conducted at Bushland, TX in the Southern High Plains. Harvest index (HI) was defined and determined as the slope of the linear relationship between Yd, plant grain yield in Mg ha−1 on a dry basis, and DM, aerial (field) dry matter yield in Mg ha−1, as contrasted to the traditional definition of HI as the ratio YdDM. Simple linear relationships had coefficients of determination of 0.95 for the seven grain sorghum experiments and 0.75 for the five winter wheat experiments at Bushland and standard errors of the estimates of 0.47 Mg ha−1 and 0.63 Mg ha−1, respectively. The HI of winter wheat and grain sorghum at Bushland was 0.35 and 0.47, respectively, and largely unaffected by fertility, water use, row spacing, and many other cultural practices like tillage and profile modification, and growing season environment. The linear regressions indicated a significant (0.05 probability level) intercept value of −0.53 Mg ha−1 for grain sorghum while the intercept value 0.16 Mg ha−1 for winter wheat was not significant (0.05 probability level).
Soil Water Assessment Model for Several Crops in the High Plains
Authors: Robinson J. M. , Hubbard K. G.
Published: July 2010

Soil properties, soil water content and precipitation vary widely within the High Plains of the USA. Reliable estimates of crop water status have been hampered by a general sparsity of soil water monitoring. This study examined the feasibility of determining soil water status using a soil water balance model. Soil water content was measured under corn (Zea mays L.), wheat (Triticum aestivum L.), sorghum (Sorghum vulgare L.) and soybean (Glycine max L.) at different sites in the High Plains during 1986 and 1987. Surface weather data collected from the High Plains Automated Weather Data Network (AWDN) served as input to a model that estimates evapotranspiration (ET) and soil water content on a daily time step. Atmospheric demand was represented by potential evapotranspiration (ETp) calculated from the Penman method. Model estimates of total water in the root zone were compared to measured values using statistical measures including the D index of agreement. Comparison at one site between measured and estimated soil water by individual soil layers beneath a corn indicated that water content was slightly underestimated in the upper layers and overestimated in the lower layers. The performance of the model in estimating total soil water over a range of soil types, crops and weather was satisfactory, with the majority of D index values exceeding 0.75. Based on the results of this study, we conclude that it is now possible to accurately estimate soil water conditions in a timely fashion under reasonably flat terrain, provided near‐real time weather data are available.
Reseeding, Biomass, and Nitrogen Content of Selected Winter Legumes in Grain Sorghum Culture
Authors: Boquet D. J. , Dabney S. M.
Published: July 2010

Winter legumes as green manure crops in grain sorghum, Sorghum bicolor L. Moench, production on clay soils in the southern USA would be facilitated by increased knowledge of growth responses and reseeding capability of legume cultivars. This study evaluated ‘Tibbee’ crimson, Trifolium incarnatum L.; ‘Bigbee’ berseem, T. alexandrinum L.: ‘Yuchi’ arrowleaf, T. vesiculosum Savi. and ‘Woogenellup’ subterranean, T. subterraneum L. clovers and ‘Woodford’ big flower vetch, Vicia grandiflora Scop., for reseeding, biomass and N content at seven growth termination dates (GTD) 20 and 31 March, 10 and 21 April, and 1, 13, and 22 May 1986. The field experiment was initially planted on 15 Oct. 1985 on a Mhoon silty clay (fine‐silty, mixed, nonacid, thermic, Typic Fluvaquents). No legume was able to reseed the first year when the GTD was on or before 10 April. Crimson and subterranean clover and big flower vetch successfully reseeded at a GTD of 21 April. Berseem clover did not reseed unless the GTD was as late as 13 May, and arrowleaf clover did not reseed at any GTD. The legumes that reseeded the first year also reseeded a second year. Maximum biomass:N (kg ha−1) accumulation was 5500:150 for crimson; 6550:190 for berseem; 6350:152 for subterranean; 6300:203 for arrowleaf clovers; and 2700:80 for big flower vetch. Maximum biomass and N accumulation occurred by the date of reseeding for all five legumes; thus, growth of these legumes need not extend beyond this date to realize all of the green manure benefits. Nitrogen content of all legumes, except big flower vetch, was theoretically sufficient to meet the requirements of a grain sorghum crop without additional N fertilizer.
Quantitative Determination of Total Sulfur in Plant Tissues using Acid Digestion and Ion‐chromatography
Authors: Hafez Ahmed A. , Goyal Sham S. , Rains D. W.
Published: July 2010

Total sulfur determination in plant material can be done either by expensive and sophisticated equipment such as an inductively coupled plasma atomic emission spectrophotometer (ICP‐AES), or tedious and time consuming procedures like the Johnson and Nishita or oxygen combustion method, or by S‐auto‐analyzers. Since ion‐chromatography has demonstrated versatility in inorganic ion analysis, it was adopted in this paper to measure SO4 in wet acid digests of plant materials. Plant tissues (200 mg) were digested with 2 mL HNO3 + 1 mL 70% HClO4 and subsequently evaporated to dryness in order to minimize the HClO4 concentration for efficient ion‐chromatography. Magnesium oxide was dissolved in HNO3 at a rate of 1.25 g L−1 to provide cations to prevent the losses of S gases. Dionex OmniPac PAX‐500 analytical column was used to provide simultaneous anion exchange and reverse‐phase ion‐chromatography. Using 25 mM NaOH in 45% acetonitrile as eluent at a rate of 0.8 mL min−1, the analysis time was 10 min/sample. A complete recovery of total S from plant materials and with sulfur added as cysteine, methionine, glutathione, and sulfate is demonstrated. The method is simple, accurate, reproducible, and can be automated.
Potassium Utilization by No‐till Full‐Season and Double‐Crop Soybean
Authors: Coale F. J. , Grove H. J.
Published: July 2010

Although K accumulation by soybean [Glycine max (L.) Merr.] has been studied extensively, data on differential K utilization by full‐season and double‐crop soybean are not available. Potassium utilization by no‐till soybean grown at two levels of soil K fertiliiy and two row widths was evaluated under full‐season and double‐crop planting dates. Plant component dry weight and K concentration were determined at growth stages R1, R5, and R7. For both planting dates, high soil K fertility resulted in elevated tissue K concentration and K accumulation in all plant parts at all three growth stages. At R1, double‐crop soybean tissue K concentrations were greater than that of full‐season soybean. At R7, double‐crop soybean leaf and abscised tissue K concentrations were lower than those of full‐season soybean, suggesting a disproportionately greater translocation of K out of the double‐crop soybean leaf during seed‐fill. At R7, seed K accounted for 64 and 38% of total plant K for low and high K fertilily regimes, respectively. seed IC at R7 was a constant proportion of total K accumulated for both full‐season and double‐crop planting dates. Row spacing did not alter shoot K concentration or accumulation for either planting date. Potassium accumulation rate was greatest between R1 and R5, was increased by high K fertility conditions, and was not different between full‐season and double‐crop planting dates except during the seed‐filling period when the fullseason soybean K uptake rate was greater. Full‐season soybean maintained a greater soil K uptake rate during seed‐fill while double‐crop soybean seed K supply was apparently more dependent on redistribution of K from other plant tissues.
General Model for Predicting Crop Response to Fertilizer
Authors: Johnson G. V.
Published: July 2010

Predicting crop response to fertilizers is fundamental to determining fertilization profitability. This paper describes development of a general model to predict crop response to N, P, and K fertilizers. The Mitscherlich percent sufficiency concept and Bray mobility concept are the general underlying principles upon which the model is developed. Crop yields are projected within the limits of a maximum equal to the yield goal and a minimum calculated as a fraction of the yield goal based on percent sufficiency–calibrated P and K soil tests, and available mineral and organic N. Organic N contributions are estimated from algorithms developed to provide a means of indexing the degree to which crops in the past were grown in a N‐rich environment and easily mineralizable organic N accumulated. Output of the model generates N, P, and K response surfaces typical of those generally found in the literature. Evaluation of the quadratic P response components in the model indicate that a coefficient of 2 for the linear term and 1 for the squared term are good first approximations. Magnitude of P and K fertilizer responses is related directly to soil test value and amount of nutrient applied. Response to N fertilizer is large and nearly linear when the yield average is small compared to the yield goal. The response decreases and becomes more curvilinear as the yield average approaches the yield goal. The model is general enough to have broad application, yet allows for local specificity through use of the soil test and yield goal information.
Potato Uptake and Recovery of Nitrogen‐15‐Enriched Ammonium Nitrate from Periodic Applications
Authors: Roberts S. , Cheng H. H. , Farrow F. O.
Published: July 2010

There is a trend in potato (Solanum tuberosum L.) production to make repeated additions of N fertilizer in sprinkler irrigation water for an extended part of the season. More information is needed on scheduling (rate and timing) these N supplements. A 3‐yr study on the use of frequent supplements of 15NH4‐15NO3 by ‘Russet Burbank’ potato was conducted on Quincy loamy sand (mixed, mesic Xeric Torripsamment). The purpose of the experiment was to trace changes in the uptake and partitioning of 15N in vines and tubers from starter and periodic additions totaling 336 kg N ha−1. Labeled N fertilizer was sprayed on a different set of replicated potato plots according to the application schedule. Plant tissue samples were taken and analyzed regularly for labeled N uptake. Whole potato plants over the season recovered a maximum of 61 to 67% of the 15N‐enriched increments of fertilizer applied, as compared to a maximum of 42 to 54% partitioning of the labeled N in tubers at final harvest. Recovery of 15NO3 was significantly higher on the average than recovery for 15NH4. Furthermore, in many cases the average recovery was highest from labeled N applied during tuber bulking early in July, which suggests that this is a crucial time for maintaining adequate N fertility.
Seed Rate and Row Spacing of No‐Till Winter Wheat
Authors: Tompkins D. K. , Hultgreen G. E. , Wright A. T. , Fowler D. B.
Published: July 2010

A snow management system, which utilizes no‐till seeding into standing stubble immediately after harvest of the previous crop, has permitted the expansion of winter wheat (Triticum aestivum L.) production in western Canada. The effect of seed rate and row spacing on grain yield and yield components of no‐till winter wheat were evaluated in 21 trials conducted in Saskatchewan from 1986 to 1988. Two winter wheat cultivars were evaluated in eight of the trials. The relationship between grain yield (Y) and seed rate was best described by a modified inverse polynomial: Y = uSR(1‐SR/566)/(SR + u/104) where u represents the upper limit of yield when seed rate is not limiting. This curve accounted for 98% of the observed variation in grain yield. Optimum seed rate varied from 58 kg ha−1 at a very dry trial to 148 kg ha−1 in a trial with more favorable growing conditions. Grain yield increased as row spacing decreased and the effect of row spacing on pain yield was increased under more favorable growing conditions. Increased seed rate and decreased row spacing interacted positively to increase grain yield so optimum seed rate increased as row spacing decreased. Increased spikes per square meter was responsible for the increase in grain yield associated with high seed rate and narrow row spacing. In contrast, kernel weights were slightly higher with low seed rate and kernels per spike were higher with low seed rate and wide row spacing. Optimum seed rate was higher for the cultivar ‘Norstar’ than for ‘Norwin’ due to higher yield potential of Norstar under the conditions experienced in this study.
Soybean Dry Matter Allocation under Subambient and Superambient Levels of Carbon Dioxide
Authors: Allen L. H. , Bisbal E. C. , Boote K. J. , Jones P. H.
Published: July 2010

Rising atmospheric carbon dioxide concentration [CO2] is expected to cause increases in crop growth and yield. The objective of this study was to investigate effects of subambient, as well as superambient, [CO2] on soybean [Glycine max (L.) Merr.] dry matter production and allocation for two reasons: to assess response of plants to prehistoric as well as future expected CO2 levels and to increase confidence in [CO2] response curves by imposing a wide range of [CO2] treatments. Soybean was grown in outdoor, sunlit, controlled‐environment chambers at CO2 levels of 160, 220, 280, 330, 660, and 990 µmol (CO2) mol−1 (air). Total dry matter growth rates during the linear phase of vegetative growth were 5.0, 8.4, 10.9, 12.5, 18.2, and 20.7 g m−2 d−1 for the above respective [CO2]. Samples taken from 24 to 94 d after planting showed that the percentage of total plant mass in leaf trifoliolates decreased with increasing [CO2] whereas the percentage in structural components (petioles and stems) increased. At final harvest the respective [CO2] treatments resulted in 38, 53, 62, 100, 120, and 92% seed yield with respect to the 330 µmol mol−1 treatment. Total dry weight responses were similar. Late season spider mite damage of the 990 and 280 µmol mol−1 treatments reduced yields. These data confirm not only that rising CO2 should increase plant growth, but also that plant growth was probably seriously limited by atmospheric [CO2] in preindustrial revolution times back to the previous global glaciation.
Propagation of Hybrid Bermudagrasses from Harvested Culms
Authors: Greene B. B. , Lancaster D. M. , Pee K. C. , Turpin J. M. , Eichhorn M. M.
Published: July 2010

Production of hybrid bermudagrass [Cynodon dactylon (L.) Pers.] requires stand establishment by vegetative means. Sprigs (rhizomes and rooted stolons) are the method of choice, but vegetative culms (cuttings) are often used because of lower planting material costs. Two studies, one in raised beds in a greenhouse (1987 and 1989) and one under field conditions (1989), were conducted during the summers of those years to investigate differences in survival of cuttings from four hybrid bermudagrass cultivars at 2, 4, 6, 8, and 10 wk of age. In raised beds, percent survival of Coastal (49%) was higher than Grazer (31%) and Tifton‐44 (24%); Brazos (41%) was higher than Tifton‐44. Cutting length and number of nodes were related to survival and reduced the proportion of variation in percent survival attributable to cutting age when included in analysis of variance models as covariates. Grazer and Brazos had higher survival than Coastal and Tifton‐44 after adjusting data for cutting length. A cultivar‐×‐age interaction affected survival in the field study. All the above results were significant at P < 0.05. Analysis of data by cultivar resulted in significant effects of age on survival of Brazos clippings, and no effect (P > 0.05) of age on survival of other cultivars.
Management and Dynamics of Potassium in a Humid Tropical Ultisol under a Rice‐Cowpea Rotation
Authors: Cox F. R. , Uribe E.
Published: July 2010

Little is known about the role of K fertilization, stover management, and tillage methods on soil K availability as they affect rice (Oryza sativa L.) and cowpea [Vigina unguiculata (L.) Walp.] productivity on Ultisols of the humid tropics. The effects of five K rates (0‐120 kg K ha−1), returning or removing stover, and three tillage methods (no‐till, strip, and conventional) were evaluated during 12 crops of rice and cowpea grown for a 4‐yr period. Fertilizer K was applied to the first seven crops. The site was a recently cleared, 18‐yr‐old secondary forest in the Peruvian Amazon Basin. The soil was a fine‐loamy, siliceous, isohyperthermic Typic Paleudult. Soils samples were collected at each crop harvest to 90 em in 15‐cm increments. Potassium fertilizer always increased grain yields when stover was removed. Conversely, responses to K additions were seldom obtained when the stover was returned. The extractable K (Modified Olsen) critical level for both upland rice and cowpeas was calculated to be 0.10 cmol L−1. Returning stover with no K fertilization maintained soil K concentrations above critical levels for both species up to the last crop of the rotation. Residual effects of fertilizer K were prolonged by returning the stover. When stover was returned, subsoil exchangeable K increased with increasing rate of K fertilization. Removal of stover resulted in greater increases in subsoil exchangeable K at the 40 kg K ha−1 rate than at 120 kg K ha−1, apparently because the higher rate resulted in K fixation. Tillage methods did not affect crop yields.
Comparison of Methods for Determining Critical Concentrations of Soil Test Phosphorus for Corn
Authors: Mallarino A. P. , Blackmer A. M.
Published: July 2010

Critical concentrations of soil‐test P (STP) are used to identify soils where response to P fertilization should be expected. There is, however, little agreement concerning the methods that should be used to identify critical STP concentrations. This study compares the efficacy of critical STP concentrations generated by using various methods. Twenty‐five P fertilization trials with corn (Zea mays L.) were established in Iowa. Available soil P at each site was estimated by the Bray‐P1, Mehlich‐3, and Olsen extractants. Corn yield response was expressed in both absolute and relative terms and then related to STP values by using various statistical models (Cate‐Nelson split, linearplateau and quadratic‐plateau segmented polynomials, the quadratic polynomial, an exponential Mitscherlich‐type equation, and a multivariate polynomial). The use of various combinations of the extractants, expressions of yield response, and models resulted in a wide variety of critical STP concentrations. Comparisons of the ability of each critical concentration to generate economic returns when used to guide fertilization across the 25 sites showed that selection of the model was much more important than selection of the extractant or the expression of yield response. The best model was the Cate‐Nelson, which identified critical concentrations of 13 rag kg−1 for the Bray‐P1, 12 mg kg−1 for the Mehlich‐3, and 5 mg kg−1 for the Olsen extractants. Overall, the results of this study demonstrate that selection of the most appropriate critical STP concentration can be a major factor affecting the profitability of fertilization in areas having an abundance of soils testing high in P.
Crimson Clover Management to Enhance Reseeding and No‐Till Corn Grain Production
Authors: Ranells N. N. , Wagger M. G.
Published: July 2010

Economic savings and increased legume‐N use efficiency may result from natural reseeding of winter annual legume cover crops. A 3‐yr experiment was conducted on a Cecil fine sandy loam (clayey, kaolinitic, thermic Typic Kanhapludult) to examine the effects of crimson clover (Trifolium incarnatum L.) strip desiccation width (25, 50, and 75% of row area) and orientation (parallel or perpendicular to plant row) on soil water depletion, corn (Zea mays L.) growth and grain yield, and clover reseeding. Additional treatments included early desiccation (25% parallel strip 2 wk before corn planting), annual seeding (complete desiccation at corn planting), and mechanical disruption of clover growth by the no‐tillage planter. Early‐season soil water was lower in annual seeded plots compared to the 25% strip treatments each year, however, soil water was limiting in only one of 3 yr. Crimson clover successfully reseeded in all strip treatments each year, with dry matter production ranging from 3.0 to 5.2 Mg ha−1 in 1990 and from 3.9 to 5.2 Mg ha−1 in 1991. Nitrogen content of reseeded crimson clover biomass ranged from 86 to 134 kg ha−1 in 1990 and 93 to 111 kg ha−1 in 1991. Corn grain yield was only marginally affected by clover strip management in two out of 3 yr. Results suggest that under adequate moisture conditions a 50% desiccated strip has the potential to maximize clover N contribution. However, a 75% strip‐width can minimize potential competition with corn for water and reduce physical impedance of the clover cover crop on corn growth.
Fallow and Sesbania Effects on Soil Nitrogen Dynamics in Lowland Rice‐Based Cropping Systems
Authors: Buresh R. J. , Chua T. T. , Castillo E. G. , Liboon S. P. , Garrity D. P.
Published: July 2010

Vast areas of rice‐growing (Oryza sativa L.) lowlands in Asia are fallowed or cropped with non‐rice crops for part of the year. Nitrate can accumulate during the fallow or non‐rice crop, but this nitrate can be lost upon flooding for rice production. To determine fallow and green manure crop effects on soil nitrate and ammonium dynamics in lowland riceland, a 2‐yr field study was conducted in the Philippines. Treatments before wet season rice were (i) Sesbania rostrata grown for either 45 or 60 d, (ii) weedy fallow, and (iii) weed‐free fallow. Sesbania rostrata was sown with irrigation in late April‐early May, rains started in early (1989) or mid‐May (1990). Weeds and S. rostrata were incorporated after soil flooding on 23 June. Rains increased soil water‐filled pore space to above 0.75 mL mL−1 between mid‐May and soil flooding. Weeds and S. rostrata assimilated soil nitrate, as evidenced by lower (P < 0.05) nitrate in those treatments than in the weed‐free fallow. The decrease in soil nitrate in the weedfree fallow from 24 April to before soil flooding (15 kg N ha−1) was apparently due to denitrification or leaching; additional nitrate (19 kg N ha−1 in 1990) disappeared after soil flooding. Ammonium‐N was rapidly released from incorporated weeds and S. rostrata. It reached a maximum by 36 d after incorporation, which correlated (r = 0.95) with N accumulation by rice at 45 d after transplanting. Results suggest that weeds and crops before rice can reduce soil N loss by assimilating nitrate‐N and then cycling this N through incorporated plant residues back to the soil where it is rapidly mineralized and used by rice.
Soybean Stover Nitrogen Affected by Dinitrogen Fixation and Cultivar
Authors: Ravuri V. , Hume D. J.
Published: July 2010

Grain legumes often are credited with leaving residual N for crops that follow in the rotation. This study was conducted to determine if increasing N2 fixation in soybean [Glycine max (L.) Merr.] would result in higher amounts of stover N at harvest. Eleven early‐maturing cultivars (Maturity group 00 and 0) in 1988 and 16 in 1989 were grown with five inoculant strain treatments and alone as uninoculated controls. There were slight cultivar‐by‐inoculant interactions but main effects were much larger. The order of N2 fixation with inoculant treatments, measured by the difference method, was 532C or three‐strain mixture > USDA 110 > CB 1809 > HH303. Dinitrogen fixation ranged from 60 to 125 kg ha−1 in 1988 and from 31 to 84 in 1989. Higher N2 fixation caused related significant (P ≤ 0.05) increases in stover dry matter and stover N yields in both years, despite concomitant increases in the apparent harvest index (AHI) and apparent NHI. Stover N concentration was not affected by increased N2 fixation in either year. In 1988, cultivars differed only slightly in stover N content. In 1989, amounts of stover N in different cultivars depended on how completely N was translocated to seed. Over the 2 yr, amounts of N in harvestable stover of the early‐maturing cultivars ranged from 9 to 24 kg ha−1, averaged across inoculant treatments. Although stover N increased with N2 fixation in both years, the amount of stover N available for return to the soil was quite low.
Nitrification Inhibitor Influences on Potato
Authors: Martin H. W. , Graetz D. A. , Locascio S. J. , Hensel D. R.
Published: July 2010

Nitrification inhibitors may reduce loss of fertilizer N from the root zone by reducing leaching and denitrification. This reduced N loss should be reflected in increased crop yields. These studies were conducted to determine if potato yield, specific gravity, or leaf N at flowering would be increased by use of nitrification inhibitors. Nitrification inhibitors dicyandiamide (DCD) and 2‐chloro‐6‐(trichloromethyl)‐ pyridine (nitrapyrin) were evaluated in five studies on potato (Solanum tuberosum L. cv. Atlantic) in Northeast Florida on an Arenic Ochraqualf, a Grossarenic Paleudult, and a Grossarenic Paleaquult. Treatments were combinations of N at 67, 134, and 202 kg ha−1; DCD at 0, 5.6, and 11.2 kg ha−1; nitrapyrin at 0.56 and 1.12 kg ha−l; and isobutylidene diurea (IBDU) applied as one‐third of the N. Tuber yields were not affected by nitrification inhibitors in four of five tests but were increased 14% in one test. Nitrification inhibitors increased leaf N concentration at flowering in three of four tests. Tuber yields were higher with DCD than with nitrapyrin in three of five tests. In several year‐location combinations, use of IBDU resulted in greater tuber yield and leaf N concentration at flowering than did nitrification inhibitors. Based on these results, nitrification inhibitors can not be recommended for potato production on hyperthermic, sandy, irrigated soils.
Early Season Ethephon Application Effects on Cotton Photosynthesis
Authors: Pettigrew W. T. , Heitholt J. J. , Meredith W. R.
Published: July 2010

Cotton (Gossypium hirsutum L.) can compensate for a limited amount of early floral bud (square) loss induced by early ethephon ethephon [(2‐chloroethyl)phosphonic acid] application, but ethephon has been found to alter the photosynthetic process in many species. A field study was conducted in 1989 and 1990 to determine how early season ethephon application affected cotton photosynthesis throughout the growing season. Early season squares were removed by hand or induced to abscise with a spray application of 0.28 kg ha−1 ethephon. Dry matter harvests were collected and light‐saturated leaf CO2 exchange rates (CER) measured periodically throughout both growing seasons. Concentrations of leaf chlorophyll, soluble protein, ribulose‐1,5‐bisphosphate carboxylase‐oxygenase (Rubisco), and thylakoid proteins CP1 and light harvesting complex along with the specific leaf weights were periodically determined on leaves tested for CER. The net assimilation rate was 13 to 17% lower in the ethephon‐treated plots directly after treatment application in both years. In 1990, leaf CER was 15% lower in the ethephon‐treated plants than either the check or hand‐removal treatments 2 d after treatment application, but was 5% greater than the two other treatments 13 d later. Stomatal conductance of the ethephon‐treated plants was 23% lower during the period of lower CER and net assimilation rate, but the internal CO2 concentration was unchanged, suggesting depressed photosynthetic activity in the chloroplasts, in addition to stomatal closure. Other than the 1‐ to 2‐wk period after treatment application, CER was unaffected by treatments. Perhaps superior carbohydrate partitioning or remobilization is more important than elevated photosynthesis in compensating for early square loss.
Spring Nitrogen on Winter Wheat: II. A Flexible Multicomponent Rate Recommendation System
Authors: Scharf Peter C. , Alley Marcus M.
Published: July 2010

A recently developed system to predict the optimum N fertilizer rate for winter wheat (Triticum aestivum L. emend. Theil) at Zadoks growth stage (GS) 30 is based on the relationship between measured economic optimum N rate at GS 30 and wheat tissue N content measured at GS 30. However, winter wheat often needs an earlier application of spring N to achieve optimum yield. We therefore developed a test to determine which fields need this earlier (GS 25) application, and to predict the optimum N rate with split‐application management using the tissue test or as a single spring application. The optimum N rate at GS 25 was measured over 5 yr, both with and without GS 30 N applications. These measured optimum N rates were regressed against a variety of possible predictor variables measured in the same fields. Tiller density at GS 25 was a good predictor of optimum N rate at GS 25 in a split spring application program. Using this relationship along with the GS 30 tissue test to make N recommendations for winter wheat increased estimated profit relative to using the tissue test alone. Soil NO3 measured to 0.9 m depth was the best predictor of optimum N rate at GS 25 when that is to be the only spring N application, and improved estimated profit relative to applying 90 kg N ha−1 at all sites; however, the economic performance of split spring N applications was substantially better than for any single spring applications. The recommendation system developed by integrating these component relationships is powerful and flexible, and provides field‐specific N rate recommendations for all spring N applications to winter wheat, regardless of management decisions about splitting spring N applications.