bluuebunny/crossref_metadata_2025 huggingface dataset:
Single Leaf and Canopy Photosynthesis Response to Plant Age in Cotton
Authors: Peng Shaobing , Krieg Daniel R.
Published: July 2010

This study was conducted to determine the single leaf and canopy photosynthesis response to plant age in cotton (Gossypium hirsutum L.). Field experiments were conducted with different row spacings and leaf types to provide a range of plant and leaf distribution patterns. Single leaf gas exchange measurements were made on uppermost, fully expanded, main stem leaves throughout the growing season when air temperature was about 27 °C and photosynthetically active radiation exceeded 1800 μmol m−2 s−1. Canopy photosynthetic rate per unit ground area was measured concurrently with the single leaf gas exchange rate. Leaf water potential and light interception were determined when the gas exchange measurements were made. Leaf area was measured to calculate canopy photosynthetic rate per unit leaf area. Single leaf photosynthetic rates declined 27 to 38% as plant age increased from 70 to 115 d after planting, the period of maximum dry matter accumulation. The canopy photosynthetic rate per unit ground area reached a maximum between 80 and 90 days after planting, as leaf area increased, but then declined rapidly. The decline in canopy photosynthetic rate per unit ground area was mainly due to the decline in single leaf photosynthesis rather than loss of existing leaf area as plant age increased, as indicated by a corresponding decline in canopy photosynthetic rate per unit leaf area. The decline in photosynthesis as plants aged was not caused by environmental limitations or carbon evolution from the soil. The rapidly developing fruit load and associated C evolution accounted for only 20% of the decline in canopy photosynthetic rate per unit ground area.
Reflectances from Four Wheat Residue Cover Densities as Influenced by Three Soil Backgrounds
Authors: Aase J. K. , Tanaka D. L.
Published: July 2010

It is important to know quantity of crop residue on the soil surface to maintain or to improve soil physical and chemical properties and to assess the soil's susceptibility to erosion. Our objective was to use remote sensing techniques to examine the potential for remotely differentiating among wheat residue quantities and bare soils. We used three soils of the northern Great Plains (Williams loam [fineloamy, mixed Typic Argiboroll], Vanda Clay [fine‐silty, mixed calcareous, frigid Ustic Torriorthents], and Lambert silt loam [finesilty, mixed calcareous, frigid Typic Ustorthents]) that had either dry or wet surfaces and 0, 33, 66, and 100% wheat residue covering the soil surfaces. A portable spectroradiometer, and a hand‐held four‐band radiometer were used to measure spectral response and an infrared thermometer to measure surface temperatures. The infrared thermometer results allowed for differentiation among wet and dry surfaces and among residue quantities when the soil background was wet. Temperature differences between wet and dry surfaces became smaller as residue quantities increased and were near the same at 100% cover. Data obtained from the two radiometers were similar. Based on the type of measurements made in our study and indices calculated, the conclusions are that remotely sensed temperatures may be useful to assess surface soil residue covers when all soil backgrounds are wet. Linear combinations of n spectral bands in n‐dimensional space were calculated to form spectral indices, referred to as n‐space indices. The first n‐space index probably holds the best promise for developing any type of relationship to determine amount of residue cover on an otherwise bare soil surface, albeit, it appears from the data that the usefulness of such a relationship would be limited to soils that are naturally dark colored or that are darkened by the effect of water.
Instrument for Indirect Measurement of Canopy Architecture
Authors: Welles J. M. , Norman J. M.
Published: July 2010

Leaf area index (LAI) and leaf angle distribution are widely used indices of vegetative canopy structure that are difficult to measure directly. This study was conducted to test a commercially available instrument for rapidly determining LAI and foliage inclination information from “fisheye” measurements of light interception. The instrument's estimates of LAI are compared with direct measurements in soybean [Glycine max (L.) Merr.], winter wheat (Triticum aestivum L.), and prairie grass. The dominant grass species in the plots were indian grass [Sorghastrum nutans (L.) Nash], switchgrass (Panicum virgatum L.), and big bluestem (Andropogon gerardii Vitman). The instrument's LAI resolution was better than 3%, and its LAI error was generally less than 15%. Variations in sky brightness patterns caused variations in LAI estimates in winter wheat of less than 10%, and the presence of direct solar radiation increased LAI errors to more than 30% in canopies of differing species and LAI. In the presence of gaps in the canopy, the sensor's azimuthal view should be reduced. A simple test indicates if a canopy's gaps are significant.
Statistical Analysis of Yield Trials with MATMODEL
Authors: Gauch H. G. , Furnas R. E.
Published: July 2010

Yield trials guide agronomic recommendations and breeding selections, but often are limited by inaccuracy, missing data, and the difficulty of understanding complex genotype‐environment interactions. Recent studies have shown that a statistical model rather new to agriculturalists, the Additive Main Effects and Multiplicative Interaction (AMMI) model, can reduce these limitations. This paper introduces MATMODEL, a convenient program for the required calculations that runs on IBM compatible personal computers with MS‐DOS (PC‐DOS) 2.1 or higher and on the Apple Macintosh. MATMODEL enables one to (i) increase the accuracy of yield estimates, (ii) improve selections, (iii) impute missing data, (iv) model and understand the genotypes, environments, and interaction, particularly with a biplot graph, and (v) design flexible and efficient experiments. MATMODEL routinely provides yield estimates as accurate as raw treatment means based upon two to five times as many replications, so MATMODEL offers a remarkably cost‐effective option for gaining accuracy. This option is particularly valuable in light of recent trends towards testing genotypes in more environments with fewer replications.
Chlorophyll Meter to Predict Nitrogen Topdress Requirement for Semidwarf Rice
Authors: Turner Fred T. , Jund Michael F.
Published: July 2010

Semidwarf rice (Oryza sativa L.) tolerates excessive N fertilizer without lodging. In fact, it is difficult to maximize semidwarf rice yield without applying excessive N fertilizer since most farmers have not found a quick, unbiased, reliable method for assessing the N requirement for rice plants. A portable chlorophyll meter that instantly provides a measure of leaf chlorophyll may quickly monitor the need for additional N fertilizer. The Minolta model SPAD 502 chlorophyll meter was evaluated during a 3‐yr period for its potential to determine the need for N fertilizer by semidwarf ‘Lemont’ rice grown in research plots on several soils and locations in Texas. Preplant N rates ranging from 56 to 280 kg N ha−1 were applied to paired plots to develop plots with a range in leaf chlorophyll. At one of four plant growth stages, one of the pair of plots was topdressed with 50 kg N ha−1 after measuring leaf chlorophyll. At the prepanicle initiation and panicle differentiation stages, the rice yield increase due to N topdressing dropped from about 1600 to 100 kg ha−1 as the chlorophyll meter readings of the most recently matured leaf increased from 24 to 42, respectively. As chlorophyll readings exceeded 40, N fertilizer did not increase yield. However, at the tillering and heading growth stages chlorophyll readings were not well correlated with N fertilizer needs. These data provide evidence that the chlorophyll meter can be used to determine topdress N needs of semidwarf rice at pre‐panicle initiation and panicle differentiation.
Estimating Pearl Millet Leaf Area and Specific Leaf Area
Authors: Payne W. A. , Wendt C. W. , Hossner L. R. , Gates C. E.
Published: July 2010

Leaf area and specific leaf area (SLA) are important parameters in many agronomic and ecological processes, but can be difficult and expensive to measure. This study was made to test simplified methods of estimating pearl millet [Pennisetum glaucum (L.) R. Br.] leaf area and SLA. Leaf length, maximum width, area, and dry mass data were obtained at 2‐wk intervals from plants grown in 75‐L pots. Pots contained 85 kg of acidic, P‐deficient Betis sand (sandy, silicious, thermic Psammentic Paleustalf) and were treated with four P levels and two water treatments (stressed and nonstressed). Individual leaf area was estimated non‐destructively with the following equations: Leaf area = 0.68 ✕ (leaf length ✕ maximum width) −0.114 (R2 = 0.955) and Ln(leaf area) = 2.08 ✕ Ln(length) −3.53 (R2 = 0.939). Individual leaf area and whole plant leaf area were calculated from leaf dry mass by the following linear and nonlinear equations: Leaf area = 133.6 ✕ Leaf mass + 22.69 (R2 = 0.900), and Leaf area = 162.84 ✕ Leaf mass0.687 (R2 = 0.973). Residual errors indicated that the nonlinear equation was more accurate for area estimation of small leaves (≤0.20 g), and that leaf area data were heteroscedastic. Leaf dry mass was also used to calculate SLA by the nonlinear equation SLA = 176.7 × Leaf mass−0.216 (R2 = 0.918), which gave excellent fit to experimental data independent of harvest date, P level and watering treatment. Our results demonstrate that pearl millet leaf area and SLA can be accurately estimated and easily simulated from simple regression equations.
Pearl Millet Growth as Affected by Phosphorus and Water
Authors: Payne W. A. , Lascano R. J. , Hossner L. R. , Wendt C. W. , Onken A. B.
Published: July 2010

The interaction of soil water and P supply is of paramount importance to pearl millet [Pennisetum glaucum (L.) R. Br.] growth in Sahelian Africa due to unreliable rainfall and low soil P availability. This study was conducted to quantify the growth response of pearl millet to water supply and P under conditions analogous to the Sahel in terms of climate and soil. Millet was grown for 84 d in pots containing 85 kg of Betis: sand (sandy, silicious, thermic Psammentic Paleustalf) at a semiarid location near Lubbock, TX, and harvested at regular intervals. Pots were treated with four levels of applied P (0.00, 1.15, 3.38, and 7.77 g P m−2) and two water levels (water stressed and non‐water stressed). Whole plant biomass at final harvest increased within the non‐water stressed treatment from 145 g per pot in the 0.00 g P m−2 level to 626 g per pot in the 7.77 g P m−2 level, and from 64 to 220 g per pot within the water stressed treatments. Analysis of variance showed highly significant statistical interaction between water and P level during most of the experiment. Maximum whole plant production rates for non‐water stressed plants occurred between 42 and 58 days after emergence (DAE), increasing from 5.0 g d−1 in the 0.00 g P m−2 level to 18.5 g d−1 in the 7.77 g P m−2 level, and between 28 and 42 DAE for water stressed plants, increasing from 1.3 g d−1 to 8.5 g d−1. Growth rates of plant organs also increased with P level irrespective of water level. Our study quantifies the strong influence and interaction of P and water supply on pearl millet growth and development in Sahel‐like environments, and demonstrates that water supply under such conditions cannot be effectively managed for pearl millet production without addressing soil fertility constraints.
Potato Response to Legume and Fertilizer Nitrogen Sources
Authors: Griffin T. S. , Hesterman O. B.
Published: July 2010

Production of potato (Solatium tuberosum L.) in rotation with an N2‐fixing legume requires better information on the N contribution from the legume and on management of N fertilizer following a legume. Objectives of this research were to: (i) quantify N accumulation by legumes grown as either green manure or hay; and (ii) evaluate the vine and tuber yield response of a subsequent potato crop to legume and fertilizer N. We established rotations at two Michigan locations in 1987 on McBride sandy loam (coarse‐loamy, mixed, frigid Alfic Fragiothods) and Oshtemo sandy loam (coarse‐loamy, mixed, mesic Typic Hapludalfs). First‐year crops included: alfalfa (Medicago sativa L.), birdsfoot trefoil (Lotus corniculatus L.), and red clover (Trifolium pratense L.) grown as both green manure (0 harvests) and hay (two or three seeding‐year harvests); non‐dormant ‘Nitro’ alfalfa hay; sweetclover (Melilotus spp.) and hairy vetch (Vicia villosa Roth) green manures; corn (Zea mays L.); fallow; and potato. The second‐year crop was potato, fertilized with 0, 75, 150, or 225 kg N ha−1. Plowdown N yield [PDN = fall(herbage + root)N + spring herbage N] of legumes ranged from 33 (fall‐seeded hairy vetch) to 238 kg N ha−1 (sweetclover), with the PDN yield of alfalfa, red clover, sweetclover, and spring‐seeded hairy vetch generally exceeding 150 kg ha−1. Seeding‐year harvest of legumes tended to have little effect on PDN yield, compared to a green manure crop of the same species. Potato vine dry matter and N content late in the season were 61 to 100 and 75 to 145% higher, respectively, following legumes than following non‐legumes, but total and marketable tuber yields were not affected by rotation at either location. Fertilizer N rate increased total, marketable, and cull tuber yield at MRF, with optimum N rates of about 120 and 170 kg ha−1 for marketable and total tuber yield, respectively. Nitrogen rate had no effect on tuber yield at KBS, suggesting that moisture, not available N, limited tuber yield. The difference in vegetative and tuber yield responses to rotation indicates that legume N eventually became available to the potato crop, but probably not early enough in the growing season to affect tuber initiation.
Rice Shoot Response to Root Confinement within a Membrane
Authors: Slaton N. A. , Beyrouty C. A.
Published: July 2010

A porous membrane has been used for root studies of upland crops but not for crops grown under submerged conditions. A field study was conducted to compare the growth of paddy rice (Oryza sativa L.) with and without root confinement within a porous membrane. Three membrane configurations were compared: (i) a narrow membrane; (ii) a wide membrane; and (iii) a modified wide membrane. Root confinement within membranes reduced all shoot growth and yield parameters compared to soil‐grown plants (control). Reductions in shoot growth and yield parameters were usually least for the modified wide membrane and greatest for the narrow membrane.
Relationships between Corn Yields and Soil Nitrate in Late Spring
Authors: Binford G. D. , Blackmer A. M. , Cerrato M. E.
Published: July 2010

Recent studies have shown good correlations between corn (Zea mays L.) yields and concentrations of NO3 in the surface 30‐cm layer of soil in late spring. Here we report additional correlations and evaluate the benefits of sampling to 60 cm instead of to 30 cm only. The study involved 45 site‐years (1346 plot‐years) of data collected in 1987, 1988, and 1989 in Iowa. Weather conditions were dryer than normal, with a severe drought occurring in 1988. Each site‐year included seven to 10 rates of N applied before planting. Samples representing the surface 0‐ to 30‐cm and the 30‐ to 60‐cm layers of soils were collected when corn plants were 15 to 30 cm tall. Nitrate concentrations in these soil layers were correlated with grain yields. The deeper sampling slightly improved the correlations between grain yields and soil NO3 concentrations, but the advantage was probably not great enough to justify the costs of the deeper sampling. The critical concentration of NO3 was 23 to 26 mg N kg−1 in the surface 30‐cm layer of soil and 16 to 19 mg N kg−1 in the surface 60‐cm layer of soil. Overall, the results support the idea that a soil test based on concentrations of NO3 in the surface 30‐cm layer of soil when corn plants are 15 to 30 cm tall has great promise for improving N management during corn production.
Physiological Traits Associated with Grazing‐Tolerant Alfalfa
Authors: Brummer E.C. , Bouton J.H.
Published: July 2010

Many alfalfa (Medicago sativa L.) cultivars do not persist under long‐term, continuous grazing. This study was conducted to examine the variation of physiological traits that may contribute to grazing tolerance. Plants of the grazing‐tolerant cultivars Alfagraze and Travois and the grazing‐intolerant cultivar Florida 77 were grown from seed (Study 1) and from cuttings (Study 2) in the greenhouse. Populations from each cultivar that survived 2 yr of continuous grazing in the field were also tested in Study 2. Plants were clipped either frequently (weekly) or infrequently (every 4 wk) for 20 wk. Measurements of root total nonstructural carbohydrates (TNC), root weight, top and stubble herbage yield, and stubble leaf area were taken at Weeks 0, 2, 4, 10, 12, 18, and 20. No differences were noted between populations in Study 2. Under infrequent clipping TNC levels for all cultivars were higher at 4 than 2 wk after clipping. Florida 77 produced high TNC and root and top weights only under infrequent clipping but had low TNC and root weights under both clipping regimes, produced low top and stubble herbage dry matter, but maintained high stubble leaf areas under frequent clipping. Alfagraze produced and maintained high TNC and root weights under both clipping treatments, but produced high stubble dry matter and leaf area under frequent clipping. The genetic potential of a cultivar to store large amounts of carbohydrates may enhance its grazing tolerance, although stubble leaf area is probably important in allowing maintenance of total nonstructural carbohydrates under frequent defoliation.
Forage Potential of Kura Clover and Birdsfoot Trefoil when Grazed by Sheep
Authors: Sheaffer C.C. , Marten G.C. , Jordan R.M. , Ristau E.A.
Published: July 2010

Kura clover (Trifolium ambiguum M. Bieb.) is a rhizomatous perennial legume that has not been adequately evaluated in the USA under grazing. Our objective was to compare kura clover and birdsfoot trefoil (Lotus corniculatus L.) persistence and productivity when seeded in monoculture and in a binary mixture and grazed by lambs. A controlled, high herbage allowance (mean of 7.4% of lamb body weight in forage dry matter per day) was applied for 4 yr to pastures on a Waukegan silt loam (fine‐silty over sandy, mixed, mesic Typic Hapludoll). Initial seeded legume composition of monocultures was >95%, while the composition of the kura clover‐birdsfoot trefoil mixture was initially 10 and 90%, respectively. By the fourth year of grazing, the kura clover monoculture and mixture had >99% kura clover, while the birdsfoot trefoil monoculture had only 20% birdsfoot trefoil (80% broadleaf weeds). At the initiation of grazing, kura clover had 20% greater leafiness and higher forage quality than birdsfoot trefoil. Animal days per hectare and liveweight gain per hectare were initially similar for the legume monocultures and mixtures, but by the fourth year were 105% and 86% greater, respectively, for the kura clover dominated mixture and the kura clover monoculture than for the birdsfoot trefoil monoculture. Average daily lamb gain was similar (4‐yr mean of 199 g per lamb) for the treatments each year. Seeding with birdsfoot trefoil did not reduce the incidence of lamb bloat (6%) that occurred on kura clover pastures when kura clover comprised 20% or more of the mixture. Kura clover has potential as a pasture legume in the northern USA because of its excellent persistence, ability to spread, and high forage quality. Additional evaluation of animal performance under lower herbage allowance and on determination of kura clover compatibility with grasses in mixtures is warranted.
In Situ Ruminal Protein Degradation of Switchgrass and Smooth Bromegrass
Authors: Mullahey J.J. , Waller S.S. , Moore K.J. , Moser L.E. , Klopfenstein T.J.
Published: July 2010

Performance of livestock grazing warm‐season, perennial grasses is generally greater than would be expected given their relatively low protein concentrations. Two experiments were conducted to assess ruminal escape protein using an in situ rumen technique for switchgrass (Panicum virgatum L.) and smooth bromegrass (Bromus inermis Leyss.). Whole‐plant, leaf, and stem samples were harvested at specific stages of maturity in 1987. Duplicate samples of each grass were incubated for 12 h in situ. Escape protein values were expressed as concentration [grams escape protein per kilogram dry matter (DM) adjusted for acid detergent insoluble nitrogen (ADIN)] and as a percentage of total plant protein concentration (grams protein per kilogram DM adjusted for ADIN) to characterize protein composition. Whole‐plant escape protein concentration was greater (P < 0.05) in switchgrass (31.8 g kg−,1 DM) than smooth bromegrass (22.3 g kg−1 DM), averaged across all growth stages, and generally declined with maturity in both species. Escape protein concentration was consistently greater (P < 0.05) in leaves (50.8 g kg<1 DM) than in stems (19.3 g kg<1 DM) averaged over species and growth stages. As the proportion of stem to leaf increased during maturation, whole‐plant escape protein concentration decreased. Escape protein percentage was similar for smooth bromegrass leaves and stems while switchgrass stems were generally higher than leaves. Escape protein percentage of whole‐plant switchgrass (50.9%) was greater (P = 0.08) than smooth bromegrass (20.5%) over all harvest dates. Anatomical differences between switchgrass (C4) and smooth bromegrass (C3) may partially explain differences in ruminal protein degradation and subsequent animal performance.
No‐till Plot Planter with Row Space and Fertilizer Placement Capabilities
Authors: Kushnak G.D. , Thaut R.E.
Published: July 2010

No‐till research involving row space and subsurface fertilizer placement variables requires a planter that allows quick adjustment to provide a wide range of row space and fertilizer placement positions. A no‐till planter with adjustable row spacing was constructed to allow fertilizer placement below seed, with seed, and any distance between seed rows. Row space was quickly changed to any width, including paired‐row configurations, from 0.15 to 1.27 m. With two people it required 10 min to change row space, fertilizer placement, and rate. The planter was used to establish small grains, large‐ and small‐seeded legumes, and wheatgrass. Planting was successful through 2200 and 3018 kg ha−1 of prostrate and standing small‐grain residue, respectively. Higher residue levels were not tested. The planter was mounted on a 50‐hp tractor with a three‐point hitch.
Quantitative Physical Assessment of Organic Materials Used in Sports Turf Rootzone Mixes
Authors: McCoy Edward L.
Published: July 2010

Peats and other organic materials are commonly used in sports turf rootzone mixes, yet few quantitative guidelines exist for selecting appropriate materials and incorporation rates. This study was conducted to assess the relative merits of organic sources and to identify a physical measure to assess the role of organic materials in rootzones. Five organic materials with organic contents ranging from 96 to 40% by weight and fiber contents ranging from 54 to 7% by weight were mixed with a mason sand at rates of 10, 20, and 30% by volume. Standard physical measures of bulk density, compressibility, saturated hydraulic conductivity, non‐capillary porosity, and plant‐available water revealed few differences between the organic sources for a given mixing rate. Regression relations between organic matter by weight and bulk density, and available water suggest that 3% organic matter (by weight) is required in order to attain bulk densities < 1.45 Mg m−3, and 3.5% organic matter is required for available water contents >0.2 m3 m−3. Water retention curves were used to determine the pore volume distribution for each organic source and mixing rate. The pore volume distributions were bimodal and revealed differences between the organic sources and mixing rates that were not apparent from standard physical tests. Analysis of these distributions suggest that organic sources having fiber contents >45% may be excessively coarse, and organic material incorporation rates should be selected so the final mix does not exceed 3.5% organic matter by weight.
Utilizing Genotype–by–Weather Interactions for Selecting Wheat Cultivars
Authors: Feyerherm A.M. , Sears R.G. , Paulsen G.M.
Published: July 2010

Crop cultivars should be widely adapted to varying climatic regions for optimum performance, but genotype by weather interactions often limit adaptation to subregions. Our objective was to quantify genotype by weather interaction effects between pairs of cultivars and thereby identify subregions where new cultivars could be expected to outyield established ones with prescribed confidence. Genotype by weather interaction effects were quantified by regressing yield differences (D) between a new and an established cultivar on weather variables using cultivar performance trial data for winter wheat (Triticum aestivum L.). A predicted value (D̂) was assumed to estimate the mean, E(D), of a hypothetical population of performance trials for a specified location‐year. If the 95% confidence interval for E(D) covered only positive values, it is highly likely that E(D) was greater than zero and the new cultivar outyielded the established one in that location‐year. For a specific location, inferences were extended to years not included in model development using the regression equation and associated confidence intervals for E(D). Results indicated that a new cultivar Karl would have outyielded a popular cultivar Newton in more than 50% of the years from 1950 through 1989 at locations in Kansas with mean annual precipitation exceeding 711 mm. Further, the mean yield of Karl would have exceeded that of another popular cultivar Arkan in over 50% of the years over all of Kansas. The methodology for quantifying genotype by weather interactions and extending results to years not included in model development provides important information for recommending new cultivars for specific subregions.
Early‐Season Production Systems Utilizing Indeterminate Soybean
Authors: Savoy B. R. , Cothren J. T. , Shumway C. R.
Published: July 2010

Soybean [Glycine max (L.) Merr.] yield and yield components can be influenced by production practices that affect soil moisture and plant architecture. This study evaluated the effects of variations in soil moisture and inter‐row spacing on seed yield and yield components of an indeterminate soybean grown in an early‐season production environment in south‐central Texas. ‘Williams 82’ soybean (Maturity Group III) was planted in mid‐April in 1988 and 1989 near College Station, TX (30° 32′ 33″ N lat) in a Ships clay (very fine, mixed, thermic Udic Chromusterts) that is intergraded with Weswood silt loam (Fluventic Ustochrepts). Harvest occurred in late August. Soil moisture regimes were irrigation and no irrigation; inter‐row spacings were 0.36 and 1.02 m. Seed yields were greater in 1989 (4260 kg ha−1) than in 1988 (3550 kg ha−1). Soil moisture level and row‐spacing treatments had no effect on seed yield either year. Year‐by‐inter‐row spacing interactions were significant for single seed mass and total seed and pod number. Seed size was greater in 1989 than in 1988. The year‐by‐soil moisture level interaction was significant for mean seed per pod. Both years, yield component characteristics were more consistent in 1.02‐m rows than in 0.36‐m rows. These results indicate that adequate yields, with maturation in late‐August, are possible using an adaptable indeterminate soybean in an early‐season production environment in south‐central Texas.
Total Nonstructural Carbohydrates and Nitrogen of ‘Florigraze’ Rhizoma Peanut
Authors: Saldivar A.J. , Ocumpaugh W.R. , Gildersleeve R.R. , Prine G.M.
Published: July 2010

‘Florigraze’ rhizoma peanut (Arachis glabrata Benth.) is a perennial, rhizomatous forage legume that is grown in Florida and the southern Gulf Coast. Little is known about total nonstructural carbohydrate (TNC) or N concentrations in plant parts of rhizoma peanut. Two field studies were conducted near Gainsville, FL on Arredondo loamy sands (loamy, siliceous, hyperthermic Grossarenic Paleudults) to determine (i) which plant component(s) serves as primary TNC and N storage organ(s), (ii) pattern of TNC and N accumulation in undisturbed plants, and (iii) effects of defoliation upon TNC and N. An establishment‐year study was conducted in 1980 and 1981 using spaced plants, and a defoliation‐frequency study (undefoliated vs. defoliated every 2, 6, or 8 wk) was conducted in 1981 on plants that were undisturbed in 1980. Entire plants (hills) were dug every 3 to 8 wk throughout the year and separated into shoots and primary and secondary rhizomes. Shoot TNC concentration showed no pattern of accumulation. Concentrations of TNC and N were similar in primary and secondary rhizomes. In new plantings, rhizome TNC declined in early‐season to 100 g kg−1, was low and variable (100–200 g kg−1) from May through September, and increased to 400 g kg−1 by November. Rhizome N declined from 30 g kg−1 in spring to 20 g kg−1 during the establishment year with a slight increase in autumn. All defoliation treatments reduced TNC and N concentrations of rhizomes compared to nondefoliated peanuts. Florigraze accumulates a high concentration of TNC (400–700 g kg−1) in its rhizomes in autumn. Our data suggest that defoliation should be avoided for establishing plants and plants that will be used as a source of rhizomes for propagation.
Growth Analysis of ‘Florigraze’ Rhizoma Peanut: Shoot and Rhizome Dry Matter Production
Authors: Saldivar A. J. , Ocumpaugh W. R. , Gildersleeve R. R. , Prine G. M.
Published: July 2010

‘Florigraze’ rhizoma peanut (Arachis glabrata Benth.) is a perennial tropical forage legume grown in Florida and the southern Gulf Coast. It is vegetatively propagated with rhizomes and regrows from rhizomes in the spring following winter frost‐kill, but little is known about its growth and development. Two studies were conduced near Gainesville, FL, on Arredondo loamy sands (loamy, siliceous, hyperthermic Grossarenic Paleudults) in 1980 and 1981 to characterize aerial and underground growth of Florigraze. The establishment‐year study used spaced‐planted hills (three to five rhizomes per hill) in 1980 and 1981. The defoliation‐frequency study (undefoliated vs. defoliated every 2, 6, or 8 wk) was conducted in 1981 on plants (hills) that were undisturbed at the 1980 site. Entire hills were dug every 3 to 8 wk, and separated into shoots and primary and secondary rhizomes. In the establishment year, accumulated dry matter (DM) of shoots and rhizomes increased until September, when shoot growth plateaued or declined while rhizome growth continued. During cooler autumn months, photosynthate produced in shoots was partitioned into rhizome growth. Secondary rhizomes (smaller non‐branched rhizomes) constituted the bulk of rhizome mass. Shoot/rhizome ratios increased from zero at planting to about 1.5 to 2 by late summer, then declined to about 0.5 in autumn. Defoliation treatments decreased rhizome DM production by one‐half (8 wk) to two‐thirds (2 and 6 wk) that of the undefoliated control. Our results indicate that defoliation should be avoided for establishing plants and plants that will be used as a source of rhizomes for propagation.
Reduced Phosphorus Application on Bahiagrass and Water Quality
Authors: Rechcigl J. E. , Payne G. G. , Bottcher A. B. , Porter P. S.
Published: July 2010

Phosphorus is considered to be the major factor causing eutrophication of Lake Okeechobee and other waterways in Florida. An important source of P for Lake Okeechobee is runoff of soluble P fertilizer applied to bahiagrass (Paspalum notatum Flugge) pastures. A study was conducted to ascertain whether P application levels could be reduced below current agronomic recommendations without affecting pasture yields or quality and to determine the effects of P application on surface water quality. A field study was conducted on a bahiagrass pasture to assess the yield response of bahiagrass to five annual rates of P (0, 6, 12, 24, and 48 kg ha−1) and two application times (dry season and wet season). Fertilizer treatments were arranged in a randomized complete block design with four replications on an Immokalee fine sand (sandy, siliceous, hyperthermic Arenic Haplaquods). Results indicate that P fertilization rates could be reduced from 48 to 24 kg P ha−1 without affecting yields or quality of bahiagrass. Yields in 1989 averaged 11.4, 14,7, and 10.4 Mg ha−1 for the 48, 24, and 0 kg P ha−1 treatments, respectively. Time of P application had no effect on yields or quality of bahiagrass. There was a linear increase in Mehlich I extractable P in the A and E horizons and a quadratic increase to P in the Bh horizon in 1989. Extractable P ranged from 3.8 to 22.5, 1.3 to 2.5, and 21 to 55 mg P kg−1 for the A, E, and Bh horizons, respectively. Phosphorus concentrations in surface water runoff was reduced from 33 to 60% as P application rates were decreased from 48 to 12 kg P ha−1 while total P loss was reduced from 17 to 78%, respectively. Recommended reductions in P application should result in substantial cost savings to producers and also reduce P inputs into surface water.
Seed Yield and Water‐Use Efficiency of White Lupin as Influenced by Irrigation, Row Spacing, and Weeds
Authors: Putnam D. H. , Wright J. , Field L. A. , Ayisi K. K.
Published: July 2010

When grown on sandy soil, spring‐seeded sweet white lupin (Lupinus albus L.) is usually subject to moisture stress. Late‐germinating broadleaf weeds also compete with the crop and reduce yields. The objectives of this study were to determine the effects of five irrigation levels, two row spacings (15 and 76 cm), and late‐germinating weeds on lupin seed yield, seed protein content, and water‐use efficiency. The cultivar Ultra was grown on a loamy sand (Udotrantic Haploborolls) and irrigated with a line‐source sprinkler system. Full irrigation increased seed yield an average of 553% over non‐irrigated controls in 1988, 229% in 1989, and 52% in 1990, but seed protein concentration was reduced 2.5 to 7.9 percentage points. Applied water‐use efficiency and crude protein applied water‐use efficiency were maximized at 300 to 400 mm or less of total effective water depending upon year. Irrigation increased lupin seed yield primarily by increasing numbers of fertile branches and mainstem pods. Irrigation also increased number of seeds per pod and seed weight. Lack of late season weed control reduced yields by an average of 17% in 1988 and 1989, and 28% in 1990. Yields from narrow rows were 23 to 50% higher than those from wide rows. Generally, weed count was reduced in narrow rows. Substantial benefits of irrigation to white lupin productivity were observed on these soils, but it is unlikely that applications of more than 350 to 400 mm of irrigation water plus rainfall would increase seed yield or water‐use efficiency for spring‐sown white lupin.
Temporal Importance of Greater Light Interception to Increased Yield in Narrow‐Row Soybean
Authors: Board J. E. , Kamal M. , Harville B. G.
Published: July 2010

Increased light interception is considered the main factor explaining greater yield in narrow‐ compared to wide‐row spacing in soybean [Glycine max (L.) Merr.]. Controversy exists, as to when during the growth cycle the greater light interception of the narrow rows has an enhancing effect on yield. The objectives of this study were to analyze crop growth rate and yield components to determine the importance of greater light interception during vegetative (E‐R1), early reproductive (R1‐R5), and late reproductive (R5‐R7) periods to increased yield in narrow‐row culture. Field studies were conducted during 1989 and 1990 at a late (July) planting date with ‘Centennial’ soybean (determinate, Maturity Group VI) at row spacings of 100, 75, 50, and 25 cm. The test was conducted at Baton Rouge, LA on a Mhoon silty clay soil (fine‐silty, mixed, nonacid, thermic, Typic Fluvaquents). Yield increased with greater light interception as row spacing was reduced from 100 to 75 and 50 cm. Although greater light interception occurred throughout the growing season in narrow compared to wide rows, increased crop growth rate occurred only during vegetative and early reproductive periods. The main factors responsible for increased yield in narrow rows were greater fertile node production and increased pod per fertile node. These yield components are primarily determined during the vegetative and early reproductive periods. In conclusion, analyses of crop growth rate and yield components revealed that greater light interception during the vegetative and early reproductive periods was responsible for increased yield in narrow‐row culture.
Seed Yield of Bahiagrass in Response to Sward Management by Phenology
Authors: Adjei M. B. , Mislevy P. , Chason W.
Published: July 2010

Although seed yield of bahiagrass (Paspalum notatum Fluegge) can be increased by burning and N fertilization, there is a need to establish the optimum stage of plant development for the application of such practices. A ‘Pensacola’ bahiagrass pasture, grown on Pomona fine sand (sandy, siliceous, hyperthermic, Ultic Haplaquods), was either burned or mowed at five stages of plant development: dormant, early vegetative, first‐raceme‐visible, and 2 or 4 wk after first‐raceme‐visible. After residue removal, plots were fertilized with 0, 50, or 108 kg ha−1 N. Seed yield, number of inflorescences, seed weight, and seed quality (1987 only) were determined in 1987 and 1988. Stage of plant development at time of residue removal affected all traits (P ≤ 0.05). Seed yield, seed weight, and seed quality were highest when residue was removed at the dormant or early‐vegetative stages of plant development. Seed dormancy, however, decreased as stage of plant development increased. Method of residue removal (burn vs mow) did not significantly (P ≤ 0.05) affect any trait except number of inflorescences in 1987, when more inflorescences were produced following mowing than burning. Nitrogen fertilization significantly (P ≤ 0.05) increased seed yield and number of inflorescences, but had no affect on seed weight or seed quality. Residue removal by burning or mowing prior to the first‐raceme‐visible stage of plant development, followed by application of 50 kg ha−1 N, produced high yields of quality bahiagrass seed.
Fertilizer‐Nitrogen Use Efficiency of Irrigated Wheat: II. Partitioning Efficiency of Preplant versus Late‐Season Application
Authors: Wuest S. B. , Cassman K. G.
Published: July 2010

Partitioning of N to grain is an important determinant of N‐use efficiency in wheat (Triticum aestivum L.). This study evaluated the effects of N‐fertilizer treatments on N partitioning, and compared the partitioning of labeled N applied at planting with labeled N applied at anthesis. A 2‐yr field experiment was conducted with applications of 120, 180, or 240 kg N ha−1 at planting and 0, 30, or 60 kg N ha−1 at anthesis. The mean N harvest index (NHI) of N acquired from fertilizer applied at planting was 0.70, compared to 0.89 for that N acquired from fertilizer applied at anthesis. Mean NHI of total plant N derived from all sources (fertilizer and soil) was 0.74. The amount of N applied at anthesis had little effect on N partitioning, but increasing rates of preplant N from 120 to 240 kg N ha−1 caused a decrease in NHI averaging 0.10 the first yr and 0.04 the second yr. A second 2‐yr experiment, using similar N treatments and a small dose (<1 kg ha−1) of NH4−15N injected into the soil at anthesis verified these results. In the second experiment the effects of preplant N on NHI differed between cultivars; Yecora Rojo was considerably more efficient than Anza at high preplant N rates. Fertilizer N applied at anthesis was found in leaf, stem, and spike tissue 14 days after anthesis and contributed 4.2 to 16.8% of the N in each tissue at that time. Anthesis N fertilizer was also well distributed among structural, soluble, and ribulose‐1,5‐diphosphate carboxylase N feactions of flag leaves. This study demonstrated that the early season N environment has a large influence on N partitioning at maturity, whereas N applied at anthesis has little effect on N partitioning and is allocated more efficiently to grain.
Season Length and Cultivar Determine the Optimum Evapotranspiration Deficit in Cotton
Authors: Orgaz F. , Mateos L. , Fereres E.
Published: July 2010

In areas where the growing‐season length limits cotton (Gossypium hirsutum L.) production, irrigation practices that meet the maximum evapotranspiration (ET) demand have been shown to promote excessive vegetative growth and to reduce yield. Past experiments using limited irrigation in cotton do not provide generalized information on the magnitude of ET deficits that optimize lint yields, however. A study was conducted to determine how season length and cultivar maturity affected the response functions to ET deficits in cotton. Four cultivars (Acala SJ‐C1, GC‐510, Coker‐310, and Jaen) were studied at Cordoba (southwestern Spain) on a Typic Xerofluvent soil under variable irrigation. In 1985 and 1986, ET levels ranging from 40 to 100% of maximum ET (ETmax) were generated with a sprinkler line source. In all cultivars, biomass production and number of bolls set decreased as ET decreased, but earliness was hastened by ET deficits. The water production function of Jaen was linear; seed yield was 5300 kg ha− at ETmax (820 mm). In contrast, the production function of the three other cultivars was linear up to 85% of ETmax, but levelled off as ET approached ETmax (830 mm) because a fraction of the bolls set did not open by harvest at high ET levels. Sequential harvests up to the final date showed that, for a given genotype, the ET deficit giving maximum yield decreases as length of season increases. Thus, it is possible to define an optimum ET deficit for cotton based on cultivar earliness, growing‐season length, and availability of irrigation water.
Pressurized‐Wall Minirhizotron for Field Observation of Root Growth Dynamics
Authors: Merrill Stephen D.
Published: July 2010

Data derived from minirhizotrons, tubes installed in the field for observation of root growth, can suffer from particular conditions at the interface between tube and soil. These include the interface being excessively tight–leading to under observation of roots–or to gaps between wall and soil–leading to visibility problems and over‐proliferation of roots at the wall. Details are presented for a minirhizotron designed to overcome these problems by use of flexible and constantly pressurized outer walls. The 0.5‐mm thick, clear polyvinyl outer wall is concentric with and sealed to an inner wall of extruded acrylic. Air pressure of 10 to 20 kPa is maintained between inner and outer walls. The system appears to have yielded data of a comparable or better quality than other described rhizotron‐type devices and is recommended for usage by workers with soils that present problems to minirhizotron usage.
Productivity and Persistence of Rhizoma Peanut Pastures under Different Grazing Managements
Authors: Ortega‐S. J. A. , Sollenberger L. E. , Quesenberry K. H. , Jones C. S. , Cornell J. A.
Published: July 2010

‘Florigraze’ rhizoma peanut (Arachis glabrata Benth.) is a perennial legume of high forage quality adapted to warm climates, but there has been no comprehensive evaluation of its responses to grazing management. In 1988 and 1989, the effects of grazing frequency and intensity on Florigraze persistence and herbage accumulation (HA) were evaluated on a loamy, siliceous, hyperthermic Grossarenic Paleudults soil. All 12 combinations of three levels of residual dry matter after grazing (RDM, 500, 1500, and 2500 kg ha‐') and four grazing cycle lengths (GC; 7, 21, 42, and 63 d between grazings, including a 0.5‐ to 2‐d grazing period) were replicated twice. Data were analyzed by fitting multiple regression equations starting with a second order polynomial model. In 1988, rhizoma peanut HA ranged from 6130 to 10 240 kg ha− and increased linearly as GC and RDM increased. There was a GC‐by‐RDM interaction for rhizoma peanut HA in 1989, whereby at low RDM, increasing GC increased HA, but GC had less effect as RDM increased. In 1989, rhizoma peanut HA of at least 8800 kg ha− was estimated to occur with GC of 42 d or longer when RDM was 1500 kg ha− or greater. Rhizoma peanut percentage in HA was greatest with high RDM and long GC, but values of 80% or greater in the second year were estimated for RDM as low as 1300 kg ha− when GC was 63 d, or with GC as low as 7 d when RDM was above 2300 kg ha−. Lowest values were obtained with low RDM and short GC. These data indicate that unlike most tropical legumes, rhizoma peanut is productive and persistent over a relatively wide range of grazing management practices.
Irrigation Method and Water Quality Effects on Corn Yield in the Mid‐Atlantic Coastal Plain
Authors: Adamsen F. J.
Published: July 2010

Deep well sodic sources of irrigation water are often more readily available than high quality shallow or surface sources for corn (Zea mays L.) grown in the U.S. Southeast. The objective of this study was to determine the effect of irrigation water quality and irrigation method on corn production in the Virginia‐North Carolina coastal plain. Pioneer 3320 corn was grown in rotation with peanut (Arachis hypogaea L.) on a Kenansville loamy sand (loamy, siliceous, thermic Arenic Hapludult) in Suffolk, VA, in 1984, 1985, 1986, and 1988. Corn was irrigated with either overhead sprinklers or trickle lines buried 0.35 to 0.41 m below each row with sodic deep well (142 m) and non‐sodic shallow (10 m) water. Sodic water had 220 mg Na L−1, a pH of 8.5, and a sodium adsorption ratio (SAR) of 103. Non‐sodic water had 4.8 mg Na L−1, a pH of 4.8, and an SAR of 3.1. Corn yields averaged 9970 kg ha−1 with irrigation and 7650 kg ha−1 without. Irrigation method and water quality did not affect yields of irrigated corn. Soil pH increased during the study but appeared to stabilize between 6 and 7 in the surface soil. No evidence of an increase in subsoil acidity was detected. Winter rainfall and gypsum applied to the rotational peanut crop appear to be adequate to prevent the soil exchange from being dominated by Na. The results indicate that sodic water can be used to irrigate corn in the mid‐Atlantic coastal plain and that trickle irrigation can reduce water input for corn by 30% or more.