bluuebunny/crossref_metadata_2025 huggingface dataset:
Crop Yield as Affected by Rotation and Nitrogen Rate. I. Soybean
Authors: Peterson Todd Andrews , Varvel G. E.
Published: July 2010

Crop rotation is reported to increase seed yield of soybean [Glycine max (L.) Merr.], but rotation effects are less pronounced than for cereal crops. This study compares yield of soybean grown in continuous monoculture with that of soybean grown (i) in a 2‐yr rotation with corn [Zea mays L.]; (ii) in a 2‐yr rotation with grain sorghum [Sorghum bicolor (L.) Moench]; (iii) in a 4‐yr grain sorghum‐oat+clover [Avena sativa (L.) + 80% Melilotus officinalis (L.) Lam., 20% Trifolium pratense]‐corn‐soybean rotation; and (iv) in a 4‐yr corn‐oat+clover‐grain sorghum‐soybean rotation. Interactions between crop rotation and fertilizer N rate were also determined. The study was conducted for 4 yr on a Sharpsburg silty clay loam (fine, montmorillonitic, mesic Typic Argiudoll) near Mead, NE. Continuous soybean produced less seed (2.4 Mg ha−1) than soybean in rotation (2.7 Mg ha−1 average). Rotations in which soybean followed sorghum in rotation produced higher seed yield (2.8 Mg ha−1) than soybean following corn (2.6 Mg ha−1), mainly because soybean following sorghum responded positively to N applications, while soybean following corn did not.
Genotype ✕ Environment Interactions on Soft White Winter Wheat Quality
Authors: Bassett L. M. , Allan R. E. , Rubenthaler G. L.
Published: July 2010

Enhanced quality is essential to improve marketability of northwestern USA soft white winter (SWW) wheat (Triticum aestivum L.). The objectives were to compare four major SWW cultivars for six quality criteria and their relative environmental stabilities. Cultivars Daws, Lewjain, Nugaines, and Stephens were grown in 63 site years and evaluated for flour yield, cookie diameter, percent flour protein, alkaline water retention capacity (AWRC), hardness, and sedimentation. Cultivar and environmental effects were significant (P<0.01) for all traits. Genotype ✕ environment interactions were small, but significant. Among the variance components, years contributed most to total variance for percent protein, sedimentation, and AWRC. The year ✕ site component was greatest for flour yield, cookie diameter, and hardness. Relatively large cultivar ✕ environment components for cookie diameter, hardness, and AWRC required their evaluation across multiple site years. All cultivars had satisfactory overall SWW wheat quality, yet Lewjain and Stephens had the best cookie diameter and flour yield, respectively. Daws was marginal for cookie diameter and hardness, and Nugaines was usually low for flour yield. Stephens and Lewjain were generally the least and most sensitive to environmental variation for quality parameters. Most quality traits were correlated (P < 0.05) with each other within cultivars. The AWRC gave low and usually nonsignificant correlations with all quality parameters except cookie diameter. Intragenotypic differences in grain yield and grain volume weight were correlated (P < 0.05) with all quality traits except AWRC. Grain volume weight differences accounted for 26 to 40% and 36 to 67% of the variation in cookie diameter and flour yield, respectively.
Cotton Management Strategies for a Short Growing Season Environment: Water‐Nitrogen Considerations
Authors: Morrow M. R. , Krieg D. R.
Published: July 2010

The Southern High Plains of Texas represents the largest contiguous cotton (Gossypium hirsutum L.) production area in the USA. Water supply represents the greatest limitation to production under rainfed conditions. Where supplemental irrigation is used, growing season length represents a major limitation to attainment of high yields of desirable quality fiber and seed. The primary objective of this research project was to determine the inter‐relationships between H2O, N, and heat unit supplies as they affect lint yield of cotton. Field experiments were conducted during a 4‐yr period at a sandy soil (fine, loamy, mixed, thermic family of Aridic Paleustalf) site. Water supply was varied through irrigation with treatments ranging from dryland to fully irrigated. Superimposed on the water supplies were N rate treatments applied preplant and sidedress in a factorial design. Lint yield (LY) was defined as a function of components including plant density, bolls per plant and average boll size. Regression analysis was used to determine LY response to treatments. Lint yield was most highly correlated with boll number per unit ground area with equal contribution from plant density and bolls per plant. Water supply was most responsible for boll number; however, increasing N supply within each H2O regime resulted in a positive response in boll number per plant. Multiple regression analysis revealed that LY responded to H2O and N supplies during the fruiting period to a greater extent than to preflower supplies. Within any heat unit regime, LY was maximized as water supply increased by maintaining a constant ratio of 0.2 kg N ha−1 mm−1 H2O.
Seed Weight Response to Decreased Seed Number in Maize
Authors: Kiniry J. R. , Wood C. A. , Spanel D. A. , Bockholt A. J.
Published: July 2010

Weight per seed (SDWT) of maize (Zea mays L.) has been rcported to show no response when seed number was manually decreased. This field experiment was designed to test the generality of this lack of response across techniques of reducing seeds per ear and across genotypes. Bagging ears of a dent hybrid 2 to 4 d after silking reduced seed number by 15 to 45% and increased SDWT by 19 to 25%. The same treatment applied to a popcorn hybrid reducvd seed number by 12 to 36% with no significant increase in SDWC. Open pollinated varieties representing different seed sizes showed similar variability in SDWT response to reduced seed number. When SDWT of the dent hybrid and one of the varieties increased in response to reduced reed number, seed volume increased by a similar fraction. Removal of the apical half of the ear of the dent hybrid caused a different SDWT response than ear bagging. Such removal 5 to 15 d after silking decreased SDWT while removal 20 to 25 d after silking produced no significant change. Thus, it appeared that the response of SDWT to reduced seed number depended on genotype, how seed number was reduced, and when the reduction occurred. The reduction in SDWT due to early ear cutting was not due to a reduction in number of endosperm cells or volume of the developing seeds. The possibility of a physical restraint on SDWT by the developing pericarp of some cultivars was discussed.
Quantifying the Nitrogen Contribution from Alfalfa to Soil and Two Succeeding Crops Using Nitrogen‐15
Authors: Harris G. H. , Hesterman O. B.
Published: July 2010

With the current interest in sustainable agricultural systems, the use of legumes in crop rotations to provide N to subsequent crops is increasing. The objective of this study was to quantify the N contribution from different alfalfa (Medicago sativa L.) plant parts to a subsequent corn (Zea mays L.) crop, various soil fractions, and a 2nd yr spring barley (Hordeum vulgare L.) crop. The study was conducted at two field locations in Michigan, on a Capac loam (fineloamy, mixed, mesic, Aerie Ochraqualf) in East Lansing (EL) and on an Oshtemo sandy loam (coarse‐loamy, mixed, mesic, Typic Hapludalf) at the Kellogg Biological Station (KBS) in Hickory Corners. Alfalfa shoots and roots/crowns labeled with 15N were applied separately to microplots in Fall 1985 and Spring 1986 at a rate equivalent to 112 kg N ha−1. Corn was harvested and soil was sampled from all microplots in Fall 1986 and analyzed for 15N. Corn recovered 17 and 25% of the alfalfa‐15N applied to the loam and sandy loam soils at ELand KBS, respectively. Alfalfa‐15N remaining in soil averaged 46% of the initial input for both locations. Most (96%) of the alfalfa‐15N remaining in soil was recovered in the organic fraction, with microbial biomass accounting for 18% of this recovery. More 15N was recovered by corn and in soil from alfalfa shoots than roots/crowns at both locations, and from spring‐incorporated than fall‐incorporated plant material on the loam soil. Only 1% of the alfalfa‐15N from the original application was recovered by a 2nd yr spring barley crop at both locations
Comparison of Models for Describing; Corn Yield Response to Nitrogen Fertilizer
Authors: Cerrato M. E. , Blackmer A. M.
Published: July 2010

Decisions concerning optimum rates of fertilization directly or indirectly involve fitting some type of model to yield data collected when several rates of fertilizer are applied. Although several different models are commonly used to describe crop yield response to fertilizers, it is seldom explained why one model is selected over others. The objective of the work reported here was to compare and evaluate several models (linear‐plus‐plateau, quadratic‐plus‐plateau, quadratic, exponential, and square root) commonly used for describing the response of corn (Zea mays L.) to N fertilizer. The evaluation involved 12 site‐years of data, each having 10 rates of N appied preplanting. All models fit the data equally well when evaluated by using the R2 statistic. All models indicated similar maximum yields, but there were marked discrepancies among models when predicting economic optimum rates of fertilization. Mean (across all site‐years) economic optimum rates of fertilization as indicated by the various models ranged from 128 to 379 kg N ha−1 at a common fertilizer‐to‐corn price ratio. Statistical analyses indicated that the most commonly used model, the quadratic model, did not give a valid description of the yield responses and tended to indicate optimal rates of fertilization that were too high. The quadratic‐plus‐plateau model best described the yield responses observed in this study. The results clearly show that, especially amid increasing concerns about the economic and environmental effects of overfertilization, the renson for selecting one model over others deserves more attention than it has received in the past.
Dynamics of a Heat Balance Stem Flow Gauge during High Flow
Authors: Ham J. M. , Heilman J. l.
Published: July 2010

The heat balance technique shows promise as a method for determining mass flow of sap in stems of intact plants. Previous work has been limited to plants with stems diameters near 10 mm transpiring at low rates. We evaluated the performance of several heat balance stem flow gauges during periods of high transpiration in sunflower (Helianthus annuus L.) with stems approximately 16 mm in diameter. Measurements in a controlled environment were used to compare gauge measurements to gravimetric estimates of transpiration. Gauges having heater widths of 10 mm severely overestimated flow as transpiration approached 200 g/h. Dynamics of the heat balance and temperature profiles suggested that failure of the gauge was due to a lack of thermal equilibrium between the xylem fluid and sensors on the stem surface. Increasing the heat applied to the stem did not improve gauge performance. A gauge with a heater width of 20 mm was constructed and evaluated under similar conditions. Increasing the heater width greatly improved gauge performance and the sensitivity of the measurement during high flow. Additionally, the gauge had the ability to react to large changes in flow over short time intervals. The gauge with the wide heater measured cumulative water loss over a 15‐h period to within 5% of that determined gravimetrically. The study indicates that the relationship between stem diameter and heater width is a crucial component of gauge design, and should be rigorously evaluated when applying the technique to stems with previously untested characteristics. Results suggest that heater width should be enlarged as stem diameter increases.
Herbage Production and Nitrogen Accumulation by Alfalfa and Cicer Milkvetch in the Southern Plains
Authors: Berg William A.
Published: July 2010

Sixty to 100 yr of farming upland soils in the Southern Plains has depleted much of the N available to plants. This field study valuated alfalfa (Medicago sativa L.) and cicer milkvetch (Astragalus cicer L.) for persistence, herbage production, and N accumulation on two N‐deficient soils (Woodward fine sandy loam, coarsesilty, mixed, thermic Typic Ustocrept; Pratt loamy sand, sandy, mixed, thermic Psammentic Haplustalf). A grass (Bothriochloa ischaemum L.) was grown as a control against which to measure N accumulation. After establishment in 1981 with sprinkle irrigation, the study was conducted under dryland conditions the following 5 yr when precipitation was near the long‐term mean of 596 mm yr−1, Herbage was not harvested the year of establishment. On the Woodward sandy loam, average herbage yields were: alfalfa 4.5, cicer milkvetch 3.1, and grass 1.0 ha−1 yr−1; herbage N yields were 171, 124, and 9 kg N ha−1 yr−1, respectively. Residual N in stubble, crowns, litter, roots, and surface 10 cm of soil after six growing seasons was 1670, 1364, and 996 kg N ha−1 for alfalfa, cicer milkvetch, and grass, respectively. Cicer milkvetch on the Pratt loamy sand died during the dry summer of the second harvest season. Thus, cicer milkvetch appears marginally adapted to loamy upland soils and not adapted to deep sandy soils in the Southern Plains. Alfalfa persisted on the Pratt loamy sand with herbage yields about 87% of yields on the Woodward sandy loam. The performance of alfalfa, including apparent N2 fixation averaging 219 kg N ha−1 yr−1, is encouraging for use on marginal farmlands in the region.
Compatibility of Cicer Milkvetch in Mixtures with Cool‐Season Grasses
Authors: Townsend C. E. , Kenno H. , Brick M. A.
Published: July 2010

Cicer milkvetch (Astragalus cicer L.) is a promising forage legume, but little information is available on its forage production potential, particularly in mixtures with grasses. The objectives of these studies were to: (i) determine the compatibility of irrigated cicer milkvetch (CMV) with seven cool‐season grasses each planted in alternate rows, and (ii) compare the influence of three planting patterns on the compatibility of irrigated CMV with each of four cool‐season grasses. The seven grass species used in the first study were: smooth bromegrass (Bromus inermis Leyss.), meadow bromegrass (B. biebersteinii Roem. and Schult.), crested wheatgrass [Agropyron cristatum (L.) Beauv. ssp. pectinatum (Bieb.) Tzvel.], intermediate wheatgrass [Thinopyrum intermedium (Host.) Barkworth & Dewey], pubescent wheatgrass [T. intermedium ssp. barbulatum (Schur.)], tall wheatgrass [T. elongatum (Host.) Dewey], and creeping foxtail (Alopecurus arundinaceus Poir.). The grasses used in the second study were smooth bromegrass, meadow bromegrass, intermediate wheatgrass, and orchardgrass (Dactylis glomerata L.). The soil was a Nunn clay loam (mesic Aridic Agriustoll). Tall wheatgrass did not persist beyond the second harvest year. There was little, if any, difference among the other six grasses for compatibility with CMV because by the sixth harvest year the amount of CMV in the mixtures ranged from 76 to 83%. By the third harvest year, the legume content of the forage for the three planting patterns was similar and ranged from about 80 to 90%. Once established, CMV was very competitive with all cool‐season grasses and its forage yields alone and in grass mixtures were very similar to those of alfalfa.
Critical Phosphorus Levels for Corn and Cowpea in a Brazilian Amazon Oxisol
Authors: Smyth T. J. , Cravo M. S.
Published: July 2010

Phosphorus soil test interpretations in the Brazilian Amazon currently do not account for differences in P requirements among crops and lack information on the changes in available soil P per unit of applied fertilizer P. A long‐term P experiment in a Xanthic Hapludox near Manaus, Brazil was used to determine soil and leaf P critical levels for corn (Zea mays L.) and cowpea (Vigna unguiculata L.). A total of six corn crops were planted in annual rotation with five crops of cowpea during five consecutive years. Critical levels were established by a segmented linear regression, a linear plateau, of relative crop yields on soil test or leaf P concentrations for each crop species. Mehlich 1 (1:10) critical P levels were 6 and 8 mg kg−1 for corn and cowpea, respectively. Relationships between soil test P and crop yields were similar for fertilizer P placement as either broadcast and/or frequent bands. Fertilizer P required to raise the initial Mehlich 1 soil P to the critical levels were 41 and 60 kg P ha−1 for corn and cowpea, respectively. Higher amounts of P were extracted by Bray 1 than by Mehlich 1, but both extractants were effective in relating available soil P to yield and applied fertilizer P. Critical foliar P concentrations for corn and cowpea were 1.6 and 1.8 g kg−1, respectively. Higher soil and leaf P critical levels for cowpea relative to corn were attributed to greater P requirements for plants depending on symbiotic N2 fixation for their N supply.
Chemical Regulation of Tall Fescue Reproductive Development and Quality with Amidochlor
Authors: Roberts C. A. , Moore K. J.
Published: July 2010

Many studies have shown that the quality of tall fescue (Festuca arundinacea Schreb.) forage can be improved by chemically regulating reproductive development. This study was conducted in order to determine whether tall fescue reproductive development and quality could be regulated by amidochlor {N‐[(acetylamino)methyl]2‐chloro‐N‐(2,6‐diethylphenyl)acetamide}, a growth regulating chemical currently used for industrial turf management. In 1985 and 1986, unimproved tall fescue pastures which were located on an Alford silt loam (fine‐silty, mixed, mesic Typic Hapludalf) soil at the Dixon Springs Agricultural Research Center, near Simpson, IL, received amidochlor at 0,0.56, and 1.12 kg a.i. ha−1, Initial growth was harvested at 0, 14, 28, and 42 d after boot stage and regrowth harvested at 6 wk after initial cutting. Each year, treatments were replicated four times and plots were randomized in a split‐plot design. Because of unusual seedhead production during 1986, data were different between years and were not combined for statistical analysis. In 1985, seedhead formation decreased as amidochlor rate increased. For both initial growth and regrowth, crude protein and in vitro dry matter digestibility increased and cell wall concentration decreased as amidochlor increased. In 1986, however, untreated plots contained only 45 seedheads m−2 and amidochlor did not regulate flowering. The higher quality of forage in 1986 resulted from prevalent vegetative tissue. We concluded that amidochlor can improve forage quality of tall fescue if tillering has not been limited the previous fall.
Salinity Effects on Emergence, Vegetative Growth, and Seed Yield of Guar
Authors: Francois L. E. , Donovan T. J. , Maas E. V.
Published: July 2010

Guar [Cyamopsis tetragonoloba (L.) Taub] seed is an important source of galactomannan gum used in food and industrial products. Increased demand and an insufficient domestic supply has led to an increased interest in this crop in the semi‐arid western USA where many soils are, or have the potential to become, highly saline. This study was conducted to determine the effect of soil salinity on vegetative growth and seed yield of two cultivars, 'Kinman' and 'Esser,' grown under field conditions. Six salinity treatments were imposed on a Holtville silty clay [clayey over loamy, montmorillonitic (calcareous), hyperthermic Typic Torrifluvent] by irrigating with waters salinized with NaCl and CaCl2 (1:1 by weight). Electrical conductivities of the irrigation waters were 1.3, 2.5, 5.0, 7.4,10.0, and 12.4 dS/m during the 1st yr, and 1.2, 2.5, 4.5, 5.5, 6.5, and 7.5 dS/m during the 2nd yr. Seed yield of both cultivars was unaffected by soil salinity up to 8.8 dS/m (mean electrical conductivity of the saturated‐soil extracts in the rootzone). Each unit increase in salinity above 8.8 dS/m reduced seed yield by 17%, which places guar in the moderately tolerant category for seed production. Reduction in the number of pods per plant and weight per seed were the primary factors contributing to reduced yields. Vegetative growth was decreased 9.6% for each unit increase in salinity above 4.9 dS/m. Plant emergence was determined in greenhouse sand cultures with irrigation waters of 0.8, 4.4, 8.5,11.3,15.7, and 18.8 dS/m. Emergence was unaffected by salt levels up to 8.5 dS/m; greater levels delayed but did not significantly reduce the percent emerged.
Norm Range Size Effects in Calculating Diagnosis and Recommendation Integrated System Indices
Authors: Savoy H. J. , Robinson D. L.
Published: July 2010

Calculation of Diagnosis and Recommendation Integrated System (DRIS) indices using a norm range may minimize incorrectly diagnosed deficiencies and maximize correct diagnoses of nutrient balance. This study evaluated the effects of size of the norm range on DRIS P and K overall‐diagnostic and response‐prediction accuracies in order to identify an optimum norm range for practical application. Field data were obtained from P and K rate experiments with Louisiana S‐1 white clover (Trifolium repens) on Dexter loam (fine‐silty, mixed, thermic Ultic Hapludalf) and Providence silt loam (fine‐silty, mixed, thermic Typic Fragiudalf) soils of adequate and relatively low, respectively, P and K levels. The DRIS indices were calculated at norm ranges of 0/3 (the norm value ±0), 4/3, 8/3,12/3, and 16/3 σ and verified for correctness. The use of a norm range in the calculation of DRIS indices increased P and K overall‐diagnostic accuracies as much as 23 and 27%, respectively, on the Dexter soil. for the Providence soil these values were 5 and 21%, respectively. Widest norm ranges resulted in a decrease in P and K responseprediction accuracies of 10 and 23%, respectively, on the responsive Providence soil. The importance of using a norm range for the calculation of DRIS indices was demonstrated by these results. It appears that the greatest benefit may be realized in nonresponsive to moderately responsive systems. The norm range of 8/3 σ appears to be an acceptable compromise for calculation of DRIS indices at sites where the nutrients of interest are in relatively low supply. A wider norm range of 12/3 or 16/3 σ was indicated at sites with adequate nutrient supplies.
Relationships between Grain Nitrogen Concentrations and the Nitrogen Status of Corn
Authors: Cerrato M. E. , Blackmer A. M.
Published: July 2010

Grain analysis is frequently used to determine the N status of corn (Zea mays L.). The objective of this study was to assess the reliability of N concentration in grain as an indicator of the N status of corn. The study involved 12 site‐years of data, each having 10 rates of N applied preplanting. Nitrogen concentrations in grain tended to increase with increases in rates of N application. Nitrogen concentrations also tended to increase with increases in relative yields, but the relationships often were C‐shaped, and there was no basis for establishing critical N concentrations. The relationships between N concentrations in grain and adjusted rates of N fertilization (i.e., rates of fertilization expressed relative to economic optimum) were statistically significant, but they had low predictability. For example, only 19% of the variability in N concentrations could be explained by a model that considered only data between ± 100 kg N ha−1 from economic optimum rates of fertilization. Only 1% of the variability could be explained by a model that considered only data between ±50 kg N ha−1 from economic optimum. These observations indicate that, especially where the availability of N is near or above optimal, N concentration in grain does not provide a reliable indicator of the N status of corn.
Line‐Source vs. Irrigated/Nonirrigated Treatments for Evaluation of Genotype Drought Response
Authors: Mahalakshmi V. , Bidinger F. R. , Rao G. D. P.
Published: July 2010

The need for efficient and effective screening for drought response of crops is well recognized. The line‐source sprinkler technique used in many crop breeding programs to evaluate genotype response to drought stress has the advantage over the traditional irrigated/nonirrigated or uniform plot technique in that it creates a continuous range of moisture deficits which permit the estimation of genotype response. In situations where the response is linear, however, the line source may not provide additional information compared to that available from the uniform plot, if both techniques sample the same range of moisture deficits. Field experiments were conducted over 2 yr to compare both screening techniques for evaluating genotype response of pearl millet [Pennisetum glaucum (L.) R. Br.] to water deficit at grain filling. The soil was an Alfisol (Udic Rhodustalf) with approximately 60 mm of plant‐available moisture. Mean grain yields for individual positions along the moisture gradient in the line source, and means over genotypes for each replicate in the uniform plot were used as independent variables (environment means) to estimate individual genotype stress response by regression. Predicted genotype grain yield at 250 g m−2 mean yield and genotype regression coefficients were compared. There were no differences in the estimated genotype grain yields at 250 g m−2 mean grain yield from the two techniques in either year. Slopes differed in only four of the 32 genotypes in 1982 and two of the eight genotypes in 1984. When genotype response to the stress gradient is linear, the simpler uniform plot technique can be used for preliminary genotype evaluation with little loss of information.
Plant Height, Disk, and Capacitance Meters Used to Estimate Bermudagrass Herbage Mass
Authors: Gonzalez M. A. , Hussey M. A. , Conrad B. E.
Published: July 2010

Rapid and reliable techniques for estimating herbage mass (HM) are essential for germplasm evaluation and proper grazing management. Since hand‐clipping small quadrats is time consuming, mathematical relationships between easy to use, nondestructive techniques and hand‐clipped estimates of HM (double sampling) have been utilized. This study was conducted to quantify relationships between HM and three commonly utilized nondestructive sward measurement techniques [plant height (HT), settled disk meter height (DISK), and capacitance (CAP)] in field plantings of ‘Brazos’ bermudagrass [Cynodon dactylon (L.) Pers.]. Estimates of HM, HT, DISK, and CAP were obtained from the same location in irrigated plots and nonirrigated, grazed pastures. Linear equations were observed to describe the relationship between HM and HT [ Y = 414 + 12.9X (r2 = 0.86), Y = 37 + 21.7X (r2 = 0.86)] and CAP [ Y = ‐1276 + 2.4X(r2 = 0.77), Y = 1289 + 2.8X (r2 = 0.89)] for plots and pastures, respectively. The relationship between HM and DISK was linear [ Y = 282 + 29.3X (r2 = 0.91)] and quadratic [ Y = 421 + 44.9X ‐ 0.7X2 (r2 = 0.80)] for the pasture and plot studies, respectively. For all HM relationships, the ability to predict HM was generally better in pastures than in small plots. Problems associated with lodged herbage in plots greatly influenced the HM predictive relationships of all techniques presumably by increasing the variability at high HM levels. Due to the large differences in the range of HM, in tiller height and tiller density, separate equations were required to predict HM in pastures and plots, regardless of the technique utilized. No single technique was observed to best predict HM. In the pastures, CAP and DISK were more efficient at estimating HM, while in the plots HT was the most efficient estimator of HM. This study suggests, while double‐sampling may allow for the estimation of HM in bermudagrass, factors such as tiller height and tiller density will influence the predictive relationships of all techniques requiring separate prediction equations to be developed where differences in sward composition are expected.
Seedling Kentucky Bluegrass Growth Responses to Chelated Iron and Biostimulator Materials
Authors: Goatley J. M. , Schmidt R. E.
Published: July 2010

Enhanced growth of seedling turfgrasses with biostimulator materials or chelated Fe could accelerate the rate of establishment. Field experiments in the spring and fall of 1987 and in the greenhouse in the winter of 1988 were designed to measure seedling Kentucky bluegrass (Poa pratensis L.) growth responses to foliar applications of benzyladenine (BA, 6‐benzylaminopurine), propiconazole [1‐{[2‐(2,4‐dichlorophenyl)‐4‐propyl‐1,3‐dioxolan‐2‐yl]methyl}‐l‐(1H‐1,2,4‐triazole], triadimefon [l‐(4‐chlorophenoxy)‐3,3‐dimethyl‐l‐(1H‐1,2,4‐triazol‐1‐yl)‐2‐butanone], or a fortified seaweed extract (SWE, containing 500 µg L−1 of glycol kinetin and 500 µg L−1 gibberellins) applied alone or in combination with chelated Fe (8% Fephosphate citrate). The seaweed extract (0.03 mL product m−2) significantly increased root and shoot growth 6 wk after treatment (WAT) in the spring experiment, and 4 and 6 WAT in the winter greenhouse experiment. The SWE also increased the gross CO2 exchange rate (CER) on a land area basis 4 and 6 WAT in the winter experiment. Propiconazole (42 mg m−2) significantly increased seedling leaf number 6 WAT in the fall experiment. Triadimefon (150 mg m−2)or BA (6 mg m−2)applications generally were not as effective in increasing seedling growth as were the SWE or propiconazole. Foliar Fe applications (112 mg m−2), either alone or in combination with biostimulators, significantly increased root and shoot growth and gross CER on a land area basis 4 and 6 WAT in the winter greenhouse experiment. Applications of Fe increased root dry weight 6 WAT in the spring field experiment. Growth responses to individual biostimulator and Fe combinations were highly variable among experiments, suggesting possible interactions between the growth response mechanisms of the treatments.
Irrigation of Turfgrass with Secondary Sewage Effluent: I. Soil and Leachate Water Quality
Authors: Hayes A. R. , Mancino C. F. , Pepper I. L.
Published: July 2010

In arid climates water is a limited resource, and turfgrass is often irrigated with municipal effluent. However, the effects of continuous turfgrass irrigation with sewage effluent on soil and leachate water quality needs to be evaluated. The objective of this field experiment was to evaluate the effect of secondary treated municipal effluent irrigation on soil and leachate properties under a turf groundcover during the first 16 mo of irrigation. Research plots were irrigated identically with either effluent or potable water using a leaching fraction of approximately 20%. Effluent irrigation resulted in significant changes in soil properties after a relatively short period of time. After 16 mo of use, when compared with potable irrigation, effluent was found to increase electrical conductivity (EC) by 0.5 dS m−1, NO3–N by 7.8 mg kg−1, P by 31.7 mg kg−1, K by 134 mg kg−, Na by 6.0 mmol L−1 and the exchangeable sodium percentage (ESP) by 6.8. Soil Ca + Mg concentrations were greater under effluent irrigation by 0.5 mmol L−1 but decreased during the study period. Soil pH was not significantly different from potable irrigation. Leachates collected at 0.61‐m depth indicated that effluent soil leachates were higher than potable leachates primarily in EC by 0.2 dS m−1 and Na content by 0.8 mmol L−1. The increase did not exceed current recommended limits for drinking water quality.
A Concise Table for Path Analysis Statistics
Authors: Williams W. A. , Demment M. W. , Jones M. B.
Published: July 2010

A concise format for presenting path analysis statistics is demonstrated in which the path coefficients are placed in the main diagonal of a matrix, and the indirect effects are placed as off‐diagonal elements. This arrangement makes it easier to compare within and among path analyses than with the currently used format, thus facilitating interpretation.
Rainfall Distribution under a Corn Canopy: Implications for Managing Agrochemicals
Authors: Parkin T. B. , Codling E. E.
Published: July 2010

A greater understanding of the spatial patterns of water inputs to soil will aid the development of agricultural practices to reduce leaching and runoff of agrochemicals. This study was initiated to investigate the process of stemflow, and to provide quantitative data on the distribution of rainfall under a corn (Zea mays L.) canopy. Rainfall distribution under the canopies of replicate conventional till corn plots was investigated by placing rainfall collectors at discrete locations within small 1.6‐m by 0.76‐m areas of the plots. Collection cups were also fixed around the stalks of individual corn plants to quantify stemflow. Results obtained from eight storm events in 1987 revealed that corn plants channel 19 to 49% of the total rain inputs down the stem to the base of the stalk. This stemflow plus the rainfall impinging directly in the planting furrow, accounted for approximately 42% of the total water inputs from a given storm event. These increased water inputs to the planting furrow may have implications in modeling solute leaching and runoff as well as to modifying current fertilizer and pesticide application methods.
Rapid Measurement of Crop Canopy Cover
Authors: Armbrust D. V.
Published: July 2010

Studies of photosynthesis, transpiration, water erosion, and wind erosion can require measurement of crop canopy cover, the percent of the soil surface covered by plant foliage. This study was conducted to evaluate the meter‐stick method and an electronic method of measuring canopy cover for accuracy, speed, and ease of use. Canopy cover of winter wheat [Triticum aestivum L.], corn [Zea mays L.], and soybean [Glycine max (L.) Merr] was measured weekly in 1988, using a meter stick and a DECAGON Ceptometer. Canopy cover ranged from 74 to 97% for wheat, 2 to 95% for corn, and 2 to 65% for soybean. There were no significant differences in canopy cover determinations by the two methods. The Ceptometer was faster, simpler, and as accurate as the meter stick.
The Rothamsted Long‐Term Experiments: Are They Still of Use?
Authors: Jenkinson D. S.
Published: July 2010

The Rothamsted long‐term experiments—the Classicals—were started almost 150 yr ago. These experiments were originally designed to study the N, P, K, Na, Mg, and Si needs of the field crops then grown in England. This was done by comparing these inorganic nutrients, in various combinations, with farmyard manure, the traditional source of fertility at that time. Although the questions the experiments were originally designed to answer have long been re‐solved, the experiments continue to give results of interest to agronomists, ecologists, soil scientists, plant pathologists, and others. The experiments show that grain yields can be sustained (and even increased) for almost 150 years in monocultures of wheat and barley given organic or inorganic fertilizer annually. They provide data on the long‐term effects of inorganic fertilizers and organic manures on soil organic matter levels. These data have been used to test computer‐based models for the turnover of organic matter in soil. Again, long‐term N balances show that there are considerable inputs of N to the soil/plant system, amounting to some 30 kg N ha−1 yr−1 in unfertilized wheat and up to 65 kg ha−1 yr−1 in an arable soil reverting to woodland. These and other results are used to consider the advantages and disadvantages of long‐term experiments. Wisely used, long‐term experimental sites provide information on the long‐term sustainability of agricultural systems that can be obtained in no other way.
Lysimetric Evaluation of Daily Potential Evapotranspiration Models for Grain Sorghum
Authors: Steiner J. L. , Howell T. A. , Schneider A. D.
Published: July 2010

Evapotranspiration (Et) information is needed for many applications in agricultural and natural resource management, but commonly used prediction equations have not been adequately tested far the dry, high radiation, windy conditions of the Southern Great Plains. In order to test such equations, two precise weighing lysimeters at Bushland, TX, were used to measure daily Et from wellwatered, irrigated grain sorghum [Sorghum bicolor L.) Moench] in 1987 and 1988. Forms of the Penman, Penman‐Monteith, Jensen‐Haise, and Priestley‐Taylor models were evaluated for prediction of potential evapotranspiration (Etp). The Penman‐Monteith model provided the best predictions of Etp and predicted well across the entire range of measured Et. Forms of the Penman model with empirically fit wind functions overpredicted Etp by 20 to 409/0, and aftempts to fit a linear wind function to our data were not satisfactory The Jensen‐Hake model, requiring only daily mean temperature and solar radiation data, overpredicted by 30%, but performed consistently across the range of Et measured. Modification of the Priestley‐Taylor model with vapor pressure deficit or temperature advection terms is recommended. Without such modification, the model overpredicts at low Et rates and underpredicts at high Et rates.
Plant Population Effects on Growth and Yield in Water‐Seeded Rice
Authors: Miller Baird C. , Hill James E. , Roberts Stacey R.
Published: July 2010

Initial management strategies, such as established plant stand, significantly affect rice (Oryza sativa L.) crop development, grain yield, and final profits. Critical rice plant population for optimum yield differs greatly among various cultural systems. The objectives of this study were to: (i) characterize effects of increasing plant population on tillering, yield components, yield, and phytomass development in continuously flooded, direct water‐seeded rice culture; and (ii) identify which crop development parameters are associated with optimum grain yield in this cultural system. Two cultivars, S‐201 and M‐201, were seeded at rates ranging from 120 to 840 seeds m−2 on Stockton clays (fine, montmorillonite, thermic, Typic Pelloxererts) in Butte and Colusa counties, California, in 1984 and 1985. Plant populations ranged from 122 to 458 plants m−2. Initial rapid tillering resulted in a maximum tiller density within 37 to 63 d after seeding (DAS). Total above‐ground phytomass (TAGPM) was not significantly different among the plant populations, either during or at the end of the growing season. Although final vegetative above‐ground phytomass (VAGPM) increased as a function of tiller density, VAGPM above 850 g m2 did not result in further yield increases. Grain yields were dependent on final tiller density (FTD) rather than plant population, with yields increasing as FTD increased to 700 tillers m−2, Panicles m−2, a direct result of FTD, was the most important component of yield accounting for 89% of the variation in yield. Final tiller density or the tillering capacity of the rice crop is determined by the environmental limitations and favorability of the growing conditions. Under continuously flooded, direct water‐seeded culture, the rice crop functioned more as a population of tillers than a population of plants.
Inhibition of Weed Seed Germination by Microwaves
Authors: Barker Allen V. , Craker Lyle E.
Published: July 2010

Irradiation with radiofrequency energy (RF), which includes microwaves, brings about dielectric heating of moist materials. Some agricultural applications of dielectric heating by RF have included insects control in stored grains and improved germination of seed stocks. The objective of the present research was to evaluate microwave heating of soils as a technique for weed control. Approximately 800‐g masses of soil of variable wetness (10‐280 g H2O/kg soil) containing seeds of oat (Arena sativa L.) and indigenous weeds were heated in a microwave (2.45 GHz) oven for 15 to 240 s. Soil masses were 5 cm deep in flats. Oat seeds were placed 2 cm deep into the soil. Hearing of soils to 80 °C or higher inhibited emergence of oats and weed species. About 120 s of heating were needed to reach 80 °C. Maintaining this temperature for 30 s was needed for strong inhibition. Moisture content in this experiment had little effect on dielectric heating. Time required to heat soil to killing temperatures appears to be a factor limiting application of this technique. The procedure may be applicable to soil sterilization in cases in which other physical processes or chemical means are inconvenient or undesirable.
Model for Steady State Coupled Transport in Xylem and Phloem
Authors: Boersma L. , Lindstrom F. T. , Childs S. W.
Published: July 2010

Knowledge of water potentials throughout the xylem and phloem elements is required for understanding effects of water stress on transport of water, solutes, and carbohydrates in plants. The interaction between water potentials in xylem and phloem is of particular concern. This knowledge is difficult to obtain through experimentation but insights can be gained by means of computer programs based on mathematical statements of the processes involved. A steady state transport model was developed to gain better understanding of this interaction. The model consists of a set of equations developed from compartmental analysis of coupled xylem and phloem transport in plant roots, stems, and leaves. The set of equations is solved using a Newton‐Raphson iterative procedure. Simulations with user specified air temperature, relative humidity, water potential at the root surface, and carbohydrate concentrations in leaf and root as input variables show the effect of water stress on rate of xylem and phloem transport at six points in time during a 1 d cycle of changing air temperature and relative humidity. Maintenance of phloem pressure gradients is shown to be very sensitive to changing environmental conditions. Using user specified input, xylem and phloem transport rates were highest at midday. At 1800 h the xylem and phloem transport rates were 83 and 30% of maximum rates that occurred for both rates at 1200 h. The model provides a basis for conceptual analysis of effects of water stress on the food distribution in plants. Further development requires a systematic sensitivity analysis and comparison with experimental results.
Yield, Digestibility, and Chemical Composition of Endophyte Free and Infected Tall Fescue
Authors: Fritz J. O. , Collins M.
Published: July 2010

Utilization of low‐endophyte (Acremonium coenophialum Morgan‐Jones and Gams) cultivars of tall fescue (Festuca arundinacea Schreb.) has been shown to improve animal performance; however, insufficient information is available on the direct effects of endophyte infection on the productivity and composition of tall fescue herbage. A 2‐yr field study was conducted to assess the effects of A. coenophialum infection on the yield, digestibility, and chemical composition of tall fescue. Endophyte‐free (EF) and endophyte‐infected (EI) plots for each of two tall fescue cultivars (Kenhy and Kentucky 31) were established in August 1985 on a Maury silt loam (fine, mixed, mesic Typic Paleudalt) soil. Dry matter yields were determined for three harvests made in 1986 and 1987. Total N, fiber composition, and in vitro rate and extent of neutral detergent fiber (NDF) digestion were determined on samples of first and second harvest forage. Dry matter yields were not affected by infection status and averaged 0.80 and 0.83 Mg ha−1 in 1986 and 1.69 and 1.79 Mg ha−1 in 1987 for EF and EI tall fescue, respectively. Endophyte infection status had no effect on the rate or extent of NDF digestion. Rate of NDF digestion averaged 0.056 and 0.055 h−1 for EF and El tall fescue, respectively. Endophytic infection also had no influence on the N concentration or fiber composition of tall fescue. The results of this study suggests that A. coenophialum does not have a significant effect on the digestibility or chemical composition of tall fescue.
Nitrogen Effects on Yield and Forage Quality of Perennial Ryegrass and Tall Fescue
Authors: Collins Michael
Published: July 2010

Negative animal effects of tall fescue (Festuca arundinacea Schreb.) infected (EI) with the endophytic fungus Acremonium coenophialum Morgan‐Jones and Gams are reduced by substituting endophyte‐ free (EF) tall fescue or other forage species. A field experiment was conducted on Maury silt loam (fine, mixed, mesic, Typic Paleudults) soil from 1986 to 1988 to compare forage yields and quality of ‘Kenhy’‐EF, Kenhy‐EI, and ‘Johnstone’ tall fescue with ‘Ensilo’ (diploid) and ‘Reveille’ (tetraploid) perennial ryegrass (Lolium perenne L.) and ‘Bison’ ryegrass (Lolium intermediate). Each cultivar received 0, 75, or 150 kg ha−1 of N annually. At 150 kg ha−1 of N, Johnstone produced the highest 1987 to 1988 average dry matter (DM) yields of 6.7 Mg ha−1 compared with 5.7 Mg ha−1 for Kenhy‐EI. Tall fescue generally produced higher yields than ryegrass. Ground cover after 3 yr for Reveille of 72% did not differ from Kenhy‐EI (79%), but Ensilo (61%) and Bison (31%) were lower. Endophyte effects on yield and quality of Kenhy were seldom significant. Two‐year weighted average in vitro dry matter disappearance (IVDMD) values were 685, 663, 626, 628, and 641 g kg−1 for Reveille, Ensilo, Kenhy‐EF, Kenhy‐EI, and Johnstone, respectively. Increasing N levels increased N concentration of tall fescue but did not consistently affect that of ryegrass. These results indicate that some cultivars of ryegrass can persist at this location, but that summer productivity is well below that of tall fescue. However, some potential may exist for germplasm improvement of perennial ryegrass based on existing cultivars. Endophyte effects on yield and quality of Kenhy tall fescue under the conditions of this study were small.
Aflatoxin in Corn Hybrids Field Inoculated with Aspergillus flavus
Authors: Scott G. E. , Zummo N. , Lillehoj E. B. , Widstrom N. W. , Kang M. S. , West D. R. , Payne G. A. , Cleveland T. E. , Calvert O. H. , Fortnum B. A.
Published: July 2010

Corn (Zea mays L.) genotypes with resistance to Aspergillus flavus Link ex Fr. are needed to reduce aflatoxin contamination of grain. The primary objective of this study was to determine if the pinbar inoculation technique was effective in separating hybrids for resistance and susceptibility to kernel infection by A. flavus and aflatoxin contamination of the grain at a number of locations, but other inoculation techniques were evaluated at individual locations. Two single crosses, Mo18W × Mp313E and SC54 × Tx601, previously classified as resistant to kernel infection by A. flavus and two susceptible crosses, Mp68:616 × SC212M and GT106 × T202, were used. We found that hybrids previously classified as resistant to kernel infection by A. flavus had fewer kernels infected and lower aflatoxin concentration in the corn grain at harvest. However, these differences were not significant at all locations. Over six locations, resistant hybrids contained 58% less aflatoxin in the grain and 41% fewer infected kernels than susceptible hybrids. In addition to the pinbar, the side‐needle, and to a lesser extent the knife inoculation technique, differentiated hybrid response to ear inoculation with A. flavus.
Sorghum Harvest Index in Relation to Plant Size, Environment, and Cultivar
Authors: Prihar S. S. , Stewart B. A.
Published: July 2010

There are reports in the literature showing that harvest index (HI) does and does not increase with increase in plant size. The slope of the upper‐bound line passing through the origin in the grain yield vs. dry matter yield plots has been proposed to approximate the “genetic” HI for a given environment and inter‐cultivar comparison. The objectives of this study were to determine what changes occur in HI of sorghum [Sorghum bicolor (L.) Moench] as plant size, environment, and cultivar vary. Several environments were established in two replicated field experiments on Pullman clay loam (fine, mixed, thermic Torrertic Paleustoll), one with eight cultivars, and the other with two cultivars, three seeding dates, and three irrigation regimes. Cultivar DK‐41Y were common to both experiments. Variation in plant size was created by thinning the original stands to varying degrees. Harvest index was determined for different plant densities based on individual plant data. Lack of non‐zero intercepts of grain‐yield vs. dry‐matter‐per‐plant regressions and constancy of HI with change in plant mass, under a given environmental condition, showed that HI was independent of plant size. Harvest index values, based both on average grain and dry matter yield, and slope of the upper‐bound line, were sensitive to environments. Upperbound HI values of cultivars DK‐42, DK‐41Y, and Sprint (0.50–0.52) were significantly higher than those of Funks 499, Richardson 9112, and DK‐46 (0.46–0.48).