bluuebunny/crossref_metadata_2025 huggingface dataset:
Modeling Freezing Injury in Alfalfa to Calculate Forage Yield: II. Model Validation and Example Simulations
Authors: Kanneganti V. Rao , Bland William L. , Undersander Daniel J.
Published: July 2010

Freezing injury can cause extensive yield loss in alfalfa (Medicago sativa L.) exposed to severe winters in cold climates. Alfalfa models must simulate freezing injury effects in a cumulative way, so that forage dry matter (DM) yield can be accurately calculated during multiple years of a crop. A companion paper presents ALFACOLD, an alfalfa simulation model developed by integrating functions of cold tolerance, fall dormancy, and freezing injury into the ALSIM 1 (Level 2) alfalfa model. The ALFACOLD model calculates forage yield on a daily basis, while simulating freezing injury across multiple years of the same crop. The objective of this study was to test the ALFACOLD model's ability to calculate field‐measured forage DM yield. The model was tested against measured forage yield from 39 cultivars seeded in two years and managed under a 4‐cut system for 3 yr after the seeding year at two sites in Wisconsin. Averaged across the sites, cultivars, and years, the ALFACOLD model calculated annual forage DM yield to within 12% of the measured yield, compared with an error of 35% with the ALSIM model. A regression of field‐measured yield of individual harvests (n = 874) on the corresponding ALFACOLD calculated yield indicated that 70% of the measured variability in forage yield was explained by the model. The average difference between measured and calculated DM yield for Harvests 1, 2, and 3 was <7%, but the model overcalculated fourth‐cut yield by 38%. Averaged across all sites, cultivars, years, and cuts, the ALFACOLD model calculated yield with an average SD of 600 kg ha−1 cut−1.
Rotational vs. Continuous Intensive Stocking Management of Bahiagrass Pasture for Cows and Calves
Authors: Williams M. J. , Hammond A. C.
Published: July 2010

Rapid growth of warm‐season grasses such as bahiagrass (Paspalum notatum Flügge) is associated with their rapid decline in nutritional value. Grazing management that better matches forage growth and animal intake may improve animal performance on warm‐season grass pastures. A 3‐yr study (1989‐1991) was conducted at the USDAARS Subtropical Agricultural Research Station, Brooksville, FL, to determine the effect of the same stocking rate with either rotational or continuous intensive stocking (CIS; temporary increase in stocking density during periods of rapid forage growth) management on herbage mass, forage crude protein and in vitro organic matter digestibility (IVOMD), and the performance of cows and calves (Bos taurus). Cow performance was judged on weight, body condition score (BCS), plasma urea nitrogen (PUN, mg dL−1), and pregnancy rate; calf performance was judged on average daily gain (ADG), adjusted 205‐d weaning weight, and BCS. Herbage mass of both grazing treatments was similar until the start of the rainy season (June‐July). Stocking density of CIS cattle increased by 75%, which resulted in an increase in herbage mass of 250 to 1150 kg ha−1 on rotationally grazed pastures, but this was not significant. Even at the increased stocking density, herbage mass of grazed CIS pastures continued to increase in 2 out of 3 yr, indicating that animal selectivity was not limited by grazing treatment. Crude protein and IVOMD concentrations were not affected by grazing. As a consequence, none of the animal performance variables measured was affected by grazing management. The main advantages of CIS are less labor and fencing, and reserving an area for production of winter feed. Herbage mass on ungrazed CIS pastures (3000–4200 kg ha−1) would have produced between 1700 and 2400 kg hay ha−1.
Soil Management and Supplemental Irrigation Effects on Potato: I. Soil Properties, Tuber Yield, and Quality
Authors: Porter Gregory A. , Bradbury W. Bart , Sisson Jonathan A. , Opena Geraldine B. , McBurnie Jeffrey C.
Published: July 2010

Rainfall in the northeastern United States can be erratic, causing fluctuations in the supply and quality of potato (Solanum tuberosum L.). To address these problems, yield and quality of potato were studied during three growing seasons to determine their response to soil management treatments designed to increase soil organic matter. The soil management treatments, consisting of rotation crop [oat (Avena sativa L. cv. Porter vs. green manure] and annual soil amendment applications [none vs. 22 t ha−1 compost and 45 t ha−1 manure from beef cattle (Bos taurus L.)], were tested in combination with supplemental irrigation treatments (none, reduced, and moderate) on a Caribou gravelly loam (fine‐loamy, mixed, frigid Typic Haplorthod). The green manure consisted of pea (Pisum sativum L. cv. Trapper), oat, and hairy vetch (Vicia villosa Roth) seeded at 168, 56, and 34 kg ha−1, respectively. After a single season, the amendments increased soil organic matter, K, Mg, Ca, cation exchange capacity, and aggregation. Modified‐Morgan soil‐test P increased and bulk density decreased after two amendment applications. Total yields were significantly increased by the amendment treatment [8.6 t ha−1 (23%), 1993; 8.1 t ha−1 (27%), 1994; and 4.0 t ha−1 (11%) for 1995], and U.S. No. 1 yields were similarly affected. The amendments increased tuber decay incidence during all 3 yr. Irrigation treatments significantly increased total yields by 10 t ha−1 (36%) in 1994 and 11.6 t ha−1 (37%) in 1995, while significantly reducing specific gravity and increasing tuber size. Irrigation also increased tuber decay incidence in 2 of 3 yr. During the time course and under the conditions of this study, the green manure rotation crop had no significant effect on yields or tuber quality compared with the oat rotation. In contrast, soil amendment and supplemental irrigation proved to be management tools that could rapidly affect productivity in this agricultural system.
Population Differentiation, Spatial Variation, and Sampling of Tall Fescue under Grazing
Authors: Liu Weiguo , Guertal Elizabeth A. , van Santen Edzard
Published: July 2010

Tall fescue [Festuca arundinacea Schreb.] is the most important cool‐season perennial forage grass in Alabama and the southeastern USA. Genetic variation is essential for breeding improved cultivars, and understanding factors influencing genetic variability in pastures is important if material from existing pastures is to be used in a breeding program. This study was conducted to determine the extent of differentiation for agronomic traits in pastures grazed long‐term and to investigate possible spatial variation and its effect on sampling. Three populations from permanent pasture treatments of the USDA SARE cropping system trial in Virginia were sampled: (i) pure tall fescue fertilized with N, stocked continuously (Fescue + N); (ii) tall fescue–alfalfa (Medicago sativa L.) mixture used as hay and pasture (Fescue + alfalfa); and (iii) tall fescue–red clover (Trifolium pratense L.) mixture used as hay and pasture (Fescue + red clover). The tall fescue cultivar was endophyte‐free Ky 31 [fescue endophyte: Neotyphodium coenophialum; syn. Acremonium coenophialum]. Plants from these paddocks were established in central Alabama in 1995. Original seed from the SARE trial were also germinated for establishing the original population. Ex situ evaluation was conducted in Alabama (1995–1997). Compared with plants derived from the original seed lot, plants derived from pastures under grazing had significantly earlier maturity, higher dry matter (DM) yield per plant, and larger plant diameter, indicating population differentiation in response to grazing. No significant differences were observed among populations with different pasture management treatments. Statistical and graphical analysis of spatial variation of agronomic traits showed no spatial relationships in any of the six sampled paddocks. Bootstrap estimates of minimum and maximum values indicated that 25 individuals per paddock captured most of the phenotypic variation within each paddock. A random walk approach covering the entire unit being sampled seems therefore to be an appropriate strategy for sampling similar pastures to obtain base material for a breeding program.
Water Use Efficiency of Rainfed and Irrigated Bread Wheat in a Mediterranean Environment
Authors: Oweis Theib , Zhang Heping , Pala Mustafa
Published: July 2010

In West Asia and North Africa, shortage of water limits wheat (Triticum aestivum L.) production. Current irrigation practices aim at maximizing grain yield, but achieve lower return for the water consumed. Maximizing water use efficiency (WUE) may be more suitable in areas where water, not land, is the most limiting factor. We examined the effects of various levels of supplemental irrigation (SI) (rainfed, 1/3 SI, 2/3 SI, full SI), N (0, 5, 10, 15 g N m−2), and sowing time (Nov., Dec., Jan.) on evapotranspiration (ET) and WUE of wheat. WUE was calculated for rain (WUEr), for total water (gross: rain + irrigation) (WUEg), and for SI water only (WUESI). ET ranged from 246 to 328 mm for rainfed crops, with grain yield ranging from 130 to 270 g m−2 and total dry matter from 380 to 1370 g m−2. Irrigated crops had ET of 304 to 485 mm, with grain yield of 170 to 500 g m−2. The degree to which water supply limits grain yield was indicated by the ratio of pre‐ to post‐anthesis ET (2.1–2.4:1). The SI treatments significantly increased WUEg: from 0.77 to 0.83 to 0.92 kg m−3 in November and December sowings for 1/3 SI and from 0.77 to 0.92 kg m−3 in November sowing for 2/3 SI. The highest WUEg and WUESI were achieved at 1/3 to 2/3 SI. WUE was substantially improved by applying 5 and 10 g N m−2, with little increase for higher rates. Delaying sowing had a negative effect on WUE for both irrigation and rainfed conditions. In this rainfed Mediterranean environment, WUE can be substantially improved by adopting deficit SI to satisfy up to 2/3 of irrigation requirements, along with early sowing and appropriate levels of N.
Row Spacing Effects at Different Levels of Nitrogen Availability in Maize
Authors: Barbieri Pablo A. , Rozas Herna´n R.Sainz , Andrade Fernando H. , Echeverria Herna´n E.
Published: July 2010

No‐tillage maize (Zea mays L.) grown without adequate N intercepts less than 95% of the incident radiation at flowering. Reducing the distance between rows could increase radiation interception and grain yield. A 2‐yr experiment was conducted at INTA Research Station, Balcarce, Argentina (37°45′ S; 58°18′ W), to study the effect of row spacing and N availability on intercepted radiation, kernel number, and grain yield of no‐till maize. Treatments consisted of a factorial combination of row width (0.35 and 0.70 m) and N (0 and 120 or 140 kg ha−1 each year) at a constant plant density. Low N decreased kernel number and grain yield. Narrow rows significantly increased kernel number per unit area and grain yield. Average increases in response to narrow rows were 14.5 and 20.5% for kernel number and grain yield, respectively. However, relative increases in response to narrow rows were greater at low N. A close association between kernel number and intercepted radiation during the bracketing–silking period was observed. With conventional row spacing, relative grain yield responses to narrower rows decreased as crop radiation intercepted at flowering increased. A decrease in row distance when N was limiting partially offset the negative effects of N deficiency on grain yield. Our results indicate that 27 to 46% increases in grain yield were obtained in response to narrow rows in N‐deficient maize crops.
Genetic Characterization of Flowering of Diverse Cultivars of Pea
Authors: Alcalde José A. , Wheeler Timothy R. , Summerfield Rodney J.
Published: July 2010

Genetically controlled responses to photoperiod and temperature combine to determine wide variations in flowering time of pea (Pisum sativum L.) and aid the breeding of crops adapted to target environments. Our objective was to model the flowering responses of eight diverse cultivars of pea to photoperiod and temperature in order to estimate their probable flowering genotype for the flowering time genes Lf, Sn, E, and Hr Plants were grown in pots in 11 contrasting semicontrolled and natural environments. Durations from sowing to flowering and nodes of first initiated flowers were recorded. Photothermal flowering responses of each cultivar were quantified using a two‐plane photothermal model that linearly relates the rate of progress from sowing to flowering with the mean preflowering values of temperature and/or photoperiod. Flowering genotypes were estimated based on the similarities of these response planes to those of reference lines of known flowering genotypes. The estimated flowering genotypes of the eight cultivars were NZ 6753, lf sn; Bolero, Lf Sn hr; Conway, Lfd Sn hr; Fjord, Lfd Sn Hr; Botánica‐INIA, Lf Sn hr; Amarilla‐INIA, Lfd Sn hr; Lebu Loma 13, lf e Sn hr; and Catrico SS, Lfd Sn Hr The flowering responses described by the linear photothermal model provided quantitative information for estimating the flowering genotype complementary to that of the usual semiquantitative approach based on the node of flower initiation. We concluded that the linear photothermal model provides a sound basis for describing the flowering responses of pea cultivars in order to estimate their probable flowering genotype.
Effects of Temperature and Photoperiod on the Phenological Development of Barnyardgrass
Authors: Swanton Clarence J. , Huang Jian Zhong , Shrestha Anil , Tollenaar Matthijs , Deen William , Rahimian Hamid
Published: July 2010

An understanding of the environmental variables influencing the phenological development of weeds is essential for simulation model development. Temperature and photoperiod are important variables governing the phenological development of weeds. Growth cabinet studies were conducted to characterize the phenological development of barnyardgrass [Echinochloa crus‐galli (L.) Beauv.] in response to variations in temperature and photoperiod and to determine the duration of the juvenile phase and the effect of temperature and photoperiod on reproductive development. Barnyardgrass was adapted to a temperature range of 6.5 to 52°C. Phenological development of barnyardgrass was described in terms of thermal days (cumulative day degrees above a base temperature for leaf appearance, tiller appearance, and shoot elongation). For modeling purposes, three development phases of barnyardgrass at a constant temperature of 20°C were described: (i) a juvenile phase of 1.5 thermal days; (ii) a photoperiod‐sensitive inductive phase of 4.1 thermal days; and (iii) a photoperiod‐sensitive postinductive phase of 19.5 thermal days. Photoperiod sensitivity of barnyardgrass did not differ with stage of development when expressed as a rate. Interpretation of constant sensitivity to photoperiod will simplify simulation of weed phenology in mechanistic models.
Evaluating Methods for Simulating Soybean Cultivar Responses Using Cross Validation
Authors: Irmak Ayse , Jones James W. , Mavromatis Theodoros , Welch Stephen M. , Boote Kenneth J. , Wilkerson Gail G.
Published: July 2010

Crop simulation models are used in research worldwide, and efforts are now being made to incorporate them into decision‐support systems for farmers and their advisors. However, their on‐farm acceptance will be limited unless methods can be found to determine model coefficients for new cultivars that are released by public and private breeders. The availability of data to determine coefficients is usually limited; however, soybean breeders routinely collect data for new cultivars from variety trials. Objectives of this research were to (i) estimate soybean crop‐model prediction errors for anthesis, maturity, and yield using variety trial data; (ii) determine the effectiveness of cross validation for estimating prediction errors of the soybean model; and (iii) compare these errors with those based on regression equations relating specific cultivar yields to simulated maturity group (MG) yields. Root mean squared errors of prediction (RMSEP) were used for comparisons. Georgia variety trial data from 1987 through 1996 for six MG VII cultivars were divided into sets for fitting model coefficients and independent validation. The RMSEP using cross validation were similar to fitting errors when all or only half of the data were used to fit cultivar coefficients. These errors were similar to those computed using independent data. The RMSEP for yield using linear regression were better than using generic MG coefficients but not as good as that found by fitting model coefficients. We conclude that soybean yield can be simulated for specific cultivars using either crop model or regression approaches, but the latter was not adequate for predicting cultivar anthesis and maturity dates.
Chicory and English Plantain Seedling Emergence at Different Planting Depths
Authors: Sanderson Matt A. , Elwinger Gerald F.
Published: July 2010

Chicory (Cichorium intybus L.) and English plantain (Plantago lanceolata L.) have been introduced in the USA as perennial herbs for pastures. A knowledge of seedling emergence and the structure of these species under different planting conditions is necessary for developing planting recommendations. We conducted controlled environment and field studies to compare the emergence and morphology of chicory and plantain seedlings from three planting depths. ‘Grasslands Puna’, ‘La Certa’, and ‘Forage Feast’ chicory, and ‘Ceres Tonic’ and ‘Grasslands Lancelot’ plantain were sown at 1, 3, and 6 cm depths in the growth chamber and greenhouse. The seedlings were destructively sampled 14 d after emergence, and the number and mass of leaves and roots (primary, lateral, basal, and adventitious) were recorded. The same cultivars were sown in field plots in July and September 1998 to determine seedling size and emergence from 1‐, 3‐, or 6‐cm planting depths. Controlled environment studies showed that deeper planting reduced the root weight, length, and number more in chicory than in plantain. Planting at 3 and 6 cm in the field reduced seedling emergence by 34 and 60% (avg. of cultivars), respectively, compared with the 1‐cm planting depth. Differences in seedling size among cultivars within species were mainly related to differences in seed mass. Plantain had better seedling emergence in the field than chicory (54 vs. 27% in July and 60 vs. 17% in Sept.), and these differences were not related to differences in seed mass. Both chicory and plantain should be planted no deeper than 1 cm for rapid establishment.
Rice—A Step Toward Use of Allelopathy
Authors: Olofsdotter Maria
Published: July 2010

Rice (Oryza sativa L.) allelopathy has been on the research agenda for a decade. Now it is important to step back and look at its progress to enable priority setting for future research. This paper aims to do so primarily using the following five‐step protocol for allelopathy research: (i) carrying out laboratory, greenhouse, and field studies to illustrate the effect of released allelochemicals; (ii) isolating, identifying, and characterizing allelochemicals; (iii) establishing a correlation between growth inhibition and allelochemicals; (iv) performing genetic mapping of quantitative trait loci (QTLs) correlated with allelopathy; and (v) breeding for allelopathic cultivars tested for competitive ability in greenhouse and field experiments. Recent research on rice allelopathy has resulted in the following research milestones:

There is large variation in allelopathy among rice cultivars.

Allelopathy plays a role under field conditions.

Allelopathic rice can suppress both mono‐ and dicot weed species.

Progress has been made in identifying rice allelochemicals.

Quantitative trait loci correlated with allelopathy have been identified.

This paper discusses the progress made in recent years and suggests some direction for future research.
Yield and Quality of Forage Soybean
Authors: Sheaffer Craig C. , Orf James H. , Devine Thomas E. , Jewett Jane Grimsbo
Published: July 2010

Tall forage soybean [Glycine max (L.) Merr.] cultivars in maturity groups V, VI, and VII have been developed to supply forage. Our objective was to determine the effect of harvest date and row spacing on the forage yield and quality of these new soybean cultivars. We grew forage and standard grain soybean in Minnesota with harvests in early and late September. Average maturity of tall forage soybean was R3 (early harvest) to R4 or R5 (late harvest) and average maturity of grain soybean was R6 (early harvest) to R7 (late harvest). Herbage of forage soybean was mostly leaves and stems at both harvests, whereas herbage of grain soybean contained an average of 400 and 595 g kg−1 pods at the early and late harvests, respectively. There was no harvest date × soybean entry interaction for forage yield or forage quality. Forage and grain soybean had similar forage yields (∼8.8 Mg ha−1). Because adapted grain soybean was more mature and had a greater pod proportion than forage soybean, grain soybean had greater crude protein (CP) and lower fiber concentration than forage soybean. Average forage CP for forage and grain types was 146 and 218 g kg−1, respectively, while neutral‐detergent fiber (NDF) concentration was 523 and 400 g kg−1, respectively. Decreasing row width from 76 to 25 cm increased forage yield 0.8 Mg ha−1 but had no effect on total herbage quality.
Row Spacing, Plant Density, and Nitrogen Effects on Corn Silage
Authors: Cox William J. , Cherney Debbie J. R.
Published: July 2010

Dairy producers in the northeastern USA who grow corn (Zea mays L.) forage in narrow rows plant at 125000 plants ha−1 and fertilize at 225 kg N ha−1 because they believe narrow‐row corn yields best at high plant densities and N rates. We evaluated corn in 1996 and 1997 at two row spacings (0.38 and 0.76 m), two harvest densities (80000 and 116000 plants ha−1), and six N rates (0, 50, 100, 150, 200, and 250 kg ha−1) to determine if row spacing × plant density × N rate interactions existed for dry matter (DM) and calculated milk yields. No interactions existed for DM yield, forage quality characteristics, and milk yields. Corn had greater DM and milk yields at 0.38‐ (20.3 and 16.1 Mg ha−1, respectively) vs. 0.76‐m spacing (18.9 and 15.2 Mg ha−1, respectively). Dry matter and milk yields had quadratic‐plus‐plateau responses to N rates with maximum yields (20.6 and 17.1 Mg ha−1, respectively) at an N rate of 150 kg ha−1. Nitrogen accumulation at harvest, which had a row spacing × N rate interaction, had a linear response to N rates at 0.38‐m spacing and a quadratic response at 0.76‐m spacing. Dairy farmers in the northeastern USA can produce corn silage at similar plant densities and N fertility, regardless of row spacing. Dairy producers who have excess animal waste could apply slightly more N to narrow‐row corn silage because it accumulates more N at harvest.
Performance of 15 Miscanthus Genotypes at Five Sites in Europe
Authors: Clifton‐Brown John C. , Lewandowski Iris , Andersson Bengt , Basch Gottlieb , Christian Dudley G. , Kjeldsen Jens Bonderup , J⊘rgensen Uffe , Mortensen J⊘rgen V. , Riche Andrew B. , Schwarz Kai-Uwe , Tayebi Koeyumars , Teixeira Fernando
Published: July 2010

Miscanthus is a genus of high‐yielding perennial rhizomatous grasses with C4 photosynthesis. Extensive field trials of Miscanthus spp. biomass production in Europe during the past decade have shown several limitations of the most widely planted clone, M. × giganteus Greef et Deu. A 3‐yr study was conducted at five sites in Europe (Sweden, Denmark, England, Germany, and Portugal) to evaluate adaptation and biomass production potential of four acquisitions of M. × giganteus (No. 1–4) and 11 other genotypes, including M. sacchariflorus (Maxim.) Benth. (No. 5), M. sinensis Andersson (No. 11–15), and hybrids (No. 6–10). At each site, three randomized blocks containing a 5‐ by 5‐m plot of each genotype were established (except in Portugal where there were two blocks) with micropropagated plants at 2 plants m−2. In Sweden and Denmark, only M. sinensis and its hybrids satisfactorily survived the first winter following planting. Mean annual yields across all sites for all surviving genotypes increased each year from 2 t ha−1 dry matter following the first year of growth to 9 and 18 t ha−1 following the second and third year, respectively. Highest autumn yields at sites in Sweden, Denmark, England, and Germany were 24.7 (M. sinensis hybrid no. 8), 18.2 (M. sinensis hybrid no. 10), 18.7 (M. × giganteus no. 3), and 29.1 t ha−1 (M. × giganteus no. 4), respectively. In Portugal, where irrigation was used, the top‐yielding genotype produced 40.9 t ha−1 dry matter (M. sinensis hybrid no. 7). Highest‐yielding genotypes in Sweden and Denmark were among the lowest yielding in Portugal and Germany, demonstrating strong genotype × environment interactions.
Relationships between Insufficient Potassium and Crop Maturity in Cotton
Authors: Pettigrew W. T.
Published: July 2010

Potassium deficiency in cotton (Gossypium hirsutum L.) depresses yield by decreasing late season growth and is reportedly more harmful to early maturing cotton genotypes. Research objectives were to determine if the accelerated maturity caused by K deficiency was partially caused by earlier flowering and to further evaluate whether early maturity cotton genotypes are more susceptible to low K levels. Field studies were conducted from 1995 to 1997 utilizing two okra‐normal leaf‐type near isoline pairs and two K fertilization rates (0 and 112 kg K ha−1). Okra leaf‐type genotypes are earlier in maturity than their normal leaf‐type counterparts. White bloom counts, dry matter partitioning, light interception, lint yield, yield components, and fiber quality data were collected. Genotypes responded similarly to K rates for all of the parameters evaluated. Early season flowering rates briefly increased 11% when plants were grown without supplemental K. Late‐season leaf area index (LAI) was 23% lower without supplemental K compared with plants fertilized with 112 kg K ha−1 in 2 of the 3 yr. The increased LAI of the K‐fertilized plants allowed them to intercept 6% more of the late season sunlight than the 0 kg K ha−1 treatment. Potassium fertilization increased yield 9% in 2 out of 3 yr, but low K had only minor effects on fiber quality. Early maturing okra‐leaf cotton genotypes are not more susceptible to low K rates because of their early maturity. The low K effect on crop maturity is due to a premature termination of reproductive growth and a brief enhancement of the early season flowering rate.
IRENE_DLL: A Class Library for Evaluating Numerical Estimates
Authors: Fila Gianni , Bellocchi Gianni , Donatelli Marcello , Acutis Marco
Published: July 2010

IRENE_DLL (Integrated Resources for Evaluating Numerical Estimates–Dynamic Link Library) is a Microsoft (MS) COM (component object model) class library providing a set of routines designed to facilitate the implementation of model evaluation techniques. Statistical procedures (difference‐based analysis, correlation–regression analysis, probability distributions, pattern analysis, statistics aggregation, and time mismatch analysis) are applied to allow comparing estimates against measurements, either individually taken or replicated. The dynamic link library (DLL) can be easily interfaced with applications developed under a MS Windows programming language. An essential description of the program is given along with the basic concepts of usage.
Experimental Test of Density and Energy‐Balance Corrections on Carbon Dioxide Flux as Measured Using Open‐Path Eddy Covariance
Authors: Ham J. M. , Heilman J. L.
Published: July 2010

Eddy covariance is the most direct technique for measuring water, C, and energy fluxes above crops and managed ecosystems. When using open‐path gas analyzers, corrections for air density fluctuations due to heat and water vapor flux must be applied, and these corrections are often larger in magnitude than the CO2 fluxes. Lack of energy balance closure, a common problem when using eddy covariance, implies that CO2 fluxes often are underestimated. Research was conducted to evaluate performance of the density corrections by making eddy covariance measurements above a large parking lot where CO2 and water vapor fluxes were almost zero. Uncorrected and corrected flux measurements were compared to the “known” values to determine accuracy. Data also were collected from a tallgrass prairie and a cedar forest to examine how density corrections and adjustments for energy balance closure affected daily C balances. Raw measurements from the parking lot showed apparent, density‐induced, downward CO2 fluxes (i.e., apparent photosynthesis) of approximately‐0.4 mg m−2 s−1 that were correlated with sensible heat. On average, the daily uncorrected CO2 flux was‐12.7 g m−2 d−1, but the density correction reduced and changed the direction of the flux to 1.8 g m−2 d−1, which was very close to independent chamber measurements of 2.8 g m−2 d−1. Density corrections in the forest and prairie changed average daily CO2 fluxes by 20 to 80%. Energy balance closure averaged 80 and 95% in the prairie and forest, respectively. Corrections based on energy balance closure changed daily C balances by 16 to 35%. A plethora of post‐measurement corrections, coupled with lack of energy balance closure, signals the need for additional research before eddy covariance can be routinely applied in agronomic research.
Canopy Structure, Light Interception, and Photosynthesis in Maize
Authors: Stewart D. W. , Costa C. , Dwyer L. M. , Smith D. L. , Hamilton R. I. , Ma B. L.
Published: July 2010

The amount and distribution of leaf area and leaf angles in a crop canopy determine how photosynthetically active radiation (PAR) is intercepted and consequently influences canopy photosynthesis and yield. Factors such as plant shape, plant populations, and row width will affect these leaf distributions and can occur in an almost infinite number of different combinations. To supplement experimentation, a mathematical model was developed to use measurements of leaf area and leaf angles in two dimensions (with height and across the row) to calculate PAR interception and canopy photosynthesis. Maize (Zea mays L.) hybrids with phenotypic differences were planted at several plant populations to produce a wide range of two‐dimensional leaf area and leaf angle patterns. The extreme phenotypes, leafy and reduced stature, were included to vary plant height and number of leaves above the ear. Measurements of average PAR at various levels were made in seven different canopies and compared with calculations from the model (R2 of 0.68 and 0.92 for two sets of data). As well, measurements of PAR at 20‐cm increments on transects perpendicular to the row were made in three canopy types at three levels and compared with theoretical calculations (R2 = 0.74). A simple numerical experiment was run to demonstrate the utility of the model where daily canopy photosynthesis was calculated for two row widths and seven plant types. One result was that depending on row widths, plants with very upright leaves can have both the smallest and largest daily canopy photosynthesis.
Yield and Nutritive Value of Summer Legumes as Influenced by Dairy Manure Compost and Competition with Crabgrass
Authors: Nguluve Damião W. , Muir James P. , Wittie Roger , Rosiere Randall , Butler Twain J.
Published: July 2010

Warm‐season legumes have the potential to improve range and pasture value as well as provide wildlife feed and habitat but are often unable to compete with aggressive annual grasses on infertile, low‐P soils. A strip split‐plot design experiment was established on a Windthorst fine sandy loam (fine, mixed, thermic, Udic Paleustalf) under irrigation to evaluate legume herbage production and nutritive value in the 1999 and 2000 growing seasons in competition with crabgrass (Digitaria ciliaris Koetz.) and with dairy manure compost as a soil amendment. Legumes included ‘Sabine’ Illinois bundleflower [Desmanthus illinoiensis Michx. Mac Mill ex B.L. Rob & Fernald], rayado bundleflower [Desmanthus virgatus (L.) Willd.], partridge‐pea [Chamaecrista fasciculata (Michx.) Greene], and phasey bean [Macroptilium lathyroides (L.) Urban] grown in either pure stands or mixed with crabgrass. The application of 15.5 Mg dry matter (DM) dairy compost ha−1 yr−1 increased P concentration in all forage species but did not influence total herbage DM yield or other nutritive factors. Illinois bundleflower was the most productive legume followed by rayado bundleflower and partridge‐pea while phasey bean was the least productive. Although Illinois bundleflower had low crude protein concentrations (152–160 g kg−1), it and rayado bundleflower had lower acid detergent fiber (166–219 g kg−1) and acid detergent lignin concentrations (37–51 g kg−1) than the other entries. Soil amendment with compost did not affect legume development but did favor crabgrass competition. Competition with crabgrass depressed legume yields during the establishment year. This was less a factor during the second year, indicating that legume stand establishment is possible, albeit slowed, in the presence of an annual grass.
Using the CROPGRO‐Peanut Model to Quantify Yield Gaps of Peanut in the Guinean Savanna Zone of Ghana
Authors: Naab J. B. , Singh Piara , Boote K. J. , Jones J. W. , Marfo K. O.
Published: July 2010

Peanut (Arachis hypogaea L.) yield in Ghana is limited by variable rainfall, low soil fertility, pests and diseases, and poor crop management. Field experiments were conducted during the 1997 and 1998 seasons at the Savanna Agricultural Research Station in Ghana to evaluate the CROPGRO‐peanut model for its ability to simulate growth, yield, and soil water balance of a peanut crop and to quantify yield losses caused by biotic and abiotic factors. Two peanut cultivars, Chinese which matures in 90 d, and F‐Mix which matures in 120 d, were grown rainfed on an Alfisol soil at three sowing dates between May and August in 1997 and at four dates in 1998. Soil water and crop growth were measured during the season and compared with crop model simulations to determine yield‐limiting factors relative to potential yield. Growth and yield were highest for the early sowing dates and decreased progressively with later sowing, a trend attributed to leaf diseases. After incorporating functions for percentage leaf defoliation and percentage diseased leaf area, the model accurately simulated soil water content fluctuations, crop growth, and yield of cultivars for the sowing dates and seasons. Simulated yield losses caused by water deficits were small (averaging 5–10%) for early sowing dates (late May to mid‐July) and increased with later sowing dates (20 and 70% for third and fourth sowings). Yield losses due to diseases and pests were simulated as a percentage of potential yield under water‐limited environments and averaged 40%, also increasing with later sowing dates. Using 13 yr of weather data, simulated yields were reduced 10 to 20% by water deficit for the two earlier (normal) sowing dates, but more for the later sowing dates, while additional yield reductions were attributed to biotic stresses. We conclude that the CROPGRO‐peanut model can be successfully used to quantify the yield potential and yield gaps associated with yield‐reducing stresses and crop management for this region.
Remotely Measuring Chlorophyll Content in Corn Leaves with Differing Nitrogen Levels and Relative Water Content
Authors: Schlemmer M. R. , Francis D. D. , Shanahan J. F. , Schepers J. S.
Published: July 2010

Measuring a crop's physiological parameters provides information for interpreting its response to the environment. Remote sensing is quickly becoming recognized as a valuable tool that has the potential to assess a wide variety of physiological properties over a large area in a short amount of time. This study examined the relationship of corn (Zea mays L.) leaf spectral response to its chlorophyll content and relative water content. The effects of N stress and water stress were examined on each of these physiological parameters. Over the years, several spectral indices have been introduced for a wide variety of applications. A number of these indices were evaluated for their ability to predict the parameters in question. The normalized difference between the first derivatives at 525 and 570 nm, as well as the wavelength location of the red edge, showed a strong association with chlorophyll content (r2 = 0.81 and 0.80, respectively). Even stronger relationships to chlorophyll content were observed with the ratios of 600/680 nm (r2 = 0.83) and 630/680 nm (r2 = 0.83). Thus, our results suggest that spectral reflectance measurements hold promise for the assessment of some physiological parameters at the leaf level. Further investigation is needed to evaluate the effectiveness of such techniques at the canopy level.
Herbage and Animal Responses to Management Intensity of Continuously Stocked Bahiagrass Pastures
Authors: Stewart R. L. , Sollenberger L. E. , Dubeux J. C. B. , Vendramini J. M. B. , Interrante S. M. , Newman Y. C.
Published: July 2010

There are about 1 million ha of bahiagrass (Paspalum notatum Flügge) pasture in Florida. Rapid population growth is reducing grassland area and may force beef cattle (Bos taurus) producers to achieve economic livelihood on less land. One alternative is to increase management intensity of existing pasture. This research evaluated management intensity effects on beef heifer and bahiagrass pasture performance. Management intensities were low (40 kg N ha−1 yr−1, 1.4 animal units [AU, one AU = 500 kg live weight] ha−1 stocking rate [SR]), moderate (120 kg N ha−1 yr−1, 2.8 AU ha−1 SR), and high (360 kg N ha−1 yr−1, 4.2 AU ha−1 SR). Across 4 yr, herbage mass (3.42 vs. 2.95 Mg ha−1) and allowance (4.8 vs. 1.4 kg forage kg−1 animal weight) were greater for low than high intensity. Herbage accumulation (41 vs. 17 kg ha−1 d−1), crude protein (140 vs. 99 g kg−1), and in vitro digestible organic matter (505 vs. 459 g kg−1) were greater for high than low intensity. Heifer average daily gain was greater for low than high intensity (0.34 vs. 0.28 kg), but gain per hectare (GHA) increased from low to high intensity (101 to 252 kg). Nitrogen fertilizer cost per additional kilogram of GHA above low intensity was $.76 for moderate and $2.01 for high intensity. Increasing management intensity increased bahiagrass herbage accumulation and nutritive value, but GHA did not increase sufficiently to compensate for the additional fertilizer cost, especially for high intensity. Therefore, if land limitations for cattle production become acute, use of more management‐responsive species than bahiagrass probably will be required.
Coppice Dunes and the Rotura Soil
Authors: Gile Leland H.
Published: July 2010

Early land survey notes and present conditions indicate that certain coppice dunes near Las Cruces, N. M. have formed since 1885. The Rotura soil, formed in mid‐Pleistocene sediments, occurs at the land surface between dunes but is buried beneath the dunes. The dunes overlie and preserve the pre‐dune surficial horizons, and the stratigraphic relationships thus preserved can be useful in genetic studies of thin upper horizons between dunes.

Coppice dune materials are not presently recognized as individual soils but are designated by such terms as “hummocky phase”. Although no A or B horizon development is apparent in the dune materials, roots and fauna have locally mixed the sediments. Coppice dunes dominate the microrelief and occupy major portions of the land surface in many areas. In addition, most dunes are thickly covered with vegetation. An alternative interpretation, therefore, is that sediments of a coppice dune constitute a soil and thus should be classified and named.
Estimation of Isotopically Exchangeable Cadmium and Zinc in Soils
Authors: Fujii R. , Corey R. B.
Published: July 2010

Isotopically exchangeable and chelate‐extractable Cd and Zn (16‐h equilibrations) were compared for a silt loam and a loamy sand with and without addition of 51 kg m−3 of sewage sludge. The chelating agents used were 5 mM DTPA (diethylenetriaminepentaacetic acid) at a soil to solution ratio of 1:5 and 5 and 1 mM EDTA (ethylenediaminetetraacetic acid) at soil to solution ratios of 1:5 and 1:2.5. The extractant best suited to estimate isotopically exchangeable Cd and Zn in the soils studied was 5 mM EDTA at a soil to solution ratio of 1:2.5. Extractions with this sulution ranged from 87 to 114% of the Cd isotopically exchangeable in 16 h and 91 to 113% of the Zn isotopically exchangeable in the two soils with and without sludge addition.
Fractal Theory Applied to Soil Aggregation
Authors: Perfect E. , Kay B. D.
Published: July 2010

Recent advances in fractal theory may be applicable to the characterization of soil structure. This study explored two such applications. Aggregates were assumed to be approximated by cubes of constant dry density. Under this condition, the fractal dimension, D, provides a measure of fragmentation. The value of D increases with increasing fragmentation. The influence of energy input (wet sieving) on the D of aggregates from a Conestogo silt loam soil (finesilty, mixed, mesic Aquic Eutrocrept) was investigated. Aggregates were obtained from five cropping treatments, ranging from 15 yr of continuous corn (Zea mays L.) to 15 yr of continuous bromegrass (Bromus inermis Leyss.). The value of D was estimated from cumulative size‐frequency distribution data plotted on a log‐log scale. Computed values of D ranged from 2.51 to 3.52. Energy input, cropping history, and their interaction all had a significant effect on D. Fragmentation increased with energy input and time under corn production. Relations between D and the breakdown of individual aggregates were investigated. A scale‐invariant breakdown model was developed and tested. The model permits calculation of apparent probabilities of failure, P, as a function of aggregate size, x. Stepwise multiple regression analysis selected the rate of change in P with x as the best predictor of D following energy input. Fractal theory offers potential for modeling aggregate breakdown, as well as characterizing the degree of fragmentation.
Influence of Added Nitrogen Interactions in Estimating Recovery Efficiency of Labeled Nitrogen
Authors: Rao A. C. S. , Smith J. L. , Papendick R. I. , Parr J. F.
Published: July 2010

The addition of N fertilizer to soil has been shown to stimulate the uptake of native soil N via a priming effect recently termed added nitrogen interaction (ANI). This ANI, due to pool substitution, can substantially affect the N‐recovery efficiency (NRE) by plants as calculated by the 15N isotopic dilution technique. We evaluated NRE in a pot study using ‘Edwall’ spring wheat (Triticum aestivum L.) with three soils (Palouse, a fine‐silty, mixed, mesic Pachic Ultic Haploxeroll; Ritzville, a coarse‐silty, mixed, mesic Calciorthidic Haploxeroll; and Shano, a coarse‐silty, mixed mesic Xerollic Camborthid) of varying organic C (OC) levels and five levels of 15N‐labeled fertilizer. Data obtained at 60 d after emergence (DAE) showed that NRE generally increased with fertilizer additions, was lowest in the soil having the greatest OC, and ranged from 57 to 79%. The NRE values estimated by the isotopic method averaged 20% lower than those estimated by the difference method, although the two estimates were strongly related. Although the magnitude of ANI showed no direct relationship to OC levels, it was strongly related to N rates, OC, soil C/N ratio, and N lost, which together explained 73% of the relationship. The magnitude of occurrence of ANI appears to be influenced by several factors and thus may be soil specific. Regression of NRE with soil properties showed that NRE was influenced primarily by the same factors that influenced ANI. This study suggests that, for accurate comparisons of nitrogen recovery efficiency between soils or treatments using the isotopic method or for comparing methods of determining N‐recovery efficiency, the role of added N interaction must be considered.
Inverse Method to Determine Soil Hydraulic Functions from Multistep Outflow Experiments
Authors: van Dam J. C. , Stricker J. N. M. , Droogers P.
Published: July 2010

Outflow experiments, in combination with inverse modeling techniques, offer a time‐efficient way to simultaneously determine retention and hydraulic conductivity functions. Using outflow data only in the objective function, and applying the optimization algorithm of Marquardt's maximum neighborhood, the multistep outflow method results in unique estimates of the retention and hydraulic conductivity functions. For the same experimental conditions the one‐step outflow method often yields nonunique solutions. For the Mualem‐van Genuchten expression of the soil hydraulic functions, four parameters (α, n, Ks and λ) were estimated for a medium‐textured soil. Fixation of λ negatively affects the estimation of K(h). The reference curve as derived by similar media scaling corresponded with curves derived by the direct averaging of soil hydraulic functions, and with those obtained by optimization of the mean outflow for a set of 20 soil samples.
Site Preparation and Fertilization Effects on Growth of Slash Pine for Two Rotations
Authors: Tiarks A. E. , Haywood J. D.
Published: July 2010

Two replicated site preparation studies were used to examine the effect of management on pine height and volume growth in the next rotation on Paleudults. Treatments included no tillage, flat disking, bedding, and fertilization. The first rotation of planted slash pine (Pinus elliottii Engelm. var. elliottii) was measured for 15 yr on one site and 20 yr at the other, harvested, and replanted without additional tillage. The second rotations were measured for 10 yr. At one site, 100 kg ha−1 P was applied to each rotation as a treatment variable. At one site, disking before the first rotation increased pine heights. Bedding before the first rotation increased pine heights at both sites. In the second rotation, the response was reversed, with pines planted on beds being the shortest. The P fertilization increased heights in both rotations but did not affect response to tillage. The P as well as N, applied only at age 7 in the second rotation, had a negative effect on the second rotation's volume, probably because of increased competition from shrubs and other understory plants. Across both sites and for all treatments, 10‐yr‐old slash pines averaged 7% less in height and 24% less in volume in the second rotation. These differences are statistically significant. Analysis at age 10 from both rotations indicates stable foliar concentrations of P and Ca, declining K, and increasing Mn and Al.
Climate change and water resources in the Lower Mekong River Basin: putting adaptation into the context
Authors: Keskinen M. , Chinvanno S. , Kummu M. , Nuorteva P. , Snidvongs A. , Varis O. , Västilä K.
Published: July 2010

Adaptation to climate change has become one of the focal points of current development discussion. This article summarises the findings from a multidisciplinary research project looking at climate change impacts and adaptation in the Mekong River Basin in Southeast Asia. The research highlights the central role that the hydrological cycle has in mediating climate change impacts on ecosystems and societies. The findings indicate that climate change should not be studied in isolation, as there are several other factors that are affecting the hydrological cycle. In the Mekong, the most important such factor is the on-going hydropower development that is likely to induce changes at least as radical as climate change, but with shorter timescales. The article concludes that climate change adaptation should broaden its view to consider environmental changes likely to occur due to different factors at various spatial and temporal scales. It is also important to recognise that climate change adaptation is a dynamic, development-orientated process that should consider also broader socio-political context. To enable this, we propose that an area-based adaptation approach should be used more actively to complement the dominant sector-based approaches.