bluuebunny/crossref_metadata_2025 huggingface dataset:
Evaluation of Nitrification Inhibitors and Urea Placement in No‐Tillage Winter Wheat
Authors: Rao Srinivas C.
Published: July 2010

Nitrification inhibitors (NIs) such as dicyandiamide (DCD) and nitrapyrin [2‐chloro‐6‐(trichloromethyl)pyridine] (NP) slow the nitrification process, thus reducing N losses from leaching and denitrification. In field studies (1990–1994) on a Renfrow silt loam (fine‐silty, mixed, thermic Udertic Paleustolls) near El Reno, OK, we evaluated these two NIs and their placement effects on nitrification of applied urea in soils and on wheat (Triticum aestivum L.) yields. Urea at 60 kg N ha−1 treated with or without NIs was placed 3 to 4 cm below the seed (BL) at seeding or was broadcast (BR) after seeding on the day of seeding, with no N as control. Mineral N forms were determined in the 0‐ to 30‐cm soil zone in fall and spring. Differences in soil mineral N concentration below the 10‐cm depth were minimal (but higher than the control) in all N treatments. In the 0‐ to 10‐cm depth, BL placement of NI‐treated urea significantly reduced nitrification in the fall compared with BR urea with or without NIs, except in 1994. Soil mineral N content in spring was similar with either placement of NI‐treated urea, but was significantly greater than untreated BR urea. Warm temperatures and dry soil in the fall tended to reduce the effectiveness of surface‐applied NIs. The highest NH4+ percentage in total soil mineral N was observed with DCD BL or NP BL, followed by NP BR and DCD BR. Urea treated with NIs increased grain yield from 7 to 31% above untreated urea. Grain yield was highest with DCD BL (31%), followed by DCD BR (26%) and NP BR (24%), compared with the broadcast untreated urea. Grain N yield was 140 g kg−1 greater with DCD‐N than with untreated urea. Deep placement of DCD under no‐till winter wheat in the southern Great Plains can reduce nitrification and increase N availability under varying year‐to‐year environmental conditions and can improve wheat grain yield and grain N compared with surface broadcast of urea with or without NI.
Alfalfa Yield and Stand Response to Irrigation Termination in an Arid Environment
Authors: Ottman Michael J. , Tickes Barry R. , Roth Robert L.
Published: July 2010

Alfalfa (Medicago sativa L.) irrigation is often withheld as a water conservation measure in arid regions. The objective of this research was to test the hypothesis that alfalfa yields and stands can be permanently damaged by withholding irrigation water in arid environments. Irrigation termination studies were conducted on a Superstition sand (sandy, mixed, hyperthermic Typic Calciorthid; 95% sand) in Yuma, AZ, and on a Casa Grande sandy loam [coarse‐loamy, mixed (calcareous), hyperthermic Typic Natrargid (reclaimed)] at Maricopa, AZ. Irrigations were terminated in the summer (July through October) and winter (November through February) in Yuma and in the summer (August through September) and summer, fall, and winter (August through mid‐March) in Maricopa. Summer irrigation termination at the Yuma site reduced stand from 43 to 16 plants m−2 and reduced hay yield from 1.50 to 0.52 Mg ha−1 per cutting after irrigation was resumed. Irrigation termination at the Maricopa site was not detrimental to stands, although hay yields per cutting were depressed from 2.90 to 2.52 Mg ha−1 following the second cycle of summer irrigation termination and from 3.10 to 2A3 Mg ha−1 following the second cycle of summer through winter irrigation termination. Winter irrigation termination at Yuma had no residual effect on yield or stand. Alfalfa water use was reduced by irrigation termination at Maricopa, even after irrigation was resumed. Total nonstructural carbohydrates in the roots were not consistently higher or lower than the control during irrigation termination. Termination of alfalfa irrigation as a water‐conserving measure is not always advisable in arid environments due to the possibility of permanent crop damage.
Tillage System and Crop Residue Effects on Surface Compaction of a Paleustoll
Authors: Dao Thanh H.
Published: July 2010

Concern of excessive compaction of soils under conservation tillage (CT) has persisted as CT practices gain acceptance in major agricultural systems. The objective of the study was to determine the cumulative effects of tillage systems [moldboard plowing (MT), stubble‐mulch tillage (ST), and no‐till (NT)] and rates of crop residues on bulk density of the near‐surface zone under annual winter wheat cropping. In the fall of 1983, tillage plots were established on Bethany (fine, mixed, thermic Pachic Paleustoll) and Renfrow (fine, mixed, thermic Udertic Paleustoll) silt loams on a 2% slope near El Reno, OK. Bulk density and water content were measured to a depth of 0.3 m in 0.025‐m increments using gamma and neutron attenuation techniques during 1991 and 1992. After planting, MT and ST soils had the lowest mean surface density; these soils consolidated as bulk density during winter wheat dormancy averaged 1.34 (±0.06), 1.30 (±0.06), 1.21 (±0.06) in 1991, and 1.31 (±0.06), 1.30 (±0.05) and 1.24 (±0.05) Mg m−3 in 1992 in MT, ST, and NT soils, respectively. Near the end of the season, surface density of ST and MT soils had increased by 1.6 and 4.8%, respectively. No‐till soil showed a decrease of 5.4% during the same overwinter period and had the lowest bulk density in the end. The inherent reduction in field operation traffic in CT systems, and a decrease in tillage intensity proportionately reduced soil surface compaction under annual wheat cropping. Bulk density increased with soil depth in all treatments; however, NT resulted in decreased soil density in and below an old restrictive layer more effectively than ST or MT management. Removal of crop residues resulted in higher bulk density, primarily in the 0.05‐ to 0.125‐m depth of MT soils, and in the 0 to 0.05‐m surface layer of NT soils. Maintaining high amounts of wheat residues at the soil surface helps improve the macroporosity of near‐surface zones of soils under conservation tillage. Severe compaction of CT soils did not appear prevalent under winter wheat production to cause physical constraints to crop growth in subhumid regions.
Management Influences on Arbuscular Mycorrhizal Fungal Species Composition in a Corn‐Soybean Rotation
Authors: Kurle James E. , Pfleger Francis L.
Published: July 2010

Crop and edaphic factors influence arbuscular mycorrhizal (AM) fungal species composition and populations. This study was conducted to determine the effect of management history, crop, and input system on species composition of AM fungal spore populations. Corn (Zea mays L.)‐soybean [Glycine max (L.) Merr.] sequences receiving no inputs (NI), organic inputs (OI), minimum inputs (MI), and conventional inputs (CI) were established in two adjacent areas with differing management histories: one area, the Koch Farm, had received no fertilizer or herbicide inputs for the past 25 yr; the other area, the experiment station, received recommended herbicide and fertilizer inputs. Fifteen AM fungal species were found in a survey of mycorrhizal fungal spore populations. Glomus aggregatum populations were positively correlated with Setaria spp. populations (r = 0.56), pH (r = 0.47), and K (r = 0.25) and negatively correlated with soil P (r = −0.57). Populations of Gl. geosporum, Gl. leptotichum, Gl. macrocarpum, and Gl. occultum were also positively correlated with soil pH and negatively correlated with soil P. Gigaspora margarita spore populations were positively correlated with soil P level (r = 0.272). Although species richness was greater (13 species vs. 10), species diversity (Hw) was lower at the Koch Farm than the experiment station (0.57 vs. 0.64) because of large Gl. aggregatum spore populations. The correlation of AM fungal spore populations with Setaria spp. and P, K, and pH indicates that management practices influence AM fungal species composition through both biotic and abiotic factors.
Soil Temperature and Planting Date Effects on Corn Yield, Leaf Area, and Plant Development
Authors: Bollero Germán A. , Bullock Donald G. , Hollinger Steven E.
Published: July 2010

Early‐season soil temperature has been reported to affect leaf appearance and expansion rates, and consequently corn (Zea mays L.) ontogeny. A 2‐yr field experiment was conducted on a Drummer silty clay loam (fine silty, mixed, mesic Typic Haplaquoll) at the Agronomy and Plant Pathology South Farm of the University of Illinois at Urbana‐Champaign. Treatments consisted of planting date (early May and early June) and soil temperature surrounding the corn growing point (5°C below ambient, ambient, and 5°C above ambient). Soil temperature was controlled using warm and cool water circulating through copper pipes buried next to the corn rows. Air temperatures were not controlled. Irrigation was used. The experimental design was a split plot in a randomized complete block with four replications. Ten plants were randomly selected within each replication and nondestructive measures of plant stage, individual leaf area, and leaf senescence were taken three times per week from emergence to V5, and once per week afterwards until complete leaf senescence. Growing degree days (GDD) were calculated using the modified growing degree day formula (MGDD). From planting to V5, MGDD were computed using the soil maximum and minimum daily temperatures from each treatment. After the soil temperature treatments were terminated, the MGDD calculations were based on maximum and minimum daily air temperatures. Lower early‐season soil temperature delayed corn development and modified individual leaf area. Plants under these cooler conditions went through vegetative developmental stages faster per unit of accumulated MGDD, showing the effect of temperature on corn ontogeny. The results also show that the current method of calculating MGDD (with base temperature of 10°C) does not adequately predict corn development under exceptionally warm or exceptionally cool soils. Warmer early‐season soil temperature linearly increased corn yield (β1 = 0.14 Mg ha−1 °C−1). Leaves in the lower half of the canopy were larger under cooler soil temperature treatments (β1 = −48.9 cm2 °C−1). There was a linear increase in the size of the leaves in the upper half of the canopy of the plants under warmer temperatures (β1 = 28.8 cm2 °C−1).
Simulating Effects of Genes for Physiological Traits in a Process‐Oriented Crop Model
Authors: White Jeffrey W. , Hoogenboom Gerrit
Published: July 2010

Recent improvements in crop simulation techniques and in understanding of crop genetics suggest the possibility of integrating genetic information on physiological traits into crop simulation models. By using known genotypes, rather than empirically fitted cultivar‐specific coefficients, a simulation model should permit more explicit testing of hypotheses concerning the genetic basis of adaptation of cultivars to different environments or production systems. This paper describes and evaluates GeneGro, a version of the dry bean (Phaseolus vulgaris L.) crop simulation model BEANGRO version 1.01 modified to incorporate effects of seven genes affecting phenology, growth habit, and seed size: Ppd, Hr, Fin, Fd, and Ssz‐l, and two more genes for seed size inferred from indirect evidence. Thirty cultivars were calibrated for BEANGRO using data from 14 trials conducted in Colombia, Guatemala, Mexico, and Florida. The resulting cultivar‐specific coefficients of BEANGRO were replaced with information on specific genotypes of cultivars to create the gene‐based model. With cultivar differences specified only by the seven genes, GeneGroe xplained 31% of observed variation for seed yield, 58% for seed weight, 84% for days to flowering, 85% for days to maturity, 52% for maximum leaf area index, and 36% for canopy dry weight at maturity, but 0% for harvest index. In testing the effectiveness of GeneGro after overall trial and cultivar effects were accounted for through regression analysis, all simulated data except for seed weight showed significant relations with observed data (P ≤ 0.01). Our results indicate that for certain traits surprisingly few genes must be characterized to simulate cultivar differences as accurately as with the BEANGRO model. Furthermore, they suggest a potential for developing models similar to GeneGro for studying the effects of genes on adaptation in other crops.
Winter Legume Cover Crop Benefits to Corn: Rotation vs. Fixed‐Nitrogen Effects
Authors: Torbert H. Allen , Reeves Donald W. , Mulvaney Richard L.
Published: July 2010

The use of winter legume cover crops for erosion control and to provide additional N to the soil is well established. Other potential benefits to legume cover crops besides N additions have been recognized, but have not been quantified. The objective of this study was to separate the fixed‐N effects from the rotation effects in a winter legume cover cropping system. A field study was initiated in 1989 on a Norfolk loamy sand (fine, loamy, siliceous, thermic Typic Kandiudult) in east‐central Alabama. Corn (Zea mays L.) was grown following (i) ‘Tibbee’ crimson clover (Trifolium incarnatum L.), (ii) a partially ineffective‐nodulating crimson clover, CH‐1, (iii) rye (Secale cereale L.), and (iv) winter fallow. The plots were split into four rates of fertilizer N (0, 56, 112, and 168 kg N ha−1) in a split‐plot experimental plan. An evaluation of different methods of distinguishing fixed‐N vs. rotation effects of the winter annual legume cover crop to a subsequent corn crop was made. Regression analysis of the effect of N application rates on N2 fixation by crimson clover (fertilized with 45 kg N ha−1) indicated that CH‐1 clover biomass contained approximately 40 and 101 kg N ha−1 and Tibbee clover contained approximately 51 and 119 kg N ha−1 in 1990 and 1991, respectively. In both years of the study, crimson clover substantially increased corn yield compared with winter fallow, with a yield increase at the highest fertilizer N application level of 7 and 22% for 1990 and 1991, respectively. Estimates of yield increases due to rotation ranged from negative to 40%. The data indicated that winter cover crops improve corn yield and that besides soil N availability, there was very little difference between the beneficial effects of clover and the rye cover crops to corn.
Comparisons between an Upland and a Pima Cotton Cultivar: I. Growth and Yield
Authors: Unruh Bryan L. , Silvertooth Jeffrey C.
Published: July 2010

American Pima cotton (Gossypium barbadense L.) is an extra‐long staple cotton produced in the southwestern USA and in other regions around the world. Pima cotton generally yields less than Upland (G. hirsutum L.), but there have not been any studies conducted to document the basis for these differences. Field trials were conducted at two south‐central Arizona locations from 1990 through 1992 for the purpose of comparing growth and yield between representative cultivars of Upland and Pima cotton. The aboveground portion of Upland ‘Deltapine 90’ (DPL 90) and Pima ‘S‐6’ were harvested and separated into stems, leaves (including petioles), burs (carpel walls), lint, and seeds. The bur fraction also included immature fruiting forms. Dry matter accumulation was modeled as a function of heat units (HU) accumulated after planting (HUAP). Both cultivars exhibited a linear increase of total dry matter over the duration of sampling. By the end of sampling, DPL 90 produced more total, stem, seed, lint, and reproductive (bur + seed + lint) dry matter than Pima S‐6; the dry matter that accumulated in leaves, bur fraction, and vegetative structures (leaf + stem) did not differ. The reproductive/vegetative ratio (RVR) was found to be similar for both cultivars, increasing rapidly with HU accumulation. Comparisons of lint dry matter accumulation as a function of RVR and harvest index (HI) revealed that DPL 90 yields more lint than Pima S‐6 due to a greater total biomass production and more efficient partitioning of dry matter into reproductive organs.
Crop Modeling: From Infancy to Maturity
Authors: Sinclair Thomas R. , Seligman No'am G.
Published: July 2010

Crop modeling, the computerized simulation of dynamic crop systems, was born about 30 years ago, when systems analysis and modern computers presented a new technique to crop scientists. Since then, crop modeling has gone through a number of developmental stages, similar to those of living organisms. From its infancy, crop modeling seemed to promise a well‐behaved, elegant surrogate for ambiguous and cumbersome field experimentation. Indeed, some of the earliest models proved to be among the most notable achievements to date. During the juvenile stage that followed, there was an impressive increase in complexity and computer sophistication, accompanied by some of the growing pains of childhood. Greater expectations led to more and more detailed descriptions of the functioning of the biotic and abiotic components of cropping systems. The results were often trivial, and the big payoff tended to recede into the future, but the need for predicting future crop performance for management and hypothesis testing, together with progress in crop science and computer technology, spurred crop modeling. The next phase, adolescence, a period marked by intense activity, confusion, and excessive confidence‐sometimes challenged by doubt‐appears to be extending into the present. Not only is the original promise turning out to be elusive, but widely accepted guidelines for scientific modeling, such as greater reductionism, universality, and validation, are being questioned. Maturity may be emerging as expectations become pragmatically adjusted to reality. Crop modeling, like advanced ecological modeling, is proving to be more a heuristic tool than a surrogate for reality. In academic, research, and applied roles, such models can be of great value when used as aids to reasoning about the functioning and response of crop systems under many relevant, nontrivial scenarios.
Analysis of Aerial Photography for Nitrogen Stress within Corn Fields
Authors: Blackmer Tracy M. , Schepers James S. , Varvel Gary E. , Meyer George E.
Published: July 2010

Spatial variability of soil parameters within fields complicates N fertilizer recommendations for corn (Zea mays L.) production. Thus, the ability to identify differences in crop N status within corn fields could lead to efficiencies in N fertilizer application and decreased ground water pollution. In this study, we digitized aerial color photographic transparencies using an eight‐bit scheme to generate digital counts for the red, green, and blue primary colors in the photographs at the R5 growth stage and related them to grain yield. Digital count responses were relative to the N treatment in which grain yield plateaued. Experiments were conducted in 1992 and 1993 for four irrigated corn hybrids with five N rates on a 6‐ha field near Shelton, NE. Red and green digital counts relative to those for the high N treatment provided better prediction of yield response than relative blue counts in both years. In 1993, black‐and‐white photographs taken with a filter centered around 536 nm also predicted yield response to N well (r2 = 0.93). These findings permit the use of low cost aerial photographs to characterize variability in crop N status throughout entire fields.
Canopy Architecture and Morphology of Switchgrass Populations Differing in Forage Yield
Authors: Redfearn Daren D. , Moore Kenneth J. , Vogel Kenneth P. , Waller Steven S. , Mitchell Robert B.
Published: July 2010

Phenotypic selection has been used to improve forage yield and in vitro dry matter disappearance (IVDMD), but the effects on canopy architecture and morphology are not understood. Our objectives were to determine if canopy architecture and morphology can explain genotype × environment (G ✕ E) yield differences in switchgrass (Panicum virgatum L.) and to evaluate canopy architecture and morphology as selection criteria for increasing yield. This study was conducted in 1993 near Mead, NE, and near Ames, IA. The experimental design was a randomized complete block experiment with a split‐plot arrangement of four replicates at each location. Whole plots were tiller population and subplots were sward maturity. Tiller populations were harvested on 9 June, 19 July, and 27 August at Ames and on 10 June, 27 July, and 26 August at Mead and were classified morphologically. Tillers were separated into primary yield components and dried at 55°C to determine total forage yield and dry matter contribution of morphological components. Genotype × environment interactions occurred for total forage yield and tiller density. Previous phenotypic selection for increased forage yield and IVDMD apparently altered morphological changes within the canopy of selected switchgrass populations. The most apparent changes were development of additional collared leaves and internodes in some populations across locations. Although canopy architecture may not be a useful selection criterion because of variability associated with individual canopy traits, indirect measurements showed that leaf area index (LAI) has some potential as a selection criterion for increasing total forage yield. However, selection for individual canopy traits may be most effective for modifying sward growth habits.
Using a Chlorophyll Meter to Estimate Specific Leaf Nitrogen of Tropical Maize during Vegetative Growth
Authors: Chapman Scott C. , Barreto Hector J.
Published: July 2010

Chlorophyll meters are used as a quick, inexpensive method of estimating leaf N concentration in both experiments and production fields. Direct use of the meter readings is complicated by effects of crop age and cultivar on leaf N concentration, at least partly due to variation in leaf thickness. Research in rice (Oryza sativa L.) shows that readings can be adjusted to account for these effects, and this study sought to establish whether similar relationships exist for tropical maize (Zea mays L.). Additionally, we examined several aspects of sampling methodology. In several field trials in Mexico in 1994 and at different stages of growth (6, 8, 14 leaves expanded) and for plots with different N treatments (0 N, 21 cultivars; 150 kg N h−1, 7 cultivars), meter readings were taken from five leaves per plot, with five readings near the middle of the leaf blade. Leaf N concentration (g N kg−1 dry matter) was significantly linearly correlated with the meter readings (y = 1.46x − 30.68, r2 = 0.81), but the coefficients of fit differed greatly across data sets and growth stages. Adjusting the meter readings by dividing by specific leaf weight (SLW, g leaf m−2 leaf) resulted in an improved fit within and across data sets (y = 33.47x − 6.55, r2 = 0.97). The meter readings were also directly correlated with specific leaf N (SLN, g N m−2 leaf) (y = 0.387x − 0.476, r2 = 0.92) with no adjustments. Analysis of sampling patterns determined that at least four leaves per plot are needed, with several observations per leaf, and that readings should be taken at a point lying between about 40 and 70% along the leaf length from the leaf base. For scientists and farmers with limited direct access to laboratory analysis for N, the meter provides a cheap and convenient estimate of leaf N per unit leaf area during vegetative growth.
Phasic Development of Rice Seedlings
Authors: Salam Moin U. , Jones James W. , Jones John G. W.
Published: July 2010

A better understanding of growth and developmental processes of rice (Oryza sativa L.) seedlings is necessary for crop management and modeling perspectives. This experiment was conducted to identify preautotrophic phases of rice seedlings, quantify seed dry matter mobilization and utilization, characterize dry matter partitioning during early growth, and observe if these processes are affected by cultivar and seed size. Seeds of two cultivars, each separated into two seed sizes, were sown in a greenhouse using field soil, and observations on seed weight loss and seedling weight gain were recorded daily for 27 d. The durations of heterotrophic and transition phases were determined as 74 and 247 thermal units (base temperature 9°C), respectively. Seeds lost 0.79 ± 0.010 g g−1 during the preautotrophic phases, while 0.42 ± 0.023 g g−1 seed weight accumulated in the seedling. Partitioning of dry matter was equal between root and shoot up to 37 thermal units, then allocation to root reduced curvilinearly until a constant root‐to‐shoot ratio (15:85) was reached at 148 thermal units and maintained thereafter. Shoot dry matter partitioning between culm and leaf was almost equal throughout the experiment except for the initial 37 thermal units when all dry matter accumulated in the culm. Early developmental processes in rice seedlings were independent of cultivar and seed size in this study. Although seed dry matter loss in proportion to the initial seed dry matter was significantly higher for larger seeds, the utilization pattern remained unaffected by seed size. This indicates that larger seeds were less efficient than smaller seeds in the utilization of reserves.
Bowen‐Ratio Comparisons with Lysimeter Evapotranspiration
Authors: Prueger John H. , Hatfield Jerry L. , Aase J. Kristian , Pikul Joseph L.
Published: July 2010

Water use in agriculture by different cropping systems is of interest in determining crop water use efficiency of different tillage practices that will lead to reduced crop production risk. Lysimeters are considered the standard for evapotranspiration (ET) measurements; however, these units are often not replicated and are few in number at any given location. Our objective was to determine if a simple Bowenratio system with nonexchanging psychrometers could provide accurate measurements of ET from lentil (Lens culinaris Medikus) in a semiarid climate. The study was conducted in 1993 and 1994 on two adjacent 180‐ by 180‐m fields with weighing lysimeters (1.68 by 1.68 by 1.83 m) located in the center of each field, on a Williams loam (fine‐loamy, mixed Typic Argiboroll) soil near Sidney, MT. A Bowen‐ratio system comprised of two nonexchanging psychrometers and anemometers at 0.25 and 1.25 m above the plant canopy surface was placed in the lentil field along with a net radiometer and soil heat flux plate. Precipitation during the growing season from planting to swathing was 367 mm in 1993 and 227 mm in 1994. In 1993, soil water content of the lysimeter was greater than the field after large precipitation events around Day of Year (DOY) 210, even though the lysimeter was drained. After this time, the lysimeter ET exceeded that measured by the Bowen‐ratio system. Agreement was closer in 1994, when precipitation was near normal and there was no excess soil water in the lysimeter. Cumulative ET totals from the lysimeter were reflective of the seasonal precipitation patterns. Differences between the lysimeter and Bowen‐ratio occurred when there was excess precipitation and inadequate drainage from the lysimeter. Halfhourly ET fluxes from lysimeter and Bowen‐ratio values agreed to within 10% throughout the season. Bowen‐ratio systems with nonexchanging psychrometers can provide satisfactory estimates of daily and seasonal ET and can be used to estimate ET in semiarid climates.
Field Testing a Rapid Method for Estimating Alfalfa Quality
Authors: Sulc R. Mark , Albrecht Kenneth A. , Cherney Jerome H. , Hall Marvin H. , Mueller Shannon C. , Orloff Steve B.
Published: July 2010

Predictive equations for alfalfa quality (PEAQ) based on height of the tallest stem and maturity stage of the most mature stem in a sample were developed to estimate neutral‐detergent fiber (NDF) and acid‐detergent fiber (ADF) concentrations in alfalfa (Medicago sativa L.). Field testing of these equations is limited outside the state of Wisconsin where they were developed. Our objectives were to test these equations for estimating alfalfa NDF and ADF across a wide geographic area and to evaluate the performance of PEAQ on a whole‐field basis by using within‐field subsampling. Alfalfa samples varying in height and maturity were collected throughout the growing season from fields in New York (n = 28), Pennsylvania (n = 23), Ohio (n = 48), California (n = 45), and Wisconsin (n = 48) in 1994 to 1996. Additional samples were collected in Ohio and Wisconsin from producer‐managed fields in which 5 to 10 subsamples per field were taken on each sampling date (n = 296 subsamples from 51 fields). Observed NDF and ADF values were regressed on estimated values. The accuracy of PEAQ in other states was at least equal to that observed in Wisconsin. Across all states, regression equations for NDF and ADF were slightly biased (b ≠ 1.0 and/or y‐intercept ≠ 0 at P < 0.01); however, prediction errors were sufficiently low to allow use of PEAQ as a preharvest management tool. Root mean square error values ranged from 19.1 to 23.9 g kg−1 for NDF and 15.0 to 19.0 g kg−1 for ADF. Prediction errors were 16.2 g kg−1 for NDF and 13.2 g kg−1 for ADF across Ohio and Wisconsin when regressing observed means on estimated means of five subsamples per fieldsampling date combination. We conclude that predictive equations for alfalfa quality based on a combination of stem height and maturity were robust across a wide range of environments.
Upper Threshholds of Nitrogen Uptake Rates and Associated Nitrogen Fertilizer Efficiencies in Irrigated Rice
Authors: Peng Shaobing , Cassman Kenneth G.
Published: July 2010

Measurements of the N uptake rate of rice (Oryza sativa L.) have usually been conducted over a period of 7 to 14 d. Such a sampling interval may not accurately determine the maximum rate, since information concerning N uptake dynamics during the first week after N topdressing is limited. In this study, N uptake dynamics and fertilizer N recovery efficiency following N topdressing were determined with more frequent samplings. Field experiments were conducted at International Rice Research Institute (IRRI) and at the Philippine Rice Research Institute (PRRI) during the 1995 dry season. Treatments consisted of 0, 50, and 100 kg N ha−1 applied at midtillering (MT) or panicle initiation (PI). Tissue N concentration and N uptake were measured 0, 2, 4, 6, 9, and 14 d after N application. Fertilizer N recovery efficiency was estimated using the difference method. At PI, maximum N uptake rates of 9 to 12 kg ha−1 d−1 were measured over the 4‐d period following application of 100 kg N ha−1, which is up to double the previously reported maximum value of 6 kg ha−1 d−1. The much larger estimates of maximum N uptake rates in our study probably resulted from more frequent sampling than in previous studies. Nitrogen uptake rates at PI were similar, regardless of N rate at MT. Recovery efficiency of N applied at PI reached 74 to 78%, and was significantly higher than that at MT. Recovery efficiency was relatively insensitive to the amount of N applied at MT and PI, which suggests that high N fertilizer efficiency can be achieved with large rates of applied N when growth conditions are favorable.
Sand and Organic Amendment Influences on Soil Physical Properties Related to Turf Establishment
Authors: McCoy Edward L.
Published: July 2010

Topsoil blending is a common practice in many metropolitan areas, yet few scientific guidelines are available for design of general‐use, lawn‐area soils. The objective of this study was to provide blending guidelines with focus on establishing a vigorous turfgrass ground cover. A Mahoning silt loam (fine, illitic, mesic Aerie Epiaqualf) and a Tioga loam (coarse‐loamy, mixed, mesic Dystric Fluventic Eutrochrept) were each blended with a spent foundry sand and a peat humus to form 28 individual soil mixes for each native soil. Soil properties and perennial ryegrass (Lolium perenne L.) growth were measured for each soil mix. Cation exchange capacity (CEC), bulk density, and plant available water exhibited changes due to soil mix that largely resulted from differences in mix organic matter (OM) content. Compression index, bubbling pressure (Hb), air‐filled porosity, and saturated hydraulic conductivity (Ksat) responded to both sand and OM contents of the soil mixes. The pore distribution parameter, λ, exhibited a response to sand and OM contents, but only at high levels of either component. Principal component analysis (PCA) of soil properties revealed that the first two principal components contained 85 to 88% of the total data variation with correlations between compression index, Hb, air‐filled porosity, Ksat, and λ contained in the first component and correlation between CEC, bulk density, and available water contained in the second component. Regression of turf clipping yield vs. PCA factor scores and regression of factor scores vs. total sand and OM contents suggested that a high‐quality, general‐use soil for lawn establishment would contain about 65% sand and have an OM content of 8% by weight. The multivariate process of relating turf yield to soil physical properties, as applied in this study, should provide more generalized mix formulation guidelines than do recommendations based on relating turf yield to mix composition.
SALTDATA: A Database of Plant Yield Response to Salinity
Authors: Ulery April L. , Teed Jennifer A. , van Genuchten Martinus Th. , Shannon Michael C.
Published: July 2010

Crop salt‐tolerance data are crucial for the effective management of salt‐affected agronomic systems in arid and semiarid regions. Numerous field and laboratory experiments have been conducted over the years to obtain these data, leading to generalized salt‐tolerance lists used by growers and researchers. Plant response to salinity is affected by several factors, including crop variety, soil texture, climate, and irrigation or other cultural practices. Consideration of these factors in growth‐response models would permit a more realistic and site‐specific prediction of crop yield as a function of soil salinity. A computerized salt‐tolerance database management program, SALTDATA, was developed to store experimental data relating observed crop yields to average rootzone salinity and other parameters affecting plant growth. The information was selectively retrieved from a large collection of published references on salt tolerance. The data were stored in their original reported units, but conversion equations were included to allow comparison of salinity and yield data of different experiments reported in different units. Thus, a comprehensive data set can be built for retrieval, export, and subsequent analysis by various crop salt‐tolerance models.
Winter Wheat Seedling Emergence from Deep Sowing Depths
Authors: Schillinger William F. , Donaldson Edwin , Allan Robert E. , Jones Stephen S.
Published: July 2010

Growers in low‐precipitation (<300 mm annual) dryland wheat‐fallow areas of the inland Pacific Northwest need winter wheat (Triticum aestivum L.) cultivars that emerge from deep sowing depths in dry soils. Stand establishment is the most important factor affecting winter wheat grain yield in this region. Despite poor resistance to disease, modest grain yield potential, and other problems, the outdated soft white winter wheat (SWWW) cultivar Moro is widely sown in these dry areas, due to its excellent emergence ability. All other SWWW cultivars are semidwarfs that carry emergence‐impeding Rht1 or Rht2 reduced‐height genes. From 12 sowing trials at 2 locations over 4 yr, we compared the emergence capability of Moro to (i) 8 SWWW cultivars and (ii) 16 SWWW advanced experimental Mororeplacement lines. Under both wet and dry soil conditions (soil water content in the seed zone ranged from 11 to 19 mm3 mm−3), seeds were sown deep, with 110 to 160 mm of soil cover. Moro always emerged fastest and achieved the best final stand compared with the semidwarf cultivars. The advanced experimental lines, which contained either no reduced‐height gene or a Rht1, Rht2, or Rht8 reduced‐height gene, had superior straw strength, disease resistance, and grain quality compared with Moro. The best‐emerging advanced experimental lines had coleoptile lengths >100 mm. Coleoptile length was associated with emergence capability among both cultivars (r2 = 0.71, P < 0.004) and advanced lines (r2 = 0.62, P < 0.001). From deep sowing depths in this study: (i) cultivars and advanced lines with Rht1 and Rht2 reduced‐height genes always emerged poorly compared with Moro; (ii) the Rht8 reduced‐height gene did not hamper emergence to the extent that Rht1 and Rht2 did; and (iii) several advanced experimental lines with long coleoptiles equaled or exceeded Moro for emergence.
Harvest Management of Switchgrass for Biomass Feedstock and Forage Production
Authors: Sanderson Matt A. , Read James C. , Reed Roderick L.
Published: July 2010

Switchgrass (Panicum virgatum L.), a warm‐season perennial grass native to North America, has potential as a biomass energy crop. Our objective was to develop harvest management recommendations for biomass feedstock and forage production. ‘Alamo’ switchgrass was established in 1992 at Stephenville and Dallas, TX. Four harvest frequencies (one to four cuts per year) and three final autumn harvests (Sept., Oct., or Nov.) were imposed from 1993 to 1996. Tiller densities were counted each spring. Neutral detergent fiber (NDF) and crude protein (CP) concentrations were measured in 1993 and 1994. Concentrations of NDF were lowest (avg. = 640 g kg−1) and of CP (avg. = 110 g kg−1) were highest in May‐harvested biomass. Forage quality of regrowth decreased with age, reaching NDF concentrations of 790 g kg−1 and CP of <20 g kg−1. Total seasonal yields decreased as harvest frequency increased; however, a severe drought reversed this trend at Dallas in 1996. The highest yields (15–20 Mg ha−1) occurred with a single harvest in mid‐September. Delaying the final harvest until November reduced yields. Harvest date and frequency did not affect tiller density, although tiller density decreased from 900 to 650 and 630 to 310 m−2 at Dallas and Stephenville, respectively, during 1994 to 1997. Thus, a single mid‐September harvest should maximize biomass yields in the south‐central USA. A two‐cut (spring‐autumn) system may allow a farmer to use initial growth as forage and the regrowth for biomass, but total yields would be reduced. More frequent harvests would reduce yields further.
Models of Yield, Grain Protein, and Residual Mineral Nitrogen Responses to Applied Nitrogen for Winter Wheat
Authors: Makowski David , Wallach Daniel , Meynard Jean‐Marc
Published: July 2010

The proper use of N fertilizer is fundamental for farm profitability and environmental protection. In France, fertilizer recommendations are generally based on the balance‐sheet method, which is not sensitive to the economic or regulatory context. A way to generalize the balance‐sheet method is to use models that describe crop response to applied N. The goal of this paper is to propose, in the case of winter wheat (Triticum aestivum L.), functional forms for the response of yield, grain protein content, and residual mineral N left in the soil at harvest to applied N. The originality of our models is that all three responses (yield, protein, and residual mineral N) are modeled, using N uptake as an intermediate variable. Furthermore, these models have two clear links with the balance‐sheet method. First, the parameters of the balance‐sheet method appear explicitly in the models. Second, the N dose recommended by the balance‐sheet method appears in our models as the smallest N dose that maximizes yield. Within this general modeling framework, three variants of the yield model, three variants of the grain protein content model, and two variants of the residual mineral N model are considered. The different models are adjusted, site‐year by site‐year, to 28 site‐years of data. All models give satisfactory fits to the data. For example, the root mean square error varies between 0.21 and 0.23 Mg ha−1 for the yield models. Almost all the adjusted parameter values vary widely from site‐year to site‐year. This must be taken into account when calculating optimal N doses for new site‐years.
Decomposition of Surface Crop Residues in Long‐Term Studies of Dryland Agroecosystems
Authors: Ma Liwang , Ahuja Lajpat R. , Shaffer Marvin J. , Rojas Kenneth W. , Peterson Gary A. , Sherrod Lucretia
Published: July 2010

Decomposition of surface crop residues is important for agricultural management, especially under conservation tillage. The objective of this study was to test several models for describing crop residue decomposition under three eastern Colorado dryland agroecosystems at Sterling, Stratton, and Walsh with a yearly mean air temperature of 9.7, 10.4, and 12.0°C, respectively. At each site, a soil toposequence common to its geographic region was chosen to include a summit, a sideslope, and a toeslope position, and several crop rotations were practiced under no‐till conditions. Grab samples were taken at planting and before harvesting for surface residue measurement since 1985. Simulation results showed that the Douglas‐Rickman model described surface crop residue decomposition better than the Gregory model during a 13‐year period, based on a normalized objective function (NOF). Our fitted decomposition rate coefficients using the Douglas‐Rickman model matched those originally published. The Douglas‐Rickman model, which uses a first‐order decay with respect to degree‐days, was further evaluated against two other first‐order decay models: one using a first‐order decay equation with respect to decomposition‐days and the other assuming a first‐order decay with respect to time (d). Although the three approaches performed equally well in terms of NOF values (P = 0.354), fitted decomposition rate coefficients were significantly different (P < 0.012) among the three experiment sites when models based on decomposition‐days or on time (in days) were used. Therefore, the Douglas‐Rickman model may be more applicable for describing long‐term crop residue decomposition because of its consistency in model parameters among experimental sites and simplicity in modeling approach.
LEACHN Simulations of Nitrogen Dynamics and Water Drainage in an Ultisol
Authors: Johnson Alan D. , Cabrera Miguel L. , McCracken Daniel V. , Radcliffe David E.
Published: July 2010

Nitrate leached from soils can contaminate drinking water and pose a health risk at concentrations > 10 mg N L−1. Computer models may be useful management tools for estimating NO3leaching, but they need to be calibrated and validated before use. The objective of this work was to calibrate and validate LEACHN to simulate soil NO3, soil NH4, water drainage, and NO3leaching in a Cecil sandy loam (fine, kaolinitic, thermic Typic Kanhapludults). The calibration was done by determining rate constants and parameters under laboratory conditions. The validation data was obtained from a two‐year study with conventionally tilled corn (Zea maysL.) during summer and either a rye (Secale cerealeL.) cover crop or fallow conditions during winter. Water drainage collected by tiles was automatically measured, subsampled, and analyzed for inorganic N concentrations. During the cold season, LEACHN underestimated soil NH4and NO3in at least half of the cases. During the warm season, the model correctly estimated soil NO375% of the time, but it overestimated soil NH4in an equal 75% of the cases. Also, LEACHN overestimated cumulative drainage and leached NO3at least 50% of the time during both cold‐ and warm‐season periods. These results suggest that the soil hydraulic properties and N mineralization rate constants determined under laboratory conditions did not apply to field conditions. Also, results obtained by changing rate constants for N transformations indicate that LEACHN was not properly simulating N immobilization from fertilizer N, or nitrification under dry conditions.
Plant‐Available Nitrogen Supply as Affected by Method and Timing of Alfalfa Termination
Authors: Mohr Ramona M. , Entz Martin H. , Janzen H. Henry , Bullied William J.
Published: July 2010

Herbicide application may provide an alternative to intensive tillage for the termination of alfalfa stands, but might alter N release and N availability to subsequent crops. Our objective was to determine, under field conditions, the effect of timing and method of termination on the pattern of N release from perennial alfalfa, and on N uptake and yield of subsequent wheat crops. Four field experiments were initiated on perennial alfalfa (Medicago sativaL.) in southern Manitoba in 1992 and 1993. A factorial of three methods (herbicide, tillage, herbicide + tillage) and two times of termination (early summer, after first alfalfa cut, and late summer, after second alfalfa cut) was arranged in a randomized complete block design. A spring‐applied herbicide treatment was also included. Spring wheat (Triticum aestivumL.) was established after alfalfa termination. Soil NO−3content, plant N uptake, and yield were then monitored for one to two years. In three of four experiments, plant‐available N in the spring after termination was higher in tilled treatments than in treatments receiving only herbicides. Regardless of method, plant‐available N in the spring after termination was reduced when termination was delayed from early to late season. Despite the lower short‐term plant‐available N supply in early‐ and late‐summer herbicide treatments, wheat yields in herbicide treatments were similar to or greater than those in tillage treatments. Differences in the N content among treatments diminished with time; by the fall of the second growing season after termination, differences in the cumulative available N supply were no longer evident. These results suggest that termination of alfalfa with herbicides may improve the synchrony between N release and N demand of a subsequent spring wheat crop, thereby improving N use efficiency.
Yield and Nitrogen Content of Corn under Different Tillage Practices
Authors: Mehdi B. B. , Madramootoo C. A. , Mehuys Guy R.
Published: July 2010

The objective of the study was to determine whether tillage and residue practices have a significant effect on the yield and N content of corn (Zea mays L.) under nonlimiting soil N conditions. Nitrate leaching has been identified as a source of non‐point‐source pollution. By identifying tillage practices which maximize corn N uptake, recommendations can be based on how to minimize N loss. A 2‐year field study was conducted in southwestern Quebec on a 2.4‐ha site of a Typic Endoaquent (Humic Gleysol) cropped to corn. Three types of tillage practice (conventional tillage, reduced tillage, and no‐till) were combined with two residue levels (with and without) in a randomized complete block design. The effect of these practices on corn yield and corn N were studied. Seedling emergence rates in spring, and corn moisture content at harvest, were also monitored. Residues hindered initial plant emergence in the no‐till plots. Corn N and moisture contents in 1996 and 1997 indicated that no‐till with residue had a delayed maturity relative to the other treatments. However, total corn biomass and grain yields were not affected by tillage or residue treatments. No correlation between corn yield and corn N content was found.