bluuebunny/crossref_metadata_2025 huggingface dataset:
Measured and Simulated Surface Soil Drying
Authors: Durar Abdu A. , Steiner Jean L. , Evett Steven R. , Skidmore Edward L.
Published: July 2010

The USDA initiated the Wind Erosion Prediction System (WEPS) to develop improved technology for predicting wind erosion. A HYDROLOGY submodel has been developed for WEPS to simulate the soil energy and water balances. This study was conducted to evaluate the performance of the HYDROLOGY submodel in predicting surface soil drying. Water content was measured gravimetrically in a bare 5‐ by 30‐m plot for 14 d after irrigation during July and August 1991. The plot was located 5 m directly north of a bare weighing lysimeter at the USDA‐ARS Conservation and Production Research Laboratory at Bushland, TX. Hourly samples were taken from depth increments of 0 to 2, 2 to 6, 6 to 10, 10 to 30, and 30 to 50 mm. Furthermore, soil cores were taken to 900 mm at 6‐h intervals. Water content was also measured daily at the lysimeter and between the lysimeter and gravimetric sampling plot using a neutron probe to 2.1 m. The submodel accurately predicted that no deep percolation occurred throughout the simulation period. Simulation results agreed well with the measured daily evaporation rates from the lysimeter (r2 = 0.96). Furthermore, the submodel reasonably estimated the soil water content profiles, particularly the status of soil water at the soil‐atmosphere interface. The mean absolute error, which describes the average absolute deviation between measured and simulated soil water contents, was 0.015 m3 m−3. The HYDROLOGY submodel of WEPS shows a potential to accurately simulate soil water dynamics, as needed for wind erosion modeling. The submodel successfully predicts the changes in water content at the soil surface, which relate to the susceptibility of the soil to wind erosion.
Nitrogen and Phosphorus Uptake in Pearl Millet and Its Relation to Nutrient and Transpiration Efficiency
Authors: Payne William A. , Hossner Lloyd R. , Onken Arthur B. , Wendt Charles W.
Published: July 2010

Depending on soil and rainfall characteristics, pearl millet [Pennisetum glaucum (L.) R. Br.] production in the Sahel can be limited by inefficient use of nutrients, especially N and P, or by inefficient use of water. This study measured pearl millet N and P uptake and compared the efficiency with which N, P, and water are used for growth under varied soil P and water availability. Millet was grown outdoors in semiarid West Texas using rain‐sheltered pots of low pH, P‐deficient sandy soil. Treatments consisted of four P levels (0–56 g−2) and two water treatments (stressed and not). Plant P concentration decreased strongly with plant age; added P and water stress increased stem and leaf P concentration. Plant N concentration also decreased with age and increased with water stress, but decreased with added P. Because of the effects of age, water availability, and P level on organ nutrient concentration, P‐use efficiency (PUE) increased with age, decreased with water stress, and decreased with added P. Nitrogen‐use efficiency (NUE) also increased with age and decreased with water stress, but tended to increase with added P. Shoot transpiration efficiency (WUET) increased with water stress and added P, and so varied inversely with PUE throughout the growth cycle. Phosphate root uptake efficiency (PRE) was less sensitive than PUE to age, P availability, and water stress, because of the compensating effect of root growth; PRE was also positively correlated with WUET and yield. For crop improvement programs interested in increasing both P‐ and water‐use efficiency, PRE is probably a better selection index than PUE.
Dry Bean Responses to Nitrogen Fertilizer in Two Tillage and Residue Management Systems
Authors: Liebman Matt , Corson Sue , Rowe Richard J. , Halteman William A.
Published: July 2010

Few data currently exist concerning dry bean (Phaseolus vulgaris L.) production systems in which minimum tillage techniques and cover crops are integrated with reduced reliance on chemical inputs. For this reason, we conducted a 2‐yr field experiment in central Maine to compare bean growth, N status, and seed yield in two tillage and residue management systems: conventional planting into a tilled seedbed and two herbicide applications vs. no‐tillage planting into a rye (Secale cereale L.) cover crop and a single herbicide application. Nitrogen fertilizer was applied at 0, 45, 90, and 135 kg N ha−1 to both systems. In 1990, a year characterized by wet early‐season conditions, bean seed yield was 26% lower in the no‐tillage‐rye mulch system than the conventional system, and increased linearly with N fertilizer rate in both systems. In contrast, in 1991, when early‐season rainfall was near normal, yield of the no‐tillage‐rye mulch system was 23% lower than that of the conventional system without N fertilizer, but increased quadratically to equal yield of the conventional system when N was applied. In both years, seed yield was significantly correlated with early and midseason leaf N concentration and late‐season leaf area index. Weed growth was greater in the no‐tillage‐rye mulch system than the conventional system in 1990, but equally low in both systems in 1991, when an additional cultivation was performed. Because the no‐tillage‐rye mulch system we examined may reduce bean growth, N status, and yield, we recommend that other management strategies be pursued. Use of legume green manures as N sources in temperate bean production systems merits attention.
Grain Yield and Weed Biomass of a Wheat–Lentil Intercrop
Authors: Carr Patrick M. , Gardner John J. , Schatz Blaine G. , Zwinger Steven W. , Guldan Steven J.
Published: July 2010

Intercropping cereal with pulse crops often increases total grain production in subtropical regions. Our objective was to determine if a yield advantage resulted when lentil (Lens culinaris Medik.) was intercropped with wheat (Triticum aestivum L. emend. Theil.) in a cool semiarid region. A field experiment was conducted during 1989, 1990, and 1991 under dryland management in south central North Dakota. Lentil and hard red spring wheat were each sown alone and intercropped in different planting patterns and populations. Plants were hand clipped at the soil surface and threshed to provide grain yield estimates in all 3 yr. In 1991, grain was also harvested with a research combine to assess if intercrops could be harvested mechanically. Grain yield of wheat was unaffected by intercropping (P < 0.05). Intercropping reduced grain yield of lentil by 87 to 95% when yield estimates were based on samples harvested manually, and by 70 to 85% when samples were harvested mechanically. The increased height at which pods formed on intercropped compared with sole‐cropped lentil plants and subsequent enhancement in mechanical harvestability of grain in intercrops partially explains this difference in yield estimates between harvesting methods. The land equivalent ratio was 1.15 for grain yield across intercrop treatments with mechanical harvest, and 1.03 for the intercrop treatments when grain was harvested manually. While harvestability of the short‐statured lentil was enhanced in this investigation by intercropping, the low lentil yield under intercropping suggests that wheat‐lentil mixtures are probably not adapted to cool semiarid regions.
Plant Density and Nitrogen Rate Effects on Sugar Beet Yield and Quality Early in Harvest
Authors: Lauer Joseph G.
Published: July 2010

The sugar beet (Beta vulgaris L.) industry has adopted an early harvest option that lengthens the processing campaign by 15 to 30 d. Field experiments were conducted near Powell, WY, from 1989 to 1991, to determine whether plant density and N rate should be adjusted for earlier harvests. Main plots were N application rates of 0, 112, 168, 224, 280, and 336 kg N ha−1; split plots were target plant densities of 37 100, 61 800, 86 500, and 111 200 plants ha−1. Harvests were at regular intervals beginning 13 September and ending 25 October. During the harvest season, root yield increased 8.0 Mg ha−1, sucrose content increased 29 g kg−1, and recoverable sucrose increased 2.44 Mg ha−1. The first 112 kg N ha−1 increased root yield 11.8 Mg ha−1, while the next 56 kg N ha−1 increased root yield 5.2 Mg ha−1. Sucrose content decreased from 164 to 157 g kg−1 as N rate increased from 0 to 336 kg ha−1. The first 168 kg N ha−1 increased recoverable sucrose 2.48 Mg ha−1. Plant density had no effect on root yield. Sucrose content increased 5 g kg−1 as plant density increased from 42 000 to 112 000 plants ha−1. Recoverable sucrose increased from 7.40 Mg ha−1 at 42 700 plants ha−1 to a maximum of 7.79 Mg ha−1 at 88 600 plants ha−1. No consistent harvest date ✕ plant density interactions were observed for yield and quality measurements, suggesting that no adjustments in plant density were needed for earlier harvest dates. A harvest date ✕ N rate interaction for recoverable sucrose implies that N rate should be decreased for earlier harvest dates.
Differences in Autotoxicity among Seven Alfalfa Cultivars
Authors: Chung Ill‐Min , Miller Darrell A.
Published: July 2010

There is a need to determine if alfalfa (Medicago sativa L. subsp. sativa) can be selected for low concentrations of allelopathic compounds. The objective of this study was to evaluate alfalfa cultivar differences in autotoxic traits in relation to various concentrations of aqueous extracts. Plant extracts from seven alfalfa cultivars (Apollo‐Supreme, Arrow, Vernal, DK‐125, Dawn, Pioneer 5472, and Magnum III) were evaluated in the laboratory for autotoxic effects on the same cultivar at four levels of extract solution (10, 20, 30, and 40% w/v). Double‐distilled water was used as a control. Germination percentage, seedling length, and seedling dry weight were measured to determine the effect of the same cultivar extracts on alfalfa growth. These parameters were significantly reduced as the extract concentration increased. The highest concentration (40%) caused the greatest reduction in hypocotyl and radicle length, seedling dry weight, germination percentage, and seedling vigor in all cultivars. It also significantly increased the time required for germination. Autotoxicity effects were significantly different among the various cultivars. Cultivars may be classified in the following order of decreasing inhibition: Pioneer 5472, Arrow, Magnum III, Vernal, Apollo‐Supreme, DK‐125 and Dawn. The results indicate that there may be genetic differences among cultivars for resistance to alfalfa autotoxicity, and that selection for low autotoxicity may be possible.
Soybean Effects on Soil Nitrogen Availability in Crop Rotations
Authors: Vanotti Matias B. , Bundy Larry G.
Published: July 2010

Soybean [Glycine max (L.) Merr.] production contributes significantly to the N supply for a following corn (Zea mays L.) crop, even though soybean N budget studies indicate that N removed in grain may substantially exceed biological fixation. Information on the N status of cereal crops during the 2nd yr following soybean may help resolve this issue. This study reports on N effects of soybean on yield response of succeeding cereal crops and soil N availability based on data from a 15‐yr crop rotation experiment (1977–1991) on a Rozetta silt loam soil (Typic Hapludalfs) at Lancaster, WI. We evaluated the yields of corn and oat (Avena sativa L.) succeeding soybean and alfalfa (Medicago sativa L.) in corn‐soybean‐corn‐oat‐alfalfa (CSCOM) and corn‐corn‐oat‐alfalfa‐alfalfa (CCOMM) crop rotations. Fertilizer N (0, 56, ll2, and 224 kg ha−1) was applied only to corn, but NO3‐N carryover usually affected oat yields as well. The legume fertilizer N replacement values based on check plot yields and the response function of 3rd‐yr corn in a corn‐corn‐corn‐alfalfa‐alfalfa sequence, were equivalent to 153 and 36 kg N ha−1 for the 1st and 2nd yr after alfalfa, respectively, and 75 kg N ha−1 for the 1st yr after soybean. In the 2nd yr after soybean (CSCOM), oat yields were significantly lower than following corn in the CCOMM rotation. Preplant soil NO3 and oat N uptake (1987–1991) indicated that oat yield differences were due to lower soil N availability in the CSCOM rotation. The average soybean effect on soil N availability in the 2nd yr was equal to a soil N debit of 36 kg N ha−1. This indicates that part of the N contribution of soybean to 1st‐yr corn is realized at the expense of subsequent reductions in soil N availability.
Water Stress and Clipping Management Effects on Guineagrass: II. Photosynthesis and Water Relations
Authors: Páez Alejandra , González O. María E.
Published: July 2010

Growth and biomass production and allocation in guineagrass are affected by clipping and water stress, but little is known about the mechanisms responsible. This study was undertaken to determine the short‐term interacting effects of clipping management and water stress on photosynthesis and water relations of guineagrass (Panicum maximum Jacq.). The experiments were conducted outdoors in pots in Maracaibo, Venezuela. After seedling emergence and establishment, plants were clipped at four frequencies and three heights for 3 mo, followed by exposure to water stress. After a stress cycle of 15 d, a group of plants was reirrigated for 21 d, to observe recovery. Photosynthesis and transpiration rates, stomatal conductance, leaf water potential, and water use efficiency (WUE) were measured. During the stress period, the most closely clipped plants had greater photosynthesis, but not increased stomatal conductance. Photosynthesis was also greater in more frequently clipped plants, and both photosynthesis and conductance were reduced by water stress. Upon rewatering, photosynthesis increased sharply. Leaf transpiration rates were not affected by clipping height or frequency during water stress. A linear decrease in WUE occurred as cutting height increased, but clipping frequency did not alter WUE. Water stress reduced leaf water potential, and this effect occurred sooner in plants clipped less frequently and to greater heights. After reirrigation, highest photosynthesis in closely clipped plants was associated with increased stomatal conductance; leaf transpiration rate, WUE, and water potential were not altered by clipping height or frequency. Partial defoliation may relieve water stress to some degree. The increase in photosynthesis caused by close clipping is not fully related to higher stomatal conductance as previously reported, so other factors must also be involved.
Evaluation of Four Intermediate Wheatgrass Populations under Grazing
Authors: Moore Kenneth J. , Vogel Kenneth P. , Klopfenstein T. J. , Masters Robert A. , Anderson Bruce E.
Published: July 2010

The grazing season in the central and northern Great Plains could be extended by use of adapted cool‐season grass pastures for spring and fall grazing to augment the native warm‐season range. A grazing trial was conducted to evaluate the forage quality of four intermediate wheatgrass [Thinopyrum intermedium (Host) Barkw. & D.R. Dewey] populations for use in forage‐livestock systems. The cultivars Slate and Oahe and two populations selected for improved IVDMD, ‘Manska’ and NE TI 1, were evaluated. Each population was seeded in the fall of 1987 in three replicated 0.4‐ha pastures arranged in a randomized complete block design. Pastures were stocked with three beef yearlings for 28 d in spring 1989 and 42 d in spring 1990 to provide a stocking rate of 7.5 steers ha−1. Duration of grazing was shorter in 1989 because of inadequate soil moisture. Average daily gain (ADG) and gain per hectare were higher (P ≤ 0.10) in 1989 than 1990, despite the lower (P ≤ 0.10) forage availability and lesser number of grazing days in 1989. Steers grazing Manska in 1989 gained 1.59 kg d−1, compared with 1.42, 1.27, and 1.43 for Oahe, Slate, and NE TI 1, respectively. There were no differences (P > 0.10) in ADG or gain per hectare among populations in 1990. The improvement in ADG resulted in 30 to 65 kg more gain per hectare from Manska compared with the other populations in 1989. These results demonstrate the excellent quality of intermediate wheatgrass for grazing livestock and the impact that modest improvements in forage quality can have on animal performance.
Straw Color for Altering Soil Temperature and Heat Flux in the Subarctic
Authors: Sharratt Brenton S. , Flerchinger Gerald N.
Published: July 2010

In the Subarctic, straw management methods are needed that improve the early season soil thermal environment of conservation tillage systems. This study determined whether soil heat and water flux are influenced by barley (Hordeum vulgare L.) straw color. Surface temperatures, thaw depth, and latent, sensible, and soil heat flux were ascertained for soil‐black straw, soil‐white straw, and soil‐natural straw surfaces during the spring of 1988 to 1990 at Fairbanks, AK. Daily soil temperatures at 0.05 m, soil surface heat flux, and thaw depth were as much as 0.5°C, 0.5 MJ m−2, and 10 mm greater, respectively, for the black straw than for the other straw color treatments. An atmosphere‐snow‐straw‐soil system model predicted greater absorption of radiation by the soil‐black straw surface, although the percentage of net radiation partitioned to soil heat was lower for the soil‐black straw surface than for the soil‐natural straw and soil‐white straw surfaces. Simulation indicated that straw color did not influence the proportion of absorbed radiation utilized in latent heat flux, but the black straw treatment had the greatest percentage of net radiation partitioned into sensible heat flux. Although the soil thermal environment was slightly altered by changing straw color, managing straw color in conservation tillage systems may aid little in optimizing the thermal regime of subarctic soils unless methods are employed to minimize sensible heat loss from the soil‐straw surface.
Plant Density and Soybean Maturity in a Soybean‐Maize Intercrop
Authors: Hiebsch C. K. , Tetio‐Kagho F. , Chirembo A. M. , Gardner F. P.
Published: July 2010

Long, warm seasons that are inadequately filled by sole crops can be more productive when more fully utilized by intercrops. The effect of plant densities and plant maturity on the magnitude of this increased productivity is not well documented. During two seasons of ≥ 190 d at 29°38′ N lat, maize (Zea mays L.) at 12 densities (from 1.0 to 10.0 plants m−2) and two soybean [Glycine max (L.) Merr.] cultivars, representing Maturity Groups VIII (Cobb) and VI (Davis), at three densities (3.0, 8.5, and 24.0 plants m−2) were grown in intercrop and sole crop in fan designs. Soybean was planted 56 d (1985) and 31 d (1986) after maize. Soybean density did not affect maize yield (P ≤ 0.05). Although predicted sole‐crop Cobb and Davis seed yields were not different (P ≤ 0.05), averaging 336 g m‐2, the two cultivars were differentially affected by maize density. Each unit increase in maize density (plants m‐2), reduced soybean seed yield 20% for Cobb and 47% for Davis at 3.0 soybean plants m−2 and 7% for Cobb and 35% for Davis at 24.0 soybean plants m−2. Cobb had two to three trifoliolates expand after maize removal, while Davis had all leaves fully developed at maize harvest. Land equivalency ratios (LER) were <1.1 for Davis‐maize and peaked at 1.4 for Cobb‐maize. Area‐time equivalency ratios (ATER) were <0.8 for Davis‐maize and peaked at 0.9 for Cobb‐maize. Davis‐maize was not a viable intercrop. The Cobb‐maize intercrop at 24 soybean plants m−2 over a range of maize densities utilized the long growing season more productively (LER = 1.4) than in sole crop; the increased productivity was due to increased season use (ATER < 1.0).
A Chilling Response Test for Early Growth Phase Maize
Authors: Hodges D. Mark , Hamilton Robert I. , Charest Christiane
Published: July 2010

Results from a new laboratory screening technique for the determination of chilling responses in maize (Zea mays L.) at the early growth phase were compared with those obtained from the field. This laboratory technique consisted of growing plants hydroponically in Styrofoam rafts floated on Hoagland's solution at a constant low temperature. Seedlings of eight inbred maize lines were pinned into the rafts and placed in controlled environment chambers at 11°C and 98% relative humidity for 28 d until the four‐leaf stage. A control test used a constant 25°C for 7 d, at which point all lines were at the four‐leaf growth stage. Total, shoot, and root dry mass, and the shoot and root water content were the responses measured. Comparisons between the chilling and the chilling/control ratios showed that they were good indicators of chilling tolerance. Field trials of the same eight inbreds were sown in Ottawa (45°24′ N, 75°43′ W) in the early spring of 1992 and 1993 and the shoot dry mass recorded at the four‐leaf stage. The chill/control ratios of the shoot dry mass of seven of the eight lines from the laboratory were correlated with the averaged field shoot dry mass (r = 0.780, P = 0.032). Thus, this laboratory screening procedure was successful in that the lines indicated by shoot dry mass to be the most chilling resistant or the most sensitive in the laboratory responded similarly in the field.
Yield and Soil Water Uptake of Sunflower Sown in Spring and Summer
Authors: D'Andria Riccardo , Chiarandà Fabrizio Quaglietta , Magliulo Vincenzo , Mori Mauro
Published: July 2010

Sunflower (Helianthus annuus L.) is both tolerant to water deficits and capable of bearing high yield in response to irrigation inputs. In both situations, knowledge of the seasonal distribution of water uptake and the quantification of water extracted in deeper soil layers are required for irrigation scheduling. In a 2‐yr field study in southern Italy, we determined water consumption in relation to seed yield of ‘Romsun HS90’ sunflower with early (spring; mid‐April) and late (summer; mid‐June) sowing dates under five irrigation regimes: a rainfed control; periodic replacement of calculated crop evapotranspiration (a meteorological approach); and one, two, or three irrigation applications at selected growth stages assumed critical for yield expression (a phenological approach). Spring‐sown crops provided significantly higher yields (3.15 vs. 1.75 t ha−1). Irrigation was necessary to achieve high production, especially for the summer crop. Three waterings gave best results in 1989 only. The treatment providing two waterings always showed similar yield and more efficient use of water with respect to the treatment irrigated according to the meteorological approach and performed better than the single irrigation. The ratio between actual and reference crop evapotranspiration was 20% higher in the period between R1 and R6 for the summer crop and 30% higher for the spring crop, with respect to the adopted crop coefficients (Kc). All the yield components were positively affected by irrigation; the most important one was found to be the diameter of calathide. Oil concentration in the achenes was always lower in the summer crop and increased when adequate irrigation was provided, especially in the grain‐filling stage.
Changes in Maize Hybrid Photosynthetic Response to Leaf Nitrogen, from Pre‐Anthesis to Grain Fill
Authors: Dwyer Lianne M. , Anderson Anne M. , Stewart Douglas W. , Ma B. L. , Tollenaar Matthijs
Published: July 2010

Improvement of nitrogen use efficiency in maize production requires quantifying genotypic variability in response to soil N. The objective of this field study was to quantify the relationship between leaf N concentration and leaf photosynthetic rate from pre‐anthesis to grain fill for six maize (Zea mays L.) hybrids. Maize hybrids were grown at the Central Experimental Farm at Ottawa in Ontario (45°23′ N, 75°43′ W) in 1991, 1992, and 1993 at three N fertilizer rates (0, 100, and 200 kg N ha−1). A method of analysis was developed to relate leaf photosynthesis measurements at comparable irradiance levels to leaf N concentration measurements. Photosynthetic response to leaf N was characterized by two fitted coefficients, N0, threshold leaf N concentration for photosynthesis, and P3, photosynthetic rate at high (30 g N kg−1 dry weight) leaf N concentration. There were no hybrid differences in N0 (P > 0.05). There were differences in P3, notably a significantly lower P3 value at anthesis for an old hybrid compared with recent commercial hybrids. In 1992, a recent commercial hybrid, Pioneer 3902, had the highest P3 value, the second highest crop growth rate (CGR) and the highest grain yield, but hybrid differences in P3 were not generally correlated with CGR or grain yield (P > 0.05). Growth stage had a significant effect on both N0 and P3; both declined at later growth stages (P ≤ 0.05). The decline in P3 was greatest in Pride 5 in 1993. Photosynthate production during grain fill was potentially limited in all hybrids by a decline in P3 as the season progressed, although the degree of decline varied with year and hybrid. This analysis quantified the relationships between leaf N concentration and leaf photosynthetic rate for different growth stages and hybrids for evaluation of hybrid N use efficiency.
Chemistry and Mechanisms of Allelopathic Interactions
Authors: Seigler David S.
Published: July 2010

Allelopathy, originally defined as chemically elicited interactions between plants or fungi, is mediated by many types of compounds with different sites and modes of biochemical action. Although it is possible to measure a generalized effect, it is unlikely that deeper insight into the basic mechanisms of of this phenomenon will be obtained until problems are more clearly and specifically delineated. Future work should include identification of the compounds found in specific interactions and their evaluation in bioassay systems that use organisms actually involved in the response. A broader range of compounds and test organisms must be considered, and the biochemical sites and mechanisms of interaction must be evaluated, even for compounds that appear to be inactive. Once active compounds have been identified, their release, movement, uptake, and effects on source and target species in the allelopathic system should be examined. The effects of plant density require additional investigation. Studies in which plants are grown in various combinations and ratios can ultimately provide information about the major sources of allelopathic interaction in communities, the role of allelopathy in succession, and the nature and extent of coadaptation of organisms. Understanding the role of allelopathy in succession will require information about the chemistry and biology of interactions, and a better understanding of the ecological factors involved. Agricultural systems can supply much needed information, as they are similar to natural systems but usually are simpler and better defined. In turn, a better understanding of allelopathy is important in many phases of modern agriculture, especially in the tropics. By attacking allelopathic interactions at several organizational levels, the effects collectively known as allelopathy can be understood, even in complex natural communities. Major advancement in understanding allelopathy will be accomplished only by the combined effort of investigators from many disciplines.
Limited Applicability of the CENTURY Model to Highly Weathered Tropical Soils
Authors: Gijsman Arjan J. , Oberson Astrid , Tiessen Holm , Friesen Dennis K.
Published: July 2010

The CENTURY soil organic matter model was developed to describe nutrient dynamics for soils of the North American Great Plains, but is now applied to other soil types and climates. Phosphorus transformations in CENTURY are based on empirical relationships, developed for soils where N is the most limiting nutrient. This restricts the model's applicability in P‐limited soils, particularly those that differ in reactivity to P and in organic matter stabilization. Moreover, nutrient ratios in plant litter from nutrient‐poor tropical soils may be much wider (e.g., C:P ratios up to 3000) than those commonly found in liter from temperate zones. Equations used in the model to partition incoming litter into slowly and rapidly cycling organic matter may not be suited for such litter. A problem in validating the model is achieving congruence between nutrient fractions that can be measured in the soil and the conceptual pools (state variables) that represent such fractions in the model. Work on P in tropical soils indicates that parameterizing CENTURY may require the use of different P fractions than those of the original version. State variables thus will change. The lack of experimental data on P fractionation in relation to P availability in highly weathered P‐deficient soils is a major restriction in formulating an adequate theoretical framework on P dynamics in tropical soils. The CENTURY model therefore has limited applicability to highly weathered low‐P soils. Various improvements in the P submodel of CENTURY are recommended.
Multinutrient Fertilization and Placement to Improve Yield and Nutrient Concentration of Tall Fescue
Authors: Sweeney Daniel W. , Moyer Joseph L. , Havlin John L.
Published: July 2010

Although tall fescue (Festuca arundinacea Schreb.) is one of the major cool‐season grasses used for animal feed in the USA, it often is unfertilized or is top‐dressed with N alone. Additional fertilizer nutrients applied with N may improve yield and quality. Subsurface placement of N has been shown to improve cool‐season grass production, but data are limited regarding effects of placement of different fertilizer combinations on elemental composition and yield of tall fescue. Thus, a field study was conducted from 1984 to 1986 to determine the effects of multinutrient fertilization (N‐only, NP, NPK, NPKSBZn, and PKSBZn without N) and placement method [broadcast, dribble (surface banding), and knifing (subsurface banding)] on nutrient concentrations and yield of tall fescue. Nitrogen was the primary nutrient limiting fescue growth. Adding N doubled yields of samples that estimated early‐grazing potential and tripled yields of hay. Supplementing N fertilization with additional nutrients increased tissue concentrations of the added nutrient, but increases in yield were small and often not significant. Broadcasting fertilizers resulted in greater yields of early‐grazing samples and higher P and K concentrations than knifing; however, by hay harvest, knifing resulted in about 10% greater yields and 20% greater N concentrations. Dribble applications generally resulted in responses intermediate between those of broadcast and knifing.
Nitrogen Deficiency Detection Using Reflected Shortwave Radiation from Irrigated Corn Canopies
Authors: Blackmer Tracy M. , Schepers James S. , Varvel Gary E. , Walter‐Shea Elizabeth A.
Published: July 2010

Techniques that measure the N status of corn (Zea mays L.) can aid in management decisions that have economic and environmental implications. This study was conducted to identify reflected electromagnetic wavelengths most sensitive to detecting N deficiencies in a corn canopy with the possibility for use as a management tool. Reflected shortwave radiation was measured from an irrigated corn N response trial with four hybrids and five N rates at 0, 40, 80, 120, and 160 kg N ha−1 in 1992 and 0, 50, 100, 150, and 200 kg N ha−1 in 1993. A portable spectroradiometer was used to measure reflected radiation (400–1100 nm in 1992, 350–1050 nm in 1993) from corn canopies at approximately the R5 growth stage. Regression analyses revealed that refiected radiation near 550 and 710 nm was superior to refiected radiation near 450 or 650 nm for detecting N deficiencies. The ratio of light reflectance between 550 and 600 nm to light reflectance between 800 and 900 nm also provided sensitive detection of N stress. In 1993, an inexpensive photometricc ell, which has peak sensitivity to light centereda t 550 nm, was also used to measurer eflected radiation from a corn canopy. Photometric ceil readings correlated with relative grain yield (P < 0.001, r2 = 0.74), but more research will be required to develop procedures to account for varying daylight conditions. These results provide information needed for the development of variable‐rate fertilizer N application technology.
Tillage and Rotation Crop Effects on Weed Dynamics in Potato Production Systems
Authors: Liebman Matt , Drummond Francis A. , Corson Sue , Zhang Jianxin
Published: July 2010

Concern over undesirable environmental impacts and low profitability of conventional potato (Solanum tuberosum L.) production systems has led to efforts to reduce agrichemical use while improving yield and net returns. Weed management based on a better understanding of weed responses to tillage and other cropping practices is a key to success in these efforts. We conducted a 4‐yr field experiment on a Caribou gravelly loam (coarse‐loamy, mixed, frigid Typic Haplorthods) in Presque Isle, ME, in which potato was grown in alternating years with either oat (Avena sativa L.) or berseem clover (Trifolium alexandrinum L.), in plots that were either moldboard plowed (MP) or chisel plowed (CP). To determine yield losses due to weed interference, potato was grown either in weed‐free conditions or with weeds that survived cultivation and hilling. Seed density, plant density, and biomass of dominant weed species (Chenopodium album L. and Brassica and Raphanus spp.) were lower following MP than CP. Average loss of U.S. No. 1 tubers due to weed interference was 12% with MP, compared with 43% with CP. Weed and potato responses to rotation crops differed between years. Weed biomass production was lower in oat than in berseem clover during the 1990 rotation crop phase. In the subsequent 1991 potato crop, yield loss due to weed infestation was 13% following oat, compared with 38% following berseem clover. No difference in weed growth was evident between oat and clover rotation crops in 1992, and there were no rotation crop effects on weed‐related yield loss in the subsequent 1993 potato crop. We present a conceptual model that incorporates these data, links weed life stages and crop performance, and illustrates the effects of interference between weed species. The model suggests that, if weed growth in rotation crops can be strongly suppressed, chisel plowing should result in low densities of annual weed species and minimal yield loss in subsequent potato crops.
SUNDIAL: A PC‐Based System for Simulating Nitrogen Dynamics in Arable Land
Authors: Smith J. U. , Bradbury N. J. , Addiscott T. M.
Published: July 2010

SUNDIAL (SimUlation of Nitrogen Dynamics In Arable Land) is a user‐friendly, PC‐based version of the Rothamsted Nitrogen Turnover Model. It comprises a menu‐driven system that allows agricultural advisers, even with minimal computing experience, to enter details of a particular field or farm and simulate N turnover. The processes involved are described by a set of parameterized zero and first‐order equations. The addition of a novel facility for calculating crop parameters enables instantaneous estimation of parameters for rough but immediate simulations of a new crop, graphical visualization of the expressions used in SUNDIAL, comparison of the parameterized expressions with experimental measurements, and further refinement of parameters by fitting individual expressions to measured data or by iteratively adjusting parameters to improve the fit of simulated results to soil and crop N and 15N measurements. The facilities in SUNDIAL for displaying the various outputs in graphical form make it particularly useful for examining the impact of different management strategies on the N cycle in arable agriculture. Graphical facilities include balance sheets, graphical plots, pie charts, and flow diagrams.
Establishment of Rhizoma Perennial Peanut with Varied Rhizome Nitrogen and Carbohydrate Concentrations
Authors: Rice Ronald W. , Sollenberger Lynn E. , Quesenberry Kenneth H. , Prine Gordon M. , French Edwin C.
Published: July 2010

Rhizoma perennial peanut (RPP; Arachis glabrata Benth.) is a vegetatively propagated forage legume characterized by inconsistent establishment, possibly related to the chemical characteristics of RPP rhizomes used for propagation. This field study evaluated effects of chemical composition of ‘Florigraze’ rhizome planting material on emerged shoot number at 80 d after planting (DAP), rhizome and shoot mass accumulation at 180 DAP, percent RPP cover at season end, and herbage yield in June of the second growing season. The soil was a loamy, siliceous, hyperthermic Grossarenic Paleudult. Rhizome planting material was obtained from grazed pastures which, through varied defoliation management, produced rhizomes with a range of total nonstructural carbohydrate (TNC) (62‐383 g kg−1) and N (12.7‐25.8 g kg−1) concentrations. In 1990, a drought year, rhizomes with TNC ranging from 260 to 300 g kg−1 and N = 21 g kg−1 produced maximum responses for shoot number (39 m−2) and rhizome (530 kg ha−1) and shoot mass (1040 kg ha−1) accumulation. During the wetter than normal spring of 1991, rhizomes with TNC and N concentrations similar to those in 1990 supported 40 to 55% greater shoot counts and almost double (1050 kg ha−1) the rhizome mass accumulation. Because much RPP production occurs on nonirrigated sandy soils, and rainfall constraints are prevalent following planting in most years, assessment of rhizome planting material quality should be based on the 1990 results. In that year, rhizomes with TNC of 230 to 250 g kg−1 and N of 20 to 20.5 g kg−1 performed well, about 70 to 90% of the maximum responses indicated above. Rhizomes with TNC of 190 to 220 g kg−1 and N of 18 to 19 g kg−1 performed at about 40 to 65% of maximum responses. Planting rhizomes with TNC ≤ 180 g kg−1 and N ≤ 17 g kg−1 is not recommended unless irrigation is available, since establishment performance was ≤ 40% of maximum predicted responses.
Total Nitrogen Determination in Plant Material by Persulfate Digestion
Authors: Purcell Larry C. , King C. Andy
Published: July 2010

Determination of total plant N concentration is important in understanding crop nutritional value, nutritional requirements, and physiological responses to the environment. Nitrogen analysis by either the Kjeldahl or Dumas method is expensive and requires specialized equipment. An alternative procedure, developed primarily for use on water samples, was optimized for digestion of vegetative soybean [Glycine max (L.) Merr.] tissue and compared with the Dumas method. Finely ground plant material (0.425 mm) was digested in alkaline potassium persulfate (K2S2O8) at 120°C (0.1 MPa) for 1.5 h in an autoclave, converting organic N to NO‐3. Nitrate in the digest was reduced to NO‐2 and quantified by the sulfanilamide‐α‐naphthyl‐ethylenediamine dihydrochloride procedure. Persulfate digests of soybean material agreed closely with determinations made by the Dumas method (r = 0.99). Digestion of NIST standard tomato (Lycopersicon esculentum Mill.) leaves (4.8 g N 100 g−1) indicated complete N recovery (4.9 ± 0.1 g N 100 g−1). Persulfate digestion of total plant N was accurate and precise, and required little initial investment.
Planting Date and Residue Rate Effects on Growth, Partitioning, and Yield of Corn
Authors: Swanson Stephan P. , Wilhelm Wallace W.
Published: July 2010

Corn (Zea mays L.) growth has been shown to be affected by planting date and amount of residue on the soil surface. The objective of this study was to determine if the adverse effects of cool soil temperatures on early seedling growth often associated with surface residues can be overcome by planting at later dates. Corn was planted at several planting dates (late April through early June) into soil that had residue applied at rates of 0, 33, 66, and 100% of that produced by the previous crop. In general, spring‐applied residue rates had little effect on measured plant responses. Planting corn before or after the optimum date resulted in reduced leaf area index, leaf area duration, total dry matter production, and grain yield. Maximum yield was achieved by planting corn about 10 May (near Lincoln, NE), regardless of the amount of residue applied in the spring. Yield declined with earlier or later planting dates: yield declined more rapidly when planting was delayed than when planting was advanced. Results indicate that, with spring residue application, planting date recommendations can be made independent of residue conditions.
Annual Ryegrass Seed Yield Response to Grazing during Early Stem Elongation
Authors: Young William C. , Chilcote David O. , Youngberg Harold W.
Published: July 2010

Spring grazing annual ryegrass (Lolium multiflorum Lam.) seed fields with sheep (Ovis aries) is a common practice. The effects of grazing duration in early stages of stem elongation on seed yield and its components are not well known. We studied four durations of spring grazing annual ryegrass with sheep over a 2‐yr period on an Argiaquic Xeric Argialboll soil. Grazing was begun before onset of stem elongation. Treatments were no grazing (G0) and grazing until one‐third (G1), two‐thirds (G2), or all (G3) primary tillers had their apical meristems removed. Leaf area was progressively reduced by grazing duration. The number of fertile tillers increased with grazing duration in the first year, but the effect was not significant in the second year. Grazing did not affect the number of spikelets per spike or florets per spikelet in the first year. In the second year, G2 and G3 reduced spikelets per spike and had no effect on the number of florets per spikelet, whereas G1 did not affect either character. Both G2 and G3 decreased seed weight in the first year, while G1 had no effect; treatments did not affect seed weight in the second year. Grazing treatment did not affect total herbage dry matter at seed maturity, seed yield, or seed quality in either year. We conclude that, in western Oregon, grazing annual ryegrass in late winter and early spring up to the time when the apical meristem of all primary tillers are removed (G3) does not reduce seed yield. Grazing until about one‐third of primary tillers lose their apical meristem (G1) may actually improve seed yield.
Comparison of Interseeded Legumes and Small Grains for Cover Crop Establishment in Cotton
Authors: Keeling J. Wayne , Matches Arthur G. , Brown C. Philip , Karnezos T. Peter
Published: July 2010

Wind erosion of soil is a potential problem in unprotected cotton (Gossypium hirsutum L.) fields on the Southern High Plains of Texas during winter and early spring. Our objective was to determine which winter annual forage legumes and small grains may be successfully established by fall interseeding into standing cotton. Thirteen plantings were made over 6 yr at three locations. Both cotton and the interseeded forages were grown under rainfed conditions. The forages were winter wheat (Triticum aestivum L. emend. Thell.), rye (Secale cereale L.), Austrian winter pea [Pisum sativum subsp. pisum var. arvense (L.) Poir.], hairy vetch (Vicia villosa Roth), subterranean clover (Trifolium subterraneum L.; 5 cultivars), rose clover (Trif. hirtum All.; 3 cultivars), crimson clover (Trif. incarnatum L.; 2 cultivars), red clover (Trif. pratense L.), berseem clover (Trif. alexandrinum L.), and barrel medic (Medicago truncatula Gaertn.; 2 cultivars). Successful stands of wheat, rye, winter pea, and hairy vetch were obtained in 69% of the plantings, but in only 53% for the other forages. Establishment of the small‐seeded legumes (clovers and medics), which must be planted at a shallow depth, seemed to be governed by the timing of effective rainfall events after seeding. Establishment of the larger‐seeded wheat, rye, winter pea, and vetch was less dependent on timely rainfall after planting. Of these winter annuals, wheat and rye were the most dependable in producing a soil cover.
Modeling Preemergent Maize Shoot Growth: I. Physiological Temperature Conditions
Authors: Weaich Karl , Bristow Keith L. , Cass Alfred
Published: July 2010

Prediction of seedling emergence is an important first step in predicting crop establishment. There are numerous models that, under nonlimiting seedbed physical conditions, can adequately predict time to emergence using heat sums based on average daily temperatures. Under more adverse seedbed physical conditions, however, such as occur in the semiarid tropics, use of such coarse indices will tend to obscure the strong influence that even temporary extremes in soil temperature or strength can have on the time and extent of emergence, yet it is in these situations that final crop establishment and ultimately yield will be particularly sensitive to emergence predictions. One way to quantify the effect that temporary extremes in seedbed conditions have on emergence is to model the emergence process (namely, preemergent shoot growth). In this paper, we model preemergent maize (Zea mays L.) shoot growth as a first step in characterizing seedling response to a high soil temperature and strength environment. The model, developed from shoot length data obtained under constant temperature conditions ranging from 20 to 40°C, uses an exponential function that predicts coleoptile and first internode growth rates as a function of temperature and sums the output to predict shoot length. Comparison of model predictions with independent measurements carried out in the 20 to 40°C range show that the model is capable of accurately simulating preemergent shoot growth under conditions where (i) temperatures are constant with time, (ii) temperatures of the whole seedbed vary diurnally, and (iii) temperatures within the seedbed vary with time and depth in the seedbed. However, the model was unable to predict shoot growth in situations where seedlings had been exposed to temperatures in excess of 40°C, indicating that further work is needed to assist modeling within the high temperature range.
Forage Potential of Dwarf Napiergrass and a Pearl Millet ✕ Napiergrass Hybrid
Authors: Cuomo Greg J. , Blouin David C. , Beatty James F.
Published: July 2010

Napiergrass [Pennisetum purpureum (L.) Schum.] and pearl millet [Pennisetum americanum (L.) Leeke; syn. Pennisetum glaucum (L.) R. Br.] ✕ napiergrass (PMN) hybrids have potential to fill a forage production void during fall months in the southeastern USA. In a 2‐yr study, ‘Mott’ dwarf napiergrass, a PMN hybrid, and pearl millet were harvested five, four, and three times per year. Objectives were to evaluate forage mass production and distribution, persistence, and forage nutritive value of these Pennisetum spp. Season total forage mass was less for pearl millet (13.2 Mg ha−1) than for napiergrass (17.5 Mg ha−1) and the PMN hybrid (18.9 Mg ha−1). Forage mass differences were the result of napiergrass producing 4.0 Mg ha−2 and the PMN hybrid 5.4 Mg ha−2 during the fall months. Pearl millet produced no herbage during this time. Leaf percent of fall regrowth was greater for napiergrass (90%) than for the PMN hybrid (56%) when averaged over years. Generally, forage nutritive value was similar among species in this study; however, napiergrass had higher crude protein (CP) (136 g kg−1) than pearl millet (127 g kg−1) or the PMN hybrid (123 g kg−1). Napiergrass was the only species to perennate in this study. There were no differences for number of napiergrass tillers in early spring among harvest management treatments. All Pennisetum spp. produced large amounts of forage through late summer; however, napiergrass and the PMN hybrid continued to grow and produce forage until frost and have the potential to fill the fall forage deficit in the southeast USA.