• Authors:
    • Suyker, A. E.
    • Verma, S. B.
  • Source: Agricultural and Forest Meteorology
  • Volume: 150
  • Issue: 4
  • Year: 2010
  • Summary: Continuous measurements of CO 2 and water vapor exchanges made in three cropping systems (irrigated continuous maize, irrigated maize-soybean rotation, and rainfed maize-soybean rotation) in eastern Nebraska, USA during 6 years are discussed. Close coupling between seasonal distributions of gross primary production (GPP) and evapotranspiration (ET) were observed in each growing season. Mean growing season totals of GPP in irrigated maize and soybean were 1738114 and 99669 g C m -2, respectively (standard deviation). Corresponding mean values of growing season ET totals were 54527 and 45423 mm, respectively. Irrigation affected GPP and ET similarly, both growing season totals were about 10% higher than those of corresponding rainfed crops. Maize, under both irrigated and rainfed conditions, fixed 74% more carbon than soybean while using only 12-20% more water. The green leaf area index (LAI) explained substantial portions (91% for maize and 90% for soybean) of the variability in GPP PAR (GPP over a narrow range of incident photosynthetically active radiation) and in ET/ET o (71% for maize and 75% for soybean, ET o is the reference evapotranspiration). Water productivity (WP or water use efficiency) is defined here as the ratio of cumulative GPP or above-ground biomass and ET (photosynthetic water productivity=SigmaGPP/SigmaET and biomass water productivity=above-ground biomass/SigmaET). When normalized by ET o, the photosynthetic water productivity (WP ETo) was 18.41.5 g C m -2 for maize and 12.01.0 g C m -2 for soybean. When normalized by ET o, the biomass water productivity (WP ETo) was 27.52.3 g DM m -2 for maize and 14.13.1 g DM m -2 for soybean. Comparisons of these results, among different years of measurement and management practices (continuous vs rotation cropping, irrigated vs rainfed) in this study and those from other locations, indicated the conservative nature of normalized water productivity, as also pointed out by previous investigators.
  • Authors:
    • Stephenson, D.
    • Miller, D.
    • Williams, B.
  • Source: Louisiana Agriculture
  • Volume: 53
  • Issue: 3
  • Year: 2010
  • Authors:
    • Fang, M.
    • Witter, J. D.
    • Spongberg, A. L.
    • Wu, C. X.
    • Czajkowski, K. P.
  • Source: Environmental Science & Technology
  • Volume: 44
  • Issue: 16
  • Year: 2010
  • Summary: Many pharmaceuticals and personal care products (PPCPs) are commonly found in biosolids and effluents from wastewater treatment plants. Land application of these biosolids and the reclamation of treated wastewater can transfer those PPCPs into the terrestrial and aquatic environments, giving rise to potential accumulation in plants. In this work, a greenhouse experiment was used to study the uptake of three pharmaceuticals (carbamazepine, diphenhydramine, and fluoxetine) and two personal care products (triclosan and triclocarban) by an agriculturally important species, soybean ( Glycine max (L.) Merr.). Two treatments simulating biosolids application and wastewater irrigation were investigated. After growing for 60 and 110 days, plant tissues and soils were analyzed for target compounds. Carbamazepine, triclosan, and triclocarban were found to be concentrated in root tissues and translocated into above ground parts including beans, whereas accumulation and translocation for diphenhydramine and fluoxetine was limited. The uptake of selected compounds differed by treatment, with biosolids application resulting in higher plant concentrations, likely due to higher loading. However, compounds introduced by irrigation appeared to be more available for uptake and translocation. Degradation is the main mechanism for the dissipation of selected compounds in biosolids applied soils, and the presence of soybean plants had no significant effect on sorption. Data from two different harvests suggest that the uptake from soil to root and translocation from root to leaf may be rate limited for triclosan and triclocarban and metabolism may occur within the plant for carbamazepine.
  • Authors:
    • Zhang, L. X.
    • Boahen, S.
  • Source: Agriculture and Biology Journal of North America
  • Volume: 1
  • Issue: 4
  • Year: 2010
  • Summary: One of the major problems associated with the early soybean production system (ESPS) in the Midsouth USA is seed shattering of early maturity group (MG) soybean that mature in the midsummer. Information is needed to measure the impact of this problem and to provide proper management strategies. Studies were conducted to investigate the problem of shattering in MG IV soybean, the dominant soybean group in ESPS, in 2006 and 2007. The objectives of this study were to determine the pattern and critical period of seed shattering of MG IV soybeans under various climatic and production conditions in the Mississippi Delta. A total of 56 and 80 MG IV soybean varieties were evaluated in the experiments in 2006 and 2007, respectively. The varieties were all selected from a Mississippi Soybean Variety Trial and the study was carried out at Stoneville, Mississippi. In 2006, only the April planting (April 19) under irrigation was investigated. In 2007, experiments were conducted on both irrigated and non-irrigated fields. On the irrigated tests, both April (April 23) and May (May 15) planting were examined. Results from both years have indicated that most pods of early MG IV soybean varieties can hold seeds relatively well for the first three weeks after maturity (WAM). However, differences were noted starting from the fourth WAM. Non-irrigated soybean shattered faster than irrigated soybean after three weeks. Irrigated soybean held seeds longer than non-irrigated soybean during the fourth week; however, seed shattering became greater after four weeks even in the irrigated study. When comparing early- and late-planted soybean under irrigated conditions, the later maturing pods held seeds better within the same period after maturity (up to 6 weeks or longer). Late-maturing pods tended to held seed better, most likely due to lower temperatures experienced after late September.
  • Authors:
    • Mackowiak, C. L.
    • Marois, J. J.
    • Wright, D. L.
    • Brennan, M.
    • Zhao, D.
  • Source: Agronomy for Sustainable Development
  • Volume: 30
  • Issue: 2
  • Year: 2010
  • Summary: Nitrogen (N) leaching from agricultural soils is a major concern in the southeastern USA. A winter cover crop following the summer crop rotation is essential for controlling N leaching and soil run-off, thereby improving sustainable development. Rotation of peanut (Arachis hypogea L.) and cotton (Gossypium hirsutum L.) with bahiagrass (Paspalum notatum) (i.e. sod-based rotation) can greatly improve soil health and increase crop yields and profitability. In the sod-based rotation, the winter cover crop is an important component. The objective of this study was to determine effects of summer crops, cotton and peanut, on growth and physiology of a subsequent oat (Avena sativa L.) cover crop in both a conventional (Peanut-Cotton-Cotton) and sod-based (Bahiagrass-Bahiagrass-Peanut-Cotton) rotations. Two rotations with an oat cover crop were established in 2000. In the 2006-07 and 2007-08 growing seasons, oat plant height, leaf chlorophyll and sap NO(3)-N concentrations, shoot biomass, and N uptake were determined. Our results showed that the previous summer crop in the two rotations significantly influenced oat growth and physiology. Oat grown in the sod-based rotation had greater biomass, leaf chlorophyll and NO(3)-N concentrations as compared with oat grown in the conventional rotation. At pre-heading stage, oat in the sod-based rotation had 44% greater biomass and 32% higher N uptake than oat in the conventional rotation; oat following peanut produced 40 to 49% more biomass and accumulated 27 to 66% more N than oat following cotton. Therefore, the sod-based rotation improved not only summer crops, but also the winter cover crop. Increased oat growth and N status from the sod-based rotation indicated greater soil quality and sustainability.
  • Authors:
    • Kolka, R.
    • Asbjornsen, H.
    • Helmers, M. J.
    • Zhou, X. B.
    • Tomer, M. D.
  • Source: Journal of Environmental Quality
  • Volume: 39
  • Issue: 6
  • Year: 2010
  • Summary: Many croplands planted to perennial grasses under the Conservation Reserve Program are being returned to crop production, and with potential consequences for water quality. The objective of this study was to quantify the impact of grassland-to-cropland conversion on nitrate-nitrogen (NO(3)-N) concentrations in soil and shallow groundwater and to assess the potential for perennial filter strips (PFS) to mitigate increases in NO(3)-N levels. The study, conducted at the Neal Smith National Wildlife Refuge (NSNWR) in central Iowa, consisted of a balanced incomplete block design with 12 watersheds and four watershed-scale treatments having different proportions and topographic positions of PFS planted in native prairie grasses: 100% rowcrop, 10% PFS (toeslope position), 10% PFS (distributed on toe and as contour strips), and 20% PFS (distributed on toe and as contour strips). All treatments were established in fall 2006 on watersheds that were under bromegrass (Bromus L.) cover for at least 10 yr. Nonperennial areas were maintained under a no-till 2-yr corn (Zea mays L.)- soybean [Glycine max. (L.) Merr.] rotation since spring 2007. Suction lysimeter and shallow groundwater wells located at upslope and toeslope positions were sampled monthly during the growing season to determine NO(3)-N concentration from 2005 to 2008. The results indicated significant increases in NO(3)-N concentration in soil and groundwater following grassland-to-cropland conversion. Nitrate-nitrogen levels in the vadose zone and groundwater under PFS were lower compared with 100% cropland, with the most significant differences occurring at the toeslope position. During the years following conversion, PFS mitigated increases in subsurface nitrate, but long-term monitoring is needed to observe and understand the full response to land-use conversion.
  • Authors:
    • Stanturf, J. A.
    • Gardiner, E. S.
    • Dey, D. C.
    • Jacobs, D. F.
    • Kabrick, J. M.
  • Source: Scandinavian Journal of Forest Research
  • Volume: 25
  • Year: 2010
  • Summary: Establishing trees in agricultural bottomlands is challenging because of intense competition, flooding and herbivory. A summary is presented of new practices and management systems for regenerating trees in former agricultural fields in the eastern USA. Innovations have come from improvements in planting stock and new silvicultural systems that restore ecological function more quickly than traditional afforestation with single-species stands. Advances in nursery production of large (e. g. 1-2 m tall; 1.5-2.0 cm basal diameter) bareroot and container seedlings with well-developed root systems have led to increases in survival and growth, and early seed production. In addition to planting high-quality seedlings, managing vegetation is critical to regeneration success. Planting seedlings with cover crops such as redtop grass (Agrostis gigantea Roth) may improve tree survival and growth by controlling competing vegetation and reducing animal herbivory. An innovative strategy that simulates natural succession involves interplanting later seral species such as Nuttall oak (Quercus nuttallii Palm.) in young plantations of pioneer species such as Populus deltoides Bartr. ex Marsh. Populus L. acts as a nurse crop for Quercus L. by reducing biomass of competing vegetation without seriously limiting Quercus L. seedling growth or function. Harvest of the short-rotation Populus L. crop releases the well-established Quercus L. trees. Success in afforestation requires planting high-quality seedlings using management practices that promote survival and growth. Restoration based on ecosystem processes, using tree species that have complementary ecological requirements, will be more successful and affordable than other methods.
  • Authors:
    • Petersen, J. L.
    • Melvin, S. R.
    • Irmak, S.
    • Martin, D. L.
    • Donk, S. J. van
    • Davison, D. R.
  • Source: Transactions of the ASABE
  • Volume: 53
  • Issue: 6
  • Year: 2010
  • Summary: Competition for water is becoming more intense in many parts of the U.S., including west-central Nebraska. It is believed that reduced tillage, with more crop residue on the soil surface, conserves water, but the magnitude of water conservation is not clear. A study was initiated on the effect of residue on soil water content and corn yield at North Platte, Nebraska. The experiment was conducted in 2007 and 2008 on plots planted to field corn ( Zea mays L.). In 2005 and 2006, soybean was grown on these plots. There were two treatments: residue-covered soil and bare soil. Bare-soil plots were created in April 2007. The residue plots were left untreated. In April 2008, bare-soil plots were recreated on the same plots as in 2007. The experiment consisted of eight plots (two treatments with four replications each). Each plot was 12.2 m * 12.2 m. During the growing season, soil water content was measured several times in each of the plots at six depths, down to a depth of 1.68 m, using a neutron probe. The corn crop was sprinkler-irrigated but purposely water-stressed, so that any water conservation in the residue-covered plots might translate into higher yields. In 2007, mean corn yield was 12.4 Mg ha -1 in the residue-covered plots, which was significantly (p=0.0036) greater than the 10.8 Mg ha -1 in the bare-soil plots. Other research has shown that it takes 65 to 100 mm of irrigation water to grow this extra 1.6 Mg ha -1, which may be considered water conservation due to the residue. In 2008, the residue-covered soil held approximately 60 mm more water in the top 1.83 m compared to the bare soil toward the end of the growing season. In addition, mean corn yield was 11.7 Mg ha -1 in the residue-covered plots, which was significantly (p=0.0165) greater than the 10.6 Mg ha -1 in the bare-soil plots. It would take 30 to 65 mm of irrigation water to produce this additional 1.1 Mg ha -1 of grain yield. Thus, the total amount of water conservation due to the residue was 90 to 125 mm in 2008. Water conservation of such a magnitude will help irrigators to reduce pumping cost. With deficit irrigation, water saved by evaporation is used for transpiration and greater yield, which may have even greater economic benefits. In addition, with these kinds of water conservation, more water would be available for competing needs.
  • Authors:
    • Egli, D. B.
  • Source: Crop Science
  • Volume: 50
  • Issue: 5
  • Year: 2010
  • Summary: The number of pods and seeds produced by soybean [ Glycine max (L.) Merr.] is related to canopy photosynthesis during flowering. The effect of low photosynthesis during only a portion of flowering (growth stage R1 to R5), however, is not well defined. Two field experiments were conducted at Lexington, KY (38degreesN), with seeds sown in mid-May in 0.76-m rows (20 seeds m -1 of row) and all plots irrigated as needed. In 2005/2006, plants (cultivars Pennyrile and Ripley) were shaded (60% in 2005 and 80% in 2006) for 4- to 9-d periods just before or just after peak pod production. These treatments had almost no effect on seed number (significant reduction in only one of eight comparisons). In a second experiment (cv. Pennyrile, 2007/2008), shade cloth (60%) was placed over plants at growth stage R1.6 and removed at 7-d intervals. The first 7 d of shade did not affect seed number, but 14 d of shade ending at roughly growth stage R3.0 reduced seed number by 16% and longer periods caused proportionally larger reductions. When shade cloth (80%) was put in place at 7-d intervals (starting at R3.4) and left in place until maturity, seed number was reduced until the last treatment (put in place 4-7 d after the beginning of growth stage R6). Seed number was tolerant of short periods (4-9 d) of low assimilate supply during flowering, but could not recover from longer periods of shade (≥14 d), even when they occurred relatively early in the flowering period.
  • Authors:
    • Guerra, L. C.
    • Persson, T.
    • Garcia y Garcia, A.
    • Hoogenboom, G.
  • Source: Agricultural Water Management
  • Volume: 97
  • Issue: 7
  • Year: 2010
  • Summary: Studies on irrigation scheduling for soybean have demonstrated that avoiding irrigation during the vegetative growth stages could result in yields as high as those obtained if the crop was fully irrigated during the entire growing season. This could ultimately also lead to an improvement of the irrigation water use efficiency. The objective of this study was to determine the effect of different irrigation regimes (IRs) on growth and yield of four soybean genotypes and to determine their irrigation water use efficiency. A field experiment consisting of three IR using a lateral move sprinkler system and four soybean genotypes was conducted at the Bledsoe Research Farm of The University of Georgia, USA. The irrigation treatments consisted of full season irrigated (FSI), start irrigation at flowering (SIF), and rainfed (RFD); the soybean genotypes represented maturity groups (MGs) V, VI, VII, and VIII. A completely randomized block design in a split-plot array with four replicates was used with IR as the main treatment and the soybean MGs as the sub-treatment. Weather variables and soil moisture were recorded with an automatic weather station located nearby, while rainfall and irrigation amounts were recorded with rain gauges located in the experimental field. Samplings for growth analysis of the plant and its components as well as leaf area index (LAI) and canopy height were obtained every 12 days. The irrigation water use efficiency ( IWUE) or ratio of the difference between irrigated and rainfed yield to the amount of irrigation water applied was estimated. The results showed significant differences ( P