• Authors:
    • Follett, R. F.
    • Alley, M. M.
    • Spargo, J. T.
    • Wallace, J. V.
  • Source: Soil & Tillage Research
  • Volume: 100
  • Issue: 1/2
  • Year: 2008
  • Summary: Carbon sequestration in agroecosystems represents a significant opportunity to offset a portion of anthropogenic CO 2 emissions. Climatic conditions in the Virginia coastal plain and modern production practices make it possible for high annual photosynthetic CO 2 fixation. There is potential to sequester a substantial amount of C, and concomitantly improve soil quality, with the elimination of tillage for crop production in this region. The objectives of our research were to: (1) measure C sequestration rate with continuous no-till management of grain cropping systems of the Virginia middle coastal plain; (2) determine the influence of biosolids application history on C content and its interaction with tillage management; and (3) evaluate the impact of continuous no-till C stratification as an indicator of soil quality. Samples were collected from 63 sites in production fields using a rotation of corn ( Zea mays L.)-wheat ( Triticum aestivum L.) or barley ( Hordeum vulgare L.)/soybean double-crop ( Glysine max L.) across three soil series [Bojac (coarse-loamy, mixed, semiactive, thermic Typic Hapludults), Altavista (fine-loamy, mixed semiactive, thermic Aquic Hapludults), and Kempsville (fine-loamy, siliceous, subactive, thermic Typic Hapludults)] with a history of continuous no-till management ranging from 0 to 14 years. Thirty-two of the sites had a history of biosolids application. Five soil cores were collected at each site from 0-2.5, 2.5-7.5 and 7.5-15 cm and analyzed for bulk density and soil C. Bulk density in the 0-2.5 cm layer decreased and C stratification ratio (0-2.5 cm:7.5-15 cm) increased with increasing duration of continuous no-till due to the accumulation of organic matter at the soil surface. A history of biosolids application resulted in an increase of 4.191.93 Mg C ha -1 (0-15 cm). Continuous no-till resulted in the sequestration of 0.3080.280 Mg C ha -1 yr -1 (0-15 cm). Our results provide quantitative validation of the C sequestration rate and improved soil quality with continuous no-till management in the region using on-farm observations.
  • Authors:
    • Wilhelm, W. W.
    • Varvel, G. E.
  • Source: Agronomy Journal
  • Volume: 100
  • Issue: 4
  • Year: 2008
  • Summary: Proposals promoting the use of massive amounts of crop residues and other lignocellulosic biomass for biofuel production have increased the need for evaluation of the sustainability of cropping practices and their effect on environment quality. Our objective was to evaluate the effects of crop rotation and N fertilizer management and their stover production characteristics on soil organic carbon (SOC) levels in a long-term high-yielding irrigated study in the western Corn Belt. An irrigated monoculture corn ( Zea mays L.), monoculture soybean [ Glycine max (L.) Merr.], and soybean-corn cropping systems study was initiated in 1991 on a uniform site in the Platte Valley near Shelton, NE. Soil samples were collected in 1991 before initiation of the study and in the spring of 2005 and analyzed for SOC. Significant differences in total SOC values were obtained between rotations and N rates at the 0- to 7.5- and 0- to 15-cm depths in 2005 and all total SOC values were equal to or greater than SOC values obtained in 1991. Residue production was greater than 6 Mg ha -1, a level that appears to be sufficient to maintain SOC levels, in all systems. Can residue amounts above this level be harvested sustainably for biofuel production in cropping systems similar to these? Though these results suggest that a portion of corn stover could be harvested without reducing SOC under the conditions of this investigation, the direct impact of stover removal remains to be evaluated.
  • Authors:
    • Santini, J. B.
    • Vyn, T. J.
    • Faghihi, J.
    • Ferris, V. R.
    • Westphal, A.
    • Creech, J. E.
    • Johnson, W. G.
  • Source: Weed Science
  • Volume: 56
  • Issue: 1
  • Year: 2008
  • Summary: Certain winter annual weeds have been documented as alternative hosts to soybean cyst nematode (SCN), and infestations of such species have become common in no-till production fields in the Midwest. This research was conducted to determine the influence of herbicide- and cover-crop-based winter annual weed management systems and crop rotation on winter annual weed growth and seed production, SCN population density, and crop yield. Two crop rotations (continuous soyabean and soyabean-maize) and six winter annual weed management systems (a nontreated control, autumn and spring herbicide applications, spring-applied herbicide, autumn-applied herbicide, autumn-sown annual ryegrass, and autumn-sown winter wheat) were evaluated in no-tillage systems from autumn 2003 to 2006 at West Lafayette and Vincennes, Indiana. Autumn or spring herbicide treatments generally resulted in lower winter annual weed densities than cover crops. Densities of henbit and purple deadnettle increased over years in the cover crop systems but remained constant in the herbicide systems. Averaged over sites and years, winter annual weed densities were nearly 45% lower in the spring than the autumn due to winter mortality. Maize yield was reduced by the cover crops at West Lafayette but not Vincennes. Winter annual weed management system had no influence on soyabean yield. SCN population density was reduced by including maize in the crop sequence but was not influenced by winter annual weed management. The density of weedy host species of SCN in the experimental area was relatively low (less than 75 plants m -2) compared to densities that can be observed in production fields. The results suggest that inclusion of maize into a cropping sequence is a much more valuable SCN management tool than winter annual weed management. In addition, control of winter annual weeds, specifically for SCN management, may not be warranted in fields with low weed density.
  • Authors:
    • Egli, D. B.
  • Source: Field Crops Research
  • Volume: 106
  • Issue: 1
  • Year: 2008
  • Summary: The increases in crop yield that played an important role in maintaining adequate food supplies in the past may not continue in the future. Soybean ( Glycine max L. Merrill) county yield trends (1972-2003) were examined for evidence of plateaus using data (National Agricultural Statistics Service) for 162 counties (215 data sets) in six production systems [Iowa, Nebraska (irrigated and non-irrigated), Kentucky and Arkansas (irrigated and non-irrigated)] representing a range in yield potential. Average yield (1999-2003) was highest in irrigated production in Nebraska (3403 kg ha -1) and lowest in non-irrigated areas in Arkansas (1482 kg ha -1). Average yield in the highest yielding county in each system was 31-88% higher than the lowest. Linear regression of yield versus time was significant ( P=0.05) in 169 data sets and a linear-plateau model reached convergence (with the intersection point in the mid-1990s) in 35 of these data sets, but it was significantly ( P=0.10) better in only three data sets (
  • Authors:
    • Graef, G. L.
    • Elmore, R. W.
    • Cassman, K. G.
    • Dobermann, A.
    • Setiyono, T. D.
    • Bastidas, A. M.
    • Specht, J . E.
  • Source: Crop Science
  • Volume: 48
  • Issue: 2
  • Year: 2008
  • Summary: The sensitivity of soybean [ Glycine max (L.) Merr.] main stem node accrual to ambient temperature has been documented in greenhouse-grown plants but not with field-grown plants in the north-central United States. Biweekly V-node and R-stage, stem node number, internode length, and other traits were quantified in an irrigated split-plot, four-replicate, randomized complete block experiment conducted in Lincoln, NE, in 2003-2004. Main plots were early-, mid-, late-May, and mid-June sowing dates. Subplots were 14 cultivars of maturity groups 3.0 to 3.9. Node appearance was surprisingly linear from V1 to R5, despite the large increase in daily temperature from early May (10-15degreesC) to July (20-25degreesC). The 2003 and 2004 May planting date regressions exhibited near-identical slopes of 0.27 node d -1 (i.e., one node every 3.7 d). Cold-induced delays in germination and emergence did delay the V1 date (relative to planting date), so the primary effect of temperature was the V1 start date of linearity in node appearance. With one exception, earlier sowings led to more nodes (earlier V1 start dates) but also resulted in shorter internodes at nodes 3 to 9 (cooler coincident temperatures), thereby generating a curved response of plant height to delayed plantings. Delaying planting after 1 May led to significant linear seed yield declines of 17 kg ha -1 d -1 in 2003 and 43 kg ha -1 d -1 in 2004, denoting the importance of early planting for capturing the yield potential available in soybean production, when moisture supply is not limiting.
  • Authors:
    • Janetos, A.
    • Backlund, P.
    • Schimel, D.
  • Source: Synthesis and Assessment Product 4.3. Washington, DC: U.S. Environmental Protection Agency, Climate Change Science Program. Miscellaneous Publication
  • Year: 2008
  • Summary: This report provides an assessment of the effects of climate change on U.S. agriculture, land resources, water resources, and biodiversity. It is one of a series of 21 Synthesis and Assessment Products (SAP) that are being produced under the auspices of the U.S. Climate Change Science Program (CCSP). This SAP builds on an extensive scientific literature and series of recent assessments of the historical and potential impacts of climate change and climate variability on managed and unmanaged ecosystems and their constituent biota and processes. It discusses the nation's ability to identify, observe, and monitor the stresses that influence agriculture, land resources, water resources, and biodiversity, and evaluates the relative importance of these stresses and how they are likely to change in the future. It identifies changes in resource conditions that are now being observed, and examines whether these changes can be attributed in whole or part to climate change. The general time horizon for this report is from the recent past through the period 2030-2050, although longer-term results out to 2100 are also considered. There is robust scientific consensus that human-induced climate change is occurring. Records of temperature and precipitation in the United States show trends consistent with the current state of global-scale understanding and observations of change. Observations also show that climate change is currently impacting the nation's ecosystems and services in significant ways, and those alterations are very likely to accelerate in the future, in some cases dramatically. Current observational capabilities are considered inadequate to fully understand and address the future scope and rate of change in all ecological sectors. Additionally, the complex interactions between change agents such as climate, land use alteration, and species invasion create dynamics that confound simple causal relationships and will severely complicate the development and assessment of mitigation and adaptation strategies. Even under the most optimistic CO 2 emission scenarios, important changes in sea level, regional and super-regional temperatures, and precipitation patterns will have profound effects. Management of water resources will become more challenging. Increased incidence of disturbances such as forest fires, insect outbreaks, severe storms, and drought will command public attention and place increasing demands on management resources. Ecosystems are likely to be pushed increasingly into alternate states with the possible breakdown of traditional species relationships, such as pollinator/plant and predator/prey interactions, adding additional stresses and potential for system failures. Some agricultural and forest systems may experience near-term productivity increases, but over the long term, many such systems are likely to experience overall decreases in productivity that could result in economic losses, diminished ecosystem services, and the need for new, and in many cases significant, changes to management regimes.
  • Authors:
    • Heitman, J. L.
    • Gaur, A.
    • Horton, R.
    • Jaynes, D. B.
    • Kaspar, T. C.
  • Source: Soil Science Society of America Journal
  • Volume: 71
  • Issue: 2
  • Year: 2007
  • Summary: Management of chemicals in soil is important, yet the complexity of field soils limits prediction of management effects on transport. To date, few methods have been available for field measurement of chemical transport properties, but a recently developed dripper-time domain reflectometry technique allows rapid collection of data for determining these properties. The objective of this work was to apply this technique for comparison of chemical transport properties for different soil management zones. Experiments were conducted in Iowa, USA, comparing four interrow management zones: no-till non-trafficked, no-till trafficked, chisel plough non-trafficked, and chisel plough trafficked. Drip emitters were positioned at 12 locations in each zone and used to apply water followed by a step input of CaCl 2 tracer solution. Breakthrough curves were measured via electrical conductivity with time domain reflectometry probes. The mobile-immobile model was fit to the breakthrough curves to determine chemical transport properties. Mean chemical transport properties were 0.34, 0.11 h -1, 10 cm h -1, 164 cm 2 h -1, and 5 cm, for the immobile water fraction, mass exchange coefficient, average pore-water velocity, mobile dispersion coefficient, and dispersivity, respectively. All five properties showed significant differences between management zones. Differences in mass exchange and mobile dispersion coefficients coincided with differences in tillage, while differences in mean pore water velocities coincided with differences in traffic. The immobile water fraction was largest for the no-till non-trafficked zone. These results represent one of very few reports for field measurement of chemical transport properties and the first application of this approach for comparison of chemical transport properties across management zones.
  • Authors:
    • Payero, J. O.
    • Schneekloth, J. P.
    • Klocke, N. L.
  • Source: Transactions of the ASABE
  • Volume: 50
  • Issue: 6
  • Year: 2007
  • Summary: Dwindling water supplies for irrigation are prompting alternative management choices by irrigators. Limited irrigation, where less water is applied than full crop demand, may be a viable approach. Application of limited irrigation to maize ( Zea mays) was examined in a study conducted at the West Central Research and Extension Centre of the University of Nebraska-Lincoln at North Platte, Nebraska, USA. Maize was grown in crop rotations with dryland, limited irrigation, or full irrigation management from 1985 to 1999. Crop rotations included maize following maize (continuous maize), maize following wheat ( Triticum aestivum), followed by soyabean ( Glycine max) (wheat-maize-soyabean), and maize following soyabean (maize-soyabean). Full irrigation was managed to meet crop evapotranspiration requirements (ETc). Limited irrigation was managed with a seasonal target of no more than 150 mm applied. Precipitation patterns influenced the outcomes of measured parameters. Dryland yields had the most variation, while fully irrigated yields varied the least. Limited irrigation yields were 80 to 90% of fully irrigated yields, but the limited irrigation plots received about half the applied water. Grain yields were significantly different among irrigation treatments. Yields were not significantly different among rotation treatments for all years and water treatments. For soil water parameters, more statistical differences were detected among the water management treatments than among the crop rotation treatments. Economic projections of these management practices showed that full irrigation produced the most income if water was available. Limited irrigation increased income significantly from dryland management.
  • Authors:
    • Ahuja, L. R.
    • Green, T. R.
    • Ma, L. W.
    • Kozak, J. A.
  • Source: Hydrological Processes
  • Volume: 21
  • Issue: 2
  • Year: 2007
  • Summary: Crop canopies and residues have been shown to intercept a significant amount of rainfall. However, rainfall or irrigation interception by crops and residues has often been overlooked in hydrologic modelling. Crop canopy interception is controlled by canopy density and rainfall intensity and duration. Crop residue interception is a function of crop residue type, residue density and cover, and rainfall intensity and duration. We account for these controlling factors and present a model for both interception components based on Merriam's approach. The modified Merriam model and the current modelling approaches were examined and compared with two field studies and one laboratory study. The Merriam model is shown to agree well with measurements and was implemented within the Agricultural Research Service's Root Zone Water Quality Model (RZWQM). Using this enhanced version of RZWQM, three simulation studies were performed to examine the quantitative effects of rainfall interception by corn and wheat canopies and residues on soil hydrological components. Study I consisted of 10 separate hypothetical growing seasons (1991-2000) for canopy effects and 10 separate non-growing seasons (1991-2000) for residue effects for eastern Colorado conditions. For actual management practices in a no-till wheat-corn-fallow cropping sequence at Akron, Colorado (study II), a continuous 10-year RZWQM simulation was performed to examine the cumulative changes on water balance components and crop growth caused by canopy and residue rainfall interception. Finally, to examine a higher precipitation environment, a hypothetical, no-till wheat-corn-fallow rotation scenario at Corvallis, Oregon, was simulated (study III). For all studies, interception was shown to decrease infiltration, runoff, evapotranspiration from soil, deep seepage of water and chemical transport, macropore flow, leaf area index, and crop/grain yield. Because interception decreased both infiltration and soil evapotranspiration, no significant change in soil water storage was simulated. Nonetheless, these findings and the new interception models are significant new contributions for hydrologists.
  • Authors:
    • Lenssen, A. W.
    • Johnson, G. D.
    • Carlson, G. R.
  • Source: Field Crops Research
  • Volume: 100
  • Issue: 1
  • Year: 2007
  • Summary: Available water is typically the biggest constraint to spring wheat production in the northern Great Plains of the USA. The most common rotation for spring wheat is with summer fallow, which is used to accrue additional soil moisture. Tillage during fallow periods controls weeds, which otherwise would use substantial amounts of water, decreasing the efficiency of fallow. Chemical fallow and zero tillage systems improve soil water conservation, allowing for increased cropping intensity. We conducted a field trial from 1998 through 2003 comparing productivity and water use of crops in nine rotations under two tillage systems, conventional and no-till. All rotations included spring wheat, two rotations included field pea, while lentil, chickpea, yellow mustard, sunflower, and safflower were present in single rotations with wheat. Growing season precipitation was below average most years, resulting in substantial drought stress to crops not following fallow. Preplant soil water, water use, and spring wheat yields were generally greater following summer fallow than wheat recropped after wheat or alternate crops. Water use and yield of wheat following summer fallow was greater than for chickpea or yellow mustard, the only other crops in the trial that followed summer fallow. Field pea performed best of all alternate crops, providing yields comparable to those of recropped spring wheat. Chickpea, lentil, yellow mustard, safflower, and sunflower did not perform well and were not adapted to this region, at least during periods of below average precipitation. Following summer fallow, and despite drought conditions, zero tillage often provided greater amounts of soil water at planting compared to conventional tillage.