• Authors:
    • Haar, M.
    • Lindquist, J.
    • Wortman, S.
    • Francis, C.
  • Source: Renewable Agriculture and Food Systems
  • Volume: 25
  • Issue: 4
  • Year: 2010
  • Summary: While weed management is consistently a top priority among farmers, there is also growing concern for the conservation of biodiversity. Maintaining diverse weed communities below bioeconomic thresholds may provide ecosystem services for the crop and the surrounding ecosystem. This study was conducted to determine if weed diversity, density and biomass differ within and among organic and conventional crop rotations. In 2007 and 2008, we sampled weed communities in four long-term crop rotations near Mead, Nebraska using seedbank analyses (elutriation and greenhouse emergence) and above-ground biomass sampling. Two conventional crop rotations consisted of a corn ( Zea mays) or sorghum ( Sorghum bicolor)-soybean ( Glycine max)-sorghum or corn-soybean sequence and a diversified corn or sorghum-sorghum or corn-soybean-wheat ( Triticum aestivum) sequence. Two organic rotations consisted of an animal manure-based soybean-corn or sorghum-soybean-wheat sequence and a green manure-based alfalfa ( Medicago sativa)-alfalfa-corn or sorghum-wheat sequence. Species diversity of the weed seedbank and the above-ground weed community, as determined by the Shannon diversity index, were greatest in the organic green manure rotation. Averaged across all sampling methods and years, the weed diversity index of the organic green manure rotation was 1.07, followed by the organic animal manure (0.78), diversified conventional (0.76) and conventional (0.66) rotations. The broadleaf weed seedbank density in the tillage layer of the organic animal manure rotation was 1.4*, 3.1* and 5.1* greater than the organic green manure, diversified conventional and conventional rotations, respectively. The grass weed seedbank density in the tillage layer of the organic green manure rotation was 2.0*, 6.1* and 6.4* greater than the organic animal manure, diversified conventional and conventional rotations, respectively. The above-ground weed biomass was generally greatest in the organic rotations. The broadleaf weed biomass in sorghum and wheat did not differ between organic and conventional rotations (CRs), but grass weed biomass was greater in organic compared to CRs for all crops. The above-ground weed biomass did not differ within CRs, and within organic rotations the grass weed biomass was generally greatest in the organic green manure rotation. The weed seedbank and above-ground weed communities that have accumulated in these rotations throughout the experiment suggest a need for greater management in long-term organic rotations that primarily include annual crops. However, results suggest that including a perennial forage crop in organic rotations may reduce broadleaf weed seedbank populations and increase weed diversity.
  • Authors:
    • Hayes, P.
    • Talbert, H.
    • Surber, L.
    • Kanazin, V.
    • Bowman, J.
    • Abdel-Haleem, H.
    • Blake, T.
  • Source: Euphytica
  • Volume: 172
  • Issue: 3
  • Year: 2010
  • Summary: More than half of the barley grown in the USA is used for livestock feed, with the remaining stocks diverted for human food and malting purposes. The use of barley grain as a major source of cattle feed has been criticized because of its rapid digestion in the rumen, which can result in digestive disorders in cattle. In sacco dry matter digestibility (ISDMD) and particle size (PS) after dry rolling have been found to play a role in the feedlot performance of barley as a feed grain. Reducing the rate of ISDMD is predicted to result in significantly improved animal health and average daily gain. A recombinant inbred line population derived from a cross between a high ISDMD, two-rowed barley cultivar (Valier) and a six-rowed Swiss landrace line (PI370970) exhibiting far slower ISDMD has been developed for studying the underlying genetic locations and mechanisms of these traits. To detect associated quantitative trait loci (QTLs), we collected and analyzed data from irrigated and rain-fed environments. A significant negative correlation was observed between ISDMD and PS. High heritability estimates for ISDMD and PS suggest that early selection for these traits during breeding would be achievable. Four QTLs were identified on chromosomes 2H, 6H, and 7H, explaining 73-85% of ISDMD phenotypic variation, while three QTLs on 2H and 7H were associated with variation in PS and explained 58-77% of its variation. A major QTL on chromosome 2H tightly linked to the morphology-modifying gene vrs1 was found to dramatically control 35-62% of the phenotypic variation of ISDMD and 26-53% of that of PS. The impact of the vrs1 locus on ISDMD was validated in two populations representing different genetic backgrounds. Our results suggest that it may also be advantageous to simultaneously overlap these QTLs around the vrs1 locus.
  • Authors:
    • Prasad, V.
    • Staggenborg, S.
    • Assefa, Y.
  • Source: Crop Management
  • Issue: November
  • Year: 2010
  • Summary: Because sorghum is a drought-tolerant crop, it is often preferred by producers in cases of expected water stress. The objectives of this review were to summarize the water requirements, effect of water stress, and hybrid variation in drought tolerance of grain sorghum, and to suggest possible solutions that could help narrow the gap between potential and actual dryland sorghum yield. We reviewed more than 70 reports in peer-reviewed journals, extension publications, books, and websites. Grain sorghum tolerates and avoids drought more than many other cereal crops, but the drought response of sorghum does not come without a yield loss. Water stress at the vegetative stage alone can reduce yield more than 36%, and water stress at the reproductive stage can reduce yield more than 55%. Eighty percent of sorghum production in the world is under dryland conditions. We deduced that by focusing on techniques that can improve water availability in sorghum growing season alone, we can double the current dryland sorghum yield with the existing genetic potential. Results of this review suggest the existence of genotypic variation in drought tolerance among sorghum hybrids due to possible physiological differences or vice versa. We concluded by presenting possible management options to reduce the effects of water stress in dryland conditions and suggesting possible areas of research.
  • Authors:
    • Wallwork, H.
    • Tester, M.
    • Hassan, M.
    • Lott, G.
    • Verbyla, A. P.
    • Oldach, K.
    • Genc, Y.
    • McDonald, G. K.
  • Source: Theoretical and Applied Genetics
  • Volume: 121
  • Issue: 5
  • Year: 2010
  • Summary: Worldwide, dryland salinity is a major limitation to crop production. Breeding for salinity tolerance could be an effective way of improving yield and yield stability on saline-sodic soils of dryland agriculture. However, this requires a good understanding of inheritance of this quantitative trait. In the present study, a doubled-haploid bread wheat population (Berkut/Krichauff) was grown in supported hydroponics to identify quantitative trait loci (QTL) associated with salinity tolerance traits commonly reported in the literature (leaf symptoms, tiller number, seedling biomass, chlorophyll content, and shoot Na + and K + concentrations), understand the relationships amongst these traits, and determine their genetic value for marker-assisted selection. There was considerable segregation within the population for all traits measured. With a genetic map of 527 SSR-, DArT- and gene-based markers, a total of 40 QTL were detected for all seven traits. For the first time in a cereal species, a QTL interval for Na + exclusion ( wPt-3114-wmc170) was associated with an increase (10%) in seedling biomass. Of the five QTL identified for Na + exclusion, two were co-located with seedling biomass (2A and 6A). The 2A QTL appears to coincide with the previously reported Na + exclusion locus in durum wheat that hosts one active HKT1; 4 ( Nax1) and one inactive HKT1; 4 gene. Using these sequences as template for primer design enabled mapping of at least three HKT1; 4 genes onto chromosome 2AL in bread wheat, suggesting that bread wheat carries more HKT1; 4 gene family members than durum wheat. However, the combined effects of all Na + exclusion loci only accounted for 18% of the variation in seedling biomass under salinity stress indicating that there were other mechanisms of salinity tolerance operative at the seedling stage in this population. Na + and K + accumulation appear under separate genetic control. The molecular markers wmc170 (2A) and cfd080 (6A) are expected to facilitate breeding for salinity tolerance in bread wheat, the latter being associated with seedling vigour.
  • Authors:
    • Kephart, K. D.
    • Klouser, L.
    • Johnston, J. A.
    • Johnston, R. H.
    • Hogg, A. C.
    • Dyer, A. T.
  • Source: Phytopathology
  • Volume: 100
  • Issue: 1
  • Year: 2010
  • Summary: Caused by a complex of Fusarium species including F. culmorum, F. graminearum, and F. pseudograminearum, Fusarium crown rot (FCR) is an important cereal disease worldwide. For this study, Fusarium population dynamics were examined in spring wheat residues sampled from dryland field locations near Bozeman and Huntley, MT, using a quantitative real-time polymerase chain reaction (qPCR) Taqman assay that detects F. culmorum, F. graminearum, and F. pseudograminearum. Between August 2005 and June 2007, Fusarium populations and residue decomposition were measured eight times for standing stubble (0 to 20 cm above the soil surface), lower stem (20 to 38 cm), middle stem (38 to 66 cm), and chaff residues. Large Fusarium populations were found in stubble collected in August 2005 from F. pseudograminearum-inoculated plots. These populations declined rapidly over the next 8 months. Remnant Fusarium populations in inoculated stubble were stable relative to residue biomass from April 2006 until June 2007. These two phases of population dynamics were observed at both locations. Relative to inoculated stubble populations, Fusarium populations in other residue fractions and from noninoculated plots were small. In no case were FCR species observed aggressively colonizing noninfested residues based on qPCR data. These results suggest that Fusarium populations are unstable in the first few months after harvest and do not expand into noninfested wheat residues. Fusarium populations remaining after 8 months were stable for at least another 14 months in standing stubble providing significant inoculums for newly sown crops.
  • Authors:
    • Starkey, S.
    • Reese, J.
    • Viswanathan, P.
    • Orozco, G. V.
    • Cardona, P. S.
    • Khan, S. A.
    • Murugan, M.
    • Smith, C. M.
  • Source: Journal of Economic Entomology
  • Volume: 103
  • Issue: 3
  • Year: 2010
  • Summary: The Russian wheat aphid, Diruaphis noxia (Kurdjumov) (Hemiptera: Aphididae), is globally one of the most devastating pests of bread wheat, Tritium aestivum L.; durum wheat, Triticum turgidum L.; and barley, Hordeum vulgare L. Host plant resistance is the foundation for cereal insect pest management programs, and several sources of D. noxia resistance have been incorporated in cultivars to manage D. noxia damage. The emergence of D. noxia North American biotype 2 (RWA2) in Colorado has made all known Dn genes vulnerable except the Dn7 gene from rye, Secale cereale, and has warranted exploration for sources of resistance to both RWA1 and RWA2. The category of resistance in resistant donor plants may exert selection pressure over the aphid population to form a new virulent population. In the current study, we report tolerance and antibiosis resistance to RWA1 and RWA2 in the barley genotype 'Stoneham'. The rate and degree of expression of resistance in Stoneham against RWA1 and RWA2, although not similar, are greater than the partial resistance in 'Sidney'. Antixenosis resistance to RWA1 or RWA2 was not observed in Sidney or Stoneham. The tolerance identified in Stoneham is encouraging because it may delay D. noxia biotype selection and fits well in a dryland barley cropping system.
  • Authors:
    • McLaughlin, M. J.
    • McBeath, T. M.
    • Noack, S. R.
  • Source: Crop & Pasture Science
  • Volume: 61
  • Issue: 8
  • Year: 2010
  • Summary: Although not commonly used in dryland cropping systems to date, foliar phosphorus (P) fertilisation may allow a tactical response to prevailing seasonal climatic conditions, with the added benefit of reduced input costs at sowing. However, variable outcomes have been reported from field trials predominantly conducted in the USA, and to a lesser degree in Australia. The effectiveness of foliar P is dependent on soil P status, soil water status, crop type, fertiliser formulation and prevailing climatic conditions. This review argues that the potential of foliar P fertilisation in Australian dryland cereal cropping could be enhanced by altering formulations for enhanced leaf penetration using adjuvants, and by accurately assessing the responsiveness of sites before application. This review demonstrates that it is important to use appropriate techniques such as isotopic labelling, to measure the efficacy and mode of action of foliar formulations.
  • Authors:
    • WCI
  • Volume: 2010
  • Year: 2010
  • Summary: Welcome to the Western Climate Initiative (WCI). The WCI is a collaboration of independent jurisdictions working together to identify, evaluate, and implement emissions trading policies to tackle climate change at a regional level. This is a comprehensive effort to reduce greenhouse gas pollution, spur investment in clean-energy technologies that create green jobs and reduce dependence on imported oil.
  • Authors:
    • Kovar, J. L.
    • Schultz, R. C.
    • Powers, W. J.
    • Russell, J. R.
    • Ahmed, S. I.
    • Mickelson, S. K.
    • Webber, D. F.
  • Source: Journal of Soil and Water Conservation
  • Volume: 65
  • Issue: 1
  • Year: 2010
  • Summary: Livestock grazing in the Midwestern United States can result in significant levels of runoff sediment and nutrient losses to surface water resources. Some of these contaminants can increase stream eutrophication and are suspected of contributing to hypoxic conditions in the Gulf of Mexico. This research quantified effects of livestock grazing management practices and vegetative filter strip buffers on runoff depth and mass losses of total solids, nitrate-nitrogen (NO3-N), and ortho-phosphorus (PO4-P) under natural hydrologic conditions. Runoff data were collected from 12 rainfall events during 2001 to 2003 at an Iowa State University research farm in central Iowa, United States. Three vegetative buffers (paddock area: vegetative buffer area ratios of 1:0.2, 1:0.1, and 1:0 no buffer [control]) and three grazing management practices (continuous, rotational, and no grazing [control]) comprised nine treatment combinations (vegetative buffer ratio/grazing management practice) replicated in three 1.35 ha (3.34 ac) plot areas. The total 4.05 ha (10.02 ac) study area also included nine 0.4 ha (1.0 ac) paddocks and 27 vegetative buffer runoff collection units distributed in a randomized complete block design. The study site was established on uneven terrain with a maximum of 15% slopes and consisted of approximately 100% cool-season smooth bromegrass. Average paddock and vegetative buffer plant tiller densities estimated during the 2003 project season were approximately 62 million and 93 million tillers ha(-1) (153 million and 230 million tillers ac(-1)), respectively. Runoff sample collection pipe leakage discovered and corrected during 2001 possibly reduced runoff depth and affected runoff contaminant mass losses data values. Consequently, 2001 runoff analysis results were limited to treatment comparisons, within the 2061 season and were not compared with 2002 and 2003 data. Analysis results from 2001 showed no significant differences in average losses of runoff, total solids, NO3-N, and PO4-P among the nine vegetative buffer/grazing practice treatment combinations. Results from 2002 indicated significantly higher losses of runoff and total solids from 1:0 no buffer/rotational grazing and 1:0 no buffer/continuous grazing treatment combination plots, respectively, compared among other 2002 season treatment combinations. The 2003 results showed significantly higher runoff and total solids losses from 1:0 no buffer/no grazing treatment combination plots compared among all 2003 treatment combinations and from 1:0.1 vegetative buffer/no grazing treatment combination plots compared among all 2003 treatment combinations and with respective 2002 treatment combinations. However, the 2003 results indicated effective vegetative buffer performance with significantly lower runoff, total solids, and NO3-N losses from the larger 1:0.2 buffer area compared among the smaller 1:0.1 buffer area and 1:0 no buffer treatment combinations. The 2003 results also indicated a highly significant increase in losses of NO3-N from 1:0.1 buffer/no grazing treatment combination plots compared among other 2003 season treatment combinations and with respective 2002 treatment combinations. Overall results from this study suggest a shift from significantly higher 2002 season plot losses Of Continuous and rotational grazing treatment combinations to significantly higher 2003 season losses of no grazing treatment combinations. We speculate this shift to significantly higher runoff and contaminant losses from no grazing treatment combination plots during 2003 reflects the variability inherent to a complex and dynamic soil-water environmental of livestock grazing areas. however, we also hypothesize the environmental conditions that largely consisted of a dense perennial cool-season grass type, high-relief landscape, and relatively high total rainfall depth may not necessarily include livestock grazing activities.
  • Authors:
    • Post, W. M.
    • Ugarte, D. J. D. L. T.
    • Nelson, R. G.
    • Marland, G.
    • Wilson, B. S.
    • Yang, B.
    • Bandaru, V.
    • Bernacchi, C. J.
    • Mueller, R.
    • Hellwinckel, C. M.
    • Baskaran, L. M.
    • Brandt, C. C.
    • West, T. O.
  • Source: Ecological Applications
  • Volume: 20
  • Issue: 4
  • Year: 2010
  • Summary: Net annual soil carbon change, fossil fuel emissions from cropland production, and cropland net primary production were estimated and spatially distributed using land cover defined by NASA's moderate resolution imaging spectroradiometer (MODIS) and by the USDA National Agricultural Statistics Service (NASS) cropland data layer (CDL). Spatially resolved estimates of net ecosystem exchange (NEE) and net ecosystem carbon balance (NECB) were developed. The purpose of generating spatial estimates of carbon fluxes, and the primary objective of this research, was to develop a method of carbon accounting that is consistent from field to national scales. NEE represents net on-site vertical fluxes of carbon. NECB represents all on-site and off-site carbon fluxes associated with crop production. Estimates of cropland NEE using moderate resolution (1 km2) land cover data were generated for the conterminous United States and compared with higher resolution (30-m) estimates of NEE and with direct measurements of CO2 flux from croplands in Illinois and Nebraska, USA. Estimates of NEE using the CDL (30-m resolution) had a higher correlation with eddy covariance flux tower estimates compared with estimates of NEE using MODIS. Estimates of NECB are primarily driven by net soil carbon change, fossil fuel emissions associated with crop production, and CO2 emissions from the application of agricultural lime. NEE and NECB for U.S. croplands were -274 and 7 Tg C/yr for 2004, respectively. Use of moderate- to high-resolution satellite-based land cover data enables improved estimates of cropland carbon dynamics.