• Authors:
    • Mollah, M.
    • Partington, D.
    • Fitzgerald, G.
  • Source: Crop and Pasture Science
  • Volume: 62
  • Issue: 10
  • Year: 2011
  • Summary: Carbon dioxide (CO2) is the most important greenhouse gas, predicted to increase globally from currently 386 to 550 μmol mol–1 by 2050 and cause significant stimulation to plant growth. Consequently, in 2007 and 2008, Australian grains free-air carbon dioxide enrichment (AGFACE) facilities were established at Horsham (36°45′07″S lat., 142°06′52″E long., 127 m elevation) and Walpeup (35°07′20″S lat., 142°00′18″E long., 103 m elevation) in Victoria, Australia to investigate the effects of elevated CO2, water supply and nitrogen fertiliser on crop growth. Understanding the distribution patterns of CO2 inside AGFACE rings is crucial for the interpretation of the crop growth data. In the AGFACE system, the engineering performance goal was set as having at least 80% of the ring area with a CO2 concentration [CO2] at or above 90% of the target concentration at the ring-centre for 80% of the time. The [CO2] was highly variable near the ring-edge where CO2 is emitted and declined non-linearly with the distance downwind and wind speeds. Larger rings maintained the target [CO2] of 550 μmol mol–1 at the ring-centres better than the smaller rings. The spatial variation of [CO2] depended on ring size and the gap between fumigation and canopy heights but not on wind speeds. The variations in the inner 80% of the rings were found to be higher in smaller rings, implying that the larger rings had more areas of relatively uniform [CO2] to conduct experiments.
  • Authors:
    • Shelton, H. M.
    • Radrizzani, A.
    • Kirchhof, G.
    • Dalzell, S. A.
  • Source: Crop and Pasture Science
  • Volume: 62
  • Issue: 4
  • Year: 2011
  • Summary: Soil organic carbon (OC) and total nitrogen (TN) accumulation in the top 0–0.15 m of leucaena–grass pastures were compared with native pastures and with continuously cropped land. OC and TN levels were highest under long-term leucaena–grass pasture (P < 0.05). For leucaena–grass pastures that had been established for 20, 31, and 38 years, OC accumulated at rates that exceeded those of the adjacent native grass pasture by 267, 140, and 79 kg/ha.year, respectively, while TN accumulated at rates that exceeded those of the native grass pastures by 16.7, 10.8, and 14.0 kg/ha.year, respectively. At a site where 14-year-old leucaena–grass pasture was adjacent to continuously cropped land, there were benefits in OC accumulation of 762 kg/ha.year and in TN accumulation of 61.9 kg/ha.year associated with the establishment of leucaena–grass pastures. Similar C : N ratios (range 12.7–14.5) of soil OC in leucaena and grass-only pastures indicated that plant-available N limited soil OC accumulation in pure grass swards. Higher OC accumulation occurred near leucaena hedgerows than in the middle of the inter-row in most leucaena–grass pastures. Rates of C sequestration were compared with simple models of greenhouse gas (GHG) emissions from the grazed pastures. The amount of carbon dioxide equivalent (CO2-e) accumulated in additional topsoil OC of leucaena–grass pastures ≤20 years old offset estimates of the amount of CO2-e emitted in methane and nitrous oxide from beef cattle grazing these pastures, thus giving positive GHG balances. Less productive, aging leucaena pastures >20 years old had negative GHG balances; lower additional topsoil OC accumulation rates compared with native grass pastures failed to offset animal emissions
  • Authors:
    • Rodriguez, L. C.
    • May, B.
    • Herr, A.
    • Farine, D.
    • O'Connell, D.
  • Source: Energy Policy
  • Volume: 39
  • Issue: 4
  • Year: 2011
  • Authors:
    • Bird, M. I.
    • Beeton, R. J. S.
    • Menzies, N. W.
    • Witt, G. B.
    • Noel, M. V.
  • Source: Agriculture, Ecosystems & Environment
  • Volume: 141
  • Issue: 1-2
  • Year: 2011
  • Authors:
    • Blanco-Canqui, H.
  • Source: Soil Use and Management
  • Volume: 27
  • Issue: 1
  • Year: 2011
  • Summary: Soil water repellency (SWR) is an intrinsic and dynamic soil property that can influence soil hydrology and crop production. Although several land use systems have been shown to induce water repellency in soil, the specific effects of no-till cropping on SWR are poorly understood. This article reviews the impacts of no-till on SWR and identifies research needs. No-till cropping generally induces 1.5 to 40 times more SWR than conventional tillage, depending on soil type. This may result from near-surface accumulation of hydrophobic organic C compounds derived from crop residues, microbial activity and reduced soil disturbance. While large SWR may have adverse impacts on soil hydrology and crop production, the level of SWR under no-till relative to conventional tillage may contribute to aggregate stabilization and intra-aggregate C sequestration. More research is needed to discern the extent and relevance of no-till induced SWR. This includes: (1) further assessment of SWR under different tillage systems across a wide range of soil textures and climates, (2) comparison of the various methods for measuring SWR over a range of water contents, (3) inclusion of SWR in routine soil analysis and its use as a parameter to evaluate management impacts, (4) assessment of the temporal and spatial changes in SWR under field conditions, (5) further assessment of the impacts of the small differences in SWR between no-till and conventionally tilled soils on crop production, soil hydrology and soil C sequestration, and (6) development of models to predict SWR for different tillage systems and soils.
  • Authors:
    • Blanco-Canqui, H.
    • Mikha, M. M.
    • Presley, D. R.
    • Claassen, M. M.
  • Source: Soil Science Society of America Journal
  • Volume: 75
  • Issue: 4
  • Year: 2011
  • Summary: Inclusion of cover crops (CCs) may be a potential strategy to boost no-till performance by improving soil physical properties. To assess this potential, we utilized a winter wheat ( Triticum aestivum L.)-grain sorghum [ Sorghum bicolor (L.) Moench] rotation, four N rates, and a hairy vetch (HV; Vicia villosa Roth) CC after wheat during the first rotation cycles, which was replaced in subsequent cycles with sunn hemp (SH; Crotalaria juncea L.) and late-maturing soybean [LMS; Glycine max (L.) Merr.] CCs in no-till on a silt loam. At the end of 15 yr, we studied the cumulative impacts of CCs on soil physical properties and assessed relationships between soil properties and soil organic C (SOC) concentration. Across N rates, SH reduced near-surface bulk density (rho b) by 4% and increased cumulative infiltration by three times relative to no-CC plots. Without N application, SH and LMS reduced Proctor maximum rho b, a parameter of soil compactibility, by 5%, indicating that soils under CCs may be less susceptible to compaction. Cover crops also increased mean weight diameter of aggregates (MWDA) by 80% in the 0- to 7.5-cm depth. The SOC concentration was 30% greater for SH and 20% greater for LMS than for no-CC plots in the 0- to 7.5-cm depth. The CC-induced increase in SOC concentration was negatively correlated with Proctor maximum rho b and positively with MWDA and cumulative infiltration. Overall, addition of CCs to no-till systems improved soil physical properties, and the CC-induced change in SOC concentration was correlated with soil physical properties.
  • Authors:
    • Chamberlain, J. F.
    • Miller, S. A.
    • Frederick, J. R.
  • Source: Agriculture, Ecosystems & Environment
  • Volume: 141
  • Issue: 3-4
  • Year: 2011
  • Summary: Use of a simulation model to predict long-term yield, greenhouse gas (GHG) emissions, and water quality impacts can be valuable for assessing land use conversion to bioenergy crops. The objective of this study is to assess the usability of DAYCENT for measuring environmental impacts due to land conversions from cotton and CRP lands (as unmanaged grasses) to switchgrass in the Southern U.S. We use published yield data to calibrate the crop growth parameters and test the calibrated model on independent data sets. We then apply the model to predict other relevant C and N parameters. In the case of cotton, the model simulates long-term mean cotton lint yield within 25% of observed yields across the South and within 4% of yields in the case study area of Darlington County, SC. DAYCENT also matches observed mature switchgrass yields within 25% of the mean in the range of expected fertilization rates across the region and within 6% in the case study area. Long-term simulations predict a decrease in GHG emissions (1.0-3.8 MtCO 2-e/ha-yr) and a reduction of nitrate runoff (up to 95%) for conversions from cotton to switchgrass at N application rates of 0-135 kgN/ha. Conversely, conversion from unmanaged grasses to switchgrass resulted in annual increases of net GHG emissions (0.2-1.4 MtCO 2-e/ha-yr) for switchgrass at no and low (45 kgN/ha) fertilization rates. Sequestration occurs due to increased soil organic C when higher levels of N are applied. At all levels of fertilization, a reduction of nitrate (50-70%) occurs when converting from unmanaged, unharvested grasses. The amount of nitrate leaching is only slightly sensitive to the fertilization rate applied to the perennial switchgrass. DAYCENT sufficiently models the "carbon debt" from land use conversion from CRP grasslands to managed switchgrass and highlights the importance of fertilization rate. Both C and N parameter results fall within published observed ranges. Thus, the long-term (10-15-year) accuracy of the model for both cotton and switchgrass offers promise as a tool for analyzing land use conversions in terms of N-managed yields and subsequent environmental impacts and benefits.
  • Authors:
    • Chen, G.
    • Weil, R. R.
  • Source: Soil & Tillage Research
  • Volume: 117
  • Year: 2011
  • Summary: The yield of rainfed crops is commonly limited by the availability of soil water during the summer growing season. Channels produced by cover crop roots in fall/winter when soils are relatively moist may facilitate the penetration of compacted soils by subsequent crop roots in summer when soils are relatively dry and hard. Our objective was to determine the effects of fall cover crops on maize (Zea mays) growth and soil water status under three levels (high, medium, and no) of imposed traffic compaction. The study was conducted on coastal plain soils (fine-loamy Typic/Aquic hapludults and siliceous, Psammentic hapludults) in the mid-Atlantic region of the United States from 2006 to 2008. Cover crop treatments were FR (forage radish: Raphanus sativus var. longipinnatus, cv. 'Daikon'), rapeseed (Brassica napus, cv. 'Essex'), rye (cereal rye: Secale cereale L, cv. 'Wheeler') and NCC (no cover crop). Maize under high compaction achieved more deep-roots following FR and rapeseed than following rye or NCC. However, maize had greater yield following all cover crops than NCC control regardless of compaction levels and soil texture. Compaction reduced maize yield only under the high compaction in the lightly textured soils. During 24 June-24 July 2008, soils at 15 and 50 cm depths were drier under no compaction than high compaction and drier following FR than other cover crop treatments. Our results suggest that FR benefited maize root penetration in compacted soils while rye provided the best availability of surface soil water; rapeseed tended to provide both benefits. However, as rapeseed is relatively difficult to kill in spring, a mixture of FR and rye cover crops might be most practical and beneficial for rainfed summer crops under no-till systems in regions with cool to temperate, humid climates.
  • Authors:
    • Cheng, L.
    • Booker, F. L.
    • Burkey, K. O.
    • Tu, C.
    • Shew, H. D.
    • Rufty, T. W.
    • Fiscus, E. L.
    • Deforest, J. L.
    • Hu, S. J.
  • Source: PLOS ONE
  • Volume: 6
  • Issue: 6
  • Year: 2011
  • Summary: Climate change factors such as elevated atmospheric carbon dioxide (CO 2) and ozone (O 3) can exert significant impacts on soil microbes and the ecosystem level processes they mediate. However, the underlying mechanisms by which soil microbes respond to these environmental changes remain poorly understood. The prevailing hypothesis, which states that CO 2- or O 3-induced changes in carbon (C) availability dominate microbial responses, is primarily based on results from nitrogen (N)-limiting forests and grasslands. It remains largely unexplored how soil microbes respond to elevated CO 2 and O 3 in N-rich or N-aggrading systems, which severely hinders our ability to predict the long-term soil C dynamics in agroecosystems. Using a long-term field study conducted in a no-till wheat-soybean rotation system with open-top chambers, we showed that elevated CO 2 but not O 3 had a potent influence on soil microbes. Elevated CO 2 (1.5 * ambient) significantly increased, while O 3 (1.4 * ambient) reduced, aboveground (and presumably belowground) plant residue C and N inputs to soil. However, only elevated CO 2 significantly affected soil microbial biomass, activities (namely heterotrophic respiration) and community composition. The enhancement of microbial biomass and activities by elevated CO 2 largely occurred in the third and fourth years of the experiment and coincided with increased soil N availability, likely due to CO 2-stimulation of symbiotic N 2 fixation in soybean. Fungal biomass and the fungi:bacteria ratio decreased under both ambient and elevated CO 2 by the third year and also coincided with increased soil N availability; but they were significantly higher under elevated than ambient CO 2. These results suggest that more attention should be directed towards assessing the impact of N availability on microbial activities and decomposition in projections of soil organic C balance in N-rich systems under future CO 2 scenarios.
  • Authors:
    • Crusciol, C. A. C.
    • Garcia, . A.
    • Castro, G. S. A.
    • Rosolem, C. A.
  • Source: Revista Brasileira de Ciência do Solo
  • Volume: 35
  • Issue: 6
  • Year: 2011
  • Summary: Especially under no-tillage, subsuface soil acidity has been a problem, because it depends on base leaching, which has been associated with the presence of low molecular weigth organic acids and companion anions. The objective of this study was to evaluate exchangeable base cation leaching as affected by surface liming along with annual urea side-dressing of maize and upland rice. Treatments consisted of four lime rates (0, 1500, 3000, and 6000 kg ha -1) combined with four nitrogen rates (0, 50, 100, and 150 kg ha -1) applied to maize ( Zea mays) and upland rice ( Oryza sativa), in two consecutive years. Maize was planted in December, three months after liming. In September of the following year, pearl millet ( Pennisetum glaucum) was planted without fertilization and desiccated 86 days after plant emergence. Afterwards, upland rice was grown. Immediately after upland rice harvest, 18 months after surface liming, pH and N-NO 3-, N-NH 4+, K, Ca, and Mg levels were evaluated in soil samples taken from the layers 0-5, 5-10, 10-20 and 20-40 cm. Higher maize yields were obtained at higher N rates and 3000 kg ha -1lime. Better results for upland rice and pearl millet yields were also obtained with this lime rate, irrespective of N levels. The vertical mobility of K, Ca and Mg was higher in the soil profiles with N fertilization. Surface liming increased pH in the upper soil layers causing intense nitrate production, which was leached along with the base cations.