• Authors:
    • Martz, L. W.
    • Pomeroy,J. W.
    • Armstrong, R. W.
  • Source: Canadian Water Resources Journal
  • Volume: 35
  • Issue: 2
  • Year: 2010
  • Summary: Physically-based atmospheric models of evapotranspiration (ET) that consider the Penman combination energy balance and aerodynamic approach have achieved acceptance as useful tools for obtaining estimates of actual ET from land surfaces. These models have been made applicable to the case of non-saturated conditions through either surface resistance formulations (e.g., Penman-Monteith) or by application of the complementary evaporation theory of feedback between the atmosphere and surface moisture states (e.g., Granger-Gray). Their application becomes complicated under conditions of drought, when extremely low soil moisture availability severely restricts ET from the soil and plants. Under such severe conditions, consideration for the surface water balance and interactions with the balance of available energy and aerodynamic principles are Important for accurately estimating actual ET A modelling application is demonstrated using the Cold Regions Hydrological Model (CRHM) platform to examine the estimation of ET under drought conditions. CRHM allows users to assemble hydrological models by linking a suite of modular physically-based algorithms that describe the individual processes. In this case, the models assembled consider infiltration, evaporation, and sod moisture accounting and are applied to a mixed prairie located at Lethbridge, Alberta, Canada under drought conditions during the growing period in 2000 and 2001. Near surface meteorological and ecological observations used as model input and for evaluating model performance were obtained through the Ameriflux network and the Agriculture and Agri-Food Canada (AFC) Lethbridge Research Centre Results show that consideration for the effective rooting zone depth of the mixed-prairie at the site is important for estimating actual ET using the Penman-Montieth and Granger-Gray models during severe moisture stress. Relative differences in ET estimates provided by the models are discussed in the context of their contrasting theoretical approaches.
  • Authors:
    • Paltridge, N.
    • Tao, J.
    • Unkovich, M.
    • Gason, A.
    • Grover, S.
    • Wilkins, J.
    • Coventry, D.
    • Tashi, N.
    • Bonamano, A.
  • Source: Crop & Pasture Science
  • Volume: 60
  • Issue: 7
  • Year: 2009
  • Summary: In the south of the Tibet Autonomous Region of China there is a network of valleys where intensive agriculture is practiced. Although considered highly productive by Tibetans, farm incomes in the region are low, leading to a range of government initiatives to boost grain and fodder production. However, there is limited information available on current farming practices, yields, and likely yield constraints. The present paper uses available data and farmer interviews to describe the agro-climate and current systems of crop and livestock production, and considers possible strategies to boost production. Although winters in Tibet are cold and dry, summer and autumn provide ideal conditions for crop growth. Cropping systems are characterised by heavy tillage, frequent irrigation, high seeding rates and fertiliser applications, some use of herbicides, and little stubble retention or mechanisation. Spring barley and winter wheat are the predominant crops, followed by rapeseed, winter barley, and minor fodder and vegetable crops. Average yields for the main grain crops are around 4.0 t/ha for spring barley and 4.5 t/ha for winter wheat, significantly lower than should be possible in the environment. Farmers typically keep five or six cattle tethered near the household. Cattle are fed diets based on crop residues but are generally malnourished and rarely produce beyond the needs of the family. It is suggested that research and extension in the areas of crop nutrition, weed control, irrigation, seeding technology, and crop varieties should enable significant increases in grain yield. Increases in cattle production will require increases in the supply of good quality fodder. Cereal/fodder intercrops or double crops sown using no-till seed drills might enable the production of useful amounts of fodder in many areas without jeopardising food grain supply, and allow more crop residues to be retained in fields for improved soil health.
  • Authors:
    • Veiga, M.
    • Pelissari, A.
    • Moraes, A.
    • Balbinot Junior, A.
    • Dieckow, J.
    • Nesi, C.
  • Source: Revista de Ciencias Agroveterinarias
  • Volume: 8
  • Issue: 1
  • Year: 2009
  • Summary: Animal trampling is one of the major causes of soil compaction in areas subjected to integrated crop-livestock system. The objective of this work was to evaluate the effect of winter annual pasture grazing, in crop-livestock system, and other winter soil uses on soil compaction. The experiment was carried out from May 2006 to February 2007 at three sites of the North Plateau of Santa Catarina State, Brazil. Five winter treatments were investigated on each site: (1) intercropping with black oat+ryegrass+vetch+arrow leaf clover without grazing and nitrogen fertilization (multicropping cover); (2) the same intercropping, with grazing and 100 kg ha -1 of nitrogen, (grazing with N); (3) the same intercropping, with grazing and without nitrogen fertilization (grazing without N); (4) oil seed radish, without grazing and nitrogen fertilization (oil seed radish); and (5) natural vegetation, without grazing and nitrogen fertilization (fallow). Undisturbed cores were collected from the layers 2 to 7 cm and 10 to 15 cm, at three times: experiments implantation (May 2006), at maize sowing in succession of winter soil use (November 2006) and close to maize physiological maturity (February 2007). Soil total porosity, bulk density and soil resistance to penetration were evaluated in these samples. According to the environmental and management conditions, as well as the time of experimentation, the livestock presence in winter pastures, winter cover crops and fallow did not affect the variables related to soil compaction.
  • Authors:
    • Dieckow, J.
    • Pelissari, A.
    • Veiga, M.
    • Moraes, A.
    • Balbinot Junior, A.
    • Carvalho, P.
  • Source: Ciencia Rural
  • Volume: 39
  • Issue: 8
  • Year: 2009
  • Summary: Soil use and management during the winter can affect soil physical properties, reminiscent straw and performance of the crop cultivated in succession. The effect of winter soil use on these variables, cultivating black bean ( Phaseolus vulgaris) under no tillage system in summer, was investigated. Three experiments were carried out in the North Plateau of Santa Catarina State, Brazil, during 2007/08 crop season, with five strategies of soil use during the winter: (1) multicropping with black oat+ryegrass+commom vetch+arrow leaf clover ( Trifolium vesiculosum) without grazing and N application (multicropping cover); (2) the same multicropping, with grazing and 100 kg N ha -1 application (pasture with N); (3) the same multicropping, with grazing and without N application (pasture without N); (4) oil seed radish, without grazing and N application (oil seed radish); and (5) natural vegetation, without grazing and N application (fallow). The highest straw dry mass was verified in multicropping cover, but the strategies of winter soil use did not affect significantly the soil bulk density and macroporosity. The soil use with winter annual pasture in crop-livestock system, cover crops and fallow did not affect the black bean performance in succession, under no tillage system.
  • Authors:
    • Kreuzer, M.
    • Wettstein, H.
    • Gomez, C.
    • Gamarra, J.
    • Bartl, K.
    • Hess, H.
  • Source: Grass and Forage Science
  • Volume: 64
  • Issue: 2
  • Year: 2009
  • Summary: The agronomic performance and nutritive value of twelve annual and perennial grasses and legumes were analysed in order to define alternatives to local forages for dry-season feeding of ruminants in the Peruvian Andes. There were twelve species and two fertilizer treatments (no fertilizer and a N;P;K fertilizer mainly applied at sowing) in an experiment with a randomized complete block design with three replicates at each of two sites. Plant height, soil cover by forage and weed species, frost damage, dry matter (DM) yield and nutritive value of herbage were evaluated in 2005 and 2006. Among the annual species, Hordeum vulgare L. cv. UNA 80 and * Triticosecale Wittm. had the highest DM yields when fertilized (8226 and 6934 kg ha -1 respectively). Without fertilizer the alternative cultivars had similar DM yields to that of the local forages. Cultivars of Avena sativa L. had lower concentrations of neutral-detergent fibre (NDF) (557 g kg -1 DM) and higher concentrations of predicted net energy for lactation (5.86 MJ kg -1 DM) than the other annual grass species (625 g kg -1 DM and 5.01 MJ kg -1 DM respectively), while the legumes were superior in concentrations of crude protein (277 g kg -1 DM) and NDF (362 g kg -1 DM). Considering the low agronomic performance of the perennial forages, a mixture of fertilized annual grasses and legumes appears the most appropriate approach to meeting the demand for forage of high nutritive value in the Peruvian highlands.
  • Authors:
    • Cao, E.
    • Andrigueti, M.
    • Carvalho, P.
    • Anghinoni, I.
    • Costa, S.
    • Souza, E.
  • Source: REVISTA BRASILEIRA DE CIENCIA DO SOLO
  • Volume: 33
  • Issue: 6
  • Year: 2009
  • Summary: The potential for adopting crop-livestock systems in southern Brazil is high, especially in untilled soybean areas with cover crops in the winter season. The long-term use of this system at different grazing intensities will result in different carbon and nitrogen stocks in the soil due to the different plant and animal residues. This research was conducted to evaluate alterations in total carbon and nitrogen pools and in organic matter fractions in a soil under different grazing intensities under no-tillage. The experiment on a Rhodic Hapludult (Oxisol) was initiated in 2001, after soybean harvest. The treatments were different cattle grazing (black oat+ryegrass) pressures (10, 20 and 40 cm sward height) and an ungrazed treatment in the winter and soybean in the summer, in a randomized block design. Soil samples were taken at the beginning of the experiment (May, 2001), after three years (May, 2004) and after six years (May, 2007) to evaluate the content and stocks of organic carbon and nitrogen. Moderate grazing intensities (20 and 40 cm plant height) resulted in an increase of total carbon and nitrogen and in the organic matter particulate fraction, similarly to the ungrazed area. However, at the most intensive grazing pressure (10 cm plant height) there were losses in the stocks of these elements and reduction in soil organic matter quality.
  • Authors:
    • Davis, A.
    • Tracy, B.
  • Source: Crop Science
  • Volume: 49
  • Issue: 4
  • Year: 2009
  • Summary: Crop and livestock production are rarely integrated together in modern farming systems. Reintegrating crops with livestock production has been shown to produce many agronomic and environmental benefits. The objective of this study was to evaluate how an integrated crop-livestock system would influence weed biomass and weed species composition compared with a conventional, continuous corn ( Zea mays L.) cropping system. The experimental farming system used in this study was established on a 90-ha site near Pana, IL, in 2002. The integrated system included two phases: (i) a corn and oat ( Avena sativa L.) cash crop rotation, grown in summer, and (ii) post-harvest grazing of corn stover with annual cover crops. Over a 4-yr period (2004-2007), weed biomass was approximately 4.5 times higher in the conventional system (8.4 g m -2) compared with the integrated system (1.8 g m -2). Weed species composition was affected by the integrated system and showed a temporal disjunction between the time of year and weed life history. Surprisingly, cattle grazing on cropland had little effect on weed biomass or species composition. The primary drivers that suppress weed biomass and change species composition appear to be use of crop rotation and annual cover crops within the integrated system. Wider adoption of integrated crop-livestock systems, such as the one used in this study, should reduce reliance on herbicides compared with more conventional cropping systems.
  • Authors:
    • Cameron, C.
    • Kearney, G.
    • Dowling, P.
    • Quigley, P.
    • Cousens, R.
    • Chapman, D.
    • Tozer, K.
  • Source: Crop & Pasture Science
  • Volume: 60
  • Issue: 11
  • Year: 2009
  • Summary: A field experiment was established in a southern Australian temperate pasture to investigate the effects of identity and proximity of perennial grasses on the demography of the annual grasses Vulpia spp. ( V. myuros, V. bromoides) and Hordeum leporinum (barley grass). Annual grasses were grown either alone or in mixtures, at different distances from rows of Dactylis glomerata (cocksfoot) and Phalaris aquatica (phalaris). Dactylis had a greater suppressive effect than Phalaris on Vulpia and Hordeum. Biomass, tiller production, and panicle production of annual grasses increased linearly with increasing distance from the perennial row. Tiller and panicle production were greater for Vulpia than Hordeum. The estimated rate of population growth (lambda) for annual grasses was greater in Phalaris than in Dactylis and in Vulpia than in Hordeum, and increased with sowing distance from perennial grass rows. It was estimated that lambda, when seeds were sown directly adjacent to a row of perennial grasses, was 1 and 0.4 for Vulpia and Hordeum, respectively, within Dactylis stands, and 7 and 3, respectively, within Phalaris stands. However, 15cm from the row, lambda reached 50 and 39 for Vulpia and Hordeum, respectively, within Phalaris stands, and 39 and 16, respectively, within Dactylis stands. In grazed, dryland pastures, perennial competition alone is therefore unlikely to prevent population growth of annual grasses, especially in systems heavily disturbed by grazing or drought. However, Dactylis showed more promise than Phalaris in limiting the abundance of these weeds.
  • Authors:
    • Smith, K. A.
    • Edwards, A. C.
    • Reay, D. S.
  • Source: Agriculture, Ecosystems & Environment
  • Volume: 133
  • Issue: 3-4
  • Year: 2009
  • Summary: Direct and indirect nitrous oxide (N2O) emissions and leaching losses from an intensively managed grazed pasture in the Ythan catchment, Aberdeenshire, UK, were measured and compared over a 17-month period. Simultaneous measurements of farm-wide leaching losses of N2O were also made and catchment-wide fluxes were estimated from existing N leaching data. The relative importance of direct and indirect N2O fluxes at the field, farm and catchment scale was then assessed. At the field scale we found that direct N2O emissions were low (1.2 kg N ha-1 year-1, 0.6% of N input) with indirect N2O emissions via drainage waters comprising a significant proportion (25%) of total N2O emissions. At the whole-farmscale, the N2O-N emission factor (0.003) for leached NO3-N (EF5-g) was in line with the IPCC's recent downward revision. At the catchment scale, a direct N2O flux of 1.9 kg N ha-1 year-1 and an indirect flux of 0.06 kg N2O-N ha-1 year-1 were estimated. This study lends further support to the recent downward revision of the IPCC emission factor for N2O arising from leached N in surface and ground waters (EF5-g) and highlights the need for multiple point sampling to ensure that the importance of indirect N2O losses via drainage waters is not misrepresented at the farm and catchment scales.
  • Authors:
    • Bryant, R. B.
    • Schmidt, J. P.
    • Kleinman, P. J.
    • Dell, C. J.
    • Skinner, R. H.
    • Soder, K. J.
    • Rotz, C. A.
  • Source: Forage and grazinglands
  • Year: 2009
  • Summary: Incorporating managed rotational grazing into a dairy farm can result in an array of environmental consequences. A comprehensive assessment of the environmental impacts of four management scenarios was conducted by simulating a 250-acre dairy farm typical of Pennsylvania with: (i) a confinement fed herd producing 22,000 lbs of milk per cow per year; (ii) a confinement fed herd producing 18,500 lbs; (iii) a confinement fed herd with summer grazing producing 18,500 lbs; and (iv) a seasonal herd maintained outdoors producing 13,000 lbs. Converting 75 acres of cropland to perennial grassland reduced erosion 24% and sediment-bound and soluble P runoff by 23 and 11%, respectively. Conversion to all perennial grassland reduced erosion 87% with sediment-bound and soluble P lossess reduced to 80 and 23%. Ammonia volatilization was reduced 30% through grazing but nitrate leaching loss increased up to 65%. Grazing systems reduced the net greenhouse gas emission by 8 to 14% and the C footprint of an all grassland farm up to 80% during the transition from cropland. The environmental benefits of grass-fed dairy production should be used to encourage greater adoption of managed rotational grazing in regions where this technology is well adapted.