• Authors:
    • McMahon,Thomas A.
    • Kiem,Anthony S.
    • Peel,Murray C.
    • Jordan,Phillip W.
    • Pegram,Geoffrey G. S.
  • Source: Journal of Hydrometeorology
  • Volume: 9
  • Issue: 6
  • Year: 2008
  • Summary: This paper introduces a new approach to stochastically generating rainfall sequences that can take into account natural climate phenomena, such as the El Nino-Southern Oscillation and the interdecadal Pacific oscillation. The approach is also amenable to modeling projected affects of anthropogenic climate change. The method uses a relatively new technique, empirical mode decomposition (EMD), to decompose a historical rainfall series into several independent time series that have different average periods and amplitudes. These time series are then recombined to form an intradecadal time series and an interdecadal time series. After separate stochastic generation of these two series, because they are independent, they can be recombined by summation to form a replicate equivalent to the historical data. The approach was applied to generate 6-monthly rainfall totals for six rainfall stations located near Canberra, Australia. The cross correlations were preserved by carrying out the stochastic analysis using the Matalas multisite model. The results were compared with those obtained using a traditional autoregressive lag-one [AR(1)], and it was found that the new EMD stochastic model performed satisfactorily. The new approach is able to realistically reproduce multiyear-multidecadal dry and wet epochs that are characteristic of Australia's climate and are not satisfactorily modeled using traditional stochastic rainfall generation methods. The method has two advantages over the traditional AR(1) approach, namely, that it can simulate nonstationarity characteristics in the historical time series, and it is easy to alter the decomposed time series components to examine the impact of anthropogenic climate change.
  • Authors:
    • Sau, F.
    • Pineiro, J.
  • Source: Fourrages
  • Issue: 190
  • Year: 2007
  • Summary: The natural conditions in Galice and northern Spain are favourable for the production of forage, compared to the rest of the country. Agriculture in the country has undergone deep restructurations for the last 50 years, especially on the dairy farms. From 1960s onwards, the acreages of grass-clover leys and of forage maize have been constantly increasing, in parallel with an increasing milk production. The proportion of milk produced from forage crops have remained at 20 to 25%, and a particular effort should be made to reach the goal of 40%. In order to overcome water shortage during summer, the farmers make silage with their spring cuts, use lucerne and purchased feeds, and irrigate at a small scale. The few trials made show that irrigated pastures can increase the average yearly production by 40-45%. Since the water resources are scarce, and must be distributed with other economic activities, there should be no large development of irrigation. To overcome the water shortage during summer, it would seem more realistic to have recourse to more intensive rotations (2 crops per year), in which a crop better adapted to high temperatures and to dry spells would take over the leys. This intensified dry-land system would increase the yearly production by from 50 to 82%.
  • Authors:
    • Schmidt, C. J. J.
    • Adriaanse, F. G.
    • Preez, C. C. du
  • Source: South African Journal of Plant and Soil
  • Volume: 24
  • Issue: 1
  • Year: 2007
  • Summary: The principle objective of this study was to establish P fertilizer guidelines for dryland maize on the South African Highveld according to the sufficiency concept of soil extractable P. Data sets from nine different P fertilizer trials at various localities in the Free State, Gauteng, Mpumalanga and North West provinces were used. Different P treatments were applied for all trials in order to establish differences in extractable soil P levels, which were expected to have corresponding effects on maize yield. Long-term rainfall varied from 765 mm per annum for the Dirkiesdorp trial in the east to 494 mm per annum for the Wolmaransstad trial in the west. The duration of trials varied between one and nine seasons. The clay content of the top 150 mm soil at these localities ranged between 8.4 and 47%. Extractable P threshold values with varying R 2 values were derived for all localities. These values were related to soil properties and it was shown that the degree of leaching and silt-plus-clay content were the parameters that explained most of the variation. However, it was decided only to explore relationships between threshold P values and silt-plus-clay contents in more detail. By excluding data from two localities of which the topsoil contained free lime, the R 2 values of the mentioned relationships improved substantially so that P threshold values could be derived from the silt-plus-clay content range of the other seven localities. The extractable soil P threshold concentrations based on Bray 1 for the top 150 mm soil layer, to obtain 90% relative yield varied from 33.5 mg kg -1 at 13% silt-plus-clay to 14.6 mg kg -1 at 60% silt-plus-clay. These P thresholds were much higher on the sandy soils than the value of 19 mg P kg -1 (Bray 1) for 95% relative yield according to the ARC-Grain Crops Institute (1994) guidelines over all soils. This may not necessarily imply that overall more P fertilizers should be applied, since the corresponding soil sampling procedure also measures residual P from enriched zones over rows where P fertilizer was band-placed. Research results used to establish the ARC-Grain Crops Institute (1994) guidelines excluded sampling from enriched zones over rows.
  • Authors:
    • Moraes, A.
    • Balbinot Junior, A.
    • Backes, R.
  • Source: PLANTA DANINHA
  • Volume: 25
  • Issue: 3
  • Year: 2007
  • Summary: Straw on the soil significantly reduces weed infestation under no-tillage system. The potential of winter cover crops and their management timing in reducing weed infestation in maize crop were studied in Canoinhas, Santa Catarina, Brazil, in 2003/04 and 2004/05. In the first experiment, 6 winter cover crops were investigated: oilseed radish, black oat [ Avena nuda], rye, ryegrass [ Lolium sp.], intercropped among black oat and common vetch [ Vicia sativa] and among oilseed radish, black oat, rye, ryegrass and common vetch. These cover crops were slashed down at three different times before maize sowing (1, 10 and 25 days). In the second experiment, the potential to reduce weed infestation was investigated in the 6 cover crops previously mentioned, plus the common vetch. The straw of ryegrass and from intercropping among the 5 species used had a high capacity to suppress weed emergence and dry matter production, while oilseed radish straw showed low weed suppression potential. The winter cover crops slashed down next to maize sowing decreased the weed infestation.
  • Authors:
    • Backes, R.
    • Moraes, A.
    • Balbinot Junior, A.
    • Souza, A.
  • Source: Scientia Agraria
  • Volume: 8
  • Issue: 2
  • Year: 2007
  • Summary: A study was undertaken in Canoinhas, Santa Catarina, Brazil, during 2004/05 season to evaluate the effect of cover crop desiccation time in relation to maize sowing on the weed infestation and maize yield. Ryegrass ( Lolium multiflorum) as a single crop and in an intercropping system (rye grass+black oat ( Avena strigosa [ A. nuda])+rye+common vetch ( Vicia sativa)+oilseed radish) were desiccated 5 times at 1, 10 20 and 30 days before maize sowing. Cover crop management near maize sowing decreased the density and mass accumulation of weeds and improved the maize grain yield.
  • Authors:
    • Bateman, G.
    • Jenkyn, J.
    • Gutteridge, R.
  • Source: Annals of Applied Biology
  • Volume: 150
  • Issue: 1
  • Year: 2007
  • Summary: Take-all disease ( Gaeumannomyces graminis var. tritici) in wheat crops is known to be suppressed by naturally occurring antagonistic fungi, closely related to the pathogen, that infect grasses and cereals. This form of suppression was re-investigated because of the changing importance and role of grass weeds and grass covers in arable farming. Natural populations of the competitive fungus Gaeumannomyces cylindrosporus, allowed to develop under rye-grass, were more effective than artificially introduced populations in suppressing the development of take-all in following wheat crops. To be effective, the antagonist needs to be present before the start of wheat cropping. Introducing G. cylindrosporus, but not G. graminis var. graminis (a potential antagonist that is faster growing), into a previous crop, or just after the previous crop, sometimes suppressed take-all, but the effect was small. It is concluded that, for any future attempts at biocontrol by these fungi, they should be introduced into a preceding crop not susceptible to take-all. Take-all inoculum in the soil should be at a minimum and effective hosts of the take-all pathogen must not be present as weeds or volunteers.
  • Authors:
    • Marshall, A.
    • Mills, A.
    • Moot, D.
    • Edwards, G.
  • Source: Proceedings of the New Zealand Grassland Association
  • Volume: 69
  • Year: 2007
  • Summary: Lucerne sown immediately or after different forage crop sequences was investigated as a pasture option for post forestry conversion. In this experiment superphosphate and lime were applied in March 2005 before final seedbed preparation and establishment of seven cropping sequences; (1) lucerne sown in April 2005; (2-5) greenfeed cereals (oats or triticale) sown in April 2005 followed by lucerne in October 2005 with or without a rape cover crop; (6-7) winter fallow followed by glyphosate presowing in October 2005 or March 2006. After all crop sequences, lucerne was successfully established and provided 100% control of woody and annual weeds. Average lucerne dry matter (DM) yield was ~7.1 t DM/ha/yr for crops after a cereal. The last crop established also contained no woody weeds but produced 10.0 t DM/ha less over the 2 years due to the long (12 month) fallow. Lucerne sown in April 2005 had to be reestablished the following October. Thus, provided soil temperatures were adequate, lucerne was successfully spring and autumn sown after plantation forests. Lucerne offers flexibility for grazing or conserving in commercial conversions where internal fences and stock water supply are often, initially, inadequate for intensive pasture management.
  • Authors:
    • Mielniczuk, J.
    • Vieira, F. C. B.
    • Dieckow, J.
    • Bayer, C.
    • Zanatta, J. A.
  • Source: Soil & Tillage Research
  • Volume: 94
  • Issue: 2
  • Year: 2007
  • Summary: Conservation management systems can improve soil organic matter stocks and contribute to atmospheric C mitigation. This study was carried out in a 18-year long-term experiment conducted on a subtropical Acrisol in Southern Brazil to assess the potential of tillage systems [conventional tillage (CT) and no-till (NT)], cropping systems [oat/maize (O/M), vetch/maize (V/M) and oat + vetch/maize + cowpea (OV/MC)] and N fertilization [0 kg N ha-1 year-1 (0 N) and 180 kg N ha-1 year-1 (180 N)] for mitigating atmospheric C. For that, the soil organic carbon (SOC) accumulation and the C equivalent (CE) costs of the investigated management systems were taken into account in comparison to the CT O/M 0 N used as reference system. No-till is known to produce a less oxidative environment than CT and resulted in SOC accumulation, mainly in the 0-5 cm soil layer, at rates related to the addition of crop residues, which were increased by legume cover crops and N fertilization. Considering the reference treatment, the SOC accumulation rates in the 0-20 cm layer varied from 0.09 to 0.34 Mg ha-1 year-1 in CT and from 0.19 to 0.65 Mg ha-1 year-1 in NT. However, the SOC accumulation rates peaked during the first years (5th to 9th) after the adoption of the management practices and decreased exponentially over time, indicating that conservation soil management was a short-term strategy for atmospheric C mitigation. On the other hand, when the CE costs of tillage operations were taken into account, the benefits of NT to C mitigation compared to CT were enhanced. When CE costs related to N-based fertilizers were taken into account, the increases in SOC accumulation due to N did not necessarily improve atmospheric C mitigation, although this does not diminish the agricultural and economic importance of inorganic N fertilization.
  • Authors:
    • Denmead, O. T.
    • Macdonald, B. C. T.
    • Bryant, G.
    • Wang, W.
    • White, I.
    • Moody, P.
  • Source: Proceedings of the Australian Society of Sugar Cane Technologists
  • Volume: 29
  • Year: 2007
  • Authors:
    • Grace,P.
  • Source: Healthy Soils Symposium
  • Year: 2007