• Authors:
    • Samu, F.
    • Sunderland, K.
  • Source: Entomologia Experimentalis Et Applicata
  • Volume: 95
  • Issue: 1
  • Year: 2000
  • Summary: A review of the literature showed that spider abundance was increased by diversification in 63% of studies. A comparison of diversification modes showed that spider abundance in the crop was increased in 33% of studies by `aggregated diversification' (e.g. intercropping and non-crop strips) and in 80% of studies by `interspersed diversification' (e.g., undersowing, partial weediness, mulching and reduced tillage). It is suggested that spiders tend to remain in diversified patches and that extending the diversification throughout the whole crop (as in interspersed diversification) offers the best prospects for improving pest control. There is little evidence that spiders walk in significant numbers into fields from uncultivated field edges, but diversification at the landscape level serves to foster large multi-species regional populations of spiders which are valuable as a source of aerial immigrants into newly planted crops. There are very few manipulative field studies where the impact of spiders on pests has been measured in diversified crops compared with undiversified controls. It is encouraging, however, that in those few studies an increased spider density resulted in improved pest control. Future work needs are identified.
  • Authors:
    • Tanni, R.
    • Pietola, L.
  • Source: Agricultural and Food Science in Finland
  • Volume: 8
  • Issue: 4/5
  • Year: 1999
  • Summary: The role of plant growth regulators (PGR) in nitrogen (N) fertilization of spring wheat and oats (CCC [chlormequat]), fodder barley (etephon/mepiquat) an oilseed rape (etephone) in crop rotation was studied in 1993-96 on loamy clay soil. Carry over effect of the N fertilization rates (0-180 kg/ha) was evaluated in 1997. N fertilization rate for the best grain/seed yield (120-150 kg/ha) was not affected by PGRs. The seed and N yields of oilseed rape were improved frequently by the recommended use of PGR. The yield of oats increased in 1995-96. Even though PGR effectively shortened the plant height of spring wheat, the grain yield increased only in 1995. N yield of wheat grains was not increased. Response of fodder barley to PGR was insignificant or even negative in 1995. The data suggest that PGRs may decrease some N leaching at high N rates by improving N uptake by grain/seeds, if the yield is improved. The carryover study showed that in soils with no N fertilization, as well as in soils of high N rates, N uptake was higher than in soils with moderate N fertilization (60-90 kg/ha), independent of PGRs. According to soil mineral N contents, N leaching risk was significant (15-35 kg/ha) only after dry and warm late seasons. After a favourable season of high yields, the N rates did not significantly affect soil mineral N contents.
  • Authors:
    • Oenema, O.
    • Silvola, J.
    • Martikainen, P.
    • Berglund, K.
    • Klemedtsson, L.
    • Kasimir-Klemedtsson, Å.
  • Source: Soil Use and Management
  • Volume: 13
  • Issue: s4
  • Year: 1997
  • Summary: The large boreal peatland ecosystems sequester carbon and nitrogen from the atmosphere due to a low oxygen pressure in waterlogged peat. Consequently they are sinks for CO2 and strong emitters of CH4. Drainage and cultivation of peatlands allows oxygen to enter the soil, which initiates decomposition of the stored organic material, and in turn CO2 and N2O emissions increase while CH4 emissions decrease. Compared to undrained peat, draining of organic soils for agricultural purposes increases the emissions of greenhouse gases (CO2, CH4, and N2O) by roughly 1t CO2 equivalents/ha per year. Although farmed organic soils in most European countries represent a minor part of the total agricultural area, these soils contribute significantly to national greenhouse gas budgets. Consequently, farmed organic soils are potential targets for policy makers in search of socially acceptable and economically cost-efficient measures to mitigate climate gas emissions from agriculture. Despite a scarcity of knowledge about greenhouse gas emissions from these soils, this paper addresses the emissions and possible control of the three greenhouse gases by different managements of organic soils. More precise information is needed regarding the present trace gas fluxes from these soils, as well as predictions of future emissions under alternative management regimes, before any definite policies can be devised.