• Authors:
    • Post, W. M.
    • West, T. O.
  • Source: Soil Science Society of America Journal
  • Volume: 66
  • Issue: 6
  • Year: 2002
  • Summary: Changes agricultural management can potentially increase the accumulation rate of soil organic C (SOC), thereby sequestering CO2 from the atmosphere. This study was conducted to quantify potential soil C sequestration rates for different crops in response to decreasing tillage intensity or enhancing rotation complexity, and to estimate the duration of time over which sequestration may occur. Analyses of C sequestration rates were completed using a global database of 67 long-term agricultural experiments, consisting of 276 paired treatments. Results indicate, on average, that a change from conventional tillage (CT) to no-till (NT) can sequester 57 +/- 14 g C m(-2) yr(-1), excluding wheat (Triticum aestivum L.)-fallow systems which may not result in SOC accumulation with a change from CT to NT. Enhancing rotation complexity can sequester an average 20 +/- 12 g C m(-2) yr(-1), excluding a change from continuous corn (Zea mays L.) to corn-soybean (Glycine mar L.) which may not result in a significant accumulation of SOC. Carbon sequestration rates, with a change from CT to NT, can be expected to peak in 5 to 10 yr with SOC reaching a new equilibrium in 15 to 20 yr. Following initiation of an enhancement in rotation complexity, SOC may reach a new equilibrium in approximately 40 to 60 yr. Carbon sequestration rates, estimated for a number of individual crops and crop rotations in this study, can be used in spatial modeling analyses to more accurately predict regional, national, and global C sequestration potentials.
  • Authors:
    • Jarvis, S. C.
    • Yamulki, S.
  • Source: Biology and Fertility of Soils
  • Volume: 36
  • Issue: 3
  • Year: 2002
  • Summary: N2O, NO, NO2, CO2 and CH4 fluxes were measured simultaneously from tilled and compacted soil in a factorial design to investigate the effect of management on trace gas emissions. Six treatments in combinations of with and without N application, tillage and compaction were investigated for a period of 3 weeks using the closed-chamber technique (for N2O, CO2 and CH4) and the open-chamber technique (for NO and NO2). Total NO emissions from the tilled plots were 2.4 times greater than from the non-tilled plots, whereas CO2 emissions were 1.8 times greater from the non-tilled plots. Compaction increased the emissions of N2O and CH4 3.5- and 4.4-fold, respectively, compared with emissions from uncompacted plots. The effects of tillage and compaction on the gaseous emissions are discussed in relation to their production, transport and lifetime within the soil. The results showed that the best option for reducing gaseous emission from fertilised soil, with regards to tillage or compaction, would be the least compacted system, regardless of the tillage status as reflected, at least in the short term, by minimal emissions of N2O and CH4 and to some extent those of NO, NO2 and CO2.
  • Authors:
    • Jellum, E. J.
    • Kuo, S.
  • Source: Agronomy Journal
  • Volume: 94
  • Issue: 3
  • Year: 2002
  • Summary: Removing cover crop top growth in the spring for forage or to prevent incorporation problems is one management option. The effects of this residue management on soil quality and productivity need to be determined. This study, conducted from 1994 to 1998 at Puyallup, WA, determined effects of various winter cover crops and residue management on soil N availability, soil C and N, and corn (Zea mays L.) yield. Included in the study were monocultures of rye (Secale cereale L.), ryegrass (Lolium multiflorum Lam), and vetch (Vicia villosa Roth subsp. villosa) and biculture of vetch and rye or ryegrass. Each year, the cover crops were seeded in the fall and incorporated into, or removed from, the soil in the spring. Average top-growth biomass was higher for the bicultures than for the monocultures. Total N accumulation was generally greatest under vetch, followed by the bicultures, and lowest for the monocultured rye or ryegrass. Whereas removing top growth of monocultured vetch or bicultures depressed presidedress soil NO3-N (Ni), the effect was generally not found for monocultured rye or ryegrass. Corn yields were affected by amounts of Ni and N fertilizer applied (r2 > 0.789), irrespective of cover crop species and residue management. Removing top growth of the cover crops limited residue C input and reduced soil organic C and N after 5 yr. Soil organic C and N accumulation, as well as increasing soil C sequestration to reduce CO2 release into atmosphere, should be considered when deciding which residue management option to choose.
  • Authors:
    • Sakamoto, K.
    • Inubushi, K.
    • Li, X.
  • Source: Biology and Fertility of Soils
  • Volume: 35
  • Issue: 2
  • Year: 2002
  • Summary: A field experiment was conducted to determine N2O concentrations in the soil profile and emissions as influenced by the application of N fertilizers and manure in a typical Japanese Andisol, which had been under a rotation of oat and carrot for the previous 3 years. The treatments include ammonium sulphate (AS). controlled-re lease fertilizer (CRF) and cattle manure (CM) in addition to a control; all the fertilizers were applied either at 150 kg N ha(-1) or 300 kg N ha(-1) at the time of sowing carrot. NO emissions from the soil surface were measured with closed-chamber techniques. while N2O concentrations in the soil profile were measured using stainless steel sampling probes inserted into the soil at depths of 10, 20. 40, 60, 80 and 100 cm. Moreover. soil water potential, soil temperature and rainfall data were also recorded. The results indicated that N2O concentrations in the soil profile were always greater than in the atmosphere, ranging from 0.36 mul N2O-N 1(-1) to 5.3 mul N2O-N l(-1). The relatively large accumulation of N2O in the lower profiles may be a significant source for N2O flux. Taking the changes of soil mineral N into consideration, most emissions of NO were probably produced from nitrification. The accumulation of NO in the soil profile and emissions to the atmosphere were differently influenced by the amendments of N fertilizers and manure. being consistently higher in CRF than in CM and AS treatments at the corresponding application rates, but no significant difference existed with respect to the various N sources.
  • Authors:
    • McQuaid, J. B.
    • Lewis, A. C.
    • Johnson, C. L.
    • Maw, S. J.
  • Source: Environmental Monitoring and Assessment
  • Volume: 74
  • Issue: 3
  • Year: 2002
  • Summary: The evolution of NOx from grass and maize silages was measured using chemiluminescence in samples kept in airtight containers, in the silos and in a 750 kg mass removed to a mixer waggon. Measurements were made on the grass and maize silos in two consecutive years. The results show that there is continuous evolution of NOx after silos have been opened and that high concentrations persist in the mass which are rapidly released on agitation at the feed-out. The maximum recorded concentrations of NO and NO2 were 1985 and 152 ppbv respectively. These values are orders of magnitude greater than for rural background levels and exceed the maximum hourly exposure of 50 ppbv for NO2 recommended by the UK expert panel for quality standards.
  • Authors:
    • Schimel, D. S.
    • Peterson, G. A.
    • Mosier, A.
    • Parton, W.
    • Ojima, D.
    • Del Grosso, S.
  • Source: Environmental Pollution
  • Volume: 116
  • Issue: Supplement 1
  • Year: 2002
  • Summary: We present evidence to show that DAYCENT can reliably simulate soil C levels, crop yields, and annual trace gas fluxes for various soils. DAYCENT was applied to compare the net greenhouse gas fluxes for soils under different land uses. To calculate net greenhouse gas flux we accounted for changes in soil organic C, the C equivalents of N2O emissions and CH4 uptake, and the CO2 costs of N fertilizer production. Model results and data show that dryland soils that are depleted of C due to conventional till winter wheat/fallow cropping can store C upon conversion to no till, by reducing the fallow period, or by reversion to native vegetation. However, model results suggest that dryland agricultural soils will still be net sources of greenhouse gases although the magnitude of the source can be significantly reduced and yields can be increased upon conversion to no till annual cropping. (C) 2001 Elsevier Science Ltd. All rights reserved.
  • Authors:
    • Bakken ,L. R.
    • Dörsch,P.
    • Holtan-Hartwig, L.
  • Source: Soil Biology and Biochemistry
  • Volume: 34
  • Issue: 11
  • Year: 2002
  • Summary: Abstract: To explore the reason for reported high field fluxes of nitrous oxide (N2O) from temperate soils in winter and early spring, we investigated the temperature response of denitrifier N2O production and reduction in soil from three arable field sites along a temperature transect reaching from Finland over Sweden to Germany. Process rates were determined in anaerobic slurries with or without added NO3-, N2O and C2H2 at 0, 5, 10, 15, and 20C (and 30C in one experiment). The experiments were conducted immediately after the soils had become anaerobic, and after a long (48 h) anaerobic pre-incubation with excess of carbon and electron acceptors. All denitrifying enzymes were found to be active in the soil at onset of anaerobiosis. Significant levels of N2O production and reduction occurred at 0 8C, both at onset of anaerobiosis and after the 2 days anaerobic pre-incubation. Temperature response of N2O production and reduction could be fitted to an Arrhenius function in the range 5-20 °C, yielding apparent activation energies between 28 and 76 kJ mol -1. The estimated activation energy of the N2O reduction was found to be similar or lower than that for N2O production. High field N2O fluxes in winter and early spring could thus not be explained by the temperature sensitivity of the two processes. However, major deviations from the regular Arrhenius response were found for two soils at near freezing temperature. The rates measured at 0 °C were much lower than those predicted by the Arrhenius function based on data in the temperature range 5-20 °C. Low temperature may thus exert a particular challenge to denitrifying communities for some reason, and the effect was found to be most severe for the N2O reduction process. When such a breakdown affects N2O reductase to a greater extent than the N2O producing enzymes (NO3-, NO2-, and NO reductase), as was found in our soils, it will result in high N2O fluxes at low temperature. The temperature response of the estimated net N2O emission potential (based on measured N2O production and reduction rates) differed significantly between the three sites, indicating inherent differences between their microbial communities.
  • Authors:
    • Grove, J. H.
    • Diaz-Zorita, M.
  • Source: Soil & Tillage Research
  • Volume: 65
  • Issue: 1
  • Year: 2002
  • Summary: The western part of the Argentine Pampas is a subhumid and semiarid region consisting of extensive plain with deep sandy and sandy-loam soils. The agricultural system includes pastures in rotation with annual grain crops and grazed crops or continuous annual row cropping. The objective of this review was to present and discuss changes in soil properties due to different soil management systems, mainly no-tillage practices, in the western part of the Argentine Pampas. The effects of tillage, crop sequences under no-till, and grazing on soil properties and crop productivity have been studied since 1990 on loamy and sandy Haplic Phaeozem (Typic Hapludolls and Entic Hapludolls) and Haplic Kastanozem (Typic Haplustolls). A database developed from the yield and soil test records of growers affiliated with Regional Consortium for Agricultural Experimentation (CREA) were also utilized in the study. The results showed that soil organic C (SOC) content depends both on soil texture and soil management. SOC decreases when the length of the row crop cycle increases and also in moldboard plow and chisel-tillage systems. Pastures and no-till row crop sequences with more years of maize (Zea mays L.) and wheat (Triticum aestivum L.), than sunflower (Helianthus annus L.) or soybean (Glycine max (L.) Merrill) tended to increase the SOC content in the 0-20 cm layer. Deep tillage of no-till soils with compacted layers improved maize dry matter production but, in the same experiment, yield was increased more by nitrogen fertilization than by subsoil tillage. The grazing of crop residues increases the soil bulk density only in the 0-5 cm layer of tilled soils, but did not significantly change bulk density on soils under continuous no-till. Crop productivity was related to SOC content of the 0-20 cm layer of the soils. Due to the positive effect of SOC on crop yields, no-till soil management and pasture-annual row crop rotations are two practices that permit the development of sustainable production systems in the western part of the Argentine Pampas.
  • Authors:
    • Jukes, M. R.
    • Ferris, R.
    • Humphrey, J. W.
    • Peace, A. J.
  • Source: Botanical Journal of Scotland
  • Volume: 54
  • Issue: 1
  • Year: 2002
  • Summary: The detrimental effects of conifer plantations on open ground habitats have been well catalogued and discussed, but the potential contribution of planted forests to the conservation of woodland biodiversity has not been quantified to the same extent. This quantification is needed urgently to help forest managers fullfil commitments to biodiversity enhancement as outlined in the UK Biodiversity Action Plan, the UK Forestry Standard and the UK Woodland Assurance Scheme (UKWAS). Results are presented from a five-year programme of research aimed at obtaining baseline information on biodiversity in planted forests and evaluating the contribution of planted forests to the conservation of native flora and fauna. Fifty-two plots were surveyed in total, covering a range of different tree crops (Scots pine Pinus sylvestris L., Sitka spruce Picea sitchensis (Bong.) Carr., Norway spruce Picea abies L. and Corsican pine Pinus nigra var maritima (Aiton) Melville) and stand ages (pre-thicket, mid-rotation, mature and over-mature) in three contrasting bioclimatic zones (upland, foothills and lowlands) throughout Britain. Additional plots were established in semi-natural woodland to allow comparisons between the biodiversity of plantations and native stands. Over 2000 species were recorded in total, including 45 Red Data Book species. Planted stands had similar or richer fungal and invertebrate communities to those of the native stands but poorer lichen and vascular plant communities. The latter were strongly affected by shading, dense, mid-rotation Sitka spruce stands having the lowest species counts. In contrast, these stands had a high diversity of mycorrhizal fungi, including a number of rare and threatened species normally associated with native pinewood. Bryophyte species-richness was related more to climate than woodland type, with the wetter upland spruce and native oak stands having the most diverse communities. Compared to the younger planted stands, over-mature planted stands had a higher proportion of species characteristic of semi-natural woodland stands. This related to greater structural diversity and higher deadwood volumes in the over-mature stands. It is concluded that conifer plantations make a positive contribution to biodiversity conservation in the UK and hence to the UK Biodiversity Action Plan. No single stand or crop type provides 'optimal' conditions for biodiversity, but the habitat value of plantations could be enhanced by increasing the area managed under alternative systems to clear-felling, such as 'continuous cover' and/or non-intervention natural reserves.
  • Authors:
    • Moerkerk, M.
    • Niknam, S. R.
    • Cousens, R.
  • Source: 13th Australian Weeds Conference: weeds "threats now and forever?", Sheraton Perth Hotel, Perth, Western Australia, 8-13 September 2002: papers and proceedings 2002
  • Year: 2002
  • Summary: This paper reports on surveys of farmers' seed boxes, which were carried out in the Wimmera and Mallee regions of Victoria in 2001. From seeds ready to be sown, 160 cereal (mainly wheat and barley) and pulse samples (mainly lentils, beans and peas) were collected and the level and species of weed seed were determined. For lentils (28 samples), the seed box survey was followed up with a paddock survey at flowering and the determination of foreign seed material in the final harvested grain. A wide range of weed species was found in the farmer-retained seed. Farmer-retained seed also contained more weed seeds than certified seed. The main foreign seeds in cereals were annual ryegrass ( Lolium rigidum), volunteer canola, volunteer barley, wild oats ( Avena spp.), silver grass ( Vulpia bromoides), volunteer wheat, lesser canary grass ( Phalaris minor), brome grass ( Bromus spp.), volunteer oats and paradoxa grass ( Phalaris paradoxa). For lentils, a number of common weeds were identified which tend to persist in the cropping system and replenish the seed bank. Annual ryegrass was identified as the most problematic weed. Other weeds such as vetch ( Vicia sativa) and bedstraw ( Galium tricornutum) could become serious problems in pulses if effective management practices are not found soon.