• Authors:
    • Parker, J. P.
    • Scott, A.
    • Ball, B. C.
  • Source: Soil & Tillage Research
  • Volume: 53
  • Issue: 1
  • Year: 1999
  • Summary: Tillage practices and weather affect the release of greenhouse gases but there have been few integrated studies of the quantities released or the mechanisms involved. No-tillage may increase emissions of nitrous oxide (N2O) and the fixation of carbon by decreasing carbon dioxide (CO2) emissions. Tillage may also decrease the oxidation rate of atmospheric methane (CH4) in aerobic soil. These effects are partly due to compaction and to the lack of both soil disturbance and residue incorporation. Our objective was to investigate how tillage practices, soil conditions and weather interact to influence greenhouse gas emissions. Here we present early measurements of N2O and CO2 emission and CH4 oxidation in two field experiments in Scotland under a cool moist climate, one involving soil compaction plus residue incorporation and the other involving no-tillage and two depths of mouldboard ploughing of a former grass sward. The experiments were located 10-15 km south of Edinburgh on a cambisol and a gleysol. In order to monitor emissions regularly, at short intervals and over long periods, a novel automatic gas sampling system which allows subsequent automated determination of both N2O and CO2 fluxes was used. Both N2O and CO2 fluxes were episodic and strongly dependent on rainfall. Peak N2O emissions were mainly associated with heavy rainfalls after fertilisation, particularly with no-tilled and compact soils. In the tillage experiment, N2O fluxes and treatment differences were greater under spring barley (Hordeum vulgare L.) (up to 600 g N ha-1 per day) than under winter barley. CO2 emissions in the few weeks after sowing were not strongly influenced by tillage and diurnal variations were related to soil temperature. However, periods of low or zero CO2 fluxes and very high N2O fluxes under no-tillage were associated with reduced gas diffusivity and air-filled porosity, both caused by heavy rainfall. Early results show that CH4 oxidation rates may best be preserved by no-tillage. The quality of the loam/clay-loams and the climate in these experiments makes ploughing, preferably to 300 mm depth, and the control of compaction necessary to minimise soil N2O and CO2 losses. The gas exchange response of different soil types to tillage, particularly methane oxidation rate which is affected by long-term soil structural damage, is a potentially useful aspect of soil quality when taken in conjunction with other qualities.
  • Authors:
    • Collins, C.
    • Chalmers, A. G.
    • Froment, M. A.
    • Grylls, J. P.
  • Source: The Journal of Agricultural Science
  • Volume: 133
  • Year: 1999
  • Summary: The effect of a range of one-year set-aside treatments on soil mineral nitrogen (SMN), during the set-aside period and in a following wheat crop were studied in a phased experiment at five sites from 1987 to 1991. Ground cover options permitted under the UK government's 'set-aside' scheme, including natural regeneration, autumn sown Italian ryegrass (Lolium multiflorum), spring-sown legumes and cultivated fallow, were compared with a control treatment of continuous cereals managed with fertilizer inputs. In the first of three phases in this experiment, an uncultivated fallow (kept weed-free) and autumn-sown forage rape (Brassica napus) were included as extra treatments. There were large differences in total SMN (0.0-0.9 m) between sites, ranging from 16 to 205 kg N/ha, reflecting differences in soil type, which ranged from clays to sands, and previous cropping husbandry. Differences in SMN between set-aside treatments during the first winter of the set-aside year were small, but increased during the following summer. Amounts of SMN were greatest after cultivated fallow (46-178 kg N/ha) and least after ryegrass (26-111 kg N/ha). Natural regeneration and spring sown legumes were more variable in their effect on SMN. Compared to continuous cereals, there was a build up in SMN during bare fallow, but a reduction under ryegrass, prior to returning to wheat cropping in the autumn after set-aside. SMN results suggest there was an increased nitrate leaching risk for bare fallow and natural regeneration set-aside, compared to sown ryegrass covers, in the winter following ploughing out of set-aside. This risk could be minimized by earlier sowing of winter cereals following set-aside or sowing with winter oilseed rape rather than cereals to maximize crop nitrogen (N) uptake, during the autumn growth period. Averaged across five sites, residual SMN supply in the spring of first test year cereal crops for all set-aside treatments was similar to that for continuous cereals, suggesting over-winter losses by N leaching or immobilization. The low residual N fertility after rotational set-aside suggested that following crop N recommendations should be the same as for continuous cereals. Amounts of SMN were less each year in spring than in the preceding autumn in both the set-aside and first test cereal crops. The results suggested that a ryegrass cover appeared to be the most environmentally favourable option for rotational set-aside management, as it minimized the amount of readily leachable N both during and immediately after the set-aside period.
  • Authors:
    • Lyon, D. J.
    • Tanaka, D. L.
    • Jones, O. R.
    • Havlin, J. L.
    • Halvorson, A. D.
    • Peterson, G. A.
    • Pennock, D. J.
  • Source: Soil & Tillage Research
  • Volume: 47
  • Issue: 3
  • Year: 1998
  • Summary: Concern about soil organic matter losses as a result of cultivation has been voiced consistently since the early part of the 20th century. Scientists working in the U.S. Great Plains recognized that organic matter losses from an already small pool could have major negative consequences on soil physical properties and N supplying capacity. The advent of reduced- and no-till systems has greatly improved our ability to capture and retain precipitation in the soil during the non-crop periods of the cropping cycle, and has made it possible to reduce fallow frequency and intensify cropping systems. The purpose of this paper is to summarize the effects of reduced tillage and cropping system intensification on C storage in soils using data from experiments in North Dakota, Nebraska, Kansas, Colorado, and Texas. Decades of farming with the wheat (Triticum aestivum L.)-fallow system, the dominant farming system in the Great Plains, have accentuated soil C losses. More intensive cropping systems, made possible by the greater water conservation associated with no-till practices, have produced more grain, produced more crop residue and allowed more of it to remain on the soil surface. Combined with less soil disturbance in reduced- and no-till systems, intensive cropping has increased C storage in the soil. We also conclude that the effects of cropping system intensification on soil C should not be investigated independent of residue C still on the surface. There are many unknowns regarding how rapidly changes in soil C will occur when tillage and cropping systems are changed, but the data summarized in this paper indicate that in the surface 2.5 cm of soil, changes can be detected within 10 years. It is imperative that we continue long-term experiments to evaluate rates of change over an extended period. It is also apparent that we should include residue C, both on the surface of the soil and within the surface 2.5 cm, in our system C budgets if we are to accurately depict residue±soil C system status. The accounting of soil C must be done on a mass basis rather than on a concentration basis.
  • Authors:
    • Smith, J. U.
    • Glendining, M. J.
    • Powlson, D. S.
    • Smith, P.
  • Source: Global Change Biology
  • Volume: 4
  • Issue: 6
  • Year: 1998
  • Summary: In this paper we estimate the European potential for carbon mitigation of no-till farming using results from European tillage experiments. Our calculations suggest some potential in terms of (a) reduced agricultural fossil fuel emissions, and (b) increased soil carbon sequestration. We estimate that 100% conversion to no-till farming would be likely to sequester about 23 Tg C y-1 in the European Union or about 43 Tg C y-1 in the wider Europe (excluding the former Soviet Union). In addition, up to 3.2 Tg C y-1 could be saved in agricultural fossil fuel emissions. Compared to estimates of the potential for carbon sequestration of other carbon mitigation options, no-till agriculture shows nearly twice the potential of scenarios whereby soils are amended with organic materials. Our calculations suggest that 100% conversion to no-till agriculture in Europe could mitigate all fossil fuel-carbon emissions from agriculture in Europe. However, this is equivalent to only about 4.1% of total anthropogenic CO2-carbon produced annually in Europe (excluding the former Soviet Union) which in turn is equivalent to about 0.8% of global annual anthropogenic CO2-carbon emissions.
  • Authors:
    • Johnson, D. E.
    • Minami, K.
    • Heinemeyer, O.
    • Freney, J. R.
    • Duxbury, J. M.
    • Mosier, A. R.
  • Source: Climatic Change
  • Volume: 40
  • Issue: 1
  • Year: 1998
  • Summary: Agricultural crop and animal production systems are important sources and sinks for atmospheric methane (CH4). The major CH4 sources from this sector are ruminant animals, flooded rice fields, animal waste and biomass burning which total about one third of all global emissions. This paper discusses the factors that influence CH4 production and emission from these sources and the aerobic soil sink for atmospheric CH4 and assesses the magnitude of each source. Potential methods of mitigating CH4 emissions from the major sources could lead to improved crop and animal productivity. The global impact of using the mitigation options suggested could potentially decrease agricultural CH4 emissions by about 30%.
  • Authors:
    • Pfadenhauer, J.
    • Klemisch, M.
    • Wild, U.
  • Source: European Journal of Soil Science
  • Volume: 49
  • Issue: 2
  • Year: 1998
  • Summary: Trace gas fluxes of N2O and CH4 were measured weekly over 12 months on cultivated peaty soils in southern Germany using a closed chamber technique. The aim was to quantify the effects of management intensity and of soil and climatic factors on the seasonal variation and the total annual exchange rates of these gases between the soil and the atmosphere. The four experimental sites had been drained for many decades and used as meadows (fertilized and unfertilized) and arable land (fertilized and unfertilized), respectively. Total annual N2O-N losses amounted to 4.2, 15.6, 19.8 and 56.4 kg ha(-1) year(-1) for the fertilized meadow, the fertilized field, the unfertilized meadow and the unfertilized field, respectively. Emission of N2O occurred mainly in the winter when the groundwater level was high. At all sites maximum emission rates were induced by frost. The largest annual N2O emission by far occurred from the unfertilized field where the soil pH was low (4.0). At this site 71% of the seasonal variation of N2O emission rates could be explained by changes in the groundwater level and soil nitrate content. A significant relationship between N2O emission rates and these factors was also obtained for the other sites, which had a soil pH between 5.1 and 5.8, though the relation was weak (R-2 = 15-27%). All sites were net sinks for atmospheric methane. Up to 78% of the seasonal variation in CH4 flux rates could be explained by changes in the groundwater level. The total annual CH4-C uptake was significantly affected by agricultural land use with greater CH4 consumption occurring on the meadows (1043 and 833 g ha(-1)) and less on the cultivated fields (209 and 213 g ha(-1)).
  • Authors:
    • Zuberer, D. A.
    • Hons, F. M.
    • Franzluebbers, A. J.
  • Source: Soil & Tillage Research
  • Volume: 47
  • Issue: 3-4
  • Year: 1998
  • Summary: Quality of agricultural soils is largely a function of soil organic matter. Tillage and crop management impact soil organic matter dynamics by modification of the soil environment and quantity and quality of C input. We investigated changes in pools and fluxes of soil organic C (SOC) during the ninth and tenth year of cropping with various intensities under conventional disk-and-bed tillage (CT) and no tillage (NT). Soil organic C to a depth of 0.2 m increased with cropping intensity as a result of greater C input and was 10% to 30% greater under NT than under CT. Sequestration of crop-derived C input into SOC was 22+-2% under NT and 9+-4% under CT (mean of cropping intensities +- standard deviation of cropping systems). Greater sequestration of SOC under NT was due to a lower rate of in situ soil CO2 evolution than under CT (0.22+-0.03 vs.0.27+-0.06 g CO2-C g-1 SOC yr-1). Despite a similar labile pool of SOC under NT than under CT (1.1+-0.1 vs. 1.0+-0.1 g mineralizable C kg-1 SOC d-1), the ratio of in situ to potential CO2 evolution was less under NT (0.56+-0.03) than under CT (0.73+-0.08), suggesting strong environmental controls on SOC turnover, such as temperature, moisture, and residue placement. Both increased C sequestration and a greater labile SOC pool were achieved in this low-SOC soil using NT and high-intensity cropping.
  • Authors:
    • Willison, T. W.
    • Poulton, P. R.
    • Murphy, D. V.
    • Howe, M.
    • Hargreaves, P.
    • Bradbury, N. J.
    • Bailey, N. J.
    • Goulding, K. W. T.
  • Source: New Phytologist
  • Volume: 139
  • Issue: 1
  • Year: 1998
  • Summary: Human activity has greatly perturbed the nitrogen cycle through increased fixation by legumes, by energy and fertilizer production, and by the mobilization of N from long-term storage pools. This extra reactive N is readily transported through the environment, and there is increasing evidence that it is changing ecosystems through eutrophication and acidification. Rothamsted Experimental Station, UK has been involved in research on N cycling in ecosystems since its inception in 1843. Measurements of precipitation composition at Rothamsted, made since 1853, show an increase of nitrate and ammonium N in precipitation from 1 and 3 kg N ha(-1) yr(-1) respectively, in 1855 to a maximum of 8 and 10 kg N ha(-1) yr(-1) in 1980, decreasing to 4 and 5 kg N ha(-1) y(-1) today. Nitrogen inputs via dry deposition do, however, remain high. Recent measurements with diffusion tubes and filter packs show large concentrations of nitrogen dioxide of c. 20 mu g m(-3) in winter and c. 10 mu g m(-3) in summer; the difference is linked to the use of central heating, and with variations in wind direction and pollutant source. Concentrations of nitric acid and particulate N exhibit maxima of 1.5 and 2 mu g m(-3) in summer and winter, respectively. Concentrations of ammonia are small, barely rising above 1 mu g m(-3). Taking deposition velocities from the literature gives a total deposition of all measured N species to winter cereals of 43.3 kg N ha(-1) yr(-1), 84 % as oxidized species, 79 % dry deposited. The fate of this N deposited to the very long-term Broadbalk Continuous Wheat Experiment at Rothamsted has been simulated using the SUNDIAL N-cycling model: at equilibrium, after 154 yr of the experiment and with N deposition increasing from c. 10 kg ha(-1) yr(-1) in 1843 to 45 kg ha(-1) yr(-1) today, c. 5 % is leached, 12% is denitrified, 30% immobilized in the soil organic matter and 53 % taken off in the crop. The 'efficiency of use' of the deposited N decreases, and losses and immobilization increase as the amount of fertilizer N increases. The deposited N itself, and the acidification that is associated with it (from the nitric acid, ammonia and ammonium), has reduced the number of plant species on the 140-yr-old Park Grass hay meadow. It has also reduced methane oxidation rates in soil by c. 15 % under arable land and 30 % under woodland, and has caused N saturation of local woodland ecosystems: nitrous oxide emission rates of up to 1.4 kg ha(-1) yr(-1) are equivalent to those from arable land receiving > 200 kg N ha(-1) yr(-1), and in proportion to the excess N deposited; measurements of N cycling processes and pools using N-15 pool dilution techniques show a large nitrate pool and enhanced rates of nitrification relative to immobilization. Ratios of gross nitrification:gross immobilization might prove to be good indices of N saturation.
  • Authors:
    • Liang, B. C.
    • Anderson, D. W.
    • Greer, K. J.
    • Gregorich, E. G.
  • Source: Soil & Tillage Research
  • Volume: 47
  • Issue: 3
  • Year: 1998
  • Summary: Because of concerns about the eventual impact of atmospheric CO2 accumulations, there is growing interest in reducing net CO2 emissions from soil and increasing C storage in soil. This review presents a framework to assess soil erosion and deposition processes on the distribution and loss of C in soils. The physical processes of erosion and deposition affect soil C distribution in two main ways and should be considered when evaluating the impact of agriculture on C storage. First, these processes redistribute considerable amounts of soil C, within a toposequence or a field, or to a distant site. Accurate estimates of soil redistribution in the landscape or field are needed to quantify the relative magnitude of soil lost by erosion and accumulated by deposition. Secondly, erosion and deposition drastically alter the biological process of C mineralization in soil landscapes. Whereas erosion and deposition only redistribute soil and organic C, mineralization results in a net loss of C from the soil system to the atmosphere. Little is known about the magnitude of organic C losses by mineralization and those due to erosion, but the limited data available suggest that mineralization predominates in the first years after the initial cultivation of the soil, and that erosion becomes a major factor in later years. Soils in depositional sites usually contain a larger proportion of the total organic C in labile fractions of soil C because this material can be easily transported. If the accumulation of soil in depositional areas is extensive, the net result of the burial (and subsequent reduction in decomposition) of this active soil organic matter would be increased C storage. Soil erosion is the most widespread form of soil degradation. At regional or global levels its greatest impact on C storage may be in affecting soil productivity. Erosion usually results in decreased primary productivity, which in turn adversely affects C storage in soil because of the reduced quantity of organic C returned to the soil as plant residues. Thus the use of management practices that prevent or reduce soil erosion may be the best strategy to maintain, or possibly increase, the worlds soil C storage.
  • Authors:
    • Wagner, G. H.
    • Buyanovsky, G. A.
  • Source: Global Change Biology
  • Volume: 4
  • Issue: 2
  • Year: 1998
  • Summary: Long-term data from Sanborn Field, one of the oldest experimental fields in the USA, were used to determine the direction of soil organic carbon (SOC) dynamics in cultivated land. Changes in agriculture in the last 50 years including introduction of more productive varieties, wide scale use of mineral fertilizers and reduced tillage caused increases in total net annual production (TNAP), yields and SOC content. TNAP of winter wheat more than doubled during the last century, rising from 2.0-2.5 to 5-6 Mg ha(-1) of carbon, TNAP of corn rose from 3-4 to 9.5-11.0 Mg ha(-1) of carbon. Amounts of carbon returned annually with crop residues increased even more drastically, from less than 1 Mg ha(-1) in the beginning of the century to 33.5 Mg ha(-1) for wheat and 5-6 Mg ha(-1) for corn in the 90s. These amounts increased in a higher proportion because in the early 509 removal of postharvest residues from the field was discontinued. SOC during the first half of the century, when carbon input was low, was mineralized at a high rate: 89 and 114 g m(-2) y(-1) under untreated wheat and corn, respectively. Application of manure decreased losses by half, but still the SOC balance remained negative. Since 1950, the direction of the carbon dynamics has reversed: soil under wheat monocrop (with mineral fertilizer) accumulated carbon at a rate about 50 g m(-2) y(-1), three year rotation (corn/wheat/clover) with manure and nitrogen applications sequestered 150 g m(2) y(-1) of carbon. Applying conservative estimates of carbon sequestration documented on Sanborn Field to the wheat and corn production area in the USA, suggests that carbon losses to the atmosphere from these soils were decreased by at least 32 Tg annually during the last 40-50 years. Our computations prove that cultivated soils under proper management exercise a positive influence in the current imbalance in the global carbon budget.