• Authors:
    • Woomer, P. L.
    • Noordwijk, M.
    • Tiessen, H.
    • Tian, G.
    • Smith, P.
    • Lal, R.
    • Janzen, H. H.
    • Andrén, O.
    • Paustian, K.
  • Source: Soil Use and Management
  • Volume: 13
  • Year: 1997
  • Summary: Agricultural soils, having been depleted of much of their native carbon stocks, have a significant CO2 sink capacity. Global estimates of this sink capacity are in the order of 20-30 Pg C over the next 50-100 years. Management practices to build up soil C must increase the input of organic matter to soil and/or decrease soil organic matter decomposition rates. The most appropriate management practices to increase soil C vary regionally, dependent on both environmental and socioeconomic factors. In temperate regions, key strategies involve increasing cropping frequency and reducing bare fallow, increasing the use of perennial forages (including N-fixing species) in crop rotations, retaining crop residues and reducing or eliminating tillage (i.e. no-till). In North America and Europe, conversion of marginal arable land to permanent perennial vegetation, to protect fragile soils and landscapes and/or reduce agricultural surpluses, provides additional opportunities for C sequestration. In the tropics, increasing C inputs to soil through improving the fertility and productivity of cropland and pastures is essential. In extensive systems with vegetated fallow periods (e.g. shifting cultivation), planted fallows and cover crops can increase C levels over the cropping cycle. Use of no-till, green manures and agroforestry are other beneficial practices. Overall, improving the productivity and sustainability of existing agricultural lands is crucial to help reduce the rate of new land clearing, from which large amounts of CO2 from biomass and soil are emitted to the atmosphere. Some regional analyses of soil C sequestration and sequestration potential have been performed, mainly for temperate industrialized countries. More are needed, especially for the tropics, to capture region-specific interactions between climate, soil and management resources that are lost in global level assessments. By itself, C sequestration in agricultural soils can make only modest contributions (e.g. 3-6% of total fossil C emissions) to mitigating greenhouse gas emissions. However, effective mitigation policies will not be based on any single 'magic bullet' solutions, but rather on many modest reductions which are economically efficient and which confer additional benefits to society. In this context, soil C sequestration is a significant mitigation option. Additional advantages of pursuing strategies to increase soil C are the added benefits of improved soil quality for improving agricultural productivity and sustainability.
  • Authors:
    • Unger, P. W.
    • Torbert, H. A.
    • Jones, O. R.
    • Potter, . N.
  • Source: Soil Science
  • Volume: 162
  • Issue: 2
  • Year: 1997
  • Summary: Limited information is available regarding soil organic carbon (SOC) distribution and the total amounts that occur in dryland cropping situations in semiarid regions. We determined crop rotation, tillage, and fertilizer effects on SOC distribution and mass in the semiarid southern Great Plains. A cropping system study was conducted for 10-years at Bushland, TX, to compare no-till and stubblemulch management on four dryland cropping systems: continuous wheat (CW) (Triticum aestivum L.); continuous grain sorghum (CS) (Sorghum bicolor [L.] Moench.); wheat/fallow/sorghum/fallow (WSF); and wheat/fallow (WF). Fertilizer (45 kg N ha-1) was added at crop planting to main plots. Subplots within each tillage and cropping treatment combination received no fertilizer. Ten years after treatment initiation, soil cores were taken incrementally to a 65-cm depth and subdivided for bulk density and SOC determination. The no-till treatments resulted in significant differences in SOC distribution in the soil profile compared with stubblemulch tillage in all four crop rotations, although differences were largest in the continuous cropping systems. Continuous wheat averaged 1.71% SOC in the surface 2 cm of soil compared with 1.02% SOC with stubblemulch tillage. Continuous sorghum averaged 1.54% SOC in the surface 2 cm of soil in no-till compared with 0.97% SOC with stubblemulch tillage. Total SOC content in the surface 20 cm was increased 5.6 t C ha-1 in the CW no-till treatment and 2.8 t C ha-1 in the CS no-till treatment compared with the stubblemulch treatment. Differences were not significantly different between tillage treatments in the WF and WSF systems. No-till management with continuous crops sequestered carbon in comparison to stubblemulch management on the southern Great Plains. Fallow limits carbon accumulation., (C) Williams & Wilkins 1997. All Rights Reserved.
  • Authors:
    • Dick, W. A.
    • Jacinthe P. -A.
  • Source: Soil & Tillage Research
  • Volume: 41
  • Issue: 3-4
  • Year: 1997
  • Summary: Nitrous oxide (N2O) is an important atmospheric trace gas due to its involvement in the postulated global warming phenomenon and in the depletion of the ozone layer. Widespread concern has been triggered by recent reports of increased atmospheric N2O concentration. Since agriculture has been implicated as one contributor to that increase, a monitoring program was undertaken during the 1993 and 1994 cropping season (May-October) to evaluate the effect of several soil management practices on N2O emission from soil. Our results show that rates of N2O emission were generally near baseline levels during most sampling occasions. Major, but short-lived, fluxes of N2O were observed after rainfall events and during the days immediately following fertilizer application. It was during these times that most of the seasonal N2O loss occurred. An excellent relationship was found between seasonal N2O loss (y) and the maximum daily flux of N2O (x) during a season (y = -0.4x2 + 43.1x + 338, r2 = 0.89, P < 0.0001). The N2O emission data were log normally distributed for both years. Average daily emissions of N2O were 6.9 ± 6.3 g (range, 0.3 - 74.7 g) N2O---N ha-1 day-1 and 17.6 ± 10.5 g (range, 0.1-326 g) N2O---N ha-1 day-1 during the 1993 and 1994 seasons, respectively. Seasonal N2O---N losses were, in general, highest in the continuous corn (CC) (Zea mays L.) plots and lowest in the soybean (Glycine max L.) plots of the corn/soybean/wheat (Triticum aestivum L.)-hairy vetch (Vicia villosa Roth) rotation (CSW-V). Average N loss as N2O during a cropping season was between 0.6 kg (for the soybean crop of the CSWV rotation and ridge till treatment) and 3.7 kg N2O---N ha-1 year-1, (for the CC rotation and the chisel till treatment). Approximately 0.5-3% of the inorganic N fertilizer added was lost as N2O. Our data show that seasonal N2O---N loss from chisel-till plots were generally significantly higher than from no-till or ridge till plots.
  • Authors:
    • Lal, R.
  • Source: Soil & Tillage Research
  • Volume: 43
  • Issue: 1-2
  • Year: 1997
  • Summary: This manuscript reviews the potential impact of residue management, conservation tillage and soil restoration on carbon sequestration in world soils. The greenhouse effect is among four principal ecological issues of global concern that include: (i) adequacy of land resources to meet needs of present and future generations; (ii) role of world soils and agricultural practices in the "greenhouse" effect; (iii) potential of crop residue management, restoration of degraded soils, and conservation tillage in carbon sequestration in soil; and (iv) minimizing risks of soil degradation by enhancing soil resilience and soil quality. Annual increase in CO, concentration in the atmosphere is 3.2 X 1015 g, and there exists a potential to mitigate this effect through C sequestration in soils. Just as world soils are an important active pool of organic carbon and play a major role in the global carbon cycle, crop residue is a major renewable resource which also has an important impact on the global carbon cycle. I have estimated the annual production of crop residue to be about 3.4 billion Mg in the world. If 15% of C contained in the residue can be converted to passive soil organic carbon (SOC) fraction, it may lead to C sequestration at the rate of 0.2 X 1015 g/yr. Similarly restoring presently degraded soils, estimated at about 2.0 billion ha, and increasing SOC content by 0.01%/yr may lead C sequestration at the rate of 3.0 Pg C/yr. Conservation tillage is an important tool for crop residue management, restoration of degraded soil, and for enhancing C sequestration in soil. Conservation tillage, any tillage system that maintains at least 30% of the soil surface covered by residue, was practised in 1995 on about 40 X 106 ha or 35.5% of planted area in USA. It is projected that by the year 2020, conservation tillage may be adopted on 75% of cropland in USA (140 X 106 ha), 50% in other developed countries (225 X 106 ha), and 25% in developing countries (172 X 106 ha). The projected conversion of conventional to conservation tillage may lead to a global C sequestration by 2020 at a low estimate of 1.5 X 1015 g, and at a high estimate of 4.9 X 1015 g of C. These potentials of C sequestration can be realized through adoption of regional, national and global soil policy that stipulate appropriate use of world soil resources.
  • Authors:
    • Kissel, D. E.
    • Havlin, J. L.
  • Source: Soil Organic Matter in Temperate Agroecosystems: Long-Term Experiments in North America
  • Volume: 1
  • Year: 1997
  • Authors:
    • Zhao, Q.
    • Sauerbeck, D.
    • Sampson, N.
    • Duxbury,J.
    • Rosenberg, N.
    • Paustian, K.
    • Mosier, A.
    • Minami, K.
    • Heinemeyer, O.
    • Freney, J.
    • Cole, C. V.
  • Source: Nutrient Cycling in Agroecosystems
  • Volume: 49
  • Issue: 1-3
  • Year: 1997
  • Summary: Technologies to reduce net emissions of carbon dioxide, methane and nitrous oxide within the agriculture sector were reviewed to estimate the global potential for mitigation of these radiatively active greenhouse gases. Our estimates of the potential reduction of radiative forcing by the agricultural sector range from 1.15-3.3 Gt C equivalents per year. Of the total potential reduction, approximately 32% could result from reduction in CO2 emissions, 42% of carbon offsets by biofuel production on 15% of existing croplands, 16% from reduced CH4 emissions and 10% from reduced emissions of N2O. Agriculture encompasses large regional differences in management practices and rates of potential adoption of mitigation practices. Acceptability of mitigation options will depend on the extent to which sustainable production will be achieved or maintained and benefits will accrue to farmers. Technologies such as no-till farming and strategic fertilizer placement and timing are now being adopted for reasons other than concern for climate change issues.
  • Authors:
    • Martel, J.
    • Beyaert, R. P.
    • Donald, R. G.
    • Simard, R. R.
    • Voroney, R. P.
    • Liang, B. C.
    • Drury, C. F.
    • Gregorich, E. G.
    • Carter, M. R.
    • Bolinder, M. A.
    • Angers, D. A.
  • Source: Soil & Tillage Research
  • Volume: 41
  • Issue: 3-4
  • Year: 1997
  • Summary: Soil organic matter storage capacity in agroecosystems varies with soil type, climate and agricultural management practices. The effects of different tillage systems on organic C and N storage were determined for a range of soils of eastern Canada mainly under continuous corn and small grain cereal production. Soil profiles from eight sites on which comparative tillage experiments had been performed for up to 11 years were sampled to a 60 cm depth in four increments (0-10, 10-20, 20-40 and 40-60cm). Organic C and N contents and dry bulk density were determined for each sampling depth. Bulk density measurements showed that the total soil mass in the soil profiles was not influenced by the tillage systems. No significant differences were found between tillage treatments in the total organic C and N storage down to 60 cm depth; the soil profiles under no-till (NT) and chisel plowing (CP) generally did not contain more C and N than those under conventional moldboard plowing (MP). However, the depth distribution of soil C and N varied with tillage. In the surface 0-10cm, C and N contents were higher under NT than under MP, whereas at deeper levels (20-40cm) the reverse trend was observed. It is concluded than under eastern Canadian conditions, where crop production and residue inputs are not affected by tillage, reduced tillage systems would not result in the storage of more soil organic matter in the entire soil profile at least in a 5-10 year period. Placement of the residues would be a major factor influencing the C and N distribution at specific depths.
  • Authors:
    • Tanaka, D. L.
    • Black, A. L.
  • Source: Soil Organic Matter in Temperate Agroecosystems
  • Year: 1997
  • Authors:
    • Turkington, T.
    • Gill, K.
    • Arshad, M.
    • Woods, D.
  • Source: Agronomy Journal
  • Volume: 89
  • Issue: 1
  • Year: 1997
  • Summary: In a field trial near Beaverlodge, Alberta, a Hythe clay loam (fine, montmorillonitic, frigid Mollic Cryoboralf) with initial pH in CaCl 2 ~5 was limed (7.5 t ha -1) in May 1991. Liming increased soil pH to 6.6 in the autumn of 1991. During 1993 to 1995, the pH of limed soil at the 0- to 10-cm depth ranged from 6.2 to 6.3 when conventionally tilled and from 5.6 to 6.2 under no-till. A slight increase at the 10- to 20-cm depth and no change below 20 cm occurred in soil pH due to liming. Liming increased NO 3-N in the 0- to 20-cm depth significantly, but no change was detected in exchangeable Al, NH 4-N and extractable P. Weed populations were not affected by liming in 1993 and 1994, but were suppressed markedly in 1995. Liming reduced brown girdling root rot (BGRR) (caused by Rhizoctonia solani) and increased seed yield of canola [rape]. Three-year mean BGRR ratings (a scale of 0 to 5 scale, from disease-free to disease-impaired) under no lime and lime, respectively, were 2.96 and 2.59 in tilled and 2.76 and 2.63 in no-till soil. The increase in canola seed yield by liming was 0.39 (37%) t ha -1 year -1 in tilled and 0.22 (17%) t ha -1 year -1 in no-till soil. Liming increased dry matter by 1.77 t ha -1 year -1 (31%). No-till plots had higher soil water and canola yields but slightly lower soil pH (0- to 20-cm depth), and lesser BGRR, compared with the tilled system. Increased soil NO 3-N and pH, fewer weeds, and reduced BGRR-all responded to liming and contributed to increased canola yields under both tilled and no-till systems.
  • Authors:
    • Voroney, R.
    • Vyn, T.
    • Janovicek, K.
  • Source: Agronomy Journal
  • Volume: 89
  • Issue: 4
  • Year: 1997
  • Summary: Research in Ontario, Canada in 1989, 1990, and 1995 evaluated no-till maize yield response to various preceding crops and examined whether in-row residue removal affected no-till maize response to rotation crops. The soil was an imperfectly drained loam (medium, mixed, weakly to moderately calcareous Typic Hapludalf). The preceding crops were: maize harvested for grain or whole-plant silage; hard red spring wheat; barley; red clover ( Trifolium pratense) cover crops, following barley, that were killed by spraying either 3 weeks (early-kill) or 1 day (late-kill) prior to sowing maize; canola [rape]; and soyabeans. In-row residue was either retained while sowing or cleared using planter-mounted, notched-disc row cleaners. Clearing in-row cover crop residue increased early-season maize growth and was associated with yield increases of 0.61 t ha -1 (8%) following early-killed red clover and 0.43 t ha -1 (6%) ( P = 0.10) following late-killed red clover. In 2 of 3 years, maize yields following early-killed red clover were similar to following soyabeans and greater than following grain maize, provided that in-row residue was cleared. Following the other crops, grain yield response to clearing in-row residue was smaller and less consistent over years. Preceding cropping affected early-season maize growth, with the largest plants at 5 weeks after sowing following either soyabeans or silage maize and the smallest following either red clover or grain maize. In 2 of 3 years, when preceding crop effects on grain yield were statistically significant, yields following either soyabeans or spring wheat were more than 1.05 t ha -1 (16%) higher than after grain maize. That yield increase occurred regardless of in-row residue placement. Removing maize stover by harvesting as silage increased maize yield by 0.86 t ha -1 (12%) over yield following grain maize. During 1995, maize yield following silage maize was less than after soyabeans, canola, barley, or wheat; thus, no-till maize yield response to rotation is not exclusively due to the presence of surface-placed stover. In-row residue placement and preceding cropping practices affected in-row soil temperature, but this could not totally account for the treatment effects on early-season maize growth and yields.