351. Long-term changes in soil carbon under different fertilizer, manure, and rotation: Testing the mathematical model ecosys with data from the Breton plots

• Authors:
  • McGill, W. B.
  • Izaurralde, R. C.
  • Robertson, J. A.
  • Juma, N. G.
  • Grant, R. F.
• Source: Soil Science Society of America Journal
• Volume: 65
• Issue: 1
• Year: 2001
• Summary: Soil C contents can be raised by land use practices in which rates of C input exceed those of C oxidation. Rates of C inputs to soil can be raised by continuous cropping, especially with perennial legumes, and by soil amendments, especially manure. We have summarized our understanding of the processes by which changes in soil C content are determined by rates of soil C input in the mathematical model ecosys. We compared model output for changes in soil C with those measured in a Gray Luvisol (Typic Cryoboralf) at Breton, Alberta, during 70 yr of a 2-yr wheat (Triticum aestivum L.)-fallow rotation vs. a 5-yr wheat-oat (Avena sativa L.)-barley (Hordeum vulgare L.)-forage-forage rotation with unamended, fertilized, and manured treatments. Model results indicated that rates of C input in the 2-yr rotation were inadequate to maintain soil C in the upper 0.15 m of the soil profile unless manure was added, but that those in the 5-yr rotation were more than adequate. Consequent changes of soil C in the model were corroborated by declines of 14 and 7 g C m-2 yr-1 measured in the control and fertilized treatments of the 2-yr rotation; by gains of 7 g C m-2 yr-1 measured in the manured treatment of the 2-yr rotation; and by gains of 4, 14, and 28 g C m-2 yr-1 measured in the control, fertilized, and manured treatments of the 5-yr rotation. Model results indicated that soil C below 0.15 m declined in all treatments of both rotations, but more so in the 2-yr than in the 5-yr rotation. These declines were corroborated by lower soil C contents measured between 0.15 and 0.40 m after 70 yr in the 2- vs. 5-yr rotation. Land use practices that favor C storage appear to interact positively with each other, so that gains in soil C under one such practice are greater when it is combined with other such practices.

352. Changes in soil carbon under long-term maize in monoculture and legume-based rotation

• Authors:
  • Baldock, J. A.
  • Drury, C. F.
  • Gregorich, E. G.
  • Greaves, Travis
• Source: Canadian Journal of Soil Science
• Volume: 81
• Issue: 1
• Year: 2001
• Summary: Legume-based cropping systems could help to increase crop productivity and soil organic matter levels, thereby enhancing soil quality, as well as having the additional benefit of sequestering atmospheric C. To evaluate the effects of 35 yr of maize monoculture and legume-based cropping on soil C levels and residue retention, we measured organic C and 13C natural abundance in soils under: fertilized and unfertilized maize (Zea mays L.), both in monoculture and legume-based [maize-oat (Avena sativa L.)-alfalfa (Medicago sativa L.)-alfalfa] rotations; fertilized and unfertilized systems of continuous grass (Poa pratensis L.); and under forest. Solid state 13C nuclear magnetic resonance (NMR) was used to chemically characterize the organic matter in plant residues and soils. Soils (70-cm depth) under maize cropping had about 30-40% less C, and those under continuous grass had about 16% less C, than those under adjacent forest. Qualitative differences in crop residues were important in these systems, because quantitative differences in net primary productivity and C inputs in the different agroecosystems did not account for observed differences in total soil C. Cropping sequence (i.e., rotation or monoculture) had a greater effect on soil C levels than application of fertilizer. The difference in soil C levels between rotation and monoculture maize systems was about 20 Mg C ha-1. The effects of fertilization on soil C were small (~6 Mg C ha-1), and differences were observed only in the monoculture system. The NMR results suggest that the chemical composition of organic matter was little affected by the nature of crop residues returned to the soil. The total quantity of maize-derived soil C was different in each system, because the quantity of maize residue returned to the soil was different; hence the maize-derived soil C ranged from 23 Mg ha-1 in the fertilized and 14 Mg ha-1 in the unfertilized monoculture soils (i.e., after 35 maize crops) to 6-7 Mg ha-1 in both the fertilized and unfertilized legume-based rotation soils (i.e., after eight maize crops). The proportion of maize residue C returned to the soil and retained as soil organic C (i.e., Mg maize-derived soil C/Mg maize residue) was about 14% for all maize cropping systems. The quantity of C3-C below the plow layer in legume-based rotation was 40% greater than that in monoculture and about the same as that under either continuous grass or forest. The soil organic matter below the plow layer in soil under the legume-based rotation appeared to be in a more biologically resistant form (i.e., higher aromatic C content) compared with that under monoculture. The retention of maize residue C as soil organic matter was four to five times greater below the plow layer than that within the plow layer. We conclude that residue quality plays a key role in increasing the retention of soil C in agroecosystems and that soils under legume-based rotation tend to be more "preservative" of residue C inputs, particularly from root inputs, than soils under monoculture.

353. Nitrous oxide emissions from an irrigated soil as affected by fertilizer and straw management

• Authors:
  • Ellert, B. H.
  • Janzen, H. H.
  • Carefoot, J. M.
  • Chang, C.
  • Hao, X.
• Source: Nutrient Cycling in Agroecosystems
• Volume: 60
• Issue: 1
• Year: 2001
• Summary: Nitrous oxide (N2O) emission from farmland is a concern for both environmental quality and agricultural productivity. Field experiments were conducted in 1996-1997 to assess soil N2O emissions as affected by timing of N fertilizer application and straw/tillage practices for crop production under irrigation in southern Alberta. The crops were soft wheat (Triticum aestivum L.) in 1996 and canola (Brassica napus L.) in 1997. Nitrous oxide flux from soil was measured using a vented chamber technique and calculated from the increase in concentration with time. Nitrous oxide fluxes for all treatments varied greatly during the year, with the greatest fluxes occurring in association with freeze-thaw events during March and April. Emissions were greater when N fertilizer (100 kg N ha-1) was applied in the fall compared to spring application. Straw removal at harvest in the fall increased N2O emissions when N fertilizer was applied in the fall, but decreased emissions when no fertilizer was applied. Fall plowing also increased N2O emissions compared to spring plowing or direct seeding. The study showed that N2O emissions may be minimized by applying N fertilizer in spring, retaining straw, and incorporating it in spring. The estimates of regional N2O emissions based on a fixed proportion of applied N may be tenuous since N2O emission varied widely depending on straw and fertilizer management practices.

354. Greenhouse gas emissions during cattle feedlot manure composting

• Authors:
  • Travis, G. R.
  • Larney, F. J.
  • Chang, C.
  • Hao, X.
• Source: Journal of Environmental Quality
• Volume: 30
• Issue: 2
• Year: 2001
• Summary: The emission of greenhouse gases (GHG) during feedlot manure composting reduces the agronomic value of the final compost and increases the greenhouse effect A study was conducted to determine whether GHG emissions are affected by composting method. Feedlot cattle manure was composted with two aeration methods-passive (no turning) and active (turned six times). Carbon lost in the forms of CO2 and CH4 was 73.8 and 6.3 kg C Mg-1 manure for the passive aeration treatment and 168.0 and 8.1 kg C Mg-1 manure for the active treatment. The N loss in the form of N2O was 0.11 and 0.19 kg N Mg-1 manure for the passive and active treatments. Fuel consumption to turn and maintain the windrow added a further 4.4 kg C Mg-1 manure for the active aeration treatment. Since CH4 and N2O are 21 and 310 times more harmful than CO2 in their global warming effect, the total GHG emission expressed as CO2-C equivalent was 240.2 and 401.4 kg C Mg-1 manure for passive and active aeration. The lower emission associated with the passive treatment was mainly due to the incomplete decomposition of manure and a lower gas diffusion rate. In addition, turning affected N transformation and transport in the windrow profile, which contributed to higher N2O emissions for the active aeration treatment. Gas diffusion is an important factor controlling GHG emissions. Higher GHG concentrations in compost windrows do not necessarily mean higher production or emission rates.

355. Evaluation of a simple model to describe carbon accumulation in a Brown Chernozem under varying fallow frequency

• Authors:
  • Blomert, B.
  • Liang, B. C.
  • Selles, F.
  • Zentner, R. P.
  • Campbell, C. A.
• Source: Canadian Journal of Soil Science
• Volume: 81
• Issue: 4
• Year: 2001
• Summary: Soil organic C (SOC) is readily influenced by crop management practices, such as summerfallowing. On the Canadian prairies, the area summerfallowed has decreased significantly in recent years. Our objectives were to determine the influence of fallow frequency on the rate of change in SOC in an Orthic Brown Chernozem, and to test the effectiveness of an empirical equation developed in an earlier study for estimating SOC changes in these rotations over 33-yr period. The rotations, which were initiated in 1967, all received adequate N and P fertilizers. They were (i) fallow-spring wheat (Triticum aestivum L.) (F-W), F-W-W, F-W-W-W-W-W and W-lentil (Lens culinaris L.) (W-Lent). Soil organic C was measured in the 0- to 15-cm and 15- to 30-cm depths in 1976, 1981, 1984, 1990, 1993, 1996 and 1999. No measurements of SOC were made in 1967; we estimated SOC starting values to be 30.5 Mg ha-1 in the 0- to 15-cm depth. In the period 1967 to 1990, when growing season precipitation was near normal for this semiarid region, SOC in the four rotations approached a steady state. However, a decade of much more favourable growing season precipitation in the 1990s increased C inputs, which resulted in a marked increase in SOC in the treatments. The empirical equation suggests, and the F-W and W-Lent rotations appear to confirm, that these rotations are approaching a new steady state at a higher level of SOC, reflecting the decade of favourable precipitation. Measured SOC levels were quite variable, emphasizing the difficulty of relying on measurements made over short time frames (e.g., 5-6yr) when quantifying SOC changes. The equation effectively simulated the trends in SOC changes in all rotations, but consistently underestimated SOC levels in the W-Lent rotation by about 2 Mg ha-1. Estimates of difference in SOC between treatments were generally similar whether expressed on a mass/fixed depth or a mass/equivalent depth basis. Based on the estimates derived by the empirical equation, we estimated rates of SOC sequestration during the 1967-1990 period to be 0.03 Mg ha-1 yr-1 for F-W, 0.10 Mg ha-1 yr-1 for F-W-W, and 0.15 Mg ha-1 yr-1 for W-Lent. If we include the decade of more favourable precipitation (1967-1999), the rates were between 0.05 Mg ha-1 yr-1 for F-W and 0.20 Mg ha-1 yr-1 for W-Lent. These values are much higher than those estimated by others using the CENTURY model. We concluded that (i) simple models, such as that used in this study, are very useful for estimating management effects on SOC changes, and (ii) we must be cautious in extrapolating C sequestration estimates based on data from short-term experiments because future weather conditions are not easily predicted and weather can have an important impact on C sequestration.

356. Spring wheat and canola response to nitrogen placement with no-till side band openers.

• Authors:
  • Hnatowich, G.
  • Hultgreen, G.
  • Lafond, G.
  • Johnston, A.
• Source: Canadian Journal of Plant Science
• Volume: 81
• Issue: 1
• Year: 2001
• Summary: The development of successful no-till crop production systems has led to the practice of applying all the seed and fertilizer in a single field operation. This study was initiated to assist producers in the selection of commercially available bolt-on side banding openers. Field trials were conducted at 10 locations in Saskatchewan, Canada, over a 2-year period (1995 and 1996) to evaluate the performance of five bolt-on side band openers on the establishment and yield of spring wheat ( Triticum aestivum) and rape ( Brassica rapa [ B. campestris]). Trial locations were selected to provide a range of soil and environmental conditions. The openers tested included the Flexi-coil Stealth, Dutch-Vern Eaglebuster, Swede SW470, GEN 200 and Morris Edge-On. Fertilizer nitrogen (N) as urea was applied in the side band at rates of 0, 40, 80 and 120 kg N ha -1 with a side banded starter fertilizer blend of phosphorus, potassium and sulfur. When properly adjusted for individual site soil conditions at sowing, no difference was recorded between the side band openers tested in the establishment and grain yield of spring wheat. Averaged across all N rates, three of the five openers showed poor rape seedling emergence, indicating inadequate seed-fertilizer separation. However, the ability of the rape crop to branch and compensate for poor crop establishment prevented any significant grain yield loss in this study. In cases where differences between openers were observed, the Flexi-Coil Stealth and GEN 200 openers provided the best crop establishment. Given the importance of crop establishment to achieving optimum grain yields, the bolt-on side band openers that provided good crop establishment should be recommended to producers.

357. Presence and persistence of volunteer canola in Canadian cropping systems.

• Authors:
  • Derksen, D.
  • Warwick, S.
  • Lajeunesse, J.
  • Pageau, D.
  • Thomas, A.
  • Simard, M.
  • Legere, A.
• Source: The BCPC Conference: Weeds, 2001, Volume 1 and Volume 2. Proceedings of an international conference held at the Brighton Hilton Metropole Hotel, Brighton, UK, 12-15 November 2001
• Year: 2001
• Summary: Risk evaluation of herbicide-tolerant (HT) crops includes the assessment of the presence and impact of volunteers. In this study, estimates of frequency and persistence of volunteer populations of rape were obtained from field surveys on farms in eastern (Quebec) and western (Manitoba, Saskatchewan and Alberta) provinces of Canada, and from field experiments conducted in both agroecological regions. Field surveys were conducted from June to August 2000 in eastern Canada, during 1995 in Saskatchewan, and during 1997 in Manitoba and Alberta. As expected, the density of rape volunteers decreased with time since the last rape crop. An average of 0.2 and 0.5 volunteer rape plants/m 2 were found in fields 5 and 4 years after rape production, in eastern and western Canada, respectively. Experimental results suggest the presence of a persistent rape seed bank, although it is likely that volunteers contribute to the replenishment of the seed bank over the years. Overwintering rape plants were also observed in eastern Canada in no-till cropping systems. Weed management in Canadian cropping systems generally provides adequate control of volunteer rape but still allows long-term persistence of low density populations.

358. Income risk analysis of alternative tillage systems for corn and soybean production on clay soils

• Authors:
  • Swanton, C.
  • Vyn, T. J.
  • Hooker, D. C.
  • Weersink, A.
  • Yiridoe, E. K.
• Source: Canadian Journal of Agricultural Economics
• Volume: 48
• Issue: 2
• Year: 2000
• Summary: Conservation tillage systems have not been widely adopted on clay soils. There are few empirical studies on the production potential and economic feasibility of conservation tillage systems for corn (Zea mays L.) and soybean (Glycine max L.) production on clay soils. On some soils in some regions, crop yields and possibly profitability can be increased and yield and net farm returns risks may be reduced through the use of conservation tillage systems. Stochastic dominance efficiency criteria are used to rank net return distributions for one conventional tillage (CT) and seven conservation tillage (including five reduced tillage and two no-till) systems conducted for corn and soybean cropping systems on two clay soils located in the 3050 to 3100 Corn Heat Unit areas of Ontario. Average yields are similar under conventional tillage and reduced tillage systems, although actual corn and soybean yield response to tillage treatment is affected by drought (year). Average net returns differ among tillage treatments due to two factors. First, actual corn and soybean yields vary among tillage systems for each soil type, depending on weather (i.e., year) effects. In addition, machinery costs that are crop-specific increase costs of production and therefore reduce net returns In general, CT systems dominate both reduced tillage and no-till systems for almost all risk intervals for both clay soils, except for slightly high-risk-preferring intervals.

359. Management options for reducing CO2 emissions from agricultural soils

• Authors:
  • Hunt, H. W.
  • Elliott, E. T.
  • Six, J.
  • Paustian, K.
• Source: Biogeochemistry
• Volume: 48
• Issue: 1
• Year: 2000
• Summary: Crop-based agriculture occupies 1.7 billion hectares, globally, with a soil C stock of about 170 Pg. Of the past anthropogenic CO2 additions to the atmosphere, about 50 Pg C came from the loss of soil organic matter (SOM) in cultivated soils. Improved management practices, however, can rebuild C stocks in agricultural soils and help mitigate CO2 emissions. Increasing soil C stocks requires increasing C inputs and/or reducing soil heterotrophic respiration. Management options that contribute to reduced soil respiration include reduced tillage practices (especially no-till) and increased cropping intensity. Physical disturbance associated with intensive soil tillage increases the turnover of soil aggregates and accelerates the decomposition of aggregate-associated SOM. No-till increases aggregate stability and promotes the formation of recalcitrant SOM fractions within stabilized micro- and macroaggregate structures. Experiments using 13C natural abundance show up to a two-fold increase in mean residence time of SOM under no-till vs intensive tillage. Greater cropping intensity, i.e., by reducing the frequency of bare fallow in crop rotations and increasing the use of perennial vegetation, can increase water and nutrient use efficiency by plants, thereby increasing C inputs to soil and reducing organic matter decomposition rates. Management and policies to sequester C in soils need to consider that: soils have a finite capacity to store C, gains in soil C can be reversed if proper management is not maintained, and fossil fuel inputs for different management practices need to be factored into a total agricultural CO2 balance.

360. Soil carbon and nitrogen dynamics following application of pig slurry for the 19th consecutive year: I. Carbon dioxide fluxes and microbial biomass carbon

• Authors:
  • Rochette,Philippe
  • Angers,Denis A.
  • Côté, D.
• Source: Soil Science Society of America Journal
• Volume: 64
• Issue: 4
• Year: 2000
• Summary: Agricultural soils often receive annual applications of manure for long periods. The objective of this study was to quantify the effects of 19 consecutive years of pig (Sus scrofa) slurry (PS) application on CO2 emissions and soil microbial biomass. Soil temperature, soil moisture, and extractable soil C were also determined to explain the variations in CO2 emissions and soil microbial biomass. Long-term (19 Sr) treatments were 60 (PS60) and 120 Mg ha(-1) yr(-1) (PS120) of pig slurry and a control receiving mineral fertilizers at a dose of 150 kg ha(-1) yr(-1) each of N, P2O5, and K2O. Very high CO2 emissions (up to 1.5 mg CO2 m(-2) s(-1)) occurred during the first 2 d after PS application. Following that peak, decomposition of PS was rapid, with one-half the total emissions occurring during the first meek after slurry application. The rapid initial decomposition was exponential and was attributed to the decomposition of the labile fraction. of the slurry C. The second phase was linear and much slower and probably involved more recalcitrant C material. Cumulative annual decomposition was proportional to the application rate, with 769 and 1658 kg C ha(-1) lost from the 60 and 120 Mg ha(-1) doses, respectively. Pig slurry application caused a rapid increase in soil microbial biomass (from approximate to 100 to up to 370 mg C kg(-1) soil), which coincided with a peak in the concentration of extractable C and in CO2 emissions. Field estimates of the microbial specific respiratory activity suggested that the difference in soil respiration between the two slurry treatments was due to differences in the size of the induced microbial biomass rather than to differences in specific activity.