H. Henry Janzen

Greenhouse gas mitigation in agriculture

Agricultural lands occupy 37% of the earths land surface. Agriculture accounts for 52 and 84% of global anthropogenic methane and nitrous oxide emissions. Agricultural soils may also act as a sink or source for CO2, but the net flux is small. Many agricultural practices can potentially mitigate greenhouse gas (GHG) emissions, the most prominent of which are improved cropland and grazing land management and restoration of degraded lands and cultivated organic soils. Lower, but still significant mitigation potential is provided by water and rice management, set-aside, land use change and agroforestry, livestock management and manure management. The global technical mitigation potential from agriculture (excluding fossil fuel offsets from biomass) by 2030, considering all gases, is estimated to be approximately 5500–6000 Mt CO2-eq. yr−1, with economic potentials of approximately 1500–1600, 2500–2700 and 4000–4300 Mt CO2-eq. yr−1 at carbon prices of up to 20, up to 50 and up to 100 US

Labile soil organic matter as influenced by cropping practices in an arid environment

t CO2-eq.−1, respectively. In addition, GHG emissions could be reduced by substitution of fossil fuels for energy production by agricultural feedstocks (e.g. crop residues, dung and dedicated energy crops). The economic mitigation potential of biomass energy from agriculture is estimated to be 640, 2240 and 16 000 Mt CO2-eq. yr−1 at 0–20, 0–50 and 0–100 US

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

t CO2-eq.−1, respectively.

Toward Improved Coefficients for Predicting Direct N2O Emissions from Soil in Canadian Agroecosystems

Abstract The dynamics of organic matter (OM) in prairie soils play an important role in long-term soil productivity and in the global carbon cycle. Temporal fluctuations in OM occur primarily in the readily-decomposable, labile fractions. We analyzed soils from a long-term study on a Brown Chernozem (Aridic Haploboroll) in southwestern Saskatchewan to determine the effect of cropping practices on OM content and composition under arid conditions. Soils (0−7.5 and 7.5–15 cm layers) from various rotations of spring wheat (Triticum aestivum L.), winter wheat, flax (Linum usitatissimum L.), lentil (Lens culinaris Medikus) and fallow were analyzed for organic C, total N and selected indicators of labile OM [light fraction(LF)-C, LF-N, mineralizable-C, mineralizable-N, microbial biomass(MB)-C and MB-N]. The indicators of labile OM were all more sensitive than total OM to agronomic variables. Treatment effects on all characteristics were usually similar in the 0−7.5 and 7.5–15 cm layers, but effects in the surface layer were often more highly significant. Frequency of fallow in the rotation was the dominant factor influencing labile OM. For example, LF-C in the 0−7.5 cm layer of well-fertilized continuously-cropped spring wheat, bare fallow-wheat-wheat and bare fallow-wheat was 3.15, 1.55 and 1.17 mg C kg−1 soil, respectively. The corresponding values for CO2-C mineralized at 21°C in 30 days were 371, 184 and 158 mg C kg−1 soil and those for cumulative net N mineralized in 16 weeks at 35°C were 126, 96 and 80 mg N kg−1 soil. MB-C and MB-N exhibited similar trends (e.g. MB-C was 368, 256 and 257 mg C kg−1 soil for the three treatments, respectively). Application of N fertilizer and substitution of winter wheat (with chemical fallow) for spring wheat (with tilled bare fallow) tended to increase labile OM, while substitution of flax or lentil for spring wheat had little effect or reduced labile OM. Differences in labile OM appeared to be related, not only to residue inputs, but also to moisture and temperature conditions. Our findings suggest that it may be possible to manipulate the timing of residue inputs and moisture through cropping practices and thereby maintain adequate labile OM concentrations and improve the synchrony of mineralization with crop requirements. Our results also imply that LF and mineralizable fractions may be useful as early indicators of OM change.

Changes in total, mineralizable and light fraction soil organic matter with cropping and tillage intensities in semiarid southern Alberta, Canada

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 aestivumL.) in 1996 and canola (Brassica napusL.) 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.

A proposed approach to estimate and reduce net greenhouse gas emissions from whole farms

Agricultural soils emit nitrous oxide (N2O), a potent greenhouse gas. Predicting and mitigating N2O emissions is not easy. To derive national coefficients for N2O emissions from soil, we collated over 400 treatment evaluations (measurements) of N2O fluxes from farming systems in various ecoregions across Canada. A simple linear coefficient for fertilizer-induced emission of N2O in non-manured soils (1.18% of N applied) was comparable to that used by the Intergovernmental Panel on Climate Change (IPCC) (1.25% of N applied). Emissions were correlated to soil and crop management practices (manure addition, N fertilizer addition and inclusion of legumes in the rotation) as well as to annual precipitation. The effect of tillage on emissions was inconsistent, varying among experiments and even within experiments from year to year. In humid regions (e.g., Eastern Canada) no-tillage tended to enhance N2O emissions; in arid regions (e.g., Western Prairies) no-tillage sometimes reduced emissions. The variability of N2O fluxes shows that we cannot yet always distinguish between potential mitigation practices with small (e.g., <10%) differences in emission. Our analysis also emphasizes the need for developing consistent experimental approaches (e.g., ‘control’ treatments) and methodologies (i.e. measurement period lengths) for estimating N2O emissions.

Weed species response to phosphorus fertilization

Abstract There has been a trend toward increased cropping intensity and decreased tillage intensity in the semiarid region of the Canadian prairies. The impact of these changes on sequestration of atmospheric CO 2 in soil organic carbon (C) is uncertain. Our objective was to quantify the changes in total, mineralizable and light fraction organic C and nitrogen (N) due to the adoption of continuous cropping and conservation tillage practices. We sampled three individual long-term experiments at Lethbridge, Alberta, in September 1992: a spring wheat ( Triticum aestivum L.)-fallow tillage study, a continuous spring wheat tillage study and a winter wheat rotation-tillage study. Treatments had been in place for 3–16 years. In the spring wheat-fallow study, different intensities (one-way disc > heavy-duty cultivator > blade cultivator) of conventional tillage (CT) were compared with minimum tillage (MT) and zero tillage (ZT). After 16 years, total organic C was 2.2 Mg ha −1 lower in more intensively worked CT treatments (one-way disc, heavy-duty cultivator) than in the least-intensive CT treatment (blade cultivator). The CT with the blade cultivator and ZT treatments had similar levels of organic C. The CT treatments with the one-way disc and heavy-duty cultivator had light fraction C and N and mineralizable N amounts that were about 13–18% lower than the CT with the blade cultivator, MT or ZT treatments. In the continuous spring wheat study, 8 years of ZT increased total organic C by 2 Mg ha −1 , and increased mineralizable and light fraction C and N by 15–27%, compared with CT with a heavy-duty cultivator prior to planting. In the winter wheat rotation-tillage study, total organic C was 2 Mg ha −1 higher in a continuous winter wheat (WW) rotation compared with that in a winter wheat-fallow rotation. The lack of an organic C response to ZT on the WW rotation may have been due to moldboard plowing of the ZT treatment in 1989 (6 years after establishment and 3 years before soil sampling), in an effort to control a severe infestation of downy brome ( Bromus tectorum L.). Our results suggest that although relative increases in soil organic matter were small, increases due to adoption of ZT were greater and occurred much faster in continuously cropped than in fallow-based rotations. Hence intensification of cropping practices, by elimination of fallow and moving toward continuous cropping, is the first step toward increased C sequestration. Reducing tillage intensity, by the adoption of ZT, enhances the cropping intensity effect.

Energy balances of biodiesel production from soybean and canola in Canada.

Greenhouse gas emissions from farms can be suppressed in two ways: by curtailing the release of these gases (especially N2O and CH4), and by storing more carbon in soils, thereby removing atmospheric CO2. But most practices have multiple interactive effects on emissions throughout a farm. We describe an approach for identifying practices that best reduce net, whole-farm emissions. We propose to develop a “Virtual Farm”, a series of interconnected algorithms that predict net emissions from flows of carbon, nitrogen, and energy. The Virtual Farm would consist of three elements: descriptors, which characterize the farm; algorithms, which calculate emissions from components of the farm; and an integrator, which links the algorithms to each other and the descriptors, generating whole-farm estimates. Ideally, the Virtual Farm will be: boundary-explicit, with single farms as the fundamental unit; adaptable to diverse farm types; modular in design; simple and transparent; dependent on minimal, attainable inputs; ...

Root mass for oilseed and pulse crops: Growth and distribution in the soil profile

Abstract Information on weed responses to soil fertility levels is needed to aid development of fertilizer management strategies as components of integrated weed management programs. A controlled environment study was conducted to determine shoot and root growth response of 22 agricultural weeds to fertilizer phosphorus (P) applied at 5, 10, 20, 40, or 60 mg kg−1 soil. An unfertilized control was included. Wheat and canola were included as control species. Shoot and root growth of all weeds increased with added P, but the magnitude of the response varied greatly among species. Many weeds exhibited similar or greater responses in shoot and root biomass to increasing amounts of soil P compared with wheat or canola. With increasing amounts of P, 17 weed species increased shoot biomass more than wheat, and 19 weed species increased shoot biomass more than canola. However, only 10 weed species exhibited greater increases in root biomass than canola, and no weed species increased root biomass more than wheat with added P. Canola was among species taking up the greatest percentage of available P at all P doses. However, percentage P uptake by wheat relative to other species varied with P dose. Only four weed species extracted more P than wheat at low P levels, but 17 weed species extracted more P at high soil P levels. These findings have significant implications as to how soil fertility may influence crop–weed competition. Nomenclature: Canola, Brassica napus L. ‘Excel’; spring wheat, Triticum aestivum L. ‘Katepwa’.

Nitrogen dynamics in soil amended with composted cattle manure

Biodiesel is currently produced in Canada mostly from recycled oils and animal fats. If biodiesel is to supply 5% of diesel usage, a government objective, first-time vegetable, likely from canola and soybean, oil will also be required to provide adequate feedstocks. In this review, we estimate the life cycle energy balances for biodiesel produced from soybean and canola oil under Canadian conditions. The three broad areas of energy inputs were crop production, oil extraction, and transesterification of the vegetable oil into biodiesel. Per unit seed yield, farm production energy inputs for canola were about three times higher than for soybean, mostly because of higher nitrogen fertilizer requirements for canola. Energy required for processing and oil extraction, per unit oil, was higher for soybean. Energy allocation for co-products was allocated using a system expansion approach. Protein meal was assigned about 12% of the energy expended for canola to grow the crop and extract the oil, and about 37% for ...