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Published in Agron J 99:1719-1725 (2007)
DOI: 10.2134/agronj2006.0327s
© 2007 American Society of Agronomy
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Symposium Papers

Can Pulse Crops Play a Role in Mitigating Greenhouse Gases from North American Agriculture?

R. L. Lemkea,*, Z. Zhonga, C. A. Campbellb and R. Zentnerc

a Saskatoon Research Centre, Agriculture & Agri-Food Canada, 51 Campus Drive, Saskatoon, SK S7N 5A8
b Eastern Cereal and Oilseed Research Centre, Agriculture & Agri-Food Canada, Ottawa, ON K1A 0C6
c Semiarid Prairie Agricultural Research Centre, Agriculture & Agri-Food Canada, Swift Current, SK, S9H 3X2 Canada

* Corresponding author (lemker{at}agr.gc.ca)


   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 PULSE CROPS AND SOIL...
 PULSE CROPS AND NITROUS...
 CONCLUSIONS
 REFERENCES
 
The atmospheric buildup of greenhouse gases (GHGs) is a serious environmental issue. Globally, agricultural activities are an important source of anthropogenic GHGs, contributing ~20% of the annual atmospheric increase. Management choices largely determine if agricultural soils will be a source, a sink, or will be neutral with respect to GHG net flux. The proportion of agricultural land that is seeded to pulse crops in the Northern Great Plains (NGP) region of North America has been increasing rapidly over the past decade. Introducing pulses into cereal-based cropping systems could influence the net GHG balance of those systems because pulse crops are thought to stimulate soil-emitted N2O, have different pesticide and fertilizer requirements, and the quality and quantity of their residues vary substantially compared with cereal crops. In this paper we briefly review the available literature, and discuss the potential impact of pulse crops on the net flux of CO2, N2O, and CH4 from soils, and the CO2 emissions associated with energy inputs for cropping systems in the NGP. We also calculate net GHG balances for two example sites. Estimating the final GHG outcome of introducing pulses into cereal-based cropping systems is still uncertain, but current information suggests that replacing a cereal with a pulse crop will likely result in no change or a small but positive net GHG benefit (lower emissions to the atmosphere) for crop rotations in the NGP region.

Abbreviations: CO2e, carbon dioxide equivalents • GHG, greenhouse gas • HI, harvest index • NGP, Northern Great Plains • SOC, soil organic carbon

Can Pulse Crops Play a Role in Mitigating Greenhouse Gases from North American Agriculture?

R. L. Lemkea,*, Z. Zhonga, C. A. Campbellb and R. Zentnerc

a Saskatoon Research Centre, Agriculture & Agri-Food Canada, 51 Campus Drive, Saskatoon, SK S7N 5A8
b Eastern Cereal and Oilseed Research Centre, Agriculture & Agri-Food Canada, Ottawa, ON K1A 0C6
c Semiarid Prairie Agricultural Research Centre, Agriculture & Agri-Food Canada, Swift Current, SK, S9H 3X2 Canada

* Corresponding author (lemker{at}agr.gc.ca)

Received for publication November 17, 2006.
The atmospheric buildup of greenhouse gases (GHGs) is a serious environmental issue. Globally, agricultural activities are an important source of anthropogenic GHGs, contributing ~20% of the annual atmospheric increase. Management choices largely determine if agricultural soils will be a source, a sink, or will be neutral with respect to GHG net flux. The proportion of agricultural land that is seeded to pulse crops in the Northern Great Plains (NGP) region of North America has been increasing rapidly over the past decade. Introducing pulses into cereal-based cropping systems could influence the net GHG balance of those systems because pulse crops are thought to stimulate soil-emitted N2O, have different pesticide and fertilizer requirements, and the quality and quantity of their residues vary substantially compared with cereal crops. In this paper we briefly review the available literature, and discuss the potential impact of pulse crops on the net flux of CO2, N2O, and CH4 from soils, and the CO2 emissions associated with energy inputs for cropping systems in the NGP. We also calculate net GHG balances for two example sites. Estimating the final GHG outcome of introducing pulses into cereal-based cropping systems is still uncertain, but current information suggests that replacing a cereal with a pulse crop will likely result in no change or a small but positive net GHG benefit (lower emissions to the atmosphere) for crop rotations in the NGP region.

Abbreviations: CO2e, carbon dioxide equivalents • GHG, greenhouse gas • HI, harvest index • NGP, Northern Great Plains • SOC, soil organic carbon


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
PULSE CROPS AND SOIL...
 PULSE CROPS AND NITROUS...
 CONCLUSIONS
 REFERENCES
 
THE ATMOSPHERIC CONCENTRATIONS of GHGs such as carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) are increasing rapidly. Concern about how this may affect the atmospheric energy balance (global warming) has prompted the establishment of international agreements (e.g., Kyoto Protocol) intended to reduce anthropogenic emissions. Globally, agricultural activities represent an important source of GHGs contributing ~20% of the annual atmospheric increase (Cole et al., 1997). These estimates are highly uncertain. Information about how farming practices may impact net GHG balances is needed.

The cropping area devoted to production of pulse crops such as dry pea (Pisum sativum L.), lentil (Lens culinaris Medik.), dry bean (Phaseolus vulgaris L.), and chickpea (Cicer arietinum L.) has expanded dramatically during the last decade in the NGP region of North America. In Saskatchewan, for example, the pulse crop area has more than doubled, with nearly two million hectares seeded to pulse crops in 2005 (Saskatchewan Agriculture, Food and Rural Revitalization, 2005). Introducing pulse crops into what had been predominantly cereal-based systems could potentially impact their overall GHG balance in several ways. Soil organic carbon (SOC) levels on agricultural land in the NGP are directly influenced by the amount of C returned to the soil in crop residue (Campbell et al., 2000a, 2000b). The quantity and quality of pulse residues often varies substantially from that of cereals, potentially influencing SOC levels. As well, pulse crops have different pesticide and fertilizer requirements than cereals which will influence the magnitude of CO2 emitted from the fossil fuel use related to the manufacture and application of these inputs. Lastly, the Intergovernmental Panel on Climate Change (1997) has proposed a standard methodology to prepare national inventories of GHG emissions. This approach assigns an N2O emission to the N in pulse residues that are returned to the soil, and a second emission to the amount of N that is biologically fixed when a pulse crop is grown. Using default values from this methodology and assuming equivalent seed yields, the estimated N2O emission per unit area can be substantially higher from pulse crops compared with a fertilized cereal crop.

In view of the growing importance of pulse crops in the NGP and their potential influence on GHG emissions, it seems prudent to consider what influence the inclusion of pulse crops may have on the net GHG balance of cropping systems in this region. This paper attempts to address this question by reviewing the published and unpublished literature currently available.


   PULSE CROPS AND SOIL ORGANIC CARBON
TOP
 ABSTRACT
 INTRODUCTION
 PULSE CROPS AND SOIL...
PULSE CROPS AND NITROUS...
 CONCLUSIONS
 REFERENCES
 
Soil organic C status reflects the balance between C inputs and C losses over time. We can represent this as

Formula 1[1]
where dCs/dt = change over time in mass of organic C stored in the soil profile; A = carbon additions (crop residues including roots); h = humification coefficient (amount of residue C stabilized as SOC); Cs = soil organic carbon pool; k = decomposition rate; and Cr = is the amount of carbon lost through erosion.

It is unclear if the redistribution of C due to erosion results in increased or decreased CO2 emissions to the atmosphere (Lal, 2007). The paired comparisons of measured SOC change and the "residue C conversion efficiency factor" used later in this paper represent the net result of all factors that influence SOC, including erosion and deposition. For the purposes of this paper we will assume that erosion has been accounted for or has a negligible impact on GHG balance. No further discussion regarding the impact of pulse crops on erosion rates is provided.

Soil organic C status is strongly related to the quantity of crop residues returned to the land (Campbell et al., 1997, 2000a, 2000b; Rasmussen et al., 1980). The quality and quantity of pulse residues may vary substantially from that of cereals. Growing a pulse in place of a cereal crop could potentially influence both A and h, thereby influencing the magnitude and direction of SOC change.

A summary of grain dry matter yields for pulses, presented as a ratio of spring wheat (Triticum aestivum L.) yield, for eight studies in the NGP is shown in Table 1 . These values indicate that, on average, pulse crops have lower grain yields compared with spring wheat. The average harvest index (HI), calculated from the same studies, did not vary much among these crops (Table 2 ), although within-crop variability was often very high. Using mean HI, and assuming that C concentration of dry matter is equivalent between crop types (Soon and Arshad 2002), aboveground residue C returns would be between 16 and 50% lower for pulses compared with spring wheat.


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  		Table 1. Seed yield of spring wheat and ratio of seed yield of three pulse crops relative to spring wheat grown at various locations in the Northern Great Plains.

 

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  		Table 2. Harvest index [grain/(grain + straw)] of spring wheat and three pulse crops grown at various locations in the Northern Great Plains.

 
Numerous workers have reported a yield advantage for wheat grown on pulse stubble compared with wheat grown on wheat stubble. Table 3 presents a summary of grain dry matter yields for wheat grown on pulse stubble, reported as a ratio to spring wheat grown on wheat stubble, for a number of studies conducted in the NGP. Overall, spring wheat grown on pulse stubble produced about 11% more grain than when grown on spring wheat stubble. Similarly, Gan et al. (2003) found that yields of durum wheat (Triticum turgidum L.) grown on pulse stubble averaged 8% higher than durum grown on spring wheat stubble. These workers also reported that durum yields were 5% higher in the second year following the pulse crop. Conversely, Campbell et al. (2000a) reported that long-term average yields for spring wheat grown on lentil stubble were not significantly different than yields of monoculture wheat. Of course, higher grain yield may not necessarily translate into higher residue returns because HI may also differ when cereals are grown on pulse stubble.


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  		Table 3. Seed yield of spring wheat grown on pulse stubble relative to spring wheat grown on cereal stubble at various locations in the Northern Great Plains.

 
Root C inputs are extremely important to SOC status (Campbell et al., 1991). Information on root C inputs is scarce as quantitative measurement is fraught with difficulty. Merrill et al. (2002) reported significantly greater rooting depth and density for spring wheat compared with dry pea or bean. We may infer from this that root biomass C may also be significantly different. This is consistent with the findings of Soon and Arshad (2002), who reported that root dry matter production in the 0- to 12.5-cm soil depth was lower for pea compared with spring wheat. We found no data in the literature for other pulse crops. There was not sufficient quantitative data available to derive an estimate of root C inputs for pulse crops. For the purpose of this paper, therefore, we assumed that root C inputs from pulse crops were comparable with wheat and used the same root–shoot ratio for all crops.

Cereals and pulses have differing growth, canopy, and rooting patterns, which could influence surface soil temperature, moisture, and N availability. In turn, these conditions could influence the rate of SOC decomposition (k value) under pulse crops. Huggins et al. (2007) demonstrated that the presence of soybean [Glycine max (L.) Merr.] in rotation with corn (Zea mays L.) accelerated SOC decomposition (higher k value) compared with continuous corn for a long-term study near Waseca, MN. However, on the semiarid Canadian prairies, Campbell et al. (2001) found that the best fit equation to simulate SOC change for continuously cropped systems utilized the same k value whether or not a pulse crop was present.

The C to N ratio of crop residues strongly influences their decomposition rate (Parr and Papendick, 1978; Reinertsen et al., 1984; Janzen and Kucey, 1988). More important to this discussion, several workers (Biederbeck et al., 1994; Campbell et al., 2000a; Drinkwater et al., 1998) have speculated that the presence of legumes in rotation may result in more efficient conversion of residue C to SOC compared with monoculture wheat. A more efficient conversion of pulse residue C to SOC would help mitigate SOC loss if residue C inputs are lower when pulse crops are grown. Of course, if residue C inputs are similar for pulse compared with cereal crops, then cereal-pulse systems should have higher SOC compared with their monoculture cereal counterparts.

Only a few field studies are available that provide an indication of the C conversion efficiency of residues of varying quality, and the results are mixed. Larson et al. (1972) found that SOC accumulation was similar for similar amounts of C added in residues despite widely varying quality attributes (C–N ratio). Jenkinson et al. (1999) reported similar C inputs for wheat-wheat versus wheat-pulse cropping systems and found no significant SOC differences after 10 yr for a semiarid site in Syria. In the Pacific Northwest (Pendleton, OR), Collins et al. (1992) reported that similar C inputs for winter wheat-pea compared with continuous wheat rotations resulted in similar SOC status after 25 yr. Conversely, in a 19-yr study in Oregon, Rasmussen et al. (1998) reported a higher SOC loss for a wheat-pea compared with a wheat-wheat rotation. In the NGP (Swift Current, SK), Campbell et al. (2001) reported lower C inputs for spring wheat-lentil compared with a continuous wheat system but similar SOC status after 20 yr.


   PULSE CROPS AND NITROUS OXIDE EMISSIONS
TOP
 ABSTRACT
 INTRODUCTION
 PULSE CROPS AND SOIL...
 PULSE CROPS AND NITROUS...
CONCLUSIONS
 REFERENCES
 
There are two questions to ask when considering how the introduction of a pulse crop into a cereal-based system may affect N2O emissions. First, does the presence of the pulse crop itself change net annual emissions? In other words, will emissions during the pulse phase of a rotation be different than during the cereal phase? Second, will pulse residues affect N2O emissions differently than cereal residues?

Many rhizobia are able to liberate gaseous N from nitrate (e.g., Rajagopalan, 1938; Ishizawa, 1939; Wilson, 1947). Therefore, inoculating pulse crops with Rhizobia could increase potential N2O loss via denitrification. However, the environmental significance of denitrification by Rhizobia is uncertain. O'Hara and Daniel (1985) suggested that rates of N loss by rhizobial denitrification from soils were similar to those of biological N2 fixation. In contrast, Garcia-Plazaola et al. (1993) found that, even with optimal conditions for denitrification and the highest rhizobial populations found in agricultural soils, the contribution of Rhizobia to total denitrification was negligible. Zhong et al. (2004) grew inoculated and noninoculated lentil and field pea in a soilless medium. Under anaerobic conditions, with or without the presence of NO3–N, N2O emissions remained negligible.

In the field, soil-emitted N2O is governed by many factors, including soil moisture and aeration status, temperature, N and C availability, and microbial community dynamics. Crop type (pulse versus cereal) can differentially affect each of these factors. At two sites in western Canada, Lemke et al. (2002) reported that growing season N2O emissions from field pea or lentil crops were significantly lower than from fertilized cereal crops and were comparable with estimated background emissions (Table 4 ). Even in higher-moisture areas of eastern Canada, Rochette et al. (2004) found that growing season N2O emissions from soybean were similar to emissions from unfertilized reference crops. In a growth room experiment, Zhong et al. (2004) compared inoculated lentils and field pea, fertilized noninoculated lentil and field pea, and fertilized and unfertilized wheat. Emissions were comparable amongst crops receiving fertilizer, while emissions from inoculated crops were much lower and comparable with the control treatments.


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  		Table 4. Estimated cumulative N2O loss measured during the frost-free period (May–October) at two locations in the Northern Great Plains.

 
Residue type has been shown to be an important factor affecting N2O emission (Aulakh et al., 1991; McKenney et al., 1993; Shelp et al., 2000). Several workers have reported a strong negative correlation between the C–N ratio of residues and cumulative N2O emissions (Bremner and Blackmer 1981; Baggs et al., 2000; Huang et al., 2004). Residues with a low C–N ratio can stimulate N2O emissions as they are both a source of N for nitrification and potentially denitrification, and a source of easily decomposable C. The latter not only provides a ready substrate for denitrifiers, but also stimulates overall microbial growth and activity, promoting oxygen consumption and creating temporary anaerobic microsites that would favor denitrification (Sahrawat and Keeney, 1986; Goek and Ottow, 1988). Accordingly, soil incorporation of legume residues could result in higher N2O losses than incorporation of nonlegume residues. Indeed, high N2O emissions have been reported after plow-down of established alfalfa (Medicago sativa L.) stands (Wagner-Riddle and Thurtell, 1998). However, N2O emissions are governed by many factors, including rainfall, existing soil mineral N status, and temperature. Lemke et al. (2002) reported that emissions from wheat grown on pulse stubble (pea or lentil) were comparable or lower than emissions from fertilized monoculture wheat (Table 4) at two sites in western Canada. Emissions generally reflected fertilizer-N inputs. At the semiarid site in Saskatchewan, fertilizer-N requirements were based on spring soil test NO3–N levels. Nitrogen requirements tended to be lower for wheat grown on pulse stubble compared with wheat grown on wheat stubble, with subsequent N2O emissions being lower from the wheat grown on pulse stubble. At the subhumid site in Alberta, equivalent rates of fertilizer N were applied to all wheat treatments irrespective of previous crop, and N2O emissions were generally similar from all wheat phases. Nitrous oxide emissions were generally similar during the spring thaw period for cereal versus pulse stubbles (Table 5 ), although the variability of these measurements was extremely high.


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  		Table 5. Estimated cumulative N2O loss measured following spring snow melt (March–April) at two locations in the Northern Great Plains.

 
The limited literature available does not suggest that the presence of nodulated (actively N-fixing) pulse crops increases N2O emissions directly. Emissions from the pulse phase of crop rotations in the NGP tend to be lower than emissions from their fertilized cereal counterparts. Similarly, emissions do not appear to be higher from fertilized cereals grown on pulse stubbles compared with fertilized cereals grown on cereal stubble.

Pulse Crops and Methane Consumption
In well-aerated soils, methanotrophs can gain energy by oxidizing CH4 to CO2. Converting native ecosystems to agricultural use tends to reduce the soil sink strength (Ojima et al., 1993; Willison et al., 1995; Dobbie et al., 1996; Prieme et al., 1997; Smith et al., 2000). The reason for this reduction is not clear because many changes occur simultaneously when native ecosystems are converted to agricultural use, but application of NH4–containing fertilizers (Mosier et al., 1991; Hütsch et al., 1994; King and Schnell 1994) and physical disturbance of the soil have been implicated as likely causes (Hütsch, 2001). A number of studies have shown that long-term application of NH4–based fertilizers can reduce CH4 oxidation capacity to negligible levels, although some studies have shown no or limited impact (Dobbie and Smith, 1996; Delgado and Mosier, 1996). In soils where CH4 oxidation capacity has been inhibited, we might surmise that avoiding the application of an NH4–based fertilizer during the year in which pulse crops are grown would benefit CH4 oxidation. However, it is not clear how rapidly CH4 oxidation capacity can be restored. If long-term fertilization with NH4–based fertilizers has affected the kinetics of the CH4–oxidizing community (King, 1992; Nesbit and Breitenbeck, 1992) it would be unlikely that this would be reversed in a single season. We will assume for the purposes of this paper that pulse crops have no significant impact on soil CH4–oxidation capacity.

Pulse Crops and Carbon Dioxide from Nonrenewable Energy Inputs
Traditional cereal-based production systems used by producers in the NGP are heavily dependent on the input of nonrenewable energy. Fossil fuel is used mainly for the manufacture and transport of fertilizers, pesticides, and machinery, and to power farm implements. Past research has shown that up to 70% of the nonrenewable energy used in cropping systems in western Canada is attributable to inorganic fertilizers, particularly N (Zentner et al., 2004). Pulse crops supply much of their N requirement through biological fixation, thereby reducing the overall fertilizer N inputs for the rotation (N substitution). Second, fertilizer N requirements are frequently reduced for the subsequent nonlegume crop (N-credit).

Nagy et al. (2000), Zentner et al. (2004), and Coxworth et al. (1996) calculated the energy inputs for representative cropping systems at four sites in western Canada. From the data they presented we selected pairs of rotations that were nearly identical—differing only in that one of the rotations included a pulse crop. For example, Nagy et al. (2000) reported on two 4-yr rotations. Each rotation included a year of spring wheat, canola (Brassica napus L.), and barley (Hordeum vulgare L.), but one rotation included a second year of barley while the alternate rotation included a year of field pea (Table 6 ). Differences in nonrenewable energy inputs between these rotation pairs can be attributed to the substitution of a pulse crop for a cereal crop. The energy input values (MJ ha–1) were converted to carbon dioxide equivalents (CO2e) using coefficients calculated by Nagy et al. (2000).


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  		Table 6. Carbon dioxide emissions related to energy inputs for rotations with and without pulse crops at four sites in Saskatchewan.

 
Rotations containing a pulse crop had lower CO2e emissions compared with their nonpulse counterparts for all comparisons (Table 6). The magnitude of the difference was much larger at Swift Current than at the other three sites primarily because a pulse crop was included once every 2 yr, whereas at the other locations a pulse crop was included only once every 4 yr.

Pulse Crops and Net Carbon Dioxide Equivalents
We have so far concluded that replacing a cereal with a pulse crop will likely have a negligible effect on CH4 consumption rates, and will reduce overall N2O emissions as well as CO2 emissions related to energy inputs. The impact on SOC levels is probably more crop specific. On the NGP, SOC levels appear to be linearly related to C inputs. Crops such as lentil or chickpea may produce less residue C, potentially reducing SOC levels, with a concomitant increase in net CO2 emissions. In contrast, residue C inputs from field pea are often comparable to the cereal counterpart, and SOC status may be unaffected. Other factors, such as changes to SOC decomposition rate, may also be affected, which could offset or enhance the changes due to differences in C inputs, making the latter conclusion particularly uncertain.

When all components are considered, how is the net GHG budget of a rotation affected by introducing a pulse crop? Table 7 presents estimated CO2e emissions based on actual measurements for a long-term study at Swift Current, SK. In this study, CO2e emissions from energy inputs and N2O emissions were lower for wheat-lentil compared with the monoculture spring wheat and measured SOC levels indicate no significant difference between the two treatments after 17 yr (Campbell et al., 2000a). Summing the components resulted in a total annual CO2e emission that was about 180 kg ha–1 lower for the wheat-lentil compared with monoculture spring wheat.


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  		Table 7. Greenhouse gas emissions, expressed as CO2 equivalents (CO2e), from energy inputs, soil organic carbon change, and direct N2O emissions from soil, for two cropping systems at Swift Current, SK.1

 
Table 8 provides a similar example from a subhumid site at Indian Head, SK. Energy inputs were reported by Zentner et al. (2004) and grain yield data by Zentner et al. (2002). No measurements of N2O or SOC status were available; therefore, we estimated potential change in SOC using residue C inputs calculated from yield data, a HI of 0.35 (Table 2), a root–straw ratio of 0.27 (assuming SOC changes are restricted to the 0–15 cm soil depth) (Campbell and De Jong 2001), and assumed that the C concentration of both roots and shoots is 0.45, and that the residue C to SOC conversion efficiency factor is ~18% (Campbell et al., 2000a). We assumed that 1.25% of fertilizer N applied was lost as N2O (Intergovernmental Panel on Climate Change, 1997). At this site, residue C inputs from the rotation that included field pea were slightly higher than the nonpulse counterpart, thus all components of the GHG budget had lower CO2e emissions from the pulse compared with nonpulse rotation. Similar to the previous example, summing the components resulted in a total annual CO2e emission that was about 170 kg ha–1 lower on the rotation that included field pea.


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  		Table 8. Greenhouse gas emissions, expressed as CO2 equivalents (CO2e), from energy inputs, soil organic carbon change, and direct N2O emissions from soil, for two cropping systems at a site in the subhumid region of Saskatchewan.

 
Previously, we indicated that mean grain yield was 48% lower for chickpea compared with spring wheat (Table 1). Using the mean spring wheat grain yield presented by Zentner et al. (2002), and making the same assumptions as in the previous example; this would result in a net SOC reduction of over 40 kg ha–1 yr–1 or a CO2e emission of nearly 160 kg ha–1 yr–1 if this rotation had included chickpea compared with one that did not. The CO2e reductions for N2O and energy inputs totaled about 160 kg ha–1 yr–1, resulting in no net change in overall CO2e emissions. We acknowledge the many assumptions and their high degree of uncertainty, but our example highlights how easily the magnitude and perhaps even the trajectory of the net GHG budget can be affected, and emphasizes the need for further research. In particular, these examples show that N2O emissions represent a substantial portion of the CO2e budget for cropping systems in the NGP. Considering the high degree of uncertainty surrounding N2O emissions estimates, this area of research appears to require particular attention. Employing properly validated simulation models would undoubtedly help to reduce the uncertainty and greatly refine these estimates.


   CONCLUSIONS
TOP
 ABSTRACT
 INTRODUCTION
 PULSE CROPS AND SOIL...
 PULSE CROPS AND NITROUS...
 CONCLUSIONS
REFERENCES
 
Data assessing SOC change and N2O emissions when pulse crops are grown in rotation for the NGP are limited, and their uncertainty is high. A summary of grain yield data from the NGP suggests that C inputs will not change significantly if field pea is introduced into a cereal-based rotation, but C inputs may be reduced if other pulses such as chickpea or lentil are grown. Lower C inputs implies a potential reduction in SOC status over time; however, data from a long-term study at Swift Current, SK, does not support this hypothesis. Field measurements show that N2O emissions tend to be lower from pulse crops compared with their fertilized cereal counterparts and emissions from cereal grown on pulse stubble was not significantly different than emissions from cereal grown on cereal-stubble. We infer from this that rotations that include a pulse will likely have lower overall N2O emissions compared with rotations that do not include a pulse crop. Similarly, CO2e emissions from energy inputs are reduced in proportion to the frequency of pulse in the cropping cycle and the typical rate of fertilizer N applied on the nonpulse crops. Overall, replacing a cereal with a pulse crop will likely result in no change or a small but positive net CO2e benefit (lower emissions to the atmosphere) for crop rotations in the NGP region.


   REFERENCES
TOP
 ABSTRACT
 INTRODUCTION
 PULSE CROPS AND SOIL...
 PULSE CROPS AND NITROUS...
 CONCLUSIONS
 REFERENCES
 





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