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Symposium Papers

Adaptation of Pulse Crops to the Changing Climate of the Northern Great Plains

^a Agriculture and Agri-Food Canada, P.O. Box 1030, Swift Current, SK S9H3X2, Canada
^b Agriculture and Agri-Food Canada, Lethbridge Research Centre, Lethbridge, AB T1J4B1, Canada
^c USDA-ARS, 303 Johnson Hall, Pullman, WA 99164-6434
^d Dep. Land Resources and Environmental Sci., Montana State Univ., Bozeman, MT59717

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

	ABSTRACT

TOP ABSTRACT INTRODUCTION ADOPTION AND ROLE OF... PULSE CROPS AND THE... NOTES CLIMATE CHANGE ON THE... PULSE RESPONSE TO FUTURE... ADAPTATION TECHNOLOGIES AND... SUMMARY REFERENCES

 
Climate over the northern Great Plains has generally warmed over the last 60 yr. The rate of warming has varied temporally and spatially, confounding trend analysis for climate indicators such as increased length of the growing season. Change in precipitation has been even more variable. Despite this variability, present-day trends in temperature and precipitation generally coincide with the predicted direction of climate change. The synchrony of current and future trends reinforces the need for investigating adaptation in agriculture to changing climate. Our review is focused on sustainability of pulse crops in the northern Great Plains and the repercussions of climate change, focusing on the growth and yield response to temperature and water, and the climate restrictions that define their current geographic locations. The resilience of pulse crops to present-day weather extremes such as drought, excess water, heat, cool weather during grain filling, and early frost are considered to predict adaptation to future climate change. Features discussed include changes to crop water-use efficiency brought on by increased CO₂ fertilization, accelerated growth rates resulting from higher air temperatures, and total crop failures caused by an increased occurrence and magnitude of weather extremes. Adaptation strategies that are discussed include earlier seeding of pulse crops, use of winter pulses, crop sequencing within crop rotations, and alterations to the microclimate such as direct seeding into standing stubble.

Abbreviations: ET, evapotranspiration • GCM, global climate model • WUE, mean water use efficiency

Adaptation of Pulse Crops to the Changing Climate of the Northern Great Plains

^a Agriculture and Agri-Food Canada, P.O. Box 1030, Swift Current, SK S9H3X2, Canada
^b Agriculture and Agri-Food Canada, Lethbridge Research Centre, Lethbridge, AB T1J4B1, Canada
^c USDA-ARS, 303 Johnson Hall, Pullman, WA 99164-6434
^d Dep. Land Resources and Environmental Sci., Montana State Univ., Bozeman, MT59717

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

Received for publication November 6, 2006.
Climate over the northern Great Plains has generally warmed over the last 60 yr. The rate of warming has varied temporally and spatially, confounding trend analysis for climate indicators such as increased length of the growing season. Change in precipitation has been even more variable. Despite this variability, present-day trends in temperature and precipitation generally coincide with the predicted direction of climate change. The synchrony of current and future trends reinforces the need for investigating adaptation in agriculture to changing climate. Our review is focused on sustainability of pulse crops in the northern Great Plains and the repercussions of climate change, focusing on the growth and yield response to temperature and water, and the climate restrictions that define their current geographic locations. The resilience of pulse crops to present-day weather extremes such as drought, excess water, heat, cool weather during grain filling, and early frost are considered to predict adaptation to future climate change. Features discussed include changes to crop water-use efficiency brought on by increased CO₂ fertilization, accelerated growth rates resulting from higher air temperatures, and total crop failures caused by an increased occurrence and magnitude of weather extremes. Adaptation strategies that are discussed include earlier seeding of pulse crops, use of winter pulses, crop sequencing within crop rotations, and alterations to the microclimate such as direct seeding into standing stubble.

Abbreviations: ET, evapotranspiration • GCM, global climate model • WUE, mean water use efficiency

	INTRODUCTION

TOP ABSTRACT INTRODUCTION ADOPTION AND ROLE OF... PULSE CROPS AND THE... NOTES CLIMATE CHANGE ON THE... PULSE RESPONSE TO FUTURE... ADAPTATION TECHNOLOGIES AND... SUMMARY REFERENCES

 
INTEREST IN PULSE CROPS (annual legumes) by northern Great Plains producers has risen sharply in the recent decades. Pulses included in this review are soybean (Glycine max L.), dry pea (Pisum sativum L.), lentil (Lens culinaris Medik.), and chickpea (Cicer arietinum L.). Soybean production is concentrated in the southeastern region of the northern Great Plains, that is, the subhumid regions of South and North Dakota (Fig. 1 ). Dry pea, lentil, and chickpea production is concentrated in the semiarid regions of the northern Great Plains in both Canada and the United States (agroecoregions 1 and 12, Fig. 1), but especially in Canada. Dry bean (Phaseolus vulgaris L.) is a warm-season crop similar to soybean. Although we did not focus on dry bean in our review, we recognize the increased breeding efforts in adapting dry bean to the northern Great Plains and the expanded production of dry bean in recent years. There is clear evidence that the climate of the northern Great Plains has warmed, especially over the past 50 to 60 years. Climate trends in temperature and precipitation have had and will continue to have significant impact on agriculture. For example, climate warming has had a significant impact on the rapid increase of pulse adoption to the Northern Plains. In this review, we focus on the environmental requirements of pulses, historic climate change and simulations of future climate change, and simulations of crop response to proposed climate change. We provide recommendations for research of current and developing technologies to enhance pulse adaptation to future climates.

View larger version (44K): [in this window] [in a new window]   Fig. 1. Agroecoregions of the northern Great Plains (from Padbury et al., 2002) including the provinces Alberta, Saskatchewan, and Manitoba in the Canadian Prairies; and Montana, Wyoming, North Dakota, South Dakota, Nebraska, and Minnesota of the United States. For a description of the Agroecoregions 1 to 14, see Padbury et al. (2002).

	ADOPTION AND ROLE OF PULSE CROPS

TOP ABSTRACT INTRODUCTION ADOPTION AND ROLE OF... PULSE CROPS AND THE... NOTES CLIMATE CHANGE ON THE... PULSE RESPONSE TO FUTURE... ADAPTATION TECHNOLOGIES AND... SUMMARY REFERENCES

The area sown to pulse crops in the northern Great Plains has increased steadily in the last two decades (Miller et al., 2002a). The most notable area for increased production has been in semiarid regions of the Canadian Prairies, where dry pea, chickpea, and lentil are used to extend the traditional wheat-fallow crop rotations, especially in no-till management systems. In 2002, pulse crops accounted for 24% of seeded area in the Brown soil zone of Saskatchewan, an increase from 4% in 1991 (Statistics Canada). The increased production of pulse crops on the Canadian prairies (30% between 1978 and 1999) has occurred at the expense of fallow, which has declined dramatically (Miller et al., 2002a). The introduction of dry pea, lentil, chickpea to the northern Great Plains of the United States has progressed at an accelerated rate recently. However, soybean remains the most important pulse crop grown in the northern Great Plains, but because of a long growing season, soybean production is largely restricted to South Dakota and Nebraska on the southeastern edge of the Plains.

Cause and Effect of Accelerated Climate Change
Over the past 50 to 60 yr, accumulating evidence suggests that human activities have contributed significantly to stimulating global climate change (Schneider, 1994; Skinner and Majorowicz, 1999; Intergovernmental Panel on Climate Change, 2001; Smith and Almaraz, 2004), and will continue to do so well into the 21st century (Karl et al., 1997). "The Intergovernmental Panel on Climate Change (Intergovernmental Panel on Climate Change, 2001) projects that atmospheric concentrations of CO₂ will increase from 368 µmol mol^–1 in 2000 to between 540 and 970 µmol mol^–1 in 2100. Over the same period, the IPCC estimates that accumulation of atmospheric greenhouse gases will increase air temperatures 1.4 to 5.8°C. Important regional variations will underlie these global trends" (White et al., 2004). For example, most of the evidence provided by trend analysis of long-term weather data and by climate change models suggests that climate is warming over the northern Great Plains (Karl et al., 1996; Zhang et al., 2000b). As well, many already dry regions across the earth may experience a decrease in precipitation, while other regions may receive increased precipitation. These changes will have varying and complex impacts on agricultural production. The severity of climate change effects on crop production depends on the magnitude of the temperature increase; modeling indicates that increases up to 2.5°C will cause variable effects on the agriculture sector. Temperature increases 2.5°C may promote increased agricultural production in the cooler temperature regions of the earth but decrease production in the warmer tropical regions. Temperature increases above 2.5°C will generally have negative overall effects on world agriculture (Intergovernmental Panel on Climate Change, 2001; Smith and Almaraz, 2004). "Field experiments using elevated CO₂ concentrations of 550 µmol mol^–1 typically show increased yields of well-watered and fertilized crops of 10 to 20%. Benefits of elevated CO₂ are even greater for water deficits, but yield increases under nitrogen deficits are lower than for fertile conditions" (White et al., 2004; Kimball et al., 2002).

Adapting to a Changing Climate
Ecological responses to climate change are already visible (Cayan et al., 2001; Walther et al., 2002; Parmesan and Yohe, 2003). In general, spring activities have occurred progressively earlier since at least the 1960s (Walther et al., 2002). The impact of global warming is discernable in both animal and plant biology. For example, averaged across several hundred temperate-zone species (including plants and animals), the shift in spring phenology, such as breeding or blooming, is about 5 d earlier in each decade during the past half century (Root et al., 2003). Satellite imagery has shown that between 1982 and 1999 the beginning of spring is 8 ± 4 d earlier in North America and the duration of the active growing season increased by 12 ± 5 d (Zhou et al., 2001), especially for forests, tundra, and grasslands between 30° and 80°N (Keeling et al., 1996). In western North America, earlier spring onsets since the late 1970s are a common feature of phenological and temperature records, and reflects the recent spell of warmer-than-normal springs (Cayan et al., 2001).

"The goals of adaptation strategies are to improve the knowledge and skills of farmers, to encourage adoption of new technologies, and to expand the array of options available to farmers" (Motha and Baier, 2005). However, because of the given uncertainties and serious consequences of potentially inaccurate assessments of climate change and the required adaptation strategies, Motha and Baier (2005) recommended aggressive study and research into how best to limit and mitigate the impacts of climate change on agriculture. They further caution that complacency is very risky and advise vigorous effort toward understanding and preparing for potentially serious impacts on agriculture by developing adaptation strategies.

	PULSE CROPS AND THE NORTHERN GREAT PLAINS

TOP ABSTRACT INTRODUCTION ADOPTION AND ROLE OF... PULSE CROPS AND THE... NOTES CLIMATE CHANGE ON THE... PULSE RESPONSE TO FUTURE... ADAPTATION TECHNOLOGIES AND... SUMMARY REFERENCES

 
Response to Environment
Temperature
The maturity requirements of dry pea, lentil, and chickpea are easily met at most locations in the northern Great Plains (Miller et al., 2002a). The mean cumulative degree-days at a base of 5°C (DD₅) required for early maturing soybean (00 maturity group) exceed the mean cumulative DD₅ available at many locations in the northern Great Plains except for South Dakota and Nebraska (Miller et al., 2002a). Desi chickpea (480 DD₅), dry pea (530 DD₅), and lentil (540 DD₅) require fewer degree days to reach anthesis, compared with spring wheat (600 DD₅) (Miller et al., 2001, 2002a). Dry pea (1010 DD₅) generally attains maturity sooner than spring wheat (1070 DD₅), while lentil (1060 DD₅) mature earlier than spring wheat only in years when near-normal climatic conditions have occurred. Chickpea (1120 DD₅) generally matures slightly later whereas soybeans (1590 DD₅)¹ mature substantially later than spring wheat.

Pulse crops may be categorized into cool-season (dry pea, lentil, and chickpea) and warm-season (common bean and soybean) crops based primarily on their ability to emerge in cool soil conditions and on frost tolerance (Miller et al., 2002a). Minimum temperatures for seed germination and crop growth differ among pulse crops, with soybean having a base temperature near 10°C (Raper and Kramer, 1987), compared with base temperatures near 0°C for chickpea, dry pea, and lentil (Roberts et al., 1988; Summerfield et al., 1989; Ney and Turc, 1993). Consequently, soybean typically requires a relatively later seeding date, mid-May to early June in most locations in the northern Great Plains, to reduce the risk of frost injury. Chickpea, dry pea, and lentil tolerate a moderate degree of frost, –2 to –18°C, depending on cultivar, degree of acclimation, and plant stage (Wery et al., 1993; Welbaum et al., 1997; Srinivasan et al., 1998). If a severe frost kills the shoot, axillary nodes below the soil surface generate new shoots. The resultant loss of plant vigor reduces yield potential but typically does not require reestablishment of the field because a late seeding date also has a reduced yield potential (Miller et al., 2002a). Early spring seeding will improve dry pea productivity in the Canadian semiarid prairies (Johnston et al., 1999). In a spring seeding date study at Swift Current, SK (1993–1998), frost injury was never observed in dry pea, lentil, or desi chickpea despite seedling exposure to –5 to –6°C in 4 of 6 yr (Miller et al., 1998), indicating that there is little risk to very early seeding of these cool-season pulse crops. Similarly, at Swift Current, SK, Gan et al. (2002) found early seeded chickpea and pea yields were on average 13 and 20% higher, respectively, than late-seeded yields. They concluded seed yields of both chickpea and dry pea in a semiarid environment can be enhanced by management practices that promote early seedling emergence, prolonged reproductive period, and increased pod fertility.

On the Canadian Prairie, daytime temperatures for best growth of chickpea range from 21 to about 30°C whereas the temperature range for best growth of field pea is 13 to 23°C (Hnatowich, 2000; Soltani et al., 2006; Wang et al., 2006). Temperatures exceeding 30 to 32°C limit yield of chickpea by hastening maturity and/or by decreasing seeds/plant and seed weight (Harris, 1979; Wang et al., 2006). Chickpea will tolerate higher temperatures than field pea during flowering; temperatures > 27°C will often decrease flower numbers and flowering duration for field pea (Hnatowich, 2000; Hawthorne et al., 2003). Lentil has poor tolerance for high temperatures, especially at flowering and pod set (Erskine et al., 1994).

Water
Currently available chickpea and lentil cultivars have an indeterminate growth habit and require physiological stress (i.e., drought) to terminate flowering and induce seed set (Saskatchewan Pulse Growers, 2000). This can result in significant risk for many locations in the northern Great Plains in years with wetter-than-normal growing conditions combined with an early fall frost. Seeding in early spring allows cool-season pulse crops, especially the early maturing field pea, to complete a larger portion of their growth cycle during the late spring and early summer rainy season before the onset of summer drought, which typifies the northern Great Plains, and thus minimize production risk (Miller et al., 2002a). Also, early spring seeding of chickpea and lentil enable better timing for termination of flowering and induction of seed set by the terminal droughts typifying late summer.

Cool-season pulse crops are more suited to semiarid regions of the northern Great Plains (Miller et al., 2002a). Angadi et al. (1999) compared the plant water relations among chickpea, dry pea, and lentil at Swift Current, SK, and found all three pulse crops used less water than spring wheat. Averaged across water regimes and years, spring wheat used 296 mm water compared with 278 mm for chickpea and 266 mm for dry pea. Dry pea and lentil are well adapted to semiarid Plains regions where the soil profile is often only shallowly recharged with water. Chickpea extracted more water from the soil profile than field pea or lentil (Miller et al., 2003a; Zhang et al., 2000a), especially from below 0.30 m (Angadi et al., 2003). Lentil and dry pea rooting systems effectively extracted water in the upper 0.9 m of soil while chickpea (desi type) used soil water to 1.2 m (Zhang et al., 2000a; Nielsen, 2001; Siddique et al., 2001; Angadi et al., 2003; McKenzie et al., 2004).

The mean water use efficiency (WUE) of dry pea is generally similar to that of spring wheat (Borstlap and Entz, 1994; Angadi et al., 1999; Miller et al., 2002a, 2003a), whereas the mean WUE values for all other pulse crops are generally lower than that of spring wheat (Angadi et al., 1999; Siddique et al., 2001; Miller et al., 2002a). Soybean, a warm-season pulse, has the lowest mean WUE (Miller et al., 2002a), reflecting a typically delayed seeding date and longer plant maturity, extending crop growth into the mid- and late-summer season when peak evapotranspiration (ET) demand occurs. As such, soybean generally is not as suitable to include in dryland cropping systems in semiarid regions of the northern Great Plains, especially in western regions where rainfall peaks in the late spring and early summer, not in late summer.

Pulses are generally most susceptible to water stress during the later half of the growing season (the reproductive stage), but especially during flowering and seed set (Haskett et al., 2000; Nielsen, 2001; Siddique et al., 2001). In environments where water shortages can occur at any time during the growing season and terminal droughts predominate, high-yielding genotypes tend to flower early, pod early, and have a relatively long flowering period (Siddique et al., 2001; Gan et al., 2002; Berger et al., 2004; Turner et al., 2005). Thus, drought escape is an important phenological characteristic at sites with terminal (late-season) drought. However, where drought is severe throughout the entire growth period, substantial biomass redistribution is associated with high yield, suggesting that physiological mechanisms in addition to rapid phenological development play a role in the adaptation of pulses to water-limited environments (Gan et al., 2002; Berger et al., 2004; Turner et al., 2005). Once stressed, even for short periods, water-stress-induced acceleration of senescence cannot be stopped by eliminating the stress, and short periods of water stress during seed filling may have larger-than-expected effects on yield (Brevedan and Egli, 2003).

Lentil, and to a lesser extent chickpea, have shown limited yield benefit from irrigation on the northern Great Plains (Angadi et al., 1999). The benefits of irrigation are somewhat dependent upon late-summer, fall weather. Warmer, drier weather during seed set and filling hastens maturity, reducing the risk of fall frost injury which can reduce seed yield and seed quality.

Cropping Systems: Rotations and Crop Sequencing
Crop sequencing within crop rotations can have a significant impact on the productivity of succeeding crops, and thus, on the productivity of the crop rotation as a whole. Research suggests producers would benefit by investing considerable thought towards cropping system design to meet the needs of their particular operations. Including pulse crops in a crop rotation affects wheat yield through a series of complex interactions on soil water, soil nutrient supply, and interruption of pest cycles (Miller et al., 2002a). Wheat yield responses can vary considerably depending on previous pulse crops, years, and locations (Table 1 ). Generally, most reports indicate positive effects by the previous pulse crop on a succeeding wheat crop, either through conservation of soil water and/or soil N. However, the effect of pulse crops on succeeding crops is complex and not well understood. For example, the extra N from the previous pulse crop is only beneficial for the subsequent crop when moisture is sufficient to utilize the increased N and where N is yield limiting (Miller et al., 2002a). Proper sequencing of pulses within rotations can have long-term positive yield and economic benefits for producers when good crop management practices including control of weeds, diseases and other pests, and timely seeding to better match crop phenology with seasonal water availability patterns are practiced.

Miller et al. (2002b) found grain yield for wheat was highest when grown on pulse crop stubbles, while grain yield for wheat grown on oilseed stubbles did not differ from yield of wheat grown on wheat stubble. Grain protein for wheat grown on both pulse and oilseed crop stubbles was higher than when grown on wheat stubble. Gan et al. (2003) found similar results for durum wheat grown on pulse and oilseed stubbles. Soil N contribution was increased markedly by pulse crop stubbles such that fertilizer N requirements for canola, mustard, and spring wheat grown on pulse stubble were reduced by an average of about 15 kg N ha^–1. Stubble related differences in soil available water did not affect the wheat test crop under the wetter-than-average conditions of this 5-yr trial at Swift Current, SK.

Cropping sequence benefits to cereal crops from broadleaf crops were observed only at sites with near-average growing season rainfall and not at sites experiencing severe drought (Miller and Holmes, 2005). Cropping sequence differences between wheat and flax or pea as the previous crop were not explained by soil water but were related to differences in soil N despite the use of high N fertilizer rates for the cereal test crops. Under average rainfall, cereal test crop yields following pea and chickpea ranged from 84 to 96% of the fallow control and were generally greater than that following wheat. Under severe drought, cereal test crop yields following pulse crops ranged from 21 to 41% of the fallow control and were equal or less than those following wheat.

Summarizing several years of crop sequencing research at Swift Current, SK, canola or mustard productivity was generally greater when grown on pea or lentil stubble compared with mustard and wheat stubble (Miller et al., 2003b). Under drier-than-normal conditions, pea yields were highest when grown on wheat stubble. Wheat productivity was least when grown on its own stubble. Pea and lentil provided rotational benefits to wheat, mustard, and canola and benefited most from being grown in wheat stubble, indicating a strong fit for diversified cropping systems on the semiarid northern Great Plains. Comparing across several crop sequencing research studies on the northern Great Plains, the yield increases have been attributed to increased conservation of soil water and/or soil N by inclusion of pulses within the cropping system.

	CLIMATE CHANGE ON THE NORTHERN GREAT PLAINS

TOP ABSTRACT INTRODUCTION ADOPTION AND ROLE OF... PULSE CROPS AND THE... NOTES CLIMATE CHANGE ON THE... PULSE RESPONSE TO FUTURE... ADAPTATION TECHNOLOGIES AND... SUMMARY REFERENCES

 
Historic Climate Trends
During the 20th century, temporal trends showing increases in temperature and precipitation across North America have supported the expected direction of climate change, as predicted by global climate models (GCMs) driven by an enhanced greenhouse gas effect. The GCMs predict the trend towards warming in the lower atmosphere that is generally more spatially coherent than that for increased precipitation. Although the enhanced greenhouse gas effect may not be the only factor involved in these trends, it is implicated as a key factor over the past few decades (Lean and Rind, 1998).

Temperature
The emerging trend towards global warming has been very striking over the 20th century in comparison to precipitation. On average, the temperature increase has been in the order of 0.4 to 0.8°C (Bonsal et al., 2001). The average increase in Canada has been 0.9°C (Zhang et al., 2000b) and in the United States 0.4°C (Karl et al. 1996); in general, North America has warmed 0.7°C (McCarthy et al., 2001).

There are spatial as well as temporal variations to the warming trends on the northern Great Plains. On the Canadian Prairies, between 1900 and 1998, Zhang et al. (2000b) found the annual mean daily maximum temperature (T_mx) increased generally 1.5°C, and significantly (P < 0.05) only in southern Saskatchewan. However, the annual mean daily minimum temperature (T_mn) increase was larger (generally 1.5°C) and extended across the prairies. Seasonally, the greatest warming occurred during spring (March to May). Skinner and Gullet (1993) reported that for the prairie region between 1950 and 1989, annual T_mx and T_mn have increased by 1.7 and 1.1°C, respectively. At the same time, mean winter T_mx and T_mn have increased by 2.4 and 2.1°C, respectively, while warming in the spring has been even greater at 3.8 and 2.8°C, respectively. There appears to be seasonal trends in extreme temperatures as well. Lawson (2003) reported a decrease in extreme T_mn in January and February between 1914 and 1994 across the Canadian Prairie. Corresponding to this, Raddatz et al. (1991) indicate a shift in the coldest month from February to December in the eastern Prairies. These findings are supported by Bonsal et al. (2001), who suggest "Canada is not getting hotter, but rather less cold."

For the United States, Karl et al. (1996) stated that the daily minimum temperature increased about 10% more than the maximum. In addition, there has been a decrease in the day-to-day temperature variability (Karl et al. 1995). Between 1900 and 1994 over the northern Great Plains of the United States, Karl et al. (1996) found the annual average temperature (T_mean) increased by 1 to 3°C. The largest increase in T_mean occurred in North Dakota, with generally smaller increases occurring south and west of North Dakota.

Further evidence of a warming trend is the increase in length of the growing season. From 1950, spring temperatures over the northern Great Plains have increased between 1°C in the United States to over 3°C on the Canadian Prairies. In the northern Great Plains of the United States, last spring frosts occurred earlier and the frost-free season lengthened from 1948 to 1999 (Easterling, 2002). The average date of the last spring frost occurred earlier by 1.2 d per decade (6.2 d earlier in 1999 compared with 1948) and the frost-free season lengthened by 1.7 d per decade (8.8 d longer in 1999 than in 1948). For both Canada and the United States, there was little change in the first fall frost date during that same period. Over the later half of the 20th century, the general trend on the Canadian Prairie was for the mean last spring frost date to occur earlier by 2.4 d per decade and for the mean duration of the frost-free season to increase by 3.1 d per decade (Cutforth et al., 2004). The change in frost dates or frost-free duration was not uniform across the prairies (Cutforth et al., 2004; Shen et al., 2005). The largest trends for earlier last spring frost date and increasing frost-free season occurred in northern Alberta and the Peace River region of northern British Columbia whereas some of the smallest trends occurred over much of southern Alberta and southern Manitoba.

Over the past 100 yr, the gradual warming of the Canadian Prairies (Bootsma, 1994) has coincided with an increase in the frost-free period, an increase in the number of growing degree-days, and shifts in crop production regions. For example, "the area with sufficient CHU for corn production in Alberta, calculated according to the 1973 to 2002 climate normal, has extended northward by about 200 to 300 km, when compared with the 1913 to 1932 climate normal, and by about 50 to 100 km, when compared with the 1943 to 1972 climate normal" (Shen et al., 2005). Shen et al. (2005) suggest this expansion implies that the potential exists to grow crops in more northerly regions of Alberta than was possible in the past.

Coinciding with earlier warming has been a decrease in winter snowfall (with a large portion of the decrease falling as rain) in southern Saskatchewan and an earlier spring runoff on the northern Great Plains (Cutforth et al., 1999; Cayan et al., 2001). From 1955 to 1998, spring runoff for the Swift Current Creek drainage basin in southwestern Saskatchewan started earlier at an average rate of 0.55 d yr^–1 (Cutforth et al., 1999). On average, in 1998, spring runoff from the drainage basin started 24 d earlier than in 1955.

Precipitation
The small global trend in precipitation has shown about a 1% increase over land. However, more evident has been the increase in precipitation over the 20th century during the cold months in the northern Hemisphere (Zhang et al., 2000b).

From 1900 to about 1998, the generally insignificant but positive precipitation trends in the Canadian Prairies (Zhang et al., 2000b) gradually changed to negative trends in the Northern Great Plains south of the Canada–United States border with the largest negative trends in Montana and Wyoming (Karl et al., 1996). The only positive trends in the northern Great Plains of the United States for precipitation totals were in South Dakota.

Excluding events with 0.5 mm precipitation, Akinremi et al. (1999) reported that for the Canadian Prairies between 1920 and 1995 there was a significant increase of 16 precipitation events within a year, mainly due to low-intensity events. However, during this period, the average amount of precipitation increased 0.62 mm each year. Between 1956 and 1995, there was an increase in rainfall of 16%, most of which was presumably due to the conversion of snowfall to rain in spring, coinciding with warmer and earlier springs (Akinremi et al., 2001).

From 1910 to 1996, Karl and Knight (1998) found annual precipitation amount averaged across the northern Great Plains of the United States increased slightly. Seasonally, precipitation totals increased for spring and summer and decreased for autumn and winter. The majority of the increase/decrease was accounted for by the trends of the highest class interval (the >90th percentile group). The frequency of precipitation events increased slightly on an annual basis, especially in the low to moderate precipitation class intervals. Precipitation events increased during spring and summer whereas events for autumn and winter were relatively unchanged. The proportion of total annual precipitation derived from heavy and extreme precipitation events has increased relative to more moderate precipitation events (Karl et al., 1995).

Future Climate
Forecasting climate relies on simulations of large-scale global climate models that respond to global forcing elements such as changes in greenhouse gas concentrations in the atmosphere. These models are run for a current equivalent CO₂ concentration in the atmosphere, and then for a doubling of concentration where the time for doubling is dependent on an emission scenario. The differences between these model runs for temperature and precipitation are then applied to the historic climate seasonal data to generate a future climate change scenario. Because of the very diverse outputs from individual global climate models, the Intergovernmental Panel on Climate Change recommends the use of more than one GCM for any assessment of climate impact and that the selected GCMs show a range of changes in the key climate variables, notably temperature and precipitation (Sauchyn et al., 2003).

"Most scientists agree that results of the model simulations are only indications of the potential trends in climate change conditions" (Kobiljski and Dencic, 2001). As new knowledge and understanding of climate processes are acquired, we need to assimilate this new information into climate models thereby continually updating predictions of future climates.

Temperature Change
The change forced by an enhanced greenhouse gas effect is predicted to cause global warming of 1.4 to 5.8°C by 2100 (Houghton et al., 2001). The predicted warming will not be spatially or temporally uniform and varies with the forecast model used. For a doubling of carbon dioxide concentration between 2040 and 2060, the Canadian Coupled Global Climate Model (CGCM1-A; Hengeveld, 2000) predicted that the Canadian prairies will warm by about 3.1°C (McGinn and Shepherd, 2003).

Rosenberg et al. (2003), using the HadCM2 GCM simulation for 2030, predicted temperature increases for the northern Great Plains region of the United States of <2.5°C by 2030 with increases in excess of 3°C by 2095.

Temporal and spatial patterns of temperature for the northern Great Plains were simulated using the Canadian GCM (CGCM2) and the UK GCM (HadCM3) (Fig. 2 ). By 2050, compared with the baseline (1961–1990) climate, CGCM2 predicted increases in annual mean temperature of 2 to 5°C, whereas HadCM3 predicted temperature increases of 1 to 3°C, the larger temperature increases occurring over the U.S. Northern Plains. CGCM2 predicted spring (March, April, May) temperature increases of 3 to 9°C centered on North Dakota, whereas HadCM3 predicted smaller temperature increases of 1 to 3°C. CGCM2 predicted summer (June, July, August) temperature increases of 2 to 4°C, increasing in an west to east direction, while HadCM3 predicted temperature increases of 2 to 5°C, increasing in a north to south direction. There is generally good agreement between GCMs with the direction (increasing or decreasing) of temperature change, although the magnitude of change often differs.

View larger version (41K): [in this window] [in a new window]   Fig. 2. Spring (March, April, May) temperature (left) and precipitation (right) predictions for 2050 by the Canadian (CGCM2) (top) and UK Hadley Centre (HadCM3) (bottom) global climate models. Predicted temperature (°C) and precipitation (%) changes are compared with the baseline period of 1961 to 1990 (obtained from www.pacificclimate.org/tools/select, verified 6 Sept. 2007). Image used with permission from the Pacific Climate Impacts Consortium.

Precipitation across the Canadian Prairies is predicted to increase by 4% annually, with Alberta receiving the greatest increase (Shepherd and McGinn, 2003; using CGCM1-A). Seasonal and spatial variations exist within this pattern. Most significant is that rainfall during the July to August period in southern Manitoba and southeastern Saskatchewan is predicted to decline by 30 mm.

In the United States, Giorgi et al. (1994) reported an average increase in precipitation in the cold and warm months of 21 and 16%, respectively, for a 2 x CO₂ scenario. For the central Plains, the increase for cold months was reported to be 19%, while for warm months the increase was 24%.

CGCM2 and HadCM3 predicted annual precipitation totals on the northern Great Plains for 2050 that changed little compared with the baseline (1961–1990) climate (Fig. 2). Seasonally, both CGCM2 and HadCM3 predicted spring precipitation to increase 5 to 15% on the Canadian Prairies. However, CGCM2 predicted a substantially greater spring precipitation increase (15 to >25%) over the northern Great Plains of the United States than HadCM3 (–5 to 25%). Both models predicted similar decreases (–15 to 0%) in summer precipitation; the change occurring in a northwest to southeast direction with the U.S. plains drier than the Canadian prairies.

Aridity
Sauchyn et al. (2002, 2003) developed aridity maps for the baseline time period (1961–1990) and for 2050 from temperature predictions by CGCM2 and HadCM3. For 1961 to 1990, they classified the driest region of the Canadian Prairies (southwest Saskatchewan to southeast Alberta) as dry subhumid (Fig. 3 ). The aridity index was determined by calculating potential ET using Thornthwaite's formula, which uses temperature as the sole measure of energy available for ET. By 2050, based on forecasts of temperature and precipitation, CGCM2 predicted a semiarid climate will develop in southwestern Saskatchewan and the dry subhumid area will expand substantially. By 2050, HadCM3 forecasted the least change in climate with the development of a small area of semiarid climate in southern Alberta and a slight increase in the area characterized by a dry subhumid climate. The differences between the model predictions arise chiefly because of the much larger temperature increases predicted by CGCM2.

View larger version (34K): [in this window] [in a new window]   Fig. 3. Aridity scenarios for the 2050s based on forecasts of precipitation and temperature from the Canadian (CGCM2) (top left) and UK Hadley Centre (HadCM3) (top right) global climate models. These GCM experiments represent warm-dry and cool-wet scenarios, respectively. Aridity map for the Prairie Provinces (bottom left) for the baseline period 1961–1990 (from Sauchyn et al., 2002, 2003).

	PULSE RESPONSE TO FUTURE CLIMATES

TOP ABSTRACT INTRODUCTION ADOPTION AND ROLE OF... PULSE CROPS AND THE... NOTES CLIMATE CHANGE ON THE... PULSE RESPONSE TO FUTURE... ADAPTATION TECHNOLOGIES AND... SUMMARY REFERENCES

 
Evidence suggests that the recent historic trends in climate have already forced changes in terrestrial ecosystem. Myneni et al. (1997) reported that spring time warming may be partially responsible for the increase in photosynthesis observed by satellite data in the mid to high latitudes. Evidence given by Andresen et al. (2001) for the Upper Great Lake states, suggested a relationship between increased total seasonal precipitation and decreased evaporation, and the average corn and soybean yield increase of 11.4 and 4.9 kg ha^–1 yr^–1, respectively, over the past century. A more direct impact of elevated greenhouse gas concentrations is an increase in yield of temperate grasslands of 7.5 to 9% since preindustrial time (Jones, 1997).

Response to CO₂ Fertilization
Plants growing with increased CO₂ concentration exhibit increased rates of net photosynthesis and/or reduced stomatal diameter (Kobiljski and Dencic, 2001). "Partial stomatal closure leads to reduced transpiration per unit leaf area, and together with enhanced photosynthesis often improves WUE (Haskett et al., 2000). Consequently, increased CO₂ concentration can increase yield and reduce water use. Most crops grown in cool, temperate regions are C3 plants (including pulses) that respond positively to increased CO₂. Growth rates for these C3 crops can be increased by 10 to 50% in doubled CO₂ conditions" (Kobiljski and Dencic, 2001).

Under ambient CO₂, Allen et al. (2003) found large increases in soybean canopy ET as temperature and concomitant leaf to air vapor pressure deficit increased. Under doubled CO₂, canopy ET decreased 9% at 23°C but there was no CO₂ effect on ET when temperatures were 35°C or higher. "Canopy resistance (R_c) increased with increasing CO₂ concentration but decreased as air temperature increased. Water-use efficiency increased between 50 and 60% under doubled CO₂ at 28/18°C and at 40/30°C, but decreased with increasing temperature" (Allen et al., 2003). Simulation modeling showed that, in general, increases in atmospheric CO₂ concentration and precipitation have positive effects, while increasing temperature has a negative effect on crop production for semiarid climate conditions (Phillips et al., 1996; Yu et al., 2002). Further, higher atmospheric CO₂ concentration offsets the effects of climatic change. Compared with ambient CO₂ concentration, doubling CO₂ reduces the rate at which plant biomass decreases with increasing temperature and also reduces the rate at which plant biomass increases with increasing water availability. As well, the positive effect of CO₂ enrichment was larger under harsher (drier, warmer) climate conditions.

According to Allen et al. (2003), "if global warming occurs with rising CO₂, the small savings in ET associated with increasing R_c because of stomatal closure will be considerably offset by increases in ET driven by higher temperatures, which could increase the total amount of water required for crop production."

Simulated Response to Future Climates
Simulation models have been used to evaluate the impact of climate change on pulse production in the northern Great Plains. The severity of climate change effects on crop production depends on the size of the temperature increase. As previously noted, modeling indicates that increases up to 2.5°C cause variable effects on the agricultural sector, with improvements in many cases, particularly in temperate climate regions; however, temperature increases above 2.5°C are generally projected to have negative overall effects (Intergovernmental Panel on Climate Change, 2001; Smith and Almaraz, 2004). Laurila (2001) reported that higher air temperature can reduce the maturity time of spring wheat and result in a yield loss of 20%. Combining higher CO₂ concentrations with higher temperatures, the yield increase was reduced from 142% (elevated CO₂) to 106%. The impact of earlier seeding dates reduced the negative impact of higher temperatures, and improved the associated yield increases to 178% of the baseline yield. In addition to avoiding higher temperatures and fast maturity rates that can decrease yields, earlier seeding dates of short season crops would presumably enable crops to avoid late-season drought (McGinn and Shepherd, 2003).

Simulation studies suggest soybean yields on the U.S. northern Great Plains will respond more adversely to predicted future climates than winter wheat yields (Izaurralde et al., 2003; Thomson et al., 2005). Whether the GCM used to predict future climates favored a warm and dry scenario or a cool and wet scenario, simulated yields for both soybean and winter wheat increased as CO₂ concentration increased from 365 to 560 ppm (Table 2 ). Izaurralde et al. (2003) found simulated yields for winter wheat either did not change or increased for future climate predicted by the Hadley model (cooler, wetter scenario), whereas simulated soybean yields did not change or decreased (Table 2). For each crop, the yield response was location-dependent, reflecting regionalization of predicted climate change. Thomson et al. (2005) found the response of winter wheat yields to climate change was somewhat independent of temperature but dependent on CO₂ concentration. Whether the predicted temperature increase was mild or severe, the percentage change (compared with the baseline climate) in winter wheat yield tended to decrease slightly (i.e., reduced yields) with no CO₂ fertilization, but increased between 10 and 20% with CO₂ fertilization. Simulated soybean yields were more adversely responsive to temperature increase than were simulated winter wheat yields. Generally, simulated soybean yields decreased in response to future climate scenarios; the reduction in yield was moderated somewhat by CO₂ fertilization to the extent that soybean yields increased slightly for milder temperature increases combined with CO₂ fertilization (Thomson et al., 2005).

	ADAPTATION TECHNOLOGIES AND CLIMATE CHANGE

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Aridity is expected to remain relatively unchanged or increase (i.e., climate will impose a greater stress on crops) under climate change in the northern Great Plains. Thus, to maintain agricultural viability in a climate with increasing aridity, there is a need for technologies that increase the water-use-efficiency of crops and cropping systems. Superimposed on climate change are trends in climate that cause climate normals to shift in one direction (i.e., warming, increased aridity) such that climate is no longer oscillating about a stationary average. As climate shifts, the synchrony between climate and plants commonly grown in the northern Great Plains is disrupted. These plants experience more stress as climatic parameters such as temperature and precipitation occur more often outside their coping range. Adaptation technologies are attempts to restore the synchrony or to establish new synchronization between climate and plant communities. Continued research into the adaptive capabilities of current agricultural technologies and the development of future technologies will contribute to maximizing crop production in the future (Dhungana et al., 2006). Adaptive technologies to the northern Great Plains include the following: changing seasonality of production, changing sowing date, choice of crop varieties or species, development of new varieties, improving water supply and irrigation systems including efficiency in use, changing tillage practices, and diversifying the farm enterprise (Smit and Skinner, 2002; Bradshaw et al., 2004; Burton and Lim, 2005).

Research Needs: Pulse Crop Adaptation to Climate Change
Cultivar Development
Developing new agronomic technologies will require prediction of future climatic conditions that are likely to occur. Developing new cultivars will require identification of crop traits that will allow the crop to respond well in the future climate. Coupling crop and climate simulation models will increase our understanding of the types of cultivars and the management practices necessary to optimize agriculture in the future (Dhungana et al., 2006).

Global warming is predicted to extend the growing season in the northern Great Plains through earlier springs and later falls (McGinn and Shepherd, 2003; Motha and Baier, 2005). "It will be possible to grow crop cultivars with longer times to maturity and, therefore, greater yield potentials in much of the temperate zones" (Smith and Almaraz, 2004). The high yield potential may be tempered by exposure to increased temperatures during the bloom period and seed fill that may adversely impact seed set and overall yield. Current pulse production is based predominantly on spring-sown cultivars and the emphasis in breeding is to select for earliness to flower and mature (Berger et al., 2004; Turner et al., 2005). In a changing climate, these breeding objectives are expected to remain valid especially if aridity is maintained or increased. For the segment of environments where extended periods of crop growth are possible, breeding objectives may need to be adjusted to accommodate specific yield potentials (Berger et al., 2006). Further, with increased warming and longer growing seasons, the climate of the northern Great Plains will become more favorable for the production of warm-season pulses such as dry bean and soybean. Breeding efforts can accelerate the adaptation of and contribute to the rapid expansion of the area suitable for warm-season pulse production on the northern Great Plains.

Availability of cold-tolerant, winter-hardy germplasm of both pea and lentil that allow the crop to be sown in the fall and survive the winter may provide additional options for production of pea and lentil as the traditionally cold northern Great Plains environments become milder. Specific advantages of fall-sown pea and lentil will depend largely on whether a warm and dry or a cool and wet scenario is the ultimate outcome. However, it is expected that a continuum of environments will characterize future production regions much the same as is experienced in current production regions.

Winter pea and lentil have been shown to survive temperatures as low as –9 to –12°C (Swenson and Murray, 1983). Advantages of pulse crop establishment in the fall include (i) the ability to establish the crop in warmer and drier field conditions, avoiding the risk of poor seedling establishment in the spring or limited field access in the spring due to cold, wet soil conditions; (ii) allowing a more manageable volume of field operations between the fall and spring; and (iii) maintain an increased yield potential through more efficient use of precipitation and avoidance of severe summer temperatures through early maturity.

Chickpea and lentil are susceptible to a number of foliar pathogens, which have increased prevalence during high-rainfall seasons (Martens et al., 1984; Miller et al., 2002a). Pulse industry sources in Australia, Canada, and the United States consider climatic conditions that are favorable for the development of ascochyta blight [Ascochyta rabiei (Pass.) Lab.] to be the key factors limiting adaptation of chickpea (Wiese et al., 1995). As a result, chickpea may be considered best adapted to semiarid environments of the southern and western regions of the northern Great Plains, where climatic conditions are least favorable for the development of ascochyta blight (Miller et al., 2002a). Similar to chickpea, both lentil and pea are expected to encounter increased pressure from foliar pathogens in environments with increased precipitation. Combination of genetic resistance and appropriate agronomic control practices, such as adjusting sowing time to avoid disease development, will provide the greatest potential for crop success in a changing climate.

Incorporation of winter pea and lentil in production systems will surely expose these crops to increased disease pressure from an expanded spectrum of pathogens. Most important will be the foliar fungal pathogens, Mycosphaerella pinodes (Berk. and Bloxam) Vestergr., Phoma medicaginis var. pinodella (L.K. Jones). These pathogens are favored by cool and wet conditions which typify the early spring. Additional disease pressure may be experienced from soilborne pathogens Sclerotinia sclerotiorum (Lib.) de Bary., Aphanomyces euteiches (Drechs.), and Fusarium solani (Mart.) f. sp. pisi (F.R. Jones) (W.C. Snyder and H.N. Hans). Genetic resistance to all these pathogens is available in current germplasm collections; however, in all cases it is partial and heavily influenced by environmental conditions, making breeding and selection for resistance more difficult. Increasing the level of disease resistance in all legume crops grown in the northern Great Plains region will continue to be a primary objective of plant breeding.

Cultivar Assessment: Relative Adaptability to Climate Change
There are large genotypic differences in the tolerance of pulses to drought (Anbessa and Bejiga, 2002). It appears that reduced water loss from the plant and extensive extraction of soil moisture are factors involved in the adaptation of chickpea to drought conditions. Drought escape is an important phenological characteristic at sites with terminal drought (Berger et al., 2004; Turner et al., 2005). High-yielding genotypes generally flower early, pod early, and have a relatively long flowering period. However, at sites where drought is severe throughout the growth period, high-yielding genotypes have a high degree of biomass translocation from leaves to stems to pods. Berger et al. (2004) suggest that, depending on the type of water stress, physiological mechanisms and/or phenological development play a role in the adaptation of chickpea (pulses) to water-limited environments. Also, lentil and chickpea have considerable potential for drought resistance through osmotic adjustment (Leport et al., 1998; Turner et al., 2001, 2005). Therefore, a number of mechanisms are employed by plants to survive drought conditions.

Significant variation for seed yield in response to elevated CO₂ has been observed among soybean cultivars (Ziska et al., 1998). Although all cultivars show significant increase in seed yield with increased CO₂, there is considerable variation in yield enhancement, ranging from 35 to 80% (Ziska and Bunce, 2000; Ziska et al., 2001). "The sensitivity of seed yield response to CO₂ is associated with plasticity in the ability to form new seed in axillary branches in a high CO₂ environment" (Ziska et al., 2001). Screening of soybean germplasm may be an effective strategy to begin selecting soybean lines that will maximize yield in future environments with higher CO₂ (Ziska and Bunce, 2000).

Research Needs: Cropping Systems and Climate Change
Irrigation
A large proportion of the irrigated agriculture on the western portion of the northern Great Plains is based on the many small rivers that run out of the Rocky Mountains and onto the plains (Motha and Baier, 2005). River flows rely heavily on melt from winter snow pack and from glaciers in the Rocky Mountains. As winter temperatures continue to warm, the snow pack will be reduced because of increased melt during winter and because more precipitation will fall as rain rather than snow (Cutforth et al., 1999; Motha and Baier, 2005). As well, because of increasing winter temperatures, many of these glaciers, especially in the Canadian Rocky Mountains, will continue to shrink. For instance, the Peyto glacier in Alberta has lost 70% of its mass during the last few decades. In response to decreased river flows because of reduced melt, especially on the western half of the northern Great Plains, irrigation use will continue to decrease in the future (Smith and Almaraz, 2004). This has already occurred on the western Canadian Plains where, since 1950, less water has been flowing into rivers, lowering the availability of water for crop irrigation (Demuth and Pietroniro, 2003). "Urban populations will continue to increase, and competition between urban and agricultural uses of water will intensify" (Motha and Baier, 2005). As irrigation water becomes less available, production agriculture will be forced to rely more heavily on crops adapted to dryland production. Pea, lentil, and chickpea are particularly well adapted to dryland production and can be expected to play a key role in crop rotations in increasingly arid environments.

Agronomy
Global warming will promote earlier springs that will prompt management changes such as earlier seeding (Smith and Almaraz, 2004). Under a doubled CO₂ climate scenario, seeding dates in western Canada are projected to advance by approximately 3 wk (Motha and Baier, 2005).

Producers on the semiarid Canadian prairies are faced with several major limitations to cereal production, including a lack of water and soil erosion by wind. As well, several GCMs predict aridity will increase in severity throughout the 21st century. Further, damaging winds may also increase in severity and occurrence in response to future climate change on the northern Great Plains (Wheaton, 1990). These limitations can be addressed by employing no-till practices. Stubble is left intact and standing to protect the soil from the wind (Siddoway, 1970) and to increase snow catchment and thereby soil water reserves through snow melt infiltration (Campbell et al., 1992a; Steppuhn, 1994). Not only are yields increased through the additional stored soil water, but standing stubble may also alter the microclimate to provide less stressful environmental conditions for plant growth (Campbell et al., 1992a; Cutforth and McConkey, 1997). The milder microclimate associated with stubble can also favor production of fall-sown legume crops through protection from cold temperatures and desiccating winds.

In semiarid climates, appropriate management of the previous crop stubble in combination with seeding method is important to improve growing conditions for the subsequent pulse crop (Cutforth et al., 2002). Standing stubble changes the microclimate near the soil surface by reducing soil temperatures, solar radiation, wind speed, and potential ET (Table 3 ) (Cutforth and McConkey, 1997; Cutforth et al., 2002; Nielsen et al., 2005). The microclimate effects are dependent upon stubble height and are much more pronounced for tall (0.3m) versus short (0.15 m) stubble. Pulse crops (chickpea, field pea, lentil) respond similarly and positively to the altered microclimate (Table 4 ). On average, in a semiarid environment, tall and short stubble increase grain yield by about 13 and 4% compared with cultivated stubble. Crop water use is generally not affected by stubble height, so the increased grain production is due to increased WUE (Cutforth et al., 2002). Therefore, tall and short stubble increase the average WUE by about 16 and 8%, respectively, compared with cultivated stubble. Seeding pulses into taller standing stubble tends to raise the height of the plant and the basal pods (Cutforth et al., 2002). There are three likely reasons for this: (i) natural trellising on the stubble, (ii) natural elongation response to growing in the partial shade produced by the standing stubble, and (iii) more vigorous growth due to better water conservation (Miller et al., 2002a). Thus, direct seeding into tall cereal stubble can improve harvestability, thereby expanding the effective area of suitable soil landscapes for pulse production (Miller et al., 2002a).

In wetter regions, no-till systems slow the increase of early season soil temperature, and therefore, negatively affect seed germination, seedling emergence, and final stand establishment, even though this has only a small impact on final crop yield (Hayhoe et al., 1999). In the northern Great Plains state of Montana, Chen et al. (2006) found that winter lentil yields generally increased as stubble height increased. However, for one unusually cool period of emergence and seedling development, the seed yield of winter lentil was reduced by taller (35-cm) compared with shorter (10-cm) stubble. In the heat-limited environment, lentils may have benefited from the earlier soil warming associated with the shorter stubble in early spring.

Crop Sequencing and Rotations
Rotational benefits of pulse crops are expected to play a critical role in intensifying crop production systems in the future. Rotational benefits of pulse crops for wheat and barley production include enhanced soil fertility, increased WUE, as well as decreased losses in yield and quality from weeds and soilborne disease (Derksen et al., 2002; Krupinsky et al., 2002). The rotational benefits of including pulses in cropping systems, especially in the Canadian semiarid prairies, are at least partially due to the combined effects of increased soil N supply and increased soil water conservation positively affecting other crops within the rotation (Miller et al., 1998; Angadi et al., 1999; Miller et al., 2002a, 2002b; Gan et al., 2003; Miller and Holmes, 2005). During a long-term crop rotation study at Swift Current, Campbell et al. (1992b) and Zentner et al. (2001) reported that a continuous crop rotation of lentil alternating every other year with wheat was more profitable than any other rotation in the study.

Rotational benefits from pulse crops, including the winter pulse crops, can be obtained in both semiarid and subhumid regions, but the knowledge for describing the underlying causes of rotational effects remains incomplete. Continued research into cropping system design will likely become increasingly important for the economic sustainability and viability of grain production in the northern Great Plains, especially in light of the potentially harsher climates predicted for the future. Enhanced understanding of how pulse crops influence yield and quality of succeeding crops would allow producers to alter management to capitalize on beneficial effects while minimizing negative impacts (Miller et al., 2002a).

	SUMMARY

TOP ABSTRACT INTRODUCTION ADOPTION AND ROLE OF... PULSE CROPS AND THE... NOTES CLIMATE CHANGE ON THE... PULSE RESPONSE TO FUTURE... ADAPTATION TECHNOLOGIES AND... SUMMARY REFERENCES

 
There is general consensus that global warming will continue over the next 50 to 100 yr. Global climate models and crop simulation models are valuable tools for studying the effect of predicted climate change on regional crop production. However, regional crop production under future climates is dependent upon the accuracy of these scenarios which often result in one of two contrasting outcomes, an increasingly warm and dry or increasingly cool and wet climate. Consideration of CO₂ fertilization and adaptation of crop management (e.g., seeding date, varieties) often result in enormous variation in predicted crop production (Reilly et al., 2003; Edmonds and Rosenberg, 2005). The overall impact of these changes on crops will depend on a combination of factors, including crop species response to CO₂ enrichment, regional change in precipitation and water availability, growing season temperature impact on maturity rates, and adaptive shift in seeding dates that impact both temperature and available water for growth. Other factors may emerge to limit any potential yield increases, such as soil fertility and the impact of shifts in weed, insect, and disease populations. Pulse crops are quite plastic in their growth habit and are able to adapt to a variety of environmental conditions. Significant genetic variation for plant growth characters and specific adaptation is available in germplasm collections and is available for crop improvement. Adjustments in breeding objectives and shifts in crop management will likely be slow due to uncertainty surrounding the direction and degree of change, but awareness of the likelihood for climate change will allow plant breeders to make adjustments and selections more quickly. Despite uncertainties surrounding climate change across the northern Great Plains, significant evidence is mounting in support of imminent change and production agriculture as a whole must be prepared to adjust.

Briefly, adaptative technologies for the northern Great Plains include the following:

Developing chickpea, lentil, and pea cultivars resistant to foliar blights

Developing winter pulses to avoid summer heat/drought

Developing determinant cultivars of chickpea and lentil that will be less affected by cool and wet falls

Developing chickpea and lentil cultivars with earlier phenology to escape terminal droughts (i.e., able to mature before onset of drought)

Developing warm-season pulses such as dry bean and soybean adapted to the warming climate and longer growing seasons

Identifying cultivars that have increased heat/water stress tolerance

Identifying cultivars that have higher yield response to increased CO₂

Developing irrigation practices for increased WUE

Earlier seeding in response to earlier springs

Developing and promoting seeding practices that alter microclimate in and above the crop canopy, thereby increasing crop yields and/or water use efficiencies

Developing and promoting seeding and residue management practices that conserve water and soil

Extending crop rotations by substituting pulse crops for fallow

Determining the crop sequencing within cropping rotations that optimizes yields and water use efficiencies of crops and cropping systems

	ACKNOWLEDGMENTS

 
We extend our thanks to the anonymous reviewers, and to Dr. Perry Miller and Dr. George Clayton whose comments and suggestions contributed to the completion of this review.

	NOTES

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¹ Most soybean cultivars are short-day plants, and thermal time to anthesis can be greatly extended at long day-length periods (Miller et al., 2002a).

	REFERENCES

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