Conservation Tillage and Pulse Crop Production –
Western Canada Experiences

 

Adrian Johnston, Agronomist, Melfort Research Farm, Melfort, SK
Perry Miller, Cropping Systems Agronomist, Montana State University, Bozeman, MT
Brian McConkey, Semiarid Prairie Agriculture Research Centre, Swift Current, SK

Summary

Pulse crop production has risen dramatically on the Western Canadian prairies since the early 1980's. Peas have gone from being grown in a few localized areas 20 years ago, to 2.8 million acres of yellow and green peas in 1998. Lentils have also a well established acreage of approximately 1 million acres, and chickpea is the ‘new kid on the block’, growing from 7,000 acres in 1996 to 70,000 acres in 1998. Some industry estimates predict chickpea acreage to be near ‘lentil’ proportions by 2000. Research evaluating the adaptation of grain legumes to semiarid regions indicates that when seeded early, field pea has a high yield potential under low rainfall conditions, making the crop well adapted to the region. When ample water is available, pea uses less water than other crops with the exception of lentil. When water is limiting, pea grain yields are higher than other crops, including spring wheat. Root measurements have confirmed that peas have fewer roots below 90 cm depth than spring wheat or canola. The principle advantage of crop rotations is to reduce the negative impact on crop yield and quality resulting from growing a crop on its own stubble, or monoculture. The majority of this yield penalty associated with monoculture is plant disease, and as a result the effect will be largest in areas where moisture and temperature promote humid crop canopies. Peas in rotation can have a significant effect on subsequent crop grain yield and protein content. The value of this N benefit of peas is related to the yield of the pulse crop, and the effect of growing conditions on N release the following year. Peas are well adapted to direct seeding, with the advantage being greatest in semiarid regions.

Introduction

Grain legumes, or pulse crops, have become a popular alternative cropping option on the Canadian Prairies. Much of the acreage expansion has come about with the lower prices farmers are receiving for their cereal grains, mainly spring wheat and barley, and an increased interest in the benefits of a diverse crop rotation amongst farmers using direct seeding. The area seeded without prior tillage, or direct seeding, has expanded to approximately 30% or the cultivated area in Manitoba, Saskatchewan and Alberta. While farmers have adopted direct seeding in all of the rainfall regions, it is particularly popular in the semiarid regions. Increased soil moisture storage in these dry regions has allowed farmers to successfully establish a crop each year with direct seeding, with the resulting production being driven by growing season rainfall. In fact, it is the moisture conservation with direct seeding which can take the credit for the 30% reduction in summerfallow acreage in the semiarid region between 1991 and 1998, and the flexibility it has provided farmers in their cropping decisions. In this paper we will review some of the research results of studies conducted to determine the effect of tillage system and management on the production of grain legumes on the Canadian Prairies. The adoption and integration of a grain legume into semiarid parts of this region will form the focus of this discussion.

Climatic Conditions

Soil color is the dominant characteristic used to classify the various agroclimatic zones on the Canadian Prairies. The amount of organic matter is the soil variable influencing color, with levels increasing from Brown to Dark Brown to Black, and then decreasing again in the Gray soil zone. As you move from the Southwest corner of Saskatchewan (Swift Current) to Northeastern Alberta (Beaverlodge) there is a minor increase in precipitation, a large decrease in potential evapotranspiration, and the subsequent moisture deficit (Table 1). As a result, we move from a dry semiarid climate, characterized by fallow-based rotations dominated by spring and durum wheat, to a sub-humid climate, characterized by continuous cropping and a mix of spring cereals, oilseed and pulse crops. Drought tolerant crops have traditionally been the preferred choice in the Brown soil zone, while the role of drought is usually not a factor in crop choice in the Black and Gray soil zones. This range of climatic conditions between Research Station locations across the region provides a unique advantage in the assessment of crop adaptation.

Table 1. Soil zone, temperature, precipitation, potential evapotranspiration and moisture deficit for select Research Station locations on the Canadian Prairies (Campbell et al., 1990).

Location

Soil Zone

Temperature

Precipitation

ETp?

Moisture Deficit?

Swift Current

Lethbridge

Scott

Indian Head

Melfort

Beaverlodge

 

Brown

Dark Brown

Dark Brown

Thin Black

Thick Black

Gray

° F

38

41

34

36

33

35

inches

13.1

16.3

14.0

16.8

16.2

18.4

inches

28.7

26.8

25.0

23.9

19.9

18.5

inches

15.6

10.5

11.0

7.1

3.7

0.1

? Etp is potential evapotranspiration, calculated estimate of water use by crop and loss by evap.

? Moisture deficit = precipitation – Etp.

Fallow vs. Stubble and Crop Water Use

The choice of fallow or wheat stubble for growing a pulse or oilseed crop is one of the most commonly asked questions by producers in semiarid regions. Normally, all crops will yield best on fallow. Spring plant-available water and N levels are typically much lower on wheat stubble than fallow. However, excellent crop yields on stubble can be expected when adequately fertilized, provided this is accompanied by above-average growing season rainfall. As a result the fallow versus stubble question becomes a balance between the probability of the crop on stubble returning a profit in years with average growing season precipitation, and at least covering production costs in drier than normal years. Research results from Swift Current show that pulse crops, such as chickpea, lentil and pea are good bets on wheat stubble, while mustard and canola are better suited to fallow (Table 2). There are at least two reasons to explain this, including:

  1. Wheat and the oilseed crops in this study received fertilizer N based on a yield target set for climatic conditions of ‘normal’ stored soil water and growing season precipitation. During the period of this study we experienced two years wetter than normal, three near-normal, and one drier than normal growing seasons. This was coupled with stored soil moisture levels that were generally much above normal from fall and winter recharge. Under these conditions of generally favourable moisture, wheat and mustard yields were likely limited by insufficient N supply. However, the yields of the properly inoculated pulse crops were not limited by N because of their N-fixing ability.
  2. The water use pattern of pulse crops, at least lentil and pea, provides a competitive advantage relative to other stubble sown crops. The shallow water use pattern of pea and lentil (Table 3) indicates that less soil water recharge is required to produce a good pea or lentil crop, compared to the deeper rooted wheat and mustard that rely more on stored soil water. As such, even though pea yields were lower than wheat, because pea used less water, the water-use-efficiency was practically the same for both crops.

 

Table 2. Alternative Crop yields averaged for 6 site-years on fallow and wheat stubble in a tillage experiment in Southwestern Saskatchewan.

Crop

Fallow

Stubble

Stubble/Fallow

------ lb/ac ------

%

Dry pea

Hard red spring wheat

Mustard

Desi chickpea

Lentil

Safflower

Dwarf sunflower

2600 a

2600 a

1600 b

1500 b

1400 bc

800 c

800 c

2300 a

1700 b

1000 c

1100 c

1100 c

800 c

800 c

88

66

60

76

79

93

91

Values within column followed by the same letter are not significantly different (P=0.05).

Table 3. Yield, water use, and water-use-efficiency (WUE) by 5 crops from three soil depths when grown on fully recharged fallow at Swift Current and Stewart Valley, 1996-97.

 

 

 

 

Yield

 

Soil Depth

 

 

WUE
 

 

 

24-36"

 

36-48"

 

0-48"

 

 

 

 

lb/ac

 

----------- inches of water ----------

 

lb/ac/in
CWRS wheat

 

2800a

 

1.4a

 

0.8a

 

4.9a

 

220 a
Yellow pea

 

2400b

 

0.6c

 

0.3b

 

3.5b

 

210 a
Desi chickpea

 

1700c

 

1.2ab

 

0.7a

 

5.1a

 

140 b
Laird lentil

 

1300cd

 

0.8c

 

0.3b

 

3.9b

 

110 bc
Oriental mustard

 

1300d

 

1.1b

 

0.8a

 

4.7a

 

100 c

Values within a column followed by the same letter are not different (P=0.05).

Why Rotate Crops?

A planned sequence of crops on a field is considered a crop rotation. Both research trials and producer experience have shown that monoculture, the practice of continuous production of the same crop, is always inferior to production systems where a variety of crops are grown. The principle problem associated with monoculture is the persistence of plant disease. Crop rotations are one of the oldest practices used to control disease and remains perhaps the most important cultural control measure available to producers. Recent field research trials at a number of locations continue to indicate the benefits of crop rotation, with the yield of cereals usually superior when grown on the stubble of broadleaf crops rather than cereal stubble (Table 4). Similarly the yield of a broadleaf crop like canola is superior when grown on cereal or pea stubble, and pea yield was greater on cereal or oilseed stubble.

Table 4. Relative crop yield response to stubble type at research stations in Saskatchewan.

Melfort

Scott

Indian Head

Swift Current
Stubble

Canola

Wheat

Pea

Wheat

Barley

Wheat

Wheat

Mustard

Pea

Crop yield as a % of when grown on its own stubble
Oilseed?

100

131

114

115

130

-

100

-

-
Cereal?

152

100

125

100

100

100

100

-

-
Pea

196

147

100

120

141

113

125

-

-

? Canola stubble at Melfort and Scott, Mustard stubble at Swift Current.

? Wheat stubble when considering wheat, barley stubble when considering barley, and average of wheat and barley when considering canola and pea.

Disease control by crop rotation is based on the principle that the majority of plant pathogens are generally specific to a single crop species. Diseases of cereals do not affect oilseeds, pulses or forages, and within the cereals most diseases of wheat do not occur on barley. Yield losses due to disease are usually found to be greater under monoculture than with diverse crop rotations. This is due to the build up of pathogen populations that attack the crop under monoculture. Crop rotation lengthens the time between susceptible crops allowing the pathogen population to decline to levels which prevent significant yield loss.

Pulse Crops In Rotation

Soil Fertility

When we look at the benefit of growing a pulse crop in rotation we usually point to its N contribution to the crop grown on pulse stubble. Quantifying this N benefit has been the focus of several research trials conducted across the prairies. The usual method of determining the N benefit is to grow a crop like barley, with a range of N rates, on both pea stubble and a non-legume stubble, such as wheat or canola. A recent research project by Beckie and Brandt (1997) in Saskatchewan showed that no matter how much N you applied to barley grown on wheat stubble, you could not produce the same yield as barley on pea stubble with added N. This indicates what we call a non-N benefit of pea stubble, most likely the negative effect of growing barley on cereal stubble. However, when barley was grown on canola stubble, a grain yield equivalent to growing barley on pea stubble could be achieved with fertilizer N additions, proving that it was the effect of growing a cereal on cereal stubble that prevented full expression of the barley crop to applied fertilizer N. From their study, Beckie and Brandt (1997) concluded that the N benefit of pea in rotation varied considerably between the Dark Brown soil site at Scott, and the Black soil site at Melfort. At Scott they measured a N benefit to the next crop in rotation of approximately 1/4 lb N/acre per bushel of peas produced, while at Melfort they reported three times that amount at 3/4 lb N/acre per bushel of peas. These results indicate that in regions of higher precipitation, and higher levels of soil organic matter, the benefit of peas in rotation will be superior to drier climates. However, after three site-years near Swift Current, where the N benefits for peas were factored into reduced fertilizer N rates at 0.3 lb N/ac per bushel of peas, the wheat yield on pea stubble averaged 10% higher than on mustard stubble.

The N available in pulse stubble is strongly influenced by the pulse crop yield, and in turn its N fixation. Without good moisture conditions, pulse crop grain yield response and N fixation, can be limited or nonexistent, leaving little N for the next growing season (Table 5). In turn, under dry growing conditions a cereal grown on pulse stubble may not show any yield benefit relative to cereal stubble (Table 6). In fact as the results in Table 6 show, barley yields on barley stubble were superior to pea stubble under dry conditions, reflecting lower soil water storage and little or no legume N release with the pulse residue. However, under wet growing conditions the pulse stubble resulted in barley yields which were 50% higher than barley stubble. While much of this response can be attributed to the legume N benefit, there was likely increased plant disease associated with growing barley on barley stubble in a wet year, leading to a large non-N benefit

Table 5. Pea and lentil yield response and N fixation as influenced by growing conditions.

 Crop Weather Yield
(lbs/ac)
N Fixed
(lbs/ac)
N Fixed
(%)
 Lentils  Dry  721  18  49
 Lentils  Wet  2264  65  57
 Peas  Dry  652  16  46
 Peas  Wet  2212  72  57
Innovative Acres Data, Soil Science, U of S

Table 6. Barley yield response to tillage, previous crop stubble and growing season conditions at Melfort, Saskatchewan (Black soil zone).

 Stubble

Dry
 CT  ZT
   
Wet
 CT  ZT
     --bu/acre--  
 Barley
 34 36
   
 42 40
 Pea
30  31
   
60  61
       Wright (1990)

 

for the pea stubble. These results illustrate that moisture is the driving variable in both the amount of N fixed by a pulse crop, and the subsequent release of this N the next year.

Crop Quality

While the N benefit of peas is often used to explain increases in grain yield, there can also be an improvement in grain quality, or protein content. To achieve high grain yields a crop needs an adequate supply of N during tillering and stem extension prior to heading. In general, by the time a cereal crop heads the bulk of the N taken up will be used for grain yield formation, while after this time N taken up has its greatest influence on grain protein. As a result, if growing conditions are dry and not conducive to N release from pulse residual N early in the spring, this N may be released after heading and during grain filling resulting in increased grain protein. In a tillage and rotation study conducted at Melfort wheat yields were not different whether grown on canola or pea stubble (Table 7). However, wheat protein concentration was increased on pea stubble reflecting the N released from pulse residues. At Indian Head the opposite response was recorded where wheat yield showed a 12.5% increase to pea relative to wheat stubble, while no change in grain protein was observed. In one study at Swift Current conducted during a cycle of generally wetter than average growing seasons, both wheat yield and protein were increased on pulse crop stubble relative to non-pulse stubbles, suggesting increased N supply can

Table 7. Wheat grain and grain protein response to crop stubble at Melfort, Indian Head and Swift Current.

 Location  Stubble  Grain Yield (bu/ac)  Grain Protein (%)
 Melfort  Canola
Pea
 72
74
 11.5
12.2
 Indian Head  Wheat
Pea
 32
34
 15.8
15.6
 Swift Current  Wheat
Pea
Lentil
Desi chickpea
Mustard
 30
38
37
36
30
 12.3
13.3
13.3
13.2
13.7
Johnston (unpubl. Data), Lafond (unpubl. Data) and Miller and McConkey, 1998.

be sustained over a longer period of wheat growth and development. However, in a long-term trial at Swift Current, wheat yields were similar between continuous wheat and lentil-wheat rotations (Table 8). Growing lentils every other year in rotation with wheat increased soil residual N, resulting in a fertilizer N reduction which has averaged 10 lb N/ac. Wheat grain protein has averaged 1.4% units higher on lentil stubble, reflecting late season N release from these residues.

Table 8. Spring wheat yield, grain protein and soil residual N in a continuous wheat and lentil-wheat rotation at Swift Current (1979-1994).

 Variable Continuous Wheat Lentil - Wheat
Fall soil N (lb/ac) 33 50
Spring soil N (lb/ac) 39 61
Soil water at seeding (in) 11.6 11.1
Fertilizer N applied (lb N/ac)  32 24
Wheat Yield (bu/ac) 22.4 21.4
Lentil Yield (lb/ac) N/A 812
Mean wheat protein (%) 14.8 15.9
Campbell and Zentner, 1979-94

Response of Peas to Direct Seeding

The adoption of conservation tillage practices on the prairies has been driven by machinery development and the price of non-selective herbicides. The benefits of no-till appear to be greatest in drier regions where the absence of tillage results in increased stored soil moisture, allowing rotations to be extended with less fallow, which in turn allows for increased diversification in the crop rotation. When combined with poor cereal grain returns, the interest in moving canola and peas out of their area of traditional adaptation in the Black soil zone has been accelerated. With no-till seeding a producer has a far greater chance of establishing a crop, allowing him to take advantage of the growing season precipitation, and avoid fallow. A number of tillage studies have been conducted on the prairies to evaluate the effect of tillage on grain yield of peas (Table 9). In general, peas are either unaffected or show improved grain yields in response to reduced tillage. The improved yield with no-till occurs more frequently in the locations in southern Saskatchewan, where water is often limiting grain yield.

Table 9. Pea yield response to tillage, expressed as relative to the conventional or minimum tillage treatment.

 Location Conv. Till Min-Till No-Till
 

----- Relative (%)

grain yield response ---------
 Carmen (Black soil) 100 -- 107
Portage (Black soil) 100  -- 96
Melfort (Black soil) 100 94 105
Tisdale (Gray soil) 100 99 97
Indian Head (Black soil) 100 105 108
Saskatoon (Dark Brown soil) -- 100 132
Scott (Dark Brown soil) -- 100 128
Swift Current & Assiniboia (Brown soil) -- 100  105-110

 

References

Campbell, C.A., R.P. Zentner, H.H. Janzen and K.E. Bowren. 1990. Crop rotation studies on the Canadian Prairies. Publ. 1841/E. Research Branch, Agriculture and Agri-Food Canada, Ottawa, ON.

Beckie, H.J. and S.A. Brandt. 1997. Nitrogen contribution of field pea in annual cropping systems. 1. Nitrogen residual effect. Can. J. Plant Sci. 77: 311-322.

Clancy, B. 1997. The pea, lentil and chick pea market outlook. Pulse day ‘97, Pulse Crop Development Board Proceedings. Saskatoon, SK. Pages 25-39.

Miller, P., S. Brandt, A. Slinkard, C. McDonald, D. Derksen and J. Waddington. 1998. New crop types for diversifying and extending spring wheat rotations in the Brown and Dark Brown soil zones of Saskatchewan. Canada-Saskatchewan Agric. Green Plan Tech. Rep., Agric. Agri-Food Canada Semiarid Prairie Agric. Res. Ctr., Swift Current, Saskatchewan. 138 pp.

Miller, P., S. Brandt, C. Campbell, and R. Zentner. 1996. Alternative crops in wheat country: Yield response to available water. 1996 Soils and Crops, Extension Division, University of Saskatchewan, Saskatoon, SK. Pages 375-383.

Wright, A.T. 1990. Yield effect of pulses on subsequent cereal crops in the Northern Prairies. Can. J. Plant Sci. 70: 1023-1032.


 

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