The oldest and most fundamental approach employed by people to control plant diseases, insects and weeds and to supply nutrients to plants is the use of cultural practices. The use of such measures began with early civilizations and their development has paralleled that of crop agriculture itself. Cultural practices, such as burning, tillage systems, crop rotation, soil management, and site selection, have been used to prevent or reduce plant problems and pests. Despite the advent of newer and sometimes more effective measures, e.g. the application of synthetic pesticides and the use of synthetic fertilizers, cultural practices remain an important part of present-day crop management programs in agriculture. Actually, they may be gaining in importance as the net incomes in crop production continue to decline (paraphrased from RJ Howard, Alberta Agriculture, Brooks, AB).
What contributions can crop rotations make?
I will look at only two possible replacements of inputs by the choice of an appropriate crop rotation: The supply nitrogen to following crops and the ability of a sequence of crops to reduce weeds.
How much is this worth?
Additionally crop rotations can increase yields of crops above growing the same crop on the same field.
Current Crop Rotations (1996)
First, however, we should have a look at typical crop rotation practice in Saskatchewan and then attempt to improve on the current rotation in order to replace two of the most expensive variable cash inputs required in crop production: nitrogen fertilizer and herbicides (especially grass control products).
Table 1. Current percentage of land in each crop as well as fallow in Saskatchewan
|
CD |
Cereal |
Oilseeds |
Pulse |
Alf/Hay |
Fallow |
Total |
|
1 |
59.4% |
13.7% |
1.7% |
5.9% |
19.1% |
99.8% |
|
2 |
61.9% |
7.4% |
2.5% |
3.2% |
24.9% |
99.9% |
|
3 |
57.6% |
2.2% |
1.4% |
5.0% |
33.8% |
99.9% |
|
4 |
50.2% |
2.3% |
0.9% |
6.3% |
40.0% |
99.7% |
|
5 |
57.7% |
17.1% |
1.8% |
5.5% |
17.3% |
99.5% |
|
6 |
56.3% |
12.8% |
6.1% |
3.7% |
21.0% |
99.8% |
|
7 |
53.2% |
4.7% |
4.1% |
4.9% |
32.9% |
99.8% |
|
8 |
53.1% |
1.3% |
2.3% |
2.2% |
41.0% |
99.9% |
|
9 |
61.9% |
11.7% |
1.6% |
9.8% |
14.7% |
99.8% |
|
10 |
57.0% |
18.0% |
4.1% |
3.2% |
17.6% |
99.8% |
|
11 |
54.1% |
15.3% |
3.6% |
5.3% |
21.4% |
99.8% |
|
12 |
54.0% |
10.3% |
7.3% |
4.7% |
23.6% |
99.9% |
|
13 |
54.4% |
10.7% |
2.7% |
2.4% |
29.6% |
99.9% |
|
14 |
51.0% |
19.5% |
4.9% |
11.1% |
11.5% |
98.0% |
|
15 |
56.6% |
18.7% |
5.3% |
5.2% |
13.8% |
99.7% |
|
16 |
53.9% |
17.1% |
3.4% |
11.1% |
13.7% |
99.2% |
|
17 |
51.6% |
16.0% |
2.9% |
18.8% |
10.7% |
99.9% |
|
Average |
55.5% |
11.7% |
3.3% |
6.4% |
22.7% |
Source: Statistics Canada 1996, calculations by Gary Martens, CD= Statistics Canada Census Districts
There is not much variation between Census Districts. The typical crop rotation is: Cereal-Oilseed/Pulse-Cereal-Fallow with a little bit of alfalfa and hay. The alfalfa and hay may not be in the same rotation as the annual crops. It is often grown for longer periods of time on marginal lands and so alfalfa and hay are not included in the annual crop rotation listed above.
Grower practicing direct seeding represented approximately 19% of all cropped acres in Saskatchewan in 1996. (Statistics Canada) The crop rotation listed above therefore represents mostly conventional tillage and reduced tillage rotations.
Do successful direct seeders have different crop rotations than the conventional tillage grower? Yes.
In a small survey done to prepare for a presentation to Alberta Direct Seeding Workshop at Olds College in Alberta in 1998 I interviewed a number of direct seeders. Two common trends emerged: crop rotations in direct seeding systems are more intense and more diverse than rotations on a conventional tillage farm.
An example from Census District 1 in Alberta (the extreme southeast corner) showed a typical conventional grower's crop rotation to be: Cereal-fallow-cereal-fallow. Whereas the direct seeder's crop rotation in the same area was: Cereal-oilseed-cereal-pulse.
Dr. Dwayne Beck of Dakota Lakes Research Farms says, "The [no-till and reduced tillage] systems have done an excellent job of conserving water and soil. They have been less consistent in translating water savings into the expected yield increases and/or economic returns. One notable reason for this lack of response has been the failure to change crop rotation practices at the same time as tillage practices have changed. Rotations used in conservation systems must be more intense and diverse than those with conventional tillage practices." Skillful farmers will be flexible in their choice of crop rotation based on success in the field. A mix of summer annual and perennial crops is beneficial in a crop rotation. A mix of cool season grasses, cool season broadleaf crops, warm season grasses, warm season broadleaf crops, fall planting, early spring planting, late spring planting could all contribute to a successful crop rotation. A mix of tillage systems might be considered, if one type of weed is becoming troublesome.
Pulses and forage crops in rotation can be used to replace some nitrogen that would otherwise have to be purchased. Research by Dr. Martin Entz and associates at the University of Manitoba shows that growing a relay crop of red clover or alfalfa or a double crop of chickling vetch or lentil with winter wheat or fall rye will replace a significant amount of nitrogen fertilizer (Table 2).
Table 2. Nitrogen replacement value of legumes at Winnipeg and Carman, MB.
|
N source |
1999 Winter Wheat |
1999 Fall Rye |
|
Red clover relay crop |
27 pounds/acre |
29 pounds/acre |
|
Alfalfa relay crop |
70 |
57 |
|
Chickling vetch double crop |
33 |
48 |
|
Lentil double crop |
26 |
44 |
Table 3. Value of nitrogen/ac at $325/tonne 46-0-0 minus seed cost (from Table 2).
|
N source |
1999 Winter Wheat |
1999 Fall Rye |
|
Red clover relay crop |
-$1.04 |
-$0.40 |
|
Alfalfa relay crop |
$5.52 |
$2.00 |
|
Chickling vetch double crop |
-$8.82 |
-$3.74 |
|
Lentil double crop |
$7.36 |
$12.48 |
Seed cost: Red clover $1.09/lb @ 8lb/ac, Alfalfa $1.79/lb @ 8 lb/ac, Greenfix Chickling vetch $0.25/lb @ 70lb/ac, Eston Lentil $0.15/lb @ 40 lb/ac.
Initially the nitrogen supplied by the legumes looks valuable, however when an economic analysis taking seed cost into account is done, the practice of relay cropping or double cropping for nitrogen replacement becomes marginal. The relay or double cropped legumes do however supply other benefits such as weed suppression, some disease suppression and moisture management.
Dr. Martin Entz and others have looked at ways to avoid the annual cost of seed to establish the relay or double cropped legumes. Some Australian varieties of medic supply similar amounts of nitrogen and seed themselves each year. Only one initial seeding is required to have a continuous supply of seed in and on the soil to start future generations of medic.
In another trial wheat was planted the year after legumes to determine the nitrogen replacement value of growing the legume crop (Table 4).
Table 4 Nitrogen replacement value of legumes to following crops at Winnipeg, 2000
|
N source |
Nitrogen added (lb/ac) |
Value of N $/acre |
|
Chickling vetch |
26 |
$7.36 |
|
Red clover |
38 |
$10.88 |
|
Lentil |
49 |
$14.08 |
|
Alfalfa (1 year) |
64 |
$18.24 |
46-0-0 nitrogen source used for valuation at $325/tonne ($.0.32/pound of actual N)
Dr. Hugh Beckie at Agriculture and Agri-Food Canada (AAFC) in Saskatoon found that 31 lb/ac of nitrogen fertilizer could be replaced by a crop of field peas in the moist black soil zone near Melfort, Saskatchewan. The value of the nitrogen contributed by the field peas is $9.92/ac using 46-0-0 at $325/tonne as the nitrogen source for valuation.
Typically Saskatchewan farmers use 30 pounds of N on crops following fallow and 60 pounds of N on stubble and direct seeded crops. At 32 cents per pound that is $9.60/ac, $19.20/ac and $19.20/ac respectively. A pea crop can contribute as much nitrogen as is commonly attributed to fallow.
A specific sequence of crops can reduce the requirements of annual grass control herbicides. These herbicides are the most expensive group of herbicides used in annual crop production accounting for an average cost of $13.40 in spring wheat according to the 2000 Crop Planning Guide of Saskatchewan Agriculture and Food. (Calculated as $19.40 total herbicide minus $6.00 for a broadleaf herbicide = $13.40 for annual grass herbicide)
The Glenlea Long-Term Crop Rotation study was established by Dr. Martin Entz in 1992. The summer of 2000 was the 9th year of the study. Three crop rotations were established to monitor the impact of crop rotation on crop-input levels and pest populations.
Rotation 1: wheat-peas-wheat-flax
Rotation 2: wheat-sweet clover green manure-wheat-flax
Rotation 3: wheat-alfalfa-alfalfa-flax
Table 5 Yield of Flax (bu/ac) as influenced by Crop Rotation, fertilizer and herbicides
|
Full inputs |
Low inputs |
Low inputs |
Organic |
|||||
|
Inputs |
+fert/+herb |
+fert/-herb |
-fert/+herb |
-fert/-herb |
||||
|
Crop rotation |
1995 |
1999 |
1995 |
1999 |
1995 |
1999 |
1995 |
1999 |
|
W-P-W-F |
29.9 |
21.9 |
15.5 |
9.5 |
20.9 |
16.7 |
15.2 |
9.6 |
|
W-SC-W-F |
28.8 |
29.1 |
19.6 |
17.5 |
17.6 |
25.2 |
16.2 |
15.8 |
|
W-A-A-F |
27.2 |
23.1 |
24.6 |
15.9 |
20.5 |
24.4 |
21.8 |
21.9 |
W=wheat, P=peas, F=flax, SC=sweet clover green manure, A=alfalfa
Table 5 shows that the crop rotation has a dramatic impact on the yields of flax when herbicide inputs are removed. The annual rotation of wheat-peas-wheat-flax showed a large drop in yields without the protection of herbicides. The wheat-alfalfa-alfalfa-flax rotation also showed a reduction in yield of the flax without a herbicide, but when the yield and herbicide numbers are turned into dollars per acre (Table 6) the net income per acre does not drop, in fact it increases in an appropriate rotation without herbicides.
Table 6 Economic analysis of the Glenlea Crop Rotation Study (1992-1999)
|
Crop rotation |
Full inputs |
Low inputs |
Low inputs |
Organic |
|
8 year average |
+fert/+herb |
+fert/-herb |
-fert/+herb |
-fert/-herb |
|
W-P-W-F |
Input cost $104.14 |
Input cost $77.17 |
Input cost $71.36 |
Input cost $43.44 |
|
Net return $27.87 |
Net return $30.87 |
Net return $26.67 |
Net return $40.23 |
|
|
W-A-A-F |
Input cost $71.68 |
Input cost $51.92 |
Input cost $55.92 |
Input cost $36.08 |
|
Net return $77.83 |
Net return $93.42 |
Net return $73.73 |
Net return $93.77 |
The "-herb" treatments went without herbicides every year. 1999 was the 8th crop without herbicides. A new initiative started at the University of Manitoba and Brandon AAFC proposes to skip a herbicide once in three or four years. The Pesticide Free Production system (PFP) proposes to save some money on herbicides by pre-planning a crop rotation and other pest management actions to prepare to skip a herbicide application. A major hesitation by growers in the decision to skip a herbicide is "What happens to the weed seeds that drop onto the soil?" Doesn't this just increase the weed problem in the future?" PFP research has started a number of experiments to try to determine the impact of skipping a herbicide on subsequent weed populations and herbicide use requirements. See www.pfpcanada.com for further information.
Table 6 indicates that with the appropriate crop rotation, herbicides can be removed or reduced without a financial penalty.
Field peas contribute more than just nitrogen benefits to a crop rotation. Hugh Beckie and associates were able to separate the nitrogen benefit of growing peas from the non-nitrogen benefits. Beckie was able to show that a non-nitrogen benefit of growing barley on oilseed or pulse stubble increased yield by 20.3 bushels per acre above growing barley on wheat stubble. In the same study flax yields were increased by 10.7 bu/acre when grown on cereal or pulse stubble rather than on oilseed (canola) stubble.
Growers insured by Manitoba Crop Insurance (MCIC) must submit yield records each year. The MCIC database was used to generate Table 7. This table shows the total yield benefit (nitrogen and non-nitrogen benefits) of a specific crop sequence. For example, growing wheat on wheat stubble will result in a 90% yield compared to the average wheat yield, whereas growing wheat on canola stubble will yield 106% and growing wheat on pea stubble will yield 108% of average wheat yields.
Table 7 Relative Yield Response (1994-1998) to Crop Rotation
|
Previous Crop (stubble) |
||||||
|
Crop sown |
Wheat |
Barley |
Oats |
Canola |
Flax |
Peas |
|
Wheat |
90 |
98 |
99 |
106 |
103 |
108 |
|
Barley |
101 |
88 |
97 |
105 |
107 |
107 |
|
Oats |
99 |
90 |
87 |
108 |
107 |
100 |
|
Canola |
100 |
101 |
103 |
88 |
104 |
113 |
|
Flax |
102 |
102 |
101 |
92 |
69 |
NSD |
|
Peas |
101 |
101 |
93 |
89 |
82 |
NSD |
Source: Manitoba Crop Insurance Corporation, www.mmpp.com, NSD = not sufficient data
Reducing the nitrogen fertilizer and annual grass herbicide costs and adding the increased income from an appropriate crop rotation should add something to the net income of crop production.
Further benefits of appropriate crop rotations include: economic stability, equipment and labor distribution, pest control: reduced crop disease, reduced insect problems, reduced problem weed buildup, reduced possibility of herbicide resistance occurring, allows for long term weed control strategies, soil conservation: more moisture in direct seeding systems that allow for less fallow, balanced nutrient use: when properly alternated, different nutrients are consumed in more sustainable proportions, when legumes are included soil nitrogen is maintained, reduced leaching of nitrogen into the soil water table, increased use of deep leached nitrogen, balance water use and more.
A diverse and appropriately intense crop rotation should provide an improved net income from a crop production enterprise.
1. Entz, M. H., The Glenlea Long-Term Crop Rotation Study 1992-, unpublished paper
2. Bullied, W. J., M. H. Entz, S. R. Smith and K. C. Bamford, Effect of Annual Alfalfas and Green Manure Legumes on Successive Wheat and Barley Crops, 2000, unpublished paper
3. Leeson, J. Y., J. W. Sheard, A. G. Thomas, Weed communities associated with arable Saskatchewan farm management systems, 1999, Can. J. Plant Sci. 80:177-185
4. Klossner, L. D., P. M. Porter, Variable input crop management systems at the Southwest Experiment Station: 1998 Management history and yields
5. Doug Derksen, Len Juras and David Kelner, Principles and Practices of Crop Rotations, http://www.agr.gov.sk.ca/ DOCS/crops/ integrated_pest_management/ soil_fertility_fertilizers/CPC0397.asp
6. Saskatchewan Agriculture and Food, 2000 Crop Planning Guide, http://www.agr.gov.sk.ca/…
7. Beckie, H. J., S. A. Brandt, Nitrogen contribution of field pea in annual cropping systems 1. Nitrogen residual effect, Can. J. Plant Sci. 77:311-322
8. Beckie, H. J., S. A. Brandt, J.J. Schoenau, C.A. Campbell, J.L. Henry and H.H. Janzen, Nitrogen contribution of field pea in annual cropping systems 2. Total nitrogen benefit, Can. J. Plant Sci. 77:323-331
9. Manitoba Crop Insurance Corporation, www.mmpp.com
10. Beck, D., Advancing the Art, 18th Annual Zero Tillage Workshop, Minot ND, 1996