University of Manitoba: Natural Systems Agriculture: GLTR 2005 Yield
University of Manitoba Faculty of Agricultural and Food Sciences Department of Plant Science

Glenlea Long-Term Crop Rotation:
Historical Research Results

The Glenlea Long-Term Rotation Study was established in 1992 to determine the interaction of crop rotation and crop inputs (fertilizer and herbicide). Crop rotation ranged from simple annual systems to more complex forage based systems. The present study reports on results from the first 12 years of this study. The results focus on the base plots in Plot Plan 1 before modifications occurred. For information on how the experiment is designed see Glenlea Long-Term Crop Rotation: HIstory and Description. For more recent research results, visit the links found on the Organic Crop Production page.


Test Crop Yield

Flax was grown as a test crop at the end of all rotation systems. Flax is an important organic crop in the Northern Great Plains currently receiving high prices. Flax was chosen as the test crop in this experiment due to its poor competitive ability with all weed types. The influence of crop rotation and crop inputs on yield should, therefore, be evident. Yield of this flax test crop is discussed below.

Flax is used as a "test" crop at the end of each 4-year rotation cycle. Flax yields in bu/ac for 1995, 1999 and 2003 in the three main rotations are shown below. 

Rotation Inputs 1995 1999 2003
Annual (Wheat-pea-wheat-flax) F+H+ 30 22 27
  F+H- 16 10 1.3
  F-H+ 21 17 15
  F-H- 15 10 4
Green Manure (Wheat-clover-wheat-flax) F+H+ 29 29 10
F+H- 20 18 1.2
  F-H+ 18 25 8
  F-H- 16 16 3
Alfalfa (Wheat-alfalfa-alfalfa-flax) F+H+ 27 23 21
F+H- 21 16 1.5
  F-H+ 25 24 20
  F-H- 22 22 8

Crop Rotation Effect

  • The beneficial effects of alfalfa and clover green manure appeared to be stronger in the first and second rotation cycle (1995 and 1999) than in the third rotation cycle (2003).
  • After two or three cycles of the crop rotation, when weed pressure was much higher, green manure and forage did not offer weed suppression benefits to the following flax crop.
  • A two-year stand of alfalfa had a greater effect on subsequent grain yield than did a clover green manure.
  • By 2003, organic flax yields were low in all three rotations, however. Alfalfa yields began to suffer possibly due to low soil P and S (see Soil Nutrient Status). This may have reduced alfalfa's ability to suppress weeds.

Input Effect

  • There was a greater yield loss when herbicide was removed (F+H-) from the system than when fertilizer was removed (F-H+) suggesting that weeds have a greater limiting impact on crop production than nitrogen fertility.
  • Flax yield was very low in systems that used fertilizer but no herbicide (F+H-) because weeds took better advantage of the added N fertilizer than the crop.

Interaction of Crop Rotation and Inputs

  • In both low input systems (F+H- and F-H+), flax yields were lowest in the annual crop rotation vs the sweetclover and alfalfa-containing rotations.
  • Under organic production conditions (F-H-), flax in the alfalfa-containing rotation had the highest grain yield, followed by flax in the sweetclover rotation, followed by flax in the annual crop rotation.

Why is this important?

Crop rotation is important to farming with fewer chemicals. In this study, when alfalfa or green manure were included in the rotation organic flax yield was better than when only annual crops were in the rotation. Even when these legumes were included in the rotation, by the end of the third cycle of the rotation, organic yields were low. Soil P and S may be a big limiting factor to the success of alfalfa as a weed clean-up crop. In the fourth rotation cycle, treatments will be further subdivided to include manured treatments and early and late seeding dates.

Weed Dynamics

Weed dry matter (DM) was measured at harvest time in each of the flax test crop years to determine the effect of crop rotation and input management on weed production.

Crop Rotation Effect

  • Crop rotation only had a significant effect on weed production in 1995 when weed DM was significantly less in the rotations that included green manure or forage (Figure 1, below). The biggest increase in weed DM production between 1995 and 2003 occurred in the forage rotation. This most likely can be attributed to the additional nitrogen that the alfalfa in that rotation provides to the weeds.
  • Weed DM for the annual rotation was comprised of predominantly green foxtail (millet), wild oat, lady's thumb (green smartweed) and Canada thistle (data not shown). Stinkweed (field pennycress), a winter annual weed, wild buckwheat and Canada thistle were associated with the green manure rotation. Volunteer alfalfa, dandelion and wild mustard were associated with the forage rotation.
Figure 1. The effect of crop rotation on weed dry matter (kg/ha) at flax harvest at Glenlea.

Input Effect

  • Crop input management had a strong influence on weed DM production in all three test crop years (Figure 2, below). As expected, weed DM production was consistently lower where herbicide was used (f+h+ and f-h+). In all years of the study, weed DM was greater for the fertilizer only treatment (f+h-) than for the organic treatment (f-h-). In this situation, the weeds were taking better advantge of the added fertilizer than the crop.
  • The management of crop inputs influenced the weed spectrum (data not shown). Briefly, hemp nettle was most abundant when fertilizer and herbicide were used (f+h+). This may be due to the fact that herbicides effectively controlled all other weeds thus allowing this species to occupy available niches. Wild mustard, wild buckwheat, wild oat, and stinkweed were in greatest abundance in the fertilizer only system (f+h-). When no inputs were used (f-h-) Canada thistle was more abundant than when fertilizer was used but no herbicide (f+h-).
Figure 2. The effect of crop input management on weed dry matter (kg/ha) at flax harvest at Glenlea.

Interaction of Crop Rotation and Inputs

  • During the first rotation cycle, there was an interaction between crop rotation and input management for weed DM. In 1995, when herbicide was removed but fertilizer remained (f+h-), weed DM was greater in the annual crop and green manure rotations than in the forage rotation (Figure 3, below). Therefore, the presence of alfalfa in the rotation suppressed weeds during the first rotation cycle.
  • After three rotation cycles, the decrease in yield when herbicide (f+h-) was removed from the system was similar for all rotations (2003). Thus, by the third cycle of the rotation, herbicide was necessary to decrease weed DM regardless of the crop rotation. This suggests that even when a crop known to be competitive with weeds is consistently in the crop rotation (i.e. alfalfa hay), herbicide may be necessary to control weeds.
Figure 3. The interaction of crop rotation and crop input management on weed dry matter production (kg/ha) at flax harvest in 1995 at Glenlea.

Ground Beetles

The maintenance of maximum biological diversity within a cropping system is important as biodiversity is an index of the health of the cropping system. Bioindicators are organisms within an ecosystem which are sensitive to changes in the environment, and their populations are affected by disturbance. Ground beetles are excellent bioindicators. Ground beetles have often been considered a beneficial insect as some species eat weed seeds and other eat pest insects. Therefore, the ability to maintain or enhace ground beetle populations could lead to less reliance on therapeutic pest control measures.


In this study, pitfall traps were used to trap insects from 1992 to 1999. Traps were placed in each sub-plot (i.e. F+H+, F+H-, F-H+, F-H-). Insects caught in the traps were identified, separated and counted.

Results Indicate: 

  • Ground beetle populations were higher in the annual rotation (wheat-pea-wheat-flax) than in the forage (wheat-alfalfa-alfalfa-flax) or green manure (wheat-clover-wheat-flax) rotations, because weed populations were highest in the annual rotation.
  • Beetle populations were more consistent or stable between input treatments in the forage and green manure rotations. This suggests that the forage and green manure rotations are more "robust" or less fragile than the annual rotation.
  • Beetle populations were highest in the F+H- treatment because these weedier plots provided a better habitat due to increased humidity and abundant food supply.
  • Ground beetle populations were least in the F-H+ system because of a lack of potential food source and poor habitat.
  • Four consistent associations were observed between beetle and weed species, however. These were Harpalus pensylvanicus with red root pigweed; Amara carinata with stinkweed; Agonum placidum and Calosoma calidum with wild mustard. Harpalus and Amara are weed seed eaters.
Harpalus pensylvanicus
Red Root Pigweed


Agonum placidum

Calosoma calidum

Wild Mustard

Why is this important?

The association of Harpalus and Amara the weediest subplots (F+H-) suggests that these ground beetles may be used to sustainably manage weed populations through seed predation. Other studies have indicated that 50 to 80% of weed seeds in the soil may be consumed by insect seed predators. In this study, however, the abundance of weeds in the no herbicide plots (F+H- and F-H-) was too high for the beetles to reduce weed seeds significantly. Ground beetles may be more effective in an Integrated Pest Management (IPM) system where some herbicide is used to keep weed densities at levels lower than in the present study. In a system that depends entirely on herbicide for weed control, populations of ground beetles remains small and never have the opportunity to build to beneficial levels.

Energy Use

Reducing non-renewable energy use and carbon dioxide (CO2) production, and increasing energy efficiency can make cropping systems more sustainable. Nitrogen benefits of legumes to succeeding non-leguminous crops are well documented, while organic cropping systems have reduced levels of crop inputs. The long-term effects of perennial forage legumes and organic cropping practices on energy use, CO2 production, and energy efficiency of crop production were examined at Glenlea.

  • The first objective of the current study was to examine the effectiveness of perennial forage legume crops in reducing energy use and CO2 production, and improving energy efficiency of cropping systems, by replacing a portion of the nitrogen fertilizer required for crop production with nitrogen fixed by the alfalfa.
  • The second objective of this study was to examine the effectiveness of organic crop production in reducing energy use and CO2 production, and improving energy efficiency of cropping systems, by eliminating fertilizer and pesticide inputs.


Data collected included levels of all crop inputs, such as seed, fertilizers, pesticides, and fuel and machinery needed for all field operations, and crop yields from each treatment. This information was then converted to energy values (MJ/ha) using energy coefficients assigned for each crop input, field operation, and crop harvested.

Rotational ENERGY USE was calculated by adding the energy coefficients of all the field operations and crop inputs. Rotational ENERGY PRODUCTION was calculated using energy output coefficients assigned to the different crops through laboratory bomb calorimeter tests. ENERGY EFFICIENCY was calculated for each treatment by dividing rotational energy production by rotational energy use. Rotational CO2 production was calculated by multiplying total rotational energy use by CO2 coefficients used by Gulden and Entz (1996).

Total rotational energy consumption (MJ/ha) at the Glenlea long-term cropping systems study, 1992-2003
Rotation Inputs Total Energy
Seed Energy Fuel and Lube Energy Machinery
WPWF F+H+ 68498 7902 16133 2367 7116 34980
WPWF F-H- 24233 7902 14229 2102 0 0
WAAF F+H+ 49255 3657 18184 2515 3499 21400
WAAF F-H- 22181 3657 16213 2311 0 0
WPWF = wheat-pea-wheat-flax; WAAF = wheat-alfalfa-alfalfa-flax 

Results Indicate:

Energy Use and CO2 Production

  • When comparing the same treatments between rotations, the organic and conventional wheat-pea-wheat-flax (annual) systems used 9% and 39% more energy than the organic and conventional wheat-alfalfa-alfalfa-flax (forage) systems, respectively.
  • When comparing the conventional and organic systems within rotations, the conventional forage system produced approximately 2 times as much CO2 as the organic forage system, while the conventional annual system produced approximately 2.5 times as much CO2 as the organic annual system.
  • When comparing the conventional and organic systems within rotations, the conventional forage system consumed approximately 2.2 times as much non-renewable energy as the organic forage system, while the conventional annual system consumed approximately 2.8 times as much energy as the organic annual system
  • When comparing the same treatments between rotation, the organic and conventional annual systems produced 6% and 34% more CO2 than the organic and conventional forage systems, respectively.
  • The reductions in energy use and CO2 production for the forage system were primarily through reductions in nitrogen fertilizer requirements.

Energy Production

  • Within the annual rotation, rotational energy production was 85% higher in the conventional system, while rotation energy production in the forage rotation was approximately 26% higher in the conventional system.
  • The forage systems had levels of rotational energy production that were approximately two- and three times higher than the organic and conventional systems in the annual rotation, respectively.
  • The apparent benefits of including alfalfa in the rotation becomes more and more evident, the more years that the rotation was in existence, as the systems in the annual rotation appear to have energy production that is dropping more than in the forage rotation.

Energy Efficiency

  • It was found that energy efficiency in cropping systems containing perennial forage legumes was up to 222% greater than in the conventional cropping systems, as a result of decreases in energy use and increases in energy production.
  • Within each rotation, the organic system was more efficient than the conventional system. This was primarily due to substantially higher levels of input energy in the conventional systems, where energy use was more than twice as great as in the organic systems. While output energy for both of the conventional systems was higher than in the organic systems, it was not enough to negate the higher amounts of input energy consumed, in terms of rotational energy efficiency.

Why is this important?

The findings of this study point to the importance of including legumes in cropping systems in order to improve energy efficiency. The vast majority of energy used in crop production is in the form of fossil fuels. When burned, these fossil fuels release carbon dioxide, a greenhouse gas, into the atmosphere. With ever-increasing concern over global warming as a result of greenhouse gases, any steps taken to improve the energy efficiency of agriculture should be welcome steps indeed.

Soil Nutrient Status

Soil samples were collected from the three main rotations in the fall of 2003. Only the full input (F+H+) and no-input (F-H-) systems were tested. Samples were taken in six locations per subplot in all three replicates. The replicate samples were bulked prior to lab analysis.

Results show both a strong crop input and a strong crop rotation effect for many of the nutrients (see Table below). Nitrogen levels were affected by both fertilization and crop rotation. The alfalfa-containing rotation had the highest level of N, followed by the sweetclover-containing system.

Soil nutrient status in three different crop rotations after 12 years of cropping. Rotation 1, wheat-pea-wheat-flax; rotation 2, wheat-sweet clover green manure-wheat-flax; rotation 3, wheat-alfalfa-alfalfa-flax. Values in kg available nutrients per hectare.
Rotation Input Level N P K S
wheat-pea-wheat-flax F+H+ 32 46 1316 141
wheat-pea-wheat-flax F-H- 22 33 1312 86
wheat-sclover-wheat-flax F+H+ 29 24 1169 87
wheat-sclover-wheat-flax F-H- 31 37 1116 76
wheat-alfalfa-alfalfa-flax F+H+ 81 24 1140 63
wheat-alfalfa-alfalfa-flax F-H- 37 11 1073 26

Phosphorous levels were adequate for all systems except the unfertilized alfalfa rotation (see Table). The phosphorous mining effect of alfalfa forage crops is well documented. It is important to note that these values only reflect the available P levels, yet about 50% of soil P is in the organic form (which these soil tests do not measure). Soil potassium and sulfur levels were also lowest in the unfertilized alfalfa-containing rotation (see Table).

Why is this important?

Results of the present study show no evidence of serious nutrient deficiencies in organic systems for the annual or sweetclover-containing rotations (see Table). Only in the organic alfalfa-containing rotation did signs of nutrient deficiencies occur (see Table). In a survey of commercial organic farms in the eastern prairies, Entz et al. (2001) reported that long-term organically farmed soils had extremely low levels of inorganic phosphorous.

Economic Analysis

Economic analysis of 8 years of the Glenlea Rotation Study The following table shows the cost of production and net income for the 8 years (1992-1999) of rotations 1 and 3 at Glenlea. Costs are in "1996 Canadian dollars" while commodity prices are in 1996 dollars (minus 20%). Values are averaged over the entire 8 year rotation and are shown in mean annual dollars/acre.

Crop Rotation
Full inputs
Low input
Low input
Organic system
Input cost 104.14
Net return 27.87
Input cost 77.17
Net return 30.87
Input cost 71.36
Net return 26.67
Input cost 43.44
Net return 40.23
Input cost 71.68
Net return 77.83
Input cost 51.92
Net return 93.42
Input cost 55.92
Net return 73.73
Input cost 36.08
Net return 93.77

Results Indicate:

  • With full inputs, input costs were lower and net returns were higher in the alfalfa-containing vs the annual crop rotation.
  • In the annual rotation, removing either fertilizers or herbicides did not seriously reduce the net return, but did reduce input costs (equal reduction in input costs).
  • In the alfalfa-containing rotation, removing inputs increased net return in a number of cases compared with the full inputs treatment.
  • The organic systems had the lowest cost of production and the highest net returns over the 8 year period in both the annual grain and alfalfa-based rotations.
  • Organic flax production appears to be very economically attractive when included in an alfalfa-based crop rotation.


Copyright and Liability

This page imported Nov 2012 from the former Glenlea Long-term Study website.