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University of Manitoba Faculty of Agricultural and Food Sciences Department of Plant Science

Agronomic Benefits of
Intercropping Annual Crops in Manitoba

Background

An example of mixed intercropping with crops seeded at an angle to each other.

What is intercropping?

Intercropping involves growing more than one crop in the same field at the same time.

The crops may be seeded at the same time (mixed intercropping) or they may be seeded at different times (relay intercropping). Strip intercropping is a production system where different crops are grown in wide strips (usually the width of a seeder) in the same field.

Why intercrop?

Strip intercropping.

1. Stability: Intercropping adds diversity to the cropping system and diversity tends to lead to stability.

2. Reduced chemical use. Intercropping may allow for lower input levels in a cropping system by reducing fertilizer and pesticide requirements.

3. Overyielding. Overyielding occurs when the yield produced by an intercrop is larger than the yield produced by the component crops grown in monoculture on the same total land area.

Overyielding is calculated using the Land Equivalency Ratio (LER). The LER is a measure of how much land would be required to achieve intercrop yields with crops grown as pure stands. (See example)

When the LER is greater than 1, overyielding is occurring and the intercrop is more productive than the component crops grown as sole crops. When the LER is less than 1, no overyielding is occurring and the sole crops are more productive than the intercrop.

Overyielding occurs for a variety of reasons, including the following:

  • Weed suppression and lower susceptibility to insects and diseases probably help to increase yields of intercrops.
  • Complementary resource use. A mix of different plants will use resources more efficiently than plants that are all of the same type. Plants of varying types may also provide benefits to each other, such as fixed nitrogen from legumes.

Learn more about intercropping from ATTRA - National Sustainable Agriculture Information Service (opens in new window)

Study Objectives

Wheat - canola intercrop.

The objective of this study was to grow several important annual crops (wheat, canola, and field peas) as intercrops and to evaluate the benefits of growing these crops as intercrops as compared to monocrops. Specific research questions were:

  • Does overyielding occur in these intercrops?
  • Do intercrops suppress weeds better than monocrops?
  • Is grain quality improved in intercrops?

Experiment Description

Research plots were established at two locations in Manitoba in 2001, 2002, and 2003. Spring wheat, canola, and field peas were grown as monocrops and in all possible combinations. All treatments were grown in both pesticide free (See What is PFP?) and conventional systems. Crop and weed biomass, crop yield, resource use (light, N, water), and grain quality were measured in all treatments.

Treatments:

Monocrops
 
Wheat (W)
Canola (C)
Peas (P)
Two-way intercrops
 
Wheat-Canola (WC)
Wheat-Pea (WP)
Canola-Pea (CP)
Three-way intercrop
 
Wheat-Canola-Pea (WCP)

Results

Yield

The yields of all crops varied greatly between years and locations. Therefore, the land equivalency ratios (LERs) also varied considerably. Some examples are shown below.

Grain yield and LERs at Kelburn in 2002. All intercrops had LERs equal to or greater than 1.
Grain yield and LERs at Kelburn in 2003. Wheat-pea intercrop had an LER less than 1, while other intercrops were greater than 1.

The table below shows the LERs averaged over all years and both locations, as well as the percentage of cases in which overyielding occurred. Some degree of overyielding (LERs greater than 1) occurred about two-thirds of the time. In PFP plots, only about half of the intercrops had overyielding, while in conventional plots, 75% had overyielding. The overall average of LERs was 1.11, indicating that the monocultures used about 10% more land than the intercrops.

Intercrops Land Equivalency Ratio (LER)   Frequency of occurrence of overyielding
Pesticide free Conventional Average Pesticide free Conventional Average
Wheat-Canola 1.13 1.04 1.09   40% 80% 60%
Wheat-Pea 0.87 1.10 0.99   20% 40% 30%
Canola-Pea 1.19 1.22 1.21   67% 100% 84%
Wheat-Canola-Pea 1.16 1.12 1.14   60% 80% 70%
Average 1.09 1.12 1.11   47% 75% 61%

The wheat-pea (WP) intercrop had the lowest LERs and the lowest frequency of overyielding, and also had problems with lodging.
The canola-pea (CP) intercrop had the highest LERs and most consistent overyielding.

Weed Suppression

Weed biomass was also extremely variable between crops, locations, and years. On average, weed biomass decreased as the number of crops in the mix increased, indicating that intercrops suppressed weeds better than monocrops did. Weed suppression was the best in WC, and was the poorest in WP.

When peas were added to the crop mixture, grain nitrogen content and protein content increased. This can be a great advantage in wheat, as price premiums for high protein wheat can be obtained. In 2002, the value of wheat produced in this experiment increased by 6 to 20 cents per bushel when wheat was intercropped with peas.

Future Research Needs

Although intercropping has been used traditionally for thousands of years, it is still poorly understood from an agronomic perspective. Intercropping systems are also more challenging to manage than pure stands, especially at harvest time. More research is needed to better understand how intercrops function and to develop intercropping systems that are compatible with today's farming systems.

Recommendations

  • Intercropping with common annual crops is feasible and results in overyielding about 75% of the time in conventional production.
  • The best crop combination tested in this experiment was canola-pea, which overyielded 100% of the time under conventional management.
  • The poorest combination was wheat-pea, which had problems with weeds and lodging.
  • In general, increasing the number of crops grown together resulted in better weed suppression.
  • Including peas in the combination increased grain protein content, resulting in price premiums for wheat.

See also Cultivar Mixtures, Cover Crops, and Intercropping with Organic Spring Wheat for more information on intercropping research at the University of Manitoba.

Copyright and Liability

This page created August 2004.