University of Manitoba: Natural Systems Agriculture: Crop Rotation and PFP - Carman
University of Manitoba Faculty of Agricultural and Food Sciences Department of Plant Science

Crop Rotation and Pesticide Free Production: Carman MB


Pesticide Free Production (PFP) was developed by Canadian farmers and researchers as a practical means of reducing pesticide use in certain years. PFP is a production system in which non-genetically modified crops are grown without the use of pesticide, including chemical seed treatments, from the time of crop emergence until the time of marketing (learn more about Pesticide Free Production). Residual activity of pesticides used prior to the PFP crop must have ceased, but use of non-residual pre-emergent pesticides such as Roundup is permissible. In addition to this, there are no restrictions on the use of fertilizer.

Study Objectives

The objectives were to:

  • Compare the success of PFP implemented within an annual grain cropping system to PFP implemented within a forage-grain cropping system,
  • Determine the effect of PFP frequency within the crop rotation on weed populations and crop yield, and
  • To determine whether PFP increases weeds or affects yield in post-PFP crops.

The objectives of this experiment were accomplished by measuring weed seedling density within the crop canopy, crop and weed dry matter at harvest and crop yield.

Experiment Description

This experiment was established at Carman, Manitoba in 2000 on fine sandy loam soil. The study is fully-phased meaning that all crops appeared in all years of the study (2000 to 2003) in order to remove weather effects. All crops were grown under no-till conditions. Weeds were burned off with glyphosate before crop emergence in the spring. Crops were seeded with an offset double-disc press drill. Fertilizer was added according to soil test recommendations and pesticides were used as needed on the non-PFP crops at recommended rates. Alfalfa was cut twice each year and terminated with glyphosate before second cut in the second year. The treatments were as follows:

Objective 1: Does crop rotation influence the success of PFP? Two rotations were compared.

Year 1
Year 2
Year 3
Year 4
Annual Rotation
Forage Rotation

Objective 2: Should PFP appear once or twice in the crop rotation? PFP appeared once or twice.

PFP oat only
PFP linola followed by PFP oat

Objective 3: What happens to yield and weed density in the crops after PFP? The non-PFP crops were monitored also.

Canola and Wheat
2 Years of Alfalfa


The following are a summary of results from 2000 to 2003. Note that all crops appeared in all years of the rotation to remove weather effects from any one year.
Click on the graphs below to enlarge.

Oat Yield

In 2001, when PFP linola followed one year of alfalfa, it yielded the same as sprayed linola following one year of wheat. Weed pressure was moderate in 2001.

In 2002/03, PFP linola yielded less than sprayed linola in both crop rotations. Weed pressure was much higher in 2002/03 due to timely rains.

PFP oat yielded the same as sprayed oat for both crop rotations in all years of the study. PFP oat yielded the same whether it followed PFP linola or sprayed linola.

Weed density in canola (the first year after PFP in the annual rotation) was higher following one or two years of PFP compared to following sprayed crops. Recommended rates of herbicide were used to control weeds.

Canola yield following one or two years of PFP was no different than canola yield following sprayed crops even though weed density in the spring was higher after PFP.

Total forage yield after PFP was no different than after sprayed crops, but there was 15 to 20% more weed biomass in alfalfa following PFP. It is interesting to note that there was less weed biomass after two years of PFP than one year. The second year of alfalfa was virtually weed free whether it followed PFP or sprayed crops (data not shown).


  • Oat is a superior PFP crop.
    No yield reduction occurred with PFP oat.
  • When choosing a less competitive crop for PFP, crop rotation is more important.
    When weed pressure was less intense, PFP linola yielded better in the forage rotation.
  • Two years of PFP in a row is feasible, but pay attention to order of crops.
    There was no yield reduction for PFP oat following PFP linola but PFP flax following PFP oat most likely wouldn't yield well.
  • Be prepared for higher weed populations the next year.
    Weed densities were higher after PFP.
  • Following crops should allow for weed cleanup.
    Good herbicide options or competitive crops like alfalfa should be used the year after PFP.
  • Extra herbicide should not be necessary after PFP.
    In this experiment and an on-farm experiment, no extra herbicide was needed the year after PFP.
  • Alfalfa in the rotation allowed for elimination of in-crop pesticide for three or four years out of four.

Further Information:
Producing PFP Oats - Reducing Pesticide Risk (CD-ROM available free of charge)

Further Reading: A. Schoofs, M.H. Entz, R. C. Van Acker, J. R. Thiessen Martens, and D. A. Derksen. 2004. Agronomic performance of Pesticide Free Production under two crop rotations. Renewable agriculture and food systems (under review).

Copyright and Liability

This page created August 2004.
Updated March 2005.