Organic Production Planning Through Transition

May 2008

The key to successful organic crop production is diversity.  Crop rotations are central to the holistic approach to crop production, which provides opportunities to implement cultural/management strategies that enhance diversity. It is difficult to incorporate a weed- or disease-control strategy without considering nutrients, and vice versa.  Properly planned crop rotations offer benefits to the soil, allow weed/pest control and promote biodiversity.  This holistic approach requires a broad range of expertise; therefore, it is strongly recommended that readers consult other organic production publications that are available from Saskatchewan Agriculture and on this website.

Products and practices available to organic producers vary depending on the organic certification organization to which they belong.  There may also be slightly different interpretations of "restricted use" substances.  Producers should always review the standards with which they are complying to ensure their products and practices are accepted by their certifying organization.  

Introduction

Producers considering making the transition to organic production are encouraged to do it incrementally.  By converting portions of the farm to organic production while leaving other parts in conventional production, the producer has time to learn new management skills. In addition, the income earned from conventional crops will provide a financial buffer during the three-year transition period when producers experience yield reductions but are not earning organic price premiums.

Crops grown during the transition period are not eligible for organic premiums.  The minimum conversion period is 36 months from the last application of a prohibited substance to the first certifiable harvest.  An inspection is generally required 12 months before the first certified organic harvest.

Transition

The goal of a transition strategy is to use management strategies that make soil as fertile, weed-free and healthy as possible going into the certified period.  Soil testing will provide the base from which the strategy will evolve.  Soil testing over time will also allow the producer to monitor the benefits of various agronomic practices.

There is no single crop rotation recommended for all producers. This bulletin provides information on the characteristics of commonly grown forage crops and problematic weeds, and will provide guidelines with which producers can make informed transition decisions. This bulletin will identify trends that may occur during the transition period, such as how weed populations may change with the replacement of chemical usage by increased tillage practices.  It also identifies implications of cropping choices as they pertain to soil fertility and weed dynamics.  

Transition Period and Fertility

Economic considerations play an important role during transition.  Ideally, a high nitrogen-fixing, competitive forage is planted in the early stages of transition.  Transition of the entire farm at once provides the producer with the opportunity to improve soil quality quickly, but it will reduce revenue.

The use of legume crops in organic crop rotation is essential.  Unless the harvested grain is returned to the soil through manure cycling, the land will undergo a net export of nutrients.  A 40 bu./ac. crop of wheat will require approximately 85 lb./ac. of nitrogen, while returning only 25 lb./ac. to the soil. The remaining 60 lb./ac. are exported in the seed.  Some producers will have as many as three legume crops within a seven-year rotation.  When properly inoculated with rhizobia, legumes will fix approximately 50 to 90 per cent of the required nitrogen from the air.  Legume residue has a higher level of nitrogen than non-legume residue, and is broken down quickly, making more nitrogen available for subsequent crops. 

Additional benefits of seeding legumes, other than nitrogen fixation and weed control, include improved soil structure, increased soil aeration and improved water-holding capacity.  For more details on legumes and soil quality, please see the Saskatchewan Agriculture publication Soil Improvement with Legumes.   

Although legumes are critical to successful organic production, producers must adhere to the key of successful organic production - diversity.  Not only does this apply within the selection of legume crops, but also in combination with other crop types.  

Understanding both the nutrient demands of crops as well as the nutrient-supplying abilities of crops and soils will help the organic producer manage the rotation to maintain a long-term equilibrium.  For detailed information on maintenance of fertility in an organic production system, please see the Saskatchewan Agriculture publication Organic Crop Production:  Fertility. 

Understanding the characteristics of forage crops (see Table 1) grown in Saskatchewan will help the producer prepare the land for successful organic production.

Table 1. Characteristics of Legume Forage Crops

Transition Period and Weed Control

"Seed bank" is the term for all the viable weed seeds present in the soil.  The composition of weed populations in each field is a direct result of selection pressures.  Weed seeds that are currently germinating are not necessarily those that are most abundant in the weed seed bank.  Rather, the crop type and agronomic practice being used at that time are providing those particular weeds with an advantage relative to other weed types.  Understanding the strengths and weaknesses of various weed species will help the producer understand how cropping practices can alter weed-selection pressures.  Understanding this relationship is necessary in developing management strategies.

Changing the crop type also allows the producer to change factors such as seeding date (early, late spring, fall), seeding depth, pre-plant tillage and in-crop tillage (pre- and post-emergence tillage).  Continually changing these factors reduces the likelihood of a buildup of specific weed species.  In all crops, the producer should strive for good crop establishment before weed establishment occurs, thereby allowing the crop to out-compete the weeds.  For more information on specific weed management strategies, please consult the Saskatchewan Agriculture  publication Organic Crop Production: Weed Management.

Table 2 contains information from various studies on weed characteristics that will provide better understanding of the weed/environment/management practice relationship. 

Table 2. Characteristics of Problematic Weeds 

^* temperature ranges are considered optimal; seeds will germinate outside this range

Noxious Weed Legislation

The Noxious Weeds Act, 1984 is provincial legislation that empowers municipalities to enforce the control of noxious weeds within their boundaries. Noxious weeds are those weeds that are considered a detriment to agriculture, health or the environment. They are generally non-native plants that have been imported to North America from places like Europe or Asia. Noxious weeds are also very invasive. In their place of origin, they are kept in check by insects and diseases, but here they can be the dominant species if left unmanaged. Noxious weeds are also very costly, whether through crop yield losses, livestock or human poisoning, or destruction of native habitat.

The Noxious Weeds Act states that land owners/operators are responsible for controlling noxious weeds on their land and preventing spread to neighbouring land. Weed inspectors are appointed by the municipality to enforce the Act and have the power to enter land to look for noxious weeds, to compel landowners to control noxious weeds and to perform work not completed as they have ordered. Weed inspectors are encouraged to work within the management systems of landowners to find workable solutions.  Those considering a transition to organic production must also realize that control or prevention of noxious weeds will often require more intensive management measures than conventional production. These measures may include the use of higher seeding rates, or fallow and perennial forages grown in rotation.

Five highly invasive and destructive weeds named in The Noxious Weeds Act are difficult to eliminate and can cause the order for the destruction of a crop.  These weeds are leafy spurge, hoary cress, Russian knapweed, field bindweed and toadflax. They are all persistent deep-rooted perennial weeds that, once established, will dominate an environment and often have seed that will emerge for many years. Two to three years of intensive tillage may be required to deplete root reserves of established plants. Those considering a transition to organic production should avoid land with these weeds or take measures to reduce their numbers before initiating transition.

Shifts in Weed Populations

Moving from conventional to organic production can have a dramatic effect on weed populations and community composition.

A recent trend in conventional production has been the shift from intensive tillage to direct seeding.  As a result, weed communities are increasingly comprised of winter annual and perennial species such as thistles, dandelion, flixweed and narrow-leaved hawk's-beard.  A conversion back to intensive tillage, as is required with an organic production system, will result in more annual weed species such as mustards, pigweeds and lamb's-quarters.  Some perennial weeds such as quack grass and thistles will proliferate under tillage due to the spread of reproductive root pieces, but may be controlled with intensive fallow tillage.  Some weed species, such as wild buckwheat, smartweed, stinkweed and shepherd's purse, are indifferent to tillage.  While stinkweed and shepherd's-purse are winter annuals, they can also exhibit an annual habit.  Reduced tillage can result in lower overall weed populations by increasing the mortality of weed seeds at the soil surface.  Conversely, a return to an intensive tillage system will see an increase in the number of weeds emerging from seed.

The use of herbicides is the other obvious influence in conventional systems that will be absent in organic farming systems.  Annual weeds, including lamb's-quarters, pigweed, mustard, shepherd's-purse, stinkweed, smartweed, Russian thistle, kochia and wild buckwheat, are controlled easily by several herbicides.  In the absence of herbicides, these species will be more prevalent in weed communities in organic fields than in conventionally managed fields.

Conclusion

Successful organic production requires an understanding of plant characteristics in relation to the specific conditions of your field.  Producers need to incorporate this knowledge into the art form of organic farming.   Understanding these characteristics will provide producers with a starting point from which they will need to fine-tune the rotations best suited for their conditions.

Written and edited by:

B. Recksiedler, C. Brenzil, M. Tremblay, R. McVicar, D. Jans, D. Goodwillie, Saskatchewan Agriculture

For more information, contact:

Agriculture Knowledge Centre
Saskatchewan Agriculture
Toll-free:  1-866-457-2377
E-mail: aginfo@gov.sk.ca